X-ray crystal structure of two different phases (triclinic and orthorhombic) of p-methacryloylaminophenylarsonic acid monomer

Monomer of p-methacryloylaminophenylarsonic acid (p-MAPHA) was prepared from the condensation reaction of p-aminophenylarsonic acid and methacryloyl chloride. From free radical polymerization of the monomer it is possible to obtain interesting polyelectrolyte materials with water-soluble behavior. A noteworthy feature of the p-MAPHA monomer molecule was its crystallization. We found that crystallization conditions led to three different molecule structures within two different crystal systems. The triclinic crystal comprises one molecule per asymmetric unit (two per unit cell) and belongs to a Pi space group, and orthorhombic crystal has two molecules of p-MAPHA per asymmetric unit (eight per unit cell) and belongs to a P2(1)cn space group. It is also important to note that the molecular structure has consequences on the properties of the compounds in crystal form, basically in relation to the expected second harmonic generation (SHG) properties. The latter are related to the solid state of both crystals forms of p-MAPHA. The two different crystals are characterized by an extended intermolecular hydrogen bonding system joining symmetry related molecules. Changes in H positions in the hydrogen bonds within the different phases and conformations of p-MAPHA are sufficient to induce a dramatic change in intermolecular networking and symmetry (which increases from triclinic to orthorhombic), in which case the SHG properties change. The structure of the monomer was also established by mass spectrometry, IR, H-1 and C-13 NMR spectroscopy. (C) 2001 Elsevier Science B.V. All rights reserved.