New isomeric Ni(NCS)2 coordination compounds: crystal structures, magnetic properties as well as ex situ and in situ investigations on their synthesis and transition behaviour

The reaction of Ni(NCS)(2) with 3-ethylpyridine in water leads to the formation of two known modifications of Ni(NCS)(2)(3-ethylpyridine)(4)(1-I and 1-II) as well as of Ni(NCS)(2)(3-ethylpyridine)(2)(H2O)(2) (2) that consist of discrete complexes. if the synthesis is performed in ethyl acetate, the new compound [Ni(NCS)(2)(3-ethylpyridine)(2)](n) (3-lc) formed that comprises linear and corrugated Ni(NCS)(2) chains in one crystal. By changing the solvent to dichloromethane, a solvate of compound 3 is obtained that consists exclusively of corrugated chains (3c-CH2Cl2). 3c-CH2Cl2 is unstable and transforms immediately into 3-lc. Upon heating the precursor complexes 1-I, 1-II and 2, the 3-ethylpyridine ligands are removed in two steps leading to a mixture of 3-lc and an additional isomer of 3 (3-l) in the first step that decomposes upon further heating into a compound with the composition [Ni(NCS)(2)(3-ethylpyridine)](n) (4). Ex and in situ XRPD measurements reveal that a mixture of two modifications (4-I and 4-II) is always formed, preventing their structure determination by XRPD. Time dependent investigations in solution prove that 3-l is formed under kinetic control and transforms into 3-lc within several hours that is thermodynamically stable at room-temperature. Structure analysis of 3-l shows that in contrast to 3-lc and 3c-CH2Cl2 this isomer consists exclusively of linear Ni(NCS)(2) chains. Magnetic measurements of the new chain compounds 3-l and 3-lc shows chi(T) values that are typical for Ni(II) cations with S = 1. For 3-l the exchange constant was determined by fitting of the magnetic data leading to a value that is similar to that of [Ni(NCS)(2) (2,2'-bipyridine)(2)](n).