(CNH)[FeFe(SO)(HO)]: A Framework Iron Sulfate with a Mixed = 2 and = 5/2 Honeycomb Lattice.

A new guanidinium-templated hydrated iron sulfate, [CNH][FeFe(SO)(HO)] (), was prepared from strongly acidic aqueous solutions. Its crystal structure is comprised from FeO and FeO(HO) octahedra linked by sulfate bridges forming a [FeFe(SO)(HO)] 3 framework with a layer-by-layer ordering of ferric and ferrous cations. The structural topology of the framework is related to the anhydrous rhombohedral mikasaite Fe(SO). The removal of part of the sulfate tetrahedra and the partial replacement of the Fe cations in the [Fe(SO)] framework by Fe provide a negative charge and allow the incorporation of the protonated organic species in the voids. The compound has been characterized by single-crystal X-ray diffraction, TG and DSC analyses, UV-vis-NIR spectroscopy, magnetic susceptibility, Mössbauer spectroscopy, IR and Raman spectroscopy, and density functional band-structure calculations. The magnetic behavior of shows an interplay of Fe ( = 2) and Fe ( = 5/2) sublattices that exhibit different types of antiferromagnetic couplings, one Fe-Fe ( ∼ 6.1 K) and two Fe-Fe couplings ( ∼ 1 K, ∼ 5.9 K) within corrugated honeycomb layers. These ferrimagnetic layers are coupled antiparallel to each other, resulting in an overall antiferromagnetic order below = 31 K.