metal-organic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

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Dipotassium rhodizonate

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aDepartment of Chemistry, University of Durham, Durham DH1 3LE, England
*Correspondence e-mail: jacowan@anl.gov

(Received 18 February 2004; accepted 8 March 2004; online 31 March 2004)

Dipotassium rhodizonate, 2K+·C6O62−, crystallizes in space group Fddd. The rhodizonate anions lie in hexagonal layers connected by the potassium ions, which lie between the planes and connect adjacent layers. The conformation of the rhodizonate ion is distinct from previous observations. The site symmetry of the potassium ions is 2 and the site symmetry of the centroid of the rhodizonate ions is 222.

Comment

The crystal structures of potassium and rubidium rhodizonates were determined by Neumann (1965[Neumann, M. A. (1965). PhD thesis, University of Wisconsin, USA.]); however, the coordinates were unavailable in the Cambridge Structural Database (Version 5.25, update of January 2004; Allen, 2002[Allen, F. H. (2002). Acta Cryst. B58, 380-388.]). Rubidium rhodizonate has recently been re-reported by Braga et al. (2001[Braga, D., Cojazzi, G., Maini, L. & Grepioni, F. (2001). New J. Chem. 25, 1221-1223.]). We wished to compare the cocrystallization behaviour of rhodizonic acid (C6O6H2) with 2,6-di­hydroxy­benzo­quinone (C6O4H4) and tetra­hydroxy­benzo­quinone (C6O6H4). While we have produced crystals containing these mol­ecules (Cowan et al., 2001a[Cowan, J. A., Howard, J. A. K. & Leech, M. A. (2001a). Acta Cryst. C57, 302-303.],b[Cowan, J. A., Howard, J. A. K. & Leech, M. A. (2001b). Acta Cryst. C57, 1196-1198.]), so far we have been unable to produce a cocrystal containing rhodizonic acid. We have obtained the potassium salt, (I[link]), as a by-product of this project and redetermined its structure.

[Scheme 1]

Rhodizonic acid is an intriguing mol­ecule used by crime fighters to detect traces of lead produced by gunfire (Bartsch et al., 1996[Bartsch, M. R., Kobus, H. J. & Wainwright, K. P. (1996). J. Forensic Sci. 41, 1046-1051.]). It is a weak organic acid, which should participate in a variety of different hydrogen bonds, and upon deprotonation to rhodizonate its shape and properties change significantly.

Potassium rhodizonate (Fig. 1[link]) crystallizes in space group Fddd. The metal ion lies between four rhodizonate anions, bonding with eight O atoms (Fig. 2[link]). The rhodizonate anions lie in hexagonal layers connected by the potassium ions, which lie between the planes and connect adjacent layers (Fig. 3[link]). The site symmetry of the potassium ions is 2 and the site symmetry of the centroid of the rhodizonate ions is 222. This structure is incompatable with the cell dimensions and space group, which are availiable in the CSD, of the original structure (Neumann, 1965[Neumann, M. A. (1965). PhD thesis, University of Wisconsin, USA.]) and may be a polymorph or a low-temperature phase.

There are four previously published structures containing the rhodizonate ion, in which there are two distinct conformations; the conformation in the present structure is distinct from either of those previously determined. The C—O bond lengths in the rhodizonate ion [1.254 (5) and 1.255 (3) Å] are essentially the same as those observed in the rubidium salt [1.252 (9) and 1.248 (6) Å] ; however, the C—C bond lengths [1.480 (5) and 1.479 (3) Å] are slightly longer than those in the rubidium salt [1.468 (6) and 1.469 (6) Å]. The rhodizonate ion, in contrast with the situation observed in the rubidium salt, is not planar but has a twisted-boat form (r.m.s. deviation from the plane = 0.108 Å); consequently, the molecular symmetry is not D6h but D2. It is worth noting that the rubidium salt is not isostructural with the potassium salt (Braga et al., 2001[Braga, D., Cojazzi, G., Maini, L. & Grepioni, F. (2001). New J. Chem. 25, 1221-1223.]). Lam & Mak (2001a[Lam, C.-K. & Mak, T. C. W. (2001a). Angew. Chem. Int. Ed. 40, 3453-3455.],b[Lam, C.-K. & Mak, T. C. W. (2001b). Chem. Commun. pp. 1568-1569.]) have produced organic cocrystals containing the rhodizonate ion acting as a multi-hydrogen-bond acceptor, in which the rhodizonate ion is smaller with a greater variation in its internal bond lengths; for example, a range of 1.421 (5)–1.458 (5) Å is found in the C—C bonds and 1.234 (4)–1.258 (4) Å in the C=O bonds in bis(tetra-n-butyl­ammonium) rhodizonate tetrakis­(phenyl­urea) clathrate (Lam & Mak, 2001b[Lam, C.-K. & Mak, T. C. W. (2001b). Chem. Commun. pp. 1568-1569.]).

[Figure 1]
Figure 1
The ions of the title compound, shown with 50% probability displacement ellipsoids. [Symmetry codes: (I) [5\over 4] − x, [5\over4] − y, z; (II) [5\over4] − x, y, [1\over4] − z; (III) x, [5\over4] − y, [1\over4] − z.]
[Figure 2]
Figure 2
The coordination of the potassium ion in the title compound. [Symmetry codes: (I) [1\over 4] − x, 1 − y, [{1 \over 2}] − z; (II) [1\over4] + x, 1 − y, [1\over4] + z; (III) [3\over4] − x, y, [3\over 4] − z; (IV) [{1 \over 2}] − x, −[1\over4] + y, [1\over4] + z; (V) [-{1 \over 2}] + x, [5\over4] − y, [3\over4] − z; (VI) [{1 \over 2}] − x, 1 − y, [{1 \over 2}] − z.]
[Figure 3]
Figure 3
Packing diagram illustrating a layer of rhodizonate ions. The potassium ions connect the anions above and below the plane.

Experimental

Rhodizonic acid dihydrate (approximately 0.5 g), purchased from Aldrich Chemicals, was dissolved in 0.1 M potassium hydro­xide, producing an intense deep-red solution. Crystals suitable for X-ray structure determination were prepared by slow evaporation of the solvent at room temperature.

Crystal data
  • 2K+·C6O62−

  • Mr = 246.26

  • Orthorhombic, Fddd

  • a = 8.426 (2) Å

  • b = 12.011 (3) Å

  • c = 15.671 (3) Å

  • V = 1586.0 (6) Å3

  • Z = 8

  • Dx = 2.063 Mg m−3

  • Mo Kα radiation

  • Cell parameters from 982 reflections

  • θ = 12.4–22.1°

  • μ = 1.19 mm−1

  • T = 100 (2) K

  • Block, dark red

  • 0.20 × 0.15 × 0.10 mm

Data collection
  • Bruker SMART CCD diffractometer

  • ω scans

  • 3525 measured reflections

  • 462 independent reflections

  • 392 reflections with I > 2σ(I)

  • Rint = 0.049

  • θmax = 27.5°

  • h = −10 → 10

  • k = −15 → 15

  • l = −20 → 20

Refinement
  • Refinement on F2

  • R[F2 > 2σ(F2)] = 0.038

  • wR(F2) = 0.093

  • S = 1.06

  • 462 reflections

  • 34 parameters

  • w = 1/[σ2(Fo2) + (0.034P)2 + 24.4908P] where P = (Fo2 + 2Fc2)/3

  • (Δ/σ)max < 0.001

  • Δρmax = 0.47 e Å−3

  • Δρmin = −0.47 e Å−3

Data collection: SMART-NT (Bruker, 1998[Bruker. (1998). SAINT-NT and SMART-NT. Versions 5.0. Bruker AXS Inc., Madison, Wisconsin, USA.]); cell refinement: SMART-NT; data reduction: SAINT-NT (Bruker, 1998[Bruker. (1998). SAINT-NT and SMART-NT. Versions 5.0. Bruker AXS Inc., Madison, Wisconsin, USA.]); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990[Sheldrick, G. M. (1990). Acta Cryst. A46, 467-473.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997[Sheldrick, G. M. (1997). SHELXL97. University of Göttingen, Germany.]); molecular graphics: SHELXTL/PC (Sheldrick, 1999[Sheldrick, G. M. (1999). SHELXTL/PC. Version 5.10 for Windows-NT. Bruker AXS Inc., Madison, Wisconsin, USA.]); software used to prepare material for publication: SHELXL97.

Supporting information


Computing details top

Data collection: SMART-NT (Bruker, 1998); cell refinement: SMART-NT; data reduction: SAINT-NT (Bruker, 1998); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997).

dipotassium rhodizonate top
Crystal data top
2K+·C6O62Dx = 2.063 Mg m3
Mr = 246.26Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, FdddCell parameters from 982 reflections
a = 8.426 (2) Åθ = 12.4–22.1°
b = 12.011 (3) ŵ = 1.19 mm1
c = 15.671 (3) ÅT = 100 K
V = 1586.0 (6) Å3Block, dark red
Z = 80.2 × 0.15 × 0.1 mm
F(000) = 976
Data collection top
Bruker SMART CCD
diffractometer
392 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.049
Graphite monochromatorθmax = 27.5°, θmin = 3.2°
ω scansh = 1010
3525 measured reflectionsk = 1515
462 independent reflectionsl = 2020
Refinement top
Refinement on F20 restraints
Least-squares matrix: fullPrimary atom site location: structure-invariant direct methods
R[F2 > 2σ(F2)] = 0.038Secondary atom site location: difference Fourier map
wR(F2) = 0.093 w = 1/[σ2(Fo2) + (0.034P)2 + 24.4908P]
where P = (Fo2 + 2Fc2)/3
S = 1.06(Δ/σ)max < 0.001
462 reflectionsΔρmax = 0.47 e Å3
34 parametersΔρmin = 0.47 e Å3
Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
K10.37500.52405 (7)0.37500.0107 (3)
C10.62500.62500.2194 (2)0.0115 (8)
O10.62500.62500.29940 (18)0.0159 (6)
O20.3441 (2)0.61034 (17)0.21116 (12)0.0129 (5)
C20.4733 (3)0.6199 (2)0.17206 (16)0.0114 (6)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
K10.0099 (4)0.0144 (4)0.0078 (4)0.0000.0011 (4)0.000
C10.0129 (18)0.0103 (17)0.0113 (18)0.0009 (16)0.0000.000
O10.0160 (14)0.0204 (15)0.0113 (13)0.0020 (13)0.0000.000
O20.0100 (10)0.0161 (10)0.0126 (9)0.0021 (8)0.0026 (8)0.0005 (8)
C20.0130 (13)0.0090 (12)0.0124 (13)0.0003 (11)0.0008 (11)0.0021 (11)
Geometric parameters (Å, º) top
K1—O12.7038 (13)C1—O11.254 (5)
K1—O22.781 (2)C1—C21.479 (3)
K1—O2i2.799 (2)O2—C21.255 (3)
K1—O2ii3.016 (2)C2—C2iii1.480 (5)
O1—K1—O1iv126.72 (4)O1iv—K1—O2ii164.86 (5)
O1—K1—O2v99.46 (7)O2v—K1—O2ii126.79 (5)
O1iv—K1—O2v60.09 (6)O2—K1—O2ii83.51 (3)
O1—K1—O260.09 (6)O2i—K1—O2ii79.15 (7)
O1iv—K1—O299.47 (7)O2vi—K1—O2ii55.69 (7)
O2v—K1—O2136.24 (9)O2vii—K1—O2ii98.63 (8)
O1—K1—O2i124.12 (6)O1—C1—C2120.11 (16)
O1iv—K1—O2i87.49 (5)O1—C1—C2viii120.11 (16)
O2v—K1—O2i136.21 (7)C2—C1—C2viii119.8 (3)
O2—K1—O2i73.01 (7)C1—O1—K1viii115.99 (5)
O1—K1—O2vi87.49 (5)C1—O1—K1115.99 (5)
O1iv—K1—O2vi124.12 (6)K1viii—O1—K1128.03 (11)
O2v—K1—O2vi73.01 (7)C2—O2—K1113.82 (16)
O2—K1—O2vi136.21 (7)C2—O2—K1i112.93 (17)
O2i—K1—O2vi109.58 (9)K1—O2—K1i106.99 (7)
O1—K1—O2vii164.86 (5)C2—O2—K1ix104.64 (16)
O1iv—K1—O2vii67.63 (4)K1—O2—K1ix135.52 (7)
O2v—K1—O2vii83.51 (3)K1i—O2—K1ix75.90 (6)
O2—K1—O2vii126.79 (5)O2—C2—C1120.6 (2)
O2i—K1—O2vii55.69 (7)O2—C2—C2iii119.63 (15)
O2vi—K1—O2vii79.15 (7)C1—C2—C2iii119.77 (16)
O1—K1—O2ii67.63 (4)
Symmetry codes: (i) x+1/2, y+1, z+1/2; (ii) x+1/4, y1/4, z+1/2; (iii) x, y+5/4, z+1/4; (iv) x1/2, y+5/4, z+3/4; (v) x+3/4, y, z+3/4; (vi) x+1/4, y+1, z+1/4; (vii) x+1/2, y1/4, z+1/4; (viii) x+5/4, y+5/4, z; (ix) x1/4, y+1/4, z+1/2.
 

References

First citationAllen, F. H. (2002). Acta Cryst. B58, 380–388.  Web of Science CSD CrossRef CAS IUCr Journals Google Scholar
First citationBartsch, M. R., Kobus, H. J. & Wainwright, K. P. (1996). J. Forensic Sci. 41, 1046–1051.  CAS Google Scholar
First citationBraga, D., Cojazzi, G., Maini, L. & Grepioni, F. (2001). New J. Chem. 25, 1221–1223.  Web of Science CSD CrossRef CAS Google Scholar
First citationBruker. (1998). SAINT-NT and SMART-NT. Versions 5.0. Bruker AXS Inc., Madison, Wisconsin, USA.  Google Scholar
First citationCowan, J. A., Howard, J. A. K. & Leech, M. A. (2001a). Acta Cryst. C57, 302–303.  Web of Science CSD CrossRef CAS IUCr Journals Google Scholar
First citationCowan, J. A., Howard, J. A. K. & Leech, M. A. (2001b). Acta Cryst. C57, 1196–1198.  Web of Science CSD CrossRef CAS IUCr Journals Google Scholar
First citationLam, C.-K. & Mak, T. C. W. (2001a). Angew. Chem. Int. Ed. 40, 3453–3455.  Web of Science CrossRef CAS Google Scholar
First citationLam, C.-K. & Mak, T. C. W. (2001b). Chem. Commun. pp. 1568–1569.  Web of Science CSD CrossRef Google Scholar
First citationNeumann, M. A. (1965). PhD thesis, University of Wisconsin, USA.  Google Scholar
First citationSheldrick, G. M. (1990). Acta Cryst. A46, 467–473.  CrossRef CAS Web of Science IUCr Journals Google Scholar
First citationSheldrick, G. M. (1997). SHELXL97. University of Göttingen, Germany.  Google Scholar
First citationSheldrick, G. M. (1999). SHELXTL/PC. Version 5.10 for Windows-NT. Bruker AXS Inc., Madison, Wisconsin, USA.  Google Scholar

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