The tritopic heterofunctional ligand 4-(3-(4-(diphenylphosphino)phenyl)-3-oxopropanoyl)benzonitrile (HL) combines a Pearson hard β-diketone, a soft nitrile, and an even softer phosphine group in one molecule. The hard cations Al III and Fe III selectively bind to the β-diketo site of the deprotonated ligand, but the resulting [ML 3 ] complexes could only be characterized by spectroscopic methods. The softer cations Hg II and Pd II selectively bind to the phosphine moiety rather than to the nitrile. Cross-linking of the [ML 3 ] metalloligands with soft cations affords both discrete aggregates and extended structures that could be structurally characterized. With Hg II a neutral tetranuclear rectangle is obtained in which the O,O′ and the P donors act as coordination sites. Cross-linking with Ag I involves both Pearson soft phosphane and nitrile groups and affords two porous metal−organic frameworks; in these 3D structures all three donor sites are employed. The reaction of [Cu(MeCN) 4 ]PF 6 with [AlL 3 ] leads to yet another degree of aggregation: namely, the octanuclear complex [(AlL 3 ) 4 Cu 4 ](PF 6 ) 4 . The crystal structure of this supramolecular cube features very large intra-and intermolecular voids.

Strong and weak halogen bonds (XBs) in discrete aggregates involving the same acceptor are addressed by experiments in solution and in the solid state. Unsubstituted and perfluorinated iodobenzenes act as halogen donors of tunable strength; in all cases, quinuclidine represents the acceptor. NMR titrations reliably identify the strong intermolecular interactions in solution, with experimental binding energies of approx. 7 kJ/mol. Interaction of the σ hole at the halogen donor iodine leads to a redshift in the symmetric C–I stretching vibration; this shift reflects the interaction energy in the halogen-bonded adducts and may be assessed by Raman spectroscopy in condensed phase even for weak XBs. An experimental picture of the electronic density for the XBs is achieved by high-resolution X-ray diffraction on suitable crystals. Quantum theory of atoms in molecules (QTAIM) analysis affords the electron densities and energy densities in the bond critical points of the halogen bonds and confirms stronger interaction for the shorter contacts. For the first time, the experimental electron density shows a significant effect on the atomic volumes and Bader charges of the quinuclidine N atoms, the halogen-bond acceptor: strong and weak XBs are reflected in the nature of their acceptor atom. Our experimental findings at the acceptor atom match the discussed effects of halogen bonding and thus the proposed concepts in XB activated organocatalysis.

In the rich field of metal-organic frameworks (MOFs) there is a vast number of results with O and N donor ligands, but little to no work on ligands containing P donors. A few reasons for this lack of research are obvious: the lower stability of P III , the more elaborate syntheses, and the nonexistent availability of commercially suitable candidate molecules. Nevertheless, the usage of phosphorus can enable a much greater variety of structural possibilities for MOF synthesis, as it can stabilize metal cations in low oxidation states, among other advantages.Thus, we intend to compare the abilities of the three donors by preparing the ligand 4-(3-(4-(diphenylphosphino)phenyl)-3-oxopropanoyl)benzonitrile. This multifunctional ligand contains a chelating beta-diketone and a nitrile group as O and N donors, as well as a triarylphosphine P donor group. The results show that its coordination behavior very much depends on reaction conditions. We have selectively prepared mononuclear complexes on both the O and P side, but no purely N coordinated complexes could be obtained. Furthermore, we have crystallized a bimetallic supramolecular cube in the rare cubic space group P ത 43n. Finally, the formation of a porous bimetallic MOF with an interesting topology could be achieved by the simultaneous coordination of all three donors.

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