International audienceThe electrocatalytic redn. of CO2 to CO in hydroorg. medium has been investigated at illuminated (λ \textgreater 600 nm; 20 mW cm-2) hydrogen-terminated silicon nanowires (SiNWs-H) photocathodes using three Mn-based carbonyl bipyridyl complexes as homogeneous mol. catalysts ([Mn(L) (CO)3(CH3CN)](PF6) and [Mn(bpy) (CO)3Br] with L = bpy = 2,2'-bipyridine and dmbpy = 4,4'-dimethyl-2,2'-bipyridine). Systematic comparison of their cyclic voltammetry characteristics with those obtained at flat hydrogen-terminated silicon and traditional glassy carbon electrodes (GCE) enabled us to demonstrate the superior catalytic efficiency of SiNWs-H in terms of cathodic photocurrent densities and overpotentials. For example, the photocurrent densities measured at -1.0 V vs SCE for [Mn(bpy) (CO)3(CH3CN)](PF6) at SiNWs-H exceeded 1.0 mA cm-2 in CO2-satd. CH3CN + 5% vol./vol. H2O, whereas almost zero current was measured at this potential at GCE. Such characteristics have been supported by the energetic diagrams built for the different SiNWs\textbarMn-based catalyst interfaces. The fill factor FF and energy conversion efficiency η calcd. under catalytic conditions were higher for [Mn(bpy or dmbpy) (CO)3(CH3CN)](PF6) (FF = 0.35 and 0.34; η = 3.0 and 2.0%, resp.). Further preparative-scale electrolysis at SiNWs-H photocathode with Mn-based complex catalysts in electrolytic soln. evidenced the quant. conversion of CO2 to CO with a higher stability of the [Mn(dmbpy) (CO)3(CH3CN)](PF6) complex. Finally, in order to develop technol. viable electrocatalytic devices, the elaboration of SiNWs-H photoelectrodes modified with a Mn-based complex has been successfully achieved from an electropolymerizable catalyst, and it was shown that the electrocatalytic activity of the complex was retained after immobilization

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Iron sandwich on a tungstate bun: Two new polyoxotungstates with paramagnetic iron(III) heteroatoms (see structure, W blue, Fe yellow, O red) possess S=15/2 and S=5 ground states. Both compounds are single-molecule magnets, and the hexairon species shows large hysteresis (see picture) and quantum tunneling effects at low temperature. Electrochemical studies indicate that these species are stable in solution for a wide range of pH values.

A POM to remember: Hexanuclear Fe(III) polyoxometalate (POM) single-molecule magnets (see structure) can be noncovalently assembled on the surface of single-wall carbon nanotubes. Complementary characterization techniques (see TEM image and magnetic hysteresis loops) demonstrate the integrity and bistability of the individual molecules, which could be used to construct single-molecule memory devices.

The presence of alkylammonium groups covalently grafted on bisphosphonato ligands induces photochromic properties to ligand-coordinated polyoxomolybdate systems. Such intrinsically photoactive polyanions can be used for the preparation of materials combining photochromic polyoxometalates and functional countercations.

Mn(I) carbonyl terpyridyl complexes have been synthesized and characterized. The tricarbonyl derivative exhibits interesting behaviors for controlled CO-release by both thermal and photosynthetic pathways.

Two new compounds based on O(3)PCH(2)PO(3)(4-) ligands and {Mo(V)(2)O(4)} dimeric units have been synthesized and structurally characterized. The dodecanuclear Mo(V) polyoxomolybdate species in (NH(4))(18)[(Mo(V)(2)O(4))(6)(OH)(6)(O(3)PCH(2)PO(3))(6)] x 33 H(2)O (1) is a cyclohexane-like ring in a chair conformation with pseudo S(6) symmetry. In the solid state, the wheels align side by side, thus delimiting large rectangular voids. The hexanuclear anion in Na(8)[(Mo(V)(2)O(4))(3)(O(3)PCH(2)PO(3))(3)(CH(3)AsO(3))] x 19 H(2)O (2) has a triangular framework and encapsulates a methylarsenato ligand. (31)P NMR spectroscopic analysis revealed the stability of 2 in various aqueous media, whereas the stability of 1 depends on the nature of the cations present in solution. It has been evidenced that the transformation of 1 into 2 occurs in the presence of CH(3)AsO(3)(2-) ions. This behavior shows that 1 can be used as a new precursor for the synthesis of Mo(V)/diphosphonate systems. The two complexes were very efficient both as reductants of Pt and Pd metallic salts and as capping agents for the resulting Pt(0) and Pd(0) nanoparticles. The size of the obtained nanoparticles depends both on the nature of the polyoxometalate (POM; i.e., 1 or 2) and on the [metallic salt]/[POM] ratio. In all cases, X-ray photoelectron spectroscopy (XPS) measurements have revealed the presence of Mo(VI) species that stabilize the nanoparticles and the absence of Mo(V) moieties. Diffuse-reflectance FTIR spectra of the Pt nanoparticles show that the capping Mo(VI) POMs are identical for both systems and contain the diphosphonato ligand. The colloidal solutions do not show any precipitate and the nanoparticles remain well-dispersed for several months. The electrochemical reduction of Mo(V) species was studied for 2. Cyclic voltammetry alone and electrochemical quartz crystal microbalance coupled with cyclic voltammetry show the deposition of a film on the electrode surface during this reduction.

The synthesis of nonlinear optical (NLO) active salts with stilbazolium derivatives and polyoxometalate (POM) counterions has been investigated. With known nonchiral stilbazolium derivatives, such as MOMS(+), compounds with centrosymmetric structures have been isolated, like for instance the centrosymmetric salt (MOMS)(4)[Mo(8)O(26)] (1), synthesized under hydrothermal conditions. A new chiral derivative of the known DAMS(+) molecules, named here CHIDAMS(+), has therefore been synthesized in order to force the crystallization of the hybrid ionic salts in noncentrosymmetric space groups. The CHIDAMS(+) cation has been crystallized under two polymorphic PF(6)(-) salts, (CHIDAMS)PF(6) (2a and 2b), and its reactivity with various POMs has been investigated. The ionic salt (CHIDAMS)(2)[Mo(5)O(13)(OEt)(4)(NO){Na(H(2)O)(0.5)(DMF)(0.5)}] (4) crystallizes in the noncentrosymmetric P2(1) group, but the push-pull axis of the CHIDAMS(+) cations adopts a quasi-antiparallel alignment. The ionic salt (CHIDAMS)(3)[PW(12)O(40)].2DMF (5) associating three CHIDAMS(+) cations and a PW(12)O(40)(3-) Keggin anion crystallizes also in the P2(1) space group, but the disposition of the cations in the solid state is far more favorable. Diffuse reflectance experiments have evidenced a charge transfer between the organic and inorganic components in 5, and Kurtz-Perry experiments show that this salt exhibits a second harmonic generation efficiency more than 10 times higher than those of the PF(6)(-) salts 2a and 2b, the hybrid salt 4, and all of the other NLO active POM molecular materials reported in the literature.