Syntheses, Crystal Structures and DNA-Binding of Two Manganese Complexes

Coordination polymer [Mn-3(L)(6)(H2O)(4)](n) (1) was prepared by the reaction of manganese chloride (MnCl2 center dot 4H(2)O) and 4-methyl-1,2,3-thiadiazole-5-carboxylic acid (HL) by conventional solution method, and complex [Mn-2(phen)(4)(H2O)(2)Cl-2](L)(2)center dot 3H(2)O (2) was synthesized after adding the ligand 1,10-phenanthroline (phen). The complexes were characterized by elemental analysis, infrared spectroscopy, thermogravimetric analysis, and single-crystal X-ray diffraction. The single-crystal structure analysis shows that complex 1 belongs to the monoclinic system, P2(1)/c space group. The three manganese ions are bridged in bidentate fashion by the oxygen atoms in the six thiadiazole formate groups to form a linear trinuclear molecule cluster compound. The cluster unit is connected by the coordination of nitrogen atom from one of the thiadiazole rings and the manganese atom of the other cluster unit to form a layered structure. Complex 2 belongs to the triclinic crystal system, P (1) over bar space group. The central metal manganese ion coordinated with four nitrogen atoms from two phen molecules, one chloride anion, and one oxygen atom of coordination water molecule respectively, forming a six-coordinated twisted octahedral structure cation. The thiadiazole formate anion plays the role of charge balance. Ethidium bromide fluorescence spectrometry was used to determine the interaction between HL and complexes with DNA, respectively. The results showed that the interaction between the complexes and DNA was stronger than that of HL, and complex 2 with a planar ligand had a stronger effect than that of complex 1.