Solid-state reaction study of the trans-to-cis isomerization of (eta-C(5)H(4)Me)Re(CO)[P(OPh)(3)]Br(2): a new mechanism for the isomerization reaction

Molecular Twist-Induced Single-Crystal Isomerization and Valence Tautomeric Transitions in a Cobalt-Dioxolene Complex

A mononuclear valence tautomeric (VT) complex, [Co(pycz)2(Sq)(Cat)] (1-trans), where pycz = 9-(pyridin-4-yl)-9H-carbazole, Sq⋅- = 3,5-di-tert-butyl-semiquinonato, and Cat2- = 3,5-di-tert-butyl-catecholato, is synthesized in the trans configuration, which undergoes one-step valence tautomeric transition above room temperature. Remarkably, 1-trans can transform into its isomeric structure, [Co(pycz)2(Sq)(Sq)] (1-cis), at temperature above 350 K in a single-crystal-to-single-crystal way by in situ molecular twist, and the resulting 1-cis exhibits a pronounced two-step VT transition during magnetic measurements that is rare for mononuclear VT complexes. Such drastic solid-state structural transformation is reported in VT compounds for the first time, which is actuated by a crystal surface's melting-recrystallization induced phase transition process. DFT calculations offer an underlying mechanism suggesting a concerted bond rotation during the structural transformation. The results demonstrate an unconventional approach that realizes structural transformation of VT complexes and the control of VT performance.

Solid-state 1D → 3D transformation of polynitrile-based coordination polymers by dehydration reaction

In crystal structures of two chain coordination polymers [M(tcnopr3OH)₂(H₂O)₂] (M = Ni^II and Co^II; tcnopr3OH^- = [(NC)₂CC(O(CH₂)₃OH)C(CN)₂]^-) based on a N,O or N,N'-bridge polynitrile ligand, the parallel chains are connected via, respectively, C[triple bond, length as m-dash]NH-O and O-HO hydrogen bonds between uncoordinated functional groups of the ligand and coordinated water molecules. Upon heating, both solids undergo dehydration accompanied by degradation of their single crystals. Powder X-ray diffraction showed that non-isostructural triclinic single crystals transformed to isostructural monoclinic compounds. The solid-state reaction yielded 3D coordination polymers [M(tcnopr3OH)₂] (M = Ni^II and Co^II) based on a N,N',O-connected tcnopr3OH^-. Although previously tens of complexes based on tcnopr3OH and similar anions were synthesized and X-ray characterized, none of these contain a tridentate polynitrile ligand. Thus, this study provides evidence that solid-state reactions allow obtaining novel coordination modes of polynitrile ligands. The possible pathways for the transformation of H-bonded networks to 3D coordination polymers are discussed on the basis of the topological approach. Applicability of the topological approach to predict possible networks of solid-state reaction products based on the crystal structures of initial compounds is demonstrated.

Detection and kinetics of the single-crystal to single-crystal complete transformation of a thiiranium ion into thietanium ion

The conversion of a di-tert-butyl-methylthiiranium ion into thietanium ion, that is reported in the literature as taking place spontaneously at 25 degrees C in a CD(2)Cl(2) solution, has been discovered to occur quantitatively at room temperature (RT) also in the crystalline state. The ring enlargement reaction is accompanied, in the solid phase, by a modest deterioration of the quality of the sample under investigation, and all three specimens here studied by in situ crystallography maintained their single-crystal nature up to 100% conversion. The rearrangement reaction implies the breaking of a C-S bond and the formation of a new bond of the same type, together with the migration of a methyl group. The extent of the corresponding atomic displacements has been measured by comparing the initial and final crystal structures. Several intermediate stages of the process have been investigated and characterized by the site occupancy factor of the episulfonium ion. The RT temporal evolution of this factor and that of the unit-cell volume indicate multi-step kinetics, with processes of simple molecular reorientation or displacement before and after the main, central stage, where the conversion reaction takes place. The overall kinetics is well described by an Avrami-Erofeev equation, with exponent m = 1.75(3) and rate coefficient k = 10.4(3) x 10(-8) s(-1) at 25 degrees C. Ab initio calculations in the gas phase predict a three-step mechanism resulting in a slightly spontaneous reaction with an overall decrease of entropy.

Preparation and structural characterization of trimethyltin(iv) tropolonate. Investigation of a rare methyl-migrational dismutation in the solution, solid and liquid states

The synthesis and structural characterisation, by low temperature X-ray diffraction and solid-state NMR, of the highly reactive monomeric Me(3)Sn(trop) (1) complex has been studied; 1 rearranges into Me(2)Sn(trop)(2) (2) and Me(4)Sn by methyl-transfer dismutation. Based on the NMR kinetic data it appears that complex demethylates faster in the solid and liquid than in dilute CDCl(3) solution, but with a slower rate than in dilute CD(3)OD solution.

Demethylation of the [Me3Sn(PhN2O2)]4 tetramer into dimeric [Me2Sn(PhN2O2)2]2: a thermally induced methyl-transfer between supramolecules

The single crystals of tetrameric [Me3Sn(PhN2O2)]4 (1) supramolecule demethylates into single crystals of [Me2Sn(PhN2O2)2]2 dimer (2) and volatile Me4Sn, as a result of a crystal-to-crystal supramolecular structural transformation, which occurs upon heating and it is accompanied by a significant change of the molecular and crystal structures.