X-ray crystal structures of nickel complexes with 2-methyl-8-quinolinol, Ni(mq)2(H2O)2 and Na3Ni3H6(mq)15H2O.

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Two Ni(II) complexes with 2-methyl-8-quinolinol (Hmq) were prepared and their structures determined by single-crystal X-ray diffraction techniques. In Ni(mq)2(H2O)2, which is orthorhombic, space group Pccn, Z=8 the geometry is trans(O,O), cis(N,N), and cis(H2O,H2O), and the octahedron is appreciably distorted. In Na3Ni3H6(mq)15·H2O, which is monoclinic, space group P21⁄c, Z=4, three binuclear units Ni(1)–Na(1), Ni(2)–Na(2), and Ni(3)–Na(3), are involved. All the Ni atoms are surrounded by three ligands in a mer configuration. The Na(1) and Na(2) atoms are five-coordinated with two ligands and an O atom bridging Na and Ni atoms within a dimer. The Na(3) atom has, together with the ligands, a coordinated water which is hydrogen-bonded to the O atom coordinating to the Ni(3) atom. These dimeric units are infinitely linked by intermolecular hydrogen bonds. Compared to the corresponding complexes of 8-quinolinol derivatives without 2-methyl substituent, the Ni–N is elongated by 0.06–0.12 Å, whereas the Ni–O is shortened by 0.01–0.05 Å. An increase in the bond angle (7–11 deg) between a N atom of a ligand and the donor atom (Y) which occupies the trans position to the O atom of the same ligand, reduces the steric interaction between the methyl group and Y in Hmq complexes. Shorter contacts between ligands in Hmq complexes than those in Hq complexes lead to their lower stabilities and, thus, the lower extractabilities.