Linear Trimeric Hafnium Clusters in Hf 0
The reduction of hafnium tetraiodide, HfI4, with aluminum at 600 °C or 850 °C in the presence of a NaI flux resulted in black single crystals of Hf0.86(1)I3. This composition corresponds well to the upper end of the non-stoichiometry range 0.89 ≤ x ≤ 1.00 previously reported for HfxI3. The crystal structure (a = 1250.3(2), c = 1999.6(3) pm, R-3m, Z = 18) is made up of hexagonal closest packed layers of iodide ions. One third of the octahedral holes would be filled as in TiI3 or ZrI3 if it were Hf1.00I3. In Hf0.86(1)I3, one out of six octahedral holes along [001] are, however, only occupied by 16%. In contrast to TiI3-I and ZrI3, one striking structural feature is in the formation of linear hafnium trimers with identical Hf―Hf distances of 318.3(2) pm rather than the formation of dimers. These may be associated with Hf―Hf bonding although only 2.64 electrons are available for one Hf5.16I18 column.
Revision of the structure of zirconium triiodide. The presence of metal dimers
Single-crystal x-ray studies on stoichiometric ZrI{sub 3} by film and diffractometer means show that a considerable number of very weak diffraction intensities require an orthorhombic cell and space group Pmmm (Z = 4, RuBr{sub 3}-type), while the stronger {approximately}75% of the reflection data are consistent with the hexagonal {beta}-TiCl{sub 3}-type structure (P6{sub 3}/mcm, Z = 2) commonly assigned to many trihalides. The compound contains infinite chains of confacial (ZrI{sub 6}) octahedra that are distorted through pairing of the zirconium(III) atoms; d(Zr-Zr) = 3.172 (2) and 3.507 (2) {angstrom}. Data sets collected from the same crystal in the hexagonal setting were also refined in space groups P6{sub 3}/mcm and P{bar 6}2m; the latter provides nominally satisfactory residuals but an incorrect result with less tightly bound dimers. A more complex structure (which we did not study) applies to the compound near the oxidized limit ZrI{sub 3.4-3.5}. Other structural and property studies on ZrI{sub 3} and related phases are considered relative to these findings. A smaller pairing distortion in ZrCl{sub 3} seems probable because of the less restrictive chlorine matrix. A second-order phase transition is possible between the P6{sub 3}/mcm and Pmmm structures for these trihalides, and a continuous distortion from the equallymore » spaced metals atoms of the former model can be expected, especially as a function of temperature. 33 refs., 4 tabs.« less
Developers of the hepatitis B vaccine.
air at VA facilities, one of the many pieces of unfinished business beyond those major issues that we discussed in our Commentary. We agree that all facilities where current and past military personnel serve and receive treatment should be 100% smoke-free and note the recent Institute of Medicine report Combating Tobacco in Military and Veteran Populations. The report, which was commissioned by the Department of Defense (DOD) in 2007, calls for the DOD to set a timeline to eliminate smoking on military installations. The report also recommends that the DOD stop selling tobacco products in military commissaries and exchanges, prohibit tobacco use anywhere on military installations, and treat tobacco use in the same way as other health-related behaviors, such as alcohol abuse and poor physical fitness. We join Matthews and the Institute of Medicine in urging the VA and the DOD to take more immediate steps to protect the health of the men and women who serve in the armed services, as well as the civilians (such as Dr Matthews) working to serve them.