Isothiocyanate controlled architecture, spectroscopic, and magnetic behavior of copper(II) l–arginine complexes

We synthesized an l–arginine complex with the formula [Cu(l–Arg)2(NCS)]·(NCS)·H2O (1) (l–Arg = l–arginine). Two cis-chelated l–arginine zwitterions form the basal plane, while the weakly N-bonded isothiocyanate is located at the apex of the distorted square pyramidal structure (τ = 0.143). The non-coordinated NCS− anions held layers together in a 3-D supramolecular network. The crystal structure, spectroscopic (FT–IR, Raman, NIR–Vis–UV, EPR) and magnetic properties of 1 have been compared with [Cu(l–Arg)(NCS)2] (2). For 1, two absorptions are observed for ν(C = N) stretching vibrations, corresponding to NCS− ions N-bonded to the central Cu(II) (2077 cm−1) and in the lattice (2057 cm−1). In 2 a single band is observed at 2102 cm−1, indicating equivalent NCS− ions in the structure. The EPR spectra of complexes show anisotropic signal with g⊥ and g|| 2.062, 2.235 (1), and 2.08, 2.225 (2) characteristic for cis-N2O2 and N3O donor sets in the xy plane, respectively. The unpaired electron mainly occupies the dx2–y2 orbital, also confirmed by the single envelope of d–d bands at ca. 16,000 cm−1 for 1 and 16,500 cm−1 for 2. The magnetic properties ofcompounds are characteristic of a very weak antiferromagnetic interaction with J = −0.055 cm−1 and J = −0.096 cm−1 for 1 and 2, respectively.