Six-coordinate complexes

Anionic, tridentate tris(mercaptoimidazolyl)borates [Tm ] systems are useful for isolation of T1(III) complexes. " " Six-coordinate, sandwich complexes [Tm ]2Tl C104, Tm ]2 T1)I (102), and Tm ]2Tl Tll4 have been synthesized and structurally characterized. The compound Tm ]2T1 I has been isolated as a by-product during the synthesis of a tris(mercaptoimidazolyl)boratozinc complex using a thallium(I) starting material [Tm lTl. " " r.f... 

Uranium, tetrathiocyanatotetrakis[tris-(dimethylamino)phosphine oxidc]-structure, 87 Uranium(VI) complexes liquid-liquid extraction of, 541 Uranyl complexes six-coordinate compounds structure, 53 stereochemistry, 74 Uranyl ions photoreactivity, 408 Urea... 

Xanthocobalt—see Cobalt, nitropentaammine-Xenon, pentafluoro-lone electron pair structure, 50 Xenon, trifluoro-structure, 45 Xenon(IV) complexes six-coordinate compounds structure, 53 Xenon hexafluoride geometry, 37 stereochemistry, 74 X-ray diffraction cobalt ammines, 13 configuration, 16 crystal structure, 15 Xylenol orange metallochromic indicator, 557... 

Ni(CisH28N2S2)(NCS)2] 32 ) room 3.10 Gouy, Farad trans-thiocyanate complex six-coordination suggested 73U8... 

Structures of (a) EDTA, and (b) a six-coordinate metal-EDTA complex. 

Iron hahdes react with haHde salts to afford anionic haHde complexes. Because kon(III) is a hard acid, the complexes that it forms are most stable with F and decrease ki both coordination number and stabiHty with heavier haHdes. No stable F complexes are known. [FeF (H20)] is the predominant kon fluoride species ki aqueous solution. The [FeF ] ion can be prepared ki fused salts. Whereas six-coordinate [FeCy is known, four-coordinate complexes are favored for chloride. Salts of tetrahedral [FeCfy] can be isolated if large cations such as tetraphenfyarsonium or tetra alkylammonium are used. [FeBrJ is known but is thermally unstable and disproportionates to kon(II) and bromine. Complex anions of kon(II) hahdes are less common. [FeCfy] has been obtained from FeCfy by reaction with alkaH metal chlorides ki the melt or with tetraethyl ammonium chloride ki deoxygenated ethanol. 

PF3 forms complexes with amines, ethers, and other bases as well as F , with which phosphoms becomes six-coordinate. Dry phosphoms pentafluoride does not attack glass. The yellow crystalline phosphoms pentabromide forms from the reaction of PBr and excess bromine. 

Plutonium(III) in aqueous solution, Pu " ( 4)> is pale blue. Aqueous plutonium(IV) is tan or brown the nitrate complex is green. Pu(V) is pale red-violet or pink in aqueous solution and is beUeved to be the ion PuO Pu(VI) is tan or orange in acid solution, and exists as the ion PuO. In neutral or basic solution Pu(VI) is yellow cationic and anionic hydrolysis complexes form. Pu(VII) has been described as blue-black. Its stmcture is unknown but may be the same as the six-coordinate NpO (OH) (91). Aqueous solutions of each oxidation state can be prepared by chemical oxidants or reductants... 

A large number of haUde complexes of thaUium(III) have been prepared by precipitation of the complexes from solution with a suitable cation, eg, H", (C2H )4N", (CgH )4As", and K". Both four-coordinated [HXJ and six-coordinated [HX ] ions exist in solutions and in soUd states. 

The neutral complexes of chromium, molybdenum, tungsten, and vanadium are six-coordinate and the CO molecules are arranged about the metal in an octahedral configuration as shown in stmcture (3). Vanadium carbonyl possesses an unpaired electron and would be expected to form a metal—metal bond. Steric hindrance may prevent dimerization. The other hexacarbonyls are diamagnetic. 

Coordination number The number of bonds from the central metal to the ligands in a complex ion, 409,412t four-coordinate metal complex, 413 six-coordinate metal complex, 413-414 Copper, 412 blister, 539... 

Single bond A pair of electrons shared between two bonded atoms, 167 Six-coordinate metal complex, 413-414 Skeleton structure A structure of a species in which only sigma bonds are shown, 168... 

In its complex compounds, of which there are many thousands, Co almost invariably has a +3 oxidation number. Apparently, Co+s ion accompanied by six coordinating groups is particularly stable. Cobalt complexes are important in biochemistry. Some enzyme reactions go through a cobalt-complexing mechanism. Although only small traces are needed, cobalt is essential to the diet. 

When, however, the ligand molecule or ion has two atoms, each of which has a lone pair of electrons, then the molecule has two donor atoms and it may be possible to form two coordinate bonds with the same metal ion such a ligand is said to be bidentate and may be exemplified by consideration of the tris(ethylenediamine)cobalt(III) complex, [Co(en)3]3+. In this six-coordinate octahedral complex of cobalt(III), each of the bidentate ethylenediamine molecules is bound to the metal ion through the lone pair electrons of the two nitrogen atoms. This results in the formation of three five-membered rings, each including the metal ion the process of ring formation is called chelation. 

The 14e compound MTO readily forms coordination complexes of the type MTO-L and MTO-L2 with anionic and uncharged Lewis bases [96], These yellow adducts are typically five- or six-coordinate complexes, and the Re-L system is highly labile. Apart from their fast hydrolysis in wet solvents, MTO-L adducts are much less thermally stable then MTO itself. The pyridine adduct of MTO, for instance, decomposes even at room temperature. In solution, methyltrioxorhenium displays high stability in acidic aqueous media, although its decomposition is strongly accelerated at increased hydroxide concentrations [97, 98], Thus, under basic aqueous conditions MTO decomposes as shown in Equation (4). 

The P450 reaction cycle (Scheme 10.4) starts with four stable intermediates that have been characterized by spectroscopic methods. The resting state of the enzyme is a six-coordinate, low-spin ferric state (complex I) with water (or hydroxide) coordinated trans to the cysteinate ligand. The spin state of the iron changes to high-spin upon substrate binding and results in a five-coordinate ferric ion (com-... 

Kinetics and mechanisms of isomerisation and racemisation processes of six coordinate chelate complexes. N. Serpone and D. G. Bickley, Prog. Inorg. Chem., 1972,17,391-566 (359). 

Six coordinate copper complexes with gii < g in the solid state. I. Bertini, D. Gatteschi and... 

The stereochemistry and electronic properties of fluxional six-coordinate copper(II) complexes. B. Hathaway, M. Duggan, A. Murphy, J. Mullane, C. Power, A. Walsh and B. Walsh, Coord. Chem. Rev., 1981,36, 267-324 (132). 

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