Polynuclear compounds structure

As it was shown in [15-18], such compounds, with bridging atoms of deprotonated amino alcohol, are formed when aminoalcoholate complexes of metal (III) react with bivalent 3d-metal ions. Many representatives of these compounds were synthesized in crystalline state the polynuclear compounds were also found to form in aqueous and methanol solutions. The structure of 2Co(III) - Ni(II) tri-nuclear complex, according to [17,18], is shown below in Figure 2. 

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-... 

In connection to the data described earlier, one reasonable question arises Why does the stabilizing role of a nonaqueous solvent become significant for Cu salts and remain insignificant for Cu salts It was shown (Myagchenko et al. 1989) that Cu salts (and salts of Hg and Pd as well) exist in nonaqueous solutions as polynuclear compounds. Thus, CUCI2 forms lamellar lattices with chlorine chains as bridges between copper atoms. In contrast, CuCl does not form such chain structures. 

In conclusion, the electrochemical data offer a fingerprint of the chemical and topological structure of the polynuclear compounds. Furthermore, made-to-OTder synthetic control of the number of electrons exchanged at a certain potential can be achieved. The presence of multielectron processes makes such polynuclear complexes very attractive in view of their possible application as multielectron-transfer catalysts. Examination over a more extended oxidation potential window (in a solvent like liquid SOj) should permit one to obtain an even larger variety of oxidation patterns. 

Polynuclear compounds may be either of such large extended structures as to make rational structure-based nomenclature impractical, or the structures may be undefined or partially elucidated. In these instances compositional nomenclature is most suited. 

Structural nomenclature for more complex polynuclear compounds is based on the description of the fundamental structural unit, and a logical procedure for numbering the atoms of the fundamental or central structural unit. For nonlinear clusters, descriptors such as tetrahedro, dodecahedro, etc. have traditionally been used to describe a central structural unit (CSU). However, synthetic chemistry has now advanced far beyond the utility of the limited CSU set associated... 

Cu Cu Interaction in Cu1 Polynuclear Compounds. In many of these structures there are relatively short Cu—Cu distances 2.38 to 3.2 A (Cu—Cu in metal 2.40 A). However, there are always bridges present and since Cu1 is d" metal-metal bonding would appear to be weak if existing at all. The compounds are hence best referred to as aggregates or cages and not metal atom clusters whose defining property is the existence of M—M bonds. 

Metal carbonyls are characterized by IR-active vibrations associated with the carbonyl groups. Especially studied are the carbonyl stretching vibrations around 2000cm". The vibrational spectra give important information about (a) the electronic distribution within the M-CO bond in terminally bonded carbonyl groups (b) the molecular structure associated with the number of bands observed and (c) the type of bonding in dinuclear and polynuclear compounds. 

The Cu ion is classified as a soft acid (see Hard Soft Acids and Bases), which predicts reasonably well the types of ligands that will be most stabilizing and are, thus, commonly observed in Cu complexes. The preference of Cu for softer ligands is quite apparent in the homoleptic complexes, for instance the halides discussed above. Polynuclear compounds are quite commonly seen in the chemistry of Cn. Thus, the solid-state structure cannot be reliably predicted from the reaction stoichiometry or from the empirical formula of the resulting compound. The careful selection of ligands, for instance, an appropriate macrocyclic ligand can ensnre the formation of a mononuclear complex if one is desired. 

More recently, it has become clear that many polynuclear compounds undergo electron-transfer reactions, and several reviews devoted wholly or partly to this subject have appeared 1-4). Studies of the redox properties of polymetallic species can provide information on the nature of the highest occupied molecular orbital (HOMO) or lowest unoccupied molecular orbital (LUMO), on the possible cooperativity between metal sites, on the existence of mixed-valence compounds, and on the ways in which one-electron (or, more rarely, two-electron) changes affect structure and reactivity. 

Many polynuclear aromatic compounds do not contain fused ring systems, e.g., biphenyl and triphenylmethane. Give structures and names of compounds W through 11, formed in the following syntheses of such polynuclear compounds. 

The different behaviour of iron- and tungsten-silanols presumably is best interpreted in terms of the higher steric demand of the tungsten fragment. Support for this idea is expected from the structural investigations of the siloxy-bridged polynuclear compounds, presented above. 

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