CuF2 Structural Changes in Two‐Dimensional Quantum Magnet (H2O)2(pyz) Under Pressure: Raman Study

Molecular magnetic materials are attracting considerable attention because of their possibility to modulate bulk magnetic properties by subtle synthetic variations. One of the strategies involves paramagnetic transition metal cations and organic bridging ligands such as pyrazine (pyz) to develop polymeric magnets [1]. In recently synthesized CuF2(H2O)2(pyz), the presence of hydrogen bonding interactions leads to long-range antiferromagnetic ordering below about 2.6 K [2]. Here, superexchange interactions between the magnetic Cu ions are facilitated due to the strong F•••H–O hydrogen bonds. The resulting two-dimensional (2D) antiferromagnetic square lattice is formed by the magnetic orbital of the Cu ion and characterized by spin-canting. In the crystal structure, uniform one-dimensional (1D) chains are composed of the pyrazine bridges that link the CuF2O2N2 octahedra together. The chains are linked through the hydrogen bonding to form a rigid threedimensional (3D) network. Each CuF2O2N2 octahedron exhibits an axial elongation due to the Jahn-Teller active Cu ion. Preliminary measurements of the pressure dependence of magnetization together with the structural parameters display a transition from 2D to 1D magnetization at about 0.8 GPa related to a pressure-induced switch of the Jahn-Teller axis [3]. This structural modification is connected with the transition to a higher symmetry phase at about 0.8 Gpa [3]. In order to probe microscopic lattice response of CuF2(H2O)2(pyz), we measured the Raman spectra under pressure. We observe pressure dependence for a couple of molecular modes.