Density functional theory of the Cu_A‐like Cu₂S₂ diamond core in Cu (NGuaS)₂Cl₂

Abstract

Density functional theory (DFT) calculations with localized as well as plane-wave basis functions are performed for the recently reported dicopper thiolate species Cu2 (NGuaS)2 Cl2 [NGuaS = 2-(1,1,3,3-tetramethylguanidino) benzenethiolate, C11 H16 N3 S] and its bromo derivative [Neuba et al., Angew. Chem. Int. Ed. 2012, 51, 1714.]. For both hybrid and semilocal functionals, the neutral complexes are found to have broken symmetry (BS) character, with electron paramagnetic resonance silent, antiferromagnetically coupled [Cu(2+) …Cu(2+) ] site in which the coupling is driven by super exchange interaction within the Cu2 S2 diamond core. The accurate theoretical description of the geometric structure, however, provides a major challenge for DFT: (i) the multideterminant character of the ground state wave function has to be covered by the BS approach. It requires (ii) metageneralized gradient approximations, that is hybrid functionals with an explicit dependence on the kinetic energy of the individual orbitals: In combination with a dispersion correction, the metafunctional TPSSh results in a CuCu distance close to the experimentally observed value of 2.7 Å. For the negative charge state of the complex, a mixed-valent [Cu(1.5+) …Cu(1.5+) ] electronic structure with a smaller CuCu distance of 2.6 Å is predicted, similar to the value of the CuA site of cytochrome c oxidase.

[Cu6(NGuaS)6]2+ and its oxidized and reduced derivatives: Confining electrons on a torus

“…Formally one would assign two of the Cu ions an oxidation state of +II and the remaining four +I. This might lead to the assumption that an antisymmetric spin coupling emerges which has to be treated by an open shell BS wave function as proposed by Noodleman as it is already found in the related Cu 2 S 2 diamond core . The study of the dinuclear copper core shows that the minimum wave function is described by a BS wave function.…”

“…Furthermore, it has been shown that it reproduces accurate densities which is important as we perform detailed bonding and transition analyses . The inclusion of dispersion interaction is particularly vital for the determination of the correct structure in gas phase . The dispersion forces are modeled here using the post‐scf method by Grimme with the Becke and Johnson damping .…”

“…In the bioinorganic context, Henkel and coworkers synthesized the structurally inspired Cu A model complex Cu(II) 2 (NGuaS) 2 Cl 2 (with NGuaS = o‐SC 6 H 4 NC(NMe 2 ) 2 ) . The complex has been theoretically studied in detail with respect to the broken symmetry (BS) minimum energy wave function, its bonding mechanism and the spectroscopic features . It is known that nitrogen bases, guanidine ligands in special, serve as good donors in metal bonding .…”

Detection of Copper Bisguanidine NO Adducts by UV‐vis Spectroscopy and a SuperFocus Mixer

“…Since there are still ongoing controversial discussions on whether there are Cu(I) or Cu(II) species arising and which role the nitric oxide plays in terms of oxidation states, DFT calculations and an EPR measurement of the adduct of [Cu(btmgp)Br] and NO were performed. First, a geometrical optimization was performed with the hybrid meta GGA functional TPSSh and the def2‐TZVP basis set, which proved excellent in our working group for several different cases . The Cu atom is coordinated by the two N atoms, the bromide ion, and the NO ligand in a distorted tetrahedral fashion.…”

Structural dynamics upon photoexcitation-induced charge transfer in a dicopper(i)–disulfide complex

“…[4][5][6][7][8][9][10][11][12][13][14] In order to understand the mechanism of their function, orbital structures of many copper enzymes and their model complexes were analysed both experimentally and theoretically. [15][16][17][18] Charge transfer that occurs during the catalytic cycle of a copper enzyme can be modelled by optical excitation of the metal-to-ligand or ligand-to-metal charge transfer states in a mimetic copper complex. Structural changes that accompany such photoinduced charge transfer typically occur on nanosecond timescales or faster and can thus be monitored almost exclusively by pump-probe time-resolved techniques.…”