Novel nickel(II) complexes with diazamesocyclic ligands functionalized by additional phenol donor pendant(s): synthesis, characterization, crystal structures and magnetic properties

The formation of two unique mu -phenoxo-bridged nickel(II) complexes with 1,5-diazacyclooctane (DACO) ligands functionalized by additional phenol donor pendants has been achieved and the complexes have been characterized by IR, elemental analyses, conductivity, thermal analysis, and UV-Vis techniques. Single-crystal X-ray diffraction analyses reveal that HL1 forms a phenoxo-bridged binuclear complex (in the presence of N-3(-) anions) [NiL1(N-3)](2).0.5H(2)O 1, H2L2 a phenoxo-bridged edge-sharing linear trinuclear complex [Ni-3(L-2)(2)(C2H5OH)(2)Cl-2] 2, where HL1= 1-(2-hydroxybenzyl)-1,5-diazacyclooctane and H2L2=1,5-bis(2-hydroxybenzyl)-1,5-diazacyclooctane. In 1 the two Ni-II are in five-coordinated distorted square-pyramidal environments with a intramolecular Ni . . . Ni distance of 3.1232(13) Angstrom. However in 2 the two terminal Ni-II are in nearly ideal square-pyramidal coordination environments and the central Ni-II takes an octahedral configuration by axial coordination of two ethanol molecules, the adjacent intramolecular Ni . . . Ni distance being 3.132(2) Angstrom. Such a trinuclear nickel(II) complex with square-pyramidal/octahedral/square-pyramidal coordination is unprecedented. These results also indicate that the coordination chemistry of the nickel(II) complexes with DACO ligands can be controlled by altering the pendant donors. Variable-temperature magnetic data show that both complexes display modest intramolecular antiferromagnetic coupling between adjacent nickel(II) centers, which is unusual for such linear trinuclear nickel(II) complexes. The magneto-structural correlation has been investigated for both complexes, and a rough correlation between the exchange coupling and the Ni-O-Ni angle of phenoxo-bridged binuclear nickel(II) complexes obtained and discussed.