ABSTRACT
Spin-crossover (SCO) compounds are promising materials for a wide variety of industrial applications. However, the fundamental understanding of their nature of transition and its effect on the physical properties are still being fervently explored; the microscopic knowledge of their transition is essential for tailoring their properties. Here an attempt is made to correlate the changes in macroscopic physical properties with microscopic structural changes in the orthorhombic and monoclinic polymorphs of the SCO compound Fe(PM-Bia)2(NCS)2 (PM = N-2'-pyridylmethylene and Bia = 4-aminobiphenyl) by employing single-crystal X-ray diffraction, magnetization and DSC measurements. The dependence of macroscopic properties on cooperativity, highlighting the role of hydrogen bonding, π-π and van der Waals interactions is discussed. Values of entropy, enthalpy and cooperativity are calculated numerically based on the Slichter-Drickamer model. The particle size dependence of the magnetic properties is probed along with the thermal exchange and the kinetic behavior of the two polymorphs based on the dependence of magnetization on temperature scan rate and a theoretical model is proposed for the calculation of the non-equilibrium spin-phase fraction. Also a scan-rate-dependent two-step behavior observed for the orthorhombic polymorph, which is absent for the monoclinic polymorph, is reported. Moreover, it is found that the radiation dose from synchrotron radiation affects the spin-crossover process and shifts the transition region to lower temperatures, implying that the spin crossover can be tuned with radiation damage.
ABSTRACT
During the synthesis of a series of square-planar [TeCl2(stu)2] complexes, where stu represents bulky di- or tetrasubstituted thioureas, the title compound, [TeCl[(C6H11NH)2CS]3]Cl or C39H72ClN6S3Te+*Cl-, was the unexpected result when stu was N,N'-dicyclohexylthiourea. The complex is square planar, with Te-S distances of 2.5803 (4), 2.6211 (4) and 2.8214 (4) A, and a Te-Cl distance of 2.6485 (4) A, indicating a small trans influence of the thiourea ligand.
ABSTRACT
In contrast to Se[CH(2)C(O)OH](2) versus S[CH(2)C(O)OH](2), the title compound, Se[CH(2)CH(2)C(O)OH](2) or C(6)H(10)O(4)Se, is structurally quite similar to its sulfur analogue. The molecule has twofold symmetry. The C-Se-C bond angle is 96.48 (8) degrees and the Se-C bond lengths are 1.9610 (14) A. The shortest Se.O intermolecular distance is 3.5410 (11) A. The O.O distances in the carboxylic acid dimers are 2.684 (2) A. The temperature dependence of the IR spectrum suggests tautomerism in the solid state.
ABSTRACT
Deoxyuridine triphosphate nucleotidohydrolase (dUTPase), an enzyme in the nucleotide metabolism that is a pyrophosphatase hydrolyzing dUTP, has been crystallized. The crystals belong to the trigonal space group R3 and diffract beyond 2 A. The native dUTPase crystals and a mercury derivative are stable in the X-ray beam and are suitable for a high resolution X-ray structure analysis.
