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Acta Crystallogr C. 2010 March 15; 66(Pt 3): o109–o113.
Published online 2010 February 3. doi:  10.1107/S0108270110001940
PMCID: PMC2855582

Di­hydrogen phosphate mediated supra­molecular frameworks in 2- and 4-chloro­anilinium dihydrogen phosphate salts

Abstract

The title compounds, 2-chloro­anilinium dihydrogen phosphate (2CADHP) and 4-chloro­anilinium di­hydrogen phosphate (4CADHP), both C6H7NCl+·H2PO4 , form two-dimensional supra­molecular organic–inorganic hybrid frameworks. In 2CADHP, the dihydrogen phosphate anions form a double-stranded anionic chain generated parallel to the [010] direction through O—H(...)O hydrogen bonds, whereas in 4CADHP they form a two-dimensional supra­molecular net extending parallel to the crystallographic (001) plane into which the cations are linked through strong N—H(...)O hydrogen bonds.

Comment

The construction of organic–inorganic hybrid compounds has been of considerable inter­est and importance in recent years, not only because they are a powerful means of generating inter­esting supra­molecular frameworks but also due to their potential for providing new materials with magnetic, semiconducting, optical and electrolytic properties (Doyle et al., 2002 [triangle]; Zaccaro & Ibanez, 2000 [triangle]; Chisholm & Haile, 2000 [triangle]). The supra­molecular frameworks of these organic–inorganic compounds are generated by hydrogen-bond inter­actions between donor (D) and acceptor (A) moieties. Ortho­phos­pho­ric acid (H3PO4), an inorganic oxy-acid, forms dihydrogen phosphate salts with organic amines, resulting in organic–inorganic hybrid systems with potentially powerful hydrogen-bonded D/A moieties. The dihydrogen phosphate anions (H2PO4 ) form substructures in these compounds, generating anionic networks via O—H(...)O hydrogen bonds which act as a template for the assembly of cations (Shylaja et al., 2008 [triangle]). A considerable number of dihydrogen phosphate salts are recorded in the Cambridge Structural Database (CSD, Version 5.28; Allen, 2002 [triangle]). In the crystal structure of benzyl­ammonium dihydrogen phosphate monohydrate (Elaoud et al., 1998 [triangle]), the H2PO4 anions form a one-dimensional chain network, while in 3-amino-2-chloro­pyridinium dihydrogen phosphate (Hamed et al., 2007 [triangle]) they form chains of fused An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi1.jpg(8) ring motifs [for graph-set analysis, see Bernstein et al. (1995 [triangle])]. Two-dimensional nets of anionic substructures were also observed in dimethyl­ammonium dihydrogen phosphate (Pietraszko et al., 1999 [triangle]) and 2-methyl­piperazinediium di­hydrogen phosphate (Choudhury et al., 2000 [triangle]). Inter­estingly, in the structure of imidazolinium dihydrogen phosphate (Blessing, 1986 [triangle]), the H2PO4 anions form a three-dimensional cage-type framework inside which the imidazolinium cations are trapped. We have prepared the dihydrogen phosphate salts 2-chloro­anilinium dihydrogen phosphate (2CADHP) and 4-chloro­anilinium dihydrogen phosphate (4CADHP), and have determined their structures and studied the supra­molecular networks in these salts.

An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-scheme1.jpg

The salt 2CADHP crystallizes in the space group P21/n, whereas 4CADHP crystallizes in Pbca. The asymmetric units of both 2CADHP and 4CADHP contain a dihydrogen phosphate anion and a singly protonated 2- or 4-chloro­anilinium cation, respectively. In the tetra­hedral dihydrogen phosphate group of both 2CADHP and 4CADHP, the protonated P—O bond distances are P1—O1 = 1.5696 (11) Å and P1—O2 = 1.5529 (12) Å for 2CADHP, and P1—O1 = 1.541 (2) Å and P1—O2 = 1.557 (2) Å for 4CADHP. These values are as expected and are longer than the other two P—O bonds, viz. P1—O3 = 1.5036 (12) Å and P1—O4 = 1.5031 (12) Å for 2CADHP, and P1—O3 = 1.5168 (17) Å and P1—O4 = 1.4957 (19) Å for 4CADHP. The identical P1—O3 and P1—O4 bond distances observed in 2CADHP indicate delocalization of negative charge between them (Demir et al., 2006 [triangle]). The geometries of the 2- and 4-chloro­anilinium cations show characteristic values com­pared with other reported structures (Muthamizhchelvan et al., 2005 [triangle]; Glidewell et al., 2005 [triangle]). The C—N distances of the 2- and 4-chloro­anilinium cations [C1—N1 = 1.4545 (18) and 1.467 (3) Å, respectively] are longer than the neutral C—NH2 value [1.386 (4) Å; Ploug-Sørenson & Andersen, 1985 [triangle]] and this lengthening is due to the transfer of an H atom to the N atom from the ortho­phos­pho­ric acid.

The hydrogen-bonded organic–inorganic supra­molecular frameworks of 2CADHP and 4CADHP are determined primarily by a combination of O—H(...)O and N—H(...)O hydrogen bonds (Tables 1 [triangle] and 2 [triangle]).

Table 1
Hydrogen-bond geometry (Å, °) for 2CADHP
Table 2
Hydrogen-bond geometry (Å, °) for 4CADHP

In 2CADHP, the inversion-related H2PO4 anions are linked through an O1—H1D(...)O3iii hydrogen bond [symmetry code: (iii) −x + 1, −y + 1, −z + 1], forming an O—H(...)O hydrogen-bonded dimer with a ring motif of An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi1.jpg(8), with its centroid occupying the inversion centre. These dimers are inter­linked through an O2—H2D(...)O3ii hydrogen bond [symmetry code: (ii) x, y + 1, z] to form a ring motif of type An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi3.jpg(12). The alternately fused An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi1.jpg(8) and An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi3.jpg(12) supra­molecular motifs in turn generate a double-stranded inorganic H2PO4 chain made of P—OH(...)O=P hydrogen bonds extend­ing infinitely along the [010] direction (Fig. 3 [triangle]). The 2-chloro­anilinium cations are linked to the anionic substructure through three N—H(...)O hydrogen bonds and a Cl(...)O short contact [Cl(...)O = 3.1705 (14) Å]. The N1—H1A(...)O4 and N1—H1C(...)O4ii hydrogen bonds [symmetry code: (ii) x, y + 1, z], along with O2—H2D(...)O3ii, form a chain of edge-fused An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi6.jpg(10) ring motifs extending along the [010] direction, as observed in the structure of 3-acetyl­anilinium dihydrogen phosphate (Cinčić & Kaitner, 2008 [triangle]). The Cl(...)O1 inter­action, which acts as a pseudo-hydrogen bond (Bryant et al., 1998 [triangle]; Kubicki & Wagner, 2007 [triangle]), with the Cl1 atom at (x, y, z) as donor and atom O1 at (−x + An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi7.jpg, −y + An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi7.jpg, −z + An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi7.jpg) as acceptor, along with the N—H(...)O hydrogen bonds, forms a chain of fused An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi3.jpg(10) motifs extending along the [010] direction. The 21 screw-related chains of An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi6.jpg(10) and An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi3.jpg(10) motifs along (An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi13.jpg, y, An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi13.jpg) (Fig. 4 [triangle]) link the anionic substructure, resulting in the formation of an organic–inorganic sheet framework parallel to (10An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi15.jpg) (Fig. 5 [triangle]).

Figure 3
Part of the crystal structure of 2CADHP, showing the formation of the double-stranded H2PO4 anionic chain built from An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi1.jpg(8) and An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi3.jpg(12) rings through O2—H2D(...)O3ii and O1—H1D(...)O3iii hydrogen bonds extending ...
Figure 4
Part of the crystal structure of 2CADHP, showing the 21 screw-related chains of fused An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi6.jpg(10) and An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi3.jpg(10) rings extending along the [010] direction and linked to the H2PO4 anions through N1—H1A(...)O4, N1—H1C ...
Figure 5
Part of the crystal structure of 2CADHP, showing the formation of the organic–inorganic supra­molecular (10An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi15.jpg) sheet built from An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi1.jpg(8), An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi3.jpg(12), An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi6.jpg(10) and An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi3.jpg(10) rings via N—H(...)O and O—H(...)O hydrogen bonds and a Cl(...)O ...

In 4CADHP, the H2PO4 anions form dimers through an O2—H2D(...)O3iv hydrogen bond [symmetry code: (iv) −x + 1, −y, −z + 1], with the characteristic ring motif of An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi1.jpg(8), in which the centroid of the dimer occupies the crystallographic inversion centre. The O1—H1D(...)O4iii hydrogen bond [symmetry code: (iii) −x + An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi17.jpg, y − An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi7.jpg, z] generates a C4 chain which connects the glide-related anionic dimers with the glide plane perpendicular to the [100] direction, the glide component of which is [0, An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi19.jpg, 0]. This forms an infinite two-dimensional layer in the form of a net extending parallel to the (001) plane. This inorganic supra­molecular net of H2PO4 anions is built from An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi1.jpg(8) and An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi21.jpg(24) ring motifs (Fig. 6 [triangle]). The 4-chloro­anilinium cations are anchored to the H2PO4 anionic net through N1—H1A(...)O4i [symmetry code: (i) −x + 1, −y + 1, −z + 1], N1—H1B(...)O3 and N1—H1C(...)O3ii [symmetry code: (ii) −x + An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi17.jpg, y + An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi7.jpg, z] hydrogen bonds, forming fused-ring motifs of An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi24.jpg(14) and An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi24.jpg(12) types with O—H(...)O hydrogen bonds (Fig. 7 [triangle]). The 4-chloro­anilinium cations are pendant on both faces of the anionic net, thus resulting in the formation of two-dimensional sheet of an organic–inorganic supra­molecular framework (Fig. 8 [triangle]) extending infinitely parallel to the crystallographic (001) plane.

Figure 6
Part of the crystal structure of 4CADHP, showing the formation of the two-dimensional (001) net of H2PO4 anions built from An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi1.jpg(8) and An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi21.jpg(24) rings through O2—H2D(...)O3iv and O1—H1D(...)O4iii hydrogen bonds. ...
Figure 7
Part of the crystal structure of 4CADHP, showing the cations linked to the anionic substructure forming An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi24.jpg(14) and An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi24.jpg(12) fused ring motifs through N1—H1A(...)O4i, N1—H1B(...)O3, N1—H1C(...)O3ii, O1—H1D(...)O4 ...
Figure 8
A projection, down [001], of part of the crystal structure of 4CADHP, showing the (001) sheet of the organic–inorganic supra­molecular framework built from An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi1.jpg(8), An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi21.jpg(24), An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi24.jpg(14) and An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi24.jpg(12) ring motifs extending parallel to the [100] and [010] ...

It is of inter­est to note that in both the title compounds, although they form different types of anionic substructures, the overall anionic–cationic supra­molecular framework results in the formation of infinite two-dimensional sheets. In 2CADHP, the formation of an anionic double-stranded substructure and the linking of the cations to it is analogous with other reported structures. In the crystal structures of 2,4-dimethyl­anilinium dihydrogen phosphate (Fábry et al., 2001 [triangle]), 2-(meth­oxycarbon­yl)anilinium dihydrogen phosphate (Shafiq et al., 2009 [triangle]) and 3,5-dimethoxy­anilinium dihydrogen phosphate (Kaabi et al., 2004 [triangle]) (Z′ = 2Z), the respective cations bound to the anionic substructures form two-dimensional sheets. In the last compound, the substructure was formed with different ring motifs than the other two structures. A three-dimensional hydrogen-bonded framework was observed for 1,3-propane­diammonium bis­(dihydrogen phosphate) (Marsh, 2004 [triangle]), in which the cation contains an additional three N—H bonds involved in hydrogen bonding. The crystal structure of 4CADHP is isomorphous with 4-bromo­anilinium dihydrogen phosphate (CSD refcode UGISEI; Zhang et al., 2001 [triangle]), but no H atoms are reported in CSD. In 4CADHP, the hydrogen-bonded anionic substructure formation and the linking of cations pendant from the supra­molecular net are analogous to the structures of 4-methyl­anilinium dihydrogen phosphate (Smirani et al., 2004 [triangle]) and 4-ethyl­anilinium dihydrogen phosphate (Kaabi et al., 2003 [triangle]), but it has markedly different cell dimensions from 4-bromo­anilinium dihydrogen phosphate, even though they belong to the same Pbca space group.

Experimental

Ethanol solutions containing equimolar quanti­ties of 2-chloro­aniline and orthophospho­ric acid were mixed to produce a white precipitate, which was filtered off, dried for a few hours, dissolved in ethanol and allowed to recrystallize to afford colourless single crystals of 2CADHP after a period of about two weeks.

Colourless crystals of 4CADHP were obtained from a solution of 4-chloro­aniline and orthophospho­ric acid mixed at a 1:1 stoichiometric ratio in a mixed solvent of ethanol and water in equal proportions (50:50 v/v) upon gentle heating. The solution thus prepared was allowed to crystallize and crystals were obtained by slow evaporation of the solvent.

2CADHP

Crystal data

  • C6H7ClN+·H2PO4
  • M r = 225.56
  • Monoclinic, An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi26.jpg
  • a = 11.3143 (6) Å
  • b = 4.7466 (2) Å
  • c = 17.5024 (9) Å
  • β = 108.540 (3)°
  • V = 891.17 (8) Å3
  • Z = 4
  • Mo Kα radiation
  • μ = 0.59 mm−1
  • T = 292 K
  • 0.25 × 0.20 × 0.15 mm

Data collection

  • Bruker Kappa APEXII CCD area-detector diffractometer
  • Absorption correction: multi-scan (SADABS; Bruker 1999 [triangle]) T min = 0.867, T max = 0.917
  • 9738 measured reflections
  • 2044 independent reflections
  • 1902 reflections with I > 2σ(I)
  • R int = 0.018

Refinement

  • R[F 2 > 2σ(F 2)] = 0.030
  • wR(F 2) = 0.084
  • S = 1.05
  • 2044 reflections
  • 122 parameters
  • H-atom parameters constrained
  • Δρmax = 0.39 e Å−3
  • Δρmin = −0.47 e Å−3

4CADHP

Crystal data

  • C6H7ClN+·H2PO4
  • M r = 225.56
  • Orthorhombic, An external file that holds a picture, illustration, etc.
Object name is c-66-0o109-efi30.jpg
  • a = 9.7371 (19) Å
  • b = 7.8756 (16) Å
  • c = 25.141 (5) Å
  • V = 1927.9 (7) Å3
  • Z = 8
  • Mo Kα radiation
  • μ = 0.55 mm−1
  • T = 292 K
  • 0.25 × 0.20 × 0.20 mm

Data collection

  • Bruker Kappa APEXII CCD area-detector diffractometer
  • Absorption correction: multi-scan (SADABS; Bruker 1999 [triangle]) T min = 0.876, T max = 0.899
  • 8591 measured reflections
  • 1687 independent reflections
  • 1483 reflections with I > 2σ(I)
  • R int = 0.037

Refinement

  • R[F 2 > 2σ(F 2)] = 0.040
  • wR(F 2) = 0.127
  • S = 1.07
  • 1687 reflections
  • 123 parameters
  • H-atom parameters constrained
  • Δρmax = 0.50 e Å−3
  • Δρmin = −0.31 e Å−3

The positions of the H atoms bound to N and O atoms were identified from difference electron-density maps, but were subsequently geometrically optimized (O—H = 0.82 Å and N—H = 0.89 Å) and allowed to ride at the best staggered positions, with U iso(H) = 1.5U eq(O,N), except for O2 of 2CADHP whose O—H vector was allowed to rotate around the P—O bond. H atoms bound to C atoms were treated as riding atoms, with C—H = 0.93 Å and U iso(H) = 1.2U eq(C).

For both compounds, data collection: APEX2 (Bruker, 2004 [triangle]); cell refinement: APEX2 and SAINT (Bruker, 2004 [triangle]); data reduction: SAINT and XPREP (Bruker, 2004 [triangle]); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 [triangle]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 [triangle]); molecular graphics: ORTEP-3 (Farrugia, 1997 [triangle]) and Mercury (Macrae et al., 2006 [triangle]); software used to prepare material for publication: PLATON (Spek, 2009 [triangle]).

Figure 1
The independent components of 2CADHP, showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 40% probability level and H atoms are shown as small spheres of arbitrary radii.
Figure 2
The independent components of 4CADHP, showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 40% probability level and H atoms are shown as small spheres of arbitrary radii.

Supplementary Material

Crystal structure: contains datablocks 2CADHP, 4CADHP, global. DOI: 10.1107/S0108270110001940/gd3320sup1.cif

Structure factors: contains datablocks 2CADHP. DOI: 10.1107/S0108270110001940/gd33202CADHPsup2.hkl

Structure factors: contains datablocks 4CADHP. DOI: 10.1107/S0108270110001940/gd33204CADHPsup3.hkl

Acknowledgments

The authors thank Dr Babu Varghese, Senior Scientific Officer, and SAIF at IITM for providing the data-collection facility.

Footnotes

Supplementary data for this paper are available from the IUCr electronic archives (Reference: GD3320). Services for accessing these data are described at the back of the journal.

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