A solid-state hybrid density functional theory study of Prussian blue analogues and relatedchlorides at pressure

Abstract

The variations with pressure in the structural, electronic andmagnetic properties of a series of Prussian blue analogues (PBAs)KIMII[CrIII(CN)6] (M = VII,MnII andNiII) and associatedisomorphous chlorides KIMIICrIIICl6 are investigated within a series of solid-state hybrid density functional calculations. The sensitivityof the computed properties to the choice of Hamiltonian is tested by application of functionalscontaining 35%, 65% and 100% admixtures of Fock exchange. Magnetic coupling constants(J) are obtained at arange of cell volumes (V), with fits of the Bloch relationship (, ε typically 3–4)yielding exponents ε in the ranges 5.16–6.34, 8.48–12.07 and 4.00–4.51 for the antiferromagnetic (AF)VIICrIII-, ferrimagnetic(FI) MnIICrIII- andferromagnetic (FO) NiIICrIII PBAs, respectively; and 3.33–4.99, 1.86–3.09 and 1.65–3.28 for the AFVIICrIII-, FOMnIICrIII- and FONiIICrIII chlorides, respectively.The MnIICrIII PBA rangeencloses the high values ε∼9–10 obtained in a recent joint experimental and theoretical study, and it issuggested that this strong magnetostructural effect arises due to the presenceof competing AF and FO interactions in this material. Estimates of the spinordering temperatures derived from the combination of the 35%-functional couplingswith a mean field approach are in good agreement with experiment in theVIICrIII andNiIICrIII PBAs, but aretoo low in the MnIICrIII system. The variations with pressure in the structural parameters, charges and spinmoments are also detailed, the PBA and chloride energy–volume data yielding bulk moduliin the ranges 39–53 and 36–50 GPa, respectively. Finally, the energies governingCN– ligand isomerization are estimated and successfully interpreted in terms of a simple crystalfield stabilization model.