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(HCO2)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‘/kB = −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.