Zinc coordination compounds

Similarly, metals may be introduced into un symmetrically substituted metal-free phthalocyanines, e.g. formation of the zinc coordination compound 6.419... 

Square-planar zinc compounds predominate with these ligand types as would be predicted. This is in contrast to the prevalence of tetrahedral or distorted tetrahedral geometries for four-coordinate species that have been discussed thus far. Zinc porphyrin complexes are frequently used as building blocks in the formation of supramolecular structures. Zinc porphyrins can also act as electron donors and antenna in the formation of photoexcited states. Although the coordination of zinc to the porphyrin shows little variation, the properties of the zinc-coordinated compounds are extremely important and form the most extensively structurally characterized multidentate ligand class in the CSD. The examples presented here reflect only a fraction of these compounds but have been selected as recent and representative examples. Expanded ring porphyrins have also... 

Table I. Thermal Stability Data of Organic Ligands and Their Zinc Coordination Compounds in vacuo...

Electroplating. Aluminum can be electroplated by the electrolytic reduction of cryoHte, which is trisodium aluminum hexafluoride [13775-53-6] Na AlE, containing alumina. Brass (see COPPERALLOYS) can be electroplated from aqueous cyanide solutions which contain cyano complexes of zinc(II) and copper(I). The soft CN stabilizes the copper as copper(I) and the two cyano complexes have comparable potentials. Without CN the potentials of aqueous zinc(II) and copper(I), as weU as those of zinc(II) and copper(II), are over one volt apart thus only the copper plates out. Careful control of concentration and pH also enables brass to be deposited from solutions of citrate and tartrate. The noble metals are often plated from solutions in which coordination compounds help provide fine, even deposits (see Electroplating). 

Despite the weak basicity of isoxazoles, complexes of the parent methyl and phenyl derivatives with numerous metal ions such as copper, zinc, cobalt, etc. have been described (79AHC(25) 147). Many transition metal cations form complexes with Imidazoles the coordination number is four to six (70AHC(12)103). The chemistry of pyrazole complexes has been especially well studied and coordination compounds are known with thlazoles and 1,2,4-triazoles. Tetrazole anions also form good ligands for heavy metals (77AHC(21)323). 

The mechanisms of the electrophilic substitutions in the isoxazole nucleus have not yet been studied. They should not differ fundamentally from those usually accepted for the substitution of aromatic systems but the structural specificity of the isoxazole ring might give rise to some peculiarities, as recently specially discussed.One important point is that isoxazole shows a clearcut tendency to form coordination compounds. Just as pyridine and other azoles, isoxazoles coordinate with halogens and the salts of heavy metals, for example of cadmium,mercury,zinc. Such coordination... 

DNA polymerases, 5, 1007 Trans effect, 1,16, 26, 315 metal complexes, 2, 705, palladium(II) amine complexes, 5, 1115 platinum complexes, 5, 353, 493 six-coordinate compounds. 1, 49 T ransestcrification metal alkoxide synthesis, 2, 340 Transferases zinc, S, 1002... 

Because of its ionic size, cadmium(II) does not fit well into the coordination site of the porphyrin nucleus (N-centre distance 200 pm), and the complexes are readily demetalated (stability group IV, Tables land 2). The complexes can be prepared, of course, but zinc(II) compounds have been overwhelmingly favored for PDT purposes. 

Probably the first scientifically recorded observation of a completely inorganic coordination compound is the formation of the familiar tetraamminecopper(II) ion, [Cu(NH3)4]2+. The 16th century German physician and alchemist Andreas Libavius (15407—1616) noticed that aqua calcis (limewater or saturated calcium hydroxide solution) containing sal ammoniac (ammonium chloride) became blue in contact with brass (an alloy of copper and zinc).8... 

A somewhat surprising group of coordination compounds consists of the volatile heavy metal nitrates, such as those of copper, zinc, mercury, titanium, zirconium and hafnium. The structures of some of these, in the gaseous state, have been determined thus Cu(N03)2 contains two bidentate, almost planar, staggered nitrato groups. Some derivatives of metal nitrates have also been found to be volatile for example, Fe(N03)3 N204 and Al(N03)3 2MeCN.39... 

It is noteworthy that the Be—O distance (1.60 A) is of the same order as that found for other coordination compounds of beryllium and leads to the value of 1.0—1.1 A for the covalent radius of beryllium in this type of coordination.26 Clearly arguments based on relative ionic radii are invalid. Thus the dihydrate of zinc oxinate has been shown to form a distorted tetrahedron with two long Zn—H20 bonds while the lengths Zn—O and Zn—N to the ligand are 2.05 and 2.06 A respectively, whence the zinc radius is 1.38 A. Clearly the use of an ionic radius (Zn2+ = 0.74 A) would be misleading. Similarly the Cu—N bond in compounds of Cu11 with ammonia and ethylenediamine (1.99,2.05,2.01 A) implies a radius of 1.3-1.4 A in these coordination compounds, a value considerably larger than the ionic radius of 0.7 A.23... 

Although coordination compounds have sometimes been used as titrants, e.g. ferrocyanide ions for the titration of zinc(II), and permanganate or dichromate ions in redox titrations, probably the only outstanding reaction in classical titrimetry that involves the reversible formation of a coordination compound is the Liebig-Deniges reaction. 

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