SYNTHESIS OF RUBIDIUM AND CESIUM TELLUROCARBOXYLATES AND AN X-RAY STRUCTURAL-ANALYSIS OF HEAVY ALKALI-METAL MONOCHALCOGENOCARBOXYLATES

A series of rubidium and cesium tellurocarboxylates (2 and 3) were syn thesized from the reaction of O-trimethylsilyl tellurocarboxylates (1) with rubidium and cesium fluorides in moderate isolated yields and ch aracterized by H-1, C-13, and Te-125 NMR spectroscopy and X-ray diffra ction. The carbon-oxygen distance [1.235(6) Angstrom] of the telluroca rboxyl group of crystalline cesium 2-methoxybenzenecarbotelluroate (3f ) showed a typical value of the carbon-oxygen double bond. The crystal packing of 3f shows the possibility of an interaction between the ces ium cation and the aromatic ring carbon. The thio- and selenocarboxyl groups of the corresponding sulfur and selenium isologues (4 and 5) al so indicate a double bond [1.231(4) and 1.226(5) Angstrom] between the carbon and oxygen, respectively. The salts (2 and 3) readily react wi th iodomethane to afford the corresponding Te-methyl tellurocarboxylat es in good yields. The reaction between 3 and tetramethylammonium chlo ride was found to give a novel quaternary ammonium salt (8) of telluro carboxylic acid, where the dihedral angle between benzene ring and the tellurocarboxyl group of 8 is ca. 90 degrees. Crystallographic data f or 3f, 4, 5, and 8 are as follows. 3f: P2(1)/n, a=7.182(2), b=12.161(5 ), c=12.151(3) Angstrom, beta=92.57(2)degrees, V=1060.2(6) Angstrom 3, d(calcd)=2.479 g cm(-3), Z=4, R=0.035, R(w)=0.043. 4: Pbca, a=8.995(2 ), b=29.936(2), c=7.291(1) Angstrom, V=1963.3(5) Angstrom(3), d(calcd) =2 030 cm(-3), Z=8, R=0.024, R(w)=0.021. 5: Pbca, a=9.290(1), b=30.207 (2), c=7.193(2) Angstrom, V=2018.5(3) Angstrom(3), d(calcd)=2.284 g cm (-3), Z=8, R=0.029, R(w)=0.020. 8: P2(1)2(1)2(1), a=11.844(2), b=14.01 4(2), c=8.650(1) Angstrom, V=1435.8(3) Angstrom(3), d(calcd),=1.558 g cm(-3), Z=4, R=0.044, R(w)=0.047.