Synthesis and bonding analysis of pentagonal bipyramidal rhenium carboxamide oxo complexes

Seven-coordinate rhenium oxo complexes supported by a tetradentate bipyridine carboxamide/carboxamidate ligand are reported. The neutral dicarboxamide H2Phbpy-da ligand initially coordinates in an L4 (ONNO) fashion to an octahedral rhenium oxo precursor, yielding a seven-coordinate rhenium oxo complex. Subsequent deprotonation generates a new oxo complex featuring the dianionic (L2X2) carboxamidate (NNNN) form of the ligand. Computational studies provide insight into the relative stability of possible linkage isomers upon deprotonation. Structural studies and molecular orbital theory are employed to rationalize the relative isomer stability and provide insight into the rhenium-oxo bond order.

Complexation of rhenium with ethylenediaminetetraacetic acid: studies of technetium analogue using Raman spectroscopy

The complexation of rhenium, to the polyamino-polycarboxylate EDTA was investigated using Raman spectroscopy. Complexation occurred when ReVIIO4 - was placed in the presence of a Sn(II) reducing agent and EDTA. Rhenium complexation was confirmed by the Raman and UV/Vis spectra of the solution samples. Binding modes were assigned using the Raman spectra of a solid-phase sample. Three complexes are proposed, a six-coordinate dimer H4[Re2(μO)2(EDTA)2], a seven-coordinate monomer H2[ReO(EDTA)(OH2)2] and a mono-oxorhenium [ReO(EDTA)] 2- . The solubility of Re(IV)-EDTA complexes is greater than that of ReO4. If this behaviour is analogous to Tc, it is proposed that complexation to EDTA by Tc(IV) may increase the solubility and enhance the environmental transport of 99Tc from geological repositories.