A novel Cu-2(II) complex of the [18] ane-N-6 macrocycle ([18]ane-N-6 = 1,4,7,10,13,16-hexaazacyclooctadecane) was prepared from the reaction between [18] ane-N-6 and Cu-II salts such as Cu(NO3)(2) and Cu(OAc)(2). A structural study of the complex derived from Cu(OAc)(2) (1) revealed a Cu-2(II) core encircled by a [18]ane-N-6 ligand and two mu-O-OAc ligands. The facile replacement of mu-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], R-D-gluocose phosphate [PO3(C6H11O6)(2-), 3d], and DL-alpha-glycerol phosphate [PO3(OCH2CHOHCH2OH)(2-), 3e]. Structural studies of compounds 3a-d confirmed both the retention of the Cu-2{[18] ane-N-6} core and a mu-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 10(4) 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 Cu-II centers.