Pt(II)-Coordinated Tricomponent Self-Assemblies of Tetrapyridyl Porphyrin and Dicarboxylate Ligands: Are They 3D Prisms or 2D Bow Ties?

Abstract

Thermodynamically favored heteroleptic coordination of Pt(II) ions with one aza-and another oxocoordinating ligand yield tricomponent supramolecular coordination complexes (SCCs) that possess much greater structural complexity and functional diversity than traditional bicomponent SCCs containing only one of the ligands. Herein, we demonstrate that heteroleptic coordination of tetrapyridyl porphyrins (M¢TPP, M¢ = Zn or H2) and various dicarboxylate ligands (XDC) having different lengths and rigidity withcomplexes featuring a M¢TPP core and two parallel XDC linkers held together by four heteroligated Pt II (N,O) corners. Although previous reports had claimed that the self-assembly of these three components produced tetragonal prisms having two cofacial M¢TPP planes connected by four XDC linkers via eight Pt II (N,O) corners, our extensive 1 H, 31 P, and 2D NMR, ESI-MS, X-ray crystallographic, and computational studies unequivocally demonstrated that in reality, no such prism was formed, because instead of connecting two cofacial M¢TPP ligands, the XDC linkers actually bridged two adjacent pyridyl termini of an M¢TPP ligand via shared Pt II (N,O) corners, forming bow tie complexes. In addition to direct crystallographic evidence, the NMR spectra of these complexes revealed that the M¢TPP ligands contained two distinct sets of pyrrole protons (4 each)-those located inside the triangles were shielded by and coupled to adjacent XDC linkers, whereas the exposed ones were not-the unmistakable signs of bow tie structures instead of prisms. Thus, this work not only unveiled novel supramolecular architecture, but also accurately defined the actual structures and compositions of M¢TPP-based tricomponent SCCs.