Hexanuclear complexes electron 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. 

The remarkable hexanuclear complex [ NiCp ] (81), prepared by the sodium naphthalenide reduction of nickelocene, undergoes an extensive series of reversible one-electron transfer reactions cyclic voltammetry shows waves relating the six species [ NiCp 6] (Z = -2 to 3). Chemical oxidation of 81, with Ag, gave the monocation whose structure shows only a small tetragonal distortion from the octahedral array of nickel atoms in the neutral precursor (198). 

The Zr2(OPr )9 unit is also present in the centrosymmetric hexanuclear complex [ Zr2(OPr )9 Pb(jii-OPr )2Pb Zr2(OPr )9 ] in which the Pb(n) atoms are 4-coordinated or pseudo-trigonal bipyramidal, assuming the presence of the lone pair of electrons occupying the vacant equatorial site. " The centrosymmetric [(Pr 0)3Zr(/i-0Pr )3Pb(/i-OPr )Pb(jU,-OPr )2Pb(/i-OPr )Pb(Ai-OPr )3Zr(OPr )3] has a zig-zag chain structure with two pyramidal three-coordinated Pb(ii) atoms and two pseudo-trigonal bipyramidal five-coordinated. " ... 

The influence of electronic effects on the binding mode of tetraalkynylplatinate anions is apparent in the reactions of compounds of general formula Li2[Pt (C=CR)4] with thallium(l) nitrate [72]. For electrrai-rich alkynyl moieties (R = p-tolyl, 1-naphtyl), discrete hexanuclear structures are obtained (Scheme 16, top), in which each Tl center interacts with four C=C triple bonds and not with the platinum atom. The introduction of a remote electron-withdrawing substituent oti the alkynyl unit (R = p-CFsC lU) induces a dramatic change in the structure of the Lewis acid-base complex each platinum atom now involves in donor-acceptor bonds with two thaUium(I) ions (Pt-Tl 2.9355(5) and 3.0272(5) A), one oti each face of its coordination plane. These Tl2Pt units are interconnected by weak interactions of thallium with the Jt-elecfron density of the triple bonds. 

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