Hydrogenoxalate and squarate salts of (E)-4-(hydroxyiminomethyl)-pyridine - Crystal structures, spectroscopic and theoretical elucidation

(E)-4-(Hydroxyiminomethyl)-pyidinium hydrogenoxalate (1) and bis((E)-4-(hydroxyiminomethyl)pyridinium) squarate (2) were synthesized and their crystal Structures determined by means of single crystal X-ray diffraction. The structures of (1) and (2) consist of infinite layers and chains, respectively, formed by (1): N-H center dot center dot center dot O (2.852(2), 2.827(2) angstrom) and O-H center dot center dot center dot O (2.665(2) angstrom) and (2): N-H center dot center dot center dot O (2.620(2) angstrom) and O-H center dot center dot center dot O (2.600(1) angstrom) intermolecular hydrogen bonds between the cations and anions. Hydrogenoxalate ions form chains within the infinite layers by strong interanionic O-H center dot center dot center dot O interactions (2.583(2) angstrom). Antiperiplanar conformations of the cations for (1) and (2) (CC=N-OH) dihedral angle of 178.9(1)degrees (1) and 179.4(1)degrees (2) are observed. Spectroscopic properties both in solution and in the solid state were elucidated by means of H-1- and C-13-NMR, UV-spectroscopy and conventional and linear polarized IR- (IR-LD) spectroscopy. Quantum chemical calculations at the DFT, MP2 and CIS level of theory and the 6-31 ++G** basis set were employed for predicting and supporting experimentally observed optical propertied and electronic structures of the protonated (E)-4-(hydroxyiminomethyl)-pyridine. (c) 2008 Elsevier B.V. All rights reserved.