Synthesis and structural characterization of tris[3-trifluoromethyl-5-(2-thienyl)pyrazolyl]hydroborato thallium, Tl[Tp(CF3,Tn)]: A monovalent thallium complex with a highly solvent dependent J(Tl-F) coupling constant, ranging from 0 to 850 Hz

The tris[3-trifluoromethyl-5-(2-thienyl)pyrazolyl]hydroborato thallium complex, Tl[Tp(CF3,Tn)], has been prepared via the reaction of 3-trifluoromethyl-5-(2-thienyl)pyrazole with KBH4 followed by metathesis with TlNO3. Both F-19 and Tl-203 NMR spectroscopies reveal the presence of an exceptionally large 850 Hz four-bond (4)J(Tl-F) coupling constant for Tl[Tp(CF,Tn)] in chloroform at room temperature; however, the observed coupling constant is highly solvent dependent and is reduced to 0 Hz in methanol, acetonitrile and dimethyl sulfoxide. The molecular structure of Tl[Tp(CF3,Tn)] has been determined by X-ray diffraction: Tl[Tp(CF3,Tn)] is triclinic, <P(1)over bar> (no. 2), a = 8.328(1), b = 11.432(2), c = 16.088(3) Angstrom, alpha = 70.58(2), beta = 82.90(2), gamma = 77.54(2)degrees, U = 1408(1) Angstrom(3), Z = 2 .