Structural studies of nickel complexes of the unsymmetrical tridentate ligand N-phenyl-N-(2-pyridyl)formamidinate

We describe the preparation and structural characterization of six nickel complexes with the unsymmetrical formamidine HPhPyF (N,N′-phenylpyridylformamidine). These six compounds include one dinuclear species Ni2(PhPyF)4 (1), two mononuclear complexes: cis-[Ni(HPhPyF)2(MeCN)2][BF4]2 (3) and Ni(HPhPyF)Br2 (6), and three trinuclear compounds: Ni3(PhPyF)4(MeCN)2(BF4)2 (2), [Ni3(PhPyF)4Cl]Cl (4), and Ni3(PhPyF)4Cl2 (5). In the dinuclear species 1, the two nickel atoms are surrounded by four formamidinate ligands. Each is pseudo-octahedral and there is long separation (≈3.41 Å) between them. One mononuclear compound, cis-[Ni(HPhPyF)2(MeCN)2][BF4]2 (3) has a distorted octahedral geometry, the other Ni(HPhPyF)Br2 (6) contains a Ni atom in a pseudo-tetrahedral environment. All three trinuclear compounds contain a linear chain of three NiII atoms wrapped by four PhPyF anions, but each has a different axial environment. There are two axially coordinated MeCN in 2, only one axial Cl anion for 4 and two axial Cl anions for 5. In 2, 4, and 5, the Ni3 6+ chains are symmetrical with relatively long Ni⋯Ni separations in the range 2.44–2.51 Å.