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Wheel and Axle Topology Driven Halogen Bonds for the Construction of Molecular Arrays in Hexa-coordinated Sn(IV)Porphyrins: A Structural and Theoretical Investigation Sushila $, P. Venugopalan, Ramesh Kataria, Dipak Kumar Das, Arvind Chaudhary, and Ranjan Patra Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.8b01489 • Publication Date (Web): 08 Jan 2019 Downloaded from http://pubs.acs.org on January 9, 2019
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Crystal Growth & Design
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Wheel and Axle Topology Driven Halogen Bonds for the Construction of Molecular Arrays in Hexa-coordinated Sn(IV)Porphyrins: A Structural and Theoretical Investigation Sushila,a P. Venugopalan,a Ramesh Kataria,a Dipak Kumar Das,a Arvind Chaudharyb and Ranjan Patra*a aDepartment
of Chemistry and Centre for Advanced Studies in Chemistry, Panjab University,
Chandigarh-160014, India. bScience
and Engineering Research Board, New Delhi-110070, India.
Email:
[email protected] 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, 1D and 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 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 σ-hole, a requisite feature to definitely show XBs in the crystalline state. The detailed structural and theoretical studies presented here clearly vouch the use of wheel and axle topology driven halogen bonds for the construction of molecular arrays in hexa-coordinated Sn(IV)-porphyrin derivatives.
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2 Photophysical studies shows that the variation of axial ligands has minimal effect on fluorescence as well as excited state life time in these complexes. Introduction Scientific research on porphyrin-based porous organic framework materials has taken new impetus with significant advancements recently, as it leads to novel 3D constructs with desired properties, often as aimed and planned with pre-conceived concepts.1-9 Considerable structural diversity can be attained on these macrocycles through easily amenable synthetic elaborations and it has become a convenient way to generate diverse porphyrin based organic frameworks. Extensive research along these lines have generated large number of porphyrinic Covalent Organic Frameworks (COFs)4-9 and the well coordinating ability of the macrocycle to diverse metal ions has further aided the synthesis of another important family of Metal Organic Frameworks (MOFs).1−3 The characteristic rigid structure, large surface area and high porosity of these framework structures make them important candidates for the application of gas storage, separation, sensing and catalysis etc.1-9 Very recently, a new class of materials named as Halogen Bonded Organic Frameworks (XBOFs) has emerged as another exciting class of compounds constructed purely by relatively weak halogen bonding interactions.10-12 The building blocks of MOFs and COFs interact via strong metal-ligand coordination and covalent bond respectively. However, the exciting idea that much weaker interactions, such as halogen bonds (XB) are effective molecular association tools for developing dimensionality in condensed matter has given tremendous impetus to understand XB in minute details (with all its intricacies) such that first level rational design principles are well laid for the generation of novel materials with targeted properties. For example, the use of ‘Gulliver Effect’ (i.e., individually weak but collectively strong)13 for the construction of Hydrogen Bonded Organic Frameworks (HOFs) is not restricted to hydrogen bonding alone, but it is equally effective in XB and can be used for generating XBOFs has opened up new avenues to generate porous materials for gas storage and allied applications.10-12 Halogen bond14-19 (XB) involving the first four members of halogen family (F, Cl, Br, I) is extensively studied and well documented through number of theoretical20-24 and experimental25-30 investigations and the seminal work of Galland et al. included the heaviest member, astatine also, completing the XB participation trend among halogens as F
