The cooperative action of multiple non-covalent interactions allowed for the assembly of a new series of Pb ^II coordination compounds.

Folding can bestow macromolecules with various properties, as evident from nature’s proteins. Until now complex folded molecules are either the product of evolution or of an elaborate process of design and synthesis. We now show that molecules, that fold in a well-defined architecture of substantial complexity, can emerge autonomously and selectively from a simple precursor. Specifically, we have identified a self-synthesizing macrocyclic foldamer with a complex and unprecedented secondary and tertiary structure, that constructs itself highly selectively from 15 identical peptide-nucleobase subunits, using a dynamic combina-torial chemistry approach. Folding of the structure drives its synthesis in 95% yield from a mixture of interconverting molecules of different ring sizes in a one-step process. Single crystal X-ray crystallography and NMR reveals a folding pattern based on an intricate network of noncovalent interactions involving residues space apart widely in the linear sequence. These results establish dynamic combinatorial chemistry as a powerful approach to developing synthetic molecules with folding motifs of a complexity that goes well beyond that accessible with current design approaches. The fact that such molecules can form autonomously implies that they may have played a role in the origin of life at earlier stages than previously thought possible.

A new supramolecular Pb(II) complex [PbL(NO₂)]_n was synthesized from Pb(NO₃)₂, N’-(1-(pyridin-2-yl)ethylidene)isonicotinohydrazide (HL) and NaNO₂. [PbL(NO₂)]_n is constructed from discrete [PbL(NO₂)] units with an almost ideal N₂O₃ square pyramidal coordination environment around Pb(II). The ligand L⁻ is coordinated through the 2-pyridyl N-atom, one aza N-atom, and the carbonyl O-atom. The nitrite ligand binds in a κ²-O,O coordination mode through both O-atoms. The Pb(II) center exhibits a hemidirected coordination geometry with a pronounced coordination gap, which allows a close approach of two additional N-atoms arising from the N=C(O) N-atom of an adjacent molecule and from the 4-pyridyl N-atom from the another adjacent molecule, yielding a N₄O₃ coordination, constructed from two Pb–N and three Pb–O covalent bonds, and two Pb⋯N tetrel bonds. Dimeric units in the structure of [PbL(NO₂)]_n are formed by the Pb⋯N=C(O) tetrel bonds and intermolecular electrostatically enforced π⁺⋯π⁻ stacking interactions between the 2- and 4-pyridyl rings and further stabilized by C–H⋯π intermolecular interactions, formed by one of the methyl H-atoms and the 4-pyridyl ring. These dimers are embedded in a 2D network representing a simplified uninodal 3-connected fes (Shubnikov plane net) topology defined by the point symbol (4∙8²). The Hirshfeld surface analysis of [PbL(NO₂)] revealed that the intermolecular H⋯X (X = H, C, N, O) contacts occupy an overwhelming majority of the molecular surface of the [PbL(NO₂)] coordination unit. Furthermore, the structure is characterized by intermolecular C⋯C and C⋯N interactions, corresponding to the intermolecular π⋯π stacking interactions. Notably, intermolecular Pb⋯N and, most interestingly, Pb⋯H interactions are remarkable contributors to the molecular surface of [PbL(NO₂)]. While the former contacts are due to the Pb⋯N tetrel bonds, the latter contacts are mainly due to the interaction with the methyl H-atoms in the π⋯π stacked [PbL(NO₂)] molecules. Molecular electrostatic potential (MEP) surface calculations showed marked electrostatic contributions to both the Pb⋯N tetrel bonds and the dimer forming π⁺⋯π⁻ stacking interactions. Quantum theory of atoms in molecules (QTAIM) analyses underlined the tetrel bonding character of the Pb⋯N interactions. The manifold non-covalent interactions found in this supramolecular assembly are the result of the proper combination of the polyfunctional multidentate pyridine-hydrazide ligand and the small nitrito auxiliary ligand.

A new coordination polymer [Hg(L^I)I]_n (1) and a new discrete coordination complex [Hg(HL^II)I₂] (2) are synthesized and X-ray characterized. The existence of positive π-holes at the spodium atoms in both compounds is evidenced by DFT calculations. In 1, a Hg–S semicoordination bond and a Hg⋯I spodium bond are formed at opposite sides of the π-hole. In 2, two different Hg⋯I spodium bonds are formed at both sides of the π-hole. This is the first study describing structure-guiding π-hole spodium bonding.