Cu₂{[18]ane-N₆} Complexes: Structures, Magnetism, and Phosphate Monoester Binding

A novel CuII2 complex of the [18]ane-N6 macrocycle ([18]ane-N6 = 1,4,7,10,13,16-hexaazacyclooctadecane) was prepared from the reaction between [18]ane-N6 and CuII salts such as Cu(NO3)2 and Cu(OAc)2. A structural study of the complex derived from Cu(OAc)2 (1) revealed a CuII2 core encircled by a [18]ane-N6 ligand and two μ-O-OAc ligands. The facile replacement of μ-O-OAc by a phosphate monoester [PO3(OR)2-] yielded a number of bis(phosphate monoester)dicopper complexes with ROPO32- as hydrogen phosphate (HPO42-, 3a), phenyl phosphate [PO3(OPh)2-, 3b], glycerol 2-phosphate [PO3(OCH(CH2OH)2)2-, 3c], α-d-gluocose phosphate [PO3(C6H11O6)2-, 3d], and dl-α-glycerol phosphate [PO3(OCH2CHOHCH2OH)2-, 3e]. Structural studies of compounds 3a−d confirmed both the retention of the Cu2{[18]ane-N6} core and a μ-O-PO3(OR) coordination mode. Displacement of acetate by a phosphate monoester in an aqueous solution was accompanied by a significant change in the visible absorption, which enables the establishment of relative association constants of PO3(OR)2- on the order of 104 in the unbuffered solution and 103 in the buffered solution (HEPES). Measurement of the magnetic susceptibility of compound 3a over the temperature range of 5−300 K and subsequent modeling revealed a weak antiferromagnetic coupling (J = −1.1 cm-1) between two CuII centers.