Crystal-packing-induced antiferromagnetic interactions of metallocenes: cyanonickelocenes, -cobaltocenes, and -ferrocenes |
| |
Authors: | Altmannshofer Sandra Herdtweck Eberhardt Köhler Frank H Miller Robert Mölle Rüdiger Scheidt Ernst-Wilhelm Scherer Wolfgang Train Cyrille |
| |
Institution: | 1. Lehrstuhl für Chemische Physik und Materialwissenschaften, Universit?t Augsburg, 86159 Augsburg (Germany);2. Department Chemie, Technische Universit?t München, 85747 Garching (Germany), Fax (+49)?89‐2891‐3762;3. Laboratoire de Chimie Inorganique et Matériaux Moléculaires, UMR CNRS 7071, Université Pierre et Marie Curie, 4 Place Jussieu, 75252 Paris (France) |
| |
Abstract: | The cyano-substituted metallocenes M(C5H4CN)2] (M=Fe, 1; Co, 2; Ni 3) and M(C5Me5)(C5H4CN)] (M=Fe, 4; Co, 5; Ni, 6) were synthesized in yields up to 58 % by treating K(C5H4CN) or Tl(C5H4CN) with suitable transition-metal precursors. Cyclic voltammetry indicated that the oxidation and reduction potentials of all the cyanometallocenes were shifted to positive values by up to 0.8 V. Single-crystal X-ray structure analysis showed that 1 had eclipsed ligands, formed planes in the lattice, and--unlike usual metallocenes--lined up in stacks perpendicular to these planes. Powder X-ray studies established that 1 and 2 are isotypic. The 1H and 13C NMR spectra were recorded for all the new compounds. Signal shifts of up to delta=1500 ppm were recorded for the paramagnetic molecules 2 and 3 and were, at a given temperature, strikingly different for solution and solid-state spectra. These results pointed to antiferromagnetic interactions as a consequence of molecular ordering in the lattice, as confirmed by magnetic measurements. The temperature-dependent susceptibilities were reproduced by Heisenberg spin-chain models (H=-J sum n- 1 i=1 SiSi+1), thus yielding J=-28.3 and -10.3 cm(-1) for 2 and 3, respectively, whereas J=-11.8 cm(-1) was obtained for 3 from the Ising spin-chain model. In accordance with molecular orbital (MO) considerations, much spin density was found to be delocalized not only on the cyclopentadienyl ligand but also the cyano substituents. The magnetic interaction was interpreted as a Heitler-London spin exchange and was analyzed based on how the interaction depends on the singly occupied MOs and the shift of parallel metallocenes relative to each other. |
| |
Keywords: | cyclic voltammetry magnetic chains metallocenes NMR spectroscopy stacked molecules |
本文献已被 PubMed 等数据库收录! |
|