Magnetic moments of hindered rotators by off‐center impurity ions

Off‐center impurity ions in solids often perform rotations around their regular lattice sites. Unlike quasifree rotors with rotational line spectra subject to textbook attention in quantum mechanics, the off‐center species are hindered rotors with spectra quantized in rotational bands. These bands occur because of tunneling through barriers arising along the orbital path. For an off‐center ion rotating along a planar orbit, such as the Li⁺ impurity nearest‐neighboring an F center in alkali halide, the hindered rotation will give rise to specific magnetic moments that couple to and quantize external magnetic fields normal to the orbital plane. We present a simple theory and estimates of Li⁺ magnetic dipoles and rotational bands to find conditions for an experimental verification. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Synthesis and structure determination of MIL-10: A monodimensional metallodiphosphonate formulated MIVO{O3P-CH2-PO3}(NH4)2 (M = Ti,V)

In the view of synthesizing microporous composite compounds, the ternary systems NH₄VO₃: alkyldiphosphonic acid:H₂O were hydrothermally investigated. Using the methylendiphosphonic acid, the mixture corresponding to the molar ratio 1:0.3:500 heated three days at 200 °C, leads to small platelets whose structure was determined by single crystal X-ray diffraction. Their symmetry is orthorhombic (space group Pnma (n° 62)) with lattice parameters: a = 7.3182(1) Å, b = 16.5633(1) Å, c = 7.5225(2) Å, V = 911.83(4) ų, Z = 4. The compound labelled MIL-10, is formulated V^IVO{O₃P-CH₂-PO₃}(NH₄)₂, and shows a monodimensional structure characterized by the presence of polyhedral chains between which ammonium cations are located. The isostructural titanium compound was also hydrothermally synthesized. Its structure was solved from single crystal data; its symmetry is orthorhombic (space group Cmcm (n° 63)) with lattice parameters: a = 16.462(1) Å, b = 7.7671(6) Å, c = 7.2830(6) Å, V = 931.2(1) ų, Z = 4.     

Conformational and solid-state studies of diphenyl 1-hydroxy-1-phenylethylphosphonate

The crystal structure of the title compound, diphenyl 1-hydroxy-1-phenylethylphosphonate ( 1 ), was determined by the single-crystal X-ray diffraction method. The crystallographic data for 1 are as follow: C₂₀H₁₉O₄P, M_r = 354.34, monoclinic, P2₁/n, a = 9.787(1) Å, b = 20.235(1) Å, c = 9.797(1) Å, β = 106.18(3)°, V = 1863.3(4) ų, Z = 4, D_calc = 1.26 g/cm³, λ(Mo-Ka) = 0.71073 Å, μ = 1.6 cm⁻¹, F(000) = 744, R = 0.018, and R_w = 0.032 for 2258 observed reflections. The solid-state structure in a dimeric packing mode exhibits intermolecular hydrogen bonding of the type P = O···H–O. Infrared solution studies (CCl₄) indicate that upon high dilution (10⁻⁴ M) the dimers completely dissociate to give conformers with and without intramolecular hydrogen bonds. Theoretical studies (PM3) were undertaken to determine the energy profile about the P–C torsional angle, which exhibited low energy barriers to rotation with no clear minimum energy conformation. © 1996 John Wiley & Sons, Inc.     

Rotational isomeric-state approximation for the unperturbed dimensions of a POLA polyester

Rotational isomeric-state theory has been applied to investigate chain configurations of a polyester prepared from 4′,5-(1,1,3-trimethyl-3-phenylindan) dicarboxylic acid and 2,2-bis(4′-hydroxyphenyl) propane (POLA polyester). Independent conformations for each repeat monomer unit of the chain have been assumed in the calculations of the unperturbed dimensions. Rotations about the oxygen-phenylene-carbon (O? ?? C) bonds are considered to be free with twofold symmetric potentials. The trans and cis conformations of the carbonyl-phenylene-carbon (O?C? ?? C) and the indan-carbonyl residues are assumed to have equal probability. Two rotational states, trans and cis, are assigned to the ester C? O bonds. Calculation of the reduced unperturbed dimensions (〈r₀²〉/M)_∞ with conformations thus assigned for the bonds in the repeat unit, and comparison with experiment (0.72 ± 0.02 Ų/g) indicate that the conformation in the ester C? O bonds is predominantly trans. An equation for the conformational potential as a function of rotational angle about the ester C? O bond has been formulated using data on potential barriers for low molecular weight compounds. This equation, yielding a potential difference between the cis the trans isomers of 2.5–3.0 kcal/mole, is in good agreement with the prediction made from the calculation of the unperturbed dimensions where a cis/trans ratio of 0.01 for the ester C? O bonds was obtained.     

Molecular structure and microwave spectra of isotopic chloro-, bromo-, and iodocyanoacetylene

The microwave spectra of the halogeno-cyanoacetylenes, X-CC-CN (X = ¹²⁷I, ⁸¹Br, ⁷⁹Br, ³⁷Cl, ³⁵Cl), have been investigated. The molecules were found to be linear. The vibration-rotation constants of the three bending vibrations and the lower stretching vibration were determined. Lines belonging to the monosubstituted ¹³C and ¹⁵N species in their natural abundances were measured and the rotational constants obtained. The bond distances based on the substitution coordinates were: for I-CC-CN r(I-C) = 1.984₆ Å, r(CC) = 1.207_o Å, r(C-C) = 1.370₂ Å, r(CN) = l.l60₄ Å; for Br-CC-CN, r(Br-C) = 1.785₈ Å, r(CC) = 1.204₁ Å, r(C-C) = 1.369₉ Å, r(CN) = 1.159₃ Å; and for C1-CC-CN, r(Cl-C) = 1.624₅ Å, r(CC) = 1.209_o Å, r(C-C) = 1.369_o Å, r(CN) = 1.160₂ Å.     

An electron diffraction and CNDO/2 investigation of the molecular structure and internal rotation of hexafluorodisilane,Si2F6

The molecular structure and internal rotation of Si₂F₆ were investigated by electron diffraction of gases. The following r⁰_α -values for the geometric parameters were obtained: r(Si-Si) = 2.317 ± 0.006 Å, r(Si-F) = 1.564 ± 0.002 Å and ∠FSiF = 108.6° ± 0.3°. The barrier to internal rotation was found to be between 0.51 ± 0.10 and 0.73 ± 0.14 kcal mol^?1, depending on different assumptions of temperature drop due to gas expansion in the nozzle. Attempts were made to calculate the potential barriers for Si₂X₆ molecules with X as H, F and Cl, using the CNDO/2 approximation. When the 3d orbitais of silicon are taken into account, these results differ widely from the experimental values in the case of Si₂Fg₆ and Si₂Cl₆. Neglecting the 3d orbitais of silicon the theoretical and experi- mental potential barriers agree very well.     

Giant Crystalline Molecular Rotors that Operate in the Solid State

Molecular motion in the solid state is typically precluded by the highly dense environment, and only molecules with a limited range of sizes show such dynamics. Here, we demonstrate the solid-state rotational motion of two giant molecules, i.e., triptycene and pentiptycene, by encapsulating a bulky N-heterocyclic carbene (NHC) Au(I) complex in the crystalline media. To date, triptycene is the largest molecule (surface area: 245 Ų; volume: 219 ų) for which rotation has been reported in the solid state, with the largest rotational diameter among reported solid-state molecular rotors (9.5 Å). However, the pentiptycene rotator that is the subject of this study (surface area: 392 Ų; volume: 361 ų; rotational diameter: 13.0 Å) surpasses this record. Single-crystal X-ray diffraction analyses of both the developed rotors revealed that these possess sufficient free volume around the rotator. The molecular motion in the solid state was confirmed using variable-temperature solid-state ²H spin-echo NMR studies. The triptycene rotor exhibited three-fold rotation, while temperature-dependent changes of the rotational angle were observed for the pentiptycene rotor.     

Crystal structure determination of AlVMoO7 from X-ray powder diffraction data

The structure of AlVMoO₇ was solved by direct methods from high resolution X-ray powder diffraction data and refined by the Rietveld method. The lattice constants are a=5.3763(3)Å, b=8.1644(3)Å and c=12.7312Å. Space group Pmcn followed from the systematic extinctions and was confirmed by the successful structure solution. Aluminum is octahedrally coordinated by oxygen, whereas vanadium possesses a distorted pyramidal coordination and molybdenum is tetrahedrally coordinated by oxygen atoms. A three dimensional framework structure results from corner and edge connection of the coordination polyhedra. VO₅ pyramids are edge linked to infinite (VO₂⁺)_∞ chains. Therefore, AlVMoO₇ can be classified as a polyvanadate.     

Measurements of inelastic cross sections for the (j,m) = (2,0)→(3,0) rotational transition of CsF in collisions with atoms and molecules

Individual state-to-state rotational transitions have been resolved in small angle scattering of polarized CsF molecules on Ne, Ar, C₂, H₆, N₂, CO, CO₂, CHF₃ at center of mass energies of about 0.1 eV. The absolute inelastic cross sections range from 5Ų up to 600Ų.     

Microwave spectrum and structure of CF3OOCl

The microwave spectrum of chloroperoxytrifluoromethane has been recorded from 12.5 to 40.0 GHz. Only a-type transitions were observed. The R-branch assignments have been made for both the CF₃OO³⁵C1 and CF₃OO³⁷Cl species for the ground vibrational state. The rotational constants are: A=4808± 12, B=1318.55±0.02, C=1278.28±0.02 MHz for the ³⁵CI species, and A=4748±300,B=1285.28±0.96, C=1246.80±0.96 MHz for the ³⁷Cl species. From a diagnostic least-squares adjustment to fit the six rotational constants the following structural parameters were obtained: r(C-0)=1.377±0.03 Å, r(O-O)=1.445± 0.049 Å, r(Cl-O)=1.69±0.04 Å, ∠COO=108.1±4.2°, ∠ClOOC=99.5±2.0°, and ∠tilt = 6.0±0.9° with reasonable assumptions for the three other structural parameters. The relatively large uncertainty in these structural parameters results from the large uncertainty in the A rotational constants. These parameters are compared to the corresponding ones in some other peroxides. The quadrupole coupling constants have been obtained and are discussed.     

How CO2 Interacts with Carboxylic Acids: A Rotational Study of Formic Acid–CO2

The rotational spectra of the 1:1 formic acid–carbon dioxide molecular complex and of its monodeuterated isotopologues are analysed in the 6.5–18.5 and 59.6–74.4 GHz frequency ranges using a pulsed jet Fourier transform microwave spectrometer and a free‐jet absorption millimetre wave spectrometer, respectively. Precise values of the rotational and quartic centrifugal distortion constants are obtained from the measured frequencies, and quadrupole coupling constants are determined from the deuterium hyperfine splittings. Structural parameters are estimated from the moments of inertia and their differences among isotopologues: the complex has a planar structure with the two subunits held together by a HC(O)OH???O=C ? O (2.075 Å) and a HC(OH)O???CO₂ (2.877 Å) interactions. The ab initio intermolecular binding energy, obtained at the counterpoise corrected MP2/aug‐cc‐pVTZ level of calculation, is D_e=17 kJ mol^?1.     

Microwave spectrum of 1,2,4-trifluorobenzene

The microwave spectrum of 1,2,4-trifluorobenzene has been observed in the range 12.5–18.0 GHz and 21.5–25.3 GHz at dry-ice temperature and assigned up to angular momentum state J = 39. The ground state rotational constants and the five quartic centrifugal distortion constants thus obtained are (in MHz): à = 3084.0037 ± 0.0108, B? = 1278.3614 ± 0.0062, C? = 903.6989 ± 0.0108, d_j = ( ?4.599 ± 0.621) · 10^?4, d_jk = (5.9757 ± 1.1586) · 10^?3, d_k = (11.4923 ± 2.0886) · 10^?3, d_wj = (4.0 ± 1.0) · 10^?7, d_wk=(?5.8± 1.1) · 10^?6.The small value of Δ = 0.029 (amu Ų) shows that the molecule is planar and an r₀ - structure using a regular hexagonal benzene ring with the bond lengths C-C = 1.397 Å, C-H = 1.084 Å and C-F = 1.312 Å, reproduces the rotational constants.     

Zur Kenntnis des RbNiCrF6-Typs. V. Neue Fluoride CsBMF6 mit B = MnII bzw. NiII und M = Ga,Fe, Rh bzw. Sc,In, Tl,Rh

On the RbNiCrF₆ Type. V. New Fluorides of the Type CsBMF₆ with B = Mn^II or Ni^II and M = Ga, Fe, Rh or Sc, In, Tl, Rh New prepared are the cubic compounds CsNiScF₆ (light yellow, a = 10.60 Å); CsNiInF₆ (lightyellow, a = 10.64 Å); CsNiTlF₆ (light yellow, a = 10.60 Å); CsNiRhF₆ (light redbrown, a = 10.37 Å); CsMnGaF₆ (pink, a = 10.42 Å); CsMnFeF₆ (light green, a = 10.55 Å) and CsMnRhF₆ (redbrown, a = 10.58 Å), all RbNiCrF₆ type of structure. The Madelung part of lattice energy, MAPLE, is calculated and discussed.     

Synthesis,Crystal Structure,and Properties of HfM′P (M′ = Fe,Co, Ni) in comparison to ZrNiP

The new phosphides HfM′P (M′ = Fe, Co, Ni) have been synthesized by arc melting of HfP and the corresponding 3 d metal, and subsequent annealing at 1400°C. The lattice constants vary from a = 6.247(2) Å, b = 3.7177(6) Å, c = 7.137(2) Å, V = 165.74(8) ų for HfFeP, a = 6.295(3) Å, b = 3.668(2) Å, c = 7.175(4) Å, V = 165.7(2) ų for HfCoP to a = 6.240(3) Å, b = 3.716(2) Å, c = 7.135(2) Å, V = 165.4(2) ų (HfNiP) in the orthorhombic space group Pnma. Although ZrNiP occurs only in the Ni₂In structure type, all three Hf phosphides crystallize in the Co₂Si structure type, isotypic to ZrFeP and ZrCoP. The structural differences between HfNiP and ZrNiP can be explained by the preference of Hf for structures with more metal-metal bonds rather than by size effects.     

Investigation at the chain segmental level of the miscibility of poly(vinyl chloride)/atactic poly(methyl methacrylate) blends

We employed high‐resolution ¹³C cross‐polarization/magic‐angle‐spinning/dipolar‐decoupling NMR spectroscopy to investigate the miscibility and phase behavior of poly(vinyl chloride) (PVC)/poly(methyl methacrylate) (PMMA) blends. The spin–lattice relaxation times of protons in both the laboratory and rotating frames [T₁(H) and T_1ρ(H), respectively] were indirectly measured through ¹³C resonances. The T₁(H) results indicate that the blends are homogeneous, at least on a scale of 200–300 Å, confirming the miscibility of the system from a differential scanning calorimetry study in terms of the replacement of the glass‐transition‐temperature feature. The single decay and composition‐dependent T_1ρ(H) values for each blend further demonstrate that the spin diffusion among all protons in the blends averages out the whole relaxation process; therefore, the blends are homogeneous on a scale of 18–20 Å. The microcrystallinity of PVC disappears upon blending with PMMA, indicating intimate mixing of the two polymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2390–2396, 2001     

Synthesis and X-ray diffraction study of ternary ferrites LaNaMnFeO5 and LaKMnFeO5

Ferrites LaNaMnFeO₅ and LaKMnFeO₅ have been synthesized by the ceramic method from lanthanum(III) and iron(III) oxides and sodium and potassium carbonates. The ferrites crystallize in the orthorhombic crystal system with the following lattice parameters: LaNaMnFeO₅: a = 10.943 ± 0.002 Å, b = 11.022 ± 0.001 Å, c = 16.165 ± 0.028 Å, V ⁰ = 1949.72 ų, Z = 16, V _{unit cell} ⁰ = 12.1.85 ų, ρ_X = 4.83, ρ_pycn = 4.76 ± 0.09 g/cm³; LaKMnFeO₅: a = 10.959 ± 0.011 Å, b = 11.036 ± 0.005 Å, c = 17.825 ± 0.074 Å, V ⁰ = 2155.81 ų, Z = 16, V _{unit cell} ⁰ = 134.74 ų, ρ_X = 4.54, ρ_pycn = 4.46 ± 0.07 g/cm³.     

Tetranuclear manganese (III) salicylaldoxime ensemble

Crystal structure of {[Mn(salicylaldoximeH)(salicylaldoxime)]₄} · 3CHCl₃ 1 formed by the interaction of MnCl₂ · 4H₂O and salicylaldoxime in a 1:1 ratio is described. The compound crystallizes in the orthorhombic space group Pbca (No 61) with the lattice parameters; a = 27.769 (3), b = 22.672 (2), c = 21.650 (2) Å, V = 13630 (2) Å³, Z = 8, R ₁ = 0.0776, wR ₂ = 0.2356, S = 1.164. The cluster with four Mn (III) centers formed by four terminal and four bridging salicylaldoxime ligands results in a central rotating wheel-like core with the Mn–Mn separation varying from 3.531 to 3.576 Å and with the diagonal distances being 4.156–4.165 Å. Four intramolecular H-bonds between a terminal oxime (NOH) group and the adjacent phenolate oxygen atom of another ligand stabilize the structure of the cluster. Spectral, magnetic, and cyclic voltammetry studies corroborate a stable Mn (III) tetramer.     

The microwave and infrared spectra and structure of hydrothiophosphoryl difluoride

The microwave spectra of ³²SPHF₂, ³⁴SPHF₂ and ³²SPDF₂ have been analyzed. The structural parameters obtained from this analysis are: d(S-P) = 1.867±0.005Å, d(P-F) = 1.551 ±0.005Å, (P-H) = 1.392±0.005Å, ∠SPF = 117.4 ± 0.2 °, ∠SPH = 119.2±0.2 °, ∠FPF = 98.6±0.2 °. Centrifugal distortion coefficients were obtained for ³²SPHF₂. The spectra of two vibrational excited states of ³²SPHF₂ were observed. The two sets of rotational constants (A) 8336.72, 3726.70, 2807.56 MHz and (B) 8344.88, 3727.73, 2798.75 MHz were associated with the vibrational states with measured infrared frequencies 419 cm^?1 and 344 cm^?1 respectively. An analysis of the infrared spectrum is included. Dipole moment measurements yielded μ = 1.87±0.03 D for ³²SPHF₂ and μ = 1.86±0.03 D for ³²SPDF₂     

Crystal Structure and Ionic Conductivity of Cesium Trifluoromethyl Sulfonate,CsSO3CF3

The crystal structures of the room and the high temperature modifications of cesium trifluoromethyl sulfonate were solved from high resolution X‐ray powder diffraction data. At room temperature, α‐CsSO₃CF₃ crystallizes in the monoclinic space group P2₁ with lattice parameters a = 9.7406(2) Å, b = 6.1640(1) Å, c = 5.4798(1) Å, and β = 104.998(1)°; Z = 2. At temperatures above T = 380 K, a second order phase transformation towards a disordered C‐centered orthorhombic phase in space group Cmcm occurs with lattice parameters at T = 492 K of a = 5.5074(3) Å, b = 19.4346(14) Å, and c = 6.2978(4) Å; Z = 4. Within the crystal structures, the triflate anions are arranged in double layers with the apolar CF₃‐groups pointing towards each other. The cesium ions are located between the SO₃‐groups. CsSO₃CF₃ shows a specific ion conductivity ranging from σ = 1.06·10^?8 Scm^?1 at T = 393 K to σ = 5.18·10^?4 Scm^?1 at T = 519 K.     

Analysis of optical absorption spectra of transition metal cluster ions by the spin-polarized DV-Xα method

Optical absorption spectra of cobalt cluster ions, Co _n ⁺ , and vanadium cluster ions, V _n ⁺ , were analyzed by a theoretical calculation based on the spin-polarized DV-Xα method, and their electronic and geometric structures were obtained. Relative absorption cross section associated with each electronic transition was calculated; the calculation enables a qualitative comparison of calculated spectrum with a measured one not only in its transition energy but also in its intensity profile. This analysis shows that Co ₄ ⁺ , Co ₃ ⁺ , and V ₄ ⁺ have, respectively, a tetrahedral structure with a bond distance of 2.00Å, an equilateral triangle with a bond distance of 2.30Å, and a distorted tetrahedral structure with five bonds having a distance of 2.34 Å and one of 2.89Å. The differences in the population between majority and minority spins (spin-difference) evaluated from the electronic structure thus obtained were 2.0, 1.7, and zero per atom in Co ₃ ⁺ , Co ₄ ⁺ , and V ₄ ⁺ , respectively. These spin differences indicate a ferromagnetic and an antiferromagnetic spin-coupling in the cobalt and vanadium cluster ions, respectively.