Modern Computational Chemistry Methods for Prediction of Ground- and Excited-State Properties in Open-Shell Systems

The main goal of the research presented in this work is to provide some important insights about computational modeling of open-shell species. Such projects are: the investigation of the size-extensivity error in Equation-of-Motion Coupled Cluster methods, the analysis of the Long-Range corrected scheme in predicting UV-Vis spectra of Cu(II) complexes with the 4-imidazole acetate and its ethylated derivative, and the exploration of the importance of choosing a proper basis set for the description of systems such as the lithium monoxide anion. The most significant findings of this research are: (i) The contribution of the left operator to the size-extensivity error of the CR-EOMCC(2,3) approach, (ii) The cause of d-d shifts when varying the range-separation parameter and the amount of the exact exchange arising from the imbalanced treatment of localized vs. delocalized orbitals via the tuned CAM-B3LYP* functional, (iii) The proper acidity trend of the first-row hydrides and their lithiated analogs that may be reversed if the basis sets are not correctly selected

Electronic Structure of Iron Porphyrin Adsorbed to the Pt(111) Surface

Systematic density functional theory calculations that treat the strong on-site 3d electron−electron interactions on iron via a Hubbard Ueff = 3.0 eV and the van der Waals (vdW) interactions between the substrate and adsorbate within the vdW-DF framework are employed to study the adsorption of the iron porphyrin (FeP) molecule to the Pt(111) surface. The more accurate vdW-DF-optPBE and vdW-DF-optB88 functionals found the same binding site to be the most stable and yielded binding energies that were within ∼20% of each other, whereas the binding energies computed with the vdW-DF-revPBE functional were substantially weaker. This work highlights the importance of vdW interactions for organometallic molecules chemisorbed to transition metal surfaces. The stability of the binding sites was found to depend upon the number of Fe−Pt and C−Pt bonds that were formed. Whereas in the gas phase the most stable spin state of FeP is the intermediate spin S = 1 state, the high spin S = 2 state is preferred for the FeP−Pt(111) system on the binding sites considered herein. The spin switch results from the elongation of the Fe−N bonds that occur upon adsorption

Synthesis, structure, and properties of bis(2-(1-ethyl-1H-imidazol-4-yl) acetate) copper(II)

Ethylation of imidazole-4-acetate methyl ester affords 1-ethyl-1H-Imidazol- 4-ylacetic acid methyl ester (1) and 1-ethyl-1H-Imidazol-5-ylacetic acid methyl ester (2) in a 3:1 ratio. Both 1 and 2 can be converted to their potassium carboxylate salts, 3 and 4, respectively. Reaction of 3 with CuCl2 in methanol yields [Cu(eia)2]·4MeOH (5·4MeOH) (eia = 1-ethyl-1H-imidazol-4-yl)acetate). EPR measurement of 5 in methanol glass exhibits near axial symmetry with g⊥ (gx = 2.060, gy = 2.087) and g∥=gz= 2.293 with A∥Cu = A zCu = 152 G, A⊥Cu∼ 10 G, and A yN = 14 G. Accordingly, the structure of 5·4MeOH reveals Cu(II) in tetragonally distorted octahedral geometry with O, N coordination from eia and elongated bonding (2.506 Å) to methanol oxygens in the axial positions. An infinite 1-dimensional hydrogen bonding network involving methanol molecules is present. DFT studies have been carried out to assist in assignment of electronic transitions. Electrochemical studies on 5 in methanol and DMF reveal quasi-reversible redox behavior for the Cu II/I couple while for MeCN a CuI/0 stripping process is seen. © 2013 Elsevier B.V. All rights reserved