Sulfur K-edge X-ray absorption near-edge spectral analysis of thiourea free ligand and its Zn(II), Co(II), and Ni(II) complexes

Electronic supporting information for the analysis and interpretation of sulfur K-edge X-ray absorption near-edge spectra of thiourea free ligand and its [Zn(TU)₄]²⁺, [Co(TU)₄]²⁺, and [Ni(TU)₆]²⁺ complexes.

Sulfur K-edge X-ray absorption spectroscopy (XAS) was employed to experimentally define the nature of coordinative bond between thiourea (TU) or thiocarbamide ligand and Zn²⁺, Co²⁺, and Ni²⁺ ions in distorted tetrahedral and octahedral homoleptic coordination environments. Comparisons of XAS spectra of the free TU ligand, [Zn(TU)₄]²⁺, [Co(TU)₄]²⁺, and [Ni(TU)₆]²⁺ complexes clearly identify spectral features emerging from the structural non-innocent TM²⁺–S(TU) bonding. Quantitative analysis of pre-edge intensities describes the covalency of Ni²⁺– and Co²⁺–S(TU) bonding to be at most 23% and 9% as expressed by the S 3p contributions per 3d electron hole. Using relevant Ni²⁺ complexes with dithiocarbamate and thioether ligands, we evaluated the empirical S 1s→3p transition dipole integrals developed for sulfur ligands and its dependence on heteroatom substitutions. With the aid of density functional theory-based ground electronic state calculations, we found evidence for the need of using a transition dipole that is dependent on the presence of conjugated heteroatom (N) substitution in the S-ligands.

Table of Contents:

Worksheets "transition dipole" and "spectral modeling summary" contain data for empirical S 1s->3p transition dipole integral estimates and summary of spectral modeling, respectively.

RAW_DATA folder:
ASCII formatted S K-edge XAS data from BL 4-3 of SSRL, and data obtained for the [Ni(TU)₆]²⁺ complex at the double-crystal monochromator beamline (formerly Canadian Beamline) of Synchrotron Research Center (the home of Aladdin), in Stoughton, Wisconsin.

SPECTRAL_MODELS folder
Electronic spreadsheets, PeakFit spectral fitting templates, spectra as user-defined functions, quantitative analysis of pre-edge feature intensities

XRD_STRUCTURES folder
Xmol (XYZ) and DSViewerPro (MSV) files for the analysis of the crystal packing environment of TU complexes.

DFT_CALCULATIONS
Gaussian09 log files for free thiourea, Co^(II) and Ni^(II) complexes at BP86/def2TZVP, B3LYP/def2TZVP, and TPSS/def2TZVP levels of theory; frequency calculations for IR vibrational spectral simulations.