Tri(pyridylmethyl)phosphine: the elusive congener of TPA shows surprisingly different coordination behavior.

Tri(pyridylmethyl)phosphine (TPPh), the remarkably elusive congener of tri(pyridylmethyl)amine (TPA), has been prepared, as well as the relative tri(N-methyl-pyridylamino)phosphine (TPAMP). The coordination properties of these new ligands have been evaluated for chromium(III), iron(II), and ruthenium(II) complexes and compared with the related TPA complexes. In all cases, a different coordination behavior has been observed whereby TPPh and TPAMP always act as tridentate ligands. A chromium(III) complex [Cr(TPPh)Cl3] has been prepared, which has shown low ethylene oligomerization activity. Octahedral low spin iron(II) complexes [Fe(TPPh)2](2+) and [Fe(TPAMP)2](2+) were obtained with two ligands bound to the metal center. Ruthenium(II) chloro complexes of TPA and TPPh undergo ligand exchange reactions in acetonitrile, and the ruthenium(II) complex [Ru(MeCN)2(TPA)](2+) can be oxidized by m-CPBA in acetonitrile to give a transient ruthenium(IV) oxo complex [Ru(O)(MeCN)(TPA)](2+). Attempts to generate high valent ruthenium(IV) oxo TPPh or TPAMP complexes could not be achieved, probably due to insufficient stabilization by these strong field ligands.

Nitridosilicates and oxonitridosilicates: from ceramic materials to structural and functional diversity.

Silicates are one of the most important classes of compounds on this planet, and more than 1000 silicates have been identified in the mineral kingdom. Additionally, several hundreds of artificial silicates have been synthesized. The substitution of oxygen by nitrogen leads to the structurally diverse and manifold class of nitridosilicates. Silicon nitride, one of the most important non-oxidic ceramic materials, is the binary parent compound of nitridosilicates, and it symbolizes the inherent material properties of these refractory compounds. However, prior to the last decades, a broad systematic investigation of nitridosilicates had not been accomplished. In the meantime, these and related compounds have reached a remarkable level of industrial application. This review illustrates recent progress in synthesis and structure-property relationships and also applications of nitridosilicates, oxonitridosilicates, and related SiAlONs.

Melamine-melem adduct phases: investigating the thermal condensation of melamine.

By studying the thermal condensation of melamine, we have identified three solid molecular adducts consisting of melamine C(3)N(3)(NH(2))(3) and melem C(6)N(7)(NH(2))(3) in differing molar ratios. We solved the crystal structure of 2 C(3)N(3)(NH(2))(3)C(6)N(7)(NH(2))(3) (1; C2/c; a=21.526(4), b=12.595(3), c=6.8483(14) A; beta=94.80(3) degrees ; Z=4; V=1850.2(7) A(3)), C(3)N(3)(NH(2))(3)C(6)N(7)(NH(2))(3) (2; Pcca; a=7.3280(2), b=7.4842(2), c=24.9167(8) A; Z=4; V=1366.54(7) A(3)), and C(3)N(3)(NH(2))(3)3 C(6)N(7)(NH(2))(3) (3; C2/c; a=14.370(3), b=25.809(5), c=8.1560(16) A; beta=94.62(3) degrees ; Z=4; V=3015.0(10) A(3)) by using single-crystal XRD. All syntheses were carried out in sealed glass ampoules starting from melamine. By variation of the reaction conditions in terms of temperature, pressure, and the presence of ammonia-binding metals (europium) we gained a detailed insight into the occurrence of the three adduct phases during the thermal condensation process of melamine leading to melem. A rational bulk synthesis allowed us to realize adduct phases as well as phase separation into melamine and melem under equilibrium conditions. A solid-state NMR spectroscopic investigation of adduct 1 was conducted.

Mixed valence europium nitridosilicate Eu2SiN3.

The mixed valence europium nitridosilicate Eu(2)SiN(3) has been synthesized at 900 degrees C in welded tantalum ampules starting from europium and silicon diimide Si(NH)(2) in a lithium flux. The structure of the black material has been determined by single-crystal X-ray diffraction analysis (Cmca (no. 64), a = 542.3(11) pm, b = 1061.0(2) pm, c = 1162.9(2) pm, Z = 8, 767 independent reflections, 37 parameters, R1 = 0.017, wR2 = 0.032). Eu(2)SiN(3) is a chain-type silicate comprising one-dimensional infinite nonbranched zweier chains of corner-sharing SiN(4) tetrahedra running parallel [100] with a maximum stretching factor f(s) = 1.0. The compound is isostructural with Ca(2)PN(3) and Rb(2)TiO(3), and it represents the first example of a nonbranched chain silicate in the class of nitridosilicates. There are two crystallographically distinct europium sites (at two different Wyckoff positions 8f) being occupied with Eu(2+) and Eu(3+), respectively. (151)Eu Mössbauer spectroscopy of Eu(2)SiN(3) differentiates unequivocally these two europium atoms and confirms their equiatomic multiplicity, showing static mixed valence with a constant ratio of the Eu(2+) and Eu(3+) signals over the whole temperature range. The Eu(2+) site shows magnetic hyperfine field splitting at 4.2 K. Magnetic susceptibility measurements exhibit Curie-Weiss behavior above 24 K with an effective magnetic moment of 7.5 mu(B)/f.u. and a small contribution of Eu(3+), in accordance with Eu(2+) and Eu(3+) in equiatomic ratio. Ferromagnetic ordering at unusually high temperature is detected at T(C) = 24 K. DFT calculations of Eu(2)SiN(3) reveal a band gap of approximately 0.2 eV, which is in agreement with the black color of the compound. Both DFT calculations and lattice energetic calculations (MAPLE) corroborate the assignment of two crystallographically independent Eu sites to Eu(2+) and Eu(3+).

Urea route to homoleptic cyanates--characterization and luminescence properties of [M(OCN)2(urea)] and M(OCN)2 with M=Sr, Eu.

A novel approach for the synthesis of urea complexes and homoleptic cyanates of alkaline earth metals and europium is described. Direct reaction of urea with elemental Sr or Eu in closed ampoules at temperatures above 120 degrees C yields [M(OCN)2(urea)] with M=Sr, Eu. According to single-crystal X-ray diffraction, the isotypic complexes exhibit a layer structure ([Eu(OCN)2(urea)]: P2(1)/c, a=7.826(2), b=7.130(1), c=12.916(3) A, beta=99.76(3) degrees , Z=4, V=710.3(2) A3). Furthermore, they were characterized by vibrational spectroscopy, thermal analysis, magnetic measurements, and photoluminescence studies. Thermal treatment of the compounds [M(OCN)2(urea)] to 160-240 degrees C affords evaporation of urea and the subsequent formation of solvent-free homoleptic cyanates of Sr and Eu. The crystal structures of Sr(OCN)2 and Eu(OCN)2 were determined from X-ray powder diffraction data and refined by the Rietveld method. Both compounds crystallize in the orthorhombic space group Fddd and adopt the Sr(N3)2 type structure (Sr(OCN)2: a=6.1510(4), b=11.268(1), c=11.848(1) A, V=821.1(2) A3; Eu(OCN)2: a=6.1514(6), b=11.2863(12), c=11.8201(12) A, V=820.63(15) A3). The cyanates are stable up to 450 degrees C. Above 500 degrees C beta-Sr(CN)2 and Eu2O2(CN)2 are formed. Excitation and emission spectra of [Eu(OCN)2(urea)], [Sr(OCN)2(urea)]:Eu2+, Eu(OCN)2, Sr(OCN)2:Eu2+ at different temperatures are reported. A strong green emission for all examined Eu-containing compounds due to a 4f(6)5d(1)-4f(7) transition is observed at low temperatures. The luminescence properties are discussed in detail and are comparable to those of thiocyanates. Compared to the latter, a blue shift of the emission bands is observed due to the higher ionicity.

Di-µ-tert-butanolato-bis-[bis-(η-cyclo-penta-dien-yl)erbium(III)].

In the centrosymmetric title compound, [Er(2)(C(5)H(5))(4)(C(4)H(9)O)(2)], each Er atom is in a distorted tetra-hedral coordination environment, coordinated by two cyclo-penta-dienyl rings and two tert-but-oxy groups, forming a dimeric complex bridged through the tert-but-oxy groups.

Precursor approach to lanthanide dioxo monocarbodiimides Ln2O2CN2 (Ln=Y, Ho, Er, Yb) by insertion of CO2 into organometallic Ln-N compounds.

We present two organometallic precursor approaches leading to the hitherto-unknown dioxo monocarbodiimides (Ln(2)O(2)CN(2)) of the late lanthanides Ho, Er, and Yb as well as yttrium. One involves insertion of CO(2), and the other one is a straightforward route using a molecular single-source precursor. To this end the reactivity of the activated amido lanthanide compound [(Cp(2)ErNH(2))(2)] towards carbon dioxide absorption under supercritical conditions was studied. Selective insertion of CO(2) into the amido complex yielded the single-source precursor [Er(2)(O(2)CN(2)H(4))Cp(4)], which was characterized by vibrational spectroscopy and thermal and elemental analyses. Ammonolysis of this amorphous compound at 700 degrees C affords Er(2)O(2)CN(2). To gain deeper insight into the structural characteristics of the amorphous precursor, a similar molecular carbamato complex was synthesized and fully characterized. X-ray structure analysis of the dimeric complex [Cp(4)Ho(2){mu-eta(1):eta(2)-OC(OtBu)NH}] shows an unusual bonding mode of the tert-butylcarbamate ligand, which acts as both a bridging and side-on chelating group. Ammonolysis of this compound also yielded dioxo monocarbodiimides, and therefore the crystalline carbamato complex turned out to be an alternative precursor for the straightforward synthesis of Ln(2)O(2)CN(2). Analogously, the dioxo monocarbodiimides of Y, Ho, Er, and Yb were synthesized by this route. The crystal structures were determined from X-ray powder diffraction data and refined by the Rietveld method (Ln=Ho, Er). Further spectroscopic characterization and elemental analysis evidenced the existence of phase-pure products. The dioxo monocarbodiimides of holmium and erbium crystallize in the trigonal space group P[over]3m1. According to X-ray powder diffraction, they adopt the Ln(2)O(2)CN(2) (Ln=Ce-Gd) structure type.

Iron-catalyzed aryl-aryl cross-coupling reaction tolerating amides and unprotected quinolinones.

The iron(III)-catalyzed cross-coupling reaction between functionalized arylcopper reagents and aromatic iodides bearing an amide function or an unprotected quinolinone leads smoothly to polyfunctionalized biphenyls in excellent yields due to an intramolecular chelating effect of the amide group.

Nanocrystalline lanthanide nitride materials synthesised by thermal treatment of amido and ammine metallocenes: X-ray studies and DFT calculations.

The decomposition process of ammine lanthanide metallocenes was studied by X-ray diffractometry, spectroscopy and theoretical investigations. A series of ammine-tris(eta(5)-cyclopentadienyl)lanthanide(III) complexes 1-Ln (Lanthanide (Ln)=Sm, Gd, Dy, Ho, Er, Yb) was synthesised by the reaction of [Cp(3)Ln] complexes (Cp=cyclopentadienyl) with liquid ammonia at -78 degrees C and structurally characterised by X-ray diffraction methods, mass spectrometry and vibrational (IR, Raman) spectroscopy. Furthermore, amido-bis(eta(5)-cyclopentadienyl)lanthanide(III) complexes 2-Ln (Ln=Dy, Ho, Er, Yb) were synthesised by heating the respective ammine adduct 1-Ln in an inert gas atmosphere at temperatures of between 240 and 290 degrees C. X-ray diffraction studies, mass spectrometry and vibrational (IR, Raman) spectroscopy were carried out for several 2-Ln species and proved the formation of dimeric mu(2)-bridged compounds. Species 1-Ln are highly reactive coordination compounds and showed different behaviour regarding the decomposition to 2-Ln. The reaction of 1-Ln and 2-Ln with inorganic bases yielded lanthanide nitride LnN powders with an estimated crystallite size of between 40 and 90 nm at unprecedented low temperatures of 240 to 300 degrees C. Temperature-dependent X-ray powder diffraction and transmission electron microscopy (TEM) investigations were performed and showed that the decomposition reaction yielded nanocrystalline material. Structural optimisations were carried out for 1-Ln and 2-Ln by employing density functional (DFT) calculations. A good agreement was found between the observed and calculated structural parameters. Also, Gibbs free energies were calculated for 1-Ln, 2-Ln and the pyrolysis reaction to the nitride material, and were found to fit well with the expected ranges.