The stereoselective synthesis of coordination compounds can be achieved by using enantiomerically pure ligands, which, on metal binding, transfer their chiral information to the metal center. [1] Siderophores, high-affinity chelators synthesized by microorganisms to solubilize iron(iii) for uptake into the cell, represent a biologically important example of this ligand type. [2] Most siderophores are enantiomerically pure amino acid derivatives, and the chirality of the molecules can play an important role in their biological activity. This is well documented for enterobactin, the native siderophore of Escherichia coli: Only the naturally occurring complex, having an l-seryl ligand backbone and a D configuration at the metal center, is able to supply iron to the cells. [3,4] Interestingly, the N 2 -fixing cells of Azotobacter vinelandii secrete azotochelin (Scheme 1), a tetradentate iron Scheme 1. siderophore which also binds molybdenum. [5, 6] The structures of relevant model complexes have been reported. [7,8] Molybdenum, as well as iron, is a component of the conventional nitrogenase, and in A. vinelandii the siderophore production depends not only on the amount of iron in the environment but also on the concentration of molybdenum. [5b, 6b] We report here that the l-lysine derivative azotochelin shows a high diastereoselectivity in forming the two possible D and L cisdioxomolybdenum complexes. Use of the azotochelin analogue H 4 -(1R,2R)-dachcam (Scheme 1) allowed us to investigate the chiral induction on molybdenum binding in the solid state and to compare the CD spectra of the model complex Further study of the magnetic properties of these irregular alternating systems are planned but a general law may be easily envisaged for homometallic systems with sequences of more than one F/AF interaction. Ferromagnetism emerges, as observed for 2, if 2n1 AF interactions are followed by one or more F interactions; the ground state here is always S 0. An alternative possibility consists of an even number of AF interactions (2n) followed by one or more (m) F interactions, as observed for 1, which induces net ferrimagnetic behavior with ground state S T m S for each (2nm) local S spin carrier. 3 ], Z 6 [10], 1 calc 1.451 g cm À3 [1.593 g cm À3 ], crystal size 0.15 Â 0.28 Â 0.50 mm [0.30 Â 0.60 Â 1.0 mm], m 0.893 mm À1 [0.807 mm À1 ]. Of 4887 [17 574] reflections collected, 3164 [6593] were observed with I > 2s(I); 289 [612] parameters. R(F) 0.0363 [0.0641], wR(F 2 ) 0.0943 [0.1861], min./max. residual electon density 1 À 0.22/0.21 e À3 [À 1.94/ 1.80 e À3 ]. The data were collected on a modified STOE [IPDS] diffractometer with Mo Ka irradiation 0.71069 [0.71073 ] at room temperature. Lorentz polarization effects, intensity decay, and absorption (DIFABS) [Lorentz polarization effects and numerical absorption (X-SHAPE, min./max. transmission 0.604/0.803)] corrections were made. Both structures were solved by direct methods and refined by full-matrix least-squares method on F 2 values. Refinement used the SHELXTL/PC packag...
