Europium-151 Moessbauer effect study of several organoeuropium(II) complexes

Abstract

The europium-151 Moessbauer spectra of several organoeuropium(II) compounds have been measured at 77 and 4.2 K. All the compounds give isomer shifts of ca. {minus}12 to {minus}13 mm/s, typical of ionic europium(II). For (C{sub 5}Me{sub 5}){sub 2}Eu, (C{sub 5}Me{sub 5}){sub 2}Eu(THF), and (C{sub 5}Me{sub 5}){sub 2}Eu(THF)(Et{sub 2}O), broad absorptions were observed, arising from spherical paramagnetic relaxation at a rate comparable to the Moessbauer time scale of 9.7 {times} 10{sup {minus}9} s. The relaxation rates are 490, 450, and 420 MHz, respectively, at 4.2 K, and the values for (C{sub 5}Me{sub 5}){sub 2}Eu(THF) and (C{sub 5}Me{sub 5}){sub 2}Eu(THF)(Et{sub 2}O) increase to 635 and 650 MHz at 77 K as a result of greater coupling of the spin with the lattice vibrations. For ((C{sub 5}Me{sub 5})Eu(THF){sub 2}({mu}-I)){sub 2} the spectrum corresponds to a relaxation rate of 1,710 MHz at 4.2 K. ((C{sub 5}Me{sub 5})Eu(THF)){sub n} shows a symmetric spectrum that is close to the fast relaxation limit with an estimated relaxation rate of 5,580 MHz. EuI{sub 2}(THF){sub 2} shows a narrow line width spectrum with a quadrupole interaction of {minus}12.9 mm/s and an asymmetric parameter of 0.58 at 4.2 K. The rate of paramagnetic relaxation correlates well with the inverse of themore » distance between Eu(II) ions, suggesting that the relaxation occurs via a spin-spin interaction. The magnetic susceptibility of (C{sub 5}Me{sub 5}){sub 2}Eu, measured between 2 and 320 K, shows it to be paramagnetic in this temperature range with a moment of 6.99 {mu}{sub B} and a Curie-Weiss temperature of 3.28 K. 23 refs., 6 figs., 2 tabs.« less