2,2ʹ-Bipyridine Complexes. I. Polarized Crystal Spectra of Tris(2,2ʹ-bipyridine)copper(II), -nickel(II), -cobalt(II), -iron(II), and -ruthenium(II)
The electronic spectra of the 2,2ʹ-bipyridine (bipy) complexes of the type M(bipy)32 + are reported for the transition metal ions Cu(ll), Ni(II), Co(II), Fe(ll), and Ru(II). Polarized optical spectra of single crystals were obtained using the hexagonal crystal M(bipy)3Br2−6H20 and the inonoclinic crystal M(bipy)3S04−7H20. Both pure crystals and those diluted with Zn(II) were used. For the nickel and cobalt complexes Dq was found to be 1280 and 1270 cm−1, respectively, while B was found to be 710 and 790 cm−1. Trigonal splitting in these ions is apparently quite low judging from the small differences in band maxima in parallel and perpendicular components. Cu(bipy)32 + gives rise to a band v1 at 6400 cm-1 allowed in the perpendicular polarization (┴1_C3) and a second band v2 at 14,400 cm−1 allowed in both polarizations (┴, ‖C2). Constancy of the spectra in solutions and various crystals indicates that the complex is probably trigonal in all environments and that the strong Jahn-Teller forces are overcome by the rigidity of the ligand. The polarization data indicate that the assignments are 2E → 2A2for v1 and 2E → 2E for v2 and further that Dq is about 1170 cm−1while K is -2600 cm−1, an extraordinarily large value. Although these assignments are based on trigonal symmetry, the hypothesis of an octahedral field with a strong tetragonal component cannot be completely ruled out and obtains some support from electron spin resonance data. In the case of Fe(bipy)32+, a careful search was made for the d-d spectrum. Except for a shoulder at 11,500 cm−1 (1A1→3T1), it was concluded that the d-d spectrum is obscured by the intense charge-transfer spectrum. The data are con istent with a substantial increase in Dq upon spin pairing. The most likely value in the spin-paired complex appears to be between 1650 and 1900 cm−1. © 1966, American Chemical Society. All rights reserved.
Palmer, RA; Piper, TS; Noyes Laboratory, WA
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