Using aqueous conditions, three new coordination polymers containing Cu2+ cations, dicyanamide (dca) anions, and pyrimidine (pym) were isolated and structurally and magnetically characterized. Comprising the bulk of the product yield, Cu(dca)(2)(pym)(2), 1, crystallizes in the monoclinic space group P2(1)/c with a = 7.3569(5) Angstrom, b = 13.4482(9) Angstrom, c = 7.4559(5) Angstrom, beta = 98.984(3)degrees, and V = 728.6(1) Angstrom and forms linear 1D chains. The second compound, Cu(dca)(NO3)(pym)(H2O), 2, is also monoclinic, P2(1)/n, with a = 7.6475(3) Angstrom, b = 12.2422(5) Angstrom, c = 11.0286(4) Angstrom, beta = 106.585(2)degrees, and V = 989.6(1) Angstrom(3). A 2D network structure consisting of both bridging mu-dca and pym ligands is formed while the NO3- and H2O are axially bonded to the Cu center. Cu-3(dca)(6)(pym)(2)(.)0.75H(2)O, 3, is triclinic, P $(1) over bar $, with a = 7.7439(4) Angstrom, b = 9.3388(5) Angstrom, c = 10.1779(5) Angstrom, alpha = 86.014(2)degrees, beta = 88.505(2)degrees, gamma = 73.623(2)degrees, and V = 704.46(g) Angstrom(3). The structure of 3 is quite unique in that [Cu-3(pym)(2)](6+) trimers are interconnected via mu-dca ligands affording a complex 3D self-penetrating framework. Magnetically, 1 exhibits extremely weak exchange interactions along the Cu-(dca)(2)-Cu ribbons while 2 and 3 display very strong magnetic couplings mediated by the mu-bonded pym ligands. Moreover, 2 shows a broad maximum in X(T) at 40 K and behaves as a uniform 1D antiferromagnetic chain with g = 2.09(1), J/k(B) = -42.6(1) K, and TIP = -66 x 10(-6) emu/mol. An S = (1)/(2) trimer model that includes intertrimer interactions successfully described the magnetic behavior of 3, yielding g = 2.10(1), J/k(B) =,-69.4(5) K, theta = -0.28(3) K, and TIP = -180 x 10(-6) emu/mol. It is found that mu-bonded dca and pym ligands mediate very weak and very strong exchange interactions, respectively, between Cu2+ centers.