Polynuclear clusters, structure

In compliance with the nuclearity principle, polynuclear clusters are subdivided into a number of other subgroups, e.g. hexanuclear, octanuclear, etc. The binuclear clusters of technetium may be classified according to the electronic structure of their Tc-Tc2 bonds. Then, the d4-d4 complexes with quadruple M-M bonds are the father of all binuclear complexes with Tc-Tc bonds. The addition or removal of electrons from Tc-Tc bonds [1,11] should result in a decrease in the formal multiplicity of M-M bonds. Thus, for instance, the formal multiplicity of Tc-Tc bonds of d3-d3 and d5-d5 binuclear complexes equals3 3, that of d4 d5 and d4-d3 complexes equals 3.5, etc. 

Abstract This review deals with spin crossover effects in small polynuclear clusters, particularly dinuclear species, and in extended network molecular materials, some of which have interpenetrated network structures. Fe(II)Fe(II) species are the main focus but Co(II)Co(II) compounds are included. The sections on dinuclear compounds include short background reviews on (i) synergism of SCO and spin-spin magnetic exchange (ii) cooperativity (memory effects) in polynuclear compounds, and (iii) the design of dinu-... 

Supported nanoparticles are related to the idea of starting with polynuclear cluster precursors. While there is no clear line that divides polynuclear clusters from nanoparticles, clusters are generally small, low nuclearity (MnL n = 3-20), structurally well-characterized species approximately 1-2 nm in size. Nanoparticles are larger (>2 nm) and frequently defined by a size distribution rather than a discrete number of atoms and ligands [41]. In the area of catalysis, gold nanopar-... 

The redox behaviour of polynuclear clusters has been examined for electrocatalytic properties27. Clusters of the type [Co4(CO)10 JC( 4-PPh)2Lx], where L is a mono-, or di-phosphine having the structures of the type shown ... 

In the extreme class III behaviour,360-362 two types of structures were envisaged clusters and infinite lattices (Table 17). The latter, class IIIB behaviour, has been known for a number of years in the nonstoichiometric sulfides of copper (see ref. 10, p. 1142), and particularly in the double layer structure of K[Cu4S3],382 which exhibits the electrical conductivity and the reflectivity typical of a metal. The former, class IIIA behaviour, was looked for in the polynuclear clusters of copper(I) Cu gX, species, especially where X = sulfur, but no mixed valence copper(I)/(II) clusters with class IIIA behaviour have been identified to date. Mixed valence copper(I)/(II) complexes of class II behaviour (Table 17) have properties intermediate between those of class I and class III. The local copper(I)/(II) stereochemistry is well defined and the same for all Cu atoms present, and the single odd electron is associated with both Cu atoms, i.e. delocalized between them, but will have a normal spin-only magnetic moment. The complexes will be semiconductors and the d-d spectra of the odd electron will involve a near normal copper(II)-type spectrum (see Section 53.4.4.5), but in addition a unique band may be observed associated with an intervalence CuVCu11 charge transfer band (IVTC) (Table 19). While these requirements are fairly clear,360,362 their realization for specific systems is not so clearly established. 

Atoms, simplest ions, and molecules di- and polychelating compounds take part as bridge-type ligands in these complexes. Di- and polynuclear structures of the simplest ligands, in terms of the number of cluster structures, are reported in the literature, cited in Sec. 1.2.2.4. 

Complexes in the 0 oxidation state may be obtained either by reduction of halides such as RuCl2(PPh3)3 with Na or Zn in the presence of CO or other ligands such as RNC, or by reaction of metal carbonyls with phosphines. Reactions of polynuclear carbonyls such as Ru3(CO)12 (Section 18-F-13) with phosphines tend to preserve the cluster structure. 

Polynuclear clusters with Ph2PNHPh2 external ligands, for example, [Cu6(Ph2PNHPPh2)4(M3-SePh)4][BF4]2 have been structurally characterized. ... 

IR-9.2.5.7 Polynuclear clusters symmetrical central structural units IR-9.3 Describing the configuration of coordination entities IR-9.3.1 Introduction... 

Polynuclear clusters symmetrical central structural units... 

A comprehensive review appeared on the chemistry and structure of polynuclear clusters containing triphenylphosphine-stabilized Au and Pd or Pt. Many of the clusters contain also additional metals, such as Ag, Cu or Hg. The nuclearity (number of metal atoms) of the clusters ranges from 3 (e.g. 56) to 25 (e.g. 57). The spectroscopic techniques used for structural characterization of these entities were NMR, fast-atom-bombardment MS (FAB-MS), UVV and XPS. Several applications in catalysis were also reviewed164. 

As used here cluster refers to molecules that contain at least 3 metal atoms and electron configurations suitable for the formation of metal-metal bonds. Molybdenum readily forms strong homoleptic metal-metal bonds seeHomoleptic Compound) and so it is not surprising that molybdenum is readily incorporated into cluster structures see Polynuclear Organometallic Cluster Complexes. 

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