Wheel and Axle Topology Driven Halogen Bonds for the Construction of Molecular Arrays in Hexacoordinated Sn(IV)Porphyrins: A Structural and Theoretical Investigation

Abstract

The present study illustrates how halogen bonds (XB) in conjunction with judiciously selected molecular scaffolds can be used for the construction of molecular arrays (ladder, one-dimensional (1D), and two-dimensional (2D) frameworks) in a series of Sn­(IV)-porphyrin derivatives, which topologically resemble a “wheel–axle” duo. In all the complexes investigated here, the wheel is constructed with Sn­(IV)-5,10,15,20-meso-tetrakis­(4-bromophenyl)­porphyrin [Sn­(L)2-TBrPP], which is relatively rigid, and the two pairs of diametrically opposite Br atoms can get involved in various kind of halogen bond interactions, depending upon the complementary atom(s) present at the axle. Detailed single crystal X-ray structural studies of these complexes reveal the diverse occurrence of Br···O, Br···Br, Br···π halogen bonds, and these XBs are not only restricted between the wheel···axle alone, but also can occur among themselves (i.e., wheel···wheel and axle···axle). Different types of XB directed molecular associations are observed; for example, ladder type supramolecular associations occur in 1 and 2, interlinked 1D framework in 4, molecular chains in 7, 2D-framework in 8, etc. Complementary theoretical studies with Hirshfeld surface analysis show the definite role of Br···Br interactions in the overall stability and mapping of electrostatic potential isosurfaces with the aid of density functional theory in 8 definitely shows the presence of a σ-hole, a requisite feature to show XBs in the crystalline state. The detailed structural and theoretical studies presented here clearly vouch for the use of wheel and axle topology driven halogen bonds for the construction of molecular arrays in hexa-coordinated Sn­(IV)-porphyrin derivatives. Photophysical studies show that the variation of axial ligands has a minimal effect on fluorescence as well as the excited state lifetime in these complexes.

Electrochemical, Photophysical, Morphological and DFT Study of Polymorphic Sn(IV)‐Porphyrins Containing Fluorinated Axial Ligand

“…The calculate σ‐hole potential shows V S,max values close to +12.5 kcal mol −1 [58] . The presence of the σ‐hole is in full agreement with earlier theoretical studies reported by us and others in the literature [58—62,17–20] …”

“…[58] The presence of the σ-hole is in full agreement with earlier theoretical studies reported by us and others in the literature. [58][59][60][61][62][17][18][19][20]…”

Hexacoordinated Sn(IV) porphyrin‐based square‐grid frameworks exhibiting selective uptake of CO2 over N2

“…In the structure of 1 , the axial chloro ligand interacts with the pyrrole ring of adjacent porphyrin unit, with distances of 3.507 Å (Cl⋯centroid) and 3.419 Å (Cl⋯C β ) (Figure 3). 42 Weak Cl–Cl interactions were also found between the axial chloro ligands with a distance of 4.568 Å. Consequently, the square structural motifs of the stacked 2D layers were well aligned, forming porous channels in 1 .…”

Porphyrin’s Ring Current as a Driving Force for Halogen Bond Interactions: A Computational Study

“…In our previous work on six coordinated tin-porphyrin complexes, [29][30][31] we observed an interesting phenomenon in the solid phase. The location of the halogen bond donor or acceptor on the porphyrin plays a critical role in the self-assembly process.…”