Diastereoselectively self-sorted low-symmetry binuclear metallomacrocycle and trinuclear metallocage.

A pyridine/aniline appended unsymmetrical bis-monodentate ligand -(3-aminophenyl)nicotinamide, is synthesized via condensation of nicotinic acid with excess -phenylene diamine. A low-symmetry binuclear complex of the PdL'L type and an extremely rare trinuclear complex of the PdL type are produced by self-assembly of the ligand with -protected palladium(II) (, PdL') and palladium(II), respectively. Two isomers ( [(2,0), (2,0)] and [(1,1), (1,1)]-forms) are theoretically possible for the PdL'L-type complex whereas nine isomers can be envisaged in the case of the PdL-type arrangement. However, one of the isomers of the PdL'L-type complex as well as the one for the PdL-type complex are experimentally obtained. The exclusive formation of specific isomers could be predicted from the 1D/2D NMR study in the solution state and the DFT calculations in the gas phase/implicit solvent media. The formation of the predicted all-(1,1)-[Pd(en)](NO) has been confirmed by a single-crystal XRD study. DFT calculations for the isomers of the PdL-type arrangement show that a [(2,2), (2,2), (2,2)] isomer is energetically favourable than the alternatively predicted [(2,2), (2,2), (2,2)] isomer. Conformational changes within the build of the exclusively formed isomers are proposed on the basis of NMR study.