ABSTRACT
The title radical Râ , synthesized by reduction of the corresponding cation R+, is thermally stable up to ~380â K in the crystalline state under anaerobic conditions. With SQUID magnetometry, single-crystal and powder XRD, solid-state EPR and TG-DSC, reversible spin-Peierls transition between diamagnetic and paramagnetic states featuring ~10â K hysteretic loop is observed for Râ in the temperature range ~310-325â K; ΔH=~2.03â kJ mol-1 and ΔS=~6.23â J mol-1 K-1. The transition is accompanied by mechanical movement of the crystals, i. e., by thermosalient behavior. The low-temperature diamagnetic P-1 polymorph of Râ consists of Râ 2 π-dimers arranged in ( Râ 2 )n π-stacks; whereas the high-temperature paramagnetic P21/c polymorph, of uniform ( Râ )n π-stacks. With the XRD geometries, CASSCF and broken-symmetry DFT jointly suggest strong antiferromagnetic (AF) interactions within Râ 2 and weak between Râ 2 for the ( Râ 2 )n stacks; and moderate AF interactions between Râ for the ( Râ )n stacks. The fully hydrocarbon archetype of Râ does not reveal the aforementioned properties. Thus, the fluorinated 1,3,2-benzodithiazolyls pave a new pathway in the design and synthesis of metal-less magnetically-bistable materials.
ABSTRACT
To search for new suitable Pd precursors for MOCVD/ALD processes, the extended series of fluorinated palladium complexes [Pd(CH3CXCHCO(R))2] with ß-diketone [tfa-1,1,1-trifluoro-2,4-pentanedionato (1); pfpa-5,5,6,6,6-pentafluoro-2,4-hexanedionato (3); hfba-5,5,6,6,7,7,7-heptafluoro-2,4-heptanedionato (5)] and ß-iminoketone [i-tfa-1,1,1-trifluoro-2-imino-4-pentanonato (2); i-pfpa-5,5,6,6,6-pentafluoro-2-imino-4-hexanonato (4); i-hfba-5,5,6,6,7,7,7-heptafluoro-2-imino-4-heptanonato (6)] ligands were synthesized with 70-80% yields and characterized by a set of experimental (SXRD, XRD, IR, NMR spectroscopy, TG) and theoretical (DFT, Hirshfeld surface analysis) methods. Solutions of Pd ß-diketonates contained both cis and trans isomers, while only trans isomers were detected in the solutions of Pd ß-iminoketonates. The molecules 2-6 and new polymorphs of complexes 3 and 5 were arranged preferentially in stacks, and the distance between molecules in the stack generally increased with elongation of the fluorine chain in ligands. The H F contacts were the main ones involved in the formation of packages of molecules 1-2, and C F, F F, NH F contacts appeared in the structures of complexes 4-6. The stability of complexes and their polymorphs in the crystal phases were estimated from DFT calculations. The TG data showed that the volatility differences between Pd ß-iminoketonates and Pd ß-diketonates were minimized with the elongation of the fluorine chain in the ligands.
Subject(s)
Fluorine , Palladium , Crystallography, X-Ray , Ligands , Models, Molecular , Palladium/chemistryABSTRACT
For the first time, lonsdaleite-rich impact diamonds from one of the largest Popigai impact crater (Northern Siberia) with a high concentration of structural defects are investigated under hydrostatic compression up to 25 GPa. It is found that, depending on the nature of a sample, the bulk modulus for lonsdaleite experimentally obtained by X-ray diffraction in diamond-anvil cells is systematically lower and equal to 93.3-100.5% of the average values of the bulk moduli of a diamond matrix. Density functional theory calculations reveal possible coexistence of a number of diamond/lonsdaleite and twin diamond biphases. Among the different mutual configurations, separate inclusions of one lonsdaleite (001) plane per four diamond (111) demonstrate the lowest energy per carbon atom, suggesting a favorable formation of single-layer lonsdaleite (001) fragments inserted in the diamond matrix. Calculated formation energies and experimental diamond (311) and lonsdaleite (331) powder X-ray diffraction patterns indicate that all biphases could be formed under high-temperature, high-pressure conditions. Following the equation of states, the bulk modulus of the diamond (111)/lonsdaleite (001) biphase is the largest one among all bulk moduli, including pristine diamond and lonsdaleite.