Schwingungsspektren und Normalkoordinatenanalyse der isotopomeren closo-Hexaiodohexaborate 11Bn10B6-nI62-, n = 0 - 6

1991 ◽  
Vol 46 (1) ◽  
pp. 19-24 ◽  
Author(s):  
J. Thesing ◽  
W. Preetz ◽  
J. Baurmeister

Normal coordinate analyses for the ten isotopomers Cs211Bn10B6-nI6, n = 0 - 6 , including the pairs of geometric isomers for n = 2, 3, 4 have been performed, based on a general valence force field. Using a set o f 8 force constants (e.g. fd(BB) = 1.45, fd(BI) = 2.33 mdyn/Å ) the calculated frequencies are in good agreement with observed IR and R am an bands measured at 10 or 80 K for Cs2B6I6 with natural abundance of B isotopes (~80% 11B , 20% 10B) as well as for 11B and 10B enriched derivatives. From the calculated atomic displacements and the potential energy distribution the classification in the 30 times more intense substituent (in-phase motions of B and I, ≤ 153 cm-1) and the weak cage vibrations (anti-phase displacements of B and I, ≥ 385 cm-1) is deduced. Only the cage modes show characteristic band patterns, explained by the superposition of the calculated spectra of the different isotopomers in accordance with their statistical abundance. There is an excellent conformity for the total symmetric A, vibration, but for the triply degenerate T lu and T 2g modes as a consequence of lowered site symmetry in the solid state more bands than calculated are observed.

1991 ◽  
Vol 46 (5) ◽  
pp. 602-608 ◽  
Author(s):  
J. Thesing ◽  
M. Stallbaum ◽  
W. Preetz

Normal coordinate analyses for the 24 mixed halogenohexaborates B6XnY6-n2-, n = 1—5, Χ ≠ Y = Cl, Br, I, including the pairs of geometric isomers for n = 2, 3, 4 have been performed, based on a general valence force field. Using the bond lengths and force constants for the homoleptic species B6X62-, which with respect to the B6 cage are weighted standardized, the calculated frequencies are in good agreement with observed IR and Raman bands. The boronhalogen stretching vibrations for symmetric molecular axes correspond with the Ra(IR) bands of the homoleptic compounds: ClB6Cl 327 (515), BrB6Br 207 (430), IB6I 152 (394) cm-1. As a characteristic feature the mixed halogeno clusters exhibit bands with nearly averaged frequencies from asymmetrical axes: ClB6Br 261 (487), ClB6I 227 (473), BrB6I 178 (409) cm-1. This complete vibrational coupling is confirmed by properly balanced potential energy distribution on BX and BY bonds. There is a slight influence of the different substituents on the internal modes of the B6 cage (pseudo-Oh), observed in the sequence A1g>T1u> Eg>T2g in the region 1220-740 cm-1. The bands are shifted about 100 cm-1 with increasing mass of halogen, broadened by boron isotopomers (max. 60 cm-1), and degenerate vibrations are split by lowered point and site symmetry up to 100 cm-1.


1990 ◽  
Vol 45 (5) ◽  
pp. 641-646 ◽  
Author(s):  
J. Thesing ◽  
W. Preetz

Normal coordinate analyses for the ten isotopomers Cs211Bn10B6-nH6, n = 0 — 6, including the pairs of geometric isomers for n = 2, 3, 4 have been performed, based on a general valence force field. The shift of the bands as well as the splitting of degenerate modes by lowered symmetry due to exchange of 10B by 11B or H by D is exactly calculated by a set of six force constants. The characteristic band patterns observed in the IR and Raman spectra of Cs2B6H6 with natural abundance of B isotopes (80.22% 11B, 19.78% 10B) measured at 10 K are explained by the superposition of the calculated spectra of the different isotopomers present, according to their statistical frequency distribution. The calculated atomic displacements and the potential energy distribution on the symmetry coordinates reveal only a small coupling (PED < 10%) between the cage (in-phase displacements of H and B) and substituent vibrations (anti-phase motions of B and H). Based on the normal coordinate analyses previously obtained assignments for several bands are revised.


1973 ◽  
Vol 27 (3) ◽  
pp. 209-213 ◽  
Author(s):  
John F. Jackovitz ◽  
Charles E. Falletta ◽  
James C. Carter

Infrared and Raman spectra for (K+) (CF3BF3−) have been obtained from 4000 to 50 cm−1. Spectral assignments were made on the basis of C3v symmetry using both 10B and 11B compounds. In addition, a normal coordinate analysis was performed to obtain the potential energy distribution of the normal modes. A Urey-Bradley type force field was used, and force constants obtained for the CF3 and BF3 groupings were compared to those in C2F6 and BF4−.


1988 ◽  
Vol 43 (5) ◽  
pp. 494-496 ◽  
Author(s):  
Lothar Ohse ◽  
Wolfgang Brockner

A normal coordinate analysis for the Hexathiometadiphosphate anion P2S62- was performed, based on a simple initial force field. The force field was refined by adjusting the symmetry force constants to approximate the observed frequencies. The final force field, potential energy distribution (PED) and mean amplitudes of vibration are also given. Based on the normal coordinate analysis a new assignment of the P2S62- frequencies is proposed.


1986 ◽  
Vol 41 (10) ◽  
pp. 1233-1237 ◽  
Author(s):  
M. Parensen ◽  
W. Brockner

Na4P2Se6 has been prepared by elemental synthesis at high temperatures and characterized by vibrational spectroscopy. The vibrational frequencies of Na4P2Se6 are assigned on the basis of eclipsed P2Se64- conformers with D3h symmetry, those of Tl4P2Se6 on the basis of staggered P2Se64- units with D3d symmetry. A normal coordinate analysis has been performed for both conformers. The refined force field, potential energy distribution (PED), mean amplitudes of vibration an Coriolis coupling constants are given.


1971 ◽  
Vol 25 (2) ◽  
pp. 207-211 ◽  
Author(s):  
Lakshmi P. Bhaskara Rao ◽  
Umesh Agarwala

The in-plane normal modes of bis-(maleonitriledithiolato)Ni(ii) anion have been assigned on the basis of the normal coordinate analysis. The potential energy distribution among various internal coordinates indicates a large amount of vibrational mixing. The value of K (C–S) suggests a considerable amount of double bond character.


1978 ◽  
Vol 33 (6) ◽  
pp. 709-713 ◽  
Author(s):  
Wolfgang Brockner ◽  
Bjørg N. Cyvin ◽  
Sven J. Cyvin

Abstract A normal coordinate analysis was performed for some Cl5MOPCl3 molecules (M = Sb, Nb, Ta). The final force field in terms of a described set of symmetry coordinates is reported for Cl5SbOPCl3. The initial force field for Cl5SbOPCl3 was applied to calculate the vibrational frequencies of the Cl5NbOPCl3 and Cl5TaOPCl3 adducts. An assignment of the vibrational frequencies of the title compounds and the corresponding potential energy distribution terms are given for Cl5SbOPCl3 . For the Cl5SbOPCl3


1988 ◽  
Vol 43 (4) ◽  
pp. 326-330
Author(s):  
L. Ohse ◽  
M. Somer ◽  
W. Brockner

Abstract A normal coordinate analysis for the cage-like molecules α-P4S4, As4S4 and As4Se4 is performed, based on a simple initial force field with three numerical parameters and valence coordinates including redundancies. The force field is refined by adjusting the symmetry force constants to fit the observed frequencies. The final force field, potential energy distribution (PED), mean amplitudes of vibration and the standard thermodynamic functions from spectroscopic data are also given for the title compounds.


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