Pyridine-2,6-dicarboxylate and perchlorate bridged hydrogen bonded 1D chains involving manganese(Ill)-cyclam moiety:: synthesis, X-ray crystal structures and magnetic study

Two compounds H[Mn(cyclam)(pyridine-2,6-dicarboxylate)(2)](H2O)-H-. (1) and [Mn-III(cyclam)Cl-2]ClO4 (2) (where cyclam = 1,4,8,11-tetraazacyclotetradecane) have been synthesized and structurally characterized. The complex I crystallizes in the monoclinic space group P2(1)/c with a = 11.4328(11), b = 14.4275(14), c = 8.5782(9) Angstrom, V = 1343.1(2) Angstrom(3), Z = 2, R = 0.0453. Complex 1 is octahedral in which [Mn(cyclam)](3+) unit occupies the basal plane having two pyridine-2,6-dicarboxylate anions in the axial positions. Molecular packing of the crystal is dominated by string of molecules along the b-axis. The strings are held together by extensive intermolecular hydrogen bonds involving N-(HO)-O-..., N-(HN)-N-... and O-(HO)-O-... which impart it an infinite 1D chain. Complex 2 on the other hand crystallizes in the space group P2(1)2(1)2(1) (No. 19) of the orthorhombic system. Mn(III) ions occupy the center of a distorted octahedron and two chloride ions occupy the axial positions. The packing diagram of 2 reveals that the complex is percholrate-bridged hydrogen bonded ID chain along a-axis. Cyclic voltammogram of complex 1 shows a reduction wave at -0.25 V coupled to an oxidation wave at -0.05 V versus SCE in aqueous solution. The complex 2 is characterized by an irreversible reduction wave at -0.11 V versus SCE and is identical to that observed for [Mn-III(cyclam)Cl-2]Cl(.)5H(2)O. The magnetic measurements in the temperature range 1.9-300 K have been carried out for complex 1 which exhibits a very weak ferromagnetic interaction at low temperature. Complex 2 shows room temperature magnetic moment value of 4.92 BM consistent with the high spin d(4) electronic configuration. (C) 2003 Elsevier B.V. All rights reserved.