Crystal structure of 2-ethyl-6-methylanilinium dihydrogenphosphate phosphoric acid, (C9H14N)H2PO4 · H3PO4

Abstract

C9H19NO8P2, orthorhombic, Pca2 (no. 29), a = 24.348(4) A, b = 8.088(2) A, c = 7.623(4) A, V= 1501.2 A3, Z = 4, Rgt(F) = 0.039, wRKf(F) = 0.049, T = 296 K. Source of material Crystals of title compound were synthesized by reaction of stirred ethanolic solution of 2-ethyl-6-methylaniline with concentrated phosphoric acid. Then, the obtained solution was evaporated in air for several days at room temperature until formation of pris- matic crystals with suitable size for X-ray analysis. Discussion The acentric space group Pca21 is confirmed by a positive (SHG) test on a powdered sample using an Nd3*: YAG laser fundamen- tal beam (1.06 μπι). The asymmetric unit consists of three funda- mentals entities, the H3PO4 molecule, the H2PC>4~ anion and the organic C9Hi4N+ cation (figure, top). The crystal structure of the title compound is built by alternate inorganic and organic layers along the a axis and linked by strong N-H-O hydrogen bonds (figure, bottom). The H2PO4- anions and H3PO4 molecules are connected alternately by O-H-O hydrogen bonds to form infi- nite corrugated inorganic chains parallel to the b,c plane and cen- tered at χ = 0 and Vi. The organic C9H14N* cations are organized in opposite direction along the c axis between the inorganic layers and situated at χ = V* and so that each one establishes another kind of strong N-H—O hydrogen bonds with the anionic chains involving the three hydrogen atoms of the NH3 group bonded to one phosphoric acid molecule and two H2PO4- anions. As a re- sult, these two types of hydrogen bonds contribute to the cohesion in the network of the present crystal structure. The comparison of this structure with that one of HisH+ · H2PO4- - H3PO4 (1) shows that both structures are built up by a large num- ber of similar hydrogen bonds formed between Λ-NH3 groups, dihydrogenphosphate anions and phosphoric acid molecules and present also infinite hydrogen-bonded layers. In spite of these similarities, the molecules of phosphoric acid are not hydrogen- bonded to each other in the latter structure (1), since the imid- azolium cations also participate on the hydrogen bonding system. The structure of the title compound is also closely related to that of (2,3-(CH3)2C6H3NH3)H2P04 (2), In fact, these two structures have a similarly typical layered organization and the same ar- rangement in opposite direction of organic cations. Furthermore, the inorganic anion chains screen the interaction between the or- ganic cations and probably lead to a non-centrosymmetric atomic arrangement in the two structures. Therefore, the title compound could be an interesting material in the non-linear optics. Its abso- lute structure could not be determined.