Optical and Magnetic Properties of Cu-Containing Borates with “Antizeolite” Structure

Abstract

Crystals of copper-doped barium fluoride borate solid solutions Ba 3 (BO 3 ) 2−x F 3x :Cu were grown from hightemperature solution. Using X-ray single-crystal diffraction, the structure was solved and refined in Pbam space group. These crystals are colored in brown, revealing linear dichroism. Optical and electron spin resonance spectroscopic investigations concluded that the light absorption of Ba 3 (BO 3 ) 2−x F 3x :Cu crystals is caused by both the exciton and f ree charge carriers. This phenomenon is similar to those observed in other colored "antizeolites" built with the positively charged framework of porous [Ba 12 (BO 3 ) 6 ] 6+ building blocks (hence named as antizeolites). The coloring of Ba 3 (BO 3 ) 2−x F 3x :Cu crystals is associated with the absorption of Cu 2+ ions as well. For the first time, constants of the hyperfine interaction of copper ions Cu 2+ in octahedral fluorine surroundings [CuF 6 ] 4− have been determined.

Crystal Chemical Design of Functional Fluoride Borates with “Antizeolite” Structure

“…Earlier it was shown that OH – groups can substitute fluorine and oxygen anions in the structure of antizeolite borates, that is, OH – → F – , OH – + e – → O 2– . , We believe that the replacement of lithium in the [LiF 4 ] 3– groups with Cu 2+ is accompanied by the replacement of the four fluorine anions in the [LiF 4 ] 3– groups and the two nearest oxygen anions of the intrachannel [BO 3 ] 3– groups with OH – groups. These lead to the formation of [Cu­(OH) 6 ] 4– octahedral complexes in the structure.…”

“…The data of X-ray diffraction analysis show that copper ions in the structure of Ba 3 (BO 3 ) 2– x F 3 x :Cu with Pbam space group may occupy both flat distorted octahedral [CuF 6 ] 4– and rectangular [CuF 4 ] 3– coordination of 19 F atoms . For the space group P4 2 bc in which the [Ba 12 (BO 3 ) 6 [BO 3 ]­[LiF 4 ] crystallizes, copper may occupy three positions: a and b with symmetry C 2 and c with symmetry C 1 .…”

“…42 Earlier it was shown that OH − groups can substitute fluorine and oxygen anions in the structure of antizeolite borates, that is, OH − → F − , OH − + e − → O 2− . 25,26 We believe that the replacement of lithium in the [ The splitting scheme of 3d 9 levels of Cu 2+ in a [Cu(OH) 6 ] 4− octahedron can be summarized as follows: a cubic field splits 3d 9 ( 2 D-term) into a lower orbital doublet involving d-orbital functions (x 2 − y 2 ) and (3z 2 − r 2 ) and an upper triplet xy, yz, zx (further referred to as d x where P f is the dipole term for the free Cu 2+ , which is 0.036 cm −1 , Δg = g − 2.0023, α 2 is the fraction of 3d x 2 −y 2 in the ground state of copper, and K is the Fermi contact term, which is usually taken to 0.43. Kuska and Rogers 45 established that K cannot be regarded as a constant value and instead of K we apply the constant of isotropic hyperfine splitting A.…”

“…In the crystal chemistry of inorganic borates in recent years, a cationic framework representation has been increasingly used. − A new class of “antizeolite” borates with positive porous framework [Ba 12 (BO 3 ) 6 ] 6+ allowing application of structure-oriented design strategy has been recently discovered. − This new class is anti-type to zeolites with negatively charged frameworks that host nonframework cations in their pore system for electrostatic charge compensation. It should be mentioned that such a term, antizeolite, was previously used for mayenite (Ca 12 Al 14 O 33 )-type compounds with [Ca 12 Al 14 O 32 ] 2+ framework building unit .…”

Experimental and Ab Initio Studies of Intrinsic Defects in “Antizeolite” Borates with a Ba12(BO3)66+ Framework and Their Influence on Properties

“…A recently discovered new class of “antizeolite” borates have made a contribution to the diversity of the crystal chemistry of borates. − They are built with a Ba 12 (BO 3 ) 6 6+ framework with channels along the c axis (Figure a), formed by altering barium-cube and anticube cages. In the case of the Ba 12 (BO 3 ) 6 [BO 3 ]­[BO 3 ] (Ba 3 B 2 O 6 ) “antizeolite”, which is a boron-enriched end member, both the anticubes and cubes are filled with disordered guest [BO 3 ] 3– groups (Figure b) .…”