Crystal structure and electronic properties of tetrakis[µ3-bis(2-pyridyl)amido]dichlorotrinickel(II)–water–acetone (1/0.23/0.5)

Abstract

The crystal structure of [Ni₃(bipyam–H)₄Cl₂]·0.23H₂O·0.5(CH₃)₂CO 1[bipyam–H = bis(2-pyridyl)-amide] has been determined using X-ray diffractometer data; C_41.5H_35.5Cl₂N₁₂Ni₃O_0.75, monoclinic, space group C2/c, with a= 37.525(7), b= 16.237(3), c= 22.550(6)Å, β= 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 Ni₃N₁₂Cl₂ chromophores of (1) and (2) involve a nearly linear Ni₃ unit, mean Ni–Ni–Ni angle 178.4(1)°, 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)Å 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° is involved between the planes of the individual pyridine rings of each bipyam–H ligand and results in a spiral configuration in the Ni₃(bipyam–H)₄Cl₂ unit. The room-temperature magnetic moment µ_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 17 700 cm^–1, and a low-intensity shoulder at 10 800 cm^–1, consistent with the two nickel(II) stereochemistries present.