A series of P-phospholyl-substituted N-heterocyclic phosphines was prepared and characterized by single-crystal X-ray diffraction and solution and solid-state (31)P NMR spectroscopy. The molecular structures are distinguished by the presence of P-P bonds of exceptionally variable lengths (2.35-2.70 A) that are all well beyond the standard distance of 2.21 A. The unique flexibility is best illustrated by a specimen 4f where minor conformational changes of remote substituents induce a deviation in P-P bond lengths of some 5 pm between crystallographically independent molecules in the same unit cell. Computational studies suggest to rationalize the bond elasticity as the consequence of a very flat potential energy basin that allows even weak forces to have large impact on bond lengths. Solid-state (31)P NMR studies show that the bond distance variation coincides with substantial changes in the magnitude and sign of (1)J(PP), which is explained in the context of a dominant Fermi contact contribution. A relation between increasing internuclear distance and decreasing magnitude of (1)J(PP) was experimentally proven by determination of effective dipolar coupling constants by the double-quantum dephasing experiment (DoDe) for the crystallographically independent conformers of 4f and further supported by comparison with calculated coupling tensors with inclusion of the anisotropic J-coupling. NMR studies revealed large discrepancies in the values of (1)J(PP) measured in solution and the solid state and a substantial temperature dependence of the former. Interpretation of this behavior was feasible by taking into account that the value of (1)J(PP) in solution is affected by both temperature-dependent equilibria between trans and gauche conformers and additional bond length relaxation that accompanies the dissolution process. Consideration of experimental observations and population analysis of computed electron densities suggested to classify the P-P bonds in the molecules under study as "dative" rather than "normal" covalent bonds and to address the compounds 4 as hybrids between covalent diphosphines and phosphenium-phospholide contact ion pairs.

The electrical conductivity of aluminium doped zinc oxide (AZO, ZnO:Al) materials depends on doping induced defects and grain structure. This study aims at relating macroscopic electrical conductivity of AZO nanoparticles with their atomic structure, which is non-trivial because the derived materials are heavily disordered and heterogeneous in nature. For this purpose we synthesized AZO nanoparticles with different doping levels and narrow size distribution by a microwave assisted polyol method followed by drying and a reductive treatment with forming gas. From these particles electrically conductive, optically transparent films were obtained by spin-coating. Characterization involved energy-dispersive X-ray analysis, wet chemical analysis, X-ray diffraction, electron microscopy and dynamic light scattering, which provided a basis for a detailed structural solid-state NMR study. A multinuclear ( 27 Al, 13 C, 1 H) spectroscopic investigation required a number of 1D MAS NMR and 2D MAS NMR techniques (T 1 -measurements, 27 Al-MQMAS, 27 Al-1 H 2D-PRESTO-III heteronuclear correlation spectroscopy), which were corroborated by quantum chemical calculations with an embedded cluster method (EEIM) at the DFT level. From the combined data we conclude that only a small part of the provided Al is incorporated into the ZnO structure by substitution of Zn. The related 27 Al NMR signal undergoes a Knight shift when the material is subjected to a reductive treatment with forming gas. At higher (formal) doping levels Al forms insulating (Al, H and C containing) side-phases, which cover the surface of the ZnO:Al particles and increase the sheet resistivity of spin-coated material. Moreover, calculated 27 Al quadrupole coupling constants serve as a spectroscopic fingerprint by which previously suggested point-defects can be identified and in their great majority be ruled out.

A new embedded cluster method (extended embedded ion method = EEIM) for the calculation of NMR properties in non-conducting crystals is presented. It is similar to the Embedded Ion Method (EIM) (ref. 1) in the way of embedding the quantum chemically treated part in an exact, self-consistent Madelung potential, but requires no empirical parameters. The method is put in relation to already existing cluster models which are classified in a brief review. The influence of the cluster boundary and the cluster charge is investigated, which leads to a better understanding of deficiencies in EIM. A recipe for an improved semi-automated cluster setup is proposed which allows the treatment of crystals composed of highly charged ions and covalent networks. EIM and EEIM results for (19)F and (31)P shielding tensors in NaF and in four different magnesium phosphates are compared with experimental values from solid state MAS NMR, some of which are measured here for the first time. The quantum part of the clusters is treated at hybrid DFT level (mPW1PW) with atomic basis sets up to 6-311G(3df,3pd). The improved agreement of EEIM allows new signal assignments for the different P-sites in Mg(2)P(4)O(12), alpha-Mg(2)P(2)O(7) and MgP(4)O(11). Conversion equations of the type sigma = A + Bdelta between calculated absolute magnetic shieldings sigma and the corresponding experimental chemical shifts delta are obtained independently from linear regressions of plots of isotropically averaged sigma versus delta values on 19 (31)P signals of small molecules.

In this contribution the preparation and structural characterization of nanoscale fluorine doped tin-oxide (SnO2:F, FTO) is described. By using a microwave assisted polyol approach, nanoparticles with different doping levels are prepared, which show narrow size distribution as measured by X-ray diffraction, electron microscopy and dynamic light scattering. They were converted into electrically conductive optically transparent films at 500 °C by a specific thermal treatment (500 °C in air followed by 250 °C in forming gas), exhibiting a specific resistivity of (1.9 × 10−1 Ω cm). Solid-state MAS NMR and 119Sn Mössbauer spectroscopy were used to study how F atoms are incorporated into the SnO2:F nanoparticles. Distance constraints were determined by 119Sn{19F} REDOR, fluorine-doping homogeneity by homonuclear dipolar recoupling experiments (SR66 2). Cross-polarization was used to investigate the immediate environment of the dopant. The experiments were supplemented by first-principles quantum-chemical calculations for possible defect site models. The combined data strongly indicate that F doping is not directly related to an increase in charge-carrier concentration, even though F atoms do occupy O vacancy sites in SnO2:F. For this study we have implemented background compensated NMR 2D pulse-sequences which reliably suppress the fluorine background originating from the NMR probe. Moreover we show that cluster calculations on the basis of the extended embedded ion method (EEIM) can be used to study the structure of diluted defects in crystalline host structures and predict NMR properties.

Classical zeolites, such as aluminosilicates and aluminophosphates, are well-established in fundamental industrial processes, e.g., substance separation, air and water conditioning, or catalysis. As they have the potential for further applications in future technologies (e.g., sensors, electronic, or optical systems), inorganic open-framework materials emerged as a research area with a multitude of compound classes in the last decades. In addition to diverse metal phosphates, germanates, and borates, there are sulfates, arsenates, or phosphonates as well as organicÀinorganic hybrid compounds with porous networks. 1,2 However, many microporous structures are thermally and chemically not sufficiently stable to make their way toward advanced materials. Consequently, it is worthwhile to synthesize novel open-framework materials that exhibit three-dimensional, rigid framework structures based on vertex-sharing tetrahedra. Since the discovery of the aluminophosphates by Flanigen et al. 3 in the 1980s, it has been attempted with great creativity and effort to access new stable frameworks with different pore sizes and shapes combined with varying chemical and physical properties. Different synthesis conditions (temperature, reaction time, pH), many different structure-directing agents (SDA), as well as a broad spectrum of solvents, including ionic liquids, were employed. The fluoride route 4 has been utilized, and other tetrahedra centers (e.g., B, Ga, Zn) were included, resulting in new zeotypes in compound classes like silicoaluminophosphates (SAPOs) and metal-containing versions (e.g., MeAPO, MeAPSO) thereof. 2,5 Thus, the field of zeolite chemistry seems quite mature which means that the search for new framework types becomes increasingly challenging.The exchange of oxygen by nitrogen in the anionic substructure is an innovative but rarely realized expansion of zeolite chemistry. Nitrido-zeolites promise beneficial chemical and physical properties (e.g., higher thermal stability or adjustable acidity/basicity) and a huge structural diversity. As compared with oxygen, nitrogen atoms are more common in three-binding situations, and they provide more flexibility as bridging atoms in networks by occasionally realizing smaller angles TÀXÀT (X = O, N). Consequently, both large rings as well as rare 3-rings can be stabilized so that novel zeolite-like frameworks become possible.This nitride concept became reality in (oxo-)nitridosilicates and (oxo-)nitridophosphates. After the proof of concept with nitridosodalites 6 and related oxonitridosodalites, 7 the benefits of nitrogen in zeolite-like framework structures have been demonstrated only for very few examples. Besides a zeolite-like SiÀN framework in Ba 2 Nd 7 Si 11 N 23 with a notable thermal stability up to 1600°C, 8 the flexibility of N bridging resulted in Li x H 12ÀxÀy+z - [P 12 O y N 24Ày ]X z for X = Cl, Br with a new zeolite topology, namely, NPO (nitridophosphate one). 9 The typical (ring-)strain Received: March 20, 2011 ABSTRACT: A novel oxonitridophospha...

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In NMR, paramagnetic dopants change the relaxation behavior and the chemical shift of the nuclei in their immediate environment. Based on the concept that the "immediate environment" in a diamagnetic host material can be described as a sphere with radius r0, we developed a function for the fraction of unperturbed nuclei (the fraction of nuclei outside the sphere) which gives a link between the effective radius and the doping concentration. In the case of a homogeneous doping scenario a characteristic dependence is observed in both theory and experiment. We validated the model on a sample series where paramagnetic Eu(II) ions are doped into crystalline SrH2. The fraction of unperturbed nuclei was determined from the (1)H NMR signal and follows the predicted curve for a homogeneous doping scenario where the radius r0 is 17 Å.

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