Ab initio calculations
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
Cadmium(II) complexes of two Schiff bases, 1,3-di(pyridine-2-carboxaldimino)propane (C15H16N4, L1) and tris[4-(2′-pyridyl)-3-aza-3-butenyl]amine (C24H27N7, L2) are described. An efficient route utilising molecular sieves for the synthesis of Schiff bases is presented. The ligands L1 and L2 can be described as linear and three-armed podands, respectively, L1 being conformationally flexible and L2 preorganised. Cadmium perchlorate in methanol with L1 yields a crystalline complex [Cd(L1)2](ClO4)2 (1), the structure of which was determined by X-ray structure analysis. The complex 1 has an unusual nonsymmetrical 8-coordinated helical structure and crystallizes in an acentric space group (Cc, no. 9) as a pure enantiomer due to spontaneous resolution. Solution studies of 1 in CHCl3/DMSO (10:1) and pure DMSO were performed using 1H-, 13C-, 113Cd-NMR and 1H,15N z-GS HMBC spectroscopy and they suggest a reorientation of 1 into the more symmetrical 4-coordinate complex due to the flexible nature of L1. The preorganised, potentially tetra-, hexa- or heptadentate, three-armed podand L2 and its in situ complexation with the Cd2+ cation were investigated by 1H-, 13C-, 113Cd-NMR and 1H,15N z-GS HMBC spectroscopy. The results support the formation of a highly symmetrical helical 6-coordinate podate [CdL2](NO3)2 (2). The structure of 2 has also been verified by ab initio HF-MO calculations using a standard 3-21G* basis set (Lan2DZ for Cd).
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