Competition of the Donor Atoms - Coordination Chemistry of a O,P,N tritopic Ligand - Complexes, Supramolecules and Metal-Organic Frameworks

In the rich field of metal-organic frameworks (MOFs) there is a vast number of results revolving around ligands based on oxygen and nitrogen donors, but little to no work on ligands containing phosphorus donors. A few reasons for this lack of research are obvious: the lower stability of phosphorus(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 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-43n. Finally, the formation of a porous bimetallic MOF. with an interesting topology, could be achieved by the simultaneous coordination of all three donors.