STRUCTURE AND REACTIVITY OF AN INTERMEDIATE IN THE 2-ELECTRON REDUCTION OF DIMOLYBDENUM(III) BY A HYDRIDE LIGAND IN THE MO-H-MO SYSTEM

The reaction between the mu-hydride dimolybdenum(III) complex [Mo2Cl8H ](3-) and carboxylic acids in aqueous solution produces a violet speci es which slowly decomposes to yield the quadruply bonded dimolybdenum( II) complex Mo-2(O(2)CR)(4) The violet intermediate in the reaction of [Mo2Cl8H](3-) with glycine was isolated by ion exchange chromatograph y and crystallized. The crystals of [Mo2H(OH)(gly)(2)Cl-4] (1) are mon oclinic, space group P2(1)/n with a=9.536(4), b=14.792(4), c=9.339(3) Angstrom, beta=109.99(3)degrees, V=1283(1) Angstrom(3) and Z=4. The tw o Mo(III) ions in this complex are bridged by one hydride ligand, one OH- group and two glycine groups through the carboxylic end. The Mo-Mo distance is 2.353(5) Angstrom, the shortest found for the Mo-H-Mo sys tem. [(H2O)(2)MoH(OH)(gly)(2)Mo(H2O)(2)](4+) is the structure proposed for the violet intermediate II in the reaction [Mo2Cl8H](3-)-->II-->H ++[Mo-2(gly)(4)]Cl-4+4Cl(-). This structure was derived from structure 1, the high ionic charge of about 4+ and the absence of chloride in t his species. The decomposition reaction of II and the relation of II w ith the red intermediate III of the reaction -)+H2O-->III-->H-2+[Mo-2( OH)(2)Cl-2](2+)+6Cl(-)+H+ is discussed.