Heteropoly Blues. IV. Spectroscopic and Magnetic Properties of Some Reduced Polytungstates

Optical, electron spin resonance, and nuclear magnetic resonance spectra of aqueous solutions of one- and two-electron blues derived from eight 1:12- and 2:18-heteropolytungstates have been measured. Esr g values for the one-electron blues are characteristic of tetragonal W(V) complexes. No hyperfine structure (W-188, I = 1/2) was observed due to the broadness of the signals (100-200 G at 77 degrees). According to nmr and esr the two-electron blues are spin-paired at 77 and 310 K. The optical spectra of the reduced species show broad mixed-valence bands at 8-20 kK. The one- and two-electron heteropoly blues are regarded as class II mixed-valence species with trapped tungsten(V) valences and with intraionic electron transfer occurring at a rate which is slow on the esr time scale (<ca. 10(9) sec(-1)). Reduction of (CoW12O406-)-W-II and (FeW12O406-)-W-III leads to heteropoly blues containing Co(II) and Fe(III) central atoms which are effectively electronically isolated from the reduced tungstate networks.