Dimethylglyoxime complexation

Transfer of coordinated NO (especially from dimethylglyoximate complexes)... 

Discussion. Nickel (200-400 fig) forms the red dimethylglyoxime complex in a slightly alkaline medium it is only slightly soluble in chloroform (35-50 fig Ni mL -1). The optimum pH range of extraction of the nickel complex is 7-12 in the presence of citrate. The nickel complex absorbs at 366 nm and also at 465-470 nm. 

Figure 2.41 A dimeric non-bridged rhodium dimethylglyoxime complex (for clarity the hydrogen atoms in the hydrogen bonds are not shown).

Nickel has been determined spectrophotometrically in seawater in amounts down to 0.5 xg/l as the dimethylglyoxime complex [521,522], In one procedure [521] dimethylglyoxime is added to a 750 ml sample and the pH adjusted to 9 -10. The nickel complex is extracted into chloroform. After extraction into 1M hydrochloric acid, it is oxidised with aqueous bromine, adjusted to pH 10.4, and dimethylglyoxime reagent added. It is made up to 50 ml and the extinction of the nickel complex measured at 442 nm. There is no serious interference from iron, cobalt, copper, or zinc but manganese may cause low results. 

In another procedure [522] the sample of seawater (0.5-3 litres) is filtered through a membrane-filter (pore size 0.7 xm) which is then wet-ashed. The nickel is separated from the resulting solution by extraction as the dimethylglyoxime complex and is then determined by its catalysis of the reaction of Tiron and diphenylcarbazone with hydrogen peroxide, with spectrophotometric measurement at 413 nm. Cobalt is first separated as the 2-nitroso-1-naphthol complex, and is determined by its catalysis of the oxidation of alizarin by hydrogen peroxide at pH 12.4. Sensitivities are 0.8 xg/l (nickel) and 0.04 xg/l (cobalt). 

Rampon and Cavelier [523] used atomic absorption spectrometry to determine down to 0.5 xg/l nickel in seawater. Nickel is extracted into chloroform from seawater (500 ml) at pH 9-10, as its dimethylglyoxime complex. Several extractions and a final washing of the aqueous phase with carbon tetrachloride... 

The formation of nickel dimethylglyoximate complex may be expressed as follows ... 

Samples of metal complexes isolated from the final solutions were subjected to microanalysis (for carbon, hydrogen, oxygen, and sulfur). Metals were determined colorimetrically by the following methods— copper as the complex formed with sodium diethyl dithiocarbamate (6) cobalt as the nitroso-R salt complex (7) nickel as the dimethylglyoxime complex (4). 

It has been mentioned that the dimethylglyoxime complexes of nickel, palladium, and platinum, and the N-methylsalicylaldimine complexes of... 

The beautiful bright red dimethylglyoxime complex of Ni2+ is used for gravimetric determination of Ni because it has low solubility and is quite selective. The planar molecules are stacked along the c0 axis as shown in Figure 4.29fl. It is a face-centered structure [3P(o)J deformed... 

Mixed O- and N-donor ligands. Studies of the reactivities of co-ordinated ligands have shown that bis-salicylaldoxime chelates of Ni, Pd, and Cu react with AlPh3 in benzene to yield grey diamagnetic complexes (12).35 Dimethylglyoxime complexes undergo similar reactions (see below). 

Separation. Palladium is precipitated in Group II as PdS it is insoluble in ammonium polysulphide solution and therefore accompanies the elements of Group IIA. It is ultimately identified in acid solution as the dimethylglyoxime complex. 

If the alternative potassium hydroxide method is employed for the separation of Groups IIA and IIB, the KOH extract may contain As, Sb, Sn, Se, Te, and part of the Mo the residue may contain, in addition to HgS, PbS, Bi2S3, CuS, CdS, and PdS, the gold and platinum partly as sulphides and possibly partly in the form of the free metals. Mo is readily identified by the potassium xanthate or a-benzoin oxime test. The Au and Pt will accompany HgS after extraction with dilute nitric acid upon dissolution in aqua regia, Pt may be identified as the dimethylglyoxime complex in the presence of m hydrochloric acid after the Pb, Bi, Cu, and Cd have been removed. 

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