摘要：

The triangular metal carbonyls formed from the Ni group transition metals are remarkable in their propensity to form high nuclearity clusters just by associating into chains. Such chains are typified by the compounds [Pt3(μ2-CO)3(CO)3] n2- (n = 2, 3, 4, 5, 6, 10). However, there is a characteristic structural difference between the "tinker-toy" construction of stacks using Ni rather than Pt; the Ni carbonyl chains have a screw axis along the main axis, whereas the Pt chains have a simple threefold axis. Reasons for stacking and the requirements of the 2- charge for all chain lengths as well as the structural differences between Ni and Pt chains are discussed in terms of the calculated electronic structure of the dimer. As well as a necessary electron count for oligomerization, there exist monomers which have specific valence electron counts. For 42 valence electrons and acceptor ligands as bridges (e.g., Pt3(CNR)6) an equilateral triangle of metals is expected. When an extra two electrons are added, calculations show that distortion to an isosceles triangle or to a larger equilateral triangle is favored. Differences in electron count of various monomers are related to the types of bridging and terminal ligands present. For instance for bridging phosphide, PR2, trimers the 44-electron species should be the stable one. The reasons for further deformation in such 44-electron trimers are addressed. In addition to oligomers, intercalation complexes are also known. For Ni there is the series [Ni12(CO)21H4-n]n- where n = 2, 3, 4 and for Pt there are the compounds [Pt3(μ2-CNR)3(CNR)3] 2Hg where R = 2,6-dimethylphenyl and [Pt(μ2-CO)3(PPh-i-Pr2)3] 2Hg2. The reasons for the stability of these compounds are discussed in terms of the electronic structure of the Pt dimers at large monomer-monomer separation. On the basis of the known monomers, intercalates, and oligomers the existence of long-chain polymers is postulated. For 1[Pt3(CO)6]∞ the calculated bond structure indicates that oxidation or reduction of the neutral chain should result in stabilization. In many ways it is similar to the tetracyanoplatinate chains discussed previously in the literature. Partially occupied bands may result in Peierls distortions leading to structures similar to those observed for the pentamer and presumably the decamer. The band structure of 1[Pt3(CO)6Hg]∞ shows a valence band with much greater dispersion than the other bands. Partial occupation of this band (by replacing Hg with Cu, Ag, or Au) will most likely result in a pairing distortion to give a semiconductor.

展开