Abstract
AbstractReaction of different molar ratios of Ni(NCS)2 and 3‐bromopyridine in water, methanol or acetonitrile leads to the formation of two polymorphs of composition Ni(NCS)2(3‐bromopyridine)4 (1‐I and 1‐II), as well as Ni(NCS)2(3‐bromopyridine)2(H2O)2 (2), Ni(NCS)2(3‐Bromopyridine)2(CH3OH)2 (3), Ni(NCS)2(3‐bromopyridine)2 ⋅ CH3CN (4) and Ni(NCS)2(3‐bromopyridine)2 (5). Compounds 1‐I, 1‐II, 2 and 3 consist of discrete octahedral complexes with terminal N‐bonded anionic ligands. In compound 4 the Ni cations are cis‐cis‐trans coordinated and linked into corrugated chains by pairs of μ‐1,3‐bridging thiocyanate anions. Solvent mediated conversion experiments prove that form 1‐I represents the thermodynamically stable polymorph at room temperature. TG‐DTA measurements reveal that upon heating compounds 1‐I, 1‐II, 2 and 3 lose their coligands stepwise and transform into the new crystalline phase 5 that can also be obtained from solution if the reaction is performed in n‐butanol. If the acetonitrile solvate molecules are removed from compound 4, it also transforms into 5. DC magnetic measurements for compound 4 show a maximum, which is indicative for antiferromagnetic ordering, whereas for compound 5 no magnetic ordering is observed. For both compounds, the ferromagnetic exchange constants were determined.
Highlights
Reaction of different molar ratios of Ni(NCS)2 and 3-bromopyridine in water, methanol or acetonitrile leads to the formation of two polymorphs of composition Ni(NCS)2(3-bromopyridine
In those cases in which compounds with bridging thiocyanate anions are not available from solution, thiocyanate coordination compounds that contain only terminal N-bonded anionic ligands can be heated, which usually leads to a stepwise removal of the coligands, and the irreversible formation of compounds with bridging thiocyanate anions.[3]
For the 2D compounds only very few networks of different topology are reported, in which e. g. the metal cations are linked into dimers that are further connected into layers by single thiocyanate anions or in which the layers consist of only single anionic ligands.[22,23]
Summary
Crystal Structures and Properties of Polymorphic and Isomeric Nickel(II)thiocyanate Coordination. G. the metal cations are linked into dimers that are further connected into layers by single thiocyanate anions or in which the layers consist of only single anionic ligands.[22,23] Regarding such 2D networks, compounds based on Co(NCS) and Ni(NCS) are of special interest, because with both cations the magnetic exchange is usually ferromagnetic and at low temperatures ferromagnetic ordering is observed In this case, the critical temperatures are always higher for Ni(II) than for Co(II), which allows the tuning of the critical temperatures by mixed crystal formation.[24,25,26].
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