Shao-Liang Zheng

Direct Observation of a Photoinduced Nonstabilized Nitrile Imine Structure in the Solid State

We report the direct observation of a bent geometry for a nonstabilized nitrile imine in a metal-coordination crystal. The photoinduced tetrazole ring rupture to release N(2) appears to depend on the size of voids around the N(3)-N(4) bond in the crystal lattice. We further observed the selective formation of the 1,3-addition product when a reactive nitrile imine was photogenerated in water. Overall, the bent nitrile imine geometry agrees with the 1,3-dipolar structure, a transient reactive species that mediates the photoinduced 1,3-dipolar cycloaddition in the aqueous medium.

Static and time-resolved photocrystallographic studies in supramolecular solids

Abstract The supramolecular solid state is a medium par excellence for photochemical studies of molecules in a well-defined environment. If the photoactive molecule is embedded within a strong photochemically-inert framework, reactions can proceed without breakdown of the crystal lattice. A number of examples of trans-cis and cis-trans reactions are presented. A variable temperature study of Zn-coordinated tiglic acid shows that the reaction is energy-controlled with a small activation energy of approx. 2 kJ/mol, dependent on the size of the cavity in which the molecule is located. Time-resolved studies of the instantaneous dimer-formation of an organic and an inorganic species are presented. The Cu(I)(NH3)2 cation forms a dimeric species with a contracted Cu(I)—Cu(I) distance through promotion of an electron from an antibonding to a weakly bonding orbital, whereas xanthone forms an excimer with decrease interplanar spacing. The concept of the photodifference map is defined and used thoughout the article.

Supramolecular solids and time-resolved diffraction

Supramolecular solids are an ideal medium for time-resolved diffraction studies at atomic resolution as they allow dilution of the active species, and the study of a species in different states of aggregation and different environments, but attention must be paid to excited-state quenching due to energy transfer. Crystallinity must be preserved up to reasonable product concentrations if chemical reactions are to be monitored at the atomic level.

Charge‐density analysis of the ground state of a photochromic 1,10‐phenanthroline zinc(II) bis(thiolate) complex

The charge density of the title compound was determined at 90 K, using a spherical crystal of 150 microm diameter. The proper treatment of the Zn atom in the pseudo-tetrahedral environment is considered in detail. A satisfactory refinement is only obtained when anharmonic Gram-Charlier parameters are included as variables in the refinement. A successful combined anharmonic/multipole refinement indicates a small polarization of the 4s shell in the anisotropic environment. One of the two toluenethiols is approximately pi-stacked with the phenanthroline ligand. A bond path is found connecting the two ligands. In addition the Zn-S bond to this ligand is slightly extended compared with the same bond to the second toluenethiol. A separate photocrystallographic and theoretical study indicates the long wavelength emission of the title compound to be due to a ligand-to-ligand charge transfer (LLCT) from a toluenethiol to the phenanthroline ligand. The charge-density results do not provide a basis for deciding which of the thiole ligands is the source of the transferred electron density. This result is in agreement with the theoretical calculations, which show comparable oscillator strengths for charge transfer from either of the ligands.

Engineering delocalizing π electronic [CuII3(μ3-OH)(μ-pz)3]2+ species into organometallic frameworks by Ag-π coordination

Reactions of [CuII3(μ3-OH)(μ-pz)3]2+-containing precursor [{Cu3(μ3-OH)(μ-pz)3(Hpz)3}2(μ6-SO4)](NO3)2·MeCN·MeOH·1.5H2O (1) with silver salts under mild conditions generate two novel Cu(II)–Ag(I) organometallic solids involving the 4-position C atom of pz− ligand bonded to the Ag centers, [Ag(Hpz)2]2[{Ag2(Hpz)2(NO3)2}{Cu6(OH)2(pz)6(Hpz)6(SO4)}2](NO3)6·4H2O (2) and [{Ag(H2O)2}{Cu3(OH)(pz)3(Hpz)3(H2O)(ClO4)3}]n (3). 1 has a 1D coordination chain structure constructed with hexanuclear cluster units and μ-nitrate bridges. A pair of [CuII3(μ3-OH)(μ-pz)3(Hpz)3]2+ units bridged by one μ3-SO42−group constitutes the hexanuclear cluster. 2 contains 0D organometallic Ag2Cu12 cluster cations formed by a pair of [{Cu3(OH)(pz)3(Hpz)3}2(μ4-SO4)]2+cluster units and one neutral Ag2(Hpz)2(NO3)2 unit viaAg-π(pz−) and Ag–O(NO3−) coordination, [Ag(Hpz)2]+ cations and nitrate anions as well as lattice water molecules. 3 contains 1D neutral organometallic chains constructed with anionic [Cu3(OH)(pz)3(Hpz)3(H2O)(ClO4)3]−cluster units and cationic [Ag(H2O)2]+ units viaAg-π(pz−) coordination. MO calculations based on the {[Cu3(OH)(pz)3(Hpz)3]–[Ag(H2O)2]–[Cu3(OH)(pz)3(Hpz)3]}5+ cation model with the related X-ray geometry were carried out. The Mayer bond orders of the Ag–C are calculated to be 0.249 and 0.275, showing that the Ag(I)- η1-C orbital interactions are significantly attractive. A Bader analysis of the electron density further shows the presence of a (3,−1) bond-critical point linking the Ag(I) and C atoms and 1.366/1.378 A away from Ag(I), which further confirms the existence of Ag(I)–C bonding between the fragments. The magnetic properties of 1–3 were also studied.

Paper Emission quenching of photoactive molecules embedded in supramolecular solids: Synthesis, structure and photoluminescence studies of benzil in a CMCR-based inclusion complex with a saturated linker molecule{

Using a fully saturated linker, DPP [DPP ~ 1,3-di-(4-piperidyl)propane], a new CMCR-based (CMCR ~ C-methylcalix[4]resorcinarene) supramolecular complex incorporating benzil, CMCR-DPP-benzilEtOH-H2O, and a corresponding benzil-free analogue CMCR-DPP-3EtOH, have been synthesized. Comparison of the TDDFT energy levels and the experimental host-absorption and guest-emission spectra, confirms that the emission quenching of benzil in a series of CMCR-linker frameworks can be attributed to the energy transfer from the guest to the host framework in the supramolecular solid and suggests strategies for increasing the lifetime of luminescent materials.

Single-crystal-to-single-crystal e → Z and Z → e isomerizations of 3-chloroacrylic acid within the nanocavities of a supramolecular framework

Single-crystal-to-single-crystal E-->Z and Z-->E photo-isomerizations of 3-chloroacrylic acid (HClA) take place with full retention of the crystal lattice in the framework cavities of the supramolecular crystals CECR.HClA.2MeOH.1.5H(2)O (CECR = C-ethylcalix[4] resorcinarene); their progress has been monitored as the reaction proceeds.

Ligand-unsupported Au(I) chains with short Au(I)⋯Au(I) contacts

A new series of solids with ligand-unsupported Au(I) chains with short Au...Au contacts were synthesized; as Ag compounds with the same structure are known, the new phases now allow unbiased comparison of Ag...Ag and Au...Au metallophilic bonds not supported by bridging ligands, which shows the latter to be consistently shorter by 0.03-0.04 A.