One-dimensional single-chain molecular magnet with a cross-linked π–π coordination network [{Co^II(Δ)Co^II(Λ)}(ox)₂(phen)₂]_n

Abstract

A one-dimensional single-chain molecular magnet [{Co^II(Δ)Co^II(Λ)}(ox)₂(phen)₂]_n with a cross-linked π–π coordination network has been synthesized hydrothermally and investigated for its structural and magnetic properties. Oxalate (ox) ligands bridge the paramagnetic Co^II metal ions, whereas phenanthroline (phen) ligands exhibit π–π coordination networks. The compound has been thoroughly investigated using room-temperature X-ray and neutron diffraction, infrared spectroscopy, dc magnetization, and reverse Monte Carlo (RMC) simulation methods. Rietveld refinement of the powder X-ray and neutron diffraction patterns at room temperature confirms the single-phase formation of the compound in the monoclinic structure with a space group P21. Structural analysis reveals that the compound assembles in the form of a one-dimensional zigzag chain-like structure. Chains consist of two asymmetric Δ- and Λ-Co^II ions and a π–π coordinating network bridged by ox and phen ligands, respectively. The chain lies in the crystallographic ac plane, infinite in length with the absence of interchain π–π overlap. dc magnetization data fitted over the high-temperature regime (T > 5 K) using the Ising chain model reveals the one-dimensional magnetic nature of the compound with alternately spaced magnetic Co^II sites with two different Landé g factors and exchange coupling constant values. Different Landé g factors (2.5 and 2.1) and negative exchange coupling constant values (−108 and −20 K) at two alternating Co^II sites indicate a ferrimagnetic behavior of this chain compound. In the low-temperature regime (T < 5 K) the compound exhibits spontaneous magnetization and hysteresis at 1.6 K, due to the occurrence of long-range three-dimensional (3-D) magnetic ordering. A prominent clustering of the C atoms around the Co atoms is ascertained by RMC analysis of diffuse scattering in the neutron diffraction pattern. The pair correlations distances between Co–Co, Co–C, Co–N, and Co–O atoms are found to be 5.0, 2.2, 2.5, and 2.4 Å, respectively, for the compound.