(R,r)-Tartrate As a Polytopic Ligand for UO22+: Mono- and Diperiodic Coordination Polymers Including Di- and Tetranuclear Subunits

(R,R)-Tartaric acid (H4tart) has been reacted with uranyl nitrate hexahydrate under solvo-hydrothermal con-ditions, in the presence of either [Ni(R,S-Me6cyclam)]2+ (R,S-Me6cyclam = 7(R),14(S)-5,5,7,12,12,14-hexam-ethyl-1,4,8,11-tetraazacyclotetradecane), quinH+ (quinuclidinium), or [Ni(bipy)3]2+ (bipy = 2,2MODIFIER LETTER PRIME-bipyridine), to give three complexes characterized by their crystal structure. [H2NMe2]2[(UO2)2(Htart)2(HCOO)2Ni(R,S- Me6cyclam)].2H2O (1) crystallizes as a monoperiodic coordination polymer in which dimeric [UO2(Htart)]22- subunits are linked by nickel(II) cations. The structure of the dimers matches that expected from solution ex-periments but not previously found in the solid state. Both [Hquin][(UO2)2(tart)(CH3COO)] (2) and [Ni(bipy)3] [(UO2)2(tart)(CH3COO)]2 (3) crystallize as diperiodic networks based on tetranuclear [(UO2)2(tart)(CH3COO)]22- subunits which contain a central U2O2 ring involving mu 2-bridging alkoxide groups. Further chelation of the two lateral uranyl cations by the carboxylate groups of adjacent subunits yields a sql-type network. Due to the different bulk of the counterions, the layers are quasi-planar in 2 and corrugated in 3. Comparison of these polynuclear subunits with those formed by the related ligands citrate, R,S-malate and R-citramalate shows that while the dimeric form is common to all, the tetranuclear subunit is specific to the tartrate ligand.