Reversible and Topotactic Solvent Removal in a Magnetic Ni(NCS)₂ Coordination Polymer

Reaction of Ni(NCS)₂ with 4-(Boc-amino)pyridine in acetonitrile leads to the formation of a new coordination polymer with the composition Ni(NCS)₂(4-(Boc-amino)pyridine)₂·MeCN (1-MeCN). In the crystal structure the Ni(II) cations are linked by the anionic ligands into chains that are further connected into layers by intermolecular N-H···O hydrogen bonding. These layers are stacked and channels are formed, in which acetonitrile molecules are located. Solvent removal leads to the ansolvate 1, which shows microporosity as proven by sorption measurements. Single crystal X-ray investigations reveal that the solvent removal leads to a change in symmetry from primitive to C-centered, which is reversible and which proceeds via a topotactic reaction leaving the network intact. The magnetic properties of 1-MeCN and 1 are governed by the ferromagnetic exchange between spins of Ni(II) forming chains. The susceptibility and specific heat for such a quantum Heisenberg chain of S = 1 spins with zero-field splitting are calculated using the DMRG method and compared with the experimental results.