SELF-ASSOCIATION OF NEW MIXED-LIGAND DIIMINE-N-ACYL-N',N'-DIALKYL THIOUREATE COMPLEXES OF PLATINUM(II) IN ACETONITRILE SOLUTION

The complexes [Pt(bipy)L]PF6 and [Pt(phen)L]PF6 (HL = N-acyl-N',N'-di- n-butylthiourea) showed pronounced self-association in CD3CN solution at 25 degrees C according to an equilibrium 2[Pt(diimine)(L-S,O)](+)re versible arrow[{Pt(diimine)(L-S,O)}(2)](2+) for which association cons tants, K-D, have been estimated from the concentration dependence of t he H-1 NMR shifts of these complexes. The values of K-D range from 1.8 to 114 M-1 depending on the structure of the diimine as well as the n ature of the N-acyl group; the values of the 1,10-phenanthroline compl exes are generally larger than those for the corresponding 2,2'-bipyri dine analogues. In general, N-1-naphthoyl-N',N'-dibutylthiourea comple xes self-associate to a lesser extent than the corresponding N-benzoyl analogues. From the temperature dependence of the K-D values, the the rmodynamic parameters Delta G, Delta H and Delta S have been estimated . An average Delta(Delta G) increment of 2.4 +/- 0.4 kJ mol(-1) per ar omatic ring of the diimine moiety co-ordinated to the complexes is con sistent with energies generally associated with pi-pi stacking and cat ion K interactions observed for other systems.