Synthesis and characterization of a constricted and rigid ligand system for five-coordinate binuclear complexes

Abstract

A generalized synthetic strategy for a rigid ligand system for binuclear metal complexes has been developed. In the case of Co(II) and Cu(II), the ligand coordination environment forces the metal to adopt a trigonal bipyramidal configuration with each of the axial bonds tilted toward each other. The dicobalt complex crystallized from CH 3CN/ether as a Ph 4P or Et 4N salt, and the dicopper complex from CH 3CN/ acetone as an Et 4N salt. Single crystal X-ray analysis of [Ph 4] 2[Co 2(μ-OAc)L] (monoclinic, space group P2 i/c, a = 13.4308(2), b = 9.374792), c = 45.9177(6) A ̊ , β = 97.54(1)°, V = 5731.5(2) A ̊ 3, R1 = 0.991 , crystal dimensions 0.3 × 0.2 × 0.2 mm, Z = 4, D cale = 1.415 g cm[ su−3, F(000) = 2528 e, where L = 2,6- cresolate, N, N, N, N′-trimethylene carboxylate and [ Et 4 N] 2[ Cu 2( μ- OAc) L] (monoclinic, space group P2 1, a = 10.626(2), b = 12.839(4), c = 14.073(3) A ̊ , β = 104.15(2)°, V = 1861.8(8) A ̊ 3, R1 = 0.0683 , crystal dimensions 0.4 × 0.3 × 0.2 mm, Z = 2, D calc = 1.448 g cm −3, F(000) = 856 e reveal that both metal ions adopt a five-coordinate trigonal bipyramidal structure, each provided by the two carboxylic oxygens, one nitrogen, one bridging phenolate oxygen and the bridging acetate group, where the non-hydrogen atoms of acetate, the two metal ions and the atoms of the benzene ring adopt a semi-coplanar configuration. The separation between the two cobalt atoms is 3.505(5) Å and the two CoO bonds (2.01(2) and 2.04(2) Å) to the acetate ligand are tilted toward each other, giving an OO internuclear distance of ≈2.2 A ̊ . The separation between the two copper is 3.550(5) Å and the two CuO bonds (1.920(7) and 2.304(7) Å) to the acetate ligand are tilted toward each other, giving an OO internuclear distance of ∼2.3 A ̊ .These results suggest that appropriate binuclear complexes of this ligand will favor coordination of O 2, but not O 2− or μ-OH. Variable temperature magnetic susceptibility measurements demonstrate weak antiferromagnetic (2 J/ k = −7.8 K) and ferromagnetic coupling (2 J/ k = 20.58 K) for the cobalt and copper complexes, respectively. The magnetic behavior, electronic spectrum and electrochemistry of the derivatives suggest that the new rigid heptadenate ligand system should resist formation μ-oxo bridges between the complexed metal atoms.