Variation of the Chain Geometry in Isomeric 1D Co(NCS) Coordination Polymers and Their Influence on the Magnetic Properties.

Two different isomers of [Co(NCS)(4-chloropyridine)] ( and ) were synthesized from solution and by thermal decomposition of Co(NCS)(4-chloropyridine)(HO) (), which show a different metal coordination leading to corrugated chains in and to linear chains in . Solvent mediated conversion experiments prove that is thermodynamically stable at room temperature where is metastable. Magnetic measurements reveal that the magnetic exchange in is comparable to that observed for previously reported related chain compounds, whereas in with corrugated chains, the ferromagnetic interaction within the chains is strongly suppressed. The magnetic ordering takes place at 2.85 and 0.89 K, for and , respectively, based on specific heat measurements. For the field dependence of magnetic relaxations in antiferromagnetically ordered ferromagnetic chains is presented. In addition, is investigated by FD-FT THz-EPR spectroscopy, revealing a ground to first excited state energy gap of 14.0 cm. Broken-symmetry DFT calculations for and indicate a ferromagnetic intrachain interaction. Ab initio CASSCF/CASPT2/RASSI-SO computational studies reveal significantly different single-ion anisotropies for the crystallographically independent cobalt(II) centers in and . Together with the geometry of the chains this explains the magnetic properties of and . The ab initio results also explain the weaker exchange interaction in and as compared to previously reported [Co(NCS)(L)] compounds with linear chains.