Seven-coordinate compounds

Seven-coordinate compounds [MoCILJ (L = anion of picolinic acid or a derivative of 8-quinolinol) have been prepared by prolonged reaction between [Mo02C12] and HL these... 

This article is concerned with six- and seven-coordinate halocarbonyl complexes of molybdenum(II) and tungsten(II) (Section II), of which earlier reviews by Colton et al.2 on substituted halocarbonyls of group 6 transition metals and on steric effects in substituted halocarbonyls of molybdenum and tungsten3 have been published. Also, reviews on the structures of seven-coordinate compounds by Drew in 19774 and by Melnik and Sharrock in 1985s contain relevant material. 

The electrochemistry of a number of such six-coordinate compounds [MnXL]+ and seven-coordinate compounds [MX2L] (with L = (203), R,R = Me and X = halide, water, triphenylphosphine oxide, imidazole, 1-methylimidazole or pyridine) has been investigated.551 The redox behaviour of these compounds was of interest because it was considered that the potentially -acceptor macrocycle (203 R = R = Me) may promote the formation of Mn° or Mn1 species or may yield a metal-stabilized ligand radical with the manganese remaining in its divalent state. For a number of macrocyclic ligand systems, it has been demonstrated that the redox behaviour can be quite dependent on axial ligation it was also of interest to study whether this was the case for the present systems. 

The most common geometries encountered are capped octahedral and capped trigonal prismatic. Many of the known seven-coordinate compounds involve /1-diketonate ligands, particularly adducts of the type Ln(diketonate)3.L (L = Lewis base e.g. H2O, py). Several... 

Neutral complexes of the thiocyanate ligands can be isolated as Lewis base adducts. Thorium and uranium form tetra(hydrate) complexes An(NCS)4(H20)4. The compound U(NCS)4(piper-azine) has been reported. The neutral adducts Th(NCS)4(L)4 and U(NCS)4(L)3 (L = N,N-diisopropylpropionamide) have been structurally characterized. The smaller size of the uranium ion is reflected in the isolation of a seven-coordinate compound, while an eight-coordinate thorium compound is formed. If more sterically demanding carbamide ligands are employed (L = N,N-diisopropylbutyramide, L = 7V,VV-dicyclohexylacetamide), seven-coordinate thorium complexes, Th(NCS)4(L)3 and Th(NCS)2Cl2(L )3, can be isolated. " ... 

In 1985, the seven-coordinate compound Ti((02CCH2)2NCH2)2)(H20) containing the hexacoor-dinate ethylenediaminetetraacetate ligand (EDTA) was structurally characterized. Similarly, the... 

A derivative of triazacyclononane was used to prepare the titanium salt [Ti((OC6H3-But)NCH2CH2)3)][BPh4].872 Most recently, the ligand (TV-ethoxo)ethylenediaminetriacetate (EEDTA) was used to prepare the seven-coordinate compound (Ti(EEDTA) (H20))(H20)2.873... 

Although the nature of seven-coordinate compounds is of intrinsic interest, perhaps of greater significance is the role of expanded coordination spheres as intermediates in the chemistry of octahedral complexes. The preparation of the thermodynamically unfavorable tmn5-Mo(CO)2-(diphos)2 isomer (5) via a seven-coordinate intermediate is an exemplary case of stereochemical control. Plausible seven-coordinate intermediates in the reactions of olefins with pentacarbonyltungstenphenylcarbene (6) can exert stereochemical control of the product distributions. 

Selenium, bis(diethyldithiocarbamato)-stereochemistry, 60 Selenium, bis(dithiofurancarbamato)-stereochemistry, 60 Selenium(II) complexes bis(dithiochelate), 60 Selenocyanate complexes linkage isomers, 186 Selenonium ions, trifluoro-stereochemistry, 37 Self-exchange reactions, 333 electron transfer rate constants, 347-353, 366 rate constants calculation, 348 rate constants, 362 Semicarbazide, 1,4-diphenylthio-ruthenium determination, 546 Semi-glycinecresol red metallochromic indicator, 557 Semi-xylenol orange metallochromic indicator, 557 Seven-coordinate compounds stereochemistry, 69-83 Sidgwick, Nevil Vincent, 16 Silicon, tris(acetylacetone)-configuration, 195... 

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