Cu(HCO2)2(pym) (pym = pyrimidine):: low-dimensional magnetic Behavior and long-range ordering in a quantum-spin lattice

We synthesized and structurally and magnetically characterized the novel 3D coordination polymer Cu(HCO2)2-(pym) (pym = pyrimidine). The compound crystallizes in the monoclinic space group C2/c with a = 14.4639(8) Å, b = 7.7209(4) Å, c = 8.5172(5) Å, β= 126.076(2)°, and V = 768.76(7) Å3. In the structure buckled layers of Cu(HC02)2 are interconnected by pym ligands to afford 1D Cu-pym-Cu chains. Bulk magnetic susceptibility measurements show a broad maximum at 25 K that is indicative of short-range magnetic ordering. Between 12 and 300 K a least-squares fit of the χ(T) data to a mean-field-corrected antiferromagnetic chain model yielded excellent agreement for g = 2.224(3), J/kB = -26.9(2) K, and zJ′lkB = -1.1(3) K. Below ∼3 K a transition to long-range magnetic ordering is observed, as suggested by a sharp and sudden decrease in χ(T). This result is corroborated by muon spin relaxation measurements that show oscillations in the muon asymmetry below TN = 2.802(1) K and rapidly fluctuating moments above TN.