The oxomolybdenum-arsonate system was investigated under hydrothermal conditions in the presence of charge-compensating copper(II)-organonitrogen complex cations as secondary building blocks. A series of materials of the Mo/O/As/Cu/ligand family has been prepared and structurally characterized. The architectures of the products reflect the identity of the arsonate component and the organonitrogen ligand, as well as the reaction conditions. The structural versatility of this emerging class of compounds is manifested by the one-dimensional structures of [{Cu(o-phen)(H2O)(2)}(2)Mo6O18(O3AsOH)(2)] (1), [{Cu(terpy)}(2)Mo4O13H(ASO(4))(2)].2H2O (2-2H(2)O), [{Cu(2,2'-bpy)(H2O)}(2)-Mo6O18(O(3)ASC(6)H(5))(2)].2H(2)O (4-2H(2)O), and [{Cu(o-phen)(H2O)}(2){Mo6O18(O3AsC6H5)(2)}].4H(2)O (5-4H(2)O), by the two-dimensional materials [{CU2(tpyprz)(H2O)(2)}Mo6O18(O3AsOH)(2)].2H(2)O (3-2H(2)O), [{Cu(terpy)}(2)Mo6O18(O3AsC6H5)(2)].H2O (6-H2O), and [{Cu-2(tpyprz)}Mo6O18(O3AsC6H5)(2)].2H(2)O (7.2H(2)O), and the molecular clusters [{Cu(2,2'-bPY)(2)}(2)Mo12O34(O3AsC6H5)(4)].2.35H(2)O (8-2.35H(2)O) and [Cu(o-phen)(H2O)(3)][Cu(o-phen)(2)Mo12O34 (O(3)ASC(6)H(5))(4)].3H(2)O (9.3H(2)O).