Hydrothermal reactions of cadmium(II) or manganese(II) salts with aryl arsenic acids RAsO3H2 (R = C6H5-, H2L1; 3-NO2-4-OH-C6H3-, H3L2) and 1,10-phenanthroline (phen) led to six new cadmium(II) and manganese(II) organo arsonates, namely, Cd(phen)(HL1)(2)(H2O) (1), M(phen)(H2L2)(2) (M = Mn, 2; Cd, 3), [M(phen)(2)(H2L2)](ClO4) center dot (H2O) (M = Mn, 4; Cd, 5), and [Mn(phen)(2)(HL1)](ClO4) center dot (H2O) (6). The structures of 1, 4, and 5 contain two types of dinuclear clusters, whereas 2 and 3 exhibit 1D chains based on dinuclear M-2(mu-O)(2) cluster units further bridged by arsonate ligands. Compound 6 features a 1D helical chain in which neighboring two metal centers are bridged by one arsonate ligand. Magnetic property measurements on compounds 2, 4, and 6 indicate that there exist very weak antiferromagnetic interactions between magnetic centers in all three compounds. Compounds 1-6 display typical ligand-centered fluorescence emission bands.