Bromine NQR and Crystal Structures of Tetraanilinium Decabromotricadmate and 4-Methylpyridinium Tribromocadmate

Abstract

Abstract The 79,81Br NQR spectra of tetraanilinium decabromotricadmate (1) and 4-methylpyridinium tribromocadmate (2 ) were studied as function of temperature and their crystal structures were determined. (C6H5NH3)4Cd3Br10 (1): Space group D1 5 2h - Pbca , Z = 4, a = 2507.8(7) pm, b = 1985.4(5)pm, c = 763.0(2)pm. Characteristic for the structure are trioctahedral units [Cd3Br10] condensed to planes. Within the units the octahedra are face connected and further condensed to planes via common corners. Two types of hydrogen bonds are observed. The 81Br NQR lines with frequencies (MHz, 298 K) of 62.98, 52.59, 43.39, 41.82, and 40.71 are little temperature dependent with positive and negative coefficients. The wide frequency range of the NQR lines is reflected by the wide range of the intraionic distances, 263 ≤ d(Br-Cd)/pm ≤300. (4-(CH3)C5H4NH)CdBr3 (2): C5 2h - P21/n, Z = 4, a = 1228.8(5}pm, b= 1168.5(5)pm, c = 758.3(3)pm, β = 95.30(1)°; the CdBr⊖ 3 ions are condensed to chains. The 81Br NQR spectrum is a triplet with frequencies (MHz, 298 K) of 66.01, 55.39, and 50.75. The temperature dependence is small, with positive and negative temperature coefficients. The distances d(Cd-Br) are 256 pm (Cd-Br(2)), 261 pm (Cd -Br(1)), and 284 pm (Cd-Br(3)) and in the chain [CdBr3]Br(1) and Br(3) are bridging atoms. The relations between Br-NQR and crystal structures are discussed.