Bis(trithiacyclononane)metal(II) compounds and Jahn-Teller distortions from octahedral geometry, electrochemistry, spectroscopy, and crystal structures of the copper bis(tetrafluoroborate) bis(acetonitrile) complex at 177 K and the cadmium bis(tetrafluoroborate) and copper bis(tetrafluoroborate) bis(nitromethane) complexes at 300 K

Abstract

The structures and the EPR spectra are described of compounds with formula M(ttcn) 2(A) 2, with ABF 4 −; MCu, Cd, Fe and the Cu(II)-doped Cd(II) and Fe(II) compounds. Single crystal structures are described for the copper compound Cu(ttcn) 2(BF 4) 2(MeCN) 2 ( 1) at low temperature, and for the cadmium compound Cd(ttcn) 2(BF 4) 2(MeNO 2) 2 ( 2) and copper compound Cu(ttcn) 2(BF 4) 2(MeNO 2) 2 ( 3) at room temperature. Compound 1 crystallizes in the space group P2 1/ c with a=20.695(2), b=14.944(1), c=8.864(1) Å, β=90.797(8)° and Z=4. The unit cell contains two crystallographically independent Cu ions, each at a crystallographic inversion center, which are structurally almost identical. The copper ion with the CuS 6 2+ chromophore appears to be nearly octahedral, just as found earlier for the room temperature structure. Relevant Cu-S distances are for Cu(A): 2.407, 2.419 and 2.458 and for Cu(B): 2.407, 2.428 and 2.461 Å. Compound 2 also crystallized in the space group P2 1/ c with a=10.314(2), b=15.138(2), c=9.461(2) Å, β=99.39(1)° and Z=2. The Cd(II) ion is octahedrally surrounded by six S atoms at almost equal distances varying from 2.649 to 2.663 Å. Compound 3 crystallizes in the space group Pbca with a=19.746(2), b=15.422(2), c=9.227(1) Å and Z=4. The copper ion occupies a crystallographic inversion center. The copper ion is significantly distorted from an octahedral arrangement of the six coordinated sulfur atoms with Cu-S distances ranging from 2.343(2) to 2.504(2) Å. Cyclic voltammetric studies on Cu(ttcn) 2 2+ in aqueous buffer at pH 3 show a reversible one-electron reduction with E o'=0.408(1) V versus AgCl/Ag reference. EPR spectra were recorded of the pure copper compound acetonitrile solvate, as well as of Cu(II) dopes in the isomorphous Fe(II) and Cd(II) compounds. The results indicate that in the case of the undiluted copper compound only a single signal ( g=2.06) is observed even down to 4 K, thereby not providing any evidence of a Jahn-Teller splitting. However, Cu(II) dopes in the isomorphous, diamagnetic Fe(II) compound show anisotropic signals below 100 K, with values for g∥ and g ⊥ of 2.113 and 2.027, respectively ( A∥=153 G). At room temperature a complex spectrum of isotropic and anisotropic lines is observed. Dopes in the corresponding Cd compounds show well-resolved spectra, with parameters similar to the Fe(II)-doped species. Heat capacity measurements on compound 3 show no phase transition in the temperature range 1.2–300 K. Such measurements on compound 1 show phase transitions near 90 and 150 K.