Molecular structure and spectral properties of bis(2,6-dimethoxybenzoato)(2,2': 6',2 ''-terpyridine)manganese(II): a five-coordinate Mn(II) complex

The mixed complex formed by Mn(ii), 2,6-dimethoxybenzoate (dmb) and 2,2':6',2"-terpyridine (terpy) was isolated in the solid state and characterised by single crystal X-ray diffraction, IR and EPR, and thermogravimetric analysis. The complex is fivefold co-ordinated with a geometry shifted toward the limiting form of the trigonal bipyramid. Two carboxylate groups and the central nitrogen atom of terpy occupy the equatorial plane, while the distal nitrogen atoms are in the axial positions. The normalised bite, the angle formed by distal nitrogen (N(d) and N(d)) atoms at the metal ion, the manganese-nitrogen distances, and the tilt angles between the pyridine rings were compared with those of other terpyridine complexes. Owing to the large dimensions of the Mn(ii) ion, the distortions observed in the N(d)-Mn-N(d) angles and in those between the pyridine rings are the largest so far observed with first-row transition metal ions. The metal-central nitrogen and metal-distal nitrogens distances are longer than with other metal ions.