A series of pyridine-substituted derivatives of octaacetatotetraplatinum(II), [Pt4(CH3COO)8-n(L)2n]n+ (L = 4-dimethylaminopyridine (dmap), pyridine (py), 4-cyanopyridine (cpy); n = 1 - 4) were prepared, and the tetra- and octasubstituted forms (n = 2 and 4) were isolated. 1H NMR spectra showed that this type of cluster undergoes a comproportionation reaction. Reactions between clusters in which n = 0 and 2, n = 0 and 4, and n = 2 and 4 afforded Pt4 clusters with n = 1, 2, and 3, respectively, as a main product in acetonitrile. The dmap-substituted clusters, trans-[Pt4(CH3COO)6(dmap)4](ClO 4)2 · 3CH3NO2 (3a(ClO4)2·3CH3NO2) and [Pt4(CH3COO)4(dmap)8](ClO 4)4·4H2O (5a(ClO4)4·4H2O), have been structurally characterized. Both 3a and 5a have a square-planar cluster core comprised of four PtII ions, and all eight out-of-plane coordination sites are occupied by acetate ligands in a bridging mode. In 5a, all of the in-plane sites are occupied by dmap ligands. In 3a, four dmap ligands occupy the coordination sites at the two mutually opposite edges of the square planar cluster skeleton, giving a trans tetrasubstituted form of [Pt4(CH3COO)8] (1). In octasubstituted 5a, adjacent dmap ligands are so closely arranged that the Pt-N distances (2.20(3), 2.30(3) Å) are longer than those in tetrasubstituted 3a (2.13(1), 2.15(1) Å) and related Pt4 clusters. Furthermore, rotation of the dmap ligand about the Pt-N bond in 5a was restricted, and the rate constant of the rotation was 4.5s-1 at 20°C from dynamic NMR study. Cluster [Pt4(CH3COO)5-(dmap)6]3+ (4a) also exhibited similar hindered rotation with the rate constants of 2.0s-1, 12s-1 and ≈ 104s-1 at 20°C depending on the coordination sites of the dmap ligands in 4a.
|ジャーナル||Chemistry - A European Journal|
|出版ステータス||Published - 2001 12月 17|
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