Jean-Marie Manoli

Heterobimetallic aggregates of copper(I) with thiotungstates and thiomolybdates. Synthesis and characterization of polymeric (NEt4)3[Cu4(NCS)5WS4], (NEt4)2[(CuNCS)3WS4] and (NEt4)2[(CuNCS)4WS4], M = Mo, W

Abstract Reaction of (NEt 4 ) 2 MS 4 (M = Mo, W) with CuCl and KSCN (or NH 4 SCN) in acetone or acetonitrile affords a new set of mixed metal–sulfur compounds: infinite anionic chains Cu 4 (NCS) 5 MS 4 3− ( 1,2 ), (CuNCS) 3 WS 4 2− ( 3 ) and two dimensional polymeric dianions (CuNCS) 4 MS 4 2− ( 4,5 ). Crystal of 1 (M = W) and 3 are triclinic, space group P 1( 1 : a = 10.356(2), b = 15.039(1), c = 17.356(2)A, α = 78.27(1)°, β = 88.89(2)° and γ = 88.60(1)°, Z = 2, R = 0.04 for 3915 independent data; 3 : a = 8.449(2), b = 14.622(4), c = 15.809(8)A, α = 61.84(3)°, β = 73.67(3)° and γ = 78.23(2)°, Z = 2, R = 0.029 for 6585 independent data). Crystals of 4 (M = W) and 5 (M = Mo) are monoclinic, space group P 2 1 / m , Z = 2 ( 4 : a = 12.296(4), b = 14.794(4), c = 10.260(3)Aand β = 101.88(3)°, R = 0.034 for 4450 independent data; 5 : a = 12.306(2), b = 14.809(3), c = 10.257(2)Aand β = 101.99(3)°, R = 0.043 for 3078 independent data). The crystal structure determinations of 4 and 5 show that four edges of the tetrahedral MS 4 2− core are coordinated by copper atoms forming WS 4 Cu 4 aggregates linked by eight-membered Cu(NCS) 2 Cu rings. A two-dimensional network is thus formed in the diagonal (101) plane. The space between the anionic two-dimensional networks is filled with the NEt 4 + cations. Additional NCS groups lead to the [Cu 4 (NCS) 5 WS 4 ] 3− ( 1 ) trianion connected by NCS bridges forming pseudo-dimers. These latter are held together by weak Cu S(NCS) interactions giving rise to infinite chains along a direction parallel to [100]. In contrast complex 3 develops infinite chains from WS 4 Cu 3 aggregates with the same Cu(NCS) 2 Cu bridges as in 4 and 5 . These chains are running along a direction parallel to [010]. The structural data of the different types of polymeric compounds containing MS 4 2− and CuNCS have been used to interpret vibrational spectroscopic data of the thiocyanate groups.

Using inorganic silicate precursor/molybdenum peroxo complexes/onium salt interfaces in aqueous acidic media to design mesoporous silica with high molybdenum content and high dispersion

Mesoporous molybdosilicate, [Mo]-MCM-41, molecular sieves with variable amounts of molybdenum ( VI ) have been synthesized in acidic media from MoO 3 , aqueous hydrogen peroxide and tetraethyl orthosilicate as the silicon source. This procedure avoids the formation of iso-(or hetero-)polyooxometalates and eliminates the need for careful control of the rate of hydrolysis of the metal precursors, e.g. alkoxides, sometimes involved in the syntheses of transition metal-containing mesoporous materials. The parent materials are calcined in air (60° Ch ’1, isothermal at 920 K for 4 h) to decompose the organic structure-directing agent. The materials have been characterized by chemical analysis, X-ray diVraction and EDS analysis, TEM, 29Si MAS NMR, UV-visible diVuse reflectance spectroscopy and nitrogen sorption isotherms. In contrast to previous preparations, such syntheses give an increase in the Mo/Si (mol/mol ) ratio of up to 0.04 and a greater dispersion of the surface species. For chemical characterization, (R)-(+)limonene epoxidation with anhydrous tert-butylhydroperoxide/decane/pentane mixtures was used as a test; high conversions and selectivities can be obtained at 20°C. DiVerent leaching behaviors were observed as a consequence of the diVerent catalyst preparation methods. A comparative IR spectroscopic study was performed to obtain evidence for the formation of [Mo]-OOt-Bu surface species.

Heterobimetallic aggregates derived from the double cubane-like structure (NMe4)4[MS4(CuCl)5Cl2] (MMo, W)

Abstract Nucleophilic substitutions in the double cubane-like structures [MS4(CuCl)5Cl2]4− (M=Mo, W) are complicated by elimination reactions. With NCS− an edge-elimination process gave the [MS4(CuNCS)4]2− anion whereas a face-elimination by PPh3 led to the monocubane structure [MS4(CuPPh3)4Cl]. Substitution by bipyridine produced the lacunary [MS4Cu3.75Cl1.75bipy2]. The different species were characterized by X-ray diffraction studies.

Characterisation of as-synthesised MOx-MCM-41 (M = Mo, W) mesophases using Raman spectrometry and 29Si MAS NMR

Abstract MCM-41 mesostructured silicas containing molybdenum and tungsten have been prepared in an acidic medium at room temperature. Two procedures were considered: the so-called oxo–peroxo route with low-nuclearity peroxo metal precursors (route A) and the oxo–polyoxo pathway, involving or generating polyoxometalates (route B). The native materials have been characterised by chemical analysis, powder X-ray diffraction, Raman spectrometry and 29 Si MAS NMR. The results show that, in route A, the use of peroxo compounds leads to a distribution of the low-nuclearity metal species throughout the silica-surfactant assembly whereas Keggin type polyoxometalates are generated in route B. The different dispersions of the MO x species (M=Mo, W) on and into the silica matrix and, hence, the formation of MO 3 (route B), previously observed for calcined materials, can be explained on the basis of different specific interactions in these organic–inorganic mesophases.

Synthesis and Characterization of Highly Dispersed Molybdenum Carbides in Mesoporous Silica

Highly dispersed molybdenum carbides in MCM-41 mesoporous silica are synthesized by temperature-programmed carburization and are characterized. Two methods of preparation are examined: (i) insertion of molybdenum during the synthesis of the MCM-41 silica and (ii) postsynthesis incorporation into a MCM-41 silica matrix by the incipient wetness method. Propene transformation (hydrogenation and metathesis) was used as a probe reaction; the observed catalytic behavior can be explained as a result of the preparation method, i.e., of the relative strength of interaction between the molybdenum oxide precursor and the support.

Novel phosphorus-doped alumina-supported molybdenum and tungsten carbides: synthesis, characterization and hydrogenation properties

The effect of atomically dispersed phosphorus on Mo2C- and WC-supported γ-Al2O3 has been studied. Phosphorus was introduced via molybdenum or tungsten heteropolyanions. Mo- and W-based heteropolyanions were used to synthesize supported materials. Propene and tetralin hydrogenation were used as molecular probe reactions to test the activity and selectivity of the alumina-supported molybdenum or tungsten carbides. The effect of phosphorus on the hydrogenation activity of materials was also considered. Catalysts were characterized by X-ray diffraction, transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS) and CO chemisorption. Phosphorus was found to increase significantly the activity of molybdenum and tungsten carbides. Supported molybdenum carbides are highly dispersed. Tungsten carbide particles are well dispersed with sizes ranging from 2 to 4 nm. To check the stability of carbides they were characterized after catalytic runs.

Derivatives of tetrathiometallates. Synthesis of [MS4M′(bpy)2] (M = Mo, W; M′ = Co, Ni, Mn, Ru) complexes. Structural characterization of [Ni(bpy)3] [(WS4)2Pd]

Abstract Reaction of M′Cl 2 (bpy) 2 (M′ = Co, Ni, Mn) with (PPh 4 ) 2 MS 4 (M = Mo, W) affords MS 4 M′(bpy) 2 . Crystals of WS 4 Co(bpy) 2 , 1 2 dmf are monoclinic space group P 2 1 / n ( a = 12.458, b = 21.862, c = 10.164 A and β = 100.0°, Z = 4, R = 0.039 for 5414 independent data). The coordination geometry around the cobalt atom is octahedrally distorted with two bipyridyl groups and two sulfur atoms being cis to each other. Reaction of M′Cl 2 (bpy) 2 with [NEt 4 ] 2 [(MS 4 ) 2 M″] (M″ = Pd, Pt) gives [M′(bpy) 3 ][(MS 4 ) 2 M″]. Crystals of [Ni(bpy) 3 ][(WS 4 ) 2 Pd] are triclinic, space group P 1 ( a = 12.771, b = 14.838, c = 12.077 A, α = 72.9, β = 116.9 and γ = 96.1°, Z = 2, R = 0.042 for 3842 independent data). In the anionic species, the central palladium atom is coordinated by two chelating WS 4 2− anions leading to a distorted PdS 4 square plane moiety, the W… Pd…W core being nearly linear (173.72(6)°). Synthesis of new ruthenium complexes [WS 4 Ru(bpy) 2 ] and [WS 4 (Ru(bpy) 2 ) 2 ][PF 6 ] 2 are also reported.

Characterization andn-heptane cracking/isomerization catalysis of tungsten oxynitrides on EMT zeolite

Catalysts made of two tungsten precursors (one of them containing phosphorus) impregnated on EMT zeolite were nitridated in flowing pure ammonia and passivated by O2 (1 vol%) in an Ar stream leading to tungsten oxynitrides/EMT (W2N/EMT) and phosphotungsten oxynitrides/EMT (PW2N/EMT). The catalysts were examined by X-ray diffraction, NMR spectroscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. The materials were tested for the cracking/isomerization ofn-heptane at atmospheric pressure and 623 K. Cracking (C3 + C4) was the major (about 90%)n-heptane reaction for all the catalysts. The influence of EMT supercages upon selectivity was observed. The yield ofn-heptane isomers was significantly enhanced for W2N/EMT and principally for PW2N/EMT showing a higher hydrogenation function.