ISSN:
1434-1948
Keywords:
Metal dichalcogenolene
;
Density functional calculations
;
Cyclic π-electron delocalization
;
Nickel
;
Chemistry
;
General Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The molecular and electronic structure of the planar nickel dithiolene (1c, R = H) and of related complexes derived from nickel dithiolene by replacement of Ni by Pd (palladium dithiolene, 2c, R = H) or by Pt (platinum dithiolene, 3c, R = H), or by replacement of S by NH (nickel diiminolene, 1a, R = H), O (nickel dioxylene, 1b, R = H) or Se (nickel diselenolene, 1d, R = H), were studied by density functional theory using the B3LYP functional and the valence triple-zeta basis set 6-311+G* for all atoms except Pd and Pt. For the latter atoms the quasirelativistic effective core potentials of the Stuttgart group were employed. The molecular structure of nickel dithiolene (1c, R = H) is satisfactorily reproduced by DFT calculations. The geometry of the corresponding platinum complexes 3a-3d is more sensitive to relativistic effects, resulting in the contraction of the X-Pt bonds. As shown with the metal dithiolenes, the two ligands are structurally related to mononegative ions of open shell structure. The C-C bond lengths of the complexes are close to those of aromatic and chain-type polymethine structures (about 1.4 Å). The nickel dithiolene (1c, R = H) and related complexes have D2h symmetry and are 14 π-electron systems with 10 π-electrons at the ligands and 4 π-electrons at the metal center. The natural population analysis has confirmed that metal M++ does accept electrons from the ligands but to a lesser extent than expected. The empty d-orbitals of M++ are only partly occupied in the molecular ground state. The positive charge of the metal decreases in the order Ni 〉 Pd 〉 Pt. The 1H chemical shifts and the nucleus-independent chemical shifts (NICSs) of the ring moieties calculated by GIAO-DFT display a pronounced electron delocalization. In agreement with the calculated C-C bond lengths the 1H chemical shifts and the NICS values show a marked bond delocalization. The NICS values show a change of the aromatic delocalization in the order Ni 〉 Pd 〈 Pt and NH 〉 O 〈 S 〈 Se. The wave numbers of the IR spectra of the complexes calculated by DFT are grouped in separate frequency regions. The very intense absorption of 1c (R = H) in the visible region of the spectrum is surprisingly well reproduced by ab initio single-only configuration interaction calculations. While the color band of the palladium complex is predicted to be red-shifted relative to the nickel complex, a blue shift is calculated on passing from the palladium to the platinum complex. The blue shift is, in part, due to the relativistic contraction of bond lengths in the Pt complexes.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
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