Paddlewheel motif

An elegant and efficient approach for the synthesis of structural models of carboxylate-rich non-heme dinuclear iron proteins involves the use of bulky ligands of the terphenyl carboxylate family [47, 48]. The resulting dinuclear iron(II) complexes can adopt two conformations, called the windmill and the paddlewheel motif (Scheme 2.9). 

The compound [Re2(HP0, )2(H2P0, )2(H20)2]-4H20 was synthesized from the reaction of Re2(02C3Fl5), Cl2 with mixture of phosphoric acid, propanoic acid, and water at 100-110 °C under an inert atmosphere [89], The Re2(HP0, )2(H2P04)2(H20)2 complex exhibits the paddlewheel motif... 

AU the three hpp complexes exhibit the paddlewheel motif with a Re2 unit coordinated to four equatorial hpp ligands and two axial anions. The three molecules have a crystallographic Inversion center at the midpoint of each Re-Re bond. The ring conformation of the hpp ligands is disordered... 

Another example of rr-delocalized radical is cyclopentadienyl 43, which was reported by Sitzmann et al. to be rendered persistent and crystalline by derivatization with /io-propyl groups as in radical 44 (Fig. 7.19). ° "° An interesting feature in the X-ray structure of 44 is that the /io-propyl groups adopt a paddlewheel-like conformation, also showing disorder in the crystal. The bond distances show that the radical is not Dsh symmetric, but that it is slightly distorted (C1-C2 = 1.412 A, C2-C3 = 1.401 A). Radical 44 also packs in a columnar motif with rings eclipsing each other... 

Fig. 17 Commonly recurring structural motifs, (a) the paddlewheel dimer of Cu05 square pyramids, (b) the tetrahedron of Zn04 tetrahedra sharing a central oxygen, and (c) the trigonal planar trimer of OO, octahedra sharing a central oxygen. Gray spheres denote carbon and red oxygen CuO,. ZnO-. and CrC>6 polyhedra are shown in dark blue, pale blue and green, respectively.

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