Structure and bonding in homoleptic transition metal hydride anions

This paper surveys aspects of the structure and bonding in homoleptic transition metal hydride anions. Most such hydrometalate anions are found in solid state ternary and quaternary transition metal hydrides also containing one or two electropositive metals although soluble MH92- (M = Tc, Re) and FeH64- derivatives are known. The principles of structure and bonding in such hydrometalates are seen to be similar to those in related transition metal complexes of other ligands. Thus the favored 18-electron configuration of the next rare gas dominates for the hydrometalates of manganese (in MnH65-) through copper (in CuH43-) although square planar and trigonal 16-electron complexes (e.g. PdH33- PdH42- and PtH42-) and linear 14-electron complexes (PdH22-) are also known. The stability of a half filled d shell for the d(5) Mn(II) is illustrated by the occurrence of the high-spin tetrahedral MnH42- ion in K3MnH5. The metal atoms in the RuH44- units of Mg2RuH4 and the RuH36- units of Mg3RuH3 can attain the 18-electron rare gas configuration through metal-metal bonding to form the polymer [RuH44-](x) and the dimer [RuH36-](2), respectively. The RhH2- anion in MgRhH forms a cyclic tetramer related but not identical to the cyclic tetramers formed by certain isoelectronic Cu(I) alkyls. (C) 2000 Elsevier Science S.A. All rights reserved.