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)][TCNCL4] COMPLEX AND OF [RB(15-CROWN-5)2][TCNCL4(OH2)]

We report the preparations and electron spin resonance (ESR) studies o f a series of Cs+ and Rb+ crown ether (15-crown-5 and 18-crown-6) salt s of [TcNCl4]- and [MoOCl4]-, and a new refinement-of the X-ray struct ure of [Cs(18-crown-6)][TcNCl4] involving a twinned P4/n scattering mo del. This refinement addresses some unsatisfactory aspects of the orig inal disordered model. The structure consists of an 'infinite sandwich ' Cs+ cation/crown ether configuration and polymeric [TcNCl4]- anions, with Tc=N distances of 1.561(36) angstrom, and anti-parallel chains o f ---Tc=N---Tc=N---with Tc...Tc separations of 4.275(4) angstrom. The structure determination of [Rb(15-crown-5)2][TcNCl4(OH2)] is also desc ribed and shows a lattice containing 2: 1 'sandwich'-type crown ether/ alkali-metal cations and isolated anions in the disordered lattice. Th e presence of Te=N infrared stretching frequencies at ca. 1074 cm-1 in dicates the absence of strong electron donors coordinated to Te in the sixth position (i.e. isolated anions), whereas the polymeric chain st ructure of [Cs(18-crown-6)][TcNCl4] is characterized by a Tc=N stretch ing frequency of 1041 cm-1. Three product compounds, the 'infinite san dwich' [Cs(18-crown-6)] [TcNCl4], [Cs(18-crown-6)][TcNC14(OH2)] with t wo Tc=N stretching frequencies at 1055 and 1046.5 cm-1 and [Cs(18-crow n-6)2][TCNCl4] Containing 2:1 crown ether/Cs+ 'sandwich' cations and i solated [TcNCl4]- anions, could be obtained from reaction of Cs+/18-cr own-6 and [TcNCl4]- depending on reaction conditions and solvent. The ESR spectra of [Cs(18-crown-6)][TcNCl4] 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 cons istent with isolated [TcNCl4]- or [TcNCl4(OH2)]- anions, with dipolar broadening effects apparent.