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The physicochemical properties of highly stable supramolecular donor–acceptor (D–A) complexes of a bis(18-crown-6)azobenzene (weak π-donor) with a series of bis(ammonioalkyl) derivatives of viologen-like molecules (π-acceptors) in acetonitrile were studied using cyclic voltammetry, UV–vis absorption spectroscopy, 1H NMR spectroscopy, and density functional theory (DFT) calculations. The crystalline structures of the bis(crown)azobenzene and its complex with a bis(ammoniopropyl) derivative of 2,7-diazapyrene were determined by X-ray diffraction analysis. In solution, all of the supramolecular D–A complexes studied have a pseudocyclic structure owing to ditopic coordination of the ammonium groups of the acceptor to the crown ether moieties of the donor. These complexes show somewhat lower stability as compared with the previously studied complexes of the related derivative of stilbene (strong π-donor), which is explained by the relatively weak intermolecular charge-transfer (CT) interactions. Time-dependent DFT calculations predict that the low-energy CT transition in the D–A complex of the bis(crown)azobenzene with a bis(ammoniopropyl) derivative of 4,4′-bipyridine lies between the local ππ* and nπ* transitions of the azobenzene. The absorption band associated with the CT transition is indiscernible in the spectrum since it is overlapped with broad and more intense ππ* and nπ* bands. It was found that the E → Z photoisomerization quantum yield of the bis(crown)azobenzene decreases by almost an order of magnitude upon the complexation with the 4,4′-bipyridine derivative. This effect was tentatively attributed to the intermolecular electron transfer that occurs in the 1ππ* excited state of the azobenzene and competes with the 1ππ* → 1nπ* internal conversion.

In combination with EtAlCl2, complexes {[WCl3(μ-Cl)(N-2,6-iPr2C6H3)]2}, [WCl4(NR)(thf)] (R = Et, iPr, cHx, Ph, 2,6-iPr2C6H3, 4-F-C6H4, and 2,4,6-F3-C6H2), and [WCl2(NR′)(PMe3)3] (R′ = Ph, 2,6-iPr2C6H3) were all productive ethylene dimerization pre-catalysts, giving turnover numbers (TONs) in the range of 400–144 000 (mol C2H4)(mol W)−1 and moderate selectivities toward 1-butene (>66%) depending on the nature of the imido substituent. The formation of C6 side-products resulted from the incorporation of 1-butene rather than direct trimerization, something that is independent of butene concentration. Stoichiometric reactions between the tungsten mono(imido) complexes and alkylaluminum reagents are described, which are consistent with the reduction of the tungsten centre playing an important part in the initiation process. Testing discrete WV and WIV mono(imido) complexes for olefin dimerization revealed the former to be significantly more active, which offers insight into the mode of action of the commercially relevant tungsten mono(imido)-selective dimerization initiators described herein.

The single-molecule conductance of metal complexes of the general forms trans-Ru(C≡CArC≡CY)2(dppe)2 and trans-Pt(C≡CArC≡CY)2(PPh3)2 (Ar = 1,4-C6H2-2,5-(OC6H13)2; Y = 4-C5H4N, 4-C6H4SMe) have been determined using the STM I(s) technique. The complexes display high conductance (Y = 4-C5H4N, M = Ru (0.4 ± 0.18 nS), Pt (0.8 ± 0.5 nS); Y = 4-C6H5SMe, M = Ru (1.4 ± 0.4 nS), Pt (1.8 ± 0.6 nS)) for molecular structures of ca. 3 nm in length, which has been attributed to transport processes arising from tunneling through the tails of LUMO states.

The asthma therapeutic theophylline exists in at least three anhydrous polymorphs and a monohydrate. The single-crystal X-ray structure of the high-temperature polymorph form I is presented for the first time, and the energetic relationship between forms I and II is investigated using the partial charges and chemical hardness analysis (PACHA) algorithm. It is shown that the interactions in the form I crystal network are stronger, especially the hydrogen bond. The single-crystal neutron structure of the monohydrate demonstrates static disorder of the water molecule as well as dynamic disorder of the methyl groups. PACHA investigations based on the neutron coordinates reveal that the homomeric interactions in this form are stronger than the interaction of the water with the host molecules. The dehydration of the hydrate should thus leave the theophylline network intact, explaining the isomorphic powder X-ray diffractograms of the monohydrate and its dehydrated form III.

International audience; The crystal structures in both irradiated and nonirradiated states of a photoinduced molecular switch based on the spin-crossover phenomenon are presented. From the structural point of view, the light-induced metastable high-spin state of the spin-crossover complex [Fe(phen)2(NCS)2] (phen = 1,10-phenanthroline) shows significant differences with the low-spin state but also with the thermally induced high-spin state.

The triplatinum compound [Pt3(CNBut)6] reacts with triorganosilanes SiR3H [SiR3= SiMe3, SiEt3, SiMe2Ph, SiMePh2, SiPh3, or Si(OEt)3] to give diplatinum complexes [{Pt(CH:NBut)(SiR3)(CNBut)}2], arising from insertion of an isocyanide ligand into a Pt–H bond, formed in an initial oxidative-addition step. The reaction with SiPh3H also afforded the bis(silyl)platinum complex [Pt(SiPh3)2(CNBut)2]. The structure of the diplatinum compounds has been established by a single-crystal X-ray diffraction study of [{Pt(CH:NBut)(SiMePh2)(CNBut)}2] which showed that the two platinum atoms, each in a square-planar environment, are bridged by HC:NBut ligands to give a six-membered ring of boat conformation. The terminal ligands are such that the silyl groups are trans to the N atoms of the central ring. The Pt–N bond is exceptionally long (2.173Å) and the trans-annular Pt ⋯ Pt distance of 3.056Å suggests little metal–metal interaction. Crystals of the title compound are monoclinic, space group P21/c, with Z= 4 in a unit cell of dimensions a= 11.649(4), b= 18.778(15), c= 21.825(15)Å, and β= 97.31(3)°. The structure has been solved by heavy-atom methods from 7 096 intensity data [l[gt-or-equal] 2.0σ(l)] measured on a four-circle diffractometer at –50 °C, and refined to R 0.057. The compound [Pt3(CNBut)6] reacts with GeMe3H to give an analogous diplatinum complex [{Pt(CH:NBut)(GeMe3)(CNBut)}2]., We thank the S.R.C. for support and the Spanish Ministry of Education and Science for the award of a Fellowship (to M. C.)