Effect of H-bonding on the ambivalence of SCN towards copper(II) |
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| Authors: | Michael GB Drew Senjuti De |
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| Institution: | a School of Chemistry, University of Reading, Whiteknights, Reading RG6 6AD, UK
b Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Raja S. C. Mullick Road, Calcutta, WB 700 032, India |
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| Abstract: | Condensations of 2-(2-aminoethyl)pyridine with 4-methylimidazole-5-carboxaldehyde and 1-methyl-2-imidazolecarboxaldehyde generate the tridentate N donor ligands L and L′ respectively. Reactions of Cu(NCS)2 with L and L′ yield respectively CuL(SCN)(NCS) (1) containing a CuN4S core and CuL′(NCS)2 (2) having a CuN5 core. Both the cores are square pyramidal with SCN− bound in 1 at the axial position through the S end. This differential behaviour of SCN− in the two complexes despite the ligands being very similar, is investigated by DFT calculations at the B3LYP/TZV level. It is found that DFT calculations predict isolation of the Cu(ligand)(NCS)2 species for both the ligands L and L′. Presence of an offsetting intermolecular H-bonding between the N atom of the thiocyanate and the N-H proton of the ligand L of an adjacent molecule makes the binding of SCN− via the S end feasible in 1 resulting in the H-bonded dimer Cu2L2(SCN)2(NCS)2. The strength of the H-bond is estimated as 27.1 kJ mol−1 from the DFT calculations. The question of such H-bonding does not arise with L′ as it lacks in a similar H atom. Dimeric 1 represents a case of two non-interacting spins. |
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| Keywords: | Copper(II) N ligands structural isomers H-bond thiocyanate DFT |
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