CHIRAL METAL COMPLEXES. PART 52. THE STRUCTURES OF CO-CRYSTALLISED DIASTEREOISOMERIC DNA PROBES SHOWING INTRAMOLECULAR π-π INTERACTIONS

Abstract

The structure of Δ-α1,2-[Co(R-picpnMe2)(S-phe)](ClO4)2-H2O where R-picpnMe2 is N',N'-dimethyl-3R-methyl-l,6-di(2-pyridyl)-2,5-diazahexane and 5-phe is the S-phenylalaninate anion has been determined to be orthorhombic, space group P212121 , with a = 9.959(4), b = 15.919(7), c= 19.59(3) Å, Dc = 1.515Mgm−3 and Z = 4. The structure was refined by least-squares methods to R = 0.050 for 2328 independent reflections with l > 2[sgrave](I) for diffractometer data collected at 293 K. The cobalt atom has the expected octahedral coordination with the N4 tetradentate adopting Δ-α topology and with the phenylalaninate ligand completing the coordi—nation sphere. Two geometric isomers possible for the asymmetric complex, α1 and α2 (depend—ing upon the relative mode of coordination of the aminoacidate relative to the trans orientation of the methyl group of the tetradentate), are observed to co-crystallise in a 1:1 ratio. In these species, the phenyl ring is weakly bonded to one of the pyridyl rings of the tetradentate, as has been found in a number of congeners. The R-phe analogue has also been synthesised. The per-chlorate salt contains both possible isomers. NMR studies indicate that the π-π interaction observed in the solid state for Δ-α1,2-[Co(R-picpnMe2)(S-phe)]2+ is preserved in solution.