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A series of five ortho-phenylene-bridged phosphorus–silicon Lewis pairs was synthesized, with phosphorus bearing isopropyl groups while the substituents at the silicon atom vary (–CH3, –Cl, –F). Possible interactions between Lewis acid and base were investigated both experimentally (NMR, XRD) and theoretically to determine the influence of the different substituents. Calculated ortho-interaction energies (OIEs) show a stabilizing interactions between the acidic and basic units which were also found for the meta- and para-interaction energies (MIEs and PIEs, respectively), indicating stabilization resulting not from direct acid–base interaction but from electronic interactions through the ring. Further spectroscopic (NMR, XRD) and theoretical (NBO, QTAIM, SAPT) investigations confirmed the absence of direct interactions between silicon and phoshorus. [ABSTRACT FROM AUTHOR]

An improved synthesis for 1,8-bis(dimethylboranyl)naphthalene (1, hydride sponge) was developed avoiding the use of tin(IV) reagents. The related 1,2-bis(dimethylboranyl)benzene (2) was prepared. 1 combined with 1,8-bis(dimethylamino)naphthalene (3, proton sponge) is a Frustrated Lewis pair (FLP) that forms adducts [1-EHn−1][3-H] with the protic compounds EHn = H2O, NH3, H2S, PH3, H2Se, HCN. Their structures show the chelation of the deprotonated substrates, except for CN− (binds to one B atom of 1). The mechanisms of formation of [1-EHn−1][3-H] were explored by NMR spectroscopy. Similar reactions took places for the FLP system 2 + 3, but the adducts [2-EHn−1][3-H] are less stable; only the PH3 adduct was isolated and AsH3 forms a chelated adduct [2-N＝C(CD3)AsH2][3-H]. FLP 1 + 3 does not react with molecular hydrogen, but the formal adduct [1-H][3-H] was isolated via salt metathesis from K[1-H] and [3-H]Cl; it is stable towards water, atmospheric oxygen and up to 100 °C; its thermal decomposition proceeds without formation of H2. The stabilities of both, the mixture 1 + 3 + H2 and the formal adduct [1-H][3-H], allow concluding that hydrogen activation of FLP 1 + 3 is kinetically prevented. [ABSTRACT FROM AUTHOR]

Equimolar mixtures of pyridine (Py) with para-halotetrafluoropyridine (BrTFP and ITFP) were investigated by VT-diffusion NMR experiments. The formation of a halogen-bond-stabilized ITFP·Py complex was detected upon cooling a solution in methylcyclohexane-d14 to 260 K; this allows monitoring a halogen-bond-driven aggregation process preceding crystallization in solution. [ABSTRACT FROM AUTHOR]

Starting with 1,2-dibromobenzene and 1,2,3,4-tetrafluorobenzene, dimethyl(2-(trimethylstannyl)phenyl)phosphane, Me2P(o-C6H4)SnMe3, and dimethyl-[2,3,4,5-tetrafluoro-6-(trimethylstannyl)phenyl]phosphane, Me2P(o-C6F4)SnMe3, were synthesized and used in tin-gold exchange reactions to prepare two gold(I) dimers, bis[(2-dimethylphosphino)phenyl]di-gold(I), [Au2(μ-2-C6H4PMe2)2], and bis[(2-dimethylphosphino)-3,4,5,6-tetrafluorophenyl]di-gold(I), [Au2(μ-2-C6F4PMe2)2], respectively. Both tin precursor molecules, as well as the gold(I) complexes, were characterized by multinuclear NMR spectroscopy, CHN analysis and X-ray diffraction experiments. Both gold(I) dimers were further investigated by the means of computational as well as photophysical methods. [ABSTRACT FROM AUTHOR]

The reactivity of the frustrated Lewis pair (FLP) (F5C2)3SnCH2P(tBu)2 (1) was investigated with respect to the activation of elemental hydrogen. The reaction of 1 at elevated hydrogen pressure afforded the intramolecular phosphonium stannate(II) (F5C2)2SnCH2PH(tBu)2 (3). It was characterized by means of multinuclear NMR spectroscopy and single crystal X‐ray diffraction. NMR experiments with the two isotopologues H2 and D2 showed it to be formed via an H2 adduct (F5C2)3HSnCH2PH(tBu)2 (2) and the subsequent formal reductive elimination of pentafluoroethane; this is supported by DFT calculations. Parahydrogen‐induced polarization experiments revealed the formation of a second product of the reaction of 1 with H2, [HP(tBu)2Me][Sn(C2F5)3] (4), in 1H NMR spectra, whereas 2 was not detected due to its transient nature. [ABSTRACT FROM AUTHOR]

9‐Br‐closo‐1,2‐C2B10H11 has been prepared and its gas‐phase structure has been examined by means of gas electron diffraction. The structure of the carbaborane core is similar to the structure of the parent compound, which is of C2v symmetry. A DFT‐based search for the corresponding reaction pathway of the bromination of closo‐1,2‐C2B10H12 revealed that the catalytic amount of aluminum reduces the barrier of the initial attack of the bromination agent toward the negatively charged part of the icosahedral carbaborane, i. e., the first transition state, from about 40 to about 27 kcalmol‐1. The Br−Br bond is weakened by an intermediate binding to the large π‐hole on the aluminum atom of AlBr3, which is the driving force for the AlBr3‐catalyzed bromination. [ABSTRACT FROM AUTHOR]

Difluorothiophosphoryl isocyanate, F2P(S)NCO was characterized with UV/vis, NMR, IR (gas and Ar‐matrix), and Raman (liquid) spectroscopy. Its molecular structure was also established by means of gas electron diffraction (GED) and single crystal X‐ray diffraction (XRD) in the gas phase and solid state, respectively. The analysis of the spectroscopic data and molecular structures is complemented by extensive quantum‐chemical calculations. Theoretically, the Cs symmetric syn‐conformer is predicted to be the most stable conformation. Rotation about the P−N bond requires about 9 kJ mol−1 and the predicted existence of an anti‐conformer is dependent on the quantum‐chemical method used. This syn‐orientation of the isocyanate group is the only one found in the gas phase and contained likewise in the crystal. The overall molecular structure is very similar in gas and solid, despite in the solid state the molecules arrange through intramolecular O⋅⋅⋅F contacts into layers, which are further interconnected by S⋅⋅⋅N, S⋅⋅⋅C and C⋅⋅⋅F contacts. Additionally, the photodecomposition of F2P(S)NCO to form CO, F2P(S)N, and F2PNCO is observed in the solid Ar‐matrix. [ABSTRACT FROM AUTHOR]

The refrigerant trans‐1,3,3,3‐tetrafluoropropene (HFO‐1234ze) is used as a replacement for former cooling agents that have been phased‐out due to their global warming potential or ozone depleting potential. Although it is used on a large scale, only a few vibrational data and no structural data of HFO‐1234ze are known. We report structure determinations based on low‐temperature single‐crystal X‐ray diffraction data as well as gas‐phase diffraction data of HFO‐1234ze and HFO‐1234yf (2,3,3,3‐tetrafluoropropene). Furthermore, vibrational spectra of HFO‐1234ze in all phases are described. The results are discussed together with quantum‐chemical calculations on the PBE0/cc‐pVTZ level of theory. Combustion experiments of HFO‐1234ze show carbonyl difluoride, carbon dioxide and hydrogen fluoride to be the main combustion products. [ABSTRACT FROM AUTHOR]

Non-covalent aryl–aryl interactions for the molecular structures of three 1,2-diaryltetramethyldisilanes X5C6–(SiMe2)2–C6Y5 (X ≠ Y; X, Y = H, F, Cl) were studied by single crystal X-ray and gas electron diffraction as well as by SAPT calculations. Aryl–aryl interactions cause all to adopt exclusively rather untypical eclipsed syn-conformers in the gas phase, and C6F5–(SiMe2)2–C6Cl5 also in the solid state. [ABSTRACT FROM AUTHOR]

Three 1,2‐diaryltetramethyldisilanes X5C6‐(SiMe2)2‐C6X5 with two C6H5, C6F5, or C6Cl5 groups were studied concerning the importance of London dispersion driven interactions between their aryl groups. They were prepared from 1,2‐dichlorotetramethyldisilane by salt elimination. Their structures were determined in the solid state by X‐ray diffraction and for free molecules by gas electron‐diffraction. The solid‐state structures of the fluorinated and chlorinated derivatives are dominated by aryl–aryl interactions. Unexpectedly, Cl5C6‐(SiMe2)2‐C6Cl5 exists exclusively as an eclipsed syn‐conformer in the gas phase with strongly distorted Si‐C6Cl5 units due to strong intramolecular interactions. In contrast, F5C6‐(SiMe2)2‐C6F5 reveals weaker interactions. The contributions to the total interaction energy were analyzed by SAPT calculations. [ABSTRACT FROM AUTHOR]

An improved synthesis of the simplest nitric acid ester, methyl nitrate, and a new synthesis of fluoromethyl nitrate use the metathesis of the corresponding iodomethanes with silver nitrate. Both compounds were identified by spectroscopy and the structures determined for in situ grown crystals by X‐ray diffraction as well as in the gas phase by electron diffraction. Fluorination leads to structures with shorter C−O and N−O bonds, has an energetically destabilizing effect and increases friction sensitivity, but decreases detonation performance. [ABSTRACT FROM AUTHOR]

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The structures of the three para‐substituted halotetrafluoropyridines with chlorine, bromine, and iodine have been determined in the solid state (X‐ray diffraction). The structures of these compounds and that of pentafluoropyridine were also determined in the gas phase (electron diffraction). Structures in the solid state of the bromine and iodine derivatives exhibit halogen bonding as a structure‐determining motif. On the way to an investigation of halogen bond formation of halotetrafluoropyridines in the solid state with the stronger Lewis base pyridine, co‐crystals of benzene adducts were investigated to gain an understanding of the influence of aryl–aryl interactions. These co‐crystals showed halogen bonding only for the two heavier halotetrafluoropyridines. In the pyridine co‐crystals halogen bonding was observed for all three para‐halotetrafluoropyridines. The formation of homodimers and heterodimers with pyridine is also supported by quantum‐chemical calculations of electron density topologies and natural bond orbitals. [ABSTRACT FROM AUTHOR]

Small‐ to medium‐sized clusters occur in various areas of chemistry, for example, as active species of heterogeneous catalysis or as transient intermediates during chemical vapor deposition. The manipulation of stable representatives is mostly limited to the stabilizing ligand periphery, virtually excluding the systematic variation of the property‐determining cluster scaffold. We now report the deliberate expansion of a stable unsaturated silicon cluster from six to seven and finally eight vertices. The consecutive application of lithium/naphthalene as the reducing agent and decamethylsilicocene as the electrophilic source of silicon results in the expansion of the core by precisely one atom with the potential of infinite repetition. A stable unsaturated Si6R6 cluster was consecutively expanded to the stable neutral and anionic clusters Si7R6, Si7R5−, and Si8R6. Key to this method is the use of decamethylsilicocene (Cp*2Si) as the electrophile with Cp*− as the leaving group. [ABSTRACT FROM AUTHOR]

The thermally unstable α-fluoroalcohol undecafluorocyclohexanol (c-C6F11OH) was prepared by addition of hydrogen fluoride to the corresponding ketone. c-C6F10(CF3)OH was obtained by protonation of its alkoxide [NMe4]+[C7F13O]−. Decafluorocyclohexane-1,1-diol (c-C6F10(OH)2) was prepared by acidic workup of the corresponding alkoxide [NMe4]+[C6F11O]− with sulfuric acid, which yielded (c-C6F10(OH)2) and fluorosulfonic acid. The structures of c-C6F10(CF3)OH·2H2O and of (c-C6F10(OH)2) were elucidated by single-crystal X-ray and gas-phase electron-diffraction studies. [ABSTRACT FROM AUTHOR]

Abstract: Disulfuryl dichloride ClSO2OSO2Cl was characterized by vibrational spectroscopy in the gaseous and liquid phase as well as in the Ar‐matrix. By varying the temperature, certain bands could be assigned to several conformers. Gas‐phase electron diffraction revealed a dominance of the anti‐conformer at ambient temperature. The same conformation was found in the solid state. Via the in situ technique for crystallization, not less than four different modifications were identified. Among these different modifications, the structural parameters of the molecules remain relatively constant, but the aggregation pattern changes. Although the molecules aggregate by chlorine⋅⋅⋅oxygen contacts in each modification, the geometrical parameters of these interaction show significant differences and were evaluated and are in part inconsistent with the halogen bonding concept. [ABSTRACT FROM AUTHOR]

Planar tridentate Lewis acids were synthesised by hydrosilylation reactions of triethynylbenzene with chlorosilanes. Hydrogenation of the rigid triethynylbenzene using hydrogen in the presence of Lindlar's catalyst resulted in the formation of trivinylbenzene. The hydrosilylation of this compound enabled the synthesis of flexible tridentate Lewis acids with SiClMe2 and SiCl2Me, SiCl3 groups. In order to increase the acidity, the chlorine substituents of the tridentate Lewis acids were substituted by fluorine and compounds with SiF2Me and SiF3 groups were obtained. The Lewis acidity of the isolated compounds was determined with the Gutmann–Beckett method. The results show the presence of cooperative effects of the silyl groups. [ABSTRACT FROM AUTHOR]

After numerous attempts over the last seven decades to obtain a structure for the simple, highly symmetric molecule tetranitromethane (C(NO2)4, TNM) that is consistent with results from diffraction experiments and spectroscopic analysis, the structure has now been determined in the gas phase and the solid state. For the gas phase, a new approach based on a four-dimensional dynamic model for describing the correlated torsional dynamics of the four C−NO2 units was necessary to describe the experimental gas-phase electron diffraction intensities. A model describing a highly disordered high-temperature crystalline phase was also established, and the structure of an ordered low-temperature phase was determined by X-ray diffraction. TNM is a prime example of molecular flexibility, bringing structural methods to the limits of their applicability. [ABSTRACT FROM AUTHOR]

Tris[tetrafluor‐4‐(trifluormethyl)phenyl]boran (BTolF) wurde durch Reaktion von Bortribromid mit tetramerem F3CC6F4‐CuI hergestellt. Letzteres wurde aus F3CC6F4MgBr und Kupfer(I)‐bromid erzeugt. Die mittels der Gutmann‐Beckett‐Methode gemessenen und aus berechneten Fluoridionenaffinitäten abgeschätzte Lewis‐Aciditäten von BTolF sind 9 bzw. 10 % höher als die von Tris(pentafluorphenyl)boran (BCF) und sogar höher als die von SbF5. Die Molekülstrukturen von BTolF und BCF wurden mithilfe von Elektronenbeugung in der Gasphase, die von BTolF auch mittels Einkristallröntgenstrukturanalyse bestimmt. Supersaures Tris[tetrafluor‐4‐(trifluormethyl)phenyl]boran (BTolF) wurde aus BBr3 und F3CC6F4‐CuI hergestellt. Es ist eine stärkere Lewis‐Säure als Tris(pentafluorphenyl)boran (BCF) und hat eine höhere Fluoridionenaffinität als SbF5. Die Strukturen von BTolF und des viel verwendeten BCF wurden per Elektronenbeugung in der Gasphase bestimmt und spiegeln die unterschiedlichen elektronischen Situationen wider. [ABSTRACT FROM AUTHOR]

Tris[tetrafluoro-4-(trifluoromethyl)phenyl]borane (BTolF) was prepared by treating boron tribromide with tetrameric F3CC6F4-CuI. The F3CC6F4-CuI was generated from F3CC6F4MgBr and copper(I) bromide. Lewis acidities of BTolF evaluated by the Gutmann-Beckett method and calculated fluoride-ion affinities are 9 and 10 %, respectively, higher than that of tris(pentafluorophenyl)borane (BCF) and even higher than that of SbF5. The molecular structures of BTolF and BCF were determined by gas-phase electron diffraction, that of BTolF also by single-crystal X-ray diffraction. [ABSTRACT FROM AUTHOR]

In this study, we investigate the ability of classical molecular dynamics (MD) and Monte-Carlo (MC) simulations for modeling the intramolecular vibrational motion. These simulations were used to compute thermally-averaged geometrical structures and infrared vibrational intensities for a benchmark set previously studied by gas electron diffraction (GED): CS2, benzene, chloromethylthiocyanate, pyrazinamide and 9,12-I2-1,2-closo-C2B10H10. The MD sampling of NVT ensembles was performed using chains of Nose–Hoover thermostats (NH) as well as the generalized Langevin equation thermostat (GLE). The performance of the theoretical models based on the classical MD and MC simulations was compared with the experimental data and also with the alternative computational techniques: a conventional approach based on the Taylor expansion of potential energy surface, path-integral MD and MD with quantum-thermal bath (QTB) based on the generalized Langevin equation (GLE). A straightforward application of the classical simulations resulted, as expected, in poor accuracy of the calculated observables due to the complete neglect of quantum effects. However, the introduction of a posteriori quantum corrections significantly improved the situation. The application of these corrections for MD simulations of the systems with large-amplitude motions was demonstrated for chloromethylthiocyanate. The comparison of the theoretical vibrational spectra has revealed that the GLE thermostat used in this work is not applicable for this purpose. On the other hand, the NH chains yielded reasonably good results. [ABSTRACT FROM AUTHOR]

Dichlorophosphanyl isocyanate, Cl2PNCO, was synthesized and characterized by IR, Raman and 31P NMR spectroscopy. The conformational properties and molecular structures were studied by using gas electron diffraction (GED), X-ray crystallography and quantum-chemical calculations. Extensive DFT and ab initio calculations show that the potential energy surface of Cl2PNCO upon rotating the P–N bond is rather flat; three conformers, namely syn, anti and gauche between the NCO group and the bisector of the ClPCl angle, were theoretically predicted. Experimentally, only one conformer was indicated by gas-phase IR spectroscopy and the preference for a gauche conformation in both gas phase and solid state was unambiguously ascertained by gas electron diffraction and X-ray crystallographic data. In the solid state, the Cl2PNCO molecules adopt a gauche conformation with two distinct dihedral angles Cl–P–N–C of −121.3(2) and 137.4(2)° and form polymeric chains through weak intermolecular C…O contacts. Additionally, the dynamic character of the position of the isocyanate group of Cl2PNCO was examined in the gas phase. [ABSTRACT FROM AUTHOR]

The gas-phase structures of the disilanes 1,1,2,2-tetrakis(trimethylsilyl)disilane [(Me3Si)2HSiSiH(SiMe3)2] (1) and 1,1,2,2-tetrakis(trimethylsilyl)dimethyldisilane [(Me3Si)2MeSiSiMe(SiMe3)2] (2) have been determined by density functional theoretical calculations and by gas electron diffraction (GED) employing the SARACEN method. For each of 1 and 2 DFT calculations revealed four C2-symmetric conformers occupying minima on the respective potential-energy surfaces; three conformers were estimated to be present in sufficient quantities to be taken into account when fitting the GED data. For (Me3Si)2RSiSiR(SiMe3)2 [R = H (1), CH3 (2)] the lowest energy conformers were found by GED to have RSiSiR dihedral angles of 87.7(17)° for 1 and -47.0(6)° for 2. For each of 1 and 2 the presence of bulky and flexible trimethylsilyl groups dictates many aspects of the geometric structures in the gas phase, with the molecules often adopting structures that reduce steric strain. [ABSTRACT FROM AUTHOR]

Fluoromethyl triflate (superfluoromethyl, SFM, FCH2OSO2CF3) and fluoromethyl fluorosulfonate (magic fluoromethyl, MFM, FCH2OSO2F) are two easily synthesized, highly effective and non-ozone depleting fluoromethylation reagents. They are analogous to the well-known and widely used methylation re-agents CH3OSO2CF3 and CH3OSO2F. Both SFM and MFM have been fully characterized by multinuclear NMR spectroscopy (1H, 13C, 17O, 19F, 33S). Their structures have been determined in the solid state on in situ grown crystals by X-ray diff-raction and in the gas phase by electron diffraction. The fluoromethylation efficiency of SFM and MFM was shown by reaction with chalcogen nucleophiles of differing nucleophilicity. All fluoromethylated products were isolated as pure com-pounds and charac-terized by NMR and vibrational spec-troscopy, as well as in some cases by single crystal X-ray diffraction., (© 2024 Wiley‐VCH GmbH.)

Starting with 1,2-dibromobenzene and 1,2,3,4-tetrafluorobenzene, dimethyl(2-(trimethylstannyl)phenyl)phosphane, Me 2 P( o -C 6 H 4 )SnMe 3 , and dimethyl-[2,3,4,5-tetrafluoro-6-(trimethylstannyl)phenyl]phosphane, Me 2 P( o -C 6 F 4 )SnMe 3 , were synthesized and used in tin-gold exchange reactions to prepare two gold(I) dimers, bis[(2-dimethylphosphino)phenyl]di-gold(I), [Au 2 (μ-2-C 6 H 4 PMe 2 ) 2 ], and bis[(2-dimethylphosphino)-3,4,5,6-tetrafluorophenyl]di-gold(I), [Au 2 (μ-2-C 6 F 4 PMe 2 ) 2 ], respectively. Both tin precursor molecules, as well as the gold(I) complexes, were characterized by multinuclear NMR spectroscopy, CHN analysis and X-ray diffraction experiments. Both gold(I) dimers were further investigated by the means of computational as well as photophysical methods.

9-Br-closo-1,2-C 2 B 10 H 11 has been prepared and its gas-phase structure has been examined by means of gas electron diffraction. The structure of the carbaborane core is similar to the structure of the parent compound, which is of C 2v symmetry. A DFT-based search for the corresponding reaction pathway of the bromination of closo-1,2-C 2 B 10 H 12 revealed that the catalytic amount of aluminum reduces the barrier of the initial attack of the bromination agent toward the negatively charged part of the icosahedral carbaborane, i. e., the first transition state, from about 40 to about 27 kcalmol -1 . The Br-Br bond is weakened by an intermediate binding to the large π-hole on the aluminum atom of AlBr 3 , which is the driving force for the AlBr 3 -catalyzed bromination., (© 2020 The Authors. ChemPlusChem published by Wiley-VCH GmbH.)

An improved synthesis of the simplest nitric acid ester, methyl nitrate, and a new synthesis of fluoromethyl nitrate use the metathesis of the corresponding iodomethanes with silver nitrate. Both compounds were identified by spectroscopy and the structures determined for in situ grown crystals by X-ray diffraction as well as in the gas phase by electron diffraction. Fluorination leads to structures with shorter C-O and N-O bonds, has an energetically destabilizing effect and increases friction sensitivity, but decreases detonation performance., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

The novel chlorosulfuryl chloroformate, ClC(O)OSO 2 Cl, was prepared by the reaction of CCl 4 and SO 3 . Alternatively, the compound was obtained from the direct insertion reaction of SO 3 to Cl 2 C═O. The latter reaction constitutes also a confirmation of the proposed mechanism for the former one. Density functional theory and MP2 theoretical approximations predict the existence of two conformers, syn-gauche and syn-anti, depending on the value adopted by the dihedral angles ϕ(Cl-C-O-S) and ϕ(C-O-S-Cl). The structure of the syn-gauche conformer was determined by gas-phase electron diffraction (GED). The existence of the syn-anti conformer can be neither confirmed nor excluded by the GED experiment. Vibrational spectra (vapor-phase and argon-matrix Fourier transform infrared and liquid Fourier transform Raman) were interpreted by an equilibrium mixture between both conformers.

The thermally unstable α-fluoroalcohol undecafluorocyclohexanol (c-C6F11OH) was prepared by addition of hydrogen fluoride to the corresponding ketone. c-C6F10(CF3)OH was obtained by protonation of its alkoxide [NMe4]+[C7F13O]-. Decafluorocyclohexane-1,1-diol (c-C6F10(OH)2) was prepared by acidic workup of the corresponding alkoxide [NMe4]+[C6F11O]- with sulfuric acid, which yielded (c-C6F10(OH)2) and fluorosulfonic acid. The structures of c-C6F10(CF3)OH·2H2O and of (c-C6F10(OH)2) were elucidated by single-crystal X-ray and gas-phase electron-diffraction studies.

Disulfuryl dichloride ClSO 2 OSO 2 Cl was characterized by vibrational spectroscopy in the gaseous and liquid phase as well as in the Ar-matrix. By varying the temperature, certain bands could be assigned to several conformers. Gas-phase electron diffraction revealed a dominance of the anti-conformer at ambient temperature. The same conformation was found in the solid state. Via the in situ technique for crystallization, not less than four different modifications were identified. Among these different modifications, the structural parameters of the molecules remain relatively constant, but the aggregation pattern changes. Although the molecules aggregate by chlorine⋅⋅⋅oxygen contacts in each modification, the geometrical parameters of these interaction show significant differences and were evaluated and are in part inconsistent with the halogen bonding concept., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

After numerous attempts over the last seven decades to obtain a structure for the simple, highly symmetric molecule tetranitromethane (C(NO 2 ) 4 , TNM) that is consistent with results from diffraction experiments and spectroscopic analysis, the structure has now been determined in the gas phase and the solid state. For the gas phase, a new approach based on a four-dimensional dynamic model for describing the correlated torsional dynamics of the four C-NO 2 units was necessary to describe the experimental gas-phase electron diffraction intensities. A model describing a highly disordered high-temperature crystalline phase was also established, and the structure of an ordered low-temperature phase was determined by X-ray diffraction. TNM is a prime example of molecular flexibility, bringing structural methods to the limits of their applicability., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A modified synthesis for carbonyl diisocyanate, CO(NCO)2, starting from trichloroisocyanuric acid and diphosgene is described. In addition to the previously reported (13)C NMR resonances, the (15)N NMR shift is determined for the first time. The structure in the solid state was determined by X-ray diffraction (XRD) on in situ grown crystals, that in the gas phase was experimentally determined by electron diffraction (GED) and for single molecules theoretically by quantum-chemical calculations. The structures are compared and discussed with related systems. Quantum-chemical calculations as well as GED and XRD prove syn-syn to be the conformation of lowest energy. In quantum-chemical calculations and GED the presence of a syn-anti conformer was confirmed and the structure of this conformer was determined.

Gas-phase structures of two isomers of dimethyl-substituted 1,5-diazabicyclo[3.1.0]hexanes, namely, 3,3-dimethyl- and 6,6-dimethyl-1,5-diazabicyclo[3.1.0]hexane molecules, have been determined by gas electron diffraction method. A new approach based on the Monte Carlo method has been developed and used for the analysis of precision and accuracy of the refined structures. It was found that at 57 °C 3,3-dimethyl derivative exists as a mixture of chair and boat conformers with abundances 68(8)% and 32(8)%, respectively. 6,6-Dimethyl-1,5-diazabicyclo[3.1.0]hexane at 50 °C has only one stable conformation with planar 5-ring within error limits. Theoretical calculations predict that the 6,6-dimethyl isomer is more stable in comparison to the 3,3-dimethyl isomer with energy difference 3-5 kcal mol(-1). In order to explain the relative stability and bonding properties of different structures the natural bond orbitals (NBO), atoms in molecules (AIM), and interacting quantum atoms (IQA) analyses were performed.