Palladium(II) driven self-assembly of non-chelating symmetrical bidentate ligand is known to provide PdnL2n type (n=2 to 7, 12, 24, 30 and 48) single-cavity cages.1 In multi 3D-cavity systems two or more 3D-cages are conjoined through a common metal centre. However, the construction of low symmetry single as well as multi-cavity cages is relatively unexplored area. Such Pd(II)-based low symmetry systems can be achieved by two ways (i)utilizing one type of low symmetry ligands (ii) by mixing two or more type of ligands(symmetrical or unsymmetrical) which undergoes integrative self-sorting.2
In the year 2014, our group reported a double decker, Pd3L4 type coordination cage where two identical cavities are conjoined in linear fashion.3 In the year 2017, Crowley and coworkers reported a linear triple cavity Pd4L4 type cage where three cavities are conjoined in a linear fashion.4 Here the environment of central cavity differs slightly from that of two peripheral cavities even though cavity sizes are equal. Recently our group also reported a Pd4L4 system where the central cavity differs in size from two equal sized peripheral cavities.5 Inspired from these reports, we designed a low symmetry triple cavity cage of formula Pd4Lun4 using an unsymmetrical tetradentate ligand (Lun). This assembly will comprise of three unequal cavity sizes. Also in the year 2020, our group reported a Pd6L6 type multi cavity cage, where one unit of a Pd3L6 type cage is peripherally decorated with three units of an equal sized Pd2L4 type cage. Taking inspiration from this work, we propose the preparation of a mix ligated assembly of [Pd6(L1un)2(L2un)2(L3un)2] type which comprises of three different types of Pd2L4 units of unequal sizes laterally conjoined to the Pd3L6 unit giving rise to a unique supramolecular architecture. These cages are expected to bind more than one type of guests in segregated manner.
References:
1. Saha, S.; Regeni, I.; Clever, G. H. Coord. Chem. Rev. 2018, 374, 1-14.
2. Sharma, S.; Sarkar, M.; Chand, D. K. Chem. Commun., 2023, 59, 535-554.
3. Bandi, S.; Pal, A.K.; Hanan, G. S.; Chand, D. K. Chem. Eur. J., 2014, 20, 13122-13126.
4. Preston, D.; Lewis J. E. M.; Crowley J. D. J. Am. Chem. Soc. 2017, 139, 2379–2386.
5. Mishra, S. S.; Krishnaswamy S., Chand, D. K. J. Am. Chem. Soc. 2024, 146, 4473–4488.
6. Samantray, S.; Chand, D. K. Nat. Commun. 2020, 11, Article 880.