Uranyl ion complexes with 2,2′:6′,2′′-terpyridine-4′-carboxylate. Interpenetration of networks involving “expanded ligands”

Abstract

2,2′:6′,2′′-Terpyridine-4′-carboxylic acid (tpycH) has been used as a ligand in the synthesis of four uranyl ion complexes under solvo-hydrothermal conditions. The homometallic complex [(UO₂)₂(tpyc)(HCOO)(OH)₂] (1) contains additional hydroxide and formate anions generated in situ and it crystallizes as a monoperiodic coordination polymer in which uranyl cations are bound to both the carboxylate group and the terpyridine N₃ site. Addition of Pb^II gives the heterometallic complex [UO₂Pb(tpyc)(HCOO)₂(OH)(H₂O)₂] (2), in which uranyl is bound to the carboxylate group while lead(II) occupies the N₃ site, further hydroxide- and formate-bridging resulting in a diperiodic arrangement. Both complexes [UO₂Ni(tpyc)₂(OH)(H₂O)]·NO₃·1.5H₂O (3) and [(UO₂)₂Ni₂(tpyc)₄(O)(H₂O)₄]·(NO₃)₂·6H₂O (4) contain the neutral, octahedral Ni(tpyc)₂ “expanded ligand” unit, the uranyl cations being bound to the divergent carboxylate groups and to bridging hydroxo or oxo groups. Complex 3 crystallizes as a heavily corrugated diperiodic assembly in which hydroxo-bridged dinuclear secondary building units are the nodes of a network of sql topology. Chiral, diperiodic polymers with the same topology but a different shape and which are involved in twofold parallel interpenetration, are formed in 4.