Ligand‐Field Strength and Symmetry‐Restricted Covalency in Cu^II Complexes – a Near‐Edge X‐ray Absorption Fine Structure Spectroscopy and Time‐Dependent DFT Study

Abstract

Keywords: Density functional calculations / Ligand effects / NEXAFS spectroscopy / X-ray absorption spectroscopy / CopperThe low-lying empty orbitals of bis(acetylacetonato)copper have been probed by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy at the Cu L 2,3 edges and timedependent density functional theory (TDDFT) calculations within the Tamm-Dancoff approximation (TDA) coupled to the relativistic zeroth-order regular approximation including spin-orbit effects (SO-ZORA TDDFT-TDA). Both the relative positions of NEXAFS features and their linear dichroism are satisfactorily reproduced. Moreover, a comparison with lit-

Theoretical Investigation of the Electronic Properties of Three Vanadium Phthalocyaninato (Pc) Based Complexes: PcV, PcVO, and PcVI

“…This was not particularly surprising because no V- or X-based AO transforms as the C 4 v a 2 IR . Incidentally, in PcM and PM complexes, ,, the 2a 1u MO corresponds to a π orbital completely localized on the macrocycle (see Figure ) and characterized by four nodal planes passing through the N py (2σ v ) and the PcM/PM meso-N/C (2σ d ) atoms. , Similar considerations hold for both the V 3d xy based MO (the 14b 2g , 16b 2 , and 18b 2 SOMOs in I – III , respectively) and the V 3d x 2 – y 2 based MO (the 16b 1g , 20b 1 and 22b 1 VMOs in I – III , respectively) as a consequence of their localization in a plane parallel (∥) to the xy plane: i.e., perpendicular to the C 4 axis ( z ) along which the apical ligand X is positioned…”

“…(iv) The role played by MLCT transitions in determining the title compounds’ V L 2,3 -edge XAS features should be found. As far as the fourth reason is concerned, it can be useful to mention that theoretical and experimental investigations carried out by some of us on the electronic properties of PcCu, TPPCu, TPP­(F)­Cu, and Cu­(acac) 2 confirmed the legitimacy of using the Cu II L 3 -edge position to get information about the ligand-field strength exerted on the Cu II center, pointing out, at the same time, the possibility of a Cu–ligand covalency underestimation if the Cu II L 2,3 -edge normalized intensities of complexes with low-lying ligand-based π* orbitals would have been used as a gauge.…”

“…Transition-metal phthalocyanine complexes (PcM) have been attracting increasing interest because of their widespread technological applications, − which, in addition to catalysis, exploit PcM peculiar properties such as semiconductivity, photoelectricity, and the structural similarity to the biologically relevant M porphyrin (PM) complexes. As part of an ongoing research project devoted to the study of the structure/reactivity relationships in materials usually labeled as energy-targeted, we have been focusing on the X-ray absorption spectroscopy (XAS) at the donor atom K-edge and at the M L 2 , 3 -edges , of a series of PcM (PcCu, PcFe, PcFe­(η 2 -O 2 )) and TPPM (TPPCu, TPP­(F)­Cu, TPPTi IV ) supported thin films from both an experimental and theoretical point of view. A comparison of the obtained results ,,, with those homogeneously achieved for different complexes characterized by the presence of the same central M ions (Cu­(acac) 2 , ,, TiCl 4 , Ti­(η 5 -C 5 H 5 )­Cl 3 , Ti­(η 5 -C 5 H 5 ) 2 Cl 2 , Fe­(acac) 3 ) allowed us to look into the role played by the M chemical environment, the M electronic configuration, and the M oxidation number in determining the overall spectrum appearance, thus legitimizing its use as a sort of a M fingerprint.…”

A Theoretical Study of the Occupied and Unoccupied Electronic Structure of High- and Intermediate-Spin Transition Metal Phthalocyaninato (Pc) Complexes: VPc, CrPc, MnPc, and FePc

“…The MPc L 2,3 -edges’ XA spectra [ 33 , 34 , 35 , 38 ] herein modelled have been collected from deposits of different thicknesses, often consisting of randomly oriented and weakly interacting molecules. Thus, according to a procedure successfully tested in the past [ 36 , 37 , 38 , 39 , 40 , 41 , 116 , 117 , 118 , 119 , 120 ], XAS outcomes have been rationalized by completely neglecting the adsorbate/substrate interactions. Now, before moving to the modelling of the MPc XAS features, a few words about the 2p → 3d excitations simply based on symmetry arguments may be useful to facilitate the forthcoming discussion.…”

K- and L-edge X-ray absorption spectrum calculations of closed-shell carbon, silicon, germanium, and sulfur compounds using damped four-component density functional response theory

“…24 For closed-shell systems the static-exchange method in a four-component relativistic setting has been employed, 25,26 and, in terms of TDDFT, investigations using the zeroth-order regular approximation have been reported. 8,27,28 In this work, we focus on the X-ray absorption spectra of metalloids and non-metals, noting that the present approach is viable only as long as a Kramers-restricted Kohn-Sham determinant provides a sufficiently accurate description of the reference state. Furthermore, the light-matter interaction is assumed to be weak and the perturbing electric field is treated by means of response theory.…”