Search

The formation of cyanopyridine (CN-py) adducts of silicon tetrahalides was investigated for 3- and 4-cyanopyridine in combination with SiF4 and SiCl4. Whereas bubbling of SiF4 through toluene solutions of 3-CN-py and 4-CN-py afforded white precipitates, which should possess the respective composition SiF4(CN-py)2, addition of SiCl4 did not cause any precipitation. Upon storage of the toluene solution of SiCl4 and 4-CN-py at 6 °C for several weeks, some crystals of the composition SiCl4(4-CN-py)2 ⋅ 2 (4-CN-py) ⋅ (toluene) were obtained. The use of SiCl4 as the solvent (i.e. SiCl4 in large excess) and dissolving 4-CN-py therein gave access to a crystalline adduct of the composition SiCl4(4-CN-py)2 ⋅ 2 (4-CN-py). 3-CN-py instead recrystallized from SiCl4 without forming an adduct with the silane. Computational analyses (B2T-PLYP level) of the single-point energy differences between starting materials SiX4 (X = F, Cl) and 'pyridine' ('pyridine' = pyridine, 3-CN-py, 4-CN-py) and their adducts SiX4('pyridine')2 revealed the tendencies toward adduct formation to decrease in the order SiF4 > SiCl4 as well as pyridine >> 4-CN-py > 3-CN-py. For SiCl4 with 4- and 3-CN-py, the energy of adduct formation (−7.0 and −5.7 kcal mol−1, respectively) is easily compensated by entropy effects at room temperature. Whereas the former explains as to why cyanopyridines and SiCl4 may co-exist without noticeable adduct formation, the crystal structures of the adducts SiCl4(4-CN-py)2 ⋅ 2 (4-CN-py) ⋅ (toluene) and SiCl4(4-CN-py)2 ⋅ 2 (4-CN-py) reveal the additional stabilization of these solids by co-crystallization with 4-cyanopyridine, which eventually enabled the isolation of the SiCl4(4-CN-py)2 moiety in a solid. Partial decomposition (hydrolysis) during attempts of recrystallization of SiF4(4-CN-py)2 and SiF4(3-CN-py)2 afforded crystals of the ionic compounds [4-CN-PyH]+[SiF5(4-CN-py)]– and [3-CN-PyH]+2[SiF6]2–, respectively. [ABSTRACT FROM AUTHOR]

The literature on aluminum coordination networks so far contains data on COO-bridged derivatives exclusively. This paper addresses the question whether or not aluminum complexes, especially carbamate-bridged {Al3(μ 3−O)}7+ units, can also form networks via the neutral ligand positions. Our findings show that a highly unexpected polymerization of the aluminum carbamates can occur during the isolation of the initially targeted compound. Although bidentate ligands bind to the neutral ligand coordination sites as expected, they do not act as linker molecules but cause an uncontrolled networking via the carbamate ligands. One- and two-dimensional solution and solid-state NMR experiments were primarily used to investigate the coordination behavior of the ligands and to elucidate the actual obtained product. [ABSTRACT FROM AUTHOR]

The formation of cyanopyridine (CN-py) adducts of silicon tetrahalides was investigated for 3- and 4-cyanopyridine in combination with SiF4 and SiCl4. Whereas bubbling of SiF4 through toluene solutions of 3-CN-py and 4-CN-py afforded white precipitates, which should possess the respective composition SiF4(CN-py)2, addition of SiCl4 did not cause any precipitation. Upon storage of the toluene solution of SiCl4 and 4-CN-py at 6 °C for several weeks, some crystals of the composition SiCl4(4-CN-py)2 ⋅ 2 (4-CN-py) ⋅ (toluene) were obtained. The use of SiCl4 as the solvent (i.e. SiCl4 in large excess) and dissolving 4-CN-py therein gave access to a crystalline adduct of the composition SiCl4(4-CN-py)2 ⋅ 2 (4-CN-py). 3-CN-py instead recrystallized from SiCl4 without forming an adduct with the silane. Computational analyses (B2T-PLYP level) of the single-point energy differences between starting materials SiX4 (X = F, Cl) and 'pyridine' ('pyridine' = pyridine, 3-CN-py, 4-CN-py) and their adducts SiX4('pyridine')2 revealed the tendencies toward adduct formation to decrease in the order SiF4 > SiCl4 as well as pyridine >> 4-CN-py > 3-CN-py. For SiCl4 with 4- and 3-CN-py, the energy of adduct formation (−7.0 and −5.7 kcal mol−1, respectively) is easily compensated by entropy effects at room temperature. Whereas the former explains as to why cyanopyridines and SiCl4 may co-exist without noticeable adduct formation, the crystal structures of the adducts SiCl4(4-CN-py)2 ⋅ 2 (4-CN-py) ⋅ (toluene) and SiCl4(4-CN-py)2 ⋅ 2 (4-CN-py) reveal the additional stabilization of these solids by co-crystallization with 4-cyanopyridine, which eventually enabled the isolation of the SiCl4(4-CN-py)2 moiety in a solid. Partial decomposition (hydrolysis) during attempts of recrystallization of SiF4(4-CN-py)2 and SiF4(3-CN-py)2 afforded crystals of the ionic compounds [4-CN-PyH]+[SiF5(4-CN-py)]– and [3-CN-PyH]+2[SiF6]2–, respectively. [ABSTRACT FROM AUTHOR]

Nitrilotris(methylenephenylphosphinic) acid (NTPAH3) was silylated using hexamethyldisilazane to produce the tris(trimethylsilyl) derivative NTPA(SiMe3)3. From the latter, upon alcoholysis in chloroform, NTPAH3 could be recovered. Thus, a new modification of that phosphinic acid formed. Meanwhile, NTPAH3 synthesized in aqueous hydrochloric acid crystallized in the space group P3c1 with the formation of O-H⋅⋅⋅O H-bonded networks (NTPAH3P), in chloroform crystals in the space group R3c formed (NTPAH3M), the constituents of which are individual molecules with exclusively intramolecular O-H⋅⋅⋅O hydrogen bonds. Both solids, NTPAH3P and NTPAH3M, were characterized by single-crystal X-ray diffraction, multi-nuclear (1H, 13C, 31P) solid-state NMR spectroscopy, and IR spectroscopy as well as quantum chemical calculations (both of their individual constituents as isolated molecules as well as in the periodic crystal environment). In spite of the different stabilities of their constituting molecular conformers, the different crystal packing interactions rendered the modifications of NTPAH3P and NTPAH3M similarly stable. In both solids, the protons of the acid are engaged in cyclic (O=P–O–H)3 H-bond trimers. Thus, the trialkylamine N atom of this compound is not protonated. IR and 1H NMR spectroscopy of these solids indicated stronger H-bonds in the (O=P–O–H)3 H-bond trimers of NTPAH3M over those in NTPAH3P. [ABSTRACT FROM AUTHOR]

Copper ores and concentrates thereof feature an increasingly notable content of impurities such as arsenic and other hazardous elements. As an alternative to the state-of-the-art partial roasting process, arsenic could be removed by the alkaline sulfide leaching of the copper concentrates. In order to optimize and understand the processes, knowledge of the speciation and oxidation states is essential. In addition to methods such as UV/Vis spectroscopy, chromatography and ICP/MS methods, 75As NMR spectroscopy may be useful for the differentiation and quantification of the various species. Although arsenate(V) has been characterized by 75As NMR some time ago, to our knowledge, there are no data on tetrathioarsenate(V) AsS43− and the mixed oxygen/sulfur substituted mono-, di- and trithioarsenates(V) AsOxS4−x3−, x = 3, 2, 1, respectively. Therefore, we investigated several model solutions and samples from Cu-As leaching with 75As NMR. The strongly alkaline conditions of the leaching solution proved to be very advantageous for that purpose. Both the tetrathioarsenate(V) and the mixed species AsOxS4−x3− (x = 1–3) could be characterized and provide valuable data for the quantification of the material flows in the leaching process. [ABSTRACT FROM AUTHOR]

The borohydrides of zirconium (Zr(BH4)4) and hafnium (Hf(BH4)4) have been prepared by solid state metatheses. The crystal structures were determined slightly below their melting temperature with in situ cryo crystallisation single crystal XRD. The melting and decomposition process was investigated using differential scanning calorimetry coupled with thermogravimetry and mass spectroscopy. The enthalpies of formation were determined using the decomposition enthalpy, the enthalpy of fusion and the heat capacity measurements in the temperature range from 5 °C to 35 °C. Standard entropy values of both compounds were obtained by DFT calculations. The determined values were optimised using the CalPhaD method. [ABSTRACT FROM AUTHOR]

4-Azidopyridine (1) and SiCl4 react with the formation of the hexacoordinate silicon complex SiCl4(4-azidopyridine)2 (2). Upon dissolving in warm chloroform, the complex dissociates into the constituents 1 and SiCl4 and forms back upon cooling. Depending on the cooling, two different crystalline modifications of 2 were obtained, which feature two different trans-conformers. Slow cooling to room temperature afforded conformer 2′, which features coplanar pyridine rings. Rapid cooling to −39 °C afforded crystals of conformer 2″, in which the planes of the pyridine ligands are nearly orthogonal to one another. Whereas 2′ resembles the molecular arrangement of various other known SiX4(pyridine)2 (X = halide) complexes, 2″ represents the first crystallographically confirmed example of a SiX4(pyridine)2 complex in this conformation. Conformers 2′ and 2″ were studied with 13C and 29Si solid state NMR spectroscopy. Their differences in 29Si chemical shift anisotropy, as well as energetic differences, were further investigated with computational analyses. In spite of the similar stabilities of the two conformers as isolated molecules, the crystal packing of 2″ is less stable, and its crystallization is interpreted as a kinetically controlled effect of seed formation. (3+2)-cycloaddition of 1 and phenylacetylene in toluene at 110 °C yields a mixture of 1-(4-pyridyl)-4-phenyl-1,2,3-triazole (1,4-3) and 1-(4-pyridyl)-5-phenyl-1,2,3-triazole (1,5-3) in approximate 1:2 molar ratio. The crystal structures of the two isomers were determined via X-ray diffraction. In chloroform (at 60 °C), this reaction is slow (less than 2% conversion within 4 h), but the presence of SiCl4 enhanced the rate of the reaction slightly, and it shifted the triazole isomer ratio to ca. 1:6 in favor of 1,5-3. [ABSTRACT FROM AUTHOR]

Although a number of oxo-bridged trinuclear transition metal complexes have been synthesised and investigated in recent decades, comparable aluminum compounds have received much less attention. The {Al3(μ3-O)}7+ carbamate complexes [Al3(μ3-O)(OOC-pyrr)6(pyrrH)3]+[Cl]−(1a), [Al3(μ3-O)(OOC-pip)6(pipH)3]+[Cl]−(2a), [Al3(μ3-O)(OOC-pyrr)6(pyridine)3]+[Cl]−(1b) and [Al3(μ3-O)(OOC-pip)6(pyridine)3]+[Cl]−(2b) are presented and elucidated by single crystal structure analyses ((1a), (2a) and (1b)) as well as temperature-dependent two-dimensional NMR spectra. The complexes (1a) and (2a) were prepared by CO2 insertion into Al–N bonds of tris(dialkylamido)alanes followed by targeted hydolysis. It was found that the neutral ligands of compounds (1a) and (2a) are exchangeable by pyridine ligands resulting in the formation of compounds (1b) and (2b). Further ligand exchange experiments possibly allow the preparation of MOF-like {Al3(μ3-O)}7+ coordination polymers. [ABSTRACT FROM AUTHOR]

Complexes of Sn(II), Sn(IV), Ge(IV), and Si(IV) with the ambidentate pyridine-2-thiolato ligand (PyS-) were synthesized and characterized by multinuclear NMR spectroscopy and single-crystal X-ray diffractometry. Comparison of the structures of E(PyS)2Cl2 (E=Sn, Ge, Si) and E(PyS)4 (E=Sn, Si) allows for insights into the group 14 coordination chemistry of this ambidentate chelator in dependence of the thiophilicity of the central atom of the corresponding complex. Furthermore, the crystal structure of Sn(PyS)2 reveals two different coordination modes of its constituents, i.e., the crystal packing features cyclic dimers and polymeric chains of Sn(PyS)2. This compound was shown to undergo oxidative addition of 2,2′-dipyridyldisulfide and sulfur with the formation of Sn(PyS)4and (PyS)2Sn(μ-S)2Sn(PyS)2, respectively.

Despite decades of research on various carbamates and their important applications, only one aluminum N,N‐dialkylcarbamate (ADC) with an aluminum:carbamate ratio of 1 : 3 has been structurally described and comprehensively studied so far, namely tris(diisopropyl)carbamate. The reasons for this situation include problems with the used synthetic routes. The process of CO2 insertion into Al−N bonds of tris(dialkylamido)alanes resolved these difficulties. Using this advantageous synthetic route, the dimethyl and diethyl, as well as the pyrrolidino, piperidino, and N‐methylpiperazino derivatives were now successfully prepared. These ADCs were investigated by solid‐state NMR spectroscopy, where line‐shape analyses of the 27Al NMR spectra allowed conclusions with respect to the determination of the quadrupole coupling parameters. Furthermore, data of an intermediate during the CO2 insertion into tris(diisopropylamido)alane were obtained by in‐situ IR spectroscopy, which were complemented by NMR measurements of samples periodically taken during the reaction. Partial hydrolysis of tris(pyrrolidino)carbamate revealed a complex Al3(μ3‐O) cluster structure, which was elucidated by single crystal X‐ray diffraction. [ABSTRACT FROM AUTHOR]

The organosilicon pyridine-2-olates 1a–1d (RSi(pyO)3, R = Me (a), Ph (b), Bn (c), Allyl (d); pyO = pyridine-2-olate) may serve as tripodal ligands toward CuCl with formation of complexes of the type RSi(μ2-pyO)3CuCl (2a–2d). In addition, for R = Allyl, formation of the more stable isomer 2d′ (κO-pyO)Si(μ2-pyO)2(μ2-Allyl)CuCl was observed. In the presence of dry air (as a source of oxygen), reactions of 1a–1d and CuCl afforded Cu(II) complexes RSi(μ2-pyO)4CuCl (3a–3d); 3a–3c in good yield, and 3d only as a side product. Reaction of Ph2Si(pyO)2 (4) and CuCl in equimolar ratio afforded, depending on reaction conditions, a series of (CuCl)n-ladder-type oligonuclear Cu(I) complexes Ph2Si(μ2-pyO)2(CuCl)n(μ2-pyO)2SiPh2 (n = 2 (52), 3 (53), 4 (54)). In all of the above compounds, the pyO group is Si–O bound and, in the case of μ2 coordination, Cu–N bound. All new compounds (1c, 1d, 2b, 2c, 2d, 2d′, 3b, 3c, 3d, 52, 53, 54) were characterized by single-crystal X-ray diffraction, and further characterization includes solution 1H, 13C, 29Si NMR spectroscopy (1c, 1d, 2b, 2c, 2d', 53, 54), solid-state 29Si (2b, 2c, 2d′, 53, 54) and 63Cu NMR spectroscopy (2c, 2d′) as well as computational analyses of the isomerization of the couple 2d, 2d′. [ABSTRACT FROM AUTHOR]

The phenyltetrel pyridine-2-olates PhE(pyO)3 (E = Si, Ge, Sn; pyO = pyridine-2-olate) were synthesized from the respective chlorides PhECl3 and 2-hydroxypyridine (2-pyridone) with the aid of a sacrificial base (triethylamine). Their solid-state structures were determined by single-crystal X-ray diffraction. PhSi(pyO)3 exhibits a three-fold capped tetrahedral Si coordination sphere ([4+3]-coordination, Si···N separations ca. 3.0 Å), in accordance with structures of previously reported silicon pyridine-2-olates. PhGe(pyO)3 adopts a related [4+3]-coordination mode, which differs in terms of the tetrahedral faces capped by the pyridine N atoms. Additionally, shorter Ge···N separations (2.8–2.9 Å) indicate a trend toward tetrel hypercoordination. PhSn(pyO)3 features heptacoordinate tin within a pentagonal bipyramidal Sn coordination sphere (Sn···N separations 2.2–2.4 Å). For the Si and Sn compounds, 29Si and 119Sn NMR spectroscopy indicates retention of their tetrel coordination number in chloroform solution. [ABSTRACT FROM AUTHOR]