The Electronic Structure of the Isoelectronic, Square-Planar Complexes [Fe^II(L)₂]^2-and [Co^III(L^Bu)₂]^-(L^2-and (L^Bu)^2-= Benzene-1,2-dithiolates):  An Experimental and Density Functional Theoretical Study

Abstract

The electronic structures of two formally isoelectronic transition-metal dithiolato complexes [Fe(L)2]2- (1) and [Co(L Bu)2]1- (2) both possessing a spin triplet ground state (St=1) have been investigated by various spectroscopic and density functional methods; H2L Bu represents the pro-ligand 3,5-di-tert-butylbenzene-1,2-dithiol and H2L is the corresponding unsubstituted benzene-1,2-dithiol. An axial zero-field splitting (D) of +32 cm(-1) for 2 has been measured independently by SQUID magnetometry, far-infrared absorption, and variable-temperature and variable-field (VTVH) magnetic circular dichroism spectroscopies. A similar D value of +28 cm(-1) is obtained for 1 on the basis of VTVH SQUID measurements. The absorption spectra of 1 and 2 are found, however, to be very different. Complex 1 is light yellow in color with no intense transition in the visible region, whereas 2 is deep blue. DFT calculations establish that the electronic structures of the [Fe(L)2](2-) and [Co(L)2]1- anions are very different and explain the observed differences in their absorption spectra. On the basis of these spectroscopic and theoretical analyses, 1 is best described as containing an intermediate spin FeII ion, whereas for the corresponding cobalt complex, oxidation states describing a d6 (CoIII) or d7 (CoII) electron configuration cannot be unambiguously assigned. The physical origin of the large zero-field splitting in both 1 and 2 is found to be due to the presence of low-energy spin-conserved d-d excitations which lead to a large Dzz through efficient spin-orbit coupling. Differential covalency effects appear to be of limited importance for this property.

Catalytic Hydrogen Evolution by Fe(II) Carbonyls Featuring a Dithiolate and a Chelating Phosphine

“…[38][39][40] The observed distortions of the bdt ligand represent clear evidence that it is partially oxidized and possesses substantial 1,2-dithiobenzosemiquinonate, π-radical character. 40 Concomitantly, the charge of the Fe center in both complexes is expected to be less than +2 (see computational studies below).…”

Zero-field splitting in nickel(II) complexes: A comparison of DFT and multi-configurational wavefunction calculations

“…Additionally, in DFT calculations we used the RI approximation with the auxiliary TZV/J fitting basis set. [61][62][63][64] For Ni(H 2 O) 4 F 2 , the coupled perturbed (CP) 65,66 and Pederson and Khanna uncoupled (PK) schemes 67 for SOC were compared. Finally, for the five-coordinated nickel(II) complexes the CP approach was used.…”

Ein quadratisch‐planarer Ruthenium(II)‐Komplex mit Low‐Spin‐ Konfiguration

“…Mit makrocyclischen, chelatisierenden und wenigen einzähnigen Liganden sind auch quadratisch-planare Eisen(II)-Komplexe mit elektronischer Intermediate-Spin-Konfiguration (S = 1, IS) bekannt (Schema 1 links). [1][2][3] Dagegen liegen vierfach koordinierte Ruthenium(II)-Verbindungen typischerweise als Low-Spin-Komplexe mit Sägebockkonformation (S = 0, LS) vor. Aufgrund des energetisch niedrig liegenden LUMO weisen solche Komplexe allerdings zumeist agostische C-H!…”

“…[4] Tatsächliche Vierfachkoordination wurde in dieser Geometrie kürzlich erstmalig beobachtet. [5] Anhand von DFT-Rechnungen wurde der PCP-Pinzettenkomplex [RuCl{HC(CH 2 NHPtBu 2 ) 2 Im Kristall (Abbildung 2) liegt das Metallzentrum von 3 mit planarer, leicht verzerrter Koordinationsgeometrie vor und weist einen typischen Bisswinkel P1-Ru1-P2 von 168.13(2)8 und eine annähernd lineare N1-Ru1-Cl1-Bindung (Winkel 179.63(6)8) auf. [12,13] Die planare Koordination des Stickstoffatoms (S Winkel = 360.08) und der besonders kleine Ru1-N1-Abstand (1.890 (2) [11,16] weisen somit auf Hyperkonjugation als vorherrschenden Mechanismus der Spindichteübertragung hin.…”