Preparation and ESR studies of salts of crown ether complex cations and nitridotechnetium(VI) anions: structures of the twinned ‘infinite sandwich’ [Cs(18-crown-6)][TcNCl ₄ ] complex and of [Rb(15-crown-5) ₂ ] [TcNCl ₄ (OH ₂ )]

Abstract

We report the preparations and electron spin resonance (ESR) studies of a series of Cs + and Rb + crown ether (15-crown-5 and 18-crown-6) salts of [TcNCl 4 ] - and [MoOCl 4 ] - , and a new refinement of the X-ray structure of [Cs(18-crown-6)] [TcNCl 4 ] involving a twinned P4/n scattering model. This refinement addresses some unsatisfactory aspects of the original disordered model. The structure consists of an ‘infinite sandwich’ Cs + cation/crown ether configuration and polymeric [TcNCL 4 ] - anions, with Tc≡N distances of 1.561(36) Å, and anti-parallel chains of –––Tc≡N–––Tc≡N –––with Tc···Tc separations of 4.275(4) Å. The structure determination of [Rb(15-crown-5) 2 ][TcNCl 4 (OH 2 )] is also described and shows a lattice containing 2:1 ‘sandwich’-type crown ether/alkali-metal cations and isolated anions in the disordered lattice. The presence of Tc≡N infrared stretching frequencies at ca . 1074 cm -1 indicates the absence of strong electron donors coordinated to Tc in the sixth position (i. e. isolated anions), whereas the polymeric chain structure of [Cs(18-crown-6)] [TcNCL 4 ] is characterized by a Tc≡N stretching frequency of 1041 cm -1 . Three product compounds, the ‘infinite sandwich’ [Cs(18-crown6)][TcNCl 4 ], [Cs(18-crown-6)] [TcNCL 4 (OH 2 )] with two Tc≡N stretching frequencies at 1055 and 1046.5 cm -1 , and [Cs(18-crown-6) 2 ][TcNCl 4 containing 2:1 crown ether/Cs + ‘sand­wich’ cations and isolated [TcNCl 4 ] - anions, could be obtained from reaction of Cs + /18-crown-6 and [TcNCL 4 ] - depending on reaction conditions and solvent. The ESR spectra of [Cs(18-crown-6)] [TcNCl 4 ] over the temperature range 130-290 K indicate the presence of exchange interactions along the linear ––– Tc≡N––– Tc≡N––– chains. Spectra for other crown ether salts are consistent with isolated [TcNCL 4 ] - or [TcNCL 4 (OH 2 )] - anions, with dipolar broadening effects apparent.

[Tc(OH2)(CO)3(PPh3)2]+: A Synthon for Tc(I) Complexes and Its Reactions with Neutral Ligands

“…As in the other few complexes containing the mer -{Tc­(CO) 3 } + motif, ,− the bonds between Tc and the two carbonyl ligands in the trans -position to each other are weakened compared to the third CO ligand, which has another ligand (here water) in the trans -position. The Tc–O­(water) bond lengths are similar to those in other Tc complexes containing aqua ligands. − One of the few structural differences between the three solid-state structures are the C1–Tc–O10 and C3–Tc–O10 angles. They are significantly smaller (83.9(1)°, 86.9(1)) in the BArF 24 – salt than in the two hydrogen-bridged dimers (90.34(7)° to 93.20(8)°), in which the two carbonyl ligands are slightly bent away from the H-bonded anions.…”

“…Despite the importance of the technetium chemistry in aqueous media, there are surprisingly few structural reports about Tc complexes with aqua ligands. Of course, there are a number of oxido and nitrido complexes, where water sometimes appears as a strongly labilized ligand trans to O 2– and N 3– ; − but this is the most labile coordination position in such molecules, and the replacement of such aqua ligands does not represent a synthetic approach to stable ligand exchange products. In addition to some instable chlorido complexes of technetium­(V) and -(IV), − there exist to the best of our knowledge hitherto only three compounds, in which aqua ligands have been proven by X-ray structural analysis (Chart ).…”

Electron-Rich Nitrido-Bridged Complexes. Structure and Bonding in Triosmium Dinitrido Compounds

“…Interesting predictions about geometric and electronic structure have been put forward for electron-rich metallonitrides. For example, calculations suggest that metallonitride polymers with d n > d 2 will adopt symmetrically bridged structures rather than the very asymmetrically bridged structures found to date for structurally characterized linear chain metallonitrides. − More generally, control over the nature of M(N)M interactions should be possible via control of the metal electron count and electronic structure. These ideas, plus our longstanding interest in the nitrido ligand as a bridging group to link transition metals in polynuclear, oligomeric, and polymeric species, − ,− sparked our interest in the study of electron-rich polynuclear metallonitrides.…”

Anion⋯anion self-assembly under the control of σ- and π-hole bonds

“…Tetrachloro-nitrido-technetate anions adopt a square pyramidal geometry and afford matere bonded infinite chains 129,138 via the approach of the nitrogen to the σ-hole at technetium opposite to the TcN bond (Fig. 12).…”