The topology of the ground-state potential energy surface of M(CN)6 with orbitally degenerate 2T2g (M = TiIII (t2g1), FeIII and MnII (both low-spin t2g5)) and 3T1g ground states (M = VIII (t2g2), MnIII and CrII (both low-spin t2g4)) has been studied with linear and quadratic Jahnâˆ’Teller coupling models in the five-dimensional space of the Îµg and Ï„2g octahedral vibrations (TgâŠ—(Îµg+Ï„2g) Jahnâˆ’Teller coupling problem (Tg = 2T2g, 3T1g)). A procedure is proposed to give access to all vibronic coupling parameters from geometry optimization with density functional theory (DFT) and the energies of a restricted number of Slater determinants, derived from electron replacements within the t2g1,5 or t2g2,4 ground-state electronic configurations. The results show that coupling to the Ï„2g bending mode is dominant and leads to a stabilization of D3d structures (absolute minima on the ground-state potential energy surface) for all complexes considered, except for [Ti(CN)6]3-, where the minimum is of D4h symmetry. The Jahnâˆ’Teller stabilization energies for the D3d minima are found to increase in the order of increasing CNâˆ’M Ï€ back-donation (TiIII < VIII < MnIII < FeIII < MnII < CrII). With the angular overlap model and bonding parameters derived from angular distortions, which correspond to the stable D3d minima, the effect of configuration interaction and spinâˆ’orbit coupling on the ground-state potential energy surface is explored. This approach is used to correlate Jahnâˆ’Teller distortion parameters with structures from X-ray diffraction data. Jahnâˆ’Teller coupling to trigonal modes is also used to reinterpret the anisotropy of magnetic susceptibilities and g tensors of [Fe(CN)6]3-, and the 3T1g ground-state splitting of [Mn(CN)6]3-, deduced from near-IR spectra. The implications of the pseudo Jahnâˆ’Teller coupling due to t2gâˆ’eg orbital mixing via the trigonal modes (Ï„2g) and the effect of the dynamic Jahnâˆ’Teller coupling on the magnetic susceptibilities and g tensors of [Fe(CN)6]3- are also addressed.
A new 1,3-dithiol-2-ylidene substituted naphthopyranone 2 has been synthesized and characterized. UVâ€“vis spectroscopic and cyclic voltammetry results, interpreted on the basis of density functional theory, show that 2 displays an intramolecular charge-transfer transition and acts like a donorâ€“acceptor (Dâ€“A) system. Furthermore, a weak fluorescence originating from the excited charge-transfer state is observed.
The cubic Prussian blue analogue Mn3[Mn(CN)6]2 Â· 15 H2O, which has the advantage of being transparent and magnetic (TN = 35 K) at the same time, has been investigated by density functional theory (DFT) calculations. The three-dimensional structure is built of MnII ions linked to MnIII ions by Î¼-bridging cyanides, to form a crystal structure, which is related to the NaCl type. In a first step, the relative stabilities of the mononuclear complexes [Mn(CN)6]z- (z = 2 to 4) have been studied as a function of the oxidation state, spin configuration, and the linkage isomerism of the cyanide ligand. The results we have obtained by this investigation are in good agreement with our chemical expertise. In addition, the calculations have been extended to the dinuclear [Mn2(CN)11]z- (z = 5 and 6) clusters. Furthermore, we used DFT to model the magnetic properties as well as the 3T1 â†’ 1T2 transition, which has been observed by single-crystal near-IR spectra of Mn3[Mn(CN)6]2 Â· 15 H2O.