Hydrothermal synthesis, crystal structure, and spectroscopic and magnetic properties of a new organically templated mixed-anion fluoro-arsenate–phosphate iron(III) compound, (C 6H 14N 2)[Fe 3(HAsO 4) 1.33(HPO 4) 0.67(AsO 4) 0.84(PO 4) 0.16F 4]0.5(H 2O)

Abstract

The new organically templated mixed-anion fluoro-arsenate–phosphate iron(III) compound, with formula (C 6H 14N 2)[Fe 3(HAsO 4) 1.33(HPO 4) 0.67(AsO 4) 0.84(PO 4) 0.16F 4]0.5(H 2O), has been synthesized by using mild hydrothermal conditions under autogeneous pressure. The crystal structure has been solved from X-ray single crystal data. The unit-cell parameters are a=18.267(1), b=10.085(1), c=20.436(2) Å, β=105.97(1)°. Monoclinic, C2/ c with Z=8. The structure consists of a three-dimensional inorganic framework formed by [Fe 3(HAsO 4) 1.33(HPO 4) 0.67(AsO 4) 0.84(PO 4) 0.16F 4] 2− inorganic layers linked by hydrogen-arsenate/phosphate anions. There are three iron atoms crystallographically independent per unit-formula. The sheets are constructed from Fe(1)Fe(3)O 6F 4 and Fe(2) 2O 8F 2 dimeric units with edge-sharing octahedra. The 1,4-diazabicyclooctane dications are located inside the cavities of the inorganic skeleton. The IR and Raman spectroscopies confirm the simultaneously existence of both the arsenate/hydrogenarsenate and phosphate/hydrogenphosphate anions. From the diffuse reflectance spectrum the Dq=1080 and Racah parameters B=1040 and C=2620 cm −1 for the d 5-high spin iron(III) cation in octahedral geometry have been calculated. The Mössbauer spectrum at room temperature is characteristic of high spin iron(III) cations. The ESR spectra are isotropic with a g-value of 1.99(1), which remains unchanged with variation in temperature. Magnetic measurements indicate the presence of antiferromagnetic interactions with a maximum in the susceptibility at around 6.0 K.