Varied dicarboxylate bridges in dinuclear trigonal prismatic manganese(II) and octahedral nickel(II) compounds containing tetradentate N-donor Schiff bases: Syntheses, structures and magnetic behaviors

Three dinuclear compounds of the types [Mn2(L1)2(μ-ap)(H2O)2](X)2·MeOH·2H2O [X = PF6− (1), BF4− (2)] and [Ni2(L2)2(μ-suc)](PF6)2 (3) [L1 = N,N′-(bis(pyridin-2-yl)benzylidene)-1,3-propanediamine, L2 = N,N′-(bis(pyridin-2-yl)benzylidene)-1,4-butanediamine; ap = adipate dianion and suc = succinate dianion] have been synthesized and X-ray crystallographically characterized. Structural analyses reveal that manganese(II) centers in 1/2 adopt a rare distorted trigonal prismatic geometry whereas nickel(II) centers in 3 are in a distorted octahedral coordination environment each with an MN4O2 chromophore. The ap unit bridges manganese(II) nuclei in 1/2 through its bis(monodentate) mode, whereas the suc connects nickel(II) ions in 3 in bis(bidentate) fashion. Four N atoms of chelated L1, one bridging O atom of ap and the O atom of coordinated water complete hexacoordination around the metal ions in 1/2. Each nickel(II) center in 3 is surrounded by four N atoms of L2 and two bridging O atoms of suc unit. The dinuclear moities in 1/2 are engaged in intramolecular/intermolecular O–H⋯O, O–H⋯F, C–H⋯N and C–H⋯F hydrogen bonds and π⋯π interactions whereas individual units of 3 self-assemble through C–H⋯F and C–H⋯O hydrogen bonds and C–H⋯π interactions in cooperative fashions to promote dimensionalities. Variable-temperature magnetic susceptibility measurements of 1–3 in the 2–300 K temperature range reveal weak antiferromagnetic interaction between two metal(II) centers presumably due to long bridging arm of the dicarboxylates.

Graphical abstractSyntheses, crystal structures and magnetic properties of two manganese(II) and one nickel(II) dinuclear complexes with dicarboxylate bridges and N-donor Schiff bases as end-capping ligands are described. Interesting variation in coordination geometries and bridging motifs are observed in the complexes. Variable-temperature magnetic susceptibility measurements show weak antiferromagnetic coupling between the metal centers mediated through long bridging arms of the dicarboxylates.Figure optionsDownload full-size imageDownload as PowerPoint slide