One, two, and three methylene phosphonic acid groups (-CH2PO3H2) on a mesitylene ring: synthesis, characterization and aspects of supramolecular aggregationElectronic supplementary information (ESI) available: Details of spectroscopic investigations of compounds 1-3. CCDC reference numbers 755660-755662. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/b9nj00691e

The ease of substitution of -CH 2 Br group on the mesitylene ring in a stepwise manner has been exploited to prepare mesitylene mono-, bis-, and tris-methylene phosphonic acids C 6 H 2 Me 3 (CH 2 PO 3 H 2 ) ( 1 ), C 6 HMe 3 (CH 2 PO 3 H 2 ) 2 ( 2 ), and C 6 Me 3 (CH 2 PO 3 H 2 ) 3 ( 3 ) in 80-90% yield, through a Michaelis-Arbuzov reaction followed by acid hydrolysis. Compounds 1-4 have been characterized by analytical and spectroscopic (IR, NMR, and MS) techniques. The X-ray structural investigations on all the three compounds reveal that the central mesitylene ring is a robust platform for hosting multiple methylene phosphonic acid groups. Mesitylene mono-methylene phosphonic acid 1 , which can be considered as the sterically encumbered modification of benzyl phosphonic acid, interestingly associates as a one-dimensional tubular structure through extensive O-H O hydrogen bonding between adjacent -PO 3 H 2 groups, albeit with no such interactions between the tubes due to the highly hydrophobic nature of the surface. The X-ray structure of mesitylene-1,3-diphosphonic acid 2 reveals that the molecules exhibit a syn -orientation of the -CH 2 PO 3 H 2 , which are involved in extensive P-OH O hydrogen bonding to result in a two-dimensional layered structure. The presence of three -PO 3 H 2 units on the same side of the mesitylene ring in 3 results in a three-dimensional framework solid. The present studies clearly reveal a linear relationship between the dimensionality of the supramolecular structure and the number of phosphonic acid moieties on the mesitylene ring. Up to three phosphonic acid moieties (-PO 3 H 2 ) can be successively added to a central mesitylene ring by a simple synthetic methodology, yielding mesitylene mono-, bis-, and tris-methylene phosphonic acids.