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

Two compounds H[Mn(cyclam)(pyridine-2,6-dicarboxylate)2] · H2O (1) and [MnIII(cyclam)Cl2]ClO4 (2) (where cyclam=1,4,8,11-tetraazacyclotetradecane) have been synthesized and structurally characterized. The complex 1 crystallizes in the monoclinic space group P2(1)/c with a=11.4328(11), b=14.4275(14), c=8.5782(9) Å, , 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–H ⋯ O, N–H ⋯ N and O–H ⋯ O which impart it an infinite 1D chain. Complex 2 on the other hand crystallizes in the space group P212121 (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 1D 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 [MnIII(cyclam)Cl2]Cl · 5H2O. 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 d4 electronic configuration.