Binary Compounds and Related Systems

Binary Systems and Related Compounds.—Halides. The thermodynamics of gas-phase equilibria in the W-F2 and W-F2-H2 systems at high temperatures have been described.The Raman spectrum of solid MoF exhibits Mo—F stretching bands at 746, 722, and 690 cm These results suggest that the compound has a similar structure to NbF4, with each molybdenum co-ordinated to six fluorine atoms.The Raman spectrum of crystalline M0F5 has also been reported and interpreted in terms of the crystal structure.The electronic spectrum of liquid M0F5 has been determined and shown to be consistent with a trigonal-bipyramidal molecular unit.  

The AH and AS values for the dissociation W2Clio(g) — 2WCl5(g) have been estimated as 26.0 Jmol and 66.5 JmoP respectively. The results of a normal co-ordinate analysis of WCl suggest that the molecules do not have octahedral symmetry.  

Metathetical exchange of BBrs with anhydrous M0CI5 and WClf, has been shown to be a convenient preparation of the corresponding bromides. Similarly, MoBr4 or Mo02Br2 may be obtained from M0O2 or M0O3, respectively.  

Binary Systems and Related Compounds.—Halides. The vapourization characteristics of ReBr3 have been studied by effusion techniques and the enthalpy and entropy of sublimation determined as 200 kJ mol and 227 e.u. (per mole of trimer), respectively.The X-ray characteristics of rhenium(iii) iodide, prepared from HRe04 and HI in MeOH at 80-90 °C, have been reported. 

The crystal structure of the P-form of ReCl4 obtained by the reaction of Re3Cl9 or SbCl3 with ReClj has been investigated. This polymorph is composed of RejClg units, each of which comprises two face-sharing ReClg octa-hedra, linked by shared terminal chlorine atoms. The Re—Re separation in 

A report claiming the resolution of the PQR structure in the i.r. vibrational spectrum of ReF has been challenged following further studies with improved resolution. The features attributed to the resolved branches are probably due to ReOFs contamination. The enthalpy of formation of ReF Cg) has been estimated as — 1350 + 10 kJ mol from hydrolysis measurements. The reaction of ReF with BCI3 under various conditions has been shown to yield ReClj as the only major solid phase, and thus the existence of ReClg is further questioned. 

The fundamental vibrational frequencies of ReF7(g) have been assigned on the basis of a normal-co-ordinate analysis assuming regular pentagonal-bipyramidal symmetry.  

Oxides. Single crystals of Re02 have been synthesized by chemical transport at 850— 900 °C using iodine as a carrier.  

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