Dimethylammonium copper formate [(CH3)2NH2]Cu(HCOO)3: A metal-organic framework with quasi-one-dimensional antiferromagnetism and magnetostriction

Metal-organic frameworks (MOFs) can exhibit many interesting properties such as multiferroic behavior, dipolar glass, gas storage, and protonic conductivity. Here we report that dimethylammonium copper formate (DMACuF) [(CH3)(2)NH2]Cu(HCOO)(3), a cation templated nonporous MOF with perovskite topology, exhibits strong one-dimensional (1D) antiferromagnetism with a Neel temperature, T-N, of 5.2 K. These conclusions are derived from detailed magnetic susceptibility, heat capacity, dielectric constant, and high-frequency electron paramagnetic resonance measurements as well as density functional theory (DFT) calculations. The magnetic susceptibility exhibits a broad maximum at similar to 50 K, suggesting low-dimensional magnetism; heat capacity measurements show a Neel temperature of 5.2 K. The magnetization versus field data at 1.8 K shows a spin-flop transition at H-sf similar to 1.7 T. The ratio T-N/J = 6.5 x 10(-2), where J is the near-neighbor exchange constant (77.4 K), and the small value (2 K) of the interchain coupling suggests that DMACuF is close to an ideal 1D magnet. In this three-dimensional crystal lattice, the 1D magnetic behavior is made possible by the Jahn-Teller distortion of the 3d(9) Cu2+ ions. Temperature dependence of the electron paramagnetic resonance field and the linewidth exhibits critical broadening for temperatures below 50 K, following a behavior quite characteristic of 1D spin systems. DFT calculations show that [(CH3)(2)NH2]Cu(HCOO)(3) has a magnetic structure in which 1D antiferromagnetic chains parallel to the c direction are weakly coupled ferromagnetically, supporting the thermomagnetic and EPR results. Dielectric measurements under applied magnetic fields of 0-7 T reveal a kink at the T-N, a clear indication of magnetostriction behavior.