Carboxylates monodentate donors

Monodentate coordination in solution is more readily proved with the kinetically inert metal ions. Thus, coordination through the amino N donor atom has been established with Cr111, Coin, Ir111, Ptu and Rhin. Monodentate coordination through the weaker field carboxyl O donor atom is not so common but has been observed with Co111 and more recently with Pt11. With the kinetically labile metal ions, monodentate coordination is sometimes observed at pH 3-5 as a minor species or can be obtained by means of blocking either the N or O donor atoms by substitution. 

Alkylphosphonate groups are monodentate donors of intermediate hardness that may replace carboxylate groups in chelating agents such as nitrilotriacetic acid (NTA), ethylenediaminetetra-acetic acid (EDTA), and diethylenetriaminepentaacetic acid (DTPA). The corresponding ligands nitrilotrimethylenephosphonic acid (NTP), 1, ethylenediaminetetramethylenephosphonic acid (EDTP),... 

The involvement of zinc in nicotinamide-based hydride-transfer reactions has led to numerous studies of Group IIB complexes of pyridine carboxylic acid derivatives. Cadmium complexes of 2-pyridinecarboxylic acid, 5 3-pyridinecarboxylic add497 and 3-pyridinecarboxamide498 have been reported. The crystal structure of [Cd(HC02)2L2(H20)2] (L = 3-pyridinecarboxamide) has also been described the metal is in an octahedral environment in which the amide acts as a monodentate N donor.498... 

Fig. 21. A summary of carboxylic donor geometries a) monodentate, b) bidentate, c) bridging bidentate, d) bridging tridentate.

A representative compound that utilizes pyrazole dicarboxylate to produce a 2-dimensional, U(VI)/Cu(II) compound is U02Cu(C5H2N204)2(H20)2 (Figure 23). Here the U02 center is in square bipyramidal geometry with four monodentate carboxylate oxygen atoms from four distinct linker molecules. Cu(II) is coordinated to two bidentate N/0 donors and two H2O groups to yield an overall octahedral geometry. Coordination site preferences can be seen in this compound as the uranyl cation is bound strictly to... 

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