Leo van Wüllen

PX4+, P2X5+, and P5X2+ (X: Br, I) Salts of the Superweak Al(OR)4- Anion [R: C(CF3)3].

PX(4) (+)[Al(OR)(4)](-) (X=I: 1 a, X=Br: 1 b) was prepared from X(2), PX(3), and Ag[Al(OR)(4)] [R=C(CF(3))(3)] in CH(2)Cl(2) at -30 degrees C in 69-86 % yield. P(2)X(5) (+) salts were prepared from 2 PX(3) and Ag[Al(OR)(4)] in CH(2)Cl(2) at -30 degrees C yielding almost quantitatively P(2)X(5) (+)[Al(OR)(4)](-) (X=I: 3 a, X=Br: 3 b). The phosphorus-rich P(5)X(2) (+) salts arose from the reaction of cold (-78 degrees C) mixtures of PX(3), P(4), and Ag[Al(OR)(4)] giving P(5)X(2) (+)[Al(OR)(4)](-) (X=I: 4 a, X=Br: 4 b) with a C(2v)-symmetric P(5) cage. Silver salt metathesis presumably generated unstable PX(2) (+) cations from PX(3) and Ag[Al(OR)(4)] (X=Br, I) that acted as electrophilic carbene analogues and inserted into the Xbond;X (Pbond;X/Pbond;P) bond of X(2) (PX(3)/P(4)) leading to the highly electrophilic and CH(2)Cl(2)-soluble PX(4) (+) (P(2)X(5) (+)/P(5)X(2) (+)) salts. Reactions that aimed to synthesize P(2)I(3) (+) from P(2)I(4) and Ag[Al(OR)(4)] instead led to anion decomposition and the formation of P(2)I(5)(CS(2))(+)[(RO)(3)Al-F-Al(OR)(3)](-) (5). All salts were characterized by variable-temperature solution NMR studies (3 b also by (31)P MAS NMR), Raman and/or IR spectroscopy as well as X-ray crystallography (with the exception of 4 a). The thermochemical volumes of the Pbond;X cations are 121 (PBr(4) (+)), 161 (PI(4) (+)), 194 (P(2)Br(5) (+)), 271 (P(2)I(5) (+)), and 180 A(3) (P(5)Br(2) (+)). The observed reactions were fully accounted for by thermochemical calculations based on (RI-)MP2/TZVPP ab initio results and COSMO solvation enthalpy calculations (CH(2)Cl(2) solution). The enthalpies of formation of the gaseous Pbond;X cations were derived as +764 (PI(4) (+)), +617 (PBr(4) (+)), +749 (P(2)I(5) (+)), +579 (P(2)Br(5) (+)), +762 (P(5)I(2) (+)), and +705 kJ mol(-1) (P(5)Br(2) (+)). The insertion of the intermediately prepared carbene analogue PX(2) (+) cations into the respective bonds were calculated, at the (RI-)MP2/TZVPP level, to be exergonic at 298 K in CH(2)Cl(2) by Delta(r)G(CH(2)Cl(2))=-133.5 (PI(4) (+)), -183.9 (PBr(4) (+)), -106.5 (P(2)I(5) (+)), -81.5 (P(2)Br(5) (+)), -113.2 (P(5)I(2) (+)), and -114.5 kJ mol(-1) (P(5)Br(2) (+)).

Superweak complexes of tetrahedral P4 molecules with the silver cation of weakly coordinating anions

The silver aluminates AgAl[OC(CF3)2(R)]4 (R = H, CH3, CF3) react with solutions of white phosphorus P4 to give complexes that bind one or two almost undistorted tetrahedral P4 molecules in an fashion: [Ag(P4)2]+[Al(OC(CF3)3)4]+ (1) containing the first homoleptic metal-phosphorus cation, the molecular species (P4)AgAl[OC(CH3)(CF3)2]4 (2), and the dimeric Ag(mu,eta2-P4)Ag bridged [(P4)AgAl[OC(H)(CF3)2]4]2 (3). Compounds 1-3 were characterized by variable-temperature (VT) 31P NMR spectroscopy (1 also by VT 32P MAS-NMR spectroscopy), Raman spectroscopy, and single-crystal X-ray crystallography. Other Ag:P4 ratios did not lead to new species, and this observation was rationalized on thermodynamic grounds. The Ag(P4)2+ ion has an almost planar coordination environment around the Ag+ ion due to d(x2 - y2)(Ag) --> sigma*(P-P) backbonding. Calculations (HF-DFT) on six Ag(P4)2+ isomers 4a-f showed that the planar eta2 form 4a is only slightly favored by 5.2 kJ mol(-1) over the tetrahedral eta2 species 4b; eta1-P4 and eta3-P4 complexes are less favorable (27-76 kJ mol(-1)). The bonding of the P4 moiety in [RhCl(eta2-P4)(PPh3)2], the only compound in which an eta2 bonding mode of a tetrahedral P4 molecule has been claimed, must be regarded as a tetraphosphabicyclobutane, and not as a tetrahedro-P4 complex, on the basis of the published NMR and vibrational spectra, the calculated geometry of [RhCl(P4)(PH3)2] (10), the highly endothermic (385 kJ mol(-1)) calculated dissociation enthalpy of 10 into P4 and RhCl(PH3)2 (11), as well as atoms in molecules (AIM) and natural bond orbital (NBO) population analyses of 10 and the Ag(P4)2+ ion. Therefore, 1-3 are the first examples of species containing eta2-coordinated tetrahedral P4 molecules.

The mechanism of Li-ion transport in the garnet Li5La3Nb2O12.

We present a detailed study on the exact location and dynamics of Li ions in the garnet-type material Li(5)La(3)Nb(2)O(12) employing advanced solid state NMR strategies. Applying temperature-dependent (7)Li-NMR, (6)Li-MAS-NMR, (6)Li-{(7)Li}-CPMAS-NMR, (6)Li-{(7)Li}-CPMAS-REDOR-NMR as well as 2D-(6)Li-{(7)Li}-CPMAS-Exchange-NMR spectroscopy, we were able to quantify the distribution of the Li cations among the various possible sites within the garnet-type structure and to identify intrinsic details of Li migration. The results indicate a sensitive dependence of the distribution of Li cations among the tetrahedral and octahedral sites on the temperature of the final annealing process. This distribution profoundly affects the mobility of the Li cations within the garnet-type framework structure. Extended Li mobility at ambient temperature is only possible if the majority of the Li cations is accommodated in the octahedral sites, as observed for the sample annealed at 900 degrees C. Octahedrally-coordinated Li cations could be identified as the mobile Li species, whereas the tetrahedral sites seem to act as a trap for the Li cations, rendering the tetrahedrally-coordinated Li cations immobile on the time scale of the NMR experiments.

Dimer-formation in the bis(arene)chromium fulleride Cr(C7H8)2 C60

Bis(toluene)chromium fulleride Cr(C7H8)2 C60 has been synthesized as a microcrystalline powder from C60 and Cr(C7H8)2 in toluene. One electron is transferred from the chromium complex to the fullerene resulting in a magnetic moment of about 2.5±0.2 μB at room temperature, which corresponds to two electron spins per formula unit. At 250 K a reversible phase transition from a primitive cubic high temperature paramagnetic phase to a triclinic low temperature dimer phase occurs. The high temperature phase (Pm3m, a=9.986 A) is constituted of dynamically disordered fulleride anions and bis(toluene)chromium (I) cations in a CsCl-type arrangement. The low temperature modification is triclinic (P1, a=13.541 A, b=13.864 A, c=14.122 A, α=120.59, β=91.78, γ=116.88) and carries one unpaired electron per formula unit (μ=1.72±0.01 μB), which according to ESR measurements is localized at the chromium site (giso=1.9870). The phase transition has been monitored by x-ray diffraction, ESR and solid state NMR spectroscopy a...

Random inorganic networks: a novel class ofhigh-performance ceramics

The preparation of amorphous inorganic networks in the system Si/B/N/C, starting from molecular single source precursors, results in high performance ceramics with outstanding and unprecedented high temperature and mechanical properties. Different ways of incorporating carbon into the final ceramics are described and new single source precursors presented. The local structure and intermediate range order in these amorphous inorganic networks are studied using conventional multinuclear 11B, 13C and 29Si magic angle spinning (MAS) NMR and advanced double resonance techniques such as 29Si-{11B} rotational echo adiabatic passage double resonance (REAPDOR), 13C-{11B} REAPDOR or 11B-{29Si} rotational echo double resonance (REDOR) NMR spectroscopy.

Inorganic Double Helices in Semiconducting SnIP

SnIP is the first atomic-scale double helical semiconductor featuring a 1.86 eV bandgap, high structural and mechanical flexibility, and reasonable thermal stability up to 600 K. It is accessible on a gram scale and consists of a racemic mixture of right- and left-handed double helices composed by [SnI] and [P] helices. SnIP nanorods <20 nm in diameter can be accessed mechanically and chemically within minutes.

The influence of halogen substituents on the course of hydrogallation and hydroalumination reactions

Treatment of trimethylsilylethynylbenzene derivatives with HGaCl(2) afforded products, [C(6)H(6-x){C(H)=C(SiMe(3))GaCl(2)}(x)], in which by a very fast cis/trans-rearrangement the Ga and H atoms occupied opposite sides of the resulting C=C double bonds. The stability of the cis-forms considerably increased upon application of 1,3-dibromo- and pentafluorophenylalkyne derivatives. Two pairs of cis/trans-isomers could be characterized by crystal structure determinations and allow the direct comparison of structural parameters. For the first time an equilibrium was detected between cis- and trans-forms in solution. Treatment of 1,4-di(tert-butylalkynyl)benzene with HAlR(2) (R = CMe(3), CH(2)CMe(3)) afforded cyclophane-type molecules by the release of AlR(3). Only the neopentyl derivative could be isolated and characterized by crystal structure determination. In contrast, the dibromo compound, 1,4-Br(2)-2,5-(Me(3)CC[triple bond]C)(2)C(6)H(2), yielded the simple addition product, C(6)H(2)Br(2){C(AlR(2))=C(H)CMe(3)}(2) (R = CMe(3)). Condensation was hindered in this case by intramolecular Al-Br interactions. Surprisingly, the simple addition product was also isolated from the reaction of 1,4-(Me(3)CC[triple bond]C)(2)C(6)H(4) with the relatively small hydride HAlEt(2). Solid-state NMR spectra of the product revealed strong intermolecular Al-C interactions involving the negatively charged terminal vinylic carbon atoms, to give one-dimensional coordination polymers.

Evidence for C60 dimerisation in the fulleride [Cr(C9H12)2]+C60-

We report a detailed study of the structure, dynamics and electronic structure of the new fulleride [Cr(C9H12)2]+C60−. Using a variety of characterization tools including EPR, NMR, SQUID magnetic measurements and high resolution X-ray powder diffraction a spin pairing of the C60− spins with decreasing temperatures could be observed. Contrary to the observed phase transition of first order in the related compound [Cr(C6H9)2]+C60− the phase transition observed in the title compound is of higher order.

Modern solid state double resonance NMR strategies for the structural characterization of adsorbate complexes involved in the MTG process

The reaction pathways in the methanol to gasoline conversion process are still not well understood. Although recent years have witnessed remarkable progress in recent years in the in situ characterization of these reactions, the nature of the bonding of the intermediates to the Bronsted acid sites of the zeolite catalyst is still the subject of intense debate. Our approach is to study the geometry of the binding of the methanol molecule to the zeolite surface using modern double resonance NMR spectroscopy. As model systems we chose the host/guest complexes formed in the systems zeolite NaX loaded with 13CH3I and zeolite HZSM-5 loaded with 13CH3OH, treated at various temperatures. By exploring the dipolar coupling strength between 13C and 27Al or 1H and 27Al using 1H–{27Al} and 13C–{27Al} rotational echo adiabatic passage double resonance (REAPDOR) NMR and simulation of the resulting dipolar evolution curves we have been able to determine carbon–aluminium and hydrogen–aluminium internuclear distances and thus to identify the nature of the adsorbate–zeolite complexes formed as a function of the processing conditions.

Subtle polymorphism of zinc imidazolate frameworks: temperature-dependent ground states in the energy landscape revealed by experiment and theory

We show by variable-temperature X-ray diffraction and differential scanning calorimetry experiments that zinc imidazolates with coi and zni framework topology, respectively represent the thermodynamically stable phase below and above a transition temperature of ≈360 °C at ambient pressure. The relative stability of the two polymorphs and the experimentally observed strong negative thermal expansion of the coi phase at high temperatures close to the phase transition were successfully modelled using density functional theory calculations. A novel metastable zinc imidazolate with neb framework topology was detected by in situ X-ray diffraction experiments as a transient crystalline phase during solvothermal crystallisation of the stable coi phase.