Structures and Magnetic Behavior of 1-, 2-, and 3D Coordination Polymers in the Cu(II)−Dicyanamide−Pyrimidine Family

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 P21/c with a = 7.3569(5) Å, b =
13.4482(9) Å, c = 7.4559(5) Å, β = 98.984(3)°, and V = 728.6(1) Å and forms linear 1D chains. The second
compound, Cu(dca)(NO3)(pym)(H2O), 2, is also monoclinic, P21/n, with a = 7.6475(3) Å, b = 12.2422(5) Å, c =
11.0286(4) Å, β = 106.585(2)°, and V = 989.6(1) Å3. A 2D network structure consisting of both bridging μ-dca
and pym ligands is formed while the NO3- and H2O are axially bonded to the Cu center. Cu3(dca)6(pym)2·0.75H2O,
3, is triclinic, P1̄, with a = 7.7439(4) Å, b = 9.3388(5) Å, c = 10.1779(5) Å, α = 86.014(2)°, β = 88.505(2)°,
γ = 73.623(2)°, and V = 704.46(9) Å3. The structure of 3 is quite unique in that [Cu3(pym)2]6+ trimers are
interconnected via μ-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 μ-bonded pym ligands. Moreover, 2 shows a broad maximum in χ(T) at 40 K and behaves as a
uniform 1D antiferromagnetic chain with g = 2.09(1), J/kB = −42.6(1) K, and TIP = −66 × 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/kB = −69.4(5) K, θ = −0.28(3) K, and TIP = −180 × 10-6 emu/mol. It is found that μ-bonded dca
and pym ligands mediate very weak and very strong exchange interactions, respectively, between Cu2+ centers.