Syntheses, Structures, and Solution Studies of Multicomponent Macrocycles and Cages Based on Versatile Ligands

摘要

Different types of multinuclear half-sandwich rhodium macrocycles and cages were designed and synthesized by using two similar multifunctional hydroxamate ligands (pyrazine-2-hydroxamic acid (NaHL_1) and 4,4'-bipyridine-2-hydroxamic acid (KHL2)) featuring one monodentate site and two pairs of chelating sites. The Rh~(III)-Pd~(II) heterometallic macrocycles were constructed by using the semi-open palladium( II) source [Pd(en)Cl_2] with two free acceptor sites. However, only one kind of macrocycle was found when the shorter ligand L_1 was used, while in for the larger ligand, various spectroscopic techniques demonstrated the coexistence of hexanuclear and octanuclear macrocycles in solution and the proportions of both components depended on concentration and temperature. The palladium salt Pd(NO_3)_2, as a source of "naked" Pd~(2+), was introduced to assemble the cuboid-shaped cage composed of two types of metal ions and three types of organic ligands. In addition, two silver(I)-containing mixed-metal complexes bridged by pyrazine were obtained, in which two forms of decanuclear complex with C2v and C2h point symmetry cocrystallized-one is a polymeric structure and the other is a discrete cage. However, the third form, with D2 point symmetry, was found in the larger cage.