Coordination numbers carboxylates

A hydroxyl group is situated ortho to a carboxyl group which as a bidentate ligand is terminally metallized on the fiber when aftertreated with dichromate. An example is Alizarine Yellow GG [584-42-9] (50) (Cl Mordant Yellow 1 Cl 14025). Cr(III) has a coordination number of six, and therefore normally two dye molecules of the sahcyhc type are chelated to the metal ion. 

A greater tendency of rhenium complexes (compared to technetium analogues) to expand their coordination numbers has been invoked to rationalize the stronger interaction of the perrhenate ion with carboxylate ligands. This association has been suggested as a possible cause of the different quantitative biodistribution and excretion characteristics of pertechnetate and perrhenate perrhenate is accumulated in thyroid to a lesser extent and renally excreted more rapidly than pertechnetate [6]. 

The geometry of the ferrous iron is trigonal bipyramidal. Thus, this structure confirms the tendency of iron complexes to coordination numbers higher than four. The two N-donors and one of the carboxylates of 5 occupy the equatorial positions. In good agreement... 

The slow acetylation of the hydroxyl group is difficult to explain. One is inclined to suggest that this group is coordinated to the metal ion and consequently rendered inactive. Such a possibility requires either a coordination number of 7 for chromium (III) or displacement of carboxylate from the coordination sphere by hydroxyl. In the latter instance an uncoordinated functional group would still be present to react with ketene (COO or COOH) and anhydride should be detected in the crude reaction product. This is not the case. 

In solution, the potential for binding is six-coordinate for edta and four-coordinate for nta. The total coordination, however, is not well known and water molecules are also involved. [Ca(edta)]2- is often represented as an octahedral complex but it would be anticipated that Ca2+ could have a coordination number in excess of six. The denticity of edta has been found to vary from one to six, and the coordination number about the metal from four to nine.349 A review of the crystal structures of Ca2+ complexes of amino acids, peptides and related model systems surveys the coordination patterns found for Ca2+-carboxyl and Ca2+-carbonyl interactions.351... 

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