¹⁸⁵ Re‐ und ¹⁸⁷ Re‐NQR‐Untersuchungen an Trimethylsilyl‐ und Trimethylgermanyl‐perrhenat

Abstract

Eingegangen a m 25. Marz 1974 In den NQR-Spektren von polykristallinem (CH3)3SiOReq und (CH,)jGeOReO, wurden alle erwarteten Frequenzubergange q(+ fund *87Re aufgefunden und zur Bestimmung der Quadrupol-Kopplungskonstanten und des Asymmetrieparameters ausgewertet. Die erhaltenen g r o k n Werte fur eZqQ/h und q weisen eine direkte kovalente Bindung der metallorganischen Reste mit dem Perrhenat-Ion nach. Die Elementarzellen der Kristalle enthalten alle Re-Atome in iiquivalenten Positionen. IESRe-and 187Re-NQR-Investigations of Trimethylsilyl and Trimethjrlgermanyl PerrbenateAll transitions YI (& t f ) and v2 (* f G? f 5 ) required by theory have been detected in the NQR spectra of (CH3)3SiOReO, and (CHj),GeOReO3 for l*5Re and I87Renuclei. These results have been evaluated to yield quadrupole coupling constants and asymmetry parameters q. The data obtained are evidence for true covalent bonding between the organometallic groups and the perrhenate anion. The unit cells of the crystals contain all Re nuclei at equivalent sites.

Bis(triphenylphosphine)silver(i) perrhenate, a cyclic dimer

“…21 Detailed 185,187 Re NQR measurements have confirmed that in this ester the ReO 4 tetrahedron is indeed strongly distorted. 22 Similar overall characteristics were found for organogermanium, -tin and -indium perrhenates. [23][24][25][26][27] The combination of perrhenate with the heavy coinage metals, Ag and Au, is poorly presented in the literature.…”

Bis(triphenylphosphine)gold(I) Perrhenate

“…The crystal structure of the trimethylsilyl compound ( R = Me) has been determined [22] and shown to have a conventional ester structure with the Si atom attached specifically to one of the oxygen atoms in an angular array. This covalent bonding has also been confirmed by 185,187 Re NQR spectroscopy studies which showed a high asymmetry parameter η for the Re atom, while for alkali perrhenates with largely undistorted ReO 4 − tetrahedra the η value deviates only slightly from zero [23]. Similar characteristics have later been found for the corresponding germanium [24] and tin compounds [25,26], the latter being aggregated through an increase in the coordination number of the tin atoms and with the ReO 4 units functioning as bridging units employing two of their four oxygen atoms.…”

Anomalous Temperature Dependence of the 127I-Quadrupole Coupling in (C6H5)4PIO4, (C6H5)4AsIO4 and (C6H5)4SbIO4

“…According to Mooberry, Spiess and Sheline [8] the orientational change of the principal axes of the EFG-tensors q ik is the reason for this remarkable behaviour. Schmidbaur, Koth and Burkert [11,12] observed similar phenomena of the 185 Re and ,87 Re NQR transitions in the compound (CH 3 ) 3 Ge0Re0 3 due to the same effect.…”

“…(a) the breakdown of d n -p n backbonding [3,4] (b) the occurrence [5] of sufficiently large negative pressure coefficients (9v/9p) T (c) charge transfer from n-to a-orbitals of adjacent atoms [6, 7] (d) continuous orientational change of the principal axes system of the electric field gradient (EFG) tensors q ik [8][9][10][11][12] (e) influence of reorientational motions [13 -18].…”