Complexes formed from 2,4,6-trimercaptotriazine (H3TMT): synthesis and structural characterization of [M(PhP(CH2CH2P(Ph)2)2(HTMT)], M = Ni(II), Pd(II), Pt(II)

Na3TMT . 9H(2)O (H3TMT = 2,4,6-trimercaptotriazine) reacts with M(PPP)Cl-2, PPP = PhP(CH2CH2PPh2)(2), M = Ni, Pd, Pt, to give the compounds [M(PPP)(HTMT)]. The nickel and palladium complexes have been characterized by single-crystal X-ray diffraction analysis. PPP is tridentate in both complexes. The nickel complex has an irregular trigonal bipyramidal configuration in which the triazine is bidentate, coordinating through one sulfur and one nitrogen donor atom. The palladium complex has an approximately square planar geometry in which the triazine forms a strong Pd-S bond in the plane and also a very weak Pd-N interaction above the plane. The P-31 NMR spectrum of the platinum complex is similar to that of the palladium complex, which is consistent with the Pt complex also having an approximately square-planar structure. Variable temperature NMR spectra show that two conformational isomers of the nickel complex are present in solution at low temperatures, though exchange is fast at room temperature. DFT calculations have confirmed the possible existence of two five-coordinate isomers of comparable stability.