Estimation Of The 79Br Nqr Frequencies Of Bromo-Containing Molecules Using Ab Initio Calculations At Different Levels

Ab initio calculations of bromo-containing molecules on the RHF, B3LYP and MP2 levels and 6−31G(d), 6−31+G(d), 6−311G(d) and 6311+G(d) basis sets were executed. They were used to estimate the 79Br NQR frequencies of these molecules. A satisfactory agreement between experimental and estimated NQR frequencies is obtained for the sum of populations of 13p- and 14p-components of the Br atom valence p-orbitals obtained from the RHF, B3LYP and MP2 calculations (particularly from RHF calculations) with the split valence basis sets 6−311G(d) and 6−311+G(d). The agreement between the experimental and estimated NQR frequencies is worse for the populations of the 9p-components of the Br atom valence p-orbitals obtained from these calculations with the basis sets 6−31G(d) and 6−31+G(d). An analogous conformity was not obtained using the populations of other components of the Br atom valence p-orbitals or their total populations obtained from all above-mentioned calculations.

35Cl and 79Br NQR Spectra and the Secondary Bonding of Chalcogen Halide Complexes

The 35Cl and 79Br NQR spectra of chalcogen halide complexes of aluminium, gallium, titanium, zirconium, hafnium, niobium, tantalum, molybdenum, tungsten, rhenium, iron, ruthenium, osmium, iridium, rhodium, platinum, palladium and gold are discussed. Three structure types of these complexes have been distinguished by X-ray structure analysis: type I with AX2 ligand and [MXn„Am] coordination polyhedron; type II with AX3 ligand and [MXn+m] coordination polyhedron; type III, dimeric complexes with M-X-M bridge (where X = Cl, Br and A = S, Se, Te). The formation of secondary M-X-A or M-X-M bonds is characteristic of most structures. The spectra were interpreted by a Townes. Dailey approximation with allowance for the electronic configuration of the metal, mutual influence of ligands and structure features of complexes. Systematic investigation of a big series of chalcogen halide complexes-analogues allowed the following changes in 35CI and 79Br NQR frequencies on secondary bonding to be established for intraligand halogen atoms: A decrease in frequency for type I complexes and an increase in frequency for type II complexes; for halogen atoms in the coordination polyhedron: a decrease in frequency for p metals and transition metals with d>6, and an increase in frequency for metals with d< 6.

Dynamic Properties and Phase Transitions in A2ZnBr4(A= (CH3)4 N and (CH3)4P) as Studied by 79Br NQR and Multinuclear NMR

In order to understand the mechanism of ferroelastic phase transitions in A2ZnBr4 (A = (CH3)4 N and (CH3)4 P), the temperature dependences of 79Br NQR frequencies and the spin-lattice relaxation times were measured. The temperature dependences of the 1H and 31P spin-lattice relaxation times were measured as well for a possible correlation between the cation dynamics and the phase transition. Although the phase transition temperatures of these two compounds differ much (~ 100 K), the correlation times for the cation reorientation at the individual transition temperatures amount to some 10-11 s for both compounds.

Peculiarities of the 35Cl and 79Br NQR Spectra of Chalcogenhalide Complexes of Some Transition Metals

The peculiarities of the 35Cl, 79Br NQR spectra of the chalcogenhalide complexes are explained in terms of intraspheric effect of ligands, formation of secondary intra-and intermolecular bonds, and electronic structure of metal atom. In the 35Cl spectra of [TeCl3 ]2[OsCl6 ] 1, [SeCl3]2[OsCl6]2 and [TeCl3]2 [ReCl6 ]3 the 7-10% increase in frequency in the low-frequency multiplet are accounted for by the disturbance of the pHal-dM π-interaction due to the formation of the peripheral coordination polyhedra [SeCl6 ] and [TeCl6 ]. The peculiarities of the 35 Cl and 79 Br spectra of [MoS2 Cl3 (SeCl2)]2 4, [MoS2 Br3 (SeCl2)]2 5, [WS2Cl3 (SeCl2)]2 6 and [WS2 Br3 (SeBr 2)] 2 7 are attributed to the disturbance of the pHal-dM π-interaction under the influence of the coordination of the SeCl2 and SeBr2 ligands and formation of secondary intramolecular bonds. For [RhCl3 (SeCl2)2]2 8, [IrCl3 (SeCl2)2]2 9 and [SCl3 ][IrCl4 (SCl2)2]10, the appearance of frequencies at 25 MHz in low-frequency triplets is attributed to the intraspheric effect of weak donors-neutral SCl2 and SeCl2 molecules; the frequencies at 18 MHz are assigned to bridging chlorine atoms. This assignment was confirmed by the dimeric structure, which was established by an X-ray structure analysis.