Topotactic reversible phase transition between room-temperature and a new low-temperature modification in the MCl3(THF)3 system

Englert, Ulli; Calderazzo, Fausto; Pampaloni, Guido

doi:10.1007/bf02252967

Cited by 5 publications

(5 citation statements)

References 13 publications

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“…The refined parameters are summarized in Tables II-IV. In all cases the refined coordination numbers and first neighbor distances are in agreement with published values 19,33,34 within error bars.…”

Section: Table I Structural Parameters For the V-n Distance In V͓tcne͔supporting

confidence: 87%

“…In these fits, the known structures of the compounds were used as initial guesses in the refinements. 19,33,34 Small splittings in first-neighbor dis-tances beyond the spatial resolution of EXAFS were neglected, and the radial distribution function was represented in those cases by an average interatomic distance, R, and the rms Gaussian disorder 2 about that distance. The refined parameters are summarized in Tables II-IV.…”

Section: Table I Structural Parameters For the V-n Distance In V͓tcne͔mentioning

confidence: 99%

“…The fit mismatch in real space is = 0.005. The V-O and V-Cl mean distances are reported as 2.08 Å and 2.34 Å, respectively, in Ref 34…”

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confidence: 99%

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Local structural order in the disordered vanadium tetracyanoethylene room-temperature molecule-based magnet

et al. 2004

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We determined the vanadium oxidation state and local coordination environment in disordered samples of magnetic V͓TCNE͔ x ͑x Ϸ 2͒ prepared by chemical vapor deposition (CVD). Systematic studies of the x-ray absorption near-edge structure (XANES) in this material and reference compounds show that V ions have a valence state near 2+. Extended x-ray absorption fine structure (EXAFS) analysis shows that vanadium ions are coordinated by 6.04± 0.25 nitrogen atoms at a room-temperature average distance of 2.084͑5͒Å. The local environment is well defined with a distribution of V-N bond lengths comparable to that commonly found in ordered compounds. This distribution is mostly vibrational in origin, with static contributions being at least four fold smaller. The small disorder in V-N distances is a consequence of strong binding between V and TCNE, with an effective local force constant of k = 87 N / m. This strong bonding leads to strong nearest neighbor coupling, which for the extended structure of V͓TCNE͔ x with six N nearest neighbors results in magnetic ordering above room temperature. The strong V-N bonding explains in part the insoluble nature of this compared to other molecule-based magnets. The room-temperature XANES and EXAFS results for the CVD-prepared samples are compared to those for V͓TCNE͔ x prepared as a powder from CH 2 Cl 2 solvent, which has a similar magnetic ordering temperature but a magnetization that is more strongly temperature dependent. This comparison suggests that coordination of 6 nitrogens around each V(II) with little variation in the V-N distances is important for achieving the high magnetic ordering temperature of 400 K associated with samples made by both the CVD and CH 2 Cl 2 solution methods.

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Section: Table I Structural Parameters For the V-n Distance In V͓tcne͔supporting

confidence: 87%

Section: Table I Structural Parameters For the V-n Distance In V͓tcne͔mentioning

confidence: 99%

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Local structural order in the disordered vanadium tetracyanoethylene room-temperature molecule-based magnet

et al. 2004

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“…[49] Chlorine interaction parameters had been derived to model a phase transition in [MCl 3 (thf) 3 ]. [50] Point charges were obtained from Extended Hückel calculations followed by Mulliken population analysis. [46] The search for the solvate was performed with the program HARDPACK.…”

Section: Methodsmentioning

confidence: 99%

Conformational Dimorphism of 1,1,3,3,5,5‐Hexachloro‐1,3,5‐trigermacyclohexane: Solvent‐Induced Crystallization of a Metastable Polymorph Containing Boat‐Shaped Molecules

Ischenko

Englert

Jansen

2005

Chemistry A European J

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Two crystalline modifications of 1,1,3,3,5,5-hexachloro-1,3,5-trigermacyclohexane have been experimentally obtained as phase pure products and studied by single-crystal X-ray diffraction. The six-membered heterocycles adopt a chair conformation in the alpha-phase; this polymorph is accessible by crystallisation from solution and from the melt. In contrast, the beta-form is built up from boat-shaped molecules; it can exclusively be crystallised from n-hexane. At the molecular level, formation energies of the 1,1,3,3,5,5-hexachloro-1,3,5-trigermacyclohexane conformers have been compared by using molecular mechanics, semiempirical and ab-initio quantum mechanical calculations. Possible reasons for the selective formation of the alpha- or beta-phase in specific solvents have been considered. Formation of the metastable phase is suggested to occur via a hypothetical intermediate of composition [(GeCl2CH2)3].0.5C6H14. For such an in-silico solvate, a crystal structure of favourable lattice energy, closely related to the experimentally observed beta-modification, has been found through global energy minimisation. Elimination of the n-hexane molecules from this computer-generated solid and subsequent simulated annealing resulted in a crystal structure that corresponds to the experimentally observed beta-phase within the limits of the force field calculations. This scenario implies solvent directed crystallisation of a metastable polymorphic molecular crystal.

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“…The unusual coordination of the Ag(I) cations in the latter two compounds will be described, and we will discuss the highly efficient packing of all the four solids in the context of a comprehensive study based on data from the Cambridge Structural Database (CSD) [34]. Efficient space filling represents an important aspect of solids in general and a relevant driving force for the formation of coordination polymers as evidenced by single-crystal-to-single-crystal reactions [9] and phase transitions [10,35]. It can also be regarded as one of the decisive criteria for the stabilization of a given polymorph of a compound [36,37].…”

Section: Introductionmentioning

confidence: 99%

Silver coordination polymers with remarkably high packing coefficients

2009

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Silver meso-and rac-tartrate and silver squarate have been synthesized, and the crystal structure of a new polymorph of the latter is reported. Three reaction products of these silver salts with pyrazine have been obtained and structurally characterized: From silver squarate, a chain polymer with linear coordination of Ag(I) by two pyrazine ligands is formed, whereas the silver tartrates yield solids in which the inner coordination sites around the metal are only partially occupied by N donors; in contrast to expectation, oxygen coordination prevails. All the four new Ag(I) coordination compounds reported show high packing coefficients in the range between 0.789 and 0.885. In order to put these results into a meaningful context, packing coefficients for the crystal structures of almost 30,000 compounds retrieved from the Cambridge Structural Database have been determined. Tartrates pack significantly closer than pyrazine complexes or metalcontaining compounds in general. The exceptionally high packing coefficient of the new polymorph of silver squarate is due to stacking of anions and concomitant AgÁÁÁAg contacts, both along the shortest lattice parameter which amounts to only 3.3990(9) Å .

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Topotactic reversible phase transition between room-temperature and a new low-temperature modification in the MCl3(THF)3 system

Cited by 5 publications

References 13 publications

Local structural order in the disordered vanadium tetracyanoethylene room-temperature molecule-based magnet

Local structural order in the disordered vanadium tetracyanoethylene room-temperature molecule-based magnet

Conformational Dimorphism of 1,1,3,3,5,5‐Hexachloro‐1,3,5‐trigermacyclohexane: Solvent‐Induced Crystallization of a Metastable Polymorph Containing Boat‐Shaped Molecules

Silver coordination polymers with remarkably high packing coefficients

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