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Saturday, July 30, 2022

Psychosynthesis

From Wikipedia, the free encyclopedia

Psychosynthesis is an approach to psychology that expands the boundaries of the field by identifying a deeper center of identity, which is the postulate of the Self. It considers each individual unique in terms of purpose in life, and places value on the exploration of human potential. The approach combines spiritual development with psychological healing by including the life journey of an individual or their unique path to self-realization.

The integrative framework of psychosynthesis is based on Sigmund Freud's theory of the unconscious and addresses psychological distress and intra-psychic and interpersonal conflicts.

Development

Psychosynthesis was developed by Italian psychiatrist, Roberto Assagioli, who was a student of Freud and Bleuler. He compared psychosynthesis to the prevailing thinking of the day, contrasting psychosynthesis for example with existential psychology, but unlike the latter considered loneliness not to be "either ultimate or essential".

Assagioli asserted that "the direct experience of the self, of pure self-awareness...—is true." Spiritual goals of "self-realization" and the "interindividual psychosynthesis"—of "social integration...the harmonious integration of the individual into ever larger groups up to the 'one humanity'"—were central to Assagioli's theory. Psychosynthesis was not intended to be a school of thought or an exclusive method. However, many conferences and publications had it as a central theme, and centres were formed in Italy and the United States in the 1960s.

Psychosynthesis departed from the empirical foundations of psychology because it studied a person as a personality and a soul, but Assagioli continued to insist that it was scientific. He developed therapeutic methods beyond those in psychoanalysis. Although the unconscious is an important part of his theory, Assagioli was careful to maintain a balance with rational, conscious therapeutical work.

Assagioli was not the first to use the term "psychosynthesis". The earliest use was by James Jackson Putnam, who used it as the name of his electroconvulsive therapy. The term was also used by C. G. Jung and A. R. Orage, who were both more aligned to Assagioli's use of the term than Putnam's use. C. G. Jung, in comparing his goals to those of Sigmund Freud, wrote, "If there is a 'psychoanalysis' there must also be a 'psychosynthesis which creates future events according to the same laws'." A. R. Orage, who was the publisher of the influential journal, The New Age, used the term as well, but hyphenated it (psycho-synthesis). Orage formed an early psychology study group (which included Maurice Nicoll who later studied with Carl Jung) and concluded that what humanity needed was not psychoanalysis, but psycho-synthesis. The term was also used by Bezzoli. Freud, however, was opposed to what he saw as the directive element in Jung's approach to psychosynthesis, and Freud argued for a spontaneous synthesis on the patient's part: "As we analyse...the great unity which we call his ego fits into itself all the instinctual impulses which before had been split off and held apart from it. The psycho-synthesis is thus achieved in analytic treatment without our intervention, automatically and inevitably."

Origins

In 1909, C.G. Jung wrote to Sigmund Freud of "a very pleasant and perhaps valuable acquaintance, our first Italian, a Dr. Assagioli from the psychiatric clinic in Florence". Later however, this same Roberto Assagioli (1888 – 1974) wrote a doctoral dissertation, "La Psicosintesi," in which he began to move away from Freud's psychoanalysis toward what he called psychosynthesis:

A beginning of my conception of psychosynthesis was contained in my doctoral thesis on Psychoanalysis (1910), in which I pointed out what I considered to be some of the limitations of Freud's views.

In developing psychosynthesis, Assagioli agreed with Freud that healing childhood trauma and developing a healthy ego were necessary aims of psychotherapy, but Assagioli believed that human growth could not be limited to this alone. A student of philosophical and spiritual traditions of both East and West, Assagioli sought to address human growth as it proceeded beyond the norm of the well-functioning ego; he wished to support the fruition of human potential—what Abraham Maslow later termed self-actualization—into the spiritual or transpersonal dimensions of human experience as well.

Assagioli envisioned an approach to the human being that could address both the process of personal growth—of personality integration and self-actualization—as well as transpersonal development—that dimension glimpsed for example in peak experiences (Maslow) of inspired creativity, spiritual insight, and unitive states of consciousness. Psychosynthesis recognizes the process of self-realization, of contact and response with one's deepest callings and directions in life, which can involve either or both personal and transpersonal development.

Psychosynthesis is therefore one of the earliest forerunners of both humanistic psychology and transpersonal psychology, even preceding Jung's break with Freud by several years. Assagioli's conception has an affinity with existential-humanistic psychology and other approaches that attempt to understand the nature of the healthy personality, personal responsibility, and choice, and the actualization of the personal self. Similarly, his conception is related to the field of transpersonal psychology (with its focus on higher states of consciousness), spirituality, and human experience beyond the individual self. Assagioli served on the board of editors for both the Journal of Humanistic Psychology and the Journal of Transpersonal Psychology.

Assagioli presents two major theoretical models in his seminal book, Psychosynthesis, models that have remained fundamental to psychosynthesis theory and practice:

  1. A diagram and description of the human person
  2. A stage theory of the process of psychosynthesis (see below).

Aims

In Psychosomatic Medicine and Bio-psychosynthesis, Assagioli states that the principal aims and tasks of psychosynthesis are:

  1. the elimination of the conflicts and obstacles, conscious and unconscious, that block [the complete and harmonious development of the human personality]
  2. the use of active techniques to stimulate the psychic functions still weak and immature.

In his major book, Psychosynthesis: A Collection of Basic Writings (1965), Assagioli writes of three aims of psychosynthesis:

Let us examine whether and how it is possible to solve this central problem of human life, to heal this fundamental infirmity of man. Let us see how he may free himself from this enslavement and achieve an harmonious inner integration, true Self-realization, and right relationships with others. (p. 21)

Model of the person

Psychosynthesis Egg Diagram
 
1: Lower Unconscious
2: Middle Unconscious
3: Higher Unconscious
4: Field of Consciousness
5: Conscious Self or "I"
6: Higher Self
7: Collective Unconscious

At the core of psychosynthesis theory is the Egg Diagram, which maps the human psyche into different distinct and interconnected levels.

Lower unconscious

For Assagioli, 'the lower unconscious, which contains one's personal psychological past in the form of repressed complexes, long-forgotten memories and dreams and imaginations', stood at the base of the diagram of the mind.

The lower unconscious is that realm of the person to which is relegated the experiences of shame, fear, pain, despair, and rage associated with primal wounding suffered in life. One way to think of the lower unconscious is that it is a particular bandwidth of one's experiential range that has been broken away from consciousness. It comprises that range of experience related to the threat of personal annihilation, of destruction of self, of nonbeing, and more generally, of the painful side of the human condition. As long as this range of experience remains unconscious, the person will have a limited ability to be empathic with self or others in the more painful aspects of human life.

At the same time, 'the lower unconscious merely represents the most primitive part of ourselves...It is not bad, it is just earlier '. Indeed, 'the "lower" side has many attractions and great vitality', and – as with Freud's id, or Jung's shadow – the conscious goal must be to 'achieve a creative tension' with the lower unconscious.

Middle unconscious

The middle unconscious is a sector of the person whose contents, although unconscious, nevertheless support normal conscious functioning in an ongoing way (thus it is illustrated as most immediate to "I"). It is the capacity to form patterns of skills, behaviors, feelings, attitudes, and abilities that can function without conscious attention, thereby forming the infrastructure of one's conscious life.

The function of the middle unconscious can be seen in all spheres of human development, from learning to walk and talk, to acquiring languages, to mastering a trade or profession, to developing social roles. Anticipating today's neuroscience, Assagioli even referred to "developing new neuromuscular patterns". All such elaborate syntheses of thought, feeling, and behavior are built upon learnings and abilities that must eventually operate unconsciously.

For Assagioli, 'Human healing and growth that involves work with either the middle or the lower unconscious is known as personal psychosynthesis '.

Higher unconscious

Assagioli termed 'the sphere of aesthetic experience, creative inspiration, and higher states of consciousness...the higher unconscious '. The higher unconscious (or superconscious) denotes "our higher potentialities which seek to express themselves, but which we often repel and repress" (Assagioli). As with the lower unconscious, this area is by definition not available to consciousness, so its existence is inferred from moments in which contents from that level affect consciousness. Contact with the higher unconscious can be seen in those moments, termed peak experiences by Maslow, which are often difficult to put into words, experiences in which one senses deeper meaning in life, a profound serenity and peace, a universality within the particulars of existence, or perhaps a unity between oneself and the cosmos. This level of the unconscious represents an area of the personality that contains the "heights" overarching the "depths" of the lower unconscious. As long as this range of experience remains unconscious – in what Desoille termed '"repression of the sublime"' – the person will have a limited ability to be empathic with self or other in the more sublime aspects of human life.

The higher unconscious thus represents 'an autonomous realm, from where we receive our higher intuitions and inspirations – altruistic love and will, humanitarian action, artistic and scientific inspiration, philosophic and spiritual insight, and the drive towards purpose and meaning in life'. It may be compared to Freud's superego, seen as 'the higher, moral, supra-personal side of human nature...a higher nature in man', incorporating 'Religion, morality, and a social sense – the chief elements in the higher side of man...putting science and art to one side'.

Subpersonalities

Subpersonalities based in the personal unconscious form a central strand in psychosynthesis thinking. 'One of the first people to have started really making use of subpersonalities for therapy and personal growth was Roberto Assagioli', psychosynthesis reckoning that 'subpersonalities exist at various levels of organization, complexity, and refinement' throughout the mind. A five-fold process of recognition, acceptance, co-ordination, integration, and synthesis 'leads to the discovery of the Transpersonal Self, and the realization that that is the final truth of the person, not the subpersonalities'.

Some subpersonalities may be seen 'as psychological contents striving to emulate an archetype...degraded expressions of the archetypes of higher qualities '. Others will resist the process of integration; will 'take the line that it is difficult being alive, and it is far easier – and safer – to stay in an undifferentiated state'.

"I"

Psychosynthesis Star Diagram
Psychosynthesis Star Diagram
formulated by Roberto Assagioli

"I" is the direct "reflection" or "projection" of Self (Assagioli) and the essential being of the person, distinct but not separate from all contents of experience. "I" possesses the two functions of consciousness, or awareness, and will, whose field of operation is represented by the concentric circle around "I" in the oval diagram – Personal Will.

Psychosynthesis suggests that "we can experience the will as having four stages. The first stage could be described as 'having no will'", and might perhaps be linked with the hegemony of the lower unconscious. "The next stage of the will is understanding that 'will exists'. We might still feel that we cannot actually do it, but we know...it is possible". "Once we have developed our will, at least to some degree, we pass to the next stage which is called 'having a will'", and thereafter "in psychosynthesis we call the fourth and final stage of the evolution of the will in the individual 'being will'" – which then "relates to the 'I' or self...draws energy from the transpersonal self".

The "I" is placed at the center of the field of awareness and will in order to indicate that "I" is the one who has consciousness and will. It is "I" who is aware of the psyche-soma contents as they pass in and out of awareness; the contents come and go, while "I" may remain present to each experience as it arises. But "I" is dynamic as well as receptive: "I" has the ability to affect the contents of awareness and can even affect awareness itself, by choosing to focus awareness (as in many types of meditation), expand it, or contract it.

Since "I" is distinct from any and all contents and structures of experience, "I" can be thought of as not a "self" at all but as "noself". That is, "I" is never the object of experience. "I" is who can experience, for example, the ego disintegrating and reforming, who can encounter emptiness and fullness, who can experience utter isolation or cosmic unity, who can engage any and all arising experiences. "I" is not any particular experience but the experiencer, not object but subject, and thus cannot be seen or grasped as an object of consciousness. This "noself" view of "I" can be seen in Assagioli's discussion of "I" as a reflection of Self: "The reflection appears to be self-existent but has, in reality, no autonomous substantiality. It is, in other words, not a new and different light but a projection of its luminous source". The next section describes this "luminous source", Self.

Self

Pervading all the areas mapped by the oval diagram, distinct but not separate from all of them, is Self (which has also been called Higher Self or Transpersonal Self). The concept of Self points towards a source of wisdom and guidance within the person, a source which can operate quite beyond the control of the conscious personality. Since Self pervades all levels, an ongoing lived relationship with Self—Self-realization—may lead anywhere on the diagram as one's direction unfolds (this is one reason for not illustrating Self at the top of the diagram, a representation that tends to give the impression that Self-realization leads only into the higher unconscious). Relating to Self may lead for example to engagement with addictions and compulsions, to the heights of creative and religious experience, to the mysteries of unitive experience, to issues of meaning and mortality, to grappling with early childhood wounding, to discerning a sense of purpose and meaning in life.

The relationship of "I" and Self is paradoxical. Assagioli was clear that "I" and Self were from one point of view, one. He wrote, "There are not really two selves, two independent and separate entities. The Self is one". Such a nondual unity is a fundamental aspect of this level of experience. But Assagioli also understood that there could be a meaningful relationship between the person and Self as well:

Accounts of religious experiences often speak of a "call" from God, or a "pull" from some Higher Power; this sometimes starts a "dialogue" between the man [or woman] and this "higher Source"...

Assagioli did not of course limit this relationship and dialogue to those dramatic experiences of "call" seen in the lives of great men and women throughout history. Rather, the potential for a conscious relationship with Self exists for every person at all times and may be assumed to be implicit in every moment of every day and in every phase of life, even when one does not recognize this. Whether within one's private inner world of feelings, thoughts, and dreams, or within one's relationships with other people and the natural world, a meaningful ongoing relationship with Self may be lived.

Stages

Writing about the model of the person presented above, Assagioli states that it is a "structural, static, almost 'anatomical' representation of our inner constitution, while it leaves out its dynamic aspect, which is the most important and essential one". Thus he follows this model immediately with a stage theory outlining the process of psychosynthesis. This scheme can be called the "stages of psychosynthesis", and is presented here.

It is important to note that although the linear progression of the following stages does make logical sense, these stages may not in fact be experienced in this sequence; they are not a ladder up which one climbs, but aspects of a single process. Further, one never outgrows these stages; any stage can be present at any moment throughout the process of Psychosynthesis, Assaglioli acknowledging 'persisting traits belonging to preceding psychological ages' and the perennial possibility of 'retrogression to primitive stages'.

The stages of Psychosynthesis may be tabulated as follows:

  1. Thorough knowledge of one's personality.
  2. Control of its various elements.
  3. Realization of one's true Self—the discovery or creation of a unifying center.
  4. Psychosynthesis: the formation or reconstruction of the personality around a new center.

Methods

Psychosynthesis was regarded by Assagioli as more of an orientation and a general approach to the whole human being, and as existing apart from any of its particular concrete applications. This approach allows for a wide variety of techniques and methods to be used within the psychosynthesis context. 'Dialogue, Gestalt techniques, dream work, guided imagery, affirmations, and meditation are all powerful tools for integration', but 'the attitude and presence of the guide are of far greater importance than the particular methods used'. Sand tray, art therapy, journaling, drama therapy, and body work; cognitive-behavioral techniques; object relations, self psychology, and family systems approaches, may all be used in different contexts, from individual and group psychotherapy, to meditation and self-help groups. Psychosynthesis offers an overall view which can help orient oneself within the vast array of different modalities available today, and be applied either for therapy or for self-actualization.

Recently, two psychosynthesis techniques were shown to help student sojourners in their acculturation process. First, the self-identification exercise eased anxiety, an aspect of culture shock. Secondly, the subpersonality model aided students in their ability to integrate a new social identity. In another recent study, the subpersonality model was shown to be an effective intervention for aiding creative expression, helping people connect to different levels of their unconscious creativity. Most recently, psychosynthesis psychotherapy has proven to activate personal and spiritual growth in self-identified atheists.

One broad classification of the techniques used involves the following headings: ' Analytical: To help identify blocks and enable the exploration of the unconscious'. Psychosynthesis stresses 'the importance of using obstacles as steps to growth' – 'blessing the obstacle...blocks are our helpers'. ' Mastery...the eight psychological functions need to be gradually retrained to produce permanent positive change'. ' Transformation...the refashioning of the personality around a new centre'. ' Grounding...into the concrete terms of daily life. ' Relational...to cultivate qualities such as love, openness and empathy'.

Psychosynthesis allows practitioners the recognition and validation of an extensive range of human experience: the vicissitudes of developmental difficulties and early trauma; the struggle with compulsions, addictions, and the trance of daily life; the confrontation with existential identity, choice, and responsibility; levels of creativity, peak performance, and spiritual experience; and the search for meaning and direction in life. None of these important spheres of human existence need be reduced to the other, and each can find its right place in the whole. This means that no matter what type of experience is engaged, and no matter what phase of growth is negotiated, the complexity and uniqueness of the person may be respected—a fundamental principle in any application of psychosynthesis.

Criticism

In the December 1974 issue of Psychology Today, Assagioli was interviewed by Sam Keen and was asked to comment on the limits of psychosynthesis. He answered paradoxically: "The limit of psychosynthesis is that it has no limits. It is too extensive, too comprehensive. Its weakness is that it accepts too much. It sees too many sides at the same time and that is a drawback."

Psychosynthesis "has always been on the fringes of the 'official' therapy world" and it "is only recently that the concepts and methods of psychoanalysis and group analysis have been introduced into the training and practice of psychosynthesis psychotherapy".

As a result, the movement has been at times exposed to the dangers of fossilisation and cultism, so that on occasion, having "started out reflecting the high-minded spiritual philosophy of its founder, [it] became more and more authoritarian, more and more strident in its conviction that psychosynthesis was the One Truth".

A more technical danger is that premature concern with the transpersonal may hamper dealing with personal psychosynthesis: for example, "evoking serenity ... might produce a false sense of well-being and security". Practitioners have noted how "inability to ... integrate the superconscious contact with everyday experience easily leads to inflation", and have spoken of "an 'Icarus complex', the tendency whereby spiritual ambition fails to take personality limitations into account and causes all sorts of psychological difficulties".

Fictional analogies

Stephen Potter's "Lifemanship Psycho-Synthesis Clinic", where you may "find the psycho-synthesist lying relaxed on the couch while the patient will be encouraged to walk up and down" would seem a genuine case of "parallel evolution", since its clear targets, as "the natural antagonists...of the lifeplay, are the psychoanalysts".

Ligand

From Wikipedia, the free encyclopedia

Cobalt complex HCo(CO)4 with five ligands

In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electron pairs often through Lewis Bases. The nature of metal–ligand bonding can range from covalent to ionic. Furthermore, the metal–ligand bond order can range from one to three. Ligands are viewed as Lewis bases, although rare cases are known to involve Lewis acidic "ligands".

Metals and metalloids are bound to ligands in almost all circumstances, although gaseous "naked" metal ions can be generated in a high vacuum. Ligands in a complex dictate the reactivity of the central atom, including ligand substitution rates, the reactivity of the ligands themselves, and redox. Ligand selection requires critical consideration in many practical areas, including bioinorganic and medicinal chemistry, homogeneous catalysis, and environmental chemistry.

Ligands are classified in many ways, including: charge, size (bulk), the identity of the coordinating atom(s), and the number of electrons donated to the metal (denticity or hapticity). The size of a ligand is indicated by its cone angle.

History

The composition of coordination complexes have been known since the early 1800s, such as Prussian blue and copper vitriol. The key breakthrough occurred when Alfred Werner reconciled formulas and isomers. He showed, among other things, that the formulas of many cobalt(III) and chromium(III) compounds can be understood if the metal has six ligands in an octahedral geometry. The first to use the term "ligand" were Alfred Werner and Carl Somiesky, in relation to silicon chemistry. The theory allows one to understand the difference between coordinated and ionic chloride in the cobalt ammine chlorides and to explain many of the previously inexplicable isomers. He resolved the first coordination complex called hexol into optical isomers, overthrowing the theory that chirality was necessarily associated with carbon compounds.

Strong field and weak field ligands

In general, ligands are viewed as electron donors and the metals as electron acceptors, i.e., respectively, Lewis bases and Lewis acids. This description has been semi-quantified in many ways, e.g. ECW model. Bonding is often described using the formalisms of molecular orbital theory.

Ligands and metal ions can be ordered in many ways; one ranking system focuses on ligand 'hardness' (see also hard/soft acid/base theory). Metal ions preferentially bind certain ligands. In general, 'hard' metal ions prefer weak field ligands, whereas 'soft' metal ions prefer strong field ligands. According to the molecular orbital theory, the HOMO (Highest Occupied Molecular Orbital) of the ligand should have an energy that overlaps with the LUMO (Lowest Unoccupied Molecular Orbital) of the metal preferential. Metal ions bound to strong-field ligands follow the Aufbau principle, whereas complexes bound to weak-field ligands follow Hund's rule.

Binding of the metal with the ligands results in a set of molecular orbitals, where the metal can be identified with a new HOMO and LUMO (the orbitals defining the properties and reactivity of the resulting complex) and a certain ordering of the 5 d-orbitals (which may be filled, or partially filled with electrons). In an octahedral environment, the 5 otherwise degenerate d-orbitals split in sets of 2 and 3 orbitals (for a more in depth explanation, see crystal field theory).

3 orbitals of low energy: dxy, dxz and dyz
2 of high energy: dz2 and dx2y2

The energy difference between these 2 sets of d-orbitals is called the splitting parameter, Δo. The magnitude of Δo is determined by the field-strength of the ligand: strong field ligands, by definition, increase Δo more than weak field ligands. Ligands can now be sorted according to the magnitude of Δo (see the table below). This ordering of ligands is almost invariable for all metal ions and is called spectrochemical series.

For complexes with a tetrahedral surrounding, the d-orbitals again split into two sets, but this time in reverse order.

2 orbitals of low energy: dz2 and dx2y2
3 orbitals of high energy: dxy, dxz and dyz

The energy difference between these 2 sets of d-orbitals is now called Δt. The magnitude of Δt is smaller than for Δo, because in a tetrahedral complex only 4 ligands influence the d-orbitals, whereas in an octahedral complex the d-orbitals are influenced by 6 ligands. When the coordination number is neither octahedral nor tetrahedral, the splitting becomes correspondingly more complex. For the purposes of ranking ligands, however, the properties of the octahedral complexes and the resulting Δo has been of primary interest.

The arrangement of the d-orbitals on the central atom (as determined by the 'strength' of the ligand), has a strong effect on virtually all the properties of the resulting complexes. E.g., the energy differences in the d-orbitals has a strong effect in the optical absorption spectra of metal complexes. It turns out that valence electrons occupying orbitals with significant 3 d-orbital character absorb in the 400–800 nm region of the spectrum (UV–visible range). The absorption of light (what we perceive as the color) by these electrons (that is, excitation of electrons from one orbital to another orbital under influence of light) can be correlated to the ground state of the metal complex, which reflects the bonding properties of the ligands. The relative change in (relative) energy of the d-orbitals as a function of the field-strength of the ligands is described in Tanabe–Sugano diagrams.

In cases where the ligand has low energy LUMO, such orbitals also participate in the bonding. The metal–ligand bond can be further stabilised by a formal donation of electron density back to the ligand in a process known as back-bonding. In this case a filled, central-atom-based orbital donates density into the LUMO of the (coordinated) ligand. Carbon monoxide is the preeminent example a ligand that engages metals via back-donation. Complementarily, ligands with low-energy filled orbitals of pi-symmetry can serve as pi-donor.

Metal–EDTA complex, wherein the aminocarboxylate is a hexadentate (chelating) ligand.
 
Cobalt(III) complex containing six ammonia ligands, which are monodentate. The chloride is not a ligand.

Classification of ligands as L and X

Especially in the area of organometallic chemistry, ligands are classified as L and X (or combinations of the two). The classification scheme – the "CBC Method" for Covalent Bond Classification – was popularized by M.L.H. Green and "is based on the notion that there are three basic types [of ligands]... represented by the symbols L, X, and Z, which correspond respectively to 2-electron, 1-electron and 0-electron neutral ligands." Another type of ligand worthy of consideration is the LX ligand which as expected from the used conventional representation will donate three electrons if NVE (Number of Valence Electrons) required. Example is alkoxy ligands( which is regularly known as X ligand too). L ligands are derived from charge-neutral precursors and are represented by amines, phosphines, CO, N2, and alkenes. X ligands typically are derived from anionic precursors such as chloride but includes ligands where salts of anion do not really exist such as hydride and alkyl. Thus, the complex IrCl(CO)(PPh3)2 is classified as an MXL3 complex, since CO and the two PPh3 ligands are classified as Ls. The oxidative addition of H2 to IrCl(CO)(PPh3)2 gives an 18e ML3X3 product, IrClH2(CO)(PPh3)2. EDTA4− is classified as an L2X4 ligand, as it features four anions and two neutral donor sites. Cp is classified as an L2X ligand.

Polydentate and polyhapto ligand motifs and nomenclature

Denticity

Denticity (represented by κ) refers to the number of times a ligand bonds to a metal through noncontiguous donor sites. Many ligands are capable of binding metal ions through multiple sites, usually because the ligands have lone pairs on more than one atom. Ligands that bind via more than one atom are often termed chelating. A ligand that binds through two sites is classified as bidentate, and three sites as tridentate. The "bite angle" refers to the angle between the two bonds of a bidentate chelate. Chelating ligands are commonly formed by linking donor groups via organic linkers. A classic bidentate ligand is ethylenediamine, which is derived by the linking of two ammonia groups with an ethylene (−CH2CH2−) linker. A classic example of a polydentate ligand is the hexadentate chelating agent EDTA, which is able to bond through six sites, completely surrounding some metals. The number of times a polydentate ligand binds to a metal centre is symbolized by "κn", where n indicates the number of sites by which a ligand attaches to a metal. EDTA4−, when it is hexidentate, binds as a κ6-ligand, the amines and the carboxylate oxygen atoms are not contiguous. In practice, the n value of a ligand is not indicated explicitly but rather assumed. The binding affinity of a chelating system depends on the chelating angle or bite angle.

Complexes of polydentate ligands are called chelate complexes. They tend to be more stable than complexes derived from monodentate ligands. This enhanced stability, the chelate effect, is usually attributed to effects of entropy, which favors the displacement of many ligands by one polydentate ligand. When the chelating ligand forms a large ring that at least partially surrounds the central atom and bonds to it, leaving the central atom at the centre of a large ring. The more rigid and the higher its denticity, the more inert will be the macrocyclic complex. Heme is a good example: the iron atom is at the centre of a porphyrin macrocycle, being bound to four nitrogen atoms of the tetrapyrrole macrocycle. The very stable dimethylglyoximate complex of nickel is a synthetic macrocycle derived from the anion of dimethylglyoxime.

Hapticity

Hapticity (represented by η) refers to the number of contiguous atoms that comprise a donor site and attach to a metal center. Butadiene forms both η2 and η4 complexes depending on the number of carbon atoms that are bonded to the metal.

Ligand motifs

Trans-spanning ligands

Trans-spanning ligands are bidentate ligands that can span coordination positions on opposite sides of a coordination complex.

Ambidentate ligand

Unlike polydentate ligands, ambidentate ligands can attach to the central atom in two places. A good example of this is thiocyanate, SCN, which can attach at either the sulfur atom or the nitrogen atom. Such compounds give rise to linkage isomerism. Polyfunctional ligands, see especially proteins, can bond to a metal center through different ligand atoms to form various isomers.

Bridging ligand

A bridging ligand links two or more metal centers. Virtually all inorganic solids with simple formulas are coordination polymers, consisting of metal ion centres linked by bridging ligands. This group of materials includes all anhydrous binary metal ion halides and pseudohalides. Bridging ligands also persist in solution. Polyatomic ligands such as carbonate are ambidentate and thus are found to often bind to two or three metals simultaneously. Atoms that bridge metals are sometimes indicated with the prefix "μ". Most inorganic solids are polymers by virtue of the presence of multiple bridging ligands. Bridging ligands, capable of coordinating multiple metal ions, have been attracting considerable interest because of their potential use as building blocks for the fabrication of functional multimetallic assemblies.

Binucleating ligand

Binucleating ligands bind two metal ions. Usually binucleating ligands feature bridging ligands, such as phenoxide, pyrazolate, or pyrazine, as well as other donor groups that bind to only one of the two metal ions.

Metal–ligand multiple bond

Some ligands can bond to a metal center through the same atom but with a different number of lone pairs. The bond order of the metal ligand bond can be in part distinguished through the metal ligand bond angle (M−X−R). This bond angle is often referred to as being linear or bent with further discussion concerning the degree to which the angle is bent. For example, an imido ligand in the ionic form has three lone pairs. One lone pair is used as a sigma X donor, the other two lone pairs are available as L-type pi donors. If both lone pairs are used in pi bonds then the M−N−R geometry is linear. However, if one or both these lone pairs is nonbonding then the M−N−R bond is bent and the extent of the bend speaks to how much pi bonding there may be. η1-Nitric oxide can coordinate to a metal center in linear or bent manner.

Spectator ligand

A spectator ligand is a tightly coordinating polydentate ligand that does not participate in chemical reactions but removes active sites on a metal. Spectator ligands influence the reactivity of the metal center to which they are bound.

Bulky ligands

Bulky ligands are used to control the steric properties of a metal center. They are used for many reasons, both practical and academic. On the practical side, they influence the selectivity of metal catalysts, e.g., in hydroformylation. Of academic interest, bulky ligands stabilize unusual coordination sites, e.g., reactive coligands or low coordination numbers. Often bulky ligands are employed to simulate the steric protection afforded by proteins to metal-containing active sites. Of course excessive steric bulk can prevent the coordination of certain ligands. 

 

The N-heterocyclic carbene ligand called IMes is a bulky ligand by virtue of the pair of mesityl groups.

Chiral ligands

Chiral ligands are useful for inducing asymmetry within the coordination sphere. Often the ligand is employed as an optically pure group. In some cases, such as secondary amines, the asymmetry arises upon coordination. Chiral ligands are used in homogeneous catalysis, such as asymmetric hydrogenation.

Hemilabile ligands

Hemilabile ligands contain at least two electronically different coordinating groups and form complexes where one of these is easily displaced from the metal center while the other remains firmly bound, a behaviour which has been found to increase the reactivity of catalysts when compared to the use of more traditional ligands.

Non-innocent ligand

Non-innocent ligands bond with metals in such a manner that the distribution of electron density between the metal center and ligand is unclear. Describing the bonding of non-innocent ligands often involves writing multiple resonance forms that have partial contributions to the overall state.

Common ligands

Virtually every molecule and every ion can serve as a ligand for (or "coordinate to") metals. Monodentate ligands include virtually all anions and all simple Lewis bases. Thus, the halides and pseudohalides are important anionic ligands whereas ammonia, carbon monoxide, and water are particularly common charge-neutral ligands. Simple organic species are also very common, be they anionic (RO and RCO
2
) or neutral (R2O, R2S, R3−xNHx, and R3P). The steric properties of some ligands are evaluated in terms of their cone angles.

Beyond the classical Lewis bases and anions, all unsaturated molecules are also ligands, utilizing their pi electrons in forming the coordinate bond. Also, metals can bind to the σ bonds in for example silanes, hydrocarbons, and dihydrogen (see also: Agostic interaction).

In complexes of non-innocent ligands, the ligand is bonded to metals via conventional bonds, but the ligand is also redox-active.

Examples of common ligands (by field strength)

In the following table the ligands are sorted by field strength (weak field ligands first):

Ligand formula (bonding atom(s) in bold) Charge Most common denticity Remark(s)
Iodide (iodo) I monoanionic monodentate
Bromide (bromido) Br monoanionic monodentate
Sulfide (thio or less commonly "bridging thiolate") S2− dianionic monodentate (M=S), or bidentate bridging (M−S−M')
Thiocyanate (S-thiocyanato) S−CN monoanionic monodentate ambidentate (see also isothiocyanate, below)
Chloride (chlorido) Cl monoanionic monodentate also found bridging
Nitrate (nitrato) ONO
2
monoanionic monodentate
Azide (azido) NN
2
monoanionic monodentate Very Toxic
Fluoride (fluoro) F monoanionic monodentate
Hydroxide (hydroxido) O−H monoanionic monodentate often found as a bridging ligand
Oxalate (oxalato) [O−CO−CO−O]2− dianionic bidentate
Water (aqua) O−H2 neutral monodentate
Nitrite (nitrito) O−N−O monoanionic monodentate ambidentate (see also nitro)
Isothiocyanate (isothiocyanato) N=C=S monoanionic monodentate ambidentate (see also thiocyanate, above)
Acetonitrile (acetonitrilo) CH3CN neutral monodentate
Pyridine (py) C5H5N neutral monodentate
Ammonia (ammine or less commonly "ammino") NH3 neutral monodentate
Ethylenediamine (en) NH2−CH2−CH2NH2 neutral bidentate
2,2'-Bipyridine (bipy) NC5H4−C5H4N neutral bidentate easily reduced to its (radical) anion or even to its dianion
1,10-Phenanthroline (phen) C12H8N2 neutral bidentate
Nitrite (nitro) NO
2
monoanionic monodentate ambidentate (see also nitrito)
Triphenylphosphine P−(C6H5)3 neutral monodentate
Cyanide (cyano) C≡N
N≡C
monoanionic monodentate can bridge between metals (both metals bound to C, or one to C and one to N)
Carbon monoxide (carbonyl) CO, others neutral monodentate can bridge between metals (both metals bound to C)

The entries in the table are sorted by field strength, binding through the stated atom (i.e. as a terminal ligand). The 'strength' of the ligand changes when the ligand binds in an alternative binding mode (e.g., when it bridges between metals) or when the conformation of the ligand gets distorted (e.g., a linear ligand that is forced through steric interactions to bind in a nonlinear fashion).

Other generally encountered ligands (alphabetical)

In this table other common ligands are listed in alphabetical order.

Ligand Formula (bonding atom(s) in bold) Charge Most common denticity Remark(s)
Acetylacetonate (acac) CH3−CO−CH2−CO−CH3 monoanionic bidentate In general bidentate, bound through both oxygens, but sometimes bound through the central carbon only,
see also analogous ketimine analogues
Alkenes R2C=CR2 neutral
compounds with a C−C double bond
Aminopolycarboxylic acids (APCAs)        
BAPTA (1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid)        
Benzene C6H6 neutral
and other arenes
1,2-Bis(diphenylphosphino)ethane (dppe) (C6H5)2P−C2H4P(C6H5)2 neutral bidentate
1,1-Bis(diphenylphosphino)methane (dppm) (C6H5)2P−CH2P(C6H5)2 neutral
Can bond to two metal atoms at once, forming dimers
Corroles

tetradentate
Crown ethers
neutral
primarily for alkali and alkaline earth metal cations
2,2,2-cryptand

hexadentate primarily for alkali and alkaline earth metal cations
Cryptates
neutral

Cyclopentadienyl (Cp) C
5
H
5
monoanionic
Although monoanionic, by the nature of its occupied molecular orbitals, it is capable of acting as a tridentate ligand.
Diethylenetriamine (dien) C4H13N3 neutral tridentate related to TACN, but not constrained to facial complexation
Dimethylglyoximate (dmgH)
monoanionic

1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)        
Diethylenetriaminepentaacetic acid (DTPA) (pentetic acid)        
Ethylenediaminetetraacetic acid (EDTA) (edta4−) (OOC−CH2)2N−C2H4N(CH2-COO)2 tetraanionic hexadentate
Ethylenediaminetriacetate OOC−CH2NH−C2H4N(CH2-COO)2 trianionic pentadentate
Ethyleneglycolbis(oxyethylenenitrilo)tetraacetate (egta4−) (OOC−CH2)2N−C2H4O−C2H4O−C2H4N(CH2−COO)2 tetraanionic octodentate
Fura-2        
Glycinate (glycinato) NH2CH2COO monoanionic bidentate other α-amino acid anions are comparable (but chiral)
Heme
dianionic tetradentate macrocyclic ligand
Iminodiacetic acid (IDA)     tridentate Used extensively to make radiotracers for scintigraphy by complexing the metastable radionuclide technetium-99m. For example, in cholescintigraphy, HIDA, BrIDA, PIPIDA, and DISIDA are used
Nicotianamine       Ubiquitous in higher plants
Nitrosyl NO+ cationic
bent (1e) and linear (3e) bonding mode
Nitrilotriacetic acid (NTA)        
Oxo O2− dianion monodentate sometimes bridging
Pyrazine N2C4H4 neutral ditopic sometimes bridging
Scorpionate ligand

tridentate
Sulfite OSO2−
2

SO2−
3
monoanionic monodentate ambidentate
2,2';6',2″-Terpyridine (terpy) NC5H4−C5H3N−C5H4N neutral tridentate meridional bonding only
Triazacyclononane (tacn) (C2H4)3(NR)3 neutral tridentate macrocyclic ligand
see also the N,N′,N″-trimethylated analogue
Tricyclohexylphosphine P(C6H11)3 or PCy3 neutral monodentate
Triethylenetetramine (trien) C6H18N4 neutral tetradentate
Trimethylphosphine P(CH3)3 neutral monodentate
Tris(o-tolyl)phosphine P(o-tolyl)3 neutral monodentate
Tris(2-aminoethyl)amine (tren) (NH2CH2CH2)3N neutral tetradentate
Tris(2-diphenylphosphineethyl)amine (np3)
neutral tetradentate
Tropylium C
7
H+
7
cationic

Carbon dioxide CO2, others neutral
see metal carbon dioxide complex
Phosphorus trifluoride (trifluorophosphorus) PF3 neutral

Ligand exchange

A ligand exchange (also ligand substitution) is a type of chemical reaction in which a ligand in a compound is replaced by another. One type of pathway for substitution is the ligand dependent pathway. In organometallic chemistry this can take place via associative substitution or by dissociative substitution.

Ligand–protein binding database

BioLiP is a comprehensive ligand–protein interaction database, with the 3D structure of the ligand–protein interactions taken from the Protein Data Bank. MANORAA is a webserver for analyzing conserved and differential molecular interaction of the ligand in complex with protein structure homologs from the Protein Data Bank. It provides the linkage to protein targets such as its location in the biochemical pathways, SNPs and protein/RNA baseline expression in target organ.

Neurophilosophy

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