The effect of azide and thiocyanate anions on the coordination mode of thiocarbohydrazone ligand in preparing Mn(II) coordination compounds

Two new Mn(II) coordination compounds, [Mn(HL)(NCS)(Cl)(CH3OH)] (1) and [Mn4(L)2(µ-N3)4(N3)0.5(Cl)1.5(CH3OH)2]·3.5(CH4O) (2), were synthesized and characterized by elemental analysis and spectroscopic methods where HL is bis-[(E)-N'-(methyl(pyridin-2-yl)methylene)]thiocarbohydrazide. The compounds were synthesized by the reaction of HL, MnCl2∙4H2O and KSCN (in 1) or NaN3 (in 2) with 1:2:4 molar ratios in methanol. The crystal structures of 1 and 2 were determined by single-crystal X-ray diffraction analysis which revealed that 1 is a mononuclear Mn(II) coordination compound while 2 is an azido bridged tetranuclear Mn(II) cluster. In both 1 and 2 the Mn(II) ions have octahedral coordination environment which is created by coordination of nitrogen and sulfur atoms from thiocarbohydrazone ligand. In compound 1 the ligand acts as a neutral tridentate N2S-donor ligand while in 2 it acts as mononegative N4S-donor ligand. In 2, the azide anions act as both terminal and bridging ligand and four Mn(II) ions are connected together by four bridging azide ligands. Furthermore, the Mn(II) ions in 2 are also connected together by sulfur atoms of the thiocarbohydrazone ligand. The FT-IR spectra of 1 and 2 show the characteristic bands of SCN– and N3– anions, respectively. The analysis indicated that the pseudo-halide SCN– and N3– anions have considerable effect on the structure and nuclearity of the coordination compounds. The formation of tetranuclear cluster in the presence of azide anion was attributed to its higher ability to act as bridging group and also its relatively basic character which influence on the coordination mode of the thiocarbohydrazone ligand.