Thyminato-bridged cyclic tetranuclear rhodium(III) complexes containing a sodium, calcium or lanthanoid ion as a template metal core

Abstract

Reactions of [(Cp∗Rh)2(μ-OH)3]OH (Cp∗=η5-C5Me5−) and thymine (=H2thym) in methanol in the presence or absence of a certain metal salt were examined. From the reaction mixture without any template metal salt, a dinuclear hydroxido-bridged complex bearing monodentate monodeprotonated thyminato ligands, [{Cp∗Rh(Hthym-κN1)}2(μ-OH)2], was isolated after recrystallization from water. In the presence of a metal salt MXn {=NaPF6, NaBF4, NaNO3, Ca(NO3)2, Ca(ClO4)2, La(NO3)3, Eu(NO3)3, Dy(NO3)3 and Er(NO3)3} were deposited orange crystals (1P, 1B, 1N, 2N, 2C, 3N, 4N, 5N and 6N, respectively) which consist of a thyminato(2-)-bridged tetranuclear Cp∗Rh complex incorporating a Mn+ cation, [(Cp∗Rh)4(μ-thym)4M]n+. All complexes were characterized by the single-crystal X-ray diffraction method, which revealed that homochiral aggregations of four RhIII centers were achieved to give metallacalix[4]arene-type clusters. It was also observed that the bridging modes of thym2− ligands were dependent on the template metal ion. In the Na+-incorporated clusters (1X, X=P, B or N) a thym2− ligand bridged two RhIII and the third Na+ ions with a μ3-1κN1:2κ2N3,O2:3κO2 mode, while in the Ln3+ analogs (Ln=La, Eu, Dy or Er: 3N–6N) thym2− exhibited a different bridging mode, μ3-1κN1:2κ2N3,O4:3κO2. In the cases of Ca2+-incorporated clusters, the bridging mode is further dependent on the associated anion; only the μ3-1κN1:2κ2N3,O2:3κO2-type cluster was obtained in the NO3− salt (2N), but the ClO4− salt (2C) afforded both types of the bridging clusters piled up alternatively in the crystals. The tetranuclear structures with a template metal cation, [(Cp∗Rh)4(μ-thym)4M]n+, are maintained in solution. The magnetic behaviors of the Dy3+- and Er3+-incorporated complexes (5N and 6N) are also reported.