Pressure-Induced Local Structure Distortions in Cu(pyz)F₂(H₂O)₂

Abstract

We employed infrared spectroscopy along with complementary lattice dynamics and spin density calculations to investigate pressure-driven local structure distortions in the copper coordination polymer Cu(pyz)F(2)(H(2)O)(2). Here, pyz is pyrazine. Our study reveals rich and fully reversible local lattice distortions that buckle the pyrazine ring, disrupt the bc-plane O-H···F hydrogen-bonding network, and reinforce magnetic property switching. The resiliency of the soft organic ring is a major factor in the stability of this material. Interestingly, the collective character of the lattice vibrations masks direct information on the Cu-N and Cu-O linkages through the series of pressure-induced Jahn-Teller axis switching transitions, although Cu-F bond softening is clearly identified above 3 GPa. These findings illustrate the importance of combined bulk and local probe techniques for microscopic structure determination in complex materials.

Implications of bond disorder in a S=1 kagome lattice

“…These interactions have proven fruitful to realize materials sensitive to external stimuli such as high pressure 12–14 or high electric fields 15 . Over the past decade, we have focused on the design, synthesis and physical characterization of open-shell transition metal coordination complexes, molecules and polymers, based on Cu(II) ( S  = 1/2), Ni(II) ( S  = 1) and Co(II) ( S  = 3/2) ions that contain the poly-HF adducts HF 2 − , H 2 F 3 − and H 3 F 4 − which have been shown, on occasion, to be effective mediators of magnetic exchange interactions 16–22 .…”

Evolution of magnetic interactions in a pressure-induced Jahn-Teller driven magnetic dimensionality switch

“…2(d)] can be explained in terms of the effect of pressure on the crystal structure and the magnetic exchange ligands. The decrease seen in J within the Q2D phase is due to the increase in the β-angle between the a and c axes [11], which leads to a misalignment of Cu-pyz-Cu chains and causes them to begin to slide past each other [19]. This serves to severely disrupt the H• • • F bonded network, decreasing the efficiency of magnetic coupling along the Cu-OH• • • F-Cu exchange pathways and thus reducing J.…”

“…The steady increase in J with applied pressure within the Q1D regime is because unlike the soft H• • • F bonded layers, the Cu-N bonds and the pyrazine rings are relatively resilient, and so no major distortions are seen within the Cu-pyz-Cu chain in the Q1D regime [11,19]. This resiliency, together with the decrease in the chain length with applied pressure [11], enhances the magnetic d-orbital density overlap along the chain and results in the increase in J.…”

Pressure‐Driven Orbital Reorientations and Coordination‐Sphere Reconstructions in [CuF2(H2O)2(pyz)]

“…The application of pressure in the study of molecule-based materials has gained considerable recent interest, in part due to the high compressibilities of these materials, but also because the relevant electronic/magnetic (low-energy) degrees of freedom in such materials are often very sensitive to pressure. [1][2][3][4][5][6][7][8][9][10][11] For example, small changes in the coordination environment around a magnetic transition-metal ion can produce quite dramatic variations in both the on-site spinorbit coupling as well as the exchange interactions between such ions when assembled into three-dimensional (3D) networks. [2][3][4][5] However, perhaps the most compelling reason to use pressure as a tool for understanding magneto-structural correlations is the possibility of focusing investigations on a single molecule or material, as opposed to using chemical means to influence the coordination environment around a metal center, for example, by studying families of seemingly related complexes that vary only in the identity of the coordinating ligands.…”

“…According to previous high-pressure studies performed on powder samples this phase change is reversible. [9,10] However, the single-crystal sample becomes polycrystalline upon release of the pressure. Moreover in the present investigation, the first phase modification is not observed until substantially higher pressures are achieved (about 1.8 GPa as opposed to 1.0 GPa [9] see also the EPR data below).…”