CRYSTAL-STRUCTURE AND ELECTRONIC-PROPERTIES OF TETRAKIS[MU-3-BIS(2-PYRIDYL)AMIDO]DICHLOROTRINICKEL(II) WATER ACETONE (1/0.23/0.5)

The crystal structure of [Ni3(bipyam-H)4Cl2].0.23H-20.05(CH3)2CO 1 [bipyam-H = bis(2-pyridyl)-amide] has been determined using X-ray diffractomer data; C41.5H35.5Cl2N12Ni3O0.75, monoclinic, space group C2/c, with a = 37.525(7), b = 16.237(3), c = 22.550(6) angstrom, beta = 110.12(2), Z = 12; 5778 measured and 5519 unique reflections gave a final R value of 0.051. The structure involves two independent Ni3(bipyam-H)4Cl2 units, (1) and (2) [(1) occupies a general position and (2) is on a C2 axis], one non-co-ordinated water molecule [site occupation factor (s.o.f.) 0.23], and one acetone molecule (s.o.f. 0.5). The Ni2N12Cl2 chromophores of (1) and (2) involve a nearly linear Ni2 unit, mean Ni-Ni-Ni angle 178.4(1)-degrees, terminated by the two chloride anions. The four separate bipyam-H ligands act as tridentate ligands, involving co-ordination to three separate nickel(II) ions with Ni-Ni distances 2.443(1) (twice) and 2.431(1) angstrom for units (1) and (2), respectively. If the Ni-Ni separations are ignored the central Ni atom in both units involves a four-co-ordinate rhombic coplanar NiN4 chromophore, generated by the four central amido nitrogens of the bipyam-H ligands. The two terminal Ni atoms involve a square-based pyramidal NiN4Cl chromophore, involving the four pyridine nitrogens of the bipyam-H ligands and an axial Cl atom. A dihedral angle of ca. 54-degrees is involved between the planes of the individual pyridine rings of each bipyram-H ligand and results in a spiral configuration in the Ni3(bipyam-H)4Cl2 unit. The room-temperature magnetic moment mu-eff of compound 1 is 2.46, consistent with a diamagnetic central NiN4 chromophore and two paramagnetic terminal NiN4Cl chromophores. The electronic spectrum involves a low-energy peak at 6500 cm-1, an intense peak at 17700 cm-1, and a low-intensity shoulder at 10800 cm-1, consistent with the two nickel(II) stereochemistries present.