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New hemi-cage compounds with the formula Pd2(L1)2(L2)2 (L1 = ditopic pyridine ligand, L2 = bpy or TMEDA) have been synthesized and characterized by spectroscopic methods, X-ray crystallography and electronic structure methods. The host–guest chemistry of these new structures, with naphthoquinone as a guest, reveals the key role of the host shape and flexibility on competitive binding processes. The influence of counteranions, solvent and non-covalent interactions to binding were quantified by Density Functional Theory calculations. Together, this study provides new insights into the concept of pre-organized guest binding when applied to charged, coordination-assembled hosts.

The self-assembly process of a Pd2L4 cage complex consisting of rigid ditopic ligands, in which two 3-pyridyl groups are connected to a benzene ring through acetylene bonds, and Pd(II) ions was firstly revealed by a recently developed QASAP (quantitative analysis of self-assembly process), with which the self-assembly process of the coordination assemblies can be investigated by monitoring the time evolution of the average composition of all the intermediates. QASAP revealed that the rate-determining steps of the cage formation are the intramolecular ligand exchanges in the final stage of the self-assembly, [Pd2L4Py*2]4+ → [Pd2L4Py*1]4+ + Py* and [Pd2L4Py*1]4+ → [Pd2L4]4+ + Py* (Py*: 3-chloropyridine, which was used as a leaving ligand on the metal source). The energy barriers for the two reactions were determined to be 22.3 and 21.9 kcal mol-1, respectively. DFT calculation of the TS (transition state) structures for the two steps indicates that the distortion of the trigonal-bipyramidal Pd(II) center at the TS geometries increases the activation free energy of the two steps.

The synthesis of a novel [2]rotaxane host system containing a bis(triazolium)acridine-based axle component is reported. (1)H NMR anion-binding titrations reveal that the rotaxane is able to recognise selectively the NO3(-) anion over a range of more basic oxoanions (AcO(-), HCO3(-) and H2PO4(-)) in a competitive organic-aqueous solvent mixture.

Financial support of the Spanish Ministry of Science and Innovation (CTQ2012-38543-C03) and Generalitat Valenciana (PROMETEO/2012/020) is acknowledged. V.M.-C. thanks the Spanish Ministry of Science and Education for a predoctoral fellowship (FPU AP2007-02562) and Generalitat Valenciana for a VALi+d postdoctoral fellowship (APOSTD/2013/041). M.D.P. thanks the Spanish Ministry of Education for a postdoctoral fellowship and UGC India for a Startup Grant.