Synthesis, X-ray characterization, and Q-band electron spin resonance studies of heterometallic, polymeric compounds formed by yttrium and lanthanide(III) nitrates with HgL2(L = C4H6NO, the anion of 2-pyrrolidone); crystal structures of [{Hg2EuL4(NO3)3}n] and [{Hg2Tb2L6(NO3)6}n]

Abstract

The complex HgL₂(L = C₄H₆NO, the anion of 2-pyrrolidone) reacts with lanthanide(III) nitrates, Ln = La to Gd (Pm not studied), in methanol to give [{Hg₂LnL₄(NO₃)₃}_n], and with Y and Ln = Tb to Yb to yield [{Hg₃Y₂L₆(NO₃)₆}_n] and [{Hg₃Ln₂L₆(NO₃)₆}_n] respectively. Each set of compounds forms an isostructural series, representative members of which, Ln = Eu and Tb respectively, have been characterized by single-crystal X-ray diffraction methods. Both compounds form polymeric chains involving 16-membered macrocycles. They differ in that the europium complex comprises continuous chains of rings interlocked at the lanthanide ion, whereas in the terbium compound each macrocycle is separated from its neighbour by an additional HgL₂ unit. In both instances the lanthanide ion is nine-co-ordinate and the polymeric chains are cross-linked by nitrate anions. Q-Band e.s.r. spectra were obtained for gadolinium(III)-doped powder samples of seven of the complexes and also for [{Hg₂ThL₄(NO₃)₄}_n] and the zero-field splitting parameters, D and λ, were obtained from the allowed transitions. Additional, much weaker sets of bands in the low-field (0–725 mT) region arising from various off-axis, in-plane and off-axis, out-of-plane turning points of forbidden (ΔM_s≠±1) transitions are reported and assigned.