Ligand-stabilization of an unusual square-based pyramidal geometry of Cd(II) and Zn(II) in an heterometallic {MPt2S2} core (M = Cd, Zn)

Two heterometallic complexes, [Pt2MCl(bipy)(PPh3)(4)(mu(3)-S)(2)][PF6] (M = Zn, 2, Cd, 3) were synthesized from [Pt-2(PPh3)(4)(mu-S)(2)] and character ized by single-crystal X-ray diffraction and electrospray ionization mass s pectrometry. Two unusual square-based pyramidal (sbp) Zn(II) and Cd(II) str uctures are evident. VT P-31-{H-1} NMR studies showed that 2 and 3 are flux ional at rt whereby rapid ligand exchange takes place by a non-dissociative mechanism. At intermediate temperatures, this motion slows down to a flipp ing movement of the {Pt2S2} ligand. At 183 K, all four phosphines are inequ ivalent in a distorted sbp model similar to that observed in the solid stat e. Nonlocal density functional theory calculations reveal that the formatio n of a trigonal bipyramidal intermediate in the fluxional process is favore d over that of the tetrahedral species for both 2 and 3. The M-Cl (M = Zn, Cd) bonds are notably strong.