Synthesis and structure of magnesium hydroxide fluoride, Mg(OH)F: a topological intermediate between brucite- and rutile-type structures

Abstract

Magnesium hydroxyfluoride, Mg(OH)F, has been synthesized by a subcritical hydrothermal route from a 1:1 molar mixture of brucite, Mg(OH)2, and sellaite, MgF2 with a rutile type structure, in excess water. Using a combination of synchrotron X-ray and time-of-flight neutron powder diffraction, the structure of Mg(OH)F has been solved in the diaspore space group Pnma with a = 10.116(3), b = 4.6888(10) and c = 3.0794(7) Å at ambient conditions. The most intense diffraction lines are [dobs (hkl) Iobs]: 2.291 (211) 10, 4.253 (101) 7, 1.747 (212) 7, 2.229 (401) 6 and 1.480 (610) (4) Å, with the largest d-spacing at 5.058 Å. Sharp infrared stretching bands are located at 3679 and 3645 cm–1, with a broader band at 3535 cm–1. The topology of the structure is intermediate between that of the OH and F endmembers, being derived through notional shearing nearly normal to the sheets of octahedra of the CdI2/Mg(OH)2-type structure. Further similar shearing at an interval 1/2a would lead to a Cd(OH)F-type structure, which is also related to the rutile structure type. The observations and model presented here indicate a close correlation between the structural properties of the endmembers and Mg(OH)F.

Synthesis and characterization of the crystal structure and magnetic properties of the hydroxyfluoride MnF2−x(OH)x (x ∼ 0.8)

“…O H F 0.89 (17) 2.05(17) 2.803 (19) 142 (15) This is qualitatively the same as that of the parent tetragonal MnF 2 , although the moment value determined from the NPD data at 3 K, 4.71(3) m B , is slightly lower than the theoretical value for high-spin d 5 Mn 2+ , probably due to chemical disorder of F À and OH À . It is not surprising that the magnetic structure is practically identical to that of MnF 2 despite strong distortion of the crystal structure.…”

“…However, since the connectivity between these polyhedra is different, one-to three-dimensional empty channels have been observed (Fig. [15][16][17][18][19][20][21][22][23] Recently, during our attempts to synthesize the LiMOF (M = Mn, Fe, and Co) compositions, we obtained new M(OH)F compounds. This structural feature has attracted considerable attention from electrochemists (ref.…”

“…The M(OH)F (M = Mg, Co, Ni, Cu, Zn, Cd, and Hg) compounds do indeed exist and their crystal structures are strongly related to the a-, band g-MnOOH polymorphs. [15][16][17][18][19][20][21][22][23] Recently, during our attempts to synthesize the LiMOF (M = Mn, Fe, and Co) compositions, we obtained new M(OH)F compounds. Fe(OH)F crystallizes with the diaspore a-AlOOH structure, whereas MnF 2Àx (OH) x (x B 0.8) crystallizes with a distorted rutile structure related to the CaCl 2 -type.…”

Synthesis and characterization of MgF2–CoF2 binary fluorides. Influence of the treatment atmosphere and temperature on the structure and surface properties

“…79 and 83) and by many earlier reports on hydroxylated MgF 2 . 1,35,36,40,[47][48][49][84][85][86][87] Verdier et al 79,83 ascribed them to the Mg(OH) 2Àx F x species. The presence of surface complexes of such a type is indicated by the values of DE F 1s -Mg 2p that are equal to 634.5-634.7 eV, which in the case of crystalline MgF 2 are about 633 eV and in that of Mg(OH) 2Àx F x they range between 634.5 and 635.0 eV.…”

Tailoring the composition of fluoride conversion coatings to achieve better corrosion protection of magnesium for biomedical applications

“…56)). Crichton et al 57 have shown that F À ions could be incorporated in Mg(OH) 2 (brucite) and OH À ions could be incorporated in MgF 2 (sellaite) to a very considerable degree. Substitution of OH À ions by F À ions in brucite was suggested by Booster et al 58,59 as well as by Verdier et al 55 The reaction between HF and Mg(OH) 2 was theoretically studied using ab initio density functional theory with periodic boundary conditions by Vaiss et al 60 They have proposed a mechanism in which the reaction between HF and Mg(OH) 2 occurs by the following steps: (i) adsorption of the HF molecule on brucite (eqn (3)); (ii) OH À liberation from brucite as a water molecule (eqn (4)); (iii) desorption of the newly formed H 2 O (eqn (5)); and (iv) rearrangement of the F À ion into a hydroxyl position, resulting in the formation of Mg(OH) 2Àx F x (eqn (6)): a GC refers to galvanic coupling; the numbers inside the parenthesis represent the cathodic to anodic area ratio.…”