DEPROTONATED THIOAMIDES AS THIOLATE S-DONOR LIGANDS WITH A HIGH TENDENCY TO AVOID M-S-M BRIDGE FORMATION - CRYSTAL AND MOLECULAR-STRUCTURE OF [NI(TMTSSA)]2

The crystal structure of [Ni(tmtssA)]2 (1a) (tmtssA = 2-hydroxy-5-methylacetophenone N,N-dimethylthiosemicarbazonato) is surprising in having a phenolate O-bridge rather than the expected imino thiolate S-bridge. This implies that deprotonated thioamides such as tmtssA, which bind in the imino thiolate form, have a much lower bridging tendency than alkane- or arenethiolates. Reasons are suggested as to why imino thiolates avoid several limitations of thiolates as ligands: bridge formation, C-S bond cleavage, and reduction of the metal. By analogy with the recognized basicity difference of syn and anti lone pairs in carboxylates, we suggest that the bridge-avoiding tendency of an imino thiolate is related to the low basicity of the S lone pair anti to the C=N group which would bind to the second metal in any dimer. Crystal data for [Ni(C12H15N3OS)]2 (1a): triclinic, space group P1BAR, a = 8.220(2) angstrom, b = 13.100(3) angstrom, c = 13.864(3) angstrom, alpha = 114.56(3)-degrees, beta = 103.59(3)-degrees, gamma = 92.07(3)-degrees, Z = 2, R = 4.26% (3637 observed reflections).