Pt(ii)-coordinated tricomponent self-assemblies of tetrapyridyl porphyrin and dicarboxylate ligands: are they 3D prisms or 2D bow-ties?

Thermodynamically favored simultaneous coordination of Pt(ii) corners with aza- and carboxylate ligands yields tricomponent coordination complexes with sophisticated structures and functions, which require careful structural characterization to paint accurate depiction of their structure-function relationships. Previous reports claimed that heteroleptic coordination of cis-(Et3P)(2)Pt-II with tetrapyridyl porphyrins (M ' TPP, M ' = Zn or H-2) and dicarboxylate ligands (XDC) yielded 3D tetragonal prisms containing two horizontal M ' TPP faces and four vertical XDC pillars connected by eight Pt(ii) corners, even though such structures were not supported by their H-1 NMR data. Through extensive X-ray crystallographic and NMR studies, herein, we demonstrate that self-assembly of cis-(Et3P)(2)Pt-II, M ' TPP, and four different XDC linkers having varied lengths and rigidities actually yields bow-tie (⋈)-shaped 2D [{cis-(Et3P)(2)Pt}(4)(M ' TPP) (XDC)(2)](4+) complexes featuring a M ' TPP core and two parallel XDC linkers connected by four heteroleptic Pt-II corners instead of 3D prisms. This happened because (i) irrespective of their length (similar to 7-11 angstrom) and rigidity, the XDC linkers intramolecularly bridged two adjacent pyridyl-N atoms of a M ' TPP core via Pt-II corners instead of connecting two cofacial M ' TPP ligands and (ii) bow-tie complexes are entropically favored over prisms. The electron-rich ZnTPP core of a representative bow-tie complex selectively formed a charge-transfer complex with highly pi-acidic 1,4,5,8,9,12-hexaazatriphenylene-2,3,6,7,10,11-heaxacarbonitrile but not with a pi-donor such as pyrene. Thus, this work not only produced novel M ' TPP-based bow-tie complexes and demonstrated their selective pi-acid recognition capability, but also underscored the importance of proper structural characterization of supramolecular assemblies to ensure accurate depiction of their structure-property relationships.