Synthesis, electrochemistry and crystal structure of the [Ni36Pt4(CO)45]6- and [Ni37Pt4(CO)46]6- hexaanions

The [Ni36Pt4(CO)(45)](6-) and [Ni37Pt4(CO)(46)](6-) clusters have been obtained in mixture upon reaction in acetonitrile of [Ni-6(CO)(12)](2-) salts with K2PtCl4 in a 2.5:1 molar ratio. The two hexaanions were indistinguishable by spectroscopic techniques. Crystallization of their trimethylbenzylammonium salts led to crystals of composition 0.5[NMe3CH2Ph](6)[Ni36Pt4(CO)(45)]-0.5[NMe3C [Ni37Pt4(CO)(46)].C3H8O, hexagonal,space group P6(3) (No. 173), a = 17.853(9). c = 27.127(n) A, Z = 2; final R = 0.057. The metal core of the [Ni36Pt4(CO)(45)](6-) anion consists of a Pt-4 tetrahedron fully encapsulated in a shell of 36 Ni atoms belonging to a very distorted and incomplete v(5) tetrahedron. The [Ni36Pt4(CO)(46)](6-)-hexaanion derives from the former by capping the unique triangular face of the metal polyhedron with an additional Ni(CO) fragment. The [Ni9Pt3(CO)(21)](6-)-[Ni37Pt4(CO)(46)](6-) mixture is rapidly degraded to the known [Ni9Pt3(CO)(21)](4-) cluster by exposure to carbon monoxide. Its reaction with protic acids initially affords the corresponding [H6-nNi36Pt4(CO)(45)](n-)-[H6-nNi37Pt4(CO)(46)](n-)(n=5. 4) derivatives, and eventually leads to rearrangement to the known [H6-nNi38Pt6(CO)(48)](n-) species. Both [Ni36Pt4(CO)(45)](6-)-[Ni-37 Pt-4(CO)(46)](6-)and [HNi36 Pt-4(CO)(45)](5-)-[Ni37Pt4(CO)(46)](5-) mixtures have been chemically and electrochemically reduced to their corresponding [Ni36Pt4(CO)(45)](n-)[Ni37Pt4(CO)(46)](n-) (n = 7-9) and [HNi36Pt4(CO)(45)](n-) -[HNi37Pt4(CO)(46)](n-)(n = 6 8) mixtures.