Solid-Phase “Self-Hydrolysis” of [Zn(NH3)4MoO4@2H2O] Involving Enclathrated Water—An Easy Route to a Layered Basic Ammonium Zinc Molybdate Coordination Polymer

Abstract

An aerial humidity-induced solid-phase hydrolytic transformation of the [Zn(NH3)4]MoO4@2H2O (compound 1@2H2O) with the formation of [(NH4)xH(1−x)Zn(OH)(MoO4)]n (x = 0.92–0.94) coordination polymer (formally NH4Zn(OH)MoO4, compound 2) is described. Based on the isostructural relationship, the powder XRD indicates that the crystal lattice of compound 1@2H2O contains a hydrogen-bonded network of tetraamminezinc (2+) and molybdate (2−) ions, and there are cavities (O4N4(μ-H12) cube) occupied by the two water molecules, which stabilize the crystal structure. Several observations indicate that the water molecules have no fixed positions in the lattice voids; instead, the cavity provides a neighborhood similar to those in clathrates. The @ symbol in the notation is intended to emphasize that the H2O in this compound is enclathrated rather than being water of crystallization. Yet, signs of temperature-dependent dynamic interactions with the wall of the cages can be detected, and 1@2H2O easily releases its water content even on standing and yields compound 2. Surprisingly, hydrolysis products of 1 were observed even in the absence of aerial humidity, which suggests a unique solid-phase quasi-intramolecular hydrolysis. A mechanism involving successive substitution of the ammonia ligands by water molecules and ammonia release is proposed. An ESR study of the Cu-doped compound 2 (2#dotCu) showed that this complex consists of two different Cu2+(Zn2+) environments in the polymeric structure. Thermal decomposition of compounds 1 and 2 results in ZnMoO4 with similar specific surface area and morphology. The ZnMoO4 samples prepared from compounds 1 and 2 and compound 2 in itself are active photocatalysts in the degradation of Congo Red dye. IR, Raman, and UV studies on compounds 1@2H2O and 2 are discussed in detail.

Thermally Induced Solid-Phase Quasi-Intramolecular Redox Reactions of [Hexakis(urea-O)iron(III)] Permanganate: An Easy Reaction Route to Prepare Potential (Fe,Mn)Ox Catalysts for CO2 Hydrogenation

“…The heat-induced quasi-intramolecular redox reactions of [ML n ]­(XO 4 ) m complexes containing reducing ligands and oxidizing anions (where M = Cu, Zn, Cd, Co; L = NH 3 or pyridine, n = 2–6, and m = 0.5–3, and X = Mn, Cl, S, or Mo) in a solid phase ensure a convenient way to prepare simple or mixed-transition metal oxides with nanometer-sized particles. − These oxides, including nanosized iron oxide composites, − are active catalysts in various industrially important processes as their structures contain defects and their metallic components have variable valence states. − …”

Electronic, magnetic, optical properties, and morphological characteristics of nanocrystalline based on zinc–cobalt molybdate prepared by soft chemistry route

“…Based on the theoretical group analysis, the total number of factor group modes due to the regular molybdate MoO 4 tetrahedron is 4 and corresponds to 9 vibrations modes possible in the molybdate compounds. We note that all four modes are Raman active, but only the antisymmetric (T d ) modes are IR active [30,31].…”

“…The Zn-O-Mo mode is designated as a wideband system around 650 cm -1 [31]. The bands observed at 433 and 435 cm -1 are specific to the bending vibration of the Co-O-Mo bands [39].…”

“…Recently, in 2017, Ghiyasiyan-Arani et al [20] investigated the effect of different parameters on the sonochemical synthesis of FeVO 4 nanocomposite. The diversity of the synthesis processes (hydrothermal [21][22][23], microwave irradiation [24,25], Pechini [26,27], sonochemical route [28], solid-solid [29,30], molybdate complexes: ligand loss [31,32] and co-precipitation [33,34]), and preparation conditions (pH, temperature, time...) have a huge influence on the microstructure and morphology of the obtained powders.…”

Structural and Raman spectroscopic characterization of tetrapyridinesilver(I) perrhenate, [Agpy4]ReO4

“…An easy way to prepare catalytically active simple or mixed transition metal oxides is a lowtemperature thermal treatment of transition metal tetraoxometallate (ClO4 -, MnO4 -, SO4 2-, MoO4 2-) complexes with reducing ligands like ammonia [1][2][3][4][5] or pyridine. [6][7][8][9][10] The key factor in the occurrence of the solid-phase quasi-intramolecular redox reactions resulting in these oxide materials is the presence of a hydrogen bond between the N-H or C-H functional groups of the ligand and the M-O moiety of the anion.…”