Ivan I. Vorontsov

Capturing and Analyzing the Excited-State Structure of a Cu(I) Phenanthroline Complex by Time-Resolved Diffraction and Theoretical Calculations

Time-resolved crystallography and density functional theory calculations are used to analyze the geometric and electronic changes that occur upon photoexcitation of [Cu(I)(dmp)(dppe)](+) in crystalline [Cu(I)(dmp)(dppe)][PF(6)] [dmp = 2,9-dimethyl-1,10-phenanthroline; dppe = 1,2-bis(diphenylphosphino)ethane]. In the pump-probe experiment, laser and X-ray pulses are synchronized to capture an image of the instantaneous molecular distortions in the transient triplet state. Parallel theoretical calculations, with the phenyl groups replaced by methyl groups, yield information on the distortion of the isolated cation and the change in electron density upon excitation. The experimental distortions are significantly less than the calculated values and are different for the two independent molecules in the asymmetric unit; these findings are attributed to the constraining influence of the crystal matrix. The calculations indicate that the electron transfer upon excitation is mostly from the dmpe ligand to the dmp ligand, while the Cu atomic charge changes by only approximately +0.1e, although the charge distribution on Cu is significantly affected. As found for homoleptic [Cu(I)(dmp)(2)](+), the change in the population of the Cu atom is close to the calculated difference between the corresponding Cu(II) and Cu(I) complexes. Charge density difference maps confirm these conclusions and show a large rearrangement of the electron density on the Cu atom upon excitation.

The structure of short-lived excited states of molecular complexes by time-resolved X-ray diffraction

Experimental and computational methods for time-resolved (TR) diffraction now allow the determination of geometry changes on molecular excitation. The first results indicate significant changes in the interatomic distances and molecular shape on photo-excitation, but also a dependence of the induced changes on the molecular environment. Though the use of high-brightness synchrotron sources is essential, it limits the time resolution to the width of the synchrotron pulse which is currently 70-100 ps. The experiments discussed fall into two categories: (i) picosecond powder diffraction experiments on the molecular excitation to a singlet state, and (ii) microsecond experiments on the excited states of inorganic complexes. Both involve reversible processes for which a stroboscopic technique can be applied.

The formation of a single-bonded (C70−)2 dimer in a new ionic multicomponent complex of cyclotriveratrylene: (Cs+)2(C70−)2·CTV·(DMF)7(C6H6)0.75

The molecular structure and properties of a single-bonded (C70−)2 dimer in a new ionic complex with cyclotriveratrylene (CTV): (Cs+)2·(C70−)2·CTV·(DMF)7·(C6H6)0.75 are presented.

Template synthesis, structure and unusual series of phase transitions in clathrochelate iron(II) α-dioximates and oximehydrazonates formed by capping with functionalized boron-containing agents

Abstract A series of clathrochelate α-dioximates and oximehydrazonates with apical long-chain paraffin and allyl substituents has been synthesized and characterized by X-ray analysis. For the hexadecylboronic FeNx3(BHd)2 complex (where Nx2− is the cyclohexanedion-1,2-dioxime dianion) in the temperature range 100–305 K, two structural phase transitions have been detected by X-ray diffractometry and 57Fe Mossbauer spectroscopy.

Time-resolved synchrotron diffraction and theoretical studies of very short-lived photo-induced molecular species

Definitive experimental results on the geometry of fleeting species are at the time of writing still limited to monochromatic data collection, but methods for modifications of the polychromatic Laue data to increase their accuracy and their suitability for pump-probe experiments have been implemented and are reviewed. In the monochromatic experiments summarized, excited-state conversion percentages are small when neat crystals are used, but are higher when photoactive species are embedded in an inert framework in supramolecular crystals. With polychromatic techniques and increasing source brightness, smaller samples down to tenths of a micrometre or less can be used, increasing homogeneity of exposure and the fractional population of the excited species. Experiments described include a series of transition metal complexes and a fully organic example involving excimer formation. In the final section, experimental findings are compared with those from theoretical calculations on the isolated species. Qualitative agreement is generally obtained, but the theoretical results are strongly dependent on the details of the calculation, indicating the need for further systematic analysis.

First trigonal-antiprismatic tris-dichloroglyoximate iron(II) clathrochelate and its reactivity in nucleophilic substitution reactions

Tris-dichloroglyoximate clathrochelate [Fe(Cl2Gm)3(SnCl3)2]2− dianion has been synthesized by a procedure differing from those described earlier for boron-capped analogs. The co-ordinately saturated SnCl62− dianion is now used as the capping agent instead of boron-containing Lewis acids. The tris-dichloroglyoximate tin-capped product obtained is far less reactive than its boron-capped analogs, and only in the case of a thiophenolate anion was the “regular” hexafunctionalized clathrochelate obtained. The complexes synthesized have been characterized by elemental analysis, PD and MALDI-TOF mass, IR, UV-vis and 1H, 13C and 119Sn NMR spectra, cyclic voltammetry, and X-ray crystallography for the clathrochelate [Fe(Cl2Gm)3(SnCl3)2]2− dianion. The geometry of the functionalized complex (the distortion angle φ and main bond lengths in the clathrochelate framework) has been deduced from the quadrupole splitting value in the 57Fe Mossbauer spectrum and EXAFS data, respectively.

On the refinement of time-resolved diffraction data : comparison of the random-distribution and cluster-formation models and analysis of the light-induced increase in the atomic displacement parameters

Expressions for the random-distribution and cluster-formation models for light-induced changes in crystals studied by time-resolved diffraction are presented. The two models can be distinguished on the basis of differences in the predicted intensities. The light-induced increase in the atomic displacement parameters is analyzed with both simulated and experimental data sets.

Reactions of chloride iron(II) clathrochelates with aliphatic amines: an unexpected influence of the nature of the amine and solvent on the reaction products

The interaction of the reactive di- and hexachloride clathrochelate iron(II) precursors with primary and secondary aliphatic amines of different nature in a wide range of donor and acceptor solvents has been studied. The partially functionalized aminic clathrochelates obtained have been characterized using elemental analysis, PD mass, IR, UV–Vis, 57Fe Mossbauer and 1H, 13C NMR spectra and crystallographically (Fe((C6H11NH)2Gm)(Cl2Gm)(BC6H5)2 · n-C5H12 and Fe((n-C4H9NH)ClGm)(Cl2Gm)2(BC6H5)2 complexes). The causes of an unexpected influence both amine and solvent nature on the product of reaction with chloride clathrochelate precursors have been discussed.

LASER - a program for response-ratio refinement of time-resolved diffraction data

The program LASER2010 is described. It is specifically designed for the refinement of externally induced structural changes in crystalline solids, including time-resolved laser-pump X-ray probe experiments. The refinement is based on the measured relative intensity changes rather than on the integrated reflection intensities.

A very large Rh-Rh bond shortening on excitation of the [Rh 2(1,8-diisocyano-p-menthane)4]2+ ion by time-resolved synchrotron X-ray diffraction

A very large Rh-Rh contraction of approximately 0.85 A occurs on excitation of the [Rh(2)(1,8-diisocyano-p-menthane)(4)](2+) ion to its triplet state.