Evolution from discrete mononuclear complexes to trinuclear linear cluster and 2D coordination polymers of Mn(II) with dihydrazone Schiff bases: Preparation, structure and thermal behavior

Abstract

Four Mn(II) coordination compounds based on the 2,6-diacetylpyridine bis(isonicotinoylhydrazone) (H2L1) and 2,6-diacetylpyridine bis(nicotinoylhydrazone) (H2L2), were prepared using different synthetic conditions and starting manganese salts: discrete mononuclear [Mn(H2L1)2(H2O)2](NO3)2 (1) and trinuclear [Mn3(H2L1)2(NCS)2Cl4(H2O)2] (2) complexes and two 2D coordination polymers {[Mn3(L1)3(H2O)2]·1.5C2H5OH}n (3) and {[MnL2]·dmf}n (4), where dmf = N,N-dimethylformamide. Single-crystal X-ray diffraction study shows that H2L1 and H2L2, which differ only by para- or meta- position of radicals with respect to the nitrogen atoms in the terminal pyridyl fragments, demonstrate chelate or chelate-bridging coordination mode with N3O2, or N4O2 and N5O2 donor atoms, respectively. The planar-chelate coordination of these ligands provides the pentagonal-bipyramidal surrounding of Mn(II) and the terminal pyridyl moieties promote bridging function and structure expansion in 2–4 as well as octahedral Cl2N4 coordination geometry for one of Mn(II) atoms in the trinuclear complex 2. All compounds have been investigated in the solid state by IR spectroscopy and thermal analysis in order to understand the influence of the inorganic anion presence/absence on the stability of synthesized compounds.