Synthesis, crystal structures, thermal and magnetic properties of Mn(NCS)2 coordination compounds with 3-cyanopyridine

Abstract

The reaction of Mn(NCS)2 and 3-cyanopyridine in different solvents leads to the formation of pure Mn(NCS)2(3-cyanopyridine)4 (1), Mn(NCS)2(3-cyanopyridine)2(H2O)2-bis(3-cyanopyridine) solvate (2) and Mn(NCS)2(3-cyanopyridine)(H2O) (4). In further investigations single crystals of Mn(NCS)2(3-cyanopyridine)2(H2O)2 (3) were accidentally obtained, but this compound cannot be prepared pure. Compounds 1-3 consist of discrete complexes with octahedrally coordinated Mn cations, whereas in compound 4 the Mn cations are linked by single µ-1,3-bridging thiocyanate anions into chains, that are further connected into layers by the 3-cyanopyridine coligands. Thermogravimetric measurements reveal that upon heating compound 1 loses some of the 3-cyanopyridine ligands and transforms into [(Mn(NCS)2)3(3-cyanopyridine)4]n (5), which is isotypic to the corresponding Cd compound reported in the literature. In this structure, the Mn cations are linked by pairs of thiocyanate anions into chains that are further connected into layers by every second 3-cyanopyridine coligand. When compound 2 is heated, a transformation into the complex 1 is observed, that upon further heating transforms into 5. Magnetic measurements for compound 4 show that the Mn-NCS-Mn exchange is dominant and antiferromagnetic, and susceptibility dependence in the paramagnetic phase is well described by the Heisenberg spin chain model. Below 2.77 K, the Mn(II) spins in 4 are ordered with a weak ferromagnetic component due to the Dzyaloshinskii-Moriya interaction.