Synthesis, structural characterization and biological properties of cyclometalated iridium(iii) complexes containing 1,2,5]-thiadiazolo-3,4-f]-1,10]-phenanthroline

Two cationic iridium(iii) complexes, Ir(ppy)(2)((tdzp))](+)(1) and Ir(bhq)(2)((tdzp))](+)(2) {ppy = 2-phenylpyridine, bhq = benzoh]quinoline, tdzp = 1,2,5]-thiadiazolo-3,4-f]-1,10]-phenanthroline}, have been synthesized and structurally characterized. The molecular structures of the iridium complexes have been confirmed by single-crystal X-ray structure determination. Extensive hydrogen bonding between lattice water molecules, solvated methanol, and chloride anions is observed in the crystal structure of complex1, which leads to the formation of 1D polymeric cyclic hybrid water-chloride-methanol clusters. The complexes show different photophysical properties in different solvents. The experimental photo-physical properties of the synthesized iridium(iii) complexes match well with the theoretically calculated results obtained by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) studies. The HOMO of complexes1and2is restricted on the iridium and cyclometalated aromatic ligands, while the LUMO, LUMO+1, and LUMO+2 are primarily restricted on the polypyridyl tdzp ligand. The interaction of the complexes with calf thymus DNA (CT-DNA) was investigated by absorption titration and emission titration experiments. Furthermore, the cytotoxicity and cellular localization properties of these complexes towards HeLa cells have been investigated

Simulations of iron K pre-edge X-ray absorption spectra using the restricted active space method

The intensities and relative energies of metal K pre-edge features are sensitive to both geometric and electronic structures. With the possibility to collect high-resolution spectral data it is important to find theoretical methods that include all important spectral effects: ligand-field splitting, multiplet structures, 3d-4p orbital hybridization, and charge-transfer excitations. Here the restricted active space (RAS) method is used for the first time to calculate metal K pre-edge spectra of open-shell systems, and its performance is tested against on six iron complexes: [FeCl6](n-), [FeCl4](n-), and [Fe(CN)(6)](n-) in ferrous and ferric oxidation states. The method gives good descriptions of the spectral shapes for all six systems. The mean absolute deviation for the relative energies of different peaks is only 0.1 eV. For the two systems that lack centrosymmetry [FeCl4](2-/1-), the ratios between dipole and quadrupole intensity contributions are reproduced with an error of 10%, which leads to good descriptions of the integrated pre-edge intensities. To gain further chemical insight, the origins of the pre-edge features have been analyzed with a chemically intuitive molecular orbital picture that serves as a bridge between the spectra and the electronic structures. The pre-edges contain information about both ligand-field strengths and orbital covalencies, which can be understood by analyzing the RAS wavefunction. The RAS method can thus be used to predict and rationalize the effects of changes in both the oxidation state and ligand environment in a number of hard X-ray studies of small and medium-sized molecular systems.QC 20210215</p

Molecular orbital simulations of metal 1s2p resonant inelastic X-ray scattering

For first-row transition metals, high-resolution 3d electronic structure information can be obtained using resonant inelastic X-ray scattering (RIXS). In the hard X-ray region, a K pre-edge (1s -&gt; 3d) excitation can be followed by monitoring the dipole-allowed K alpha (2p -&gt; 1s) or K beta (3p -&gt; 1s) emission, processes labeled 1s2p or 1s3p RIXS. Here the restricted active space (RAS) approach, which is a molecular orbital method, is used for the first time to study hard X-ray RIXS processes. This is achieved by including the two sets of core orbitals in different partitions of the active space. Transition intensities are calculated using both first- and second-order expansions of the wave vector, including, but not limited to, electric dipoles and quadrupoles. The accuracy of the approach is tested for 1s2p RIXS of iron hexacyanides [Fe(CN)(6)](n-) in ferrous and ferric oxidation states. RAS simulations accurately describe the multiplet structures and the role of 2p and 3d spin-orbit coupling on energies and selection rules. Compared to experiment, relative energies of the two [Fe(CN)(6)](3-) resonances deviate by 0.2 eV in both incident energy and energy transfer directions, and multiplet splittings in [Fe(CN)(6)](4-) are reproduced within 0.1 eV. These values are similar to what can be expected for valence excitations. The development opens the modeling of hard X-ray scattering processes for both solution catalysts and enzymatic systems

Restricted active space calculations of L-edge X-ray absorption spectra : From molecular orbitals to multiplet states

The metal L-edge (2p -&gt; 3d) X-ray absorption spectra are affected by a number of different interactions: electron-electron repulsion, spin-orbit coupling, and charge transfer between metal and ligands, which makes the simulation of spectra challenging. The core restricted active space (RAS) method is an accurate and flexible approach that can be used to calculate X-ray spectra of a wide range of medium-sized systems without any symmetry constraints. Here, the applicability of the method is tested in detail by simulating three ferric (3d(5)) model systems with well-known electronic structure, viz., atomic Fe3+, high-spin [FeCl6](3-) with ligand donor bonding, and low-spin [Fe(CN)(6)](3-) that also has metal backbonding. For these systems, the performance of the core RAS method, which does not require any system-dependent parameters, is comparable to that of the commonly used semi-empirical charge-transfer multiplet model. It handles orbitally degenerate ground states, accurately describes metal-ligand interactions, and includes both single and multiple excitations. The results are sensitive to the choice of orbitals in the active space and this sensitivity can be used to assign spectral features. A method has also been developed to analyze the calculated X-ray spectra using a chemically intuitive molecular orbital picture.Correction in: Journal of Chemical Physics, vol. 141, issue 4, article number: 149905, DOI: 10.1063/1.4908043 ISI: 000349847000064QC 20210215</p

Efficient DNA condensation by ruthenium(ii) polypyridyl complexes containing triptycenyl functionalized 1,10-phenanthroline

A series of luminescent ruthenium(ii) polypyridyl complexes containing an extended aromatic moiety derived from triptycene and 1,10-phenanthroline were synthesized and their photophysical, theoretical, and biological properties were investigated. These complexes rapidly condense DNA into nano-aggregates at room temperature. The DNA interactions and DNA condensation properties of these complexes were investigated by absorption and emission spectroscopy, electrophoretic mobility assay, and atomic force microscopy. Their DNA cleavage inactivity and low toxicity of the complexes satisfy the requirements of a good non-viral gene delivery vector

Fingerprinting Electronic Structure of Heme Iron by Ab Initio Modeling of Metal L-Edge X-ray Absorption Spectra

The capability of the multiconfigurational restricted active space approach to identify electronic structure from spectral fingerprints is explored by applying it to iron L-edge X-ray absorption spectroscopy (XAS) of three heme systems that represent the limiting descriptions of iron in the Fe-O-2 bond, ferrous and ferric [Fe(P)(ImH)(2)](0/1+) (P = porphine, ImH = imidazole), and Fe-II(P). The level of agreement between experimental and simulated spectral shapes is calculated using the cosine similarity, which gives a quantitative and unbiased assignment. Further dimensions in fingerprinting are obtained from the L-edge branching ratio, the integrated absorption intensity, and the edge position. The results show how accurate ab initio simulations of metal L-edge XAS can complement calculations of relative energies to identify unknown species in chemical reactions

Fingerprinting Electronic Structure of Heme Iron by Ab Initio Modeling of Metal L-Edge X-ray Absorption Spectra

The capability of the multiconfigurational restricted active space approach to identify electronic structure from spectral fingerprints is explored by applying it to iron L-edge X-ray absorption spectroscopy (XAS) of three heme systems that represent the limiting descriptions of iron in the Fe-O2 bond, ferrous and ferric [Fe(P)(ImH)2]0/1+ (P = porphine, ImH = imidazole), and FeII(P). The level of agreement between experimental and simulated spectral shapes is calculated using the cosine similarity, which gives a quantitative and unbiased assignment. Further dimensions in fingerprinting are obtained from the L-edge branching ratio, the integrated absorption intensity, and the edge position. The results show how accurate ab initio simulations of metal L-edge XAS can complement calculations of relative energies to identify unknown species in chemical reactions.status: publishe