Boric acid flux synthesis, structure and magnetic property of MB12O14(OH)10 (M=Mn, Fe, Zn)

Three new borates MB12O14(OH)10 (M=Mn, Fe, Zn) have been synthesized by boric acid flux methods, which are isotypic to NiB12O14(OH)10. Single-crystal XRD was performed to determine the crystal structures in detail. They all crystallize in the monoclinic space group P21/c. The size of MO6 (M=Mg, Mn, Fe, Co, Ni, Zn) octahedron shows a good agreement with the Shannon effective ionic radii of M2+. Magnetic measurements indicate MnB12O14(OH)10 is antiferromagnetic without a long-range ordering down to 2 K. The values of its magnetic superexchange constants were evaluated by DFT calculations, which explain the observed magnetic behavior. The UV–vis diffuse reflectance spectrum of ZnB12O14(OH)10 suggests a band gap ∼4.6 eV. DFT calculations indicate it has a direct band gap 4.9 eV. The optical band gap is contributed by charge transfers from the occupied O 2p to the unoccupied Zn 4s states. - Graphical abstract: Experimental and theoretical studies indicate MnB12O14(OH)10 is antiferromagnetic without a long-range ordering. DFT calculations show ZnB12O14(OH)10 has a direct band gap of 4.9 eV. Highlights: ► MB12O14(OH)10 (M=Mn, Fe, Zn) are synthesized by two-step boric acid flux method. ► Single-crystal XRD was performed to determine the crystal structures in detail. ► Size of MO6 (M=Mg, Mn, Fe, Co, Ni, Zn) agrees with the effective ionic radii. ► MnB12O14(OH)10 is antiferromagnetic without a long-range ordering down to 2 K. ► DFT calculations indicate ZnB12O14(OH)10 has a direct band gap 4.9 eV