Crystals of CdCl2(1-methylcytosine)2 belong to space group Cc, with a = 10.571(7), b = 24.35(2), c = 7.097(3) Å, β = 57.33(4)°, and Z = 4. The structure was refined over 1988 independent reflections to an R factor of 0.026. The structure consists of monomeric molecules in which cadmium has a (4 + 2)-coordination. Four strong bonds, two Cd—Cl (2.497, 2.485 Å) and two Cd—N(3) (2.281, 2.296 Å), define an approximate tetrahedron around the metal. Two carbonyl oxygens take part in weak Cd—O bonding interactions (2.677, 2.780 Å). The amino groups form only very weak intramolecular hydrogen bonds with chlorine and the difference >30° between angles Cd—N(3)—C(4) and Cd—N(3)—C(2) is ascribed to Cd—O bonding. Similar effects for other metal complexes are discussed in terms of steric hindrance of the amino group and bonding of the carbonyl group.
The physical properties of Ti&09 single crystals, grown by the vapor-transport method have been studied in order to elucidate the nature of the three phases and the origin of the two successive transitions which take place as a function of temperature at -130 K and -140 K. Two transitions are clearly observed in the lattice-parameters, the electrical-conductivity, the magnetic-susceptibility and the specific-heat measurements.The enthalpy change of the two transitions have been found to be 135~5 and 110 + 5 cal/mole, respectively.An intense EPR line is found in the low-temperature phase and it vanishes at 130 K. No changes have been observed in the crystal structure of the three phases, as determined by the classical x-ray diffraction methods. It is suggested that Ti'+-Ti'+ pairing takes place in the low-temperature phase but that the crystal contains microdomains with unpaired Ti'+ cations at the domain walls which would be responsible for the strong EPR signal. The intermediate phase is proposed to be a disordered phase as far as the Ti'*-Ti'+ pairs are concerned similar to the intermediate phase of Ti,O, . The nature of the high-temperature phase is not clear.
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