- Orotate Complexes, II. Preparation and Crystal Structures of Calcium and Zinc Orotate(2-) Hydrates
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From aqueous solutions containing orotate (dianion of 1) and calcium or zinc ions in the molar ratio of 2:1, metal orotate(2-) hydrates are readily obtained in crystalline form at pH 9.0 and 5.4, respectively.According to an X-ray crystal structure analysis, calcium orotate tetrahydrate forms a one-dimensional coordination polymer with each orotate ligand coordinated to no less than three neighboring calcium atoms.In this cation triple, the orotate(2-) anion acts as a carboxylate-O/amide-N-chelating group for the central calcium ion, but also as a carboxylate-O/O-chelating group for the first neighboring calcium ion, and as a terminal amide-O donor for the second.Each calcium ion is thus octacoordinated and linked to three orotate(2-) anions and three water molecules.The fourth water molecule is only engaged in hydrogen bonding.The new zinc orotate(2-) phase features Zn(Or)(H2O)4 units.For the hexacoordinate zinc atom bearing four water molecules the orotate(2-) ligand also acts as an O/N-chelating group.Unlike a discrete Zn(Or)(H2O)4*H2O phase reported earlier, the lattice of the new phase contains further disordered water of crystallization, with the overall composition approaching Zn(Or)*5,5H2O.The apparent stability of the M(Or) units probably reflects the well-documented carrier function of the orotate ligand for certain divalent metal ions in biological systems.Key Words: Orotate complexes / Calcium complexes / Zinc complexes
- Kumberger, Otto,Riede, Juergen,Schmidbaur, Hubert
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p. 2739 - 2742
(2007/10/02)
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