A series of new diazamesocyclic ligands based on a diazamesocycle, 1,5-diazacyclooctane (DACO), functionalized by additional donor groups-1,5-bis(N-1-methylimidazol-2-ylmethyl)-1,5-diazacyclooctane (L-1), 1-(2-hydroxybenzyl)-1,5-diazacyclooctane (HL2), 1,5-bis(2-hydroxybenzyl)-1,5-diazacyclooctane (H2L3), and 1-(N-1-methylimidazol-2-ylmethyl)-1,5-diazacyclooctane (L-4)-and their Cu(II) complexes have been synthesized and characterized. Single-crystal X-ray diffraction analysis of the four Cu(II) complexes revealed that L-1 forms a five-coordinate mononuclear complex, HL2 a N-3(-) mu-bridged binuclear complex, H2L3 an oxygen mu-bridged trinuclear complex, and L-4 a one-dimensional zigzag coordination polymeric complex with Cu(II). [(CuLClO4)-Cl-1](ClO4) (I): a = 12.194(2) Angstrom, b = 13.351(3) Angstrom, c = 14.473(3) Angstrom, beta 107.10(3)degrees, Z = 4. [CuL2(N-3)](2) (II): a 8.1864(6) Angstrom, b = 18.141(2) Angstrom, c = 9.3307(7) Angstrom, beta = 103.662(6)degrees, Z = 2. [Cu-3(L-3)(2)Cl-2] (III): a = 10.7296(13) Angstrom, b = 13.7707(17) Angstrom, c = 13.5523(17) Angstrom, beta = 106.350(3)degrees, Z = 2. ([(CuLCl)-Cl-4](2)ClO4)(infinity) (IV): a = 7.279(1) Angstrom b = 23.695(5) Angstrom, c = 19.308(4) Angstrom, beta = 100.28(3)degrees, Z = 8. All four complexes crystallize in the monoclinic crystal system with the P2(1)/(c) space group, and each Cu(II) center coordinated with DACO is pentacoordinated with a distorted square-pyramidal or trigonal-bipyrimidal coordination environment. Tn complex IV, the binuclear cation unit [(CuLCl)-Cl-4](2)(2+) constitutes the fundamental building block of an infinite alternating zigzag chain structure, and the binuclear unit contains two types of geometries around the Cu(II) centers: the Cu(1) center is a distorted square-pyramidal environment, while the Cu(2) is a distorted trigonal-bipyramidal coordination environment. To the best of our knowledge, this is the first Cu(II) complex of a diazamesocyclic ligand with an infinite polymeric structure. The magnetic properties of complexes II, III, and IV have been investigated by variable-temperature magnetic susceptibility measurements in the solid state. The obtained parameters are 2J = 2.06 cm(-1) (II), -345.56 cm(-1) (III), and -2.60 cm(-1) (IV), which differ greatly from ferromagnetic to weak and strong antiferromagnetic coupling. These results unequivocally indicate that the nature of the pendant arms is a key factor governing the structure and properties of the complexes; therefore, the coordination modes and properties of the metal complexes of a diazamesocycle can be controlled by altering the pendant donors on it. Magneto-structural correlation has been precisely analyzed, and the solution properties of these complexes have also been described.