Tris(1,2-dimethyl-3-hydroxy-4(1H)-pyridone)oxotantalum(v): a new water-soluble tantalum complex containing the [Ta=O]3+ core

The synthesis, the characterization and the X-ray crystal structure of a novel tantalum(v) complex tris(1,2-dimethyl-3-hydroxy-4(1H)-pyridone)oxotantalum(v) [TaO(C7H8O2N)3] 1 is reported. Starting from the tantalum pentaethoxide a two-step reaction was carried out observing rigorous anhydrous conditions in methanol in the first step, while the insertion of the oxo group was achieved using water as oxygen donor in the second step. X-Ray diffraction analysis of a crystal of 1 obtained upon evaporation of an aqueous solution shows a seven-coordinate monomeric complex containing the [Ta=O]3+ core in the triclinic space group P1, a = 7.282(3), b = 14.055(5), c = 16.987(6) A, alpha = 65.704(5), beta = 89.155(6), gamma = 75.270(6) degrees, V = 1525(1)A3, Z = 2. Spectroscopic investigation reveals that the complex is highly soluble and stable in water at physiological pH values; as a consequence the complex may represent a potential candidate for the development of new studies on aqueous tantalum(v) chemistry for radiopharmaceutical applications.     

Reactions of [MCl6]2− (M=Tc or Re) with salicylaldehyde. The molecular structure of tetraphenylphosphonium tetrachloro(salicylaldehydato) technetate (IV)

Summary The [PPh₄][TcCl₄(sal)] and [PPh₄][ReOCl₃(sal)] (sal=o-OC₆H₄CHO) complexes were synthesized from [PPh₄]₂[MCl₆] (M=Tc or Re) and salicylaldehyde. The complexes were characterized by elemental analysis, magnetic susceptibility and conductivity measurements and i.r. spectrometry. The structure of [PPh₄][TcCl₄(sal)] was determined by x-ray methods and consists of well-separated units of octahedral [TcCl₄(sal)]^– anions and tetrahedral [PPh₄]⁺ cations. The equatorial plane of the octahedron is formed by two Cl atoms and the chelated(2) sal group, with the resulting TcCl₂(sal) unit approximately planar. Selected values in the anion are as follows: Tc-Cl(mean) 2.34(1), Tc-O(1) 2.04(2) and Tc-O(2) 1.98(2), O(1)---O(2)(byte) 2.83 Å; O(1)-Tc-O(2) 89.3(0.7)^o.     

Translational diffusion in smectic-A phases

On the basis of a diffusion equation including a periodic potential, exact expressions are given for the longitudinal and transverse diffusion parameters measured in unaxial smectic phases by spin-echo NMR. For relatively high values of the ordering potential, an intrinsic Airhenius factor appears in the definition of the rate of jump across the smectic layers.     

Monooxorhenium(V) complexes with the tridentate Schiff baseN-(2-hydroxyphenyl)salicylideneimine

Summary The reactions of the tridentate Schiff base ligandN-(2-hydroxyphenyl) salicylideneimine (HOPhsalH) with oxotetrachlororhenate (IV) have been investigated. The complexes (Bu₄N)[ReOCl₃(HOPhsal)], (Bu₄N)[ReOCl₂(OPhsal)],cis- [ReOCl(MeOH)(OPhsal)],trans-[ReOCl(MeOH)(OPhsal)] (1), trans-[ReOCl(OH₂)(OPhsal)] · Et₂O (2), trans-[ReOCl(OH₂)(OPhsal)] · Me₂CO,cis-[ReOCl(PPh₃)(OPhsal)],cis-[ReOCl(PMe₂Ph)(OPhsal)](3) have been synthesized and characterized. The crystal structures of(1), (2) and(3) have been solved from three-dimensional x-ray data by Patterson and Fourier methods and refined by least-squares methods to R 0.10 for(1), 0.042 for(2) and 0.059 for(3). In all the three complexes, the ligands surrounding the rhenium atom are at the apices of a distorted octahedron, with the equatorial ONO donor atoms of the tridentate Schiff base bent away from the O_oxo and toward the loosely bound MeOH in(1), H₂O in(2) and Cl in(t3). The fourth equatorial substituent is Cl (1 and2) and PMe₂Ph(3) and the rhenium atoms lie 0.30–0.37 Å above the best plane through the four equatorial atoms, in the direction of the O_oxo. All interatomic distances and angles are normal.