Dinuclear Nickel(II) Complexes of an Unsymmetric “End-Off” Compartmental Ligand: Conversion of Urea into Cyanate at a Dinuclear Nickel Core (original) (raw)

1998, Inorganic Chemistry

A phenol-based "end-off" compartmental ligand, 2-[N,N-di(2-pyridylmethyl)aminomethyl]-6-{N-[2-(dimethylamino)ethyl]iminomethyl}-4-methylphenol (HL), having an iminic bidentate and an aminic tridentate chelating arms on the 2-and 6-positions of the phenolic ring, respectively, forms dinuclear nickel complexes [Ni 2 (L)-(AcO)(NCS) 2 ] (1), [Ni 2 (L)(AcO) 2 (MeOH)]PF 6 (2), and [{Ni 2 (L)(OH)(MeOH)} 2 (CO 3)](PF 6) 2 (3). Complex 1 crystallizes in the monoclinic space group P2 1 /c, a) 14.165(5) Å, b)15.198(4) Å, c) 17.395(8) Å,) 100.62-(4)°, V) 3680(2) Å 3 , and Z) 4. The pair of Ni ions present are bridged by the phenolic oxygen of Land an acetate group in syn-syn mode (Ni-Ni: 3.373(3) Å). An isothiocyanate nitrogen atom coordinates to each Ni providing an asymmetric dinuclear core with a mixed {5/6} coordination number set. Complex 2 crystallizes in the monoclinic space group P2 1 /c, a) 13.505(5) Å, b) 12.028(4) Å, c) 22.774(9) Å,) 103.78(3)°, V) 3592(2) Å 3 , and Z) 4. It has a dinuclear core bridged by the phenolic oxygen of Land two acetate groups in syn-syn mode, providing a µ-phenoxo-bis(µ-carboxylato)dinickel(II) core (Ni-Ni: 3.396(6) Å). A methanol molecule coordinates to the Ni bound to the bidentate arm, forming a dinuclear core having a {6/6} coordination number set and an asymmetric donor atom environment. Complex 3 crystallizes in the orthorhombic space group Pbcn, a) 19.056(5) Å, b) 18.997(4) Å, c) 19.919(6) Å, R)) γ) 90°, V) 7211(5) Å 3 , and Z) 8. In each dinuclear unit a pair of Ni ions are bridged by the phenolic oxygen of Land a hydroxo oxygen (Ni-Ni: 3.087(2) Å). A carbonate further bridges two of the dinuclear units to present a composite dimer. The Ni bound to the bidentate arm attains six-coordinate geometry by further interaction with two oxygens of the bridging carbonato group. The Ni bound to the tridentate arm assumes six-coordinate geometry by further coordination of a methanol oxygen. Complexes 1-3 react with urea in ethanol to form the isocyanate complexes [Ni 2 (L)-(AcO)(NCS)(NCO)] (1′), [Ni 2 (L)(AcO)(NCO)(EtOH)]PF 6 (2′), and [{Ni 2 (L)(NCO)(EtOH)} 2 (CO 3)](PF 6) 2 (3′), respectively. Complex 3′ crystallizes in the triclinic space group P1 h, a) 20.072(7) Å, b) 21.145(6) Å, c) 18.688(6) Å, R) 106.20(2)°,) 90.01(3)°, γ) 88.73(3)°, V) 7614(4) Å 3 , and Z) 4. It has a dimeric structure very similar to that of 3, except for the replacement of the hydroxy bridge and the methanol ligand in 3 by isocyanate bridge and ethanol ligand, respectively, in 3′.