Bridge, bidentate-tridentate

These structural studies emphasize the central role of polymeric metal-diphosphonate complexes in the chemistry of technetium-diphos-phonate calcium seekii agents. It is clearly the ability of diphosphonates to bridge metal centers that provides the mechanism for the initial sorption of the radiopharmaceutical onto bone. Mixed metal (technetium, tin, and calcium) diphosphonate polymeric complexes are likely to be the dominant chemical species in clinically used skeletal and myocardial infarct imaging events. An understanding of the chemistry of these polymeric species will be crucial to an understanding of the mechanisms of action of diphosphonate radiopharmaceuticals and to the development of more efficacious imaging scents. 

Financial support for this work was provided by the National Institutes of Health (Grant No. HL-21276) and the Procter Gamble Co. We gratefully acknowledge receiving pre-publication results from Professors J. L. Hoard (Cornell University), A. Davison (MIT), F. A. Cotton (Texas A M) and V. Day (University of Nebraska), and especially thank our Collettes and students for their many significant contributions to the research discussed in this review. 

New nthetic routes to technetium-99 complexes and technetium-99m radiopharmaceuticals are based on substitution of ligands onto pre- 

ACS Symposium Series American Chemical Society Washington, DC, 1980. 

Pinkerton, T. Heineman, W. R. Deutsch, E. Anal. Chem., in press. 

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

Moving toward longer aliphatic carboxylates is a succinate FIJYAZ [1 2(0411404)3(1120)2] H2O (Fig. 8). A 3D framework is observed in this structure, the neutrality of which is anticipated from the 2 3 Ln/linker ratio. Bridging bidentate and bridging tridentate coordination is observed in this compound, with each displayed by the single, unique succinate linker. Glutarate... 

The four triple bridging modes are the result of the combinations out of the two coordination modes, i.e., bidentate bridging and tridentate bridging. Of the four bridging modes, three of them are observed in anhydrous rare earth acetates ([REL3] ) with triple bidentate bridging mode, for RE = Sc with mixed triple bridging... 

Diverse coordination types have been reported for rare earth carboxylates with the most common being bidentate chelation, bidentate syn-syn bridging, and tridentate bridging with many examples being reported by Meyer and co-workers. Some of the bonding modes found in rare earth carboxylates are given in Fig. 1.2. 

The heavier rare earths (Ln=Dy, Ho-Lu, Y) also form one-dimensional polymeric chains with all Ln atoms being 7-coordinate. In this stractural type the cinnamate ligands are either bridging tridentate or bridging bidentate... 

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