Heteronuclear chelates

The heteronuclear chelate complex (105) has been prepared and its molecular structure determined. The N202 site is occupied by planar Ni, while the 0202 site is occupied by Zn. Coordinated py completes the five coordination for the zinc. The Zn—O distances average 1.95 A to the terminal oxygens and 2.09 A to the bridging oxygens the zinc is displaced from the least-squares basal plane by 0.32 A towards the py. Cu, UQ2 or VO may be used in place of zinc.764... 

A fuller account of the structural determination of this heteronuclear chelate complex has appeared.765 In addition, a paper on the general preparation of the binuclear complexes NiML where M = Zn, Cu, Co11, Fe, Mn11 and VO11 has appeared in all cases, Ni occupies the N202 site and M occupies the 0202 site.766... 

The considerable role of synthetic methods—in particular, direct gas-phase [11,15-18] and electrochemical [11,17,19] techniques—in controlled creation of coordination compounds of various types (molecular and r n-Ti-complexes, chelates, and homo- and heteronuclear compounds) is discussed. Particular attention is given to the complex compounds having standard and nonstandard coordination modes of the most widespread (typical) ligands, for example a(N)- and ji(ri6-C)-complexes... 

The formation of chromium(iii) complexes of ethanolamine-NN-diacetic acid in aqueous solution has been investigated by potentiometric and colorimetric methods. A1 1 complex is found to be formed in the pH range 3—6. At pH > 6 hydrolysis takes place. Isolation of mono-, di-, and hetero-nuclear Cr chelates of ttha (ttha = triethylaminetetra-aminehexa-acetic acid) has been accomplished. No evidence for exchange coupling was found for either the dinuclear complex or for the heteronuclear Cr, Cu complex, CrCu(Httha)2,7H20. ... 

Another area of considerable interest in polynuclear metal complex chemistry for which the -polyketones seem well suited is that of mixed metal and mixed valence complexes. When one is seeking fundamental data on how the molecular structure and properties of such compounds relate to bulk properties, it is not sufficient to be content with uncertainties concerning purity and the positions of the different ions. In this paper we report on a systematic approach to the preparation of some heteronuclear, molecular chelates, i,e, molecules containing two or more... 

Our approach to the preparation of pure heteronuclear chelates is to establish the selectivity of the two coordination sites in a ligand such as H4(BAA)2en by determining the structure of some mononuclear chelates. Once these are unambiguously characterized, they are used as ligands to bind a second metal ion with a proven preference for the available site. The two metals are chosen so as to minimize competition for the same site within the molecule. 

Preparation and Characterization of Heteronuclear Chelates. Once it was established that the two sites in SchiflF-base derivatives of 1,3,5-triketones may specifically coordinate diflFerent metal ions, it became feasible to prepare pure mixed metal complexes in which the position of the two metal ions is known. As a matter of preparative convenience in the early stages of this work, we chose to use Ni[H2(BAA)2en] as a ligand to bind a diflFerent metal ion which has a preference for the available oxygen donor site (Reaction 2). The major rationale for using the... 

The spectrum of NiCu(BAA)2en is similar to those of Zn and VO, but it is more complex in that P -Cu and related fragments are quite intense. The primary reason for recording the mass spectra was to support the conclusion that these compounds are pure heteronuclear chelates rather than mixtures of hetero- and homonuclear molecules. Since no... 

Magnetic Properties. Although the analytical and mass spectral data indicate that the heteronuclear chelates are pure, they give no clue as to whether some of the metal ions have reversed their positions during preparation. Since one of our purposes is to be able to prepare pure mixed metal compounds in which positions of the metal ions are known, such a reversal would constitute an impurity in the bulk sample. The magnetic properties of these Ni mixed metal compounds do, however, enable one to determine the metal ion positions with some certainty... 

The basic types of complexes of ligating systems under consideration are presented by the mononuclear chelates 14-18. Di-, oligo-, mono-, and heteronuclear complexes containing hetarylazomethine ligands are also known. They are considered as a function of heterocyclic azomethine... 

A mdimentary H-bond nomenclature is given in Scheme 5. H-bonds can be classified according to their strength as weak, moderate, or strong proton position as symmetric (or centric, or proton-centred) or asymmetric X-H-Y angular value as bent or linear (5.1a,b) chemical symmetry as homonuclear or heteronuclear (5.IIa,b) connectivity as two-centered, three-centered (or bifurcated), or chelated (5.IIIa-c) and topology as intermolecular (5.IVa-c) or intramolecular (5.IVd). As a mle, homonuclear H-bonds tend to be stronger than heteronuclear, two-centered than multicentered, and linear than bent ones. 

Compounds 39 were studied by electronic and heteronuclear H, Li NMR spectroscopy (Figure 10.27) [123]. They exist in the form E, which is the most characteristic for aromatic azomethines. Addition of Zn to acetonitrile solutions of 39 leads to the formation of chelates 40. Imines 39 E exhibit weak fluorescence in the range 530-550 nm with an abnormally large Stokes shift... 

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