Single Crystal X-Ray Structure of BeF2: α-Quartz

We report for the first time, the synthesis and X-ray diffraction studies of single crystals of BeF2. The crystals were obtained during the sublimation of amorphous BeF2 under static reduced pressure. BeF 2 crystallizes in the chiral trigonal space group P3121. A single-crystal X-ray diffraction study on these crystals shows that each of the Be atoms is bonded to four F atoms, and each of the F atoms is bonded to two Be atoms with associated Be-F bond distances of 1.5420(13) and 1.5471(13) Å, showing an almost regular tetrahedron. The infrared spectrum of these crystals recorded at room temperature shows distinct peaks around 770 and 410 cm -1. © 2010 American Chemical Society.by Pallavi Ghalsasi and Prasanna S. Ghalsas

Studies on TMPD:TCNB; a Donor-Acceptor with Room Temperature Paramagnetism and n-π Interaction†

A donor-acceptor compound based on N,N,N′,N′-tetramethyl-p-phenylene-diamine and 1,2,4,5-tetracyanobenzene (TMPD:TCNB) has been synthesized. The crystalstructure of the black 1:1 complex formed between TMPD and TCNB has beendetermined by single crystal X-ray diffraction at room temperature. The compoundcrystallizes in the triclinic space group P-1 with cell dimensions: a = 7.4986(15) å, b =7.6772(11) å, c = 8.0764(15) å, α = 78.822(12)°, β = 83.3779(19)°, γ = 86.289(17)°.TMPD and TCNB molecules are stacked alternately in infinite columns along the a-axis.The structure does not seem to show the usual π-π interaction between the two aromaticrings, but indicates an n-π interaction localized between the nitrogen atoms of the donorand the cyano groups of the acceptor

Temperature-dependent Raman spectroscopy of anilinium chloride near phase transition

The existence of various solid phases of organic ammonium halides, due to the presence of hydrogen bonding, has long been established but is limited to alkyl ammonium halides. On the other hand, the presence of such phase transitions was eluded in case of anilinium chloride. In the present work, we have undertaken a systematic temperature dependent Raman spectroscopic study on anilinium chloride, in the range 300-100-350K. Spectral variation in the low frequency (100-400cm-1) and high frequency (2500-3700cm-1) regions around 350 and 260K shows the signature of the phase transitions in this compound. These phase transitions were reversible in nature. The latter transition is in agreement with DSC measurements. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.by Ashok K. Vishwakarma, Pallavi P. Ghalsasi and Prasanna S. Ghalsas

Light Induced Metastable State of Silver Nitroprusside Probed by Raman Spectroscopy

Low temperature Raman spectroscopic measurements on silver nitroprusside (AgNP), Ag-2Fe(CN)(5)NO] powders display reversible features of a partially converted metastable state. The results are compared with similarly observed metastable state in case of sodium nitroprusside (NaNP) and the differences have been discussed in terms of possible resistance to metastable state formation offered by silver atoms on the basis of hard soft acid base (HSAB) theory

Back-Bonding Signature with High Pressure: Raman Studies on Silver Nitroprusside

In centrosymmetric molecules, like A(n+)M-(CN)(6)](n-) (where A is alkali metal cation), normally all stretching vibrations of cyanide (CN-) Shift to high frequency in response to nonhydrostatic pressure, whereas, in non-centrosymmetric molecules in whiCh one axial CN ligand is replaced by NO ligand, one observes unusual softening of only equatorial CN stretching modes. This effect is pronounced when A(+) is replaced by Ag+ with,difference in coordination ability of latter, resulting in expression of characteristic sign-attire of back-bonding. One can correlate this uneven stretching of cyanide to Poisson-like effect, where the axial Fe-N, Fe-C, and C-N stretching modes harden but the equatorial C-N stretching modes soften due to expansion at the equatorial plane. Thus, the present study is focused on results of non-hydrostatic high-pressure Raman measurements on silver nitroprusside tip to 11.5 GPa, for not only observing Characteristic signature of ``back-bonding'' interaction, rarely featured in literature, but also for generating reversible flexible structures akin to noncovalent interaction

Studies on TMPD:TCNB; a Donor-Acceptor with Room Temperature Paramagnetism and n-À Interactionâ€

A donor-acceptor compound based on N,N,N′,N′-tetramethyl-p-phenylene-diamine and 1,2,4,5-tetracyanobenzene (TMPD:TCNB) has been synthesized. The crystalstructure of the black 1:1 complex formed between TMPD and TCNB has beendetermined by single crystal X-ray diffraction at room temperature. The compoundcrystallizes in the triclinic space group P-1 with cell dimensions: a = 7.4986(15) Ã¥, b =7.6772(11) Ã¥, c = 8.0764(15) Ã¥, α = 78.822(12)°, β = 83.3779(19)°, γ = 86.289(17)°.TMPD and TCNB molecules are stacked alternately in infinite columns along the a-axis.The structure does not seem to show the usual À-À interaction between the two aromaticrings, but indicates an n-À interaction localized between the nitrogen atoms of the donorand the cyano groups of the acceptor

Designing Chiral, Pro-Polar Structures for Observing Ferroelectricity: Molecular Analogue of KNO₃

Observation and creation of a pro-chiral center is a prerequisite in chemical synthesis for generating chiral structures. On the other hand, temporary and reversible generation of chiral or polar structures using physical forces such as electricity is a need of present technology for observing nonlinear behavior. Thus, one can synthesize a pro-polar structure, akin to a pro-chiral center using chemical interactions, for facilitating physical forces in generating chiral/polar structures, a novel way for designing molecular materials. At room temperature, the structure of KNO₃ and anilinium nitrate (AnHNO₃) is centrosymmetric, although the latter showed molecular properties in the form of distinct helical NH···O hydrogen bonding to generate a dipole moment, which in turn gets canceled due to the formation of antiparallel double helical chains. We could separate these helical chains of NH···O hydrogen bonding, by chemical design, synthesis of analogues molecules (<i>para</i>-ethyl anilinium nitrate), and crystallization through a gel as well slow evaporation technique, to obtain a pro-polar and chiral structure with molecular ferroelectric behavior. Thus, creation of a pro-polar structure, presented here by modifying the cation in KNO₃ to observe room temperature ferroelectric behavior, will help in designing novel molecular ferroelectric materials

Amino substituted 4-pyridylbutadienes: synthesis and fluorescence investigations

Synthesis and spectroscopic investigations of a series of donor-π-acceptor systems containing pyridine as the electron withdrawing group and an amino derivative (dimethylamino, diphenylamino, carbazole and julolidine) as electron donating group, separated by a π-spacer are described. The effect of varying donors on absorption and emission properties was studied in different solvents. All the molecules investigated exhibit pronounced positive polarity dependent solvatochromic shifts of up to ∼141 nm. Strong fluorescence quantum yields are also observed for dienes containing carbazole and diphenylamine donors. This behavior suggests the presence of highly polar emitting states as a result of π -π* intramolecular charge-transfer (ICT). The observations were corroborated by a linear relation of the fluorescence maximum (νmax) versus the solvent polarity function (Δf) from the Lippert–Mataga correlation. The emission lifetime shows a decay profile consistent with the formation of one species (1 and 3) and two species (2 and 4) in the excited state.by Harsha Agnihotri, et.a