Density Functional Derived Structures and Molecular Properties of Nickel Dithiolenes and Related Complexes

Abstract

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.

Synthesis and non-linear optical properties of some novel nickel derivatives

“…The S atoms bonded to Ni, carry a negative charge of 0.26e and 0.19e for Ni(dddt) 2 and Ni(pddt) 2 , respectively. The previous observations for the electron population of Ni are in agreement with those reported in the literature [13,50]. The charges we calculated are typical for Ni(II).…”

“…10 for the case of the isolated Ni compound. It is observed that the intramolecular charge transfer (p-> p*) over the ligands (S,C), describes the first and strong UV-Vis transition, similar to what was found for other studied metal complexes [12,50,55]. The metal d orbital (d xz ) contributes to LUMO to a minor extent only [55].…”

Neutral d8 metal bis-dithiolene complexes: Synthesis, electronic properties and applications

“…On the basis of extended Hückel and DFT calculations [111,112], these absorption bands were assigned as simple HOMO-LUMO single electron transitions, however more recent works emphasize that this assignment may be somewhat misleading due to the possible multideterminantal character of the ground state wave function. As a consequence, reproduction of the absorption spectra becomes non-trivial and TD-DFT methods must be used with caution.…”

Coordination properties of 2-aminocyclopentene-1-dithiocarboxylic acid to transition metal ions as studied by ab initio calculations

“…Moreover, DFT bond lengths of second and higher row main-group elements are known to result systematically too large [39,40]. The C-S bond lengths, for instance, are overestimated by about 0.03 A.…”