In situsynthesis of magnesium hydroxides modified with tripodal ligands in an organic medium

Abstract

Layered magnesium hydroxides modified organically with tris(hydroxymethyl)aminomethane (Tris-NH) were directly synthesized from magnesium chloride dissolved in a polar organic solvent, like dimethyl sulfoxide (DMSO), containing a small amount of water. Tris-NH acted as a base for precipitating magnesium hydroxides as well as an organic modifier. In contrast to the case of an aqueous solution, the use of organic solvents substantially increased the degree of modification of layered magnesium hydroxides with Tris-NH owing to the formation of bidentate Mg-O-C linkages by Tris-NH in addition to its tridentate bonding mode. Bidentate linkages, hydrolyzed readily in water, are stable in the organic media. Pentaerythritol (Tris-CHOH), trimethylolethane (Tris-CH), and trimethylolpropane (Tris-CH) were also successfully used for the synthesis of organically-modified layered magnesium hydroxides by the addition of tetrabutylammonium hydroxide as a base with DMSO as the solvent. The synthesis of hybrid magnesium hydroxides in organic solvents is expected to expand the chemistry of organically modified layered metal hydroxides with various metallic species and a wide variety of organic functional groups.

Selective Covalent Modification of Layered Double Hydroxide Nanoparticles with Tripodal Ligands on Outer and Interlayer Surfaces

“…20 This implies that some of the tripodal ligands are bonded to the layer with bidentate linkages. 21 The particle size is similar to that of CoAl_Tris_inter(HT) (Figure 4c). Consequently, interlayer-modified LDHNPs were synthesized using Co 2+ or Ni 2+ as a divalent cation of LDHs.…”

“…We have previously reported that suppression of the hydrolysis is important for the formation of hybrid metal hydroxides whose interlayer surfaces are modified with tripodal ligands, from the study on the synthesis of hybrid metal hydroxides in organic media. 21 It is reasonable to apply this hypothesis also for synthesizing interlayer-modified LDHNPs, with certain modifications. The major difference between hybrid metal hydroxides and interlayer-modified LDHNPs is the layer charge; that is, metal hydroxides and LDHNPs consist of neutral and positively charged brucite-type layers, respectively.…”

“…Our previous studies on the synthesis of hybrid hydroxides using organic solvents have demonstrated that the stability of the bonds to hydrolysis depends strongly on the number of bonding sites. 21 Whereas only tridentate bonds are stable in water, both tridentate and bidentate bonds are stable in organic solvents. By comparing results obtained using various metal species, we also observed that constituent metals with higher electronegativity form more stable tridentate bonds because of the alteration in the stability of each M−O−C bond.…”

Hydrolysis of Methoxylated Nickel Hydroxide Leading to Single-Layer Ni(OH)2 Nanosheets

“…The SEM images of Ni–OMe reveal that Ni–OMe is the dense aggregate (Figure S4a) composed of nanoparticles of size 10–20 nm (Figure S4b). The XRD pattern of Ni–OMe shows broad diffraction peaks characteristic of interlayer-modified brucite-type metal hydroxides with small crystallites (Figure b). ,, The peak at d = 0.84 nm can be assigned to diffraction from the basal plane. The expanded basal spacing compared to the thickness of one Ni­(OH) 2 layer ( d 001 = 0.46 nm for β-Ni­(OH) 2 , JCPDS #14-0117) indicates that methoxy groups are immobilized on the surface of the stacked layers.…”

“…In order to overcome this issue, we propose the use of organic ligands forming mono or bidentate alkoxy bonds, which are susceptible to hydrolysis, as removable surface modifiers. Our previous study has shown that the use of nonaqueous solvents is effective for the modification of metal hydroxides with alkoxy groups, which are hydrolyzed in aqueous solvents . Therefore, nonmodified nickel hydroxide nanosheets can be prepared by the preparation of hybrid layered nickel hydroxides modified with mono or bidentate alkoxy bonds in an organic solvent and the subsequent hydrolysis of surface modifiers after exfoliation.…”