Abstract
The electronic structures of transition metal complexes of NO are controlled by the stereochemistry about the metal atom (stereochemical control of valence). The six-coordinate complex, trans-[CoNO(NCS)-(C(6)H(4) [As(CH(3))(2)](2))(2)](+), consists of [Co(III)-(N=O(-))](2+) (angle(Co-N-O) = 135 degrees ), while the pentacoordinate trigonal bipyramidal complex, [CoNO(C(6)H(4)[As(CH(3))(2)](2))(2)] (2+), is best formulated as [Co(I)-(N identical withO(+)](2+) (angle(Co-N-O) = 179 degrees ). Evidence indicates that complexes of (NO)(+) and N(2) are electronically similar. Hence, the principles of stereochemical control of valence may be applied to metal complexes of N(2). In a linearly coordinated M(n) m(N identical withN) complex, valence electrons can be transferred from the metal to the N(2) ligand producing a bent, protonated, and/or metallated M(n+2)-(N=N(2-)) complex. This reduction of N(2) can be effected by the addition of an appropriate ligand to M or by a change in the coordination geometry about M. Stereo-chemical control of valence leads to the rejection of one of the previously proposed mechanisms for reduction by nitrogenase.