Synthesis and structure of trans-[O2(TBP)4Tc]+ (TBP = 4-tert-butylpyridine) and related complexes

trans-K(3)[TcO(2)(CN)(4)]

The structure of the title compound, tripotassium trans-tetra-cyanidodioxidotechnetate(V), is isotypic with its Re analogue. The [TcO(2)(CN)(4)](3-)trans-tetra-cyanido-dioxido-technetate anion has a slightly distorted octa-hedral configuration. The Tc atom is located on a center of inversion and is bound to two O atoms in axial and to four cyanide ligands in equatorial positions. The Tc-O distance is consistent with a double-bond character. The two potassium cations, one located on a center of inversion and one in a general position, reside in octa-hedral or tetra-hedral environments, respectively. K⋯O and K⋯N inter-actions occur in the 2.7877 (19)-2.8598 (15) Å range.

trans-Bis[1,2-bis(dimethylphosphino)ethane]bromidonitrosyltungsten(0)

The crystal structure of the title compound, [WBr(NO)(C₆H₁₆P₂)₂], reveals a distorted octa­hedral geometry around the W centre. The W atom lies on a special position at an inversion centre (the Br and NO ligands are equally disordered). The bis­(dimethyl­phosphino)ethane ligand is also severely disordered (site occupancy factors 0.52 and 0.48). This is the first structure of a tungsten species with nitrosyl and bromide ligands.

Luminescence from the trans-Dioxotechnetium(V) Chromophore

The luminescence of trans-[TcO2(L)4]+ (L = pyridine (py) or picoline (pic)) and trans-[TcO2(CN)4]3- at room and low temperature is described and represents the first example of room temperature excited-state luminescence observed for Tc complexes. At room temperature, the complexes exhibited broad luminescence with emission maxima ranging from 745 to 780 nm. Analogous to the Re complexes (emission at 635-655 nm), the low-temperature emission spectra of microcrystalline samples of [TcO2(py)4]BPh4 and [TcO2(pic)4]BPh4 display the characteristic progressions of the symmetric O=Tc=O and Tc-L stretching modes. DFT/TDDFT calculations were performed on the trans-[MO2(L)4]+ (M = Re, Tc) congeners and predicted the dioxotechnetium emission to be 0.41 eV lower in energy than its Re analogue. Low-temperature lifetimes (8 K) ranging from 15 to 1926 mus for the series of Tc complexes are consistent with the Re analogues.

Synthesis and Crystal Structure of a New Type of Ionic Technetium(V) Dioxo Phosphine Complexes, [Tc(O)(2)(PR(3))(3)](+). Reactions with Pyridine and Crystal Structures of trans,cis,cis-[Tc(O)(2)(PR(3))(2)(py)(2)](+) Compounds

New ionic technetium complexes of the type [TcO(2)(PR(3))(3)](+) have been synthesized from the reaction of [TcO(4)](-) with the phosphine in methanol. The crystal structures of two crystallographic forms of [TcO(2)(PEt(3))(3)](BPh(4)) were determined. The first form is monoclinic, space group P2(1)/n with a = 14.353(3) Å, b = 11.731(2) Å, c = 26.478(6) Å, beta = 101.22(1) degrees, and Z = 4. The second form is also monoclinic, space group P2(1)/c with a = 10.043(3) Å, b = 21.122(4), c = 20.994(5) Å, beta = 97.43(2) degrees, and Z = 4. [TcO(2)(PPr(3))(3)](BPh(4)) belongs to the monoclinic C2/c space group with a = 34.097(7) Å, b = 16.944(4) Å, c = 19.033(4) Å, beta = 102.99(1) degrees, and Z = 8. The geometry around the Tc atom is a trigonal bipyramid with the two oxo ligands in the trigonal plane. The Tc-O bond distances are between 1.707(4) and 1.726(3) Å, while the Tc-P bonds vary from 2.507(2) to 2.528(2) Å for the axial ligands and between 2.395(1) and 2.403(1) Å for the equatorial bond. The O-Tc-O angles are in the range 141.5(2)-143.4(2) degrees. The reaction of these complexes with pyridine produced trans,cis, cis-[Tc(O)(2)(PR(3))(2)(py)(2)](+) (py = pyridine). [Tc(O)(2)(PMe(3))(2)(py)(2)](BPh(4)) is monoclinic, space group P2(1)/c with a = 30.346(8) Å, b = 12.865(4) Å, c = 21.464(9) Å, beta = 110.35(2) degrees, and Z = 8, while [Tc(O)(2)(PEt(3))(2)(py)(2)](BPh(4)) is monoclinic, space group P2(1)/c with a = 10.594(6) Å, b = 19.921(7) Å, c = 21.306(10) Å, beta = 95.31(5) degrees, and Z = 4. The geometry around the Tc atom is a distorted octahedron with the oxo ligands located in trans positions to each other, while the phosphine and the pyridine ligands are cis to each other.

Quantitative study of the structure-stability relationship of Tc complexes

By studying structural parameters (van der Waals radius and bond length from x-ray crystallography) of more than 100 known Tc compounds and using the cone packing model, a stability indicator of the Tc compounds was derived. The indicator is based on the solid angle factor sum (SAS), which is calculated from van der Waals radii and bond lengths between all coordinating atoms and Tc. The average SAS value is 0.97 +/- 0.13. The SAS value reflects the limits of the packing of ligand around Tc. The quantitative calculation of the SAS is useful for predicting stability and designing new Tc radiopharmaceuticals.