Inelastic neutron scattering (INS) study of low frequency vibrations of acid K salt of (E)-2-hydroxyimino-2-cyanoacetic acid ethyl ester and its phase situation by DSC method

Abstract

The acid potassium salt of (E)-2-hydroxyimino-2-cyanoacetic acid ethyl ester (in other words: the acid Ksalt of (E)-2-cyanoethyl ester of 2-oxime or acid Ksalt of 2-oxime, or shortly speaking acid Ksalt-) has been prepared and characterized using inelastic, incoherent neutron scattering (IINS or shortly speaking INS). The last results have been compared with those obtained from optical spectroscopy. Additionally, dimers of the acid Ksalt of 2-oxime were considered i.e. vibrational frequencies of such dimers have been calculated using RB3LYP method [20] with basis set 6-311++G(d, p). In the molecule of the acid Ksalt of 2-oxime, extra bands corresponding to hydrogen bond vibrations (λ – bending of hydrogen bond bridge, σ – stretching of hydrogen bond bridge, γ – bending out of plane of hydrogen bond, ν – stretching –OH, δ – bending in plane of hydrogen bond have been identified, namely λ at ca. 20, σ (N–O–H···O) at 109.7, 132.3, 154.8, 206.8, 248.5, 255.1, 303.9, 339.2, 359.4, 396.6, 428.8, 483.3, 537, 577.8, 782.4, 815.3, 894.7,1108, 1165. 1408.7, γ (N–O–H···O) at 1298, ν at 1583.1 cm-1, δ (N–OH···O) at 1734.4 and at 1847.4 cm-1, in the low temperature IINS spectrum. Formation of the O–H···O hydrogen bridge in the acid Ksalt of 2-oxime in comparison with the same O–H···O hydrogen bridge in pure 2-oxime is reflected in shifting of the bands of the stretching (to lower) and bending vibrations (to higher) of OH group frequencies confirming the fact of increasing of hydrogen bond power in the acid Ksalt of 2-oxime in comparison with hydrogen bond power of pure 2-oxime. Additionally the fact that acid Ksalt melts ca. 50 K higher than 2-oxime and the shorter length of hydrogen in acid Ksalt than in 2-oxime confirm the greater hydrogen bond power in the acid Ksalt than in 2-oxime