Mixed Azide and 5-(Pyrimidyl)tetrazole Bridged Co(II)/Mn(II) Polymers: Synthesis, Crystal Structures, Ferroelectric and Magnetic Behavior

The reaction of pyrimidine-2-carbonitrile, NaN3 in the presence of Co(NO3)2·6H2O or MnCl2·4H2O leads to the formation of complexes [Co(pmtz)(μ1,3-N3)(H2O)]n (1) and [Mn(pmtz)(μ1,3-N3)(H2O)]n (2) respectively, under hydrothermal condition [pmtz =5-(pyrimidyl)tetrazolate]. These two complexes have been fully characterized by single crystal X-ray diffraction. Complex 1 crystallizes in a non-centrosymmetric space group Aba2 in the orthorhombic system and is found to exhibit ferroelectric behavior, whereas complex 2 crystallizes in the P21/c space group in the monoclinic system. Variable temperature magnetic characterizations in the temperature range of 2−300 K indicate that complex 1 is a canted antiferromagnet (weak ferromagnet) with Tc = 15.9 K. Complex 1 represents a unique example of a multiferroic coordination polymer containing tetrazole as a co-ligand. Complex 2 is a one-dimensional chain of Mn(II) bridged by a well-known antiferromagnetic coupler end-to-end azido ligand. In contrast to the role played by the end-to-end azido pathway in most of the transition metal complexes, complex 2 showed unusual ferromagnetic behavior below 40 K because of spin canting.