Playing dice with zeolite secondary building blocks

Our laboratory has been using an organic soluble phosphate monoester (ArO)P(O)(OH) (Ar =  2,6-diisopropylphenyl) as the  primary building unit (PBU) to assemble a large number of polyhedral molecules that resemble one or more of zeolite secondary building units and display various functions.1-4 While the reaction of this phosphate with a divalent metal ion (e.g. Zn2+) in a donor solvent  predominantly leads to the isolation of stable tetranuclear metal phosphates [(ArO)PO3Zn(L)]4 which possess a Zn4O12P4 D4R SBU inorganic core. In recent times, however, we have unraveled that it is possible to also isolate other SBUs, starting from the same set of reactants, but by making small variations in the reaction conditions. Now it is possible to isolate hitherto unknown discrete D6R and D8R SBUs (which possessZn6O18P6 and Zn8O24P8cores, respectively) by switching the solvent from methanol to acetonitrile and the co-ligand from DMSO to either 4-formylpyridine5 or 4-cyanopyridine.6From a series of experimental observations it has now become apparent that, irrespective of the conditions employed, S4R SBUs are formed as the initial products. It is quite intuitive to conclude that a face-to-face fusion of two S4R blocks will lead to the formation of a D4R SBU. The explanation for the formation of larger SBUs such as D6R and D8R from a S4R however would need a different two-stage mechanism involving (a) side-by-side fusion of two or more S4Rsand (b) a constructive folding to close up the double-n-ring (n = 4, 6, or 8) SBUs. One cannot discount the possibility of misfolding in step (b), which will lead to the isolation of polymeric chains with a staircase conformation.  Similarly, formation of larger S6R and S8R SBUs in the initial phase of the reaction cannot also be ignored. A rationalization of these building principles will be presented in this lecture.

References:
1.	Kalita, A.C.; Roch-Marchal, C.;Murugavel, R.Dalton
        Trans., 2013, 26, 9755.
2.	Kalita, A.C.; Murugavel, R.Inorg. Chem., 2014, 53,
        3345.
3.	Kalita, A.C.; Gogoi, N.;Jangir, R.; Kupuswamy, S.; 
        Walawalkar, M. G.; Murugavel, R.Inorg. Chem.,2014,
        53, 8959.
4.	Kalita, A.C.; Sharma, K.; Murugavel, R.  Cryst. 
        Eng. Comm.2014, 16, 51.
5.	Gupta, S.K.; Dar, A. A.; Rajeshkumar, T.; 
        Kuppuswamy, S.; Langley, S. K.; Murray, K. S.; 
        Rajaraman, G.; Murugavel, R. Dalton Trans. 2015, 
        44, 5587.
6.	Gupta, S.K.; Kuppuswamy, S.; Walsh, J. P. S.; 
        McInnes, E. J. L.; Murugavel, R. Dalton Trans. 
        2015, 44, 5961.
7.	Gupta, S.K.; Kalita, A.C.; Murugavel, R. unpublished
8.	Dar, A.; Murugavel, R. unpublished
9.	Dar, A.; Sharma, S. K.; Murugavel, R. Inorg. Chem.
        2015,54, 7953. 
10.	Dar, A.; Gupta, S. K.; Sen. S.; Patwari, G. N.; 
        Murugavel, R. Inorg. Chem. 2015,54, 0000.