Coordination complexes determination

Many complexes have more than one coordination mode of BH4 featured in their structure, e.g. [U ()9 -BH4)()9 -BH4)2(dmpe)2]. Likewise, whereas [M(BH4)4] are monomeric 12-coordinate complexes for M = Zr, Hf, Np, Pu, they are polymeric for M = Th, Pa, U the coordination number rises to 14 and each metal centre is coordinated by two r) -BH4 and four bridging r) -BH4 groups. It is clear that among the factors which determine the mode adopted are the size of the metal atom and the steric requirements of the co-ligands. Many of the complexes... 

This is the most common coordination number for complexes of transition elements. It can be seen by inspection that, for compounds of the type (Ma4b2), the three symmetrical structures (Fig. 19.6) can give rise to 3, 3 and 2 isomers respectively. Exactly the same is true for compounds of the type [Mayby]. In order to determine the stereochemistry of 6-coordinate complexes very many examples of such compounds were prepared, particularly with M = Cr and Co , and in no case was more than 2 isomers found. This, of course, was only negative evidence for the octahedral structure, though the... 

Thiourea Ugands can be bounded to the metal centre through one nitrogen atom, the sulfur atom, or the C = S double bond. These coordination modes were studied by density functional theory calculations for Rh-thiourea complexes (Scheme 13). No stable structure was attained by optimisation of the nitrogen coordination mode I but optimised geometries as trigonal-bipyramidal complexes were obtained for modes II and III. An coordination is determined for the latter complex through both S and C atoms. As this... 

Originally, compounds containing coordination complexes were given common names such as Prussian blue (KFe[Fe (CN)g ]), which is deep blue, or Reinecke s salt (NH4[Cr (NH3)2 (NCS)4]), named for its first maker. Eventually, coordination compounds became too numerous for chemists to keep track of all the common names. To solve the nomenclature problem, the International Union of Pure and Applied Chemistry (lUPAC) created a systematic procedure for naming coordination compounds. The following guidelines are used to determine the name of a coordination compound from its formula, or vice versa ... 

COD)Ru(acetate)2 and (COD)Ru(trifluoroacetate)2 were not successful. In all cases, full conversion of the ligand with the precursor was determined via NMR, leading to mixtures of several, partly unidentified species. Furthermore, P-NMR experiments proved that in those cases no formation of any PP-coordinated complexes was achieved. 

Reduction of both nickel porphyrins and thiaporphyrins to Ni1 species has been studied by EPR and 2H NMR spectroscopy.179, 2 58 The Ni1 complex of 5,10,15,20-tetraphenyl-21-thiaporphyrin has been isolated and characterized. Reaction of this complex with sulfur dioxide produced a paramagnetic five-coordinated Ni1 S02 adduct, while reaction with nitrogenous base ligands (amines, pyridines, imidazoles) yielded five- and six-coordinate complexes. In addition, the crystal structure of Ni1 diphenyldi-p-tolyl-21-thiaporphyrin has been determined. The coordination geometry about the nickel center is essentially square planar with extremely short Ni—N and Ni—S bonds (Ni—N = 2.015(2) A, 2.014(12) A, and 1.910(14) A and Ni—S = 2.143(6) A).2359... 

Four-coordinate complexes with monodentate ligands have also been reported. The X-ray crystal structures of three modifications of the compound [Au(PPh3)4]BPh4 have been determined, none of which shows the expected simple tetrahedral geometry.2540 Thus, the chloroform solvate... 

There is no other vitamin which exemplifies the interdependence between the human race and microorganisms better than Vitamin B12. Mankind still relies for its very existence upon the capability of a few species of bacteria to synthesize this fascinating coordination complex. A concerted effort is being made in a number of laboratories to determine procedures for the chemical synthesis of this vitamin. However, even the most talented synthetic chemists would have to admit that the organic chemist s lament is applicable to Vitamin B12 ... 

The 9Be NMR spectroscopy has been used in determination of the chiral binaphthyldiimine Be(II) complex [49].118 The measured 8Be value of 4.84 ppm and the line width of 40 Hz indicated the presence of a four-coordinate complex. The calculated 9Be NMR parameters were in good agreement with experimental results. 

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