Intra- and intermolecular H center dot center dot center dot Cl-Ni bonding patterns in a series of highly preorganized dinuclear nickel(II) complexes

Four dinickel complexes [(LNi2)-Ni-1(mu-Cl)(Cl)2](.)2CH(3)OH (1a), [(LNi2)-Ni-1(mu-Cl)(CH3OH)](ClO4)(2) (1b), [(LNi2)-Ni-2(mu-Cl)Cl-2(H2O)2](.) H2O (2) and [(LNi2Cl2)-Ni-3(CH3OH)(2)]Cl(.)2CH(3)OH (3) were synthesized and structurally characterized. The ligand scaffolds have a central pyrazolato bridge and N-donor chelate arms that provide two proximate binding pockets for the nickel ions. While the longer ligand side arms in 1a, 1b and 2 induce (NiNi)-Ni-... distances of around 4.0 angstrom and favour incorporation of a chlorido bridge within the dimetallic pocket, a stretched (NiNi)-Ni-... separation of 4.6 angstrom with an unusual intramolecular (ClH)-H-...-O linkage is observed in 3. Various (ClH)-H-...-O hydrogen-bonding motifs are identified in the solid-state structures of 1-3, where either the H-donor (MeOH or H2O) or the H-acceptor (chlorido) or both are bound to a nickel ion, and their relative donor-acceptor distances are discussed. Magnetic coupling mediated through the pyrazolato and chlorido bridges is rather weak and antiferromagnetic, but it is even weaker for the (ClH)-H-...-O linkage. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)