A theoretical study of the L₃ pre-edge XAS in Cu(ii) complexes

Abstract

L2,3 spectra of Cu(II) complexes have been simulated by means of time dependent DFT. Besides the agreement between theory and experiment, the adopted approach provided further insights into the use of the Cu(II) L3-edge intensity and position to investigate the Cu-ligand symmetry-restricted covalency and the ligand-field strength.

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

“…More specifically, the relative intensities and relative positions of the X L 2,3 (X = I-III) features satisfactorily agreed with theoretical oscillator strength distributions ( X f). Such a result, combined with estimates of (1) a Cu-S interaction in III more covalent than the Cu-Cl one in I, [9,11] (2) a Cu-N interaction in II less covalent than the Cu-Cl one in I, [11,12] (3) a ligand field in III weaker than that in I [15] and (4) a ligand field in II stronger than that in I [15] represented a successful test of the SO-ZORA TDDFT-TDA method when applied to the modelling of CuII L 2,3 spectra. Interestingly, the composition analysis of the excitations associated with II L 3 revealed that, in addition to 2p 3/2 Ǟ 3d transitions, [18] metal-to-ligand charge-transfer (MLCT) transitions involving low-lying ligand-based π* MOs contribute to the II L 3 intensity and, thus, weaken its believed relationship with the M-L covalency.…”

“…Right panel: NEXAFS spectra for the surface oriented parallel (full lines) and nearly perpendicular (dotted lines) to the electric field; each set of spectra has been rescaled to the intensity of the white line for the surface parallel to the electric field. 924.67 [11] 925.75 [11] 925.03 Theo L 2 945.06 [11] 946.00 [11] 945.28…”

“…[11,12] (931.4 eV) as a consequence of the EE absolute calibration (see Experimental Section). film thicknesses and molecular tilts (see Experimental Section); nevertheless, the f values associated with the transitions that generate II L 3 and IV L 3 (see the upper panel of Figure 3) are consistent with a similar Cu-N and Cu-O symmetry-restricted covalency, in both cases lower than the Cu-Cl one.…”

“…[8,9] Recently, [11] some of us have successfully simulated the L 2,3 spectra of I, [8a] copper phthalocyanine (II, Figure 1) [12] and the so-called oxidized blue copper site in plastocyanin (III, Figure 1) [8a,13] through time-dependent density functional theory (TDDFT) calculations within the TammDancoff approximation (TDA) coupled to the relativistic zeroth-order regular approximation (ZORA) including SO effects. More specifically, the relative intensities and relative positions of the X L 2,3 (X = I-III) features satisfactorily agreed with theoretical oscillator strength distributions ( X f).…”

“…Both π 4 The NEXAFS spectra recorded at the Cu II L 2,3 edges of IV deposited as a thin film on Au(100) are presented and discussed with reference to the results of SO-ZORA TDDFT-TDA calculations on the isolated molecule. The adopted computational setup [11,12,26] allowed a comparison with homogeneous literature data pertaining to both I and II. Moreover, insights into the Cu-X (X = Cl, N and O) symmetry-restricted covalency of the different CuX 4 square-planar chromophores have been gained by exploiting both experimentally and theoretically the dependence of NEXAFS spectra of II and IV deposited on Au(100) on the direction of the photon electric field.…”