Zinc oxalate

Zincite). ZnO, mw 81.38, white or yellowish-white amorph odorless powd with a bitter taste, mp 1975° (subl and decomps), d 5.47—5.606 g/cc. V si sol in w. sol in mineral acids, dil acet acid and NH4OH. Coml prepn is from Zn or ores such as Franklinite or Zinc Blende by vapzn in a CO atm with subsequent oxidation of the vapors with preheated air. Lab. prepn is by converting anhya zinc oxalate to ZnO by heating at... 

The rate equation [eqn. (26)], given above for the reaction of magnesium oxalate, is also obeyed [1012] by the decomposition of zinc oxalate (620—646 K), although here the catalytic (second) term is dominant, so that behaviour approximated to the Prout—Tompkins equation [eqn. (9)]. The value of E (201 8 kJ mole 1) was the same as that found... 

C18-0033. Zinc oxalate, Zn(C2 O4), is sparingly soluble in water (Zjp = 1.4 X 10 ). The Zn ion forms a tetrahedral-shaped complex with ammonia. The formation constant for the complex is 4.1 X 10. How many moles of zinc oxalate will dissolve in 1.0Lof0.200M aqueous ammonia ... 

Figure 9.4 The effect of sintering temperature on the morphology of zinc oxide particles. Zinc oxide from zinc oxalate (a) 400 °C, (b) 800 °C. Carmox zinc oxide (c) 400 °C, (d) 800 °C (Prosser Wilson, 1982). 

None 100 Zinc formate 44 Zinc carbonate 42 Zinc sulfate 43 Zinc oxalate 39 Zinc chloride 8 Zinc acetate 7 Zinc benzoate 2 Zinc 3,5-di-tert-butyl-4-hydroxybenzoate 1... 

Maass and Eigen have shown for the zinc acetate system fos " 32 — 3.2 X 107 sec."1 The rate of loss of water from zinc equals the rate of loss of a carboxylate group from zinc. This means that the ion pair and inner sphere species of zinc acetate are present in solution in equal amounts. If we now examine the zinc oxalate system we see that we have similar rate steps. 

The properties of the complexes Zn[Cr04] and Zn[Cr04] 3.5Zn(OH)2 H20 have been investigated their reduction by CO (formed in situ from the decomposition of zinc oxalate) leads to the formation of species containing catalyticaliy active Crv and Cr111 centres.680,681... 

In our studies of the open-framework zinc oxalates, we have recently isolated monomeric, dimeric, ID linear chain, 2D layer, and 3D structures by the reaction of amine oxalates with Zn2+ ions,21 suggesting thereby that the presence of a hierarchy of structures is not unique to the phosphates alone. We believe that the evidence provided by our studies for the existence of an Aufbau principle of open-framework complex structures is of considerable significance. Many other complex inorganic structures are also likely to be formed by similar building-up processes, involving basic building units and self-assembly. 

Vaidhyanathan, R. Natarajan, S. Rao, C. N. R. Synthesis of a hierarchy of open-framework zinc oxalates from amine oxalates, communicated. 

The discussion in the previous sections should suffice to indicate the importance of the transformations of molecular compounds to materials. Studies of such transformations are only making a beginning, and there appears to be a great future for such investigations, Thus, the recent synthesis of a sodalite-related structure from a molecular zinc phosphate is noteworthy, besides the transformation of the centrosymmetric, tetrameric, molecular alumino-phosphate to open-framework structures. Preliminary investigations53 have shown that interesting transformations also occur in metal carboxylates. Thus, molecular zinc oxalate monomers and dimers are found to transform to chain or three-dimensional structures on heating with piperazine in an aqueous medium, The chain structure transforms to a layer structure, We believe that it would... 

Fig. 21 Zero-dimensional dimeric zinc oxalate species transform progressively to chain, layered and 3-D structures with increasing temperature.71 Reproduced with permission. Copyright 2005, Wiley-VCH.

The two novel structures described above are closely related. In the layered Sn(II) oxalate, the 20-membered aperture results from linkages between four-and six-coordinated Sn(II) atoms and the oxalate units. There is three-dimensional connectivity in the zinc oxalate, and yet there are certain similarities between its structure and that of the Sn(II) oxalate. An examination of the connectivity patterns between the oxalates and M2+ ions (M = Zn or Sn) in both solids reveals that the zinc oxalate can be derived from the tin oxalate structure by the replacement of the four-coordinated Sn(II) atoms with a hexa-coordinated Zn atom having two in-plane connectivities and one out-of-plane connectivity with the oxalate units as shown in Fig. 7.31. The out-of-plane connectivity is responsible for the three-dimensional nature of the structure in the zinc oxalate (Figs. 7.29 and 7.30). 

Figure 7.30. One-dimensional channels in a three-dimensional zinc oxalate formed by the linkages involving in-plane and out-of-plane linkages (Vaidhyanathan el al. [45]).

The structure of the zinc oxalate monomer consists of two oxalate units directly linked to Zn atoms, which are also bonded to two water molecules. The monomeric zinc oxalate units are held by strong hydrogen bonds with the monoprotonated guanidine (Fig. 7.32a). In the zinc oxalate dimer, two Zn atoms are connected by one oxalate unit, and possess two terminal oxalates. The dimeric zinc oxalate is hydrogen bonded to the diprotonated amine, piperazine (Fig. 7.32b). In the chain zinc oxalate, the connectivity between Zn and the oxalate units is such as to form a one-dimensional chain with each Zn... 

Figure 7.31. (a) A single 20-membered aperture in a Zn oxalate, (b) 20-membered aperture in the tin(II) oxalate. The four-coordinated Sn atom is replaced with a Zn atom with in-plane and out-of-plane connectivity giving rise to three-dimensional connectivity in the zinc oxalate (Vaidhyanathan et al. [45]). 

Figure 7.32. (a) Structure of the monomeric zinc oxalate. Dotted lines represent hydrogen-bond interactions, (b) Structure of the zinc oxalate dimer. The dimer and the amine alternate in a plane. Water molecules are omitted for clarity. Dotted lines are hydrogen-bond interactions (Vaidhyanathan el al. [49]). 

What is significant is that zinc oxalates with one-, two- and three-dimensional architectures, in addition to the monomeric and dimeric oxalates, could be synthesized by using amine oxalates. In Fig. 7.34, the various types of structure obtained are presented to demonstrate the similarities and relationships. As can be seen, the structure of the dimer can be derived from that of the monomer, the chain from the dimer, and the layer from the chain. Just as the four-membered ring monomeric phosphate unit plays a crucial role in the building of framework phosphates [18, 38], it is possible that the monomeric and dimeric oxalates are involved in the construction of the extended oxalate framework structures. 

Figure 7.33. (a) Linear chain zinc oxalate. The oxalate chains are separated by the amine, (b) Layered zinc oxalate showing the honeycomb architecture. Amine and water molecules are not shown (Vaidhyanathan et al. [49]). 

Figure 7.34. The hierarchy of zinc oxalate structures (a) monomer, (b) dimer, (c) onedimensional chain, (d) two-dimensional layer and (e) three-dimensional structure. Note the close relationships between them (Vaidhyanathan et al. [49]).

As mentioned above, the iron phosphate-oxalate layers in this material are cross-linked by the (out-of-plane) oxalate units as in most of the phosphate-oxalates. It is interesting that similar dual functionality has also been observed in the zinc oxalate described earlier. The zinc oxalate also contains both the inplane and out-of-plane oxalate linkages to create three-dimensional connectivity, and possessing channels [45]. In Fig. 7.38, we show the structure of this material to illustrate the presence of the oxalates within the layers as well as a bridge between the layers. This dual functionality of the oxalate units, in the Zn oxalate, gives rise to an elliptical aperture made by the linkages between 10 Zn and 10 oxalate units within the same plane, with the other oxalate unit... 

Action of heat All oxalates decompose upon ignition. Those of the alkali metals and of the alkaline earths yield chiefly the carbonates and carbon monoxide a little carbon is also formed. The oxalates of the metals whose carbonates are easily decomposed into stable oxides, are converted into carbon monoxide, carbon dioxide, and the oxide, e.g. magnesium and zinc oxalates. Silver oxalate yields silver and carbon dioxide silver oxide decomposes on heating. Oxalic acid decomposes into carbon dioxide and formic acid, the latter being further partially decomposed into carbon monoxide and water. 

Further investigation is needed on the combined effects of oxalic acid and fiber. In vitro studies could provide clues to the nature of the binding of minerals to oxalic acid and fiber whether oxalic acid and fiber each binds part of the zinc, or whether there is a fiber-zinc-oxalate complex formed. 

Among the inorganic open-framework compounds, the family of phosphates is a large one [3]. A large variety of open-framework metal phosphates of different architectures have been synthesized in the last few years. They include one-dimensional (ID) linear chain and ladder structures, two-dimensional (2D) layer structures and three-dimensional (3D) channel structures [4]. In the linear chain and ladder structures, four-membered metal phosphate units of the type M2P2O4 share comers and edges respectively. Zero-dimensional four-membered zinc phosphates have been synthesised and characterized recently [5]. Several open-framework metal carboxylates have also been reported [6] and the presence of a hierarchy of zinc oxalates covering the monomer, dimer, chain, honeycomb-layer and 3D structures has indeed been established [7]. 

Several open-framework metal oxalates have been synthesized and characterized in last two to three years. They include ID, 2D and 3D structures. Following the success of the amine phosphate route to open-framework metal phosphates, reactions of organic amine oxalates with metal ions have been carried out. These reactions have yielded a hierarchy of zinc oxalates as shown in Figure 7. These different structures are mutually related. 

C2H3CIO acetyl chloride 75-36-5 -112 85 1 4836 2 900 C2H4062n zinc oxalate dihydrate 122465-35-4 25.00 2.5600 1... 

One remarkable aspect of many of these materials, as well as the hybrid metal oxide materials discussed in the next section, is that templates are rarely used in their synthesis. Instead, the open architectures are a consequence of interactions between the organic and inorganic groups. One notable exception is an open-framework zinc oxalate where the organic template, guanadinium, occupies a system of channels in the structure [134]. 

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