Quasi-one-dimensional alternating spin-1/2 antiferromagnetism in perovskite metal formate framework [(NH2)2CH]Cu(HCOO)3.

Abstract

The formamidinium copper formate [(NH₂)₂CH]Cu(HCOO)₃(FMD-Cu) with a perovskite-like structure based on a nonporous metal-organic framework (MOF), is presented for its synthesis and magnetic properties. The magnetic properties and their couplings to the structure are derived from detailed magnetic susceptibility and heat capacity measurements. We also discuss the spin exchange couplings based on density functional theory (DFT) calculations. As a result, FMD-Cu exhibits the unusual quasi-one-dimensional antiferromagnetic (AFM) characteristics with the Néel temperatureT_N= 12.0 K and an intrachain coupling constantJ/k_B≈ 76.3 K. We also estimate the effective interchain couplingJ^*/k_B≈ 4.24 K, suggesting that FMD-Cu is close to an ideal candidate for one-dimensional magnet. Furthermore, the heat capacity shows a transition to an antiferromagnetic ordering state appears aroundT_N. Besides, the nonzero parameterγ= 0.089 J mol^-1K^-1obtained from the linear relationship,γT, to the low temperature-dependent zero-field heat capacity data, can be associated with the magnetic excitations in insulating quasi-one-dimensional AFM Heisenberg spin-1/2 chains. The experimental estimate and DFT calculations are entirely consistent with a model of FMD-Cu in which AFM exchange interactions originating from Jahn-Teller distortion of the Cu²⁺(3d⁹) ions, leaving a sublattice of coupled ferromagnetic (FM) chains. Hence, FMD-Cu is proposed as a canonical model of a quasi-one-dimensional Heisenberg spin-1/2 antiferromagnetic material.