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[NH2(CH3)2]3Sb2Cl9 (dimethylammonium nonachlorodiantimonate, DMACA) has, at 200 K, a monoclinic Pc space group, with a = 9.470 (3), b = 9.034 (3), c = 14.080 (4) Å, β = 95.81 (3)°, V = 1198.4 (4) Å3, Z = 2 [R = 0.024, wR = 0.025 for 4613 independent reflections with F > 4σ(F)]. At 298 K DMACA has P21/c space group with a = 9.686 (3), b = 9.037 (3), c = 14.066 (4) Å, β = 95.57 (3)°, V = 1225.3 (5) Å3, Z = 2 [R = 0.034, wR = 0.035 for 2736 reflections with F > 4σ(F)]. The anionic sublattice of DMACA consists of polyanionic (Sb2Cl9 3−), layers. In the low-temperature phase there are three crystallographically non-equivalent dimethylammonium cations in the crystal structure. One of the cations is located inside the polyanionic layers, two others – one ordered and one disordered – between the polyanionic layers. In the room-temperature phase there are two non-equivalent cations – both disordered – in the crystal structure. Temperature dependencies of lattice parameters between 200 and 300 K were determined. The occurrence of a second-order phase transition at T = 242 K was confirmed. The dependence of lengths of Sb—Cl contacts on the presence and strength of N—H...CI hydrogen bonds was discussed. It was found that lengths of Sb—Cl bonds may differ from each other by as much as 0.3 Å, because of the presence of N—H...Cl hydrogen bonds. These differences were attributed to distortion of the lone-electron pair on antimony(Ill).

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Single crystals of methyl 3-(4-methoxyphenyl)prop-2-enoate were grown by the slow evaporation technique and vibrational spectral analysis was carried out using near-IR Fourier transform Raman and Fourier transform IR spectroscopy. Ab initio quantum computations were also performed at the HF/6-311G (d,p) level to derive the equilibrium geometry, vibrational wavenumbers and intensities and first hyperpolarizability. The large NLO efficiency predicted for the first time in this new class of compounds was confirmed by powder efficiency experiments. Hartree-Fock calculations reveal that the endocyclic angle at the junction of the propeonate group and the phenyl ring is decreased from 120 • by 2.5 • , whereas the two neighbouring angles around the ring are increased by 2.1 • and 1.2 • , associated with chargetransfer interaction. Vibrational analysis indicates the lowering of asymmetric stretching modes of Me1 and Me2 due to the electronic effects simultaneously caused by back-donation and induction due to the presence of the oxygen atom. The occurrence of Fermi resonance is also identified. The carbonyl stretching vibrations were lowered owing to conjugation and the hydrogen bonding network inside the crystal. The vibrational spectra confirm that the charge-transfer interaction between the -COOCH 3 group and phenyl ring through the ethylenic bridge must be responsible for simultaneous IR and Raman activation of C 7 C 18 stretching and ring modes 8 and 19. The large intensity differences observed between the 8a and 8b modes in both the IR and Raman spectra are due to the algebraic difference of the electronic effects of the substitutents. The charge transfer interaction between the -COOCH 3 group and phenyl ring through the ethylenic bridge resulting in p-electron cloud movement from donor to acceptor can make the molecule highly polarized. Intramolecular charge transfer must be responsible for the NLO activity of MMP.

Nitramines and related N-nitro compounds have attracted significant attention owing to their use in rocket fuel and as explosives. The charge density of 1-nitroindoline was determined experimentally and from theoretical calculations. Electron-density refinements were performed using the multipolar atom formalism. In order to design the ideal restraint strategy for the charge-density parameters, R-free analyses were performed involving a series of comprehensive refinements. Different weights were applied to the charge-density restraints, namely the similarity between chemically equivalent atoms and local symmetry. Additionally, isotropic thermal motion and an anisotropic model calculated by rigid-body analysis were tested on H atoms. The restraint weights which resulted in the lowest values of the averaged R-free factors and the anisotropic H-atom model were considered to yield the best charge density and were used in the final refinement. The derived experimental charge density along with intra- and intermolecular interactions was analysed and compared with theoretical calculations, notably with respect to the symmetry of multipole parameters. A comparison of different refinements suggests that the appropriate weighting scheme applied to charge-density restraints can reduce the observed artefacts. The topological bond orders of the molecule were calculated.

The crystal structure of DMABA has been determined at 293 and 180 K. It crystallizes in the monoclinic P21/c space group. The structure was refined to R1 = 0.0466 for 1269 independent reflections at 293 K and R1 = 0.038 for 1728 reflections at 180 K. DMABA is isomorphous with the chlorine analogue, DMACA. Its anionic sublattice forms corrugated two-dimensional layers in the bc plane. There are two crystallographically independent, disordered dimethylammonium cations in the crystal structure. One of them occupies cavities inside the polyanionic layers; the other is located between the layers. The temperature dependence of lattice parameters has been determined between 100 and 290 K. The presence of the ferro-paraelectric phase transition at 164 K has been confirmed. The complex dielectric permittivity of DMABA single crystals in the frequency range 100 Hz-10 GHz between 10 K and 300 K has been measured. The dynamic dielectric behaviour of DMABA is found to be determined by the properties of two independent relaxators: a low frequency one (~1 MHz at Tc) with a critical slowing down of its dynamics and a high frequency one (~5 GHz), which is thermally activated and contributes to the electric permittivity at least from about 80 K.

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