Peter Comba, Andreas Fath, Andreas Kühner and Bernd Nuber
The tetrathiamacrocycles trans-6,13-dihydroxy-1,4,8,11-tetrathiacyclotetradecane (L1) and its benzo- (L2), syn- and anti-dibenzo-substituted derivatives (L3 and L3′, respectively) have been prepared by conventional methods, and a benzo-substituted-1,4,7,10-tetrathiacyclotridecane (L4) was obtained by substitution of o-dichlorobenzene after activation with an organometallic fragment. The structures of L1–L4 and of the four palladium(II) complexes [PdL1]Cl2·2H2O, [PdL2][PF6]2, [PdL3′][PF6]Cl and [PdL4][PF6]2 were determined by X-ray crystallography. All the experimentally determined structures were accurately reproduced by molecular mechanics calculations, using a constant-parametrization scheme. Two parameters for the evaluation of the extent of preorganization of free macrocycle molecules, based on structural and strain-energy differences of the free macrocycles and their corresponding metal complexes, are introduced and discussed on the basis of the experimentally determined and computed structural data for L1–L4, their metal complexes and other similar ligand and metal complex systems. The implications for the design of new compounds leading to high stability and high metal-ion selectivity are outlined.