The Chemistry of Bivalent Tin

Structural, vibrational and electronic properties of SnMBO4 (M = Al, Ga): a predictive hybrid DFT study

We propose two new members of the mullite-type family, SnAlBO₄ and SnGaBO₄, and carry out an in-depth study of their crystal properties using the hybrid method PW1PW. Both are isostructural to PbMBO₄ (M  =  Fe, Mn, Al, Ga), which show axial negative linear compressibility (ANLC), among other interesting features. We find that, although Sn²⁺ is susceptible of being oxidized by oxygen, a suitable range of experimental parameters exists in which the compounds could be synthesized. We observe absence of ANLC below 20 GPa and explain it by the small space occupied by the lone electron pairs, as indicated by the small length of the corresponding Liebau Density Vectors. In agreement with this fact, the structures present a low number of negative mode-Grüneisen parameters, which may also suggest lack of negative thermal expansion. The electronic properties show a remarkable anisotropic behaviour, with a strong dependence of the absorption spectra on light polarization direction.

Recent advances in heterobimetallic catalysis across a “transition metal–tin” motif

This review focuses on the efficacy of catalysts, based on a transition metal–tin (TM–Sn) motif and crafted on a single scaffold, in mediating a wide variety of organic transformations.

The crystal structure of germanium dibromide*

Germanium dibromide (GeBr2) is monoclinic, P21/c, with a = 11.68, b = 9.12, c = 7.02 Å, β = 101.9°, and eight formula weights per cell. The crystal structure as determined by x-ray diffraction consists of layers of edge-sharing distorted GeBr6 octahedra parallel to {100} with bromine bridges linking the layers. Distortion of the octahedra gives rise to chains of vertex-sharing GeBr3 trigonal pyramids within the octahedral layers. The octahedral distortion in GeBr2 and other germanium halides may be an example of the second-order Jahn-Teller effect.

Technetium-99m-labeled platelets: comparison of labeling with a new lipid-soluble Sn(II)-mercaptopyridine-N-oxide and 99mTc-HMPAO

Platelets pretinned with a neutral Sn(II)-2-mercaptopyridine-N-oxide (SN-MPO) were labeled with 99mTc and compared to those labeled with 99mTc-HMPAO. The conditions of labeling platelets, e.g. concentrations of platelets and Sn(II)-MPO, 99mTc in ACD-saline or ACD-plasma media, pH and incubation time, were optimized using canine platelets. Moderate labeling efficiency was obtained with 20 micrograms of tin(II) chloride and 30 min incubation with Sn-MPO and pertechnetate. The viability of labeled platelets was determined by platelet recovery and platelet survival times in Beagle dogs. The labeling efficiency with platelets from 43 mL of blood was 62.8 +/- 7.6%. The platelet recovery was 35.7 +/- 5.0% and exponential survival time was 34.6 +/- 3.1 h compared to 43.3 +2- 12.0% and 29.5 +/- 3.3 h for 99mTc-HMPAO-labeled platelets. These values were significantly (P less than 0.01) lower than 111In-labeled platelets. Biodistribution in dogs indicates lower retention in blood, spleen and liver after some initial 99mTc excretion in urine. The platelet deposition with 99mTc platelets (Sn-MPO method) on polyurethane angio-catheters was similar to 99mTc-HMPAO-labeled platelets. This study indicates that the platelets could be successfully labeled with pertechnetate in a cost-effective manner for the evaluation of thromboembolic complications.

The chemistry of 99mTc-labeled radiopharmaceuticals

The subject of the chemistry of 99mTc-radiopharmaceuticals consists of a collection of bits and pieces of information without a unifying theme. Since the initial impetus to the field of organ imaging was provided by radiochemists, nuclear chemists, and clinician-investigators, using easily prepared 99mTc-compounds from available off-the-shelf ligands, complete chemical characterization was not carried for the 99mTc-radiopharmaceuticals and their metabolites. The influx of coordination, organic, and analytic chemists and their systematic studies clarified some of the structures of these tracers, and promoted the general synthetic methods of a variety of ligands and the corresponding 99mTc-chelates as well as understanding of the nature of their metabolites. Although major developments for organ-imaging radiopharmaceuticals had been made, future studies will result in the simplified methodology of protein-labeling, fine-tuning of the currently available radiopharmaceuticals for higher organ-extraction, and replacement of expensive 123I-labeled tracers with the corresponding 99mTc-tracers. In general, the Tc-complexes are thermodynamically less stable and kinetically more labile than the corresponding Re-complexes. The well established chemistry of Re-compounds, the similarity of Tc-chemistry to that of Re compounds, and structure-activity relationships of a few classes of 99mTc-labeled compounds, may promote the development of new generation of 99mTc-labeled radiopharmaceuticals.