research communications\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

Journal logoCRYSTALLOGRAPHIC
COMMUNICATIONS
ISSN: 2056-9890
Volume 72| Part 2| February 2016| Pages 170-173
doi:10.1107/S2056989016000232

Sodium potassium hydrogen citrate, NaKHC6H5O7

CROSSMARK_Color_square_no_text.svg
Alagappa Rammohana and James A. Kadukb*

aAtlantic International University, Honolulu HI , USA, and bIllinois Institute of Technology, 3101 S. Dearborn St., Chicago IL 60616 , USA
*Correspondence e-mail: kaduk@polycrystallography.com

Edited by I. D. Brown, McMaster University, Canada (Received 25 November 2015; accepted 5 January 2016; online 13 January 2016)

The crystal structure of sodium potassium hydrogen citrate has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional theory techniques. The Na+ cation is six-coordinate, with a bond-valence sum of 1.17. The K+ cation is also six-coordinate, with a bond-valence sum of 1.08. The distorted [NaO6] octahedra share edges, forming chains along the a axis. The likewise distorted [KO6] octahedra share edges with the [NaO6] octahedra on either side of the chain, and share corners with other [KO6] octahedra, resulting in triple chains along the a axis. The most prominent feature of the structure is the chain along [111] of very short, very strong hydrogen bonds; the O⋯O distances are 2.414 and 2.400 Å. The Mulliken overlap populations in these hydrogen bonds are 0.138 and 0.142 e, which correspond to hydrogen-bond energies of 20.3 and 20.6 kcal mol−1.

CCDC references: 1445596; 1445595

1. Chemical context

We have carried out a systematic study of the crystal structures of Group 1 (alkali metal) citrate salts to understand the anion's conformational flexibility, ionization, coordination tendencies, and hydrogen bonding. Most of the new structures were solved using powder diffraction data (laboratory and/or synchrotron), but single crystals were used where available. The general trends and conclusions about the 16 new compounds and 12 previously characterized structures are being reported separately (Rammohan & Kaduk, 2015[Rammohan, A. & Kaduk, J. A. (2015). Acta Cryst. B72. Submitted.]). The initial study considered salts containing one type of Group 1 cation. The title compound (Fig. 1[link]) represents the beginning of an extension of the study to salts containing more than one alkali metal cation.

[Scheme 1]
[Figure 1]
Figure 1
The asymmetric unit, with the atom numbering and 50% probability spheroids.

2. Structural commentary

The root-mean-square deviation of the non-hydrogen atoms in the refined and optimized structures is only 0.088 Å. A comparison of the refined and optimized structures is given in Fig. 2[link]. The excellent agreement between the structures is strong evidence that the experimental structure is correct (van de Streek & Neumann, 2014[Streek, J. van de & Neumann, M. A. (2014). Acta Cryst. B70, 1020-1032.]). This discussion uses the DFT-optimized structure. Most of the bond lengths, and all of the bond angles and torsion angles fall within the normal ranges indicated by a Mercury Mogul Geometry Check (Macrae et al., 2008[Macrae, C. F., Bruno, I. J., Chisholm, J. A., Edgington, P. R., McCabe, P., Pidcock, E., Rodriguez-Monge, L., Taylor, R., van de Streek, J. & Wood, P. A. (2008). J. Appl. Cryst. 41, 466-470.]). Only the C6—O15 [observed = 1.281 (4), optimized = 1.268, normal = 1.20 (2) Å, Z-score = 2.7] and C1—O11 [observed = 1.260 (4), optimized = 1.318, normal = 1.330 (3) Å, Z-score = 3.9] bonds are flagged as unusual. The citrate anion occurs in the trans,trans-conformation (about C2—C3 and C3—C4), which is one of the two low-energy conformations of an isolated citrate. The central carboxyl­ate group and the hydroxyl group occur in the normal planar arrangement. The citrate chelates to Na19 through the terminal carboxyl­ate oxygen O11 and the central carboxyl­ate oxygen O16. The Na+ cation is six-coordinate, with a bond-valence sum of 1.17. The K+ cation is also six-coordinate, with a bond-valence sum of 1.08. Both cations are thus slightly crowded. The metal–oxygen bonding is ionic, based on the Mulliken overlap populations.

[Figure 2]
Figure 2
Comparison of the refined and optimized structures of sodium potassium hydrogen citrate. The refined structure is in red, and the DFT-optimized structure is in blue.

The Bravais–Friedel–Donnay–Harker (Bravais, 1866[Bravais, A. (1866). Etudes Cristallographiques. Paris: Gauthier Villars, Paris.]; Friedel, 1907[Friedel, G. (1907). Bull. Soc. Fr. Mineral. 30, 326-455.]; Donnay & Harker, 1937[Donnay, J. D. H. & Harker, D. (1937). Am. Mineral. 22, 446-467.]) morphology suggests that we might expect platy morphology for sodium potassium hydrogen citrate, with {001} as the principal faces. A 4th-order spherical harmonic preferred orientation model was included in the refinement; the texture index was only 1.013, indicating that preferred orientation was not significant in this rotated flat-plate specimen. The powder pattern is included in the Powder Diffraction File as entry 00-065-1255.

3. Supra­molecular features

In the crystal structure (Fig. 3[link]), distorted [NaO6] octahedra share edges to form chains along the a axis. The likewise distorted [KO6] octahedra share edges with the [NaO6] octahedra on either side of the chain, and share corners with other [KO6] octahedra, resulting in triple chains along the a axis. The most prominent feature of the structure is the chain along [111] of very short, very strong O—H⋯O hydrogen bonds (Table 1[link]); the refined O⋯O distances are 2.385 (15) and 2.346 (14) Å, and the optimized O⋯O distances are 2.414 and 2.400 Å. The Mulliken overlap populations in these hydrogen bonds are 0.138 and 0.142 e, which correspond to hydrogen bond energies of 20.3 and 20.6 kcal mol−1. The distances indicate that these are among the shortest O—H⋯O hydrogen bonds ever reported. H18 forms bifurcated hydrogen bonds; one is intra­molecular to O15, and the other inter­molecular to O11.

Table 1
Hydrogen-bond geometry (Å, °, e)

D—H⋯A D—H H⋯A D⋯A D—H⋯A Overlap
O11—H21⋯O11i 1.207 1.207 2.414 180.0 0.138
O13—H22⋯O13ii 1.200 1.200 2.400 180.0 0.142
O17—H18⋯O15 0.971 2.179 2.676 110.3 0.033
O17—H18⋯O11iii 0.971 2.227 3.060 143.1 0.028
Symmetry codes: (i) 1 − x, 1 − y, 1 − z; (ii) 2 − x, 2 − y, 2 − z; (iii) 1 + x, y, z.
[Figure 3]
Figure 3
Crystal structure of NaKHC6H5O7, viewed approximately down the a axis.

4. Database survey

Details of the comprehensive literature search for citrate structures are presented in Rammohan & Kaduk (2015[Rammohan, A. & Kaduk, J. A. (2015). Acta Cryst. B72. Submitted.]). A reduced cell search in the Cambridge Structural Database (Groom & Allen, 2014[Groom, C. R. & Allen, F. H. (2014). Angew. Chem. Int. Ed. 53, 662-671.]) (increasing the default tolerance from 1.5 to 2.0%, to account for the differences between ambient and low-temperature lattice parameters) yielded 35 hits, but limiting the chemistry to C, H, O, Na, and K only resulted in no hits. The powder pattern matched no entry in the Powder Diffraction File (ICDD, 2015[ICDD (2015). PDF-4+ 2015 and PDF-4 Organics 2016 (Databases), edited by Dr. Soorya Kabekkodu. International Centre for Diffraction Data, Newtown Square PA, USA.]).

5. Synthesis and crystallization

2.0832 g (10.0 mmol) H3C6H5O7(H2O) was dissolved in 10 mL deionized water. 0.5282 g Na2CO3 (10.0 mmol Na, Sigma–Aldrich) and 0.6913 g K2CO3 (10.0 mmol, Sigma–Aldrich) were added to the citric acid solution slowly with stirring. The resulting clear colourless solution was evaporated to dryness in a 393 K oven.

6. Refinement details

The powder pattern (Fig. 4[link]) was indexed using Jade 9.5 (MDI, 2012[MDI. (2012). Jade 9.5. Materials Data Inc., Livermore CA, USA.]). Pseudovoigt profile coefficients were as parameterized in Thompson et al. (1987[Thompson, P., Cox, D. E. & Hastings, J. B. (1987). J. Appl. Cryst. 20, 79-83.]) and the asymmetry correction of Finger et al. (1994[Finger, L. W., Cox, D. E. & Jephcoat, A. P. (1994). J. Appl. Cryst. 27, 892-900.]) was applied and microstrain broadening by Stephens (1999[Stephens, P. W. (1999). J. Appl. Cryst. 32, 281-289.]). The structure was solved with FOX (Favre-Nicolin & Černý, 2002[Favre-Nicolin, V. & Černý, R. (2002). J. Appl. Cryst. 35, 734-743.]) using a citrate, Na, and K as fragments. Two of the 10 solutions yielded much lower cost functions than the others. Centrosymmetric pairs of close O⋯O contacts made it clear that H21 and H22 were located on centers of symmetry between these oxygen atoms, forming very strong hydrogen bonds. The hydrogen atoms were included at fixed positions, which were re-calculated during the course of the refinement. Crystal data, data collection and structure refinement details are summarized in Table 2[link]. The Uiso of C2, C3, and C4 were constrained to be equal, and those of H7, H8, H9, and H10 were constrained to be 1.3× that of these carbon atoms. The Uiso of C1, C5, C6, and the oxygen atoms were constrained to be equal, and that of H18 was constrained to be 1.3× this value. The Uiso of H21 and H22 were fixed.

Table 2
Experimental details

  Powder data
Crystal data
Chemical formula NaK(C6H6O7)
Mr 252.19
Crystal system, space group Triclinic, P[\overline{1}]
Temperature (K) 300
a, b, c (Å) 5.99933 (18), 8.2277 (2), 10.1419 (3)
α, β, γ (°) 74.8964 (19), 76.019 (2), 71.4496 (14)
V (Å3) 451.27 (3)
Z 2
Radiation type Kα1, Kα2, λ = 1.540629, 1.544451 Å
Specimen shape, size (mm) Flat sheet, 24 × 24
 
Data collection
Diffractometer Bruker D2 Phaser
Specimen mounting Standard holder
Data collection mode Reflection
Data collection method Step
θ values (°) 2θmin = 4.908 2θmax = 99.914 2θstep = 0.020
 
Refinement
R factors and goodness of fit Rp = 0.034, Rwp = 0.046, Rexp = 0.024, R(F2) = 0.08172, χ2 = 4.040
No. of data points 4452
No. of parameters 98
No. of restraints 29
H-atom treatment Only H-atom displacement parameters refined
The same symmetry and lattice parameters were used for the DFT calculation. Computer programs: DIFFRAC.Measurement (Bruker, 2009[Bruker (2009). DIFFRAC. Bruker AXS Inc., Madison, Wisconsin, USA.]), PowDLL (Kourkoumelis, 2013[Kourkoumelis, N. (2013). Powder Diffr. 28, 137-48.]), FOX (Favre-Nicolin & Černý, 2002[Favre-Nicolin, V. & Černý, R. (2002). J. Appl. Cryst. 35, 734-743.]), GSAS (Larson & Von Dreele, 2004[Larson, A. C. & Von Dreele, R. B. (2004). GSAS. Report LAUR 86-748. Los Alamos National Laboratory, New Mexico, USA.]), EXPGUI (Toby, 2001[Toby, B. H. (2001). J. Appl. Cryst. 34, 210-213.]), DIAMOND (Putz & Brandenburg, 2015[Putz, H. & Brandenburg, K. (2015). DIAMOND. Crystal Impact GbR, Bonn, Germany.]), publCIF (Westrip, 2010[Westrip, S. P. (2010). J. Appl. Cryst. 43, 920-925.]).
[Figure 4]
Figure 4
Rietveld plot for the refinement of NaKHC6H5O7. The red crosses represent the observed data points, and the green line is the calculated pattern. The magenta curve is the difference pattern, plotted at the same scale as the other patterns. The vertical scale has been multiplied by a factor of 6 for 2θ > 41.0°, and by a factor of 20 for 2θ > 63.0°. The row of black tick marks indicates the reflection positions for the phase.

6.1. Density functional geometry optimization

A density functional geometry optimization (fixed experimental unit cell) was carried out using CRYSTAL09 (Dovesi et al., 2005[Dovesi, R., Orlando, R., Civalleri, B., Roetti, C., Saunders, V. R. & Zicovich-Wilson, C. M. (2005). Z. Kristallogr. 220, 571-573.]). The basis sets for the H, C, and O atoms were those of Gatti et al. (1994[Gatti, C., Saunders, V. R. & Roetti, C. (1994). J. Chem. Phys. 101, 10686-10696.]), the basis sets for Na and K were those of Dovesi et al. (1991[Dovesi, R., Roetti, C., Freyria-Fava, C., Prencipe, M. & Saunders, V. R. (1991). Chem. Phys. 156, 11-19.]). The calculation used 8 k-points and the B3LYP functional, and took about 42 h on a 2.8 GHz PC. The observed Uiso were assigned to the refined values.

Supporting information

CCDC references: 1445596; 1445595

Crystal structure: contains datablocks RAMM093_publ, ramm093_DFT. DOI: 10.1107/S2056989016000232/br2256sup1.cif

Structure factors: contains datablock RAMM093_publ. DOI: 10.1107/S2056989016000232/br2256RAMM093_publsup2.hkl

Rietveld powder data: contains datablock RAMM093_publ. DOI: 10.1107/S2056989016000232/br2256RAMM093_publsup3.rtv

checkCIF report


Chemical context top

We have carried out a systematic study of the crystal structures of Group 1 (alkali metal) citrate salts to understand the anion's conformational flexibility, ionization, coordination tendencies, and hydrogen bonding. Most of the new structures were solved using powder diffraction data (laboratory and/or synchrotron), but single crystals were used where available. The general trends and conclusions about the 16 new compounds and 12 previously characterized structures are being reported separately (Rammohan & Kaduk, 2015). The initial study considered salts containing one type of Group 1 cation. The title compound (Fig. 1) represents the beginning of an extension of the study to salts containing more than one alkali metal cation.

Structural commentary top

The root-mean-square deviation of the non-hydrogen atoms in the refined and optimized structures is only 0.088 Å. A comparison of the refined and optimized structures is given in Fig. 2. The excellent agreement between the structures is strong evidence that the experimental structure is correct (van de Streek & Neumann, 2014). This discussion uses the DFT-optimized structure. Most of the bond distances, and all of the bond angles and torsion angles fall within the normal ranges indicated by a Mercury Mogul Geometry Check (Macrae et al., 2008). Only the C6—O15 [observed = 1.281 (4), optimized = 1.268, normal = 1.20 (2) Å, Z-score = 2.7] and C1—O11 [observed = 1.260 (4), optimized = 1.318, normal = 1.330 (3) Å, Z-score = 3.9] bonds are flagged as unusual. The citrate anion occurs in the trans,trans-conformation (about C2—C3 and C3—C4), which is one of the two low-energy conformations of an isolated citrate. The central carboxyl­ate group and the hydroxyl group occur in the normal planar arrangement. The citrate chelates to Na19 through the terminal carboxyl­ate oxygen O11 and the central carboxyl­ate oxygen O16. The Na is six-coordinate, with a bond-valence sum of 1.17. The K is also six-coordinate, with a bond-valence sum of 1.08. Both cations are thus slightly crowded. The metal–oxygen bonding is ionic, based on the Mulliken overlap populations.

The Bravais–Friedel–Donnay–Harker (Bravais, 1866; Friedel, 1907; Donnay & Harker, 1937) morphology suggests that we might expect platy morphology for sodium potassium hydrogen citrate, with {001} as the principal faces. A 4th-order spherical harmonic preferred orientation model was included in the refinement; the texture index was only 1.013, indicating that preferred orientation was not significant in this rotated flat-plate specimen. The powder pattern is included in the Powder Diffraction File as entry 00-065-1255.

Supra­molecular features top

In the crystal structure (Fig. 3), Na share edges to form chains along the a axis. The K share edges with the Na on either side of the chain, and share corners with other K to result in triple chains along the a axis. The most prominent feature of the structure is the chain along [111] of very short, very strong hydrogen bonds (Table 1); the refined O···O distances are 2.385 (15) and 2.346 (14) Å, and the optimized O···O distances are 2.414 and 2.400 Å. The Mulliken overlap populations in these hydrogen bonds are 0.138 and 0.142 e, which correspond to hydrogen bond energies of 20.3 and 20.6 kcal mol-1. The distances indicate that these are among the shortest O—H···O hydrogen bonds ever reported. H18 forms bifurcated hydrogen bonds; one is intra­molecular to O15, and the other inter­molecular to O11.

Database survey top

Details of the comprehensive literature search for citrate structures are presented in Rammohan & Kaduk (2015). A reduced cell search in the Cambridge Structural Database (Groom & Allen, 2014) (increasing the default tolerance from 1.5 to 2.0%, to account for the differences between ambient and low-temperature lattice parameters) yielded 35 hits, but limiting the chemistry to C, H, O, Na, and K only resulted in no hits. The powder pattern matched no entry in the Powder Diffraction File (ICDD, 2015).

Synthesis and crystallization top

2.0832 g (10.0 mmol) H3C6H5O7(H2O) was dissolved in 10 mL deionized water. 0.5282 g Na2CO3 (10.0 mmol Na, Sigma–Aldrich) and 0.6913 g K2CO3 (10.0 mmol, Sigma–Aldrich) were added to the citric acid solution slowly with stirring. The resulting clear colourless solution was evaporated to dryness at in a 393 K oven.

Refinement details top

The powder pattern (Fig. 4) was indexed using Jade 9.5 (MDI, 2012). Pseudovoigt profile coefficients were as parameterized in Thompson et al. (1987) and the asymmetry correction of Finger et al. (1994) was applied and microstrain broadening by Stephens (1999).The structure was solved with FOX (Favre-Nicolin & Černý, 2002) using a citrate, Na, and K as fragments. Two of the 10 solutions yielded much lower cost functions than the others. Centrosymmetric pairs of close O···O contacts made it clear that H21 and H22 were located on centers of symmetry between these oxygen atoms, forming very strong hydrogen bonds. The hydrogen atoms were included at fixed positions, which were re-calculated during the course of the refinement. Crystal data, data collection and structure refinement details are summarized in Table 1. The Uiso of C2, C3, and C4 were constrained to be equal, and those of H7, H8, H9, and H10 were constrained to be 1.3× that of these carbon atoms. The Uiso of C1, C5, C6, and the oxygen atoms were constrained to be equal, and that of H18 was constrained to be 1.3× this value. The Uiso of H21 and H22 were fixed.

Density functional geometry optimization top

A density functional geometry optimization (fixed experimental unit cell) was carried out using CRYSTAL09 (Dovesi et al., 2005). The basis sets for the H, C, and O atoms were those of Gatti et al. (1994), the basis sets for Na and K were those of Dovesi et al. (1991). The calculation used 8 k-points and the B3LYP functional, and took about 42 h on a 2.8 GHz PC. The observed Uiso were assigned to the refined values.

Related literature top

For related literature, see: Allen (2002); Bravais (1866); Donnay & Harker (1937); Dovesi et al. (1991, 2005); Favre-Nicolin & Černý (2002); Friedel (1907); Gatti et al. (1994); ICDD (2015); MDI (2012); Macrae et al. (2008); Rammohan & Kaduk (2015); Streek & Neumann (2014).

Structure description top

We have carried out a systematic study of the crystal structures of Group 1 (alkali metal) citrate salts to understand the anion's conformational flexibility, ionization, coordination tendencies, and hydrogen bonding. Most of the new structures were solved using powder diffraction data (laboratory and/or synchrotron), but single crystals were used where available. The general trends and conclusions about the 16 new compounds and 12 previously characterized structures are being reported separately (Rammohan & Kaduk, 2015). The initial study considered salts containing one type of Group 1 cation. The title compound (Fig. 1) represents the beginning of an extension of the study to salts containing more than one alkali metal cation.

The root-mean-square deviation of the non-hydrogen atoms in the refined and optimized structures is only 0.088 Å. A comparison of the refined and optimized structures is given in Fig. 2. The excellent agreement between the structures is strong evidence that the experimental structure is correct (van de Streek & Neumann, 2014). This discussion uses the DFT-optimized structure. Most of the bond distances, and all of the bond angles and torsion angles fall within the normal ranges indicated by a Mercury Mogul Geometry Check (Macrae et al., 2008). Only the C6—O15 [observed = 1.281 (4), optimized = 1.268, normal = 1.20 (2) Å, Z-score = 2.7] and C1—O11 [observed = 1.260 (4), optimized = 1.318, normal = 1.330 (3) Å, Z-score = 3.9] bonds are flagged as unusual. The citrate anion occurs in the trans,trans-conformation (about C2—C3 and C3—C4), which is one of the two low-energy conformations of an isolated citrate. The central carboxyl­ate group and the hydroxyl group occur in the normal planar arrangement. The citrate chelates to Na19 through the terminal carboxyl­ate oxygen O11 and the central carboxyl­ate oxygen O16. The Na is six-coordinate, with a bond-valence sum of 1.17. The K is also six-coordinate, with a bond-valence sum of 1.08. Both cations are thus slightly crowded. The metal–oxygen bonding is ionic, based on the Mulliken overlap populations.

The Bravais–Friedel–Donnay–Harker (Bravais, 1866; Friedel, 1907; Donnay & Harker, 1937) morphology suggests that we might expect platy morphology for sodium potassium hydrogen citrate, with {001} as the principal faces. A 4th-order spherical harmonic preferred orientation model was included in the refinement; the texture index was only 1.013, indicating that preferred orientation was not significant in this rotated flat-plate specimen. The powder pattern is included in the Powder Diffraction File as entry 00-065-1255.

In the crystal structure (Fig. 3), Na share edges to form chains along the a axis. The K share edges with the Na on either side of the chain, and share corners with other K to result in triple chains along the a axis. The most prominent feature of the structure is the chain along [111] of very short, very strong hydrogen bonds (Table 1); the refined O···O distances are 2.385 (15) and 2.346 (14) Å, and the optimized O···O distances are 2.414 and 2.400 Å. The Mulliken overlap populations in these hydrogen bonds are 0.138 and 0.142 e, which correspond to hydrogen bond energies of 20.3 and 20.6 kcal mol-1. The distances indicate that these are among the shortest O—H···O hydrogen bonds ever reported. H18 forms bifurcated hydrogen bonds; one is intra­molecular to O15, and the other inter­molecular to O11.

Details of the comprehensive literature search for citrate structures are presented in Rammohan & Kaduk (2015). A reduced cell search in the Cambridge Structural Database (Groom & Allen, 2014) (increasing the default tolerance from 1.5 to 2.0%, to account for the differences between ambient and low-temperature lattice parameters) yielded 35 hits, but limiting the chemistry to C, H, O, Na, and K only resulted in no hits. The powder pattern matched no entry in the Powder Diffraction File (ICDD, 2015).

A density functional geometry optimization (fixed experimental unit cell) was carried out using CRYSTAL09 (Dovesi et al., 2005). The basis sets for the H, C, and O atoms were those of Gatti et al. (1994), the basis sets for Na and K were those of Dovesi et al. (1991). The calculation used 8 k-points and the B3LYP functional, and took about 42 h on a 2.8 GHz PC. The observed Uiso were assigned to the refined values.

For related literature, see: Allen (2002); Bravais (1866); Donnay & Harker (1937); Dovesi et al. (1991, 2005); Favre-Nicolin & Černý (2002); Friedel (1907); Gatti et al. (1994); ICDD (2015); MDI (2012); Macrae et al. (2008); Rammohan & Kaduk (2015); Streek & Neumann (2014).

Synthesis and crystallization top

2.0832 g (10.0 mmol) H3C6H5O7(H2O) was dissolved in 10 mL deionized water. 0.5282 g Na2CO3 (10.0 mmol Na, Sigma–Aldrich) and 0.6913 g K2CO3 (10.0 mmol, Sigma–Aldrich) were added to the citric acid solution slowly with stirring. The resulting clear colourless solution was evaporated to dryness at in a 393 K oven.

Refinement details top

The powder pattern (Fig. 4) was indexed using Jade 9.5 (MDI, 2012). Pseudovoigt profile coefficients were as parameterized in Thompson et al. (1987) and the asymmetry correction of Finger et al. (1994) was applied and microstrain broadening by Stephens (1999).The structure was solved with FOX (Favre-Nicolin & Černý, 2002) using a citrate, Na, and K as fragments. Two of the 10 solutions yielded much lower cost functions than the others. Centrosymmetric pairs of close O···O contacts made it clear that H21 and H22 were located on centers of symmetry between these oxygen atoms, forming very strong hydrogen bonds. The hydrogen atoms were included at fixed positions, which were re-calculated during the course of the refinement. Crystal data, data collection and structure refinement details are summarized in Table 1. The Uiso of C2, C3, and C4 were constrained to be equal, and those of H7, H8, H9, and H10 were constrained to be 1.3× that of these carbon atoms. The Uiso of C1, C5, C6, and the oxygen atoms were constrained to be equal, and that of H18 was constrained to be 1.3× this value. The Uiso of H21 and H22 were fixed.

Computing details top

Data collection: DIFFRAC.Measurement (Bruker, 2009) for RAMM093_publ. Data reduction: PowDLL (Kourkoumelis, 2013) for RAMM093_publ. Program(s) used to solve structure: FOX (Favre-Nicolin & Černý, 2002) for RAMM093_publ. Program(s) used to refine structure: GSAS (Larson & Von Dreele, 2004), EXPGUI (Toby, 2001) for RAMM093_publ. Molecular graphics: DIAMOND (Putz & Brandenburg, 2015) for RAMM093_publ. Software used to prepare material for publication: publCIF (Westrip, 2010) for RAMM093_publ.

Figures top
[Figure 1] Fig. 1. The asymmetric unit, with the atom numbering.
[Figure 2] Fig. 2. Comparison of the refined and optimized structures of sodium potassium hydrogen citrate. The refined structure is in red, and the DFT-optimized structure is in blue.
[Figure 3] Fig. 3. Crystal structure of NaKHC6H5O7, viewed down the a axis.
[Figure 4] Fig. 4. Rietveld plot for the refinement of NaKHC6H5O7. The red crosses represent the observed data points, and the green line is the calculated pattern. The magenta curve is the difference pattern, plotted at the same scale as the other patterns. The vertical scale has been multiplied by a factor of 6 for 2θ > 41.0°, and by a factor of 20 for 2θ > 63.0°. The row of black tick marks indicates the reflection positions for the phase.
(RAMM093_publ) sodium potassium hydrogen citrate top
Crystal data top
NaK(C6H6O7)γ = 71.4496 (14)°
Mr = 252.19V = 451.27 (3) Å3
Triclinic, P1Z = 2
Hall symbol: -P 1Dx = 1.864 Mg m−3
a = 5.99933 (18) Å Kα1, Kα2 radiation, λ = 1.540629, 1.544451 Å
b = 8.2277 (2) ÅT = 300 K
c = 10.1419 (3) Åwhite
α = 74.8964 (19)°flat sheet, 24 × 24 mm
β = 76.019 (2)°Specimen preparation: Prepared at 393 K and 101 kPa
Data collection top
Bruker D2 Phaser
diffractometer		Data collection mode: reflection
Radiation source: sealed X-ray tubeScan method: step
Ni filter monochromator2θmin = 4.908°, 2θmax = 99.914°, 2θstep = 0.020°
Specimen mounting: standard holder
Refinement top
Least-squares matrix: full98 parameters
Rp = 0.03429 restraints
Rwp = 0.0462 constraints
Rexp = 0.024Only H-atom displacement parameters refined
R(F2) = 0.08172Weighting scheme based on measured s.u.'s
χ2 = 4.040(Δ/σ)max = 0.04
Profile function: CW Profile function number 4 with 27 terms Pseudovoigt profile coefficients as parameterized in Thompson et al. (1987). Asymmetry correction of Finger et al. (1994). Microstrain broadening by Stephens (1999). #1(GU) = 2.580 #2(GV) = 0.000 #3(GW) = 1.999 #4(GP) = 0.000 #5(LX) = 4.774 #6(ptec) = 0.64 #7(trns) = 4.34 #8(shft) = 4.0539 #9(sfec) = 0.00 #10(S/L) = 0.0168 #11(H/L) = 0.0200 #12(eta) = 0.0000 Peak tails are ignored where the intensity is below 0.0050 times the peak Aniso. broadening axis 0.0 0.0 1.0Background function: GSAS Background function number 1 with 10 terms. Shifted Chebyshev function of 1st kind 1: 1400.27 2: -1034.48 3: 405.201 4: -101.434 5: 48.9076 6: -20.5280 7: -17.7840 8: 47.9002 9: -30.1492 10: 17.3246
Crystal data top
NaK(C6H6O7)β = 76.019 (2)°
Mr = 252.19γ = 71.4496 (14)°
Triclinic, P1V = 451.27 (3) Å3
a = 5.99933 (18) ÅZ = 2
b = 8.2277 (2) Å Kα1, Kα2 radiation, λ = 1.540629, 1.544451 Å
c = 10.1419 (3) ÅT = 300 K
α = 74.8964 (19)°flat sheet, 24 × 24 mm
Data collection top
Bruker D2 Phaser
diffractometer		Scan method: step
Specimen mounting: standard holder2θmin = 4.908°, 2θmax = 99.914°, 2θstep = 0.020°
Data collection mode: reflection
Refinement top
Rp = 0.034χ2 = 4.040
Rwp = 0.04698 parameters
Rexp = 0.02429 restraints
R(F2) = 0.08172Only H-atom displacement parameters refined
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
C10.6011 (16)0.4794 (8)0.6851 (9)0.0215 (12)*
C20.5815 (15)0.5669 (11)0.8023 (8)0.003 (3)*
C30.7804 (11)0.6586 (7)0.7744 (6)0.003 (3)*
C40.7535 (15)0.7282 (10)0.9061 (7)0.003 (3)*
C50.9060 (17)0.8477 (14)0.8955 (7)0.0215 (12)*
C60.7448 (13)0.8129 (8)0.6491 (6)0.0215 (12)*
H70.597180.464650.902500.003 (4)*
H80.400470.667790.814960.003 (4)*
H90.803650.613520.994920.003 (4)*
H100.558370.801680.935440.003 (4)*
O110.5025 (16)0.5759 (9)0.5848 (8)0.0215 (12)*
O120.6312 (14)0.3154 (9)0.7090 (7)0.0215 (12)*
O130.9018 (14)0.8943 (10)1.0079 (7)0.0215 (12)*
O141.0287 (14)0.9043 (10)0.7803 (7)0.0215 (12)*
O150.9008 (15)0.8051 (10)0.5379 (7)0.0215 (12)*
O160.5507 (13)0.9325 (9)0.6540 (6)0.0215 (12)*
O171.0087 (13)0.5402 (9)0.7419 (7)0.0215 (12)*
H181.109800.606230.681050.0279 (16)*
Na190.2588 (11)0.8708 (7)0.5423 (6)0.051 (3)*
K200.1831 (8)0.1991 (5)0.7186 (3)0.0406 (16)*
H210.50.50.50.03*
H221.01.01.00.03*
Geometric parameters (Å, º) top
C1—C21.507 (2)O14—Na19ii2.510 (9)
C1—O111.260 (4)O14—K20iv2.737 (8)
C1—O121.268 (4)O15—C61.281 (4)
C2—C11.507 (2)O15—Na19ii2.388 (9)
C2—C31.540 (2)O15—Na19v2.512 (9)
C3—C21.540 (2)O15—K20i2.777 (8)
C3—C41.541 (2)O16—C61.263 (4)
C3—C61.5460 (19)O16—Na192.537 (10)
C3—O171.427 (4)O16—Na19v2.508 (8)
C4—C31.541 (2)O16—K20vi2.660 (7)
C4—C51.511 (2)O17—C31.427 (4)
C5—C41.511 (2)O17—K20ii2.717 (8)
C5—O131.286 (4)Na19—O112.390 (10)
C5—O141.282 (4)Na19—O12i3.138 (10)
C6—C31.5460 (19)Na19—O14vii2.510 (9)
C6—O151.281 (4)Na19—O15vii2.388 (9)
C6—O161.263 (4)Na19—O15v2.512 (9)
O11—C11.260 (4)Na19—O162.537 (10)
O11—Na192.390 (10)Na19—O16v2.508 (8)
O11—K20i3.591 (9)K20—O11i3.591 (9)
O12—C11.268 (4)K20—O12vii3.159 (9)
O12—Na19i3.138 (10)K20—O123.100 (8)
O12—K203.100 (8)K20—O13iii2.646 (8)
O12—K20ii3.159 (9)K20—O14viii2.737 (8)
O13—C51.286 (4)K20—O15i2.777 (8)
O13—K20iii2.646 (8)K20—O16ix2.660 (7)
O14—C51.282 (4)K20—O17vii2.717 (8)
C2—C1—O11115.5 (7)C3—O17—K20ii137.1 (5)
C2—C1—O12119.5 (6)O11—Na19—O14vii101.9 (3)
O11—C1—O12119.9 (5)O11—Na19—O15vii97.2 (3)
C1—C2—C3111.3 (4)O11—Na19—O15v165.6 (4)
C2—C3—C4106.1 (4)O11—Na19—O1684.1 (3)
C2—C3—C6109.6 (4)O11—Na19—O16v113.5 (4)
C2—C3—O17110.5 (4)O14vii—Na19—O15vii78.7 (3)
C4—C3—C6109.8 (4)O14vii—Na19—O15v88.4 (3)
C4—C3—O17112.8 (4)O14vii—Na19—O1677.0 (3)
C6—C3—O17108.0 (4)O14vii—Na19—O16v133.6 (3)
C3—C4—C5115.8 (5)O15vii—Na19—O15v94.7 (3)
C4—C5—O13116.5 (4)O15vii—Na19—O16155.4 (4)
C4—C5—O14122.2 (6)O15vii—Na19—O16v123.0 (4)
O13—C5—O14121.2 (6)O15v—Na19—O1688.5 (3)
C3—C6—O15118.8 (4)O15v—Na19—O16v52.60 (18)
C3—C6—O16118.9 (4)O16—Na19—O16v77.9 (3)
O15—C6—O16121.9 (5)O12vii—K20—O12146.9 (3)
C1—O11—Na19134.1 (7)O12vii—K20—O13iii91.1 (2)
C1—O12—K20115.3 (5)O12vii—K20—O14viii71.8 (2)
C1—O12—K20ii97.7 (5)O12vii—K20—O15i68.5 (2)
K20—O12—K20ii146.9 (3)O12vii—K20—O16ix135.5 (3)
C5—O13—K20iii142.9 (5)O12vii—K20—O17vii71.9 (2)
C5—O14—Na19ii151.2 (7)O12—K20—O13iii94.6 (2)
C5—O14—K20iv125.9 (6)O12—K20—O14viii140.9 (3)
Na19ii—O14—K20iv82.7 (2)O12—K20—O15i115.0 (3)
C6—O15—Na19ii115.3 (8)O12—K20—O16ix75.2 (2)
C6—O15—Na19v89.5 (4)O12—K20—O17vii75.6 (2)
C6—O15—K20i125.5 (7)O13iii—K20—O14viii73.0 (2)
Na19ii—O15—Na19v85.3 (3)O13iii—K20—O15i149.4 (2)
Na19ii—O15—K20i117.4 (3)O13iii—K20—O16ix100.9 (3)
Na19v—O15—K20i81.9 (3)O13iii—K20—O17vii89.3 (2)
C6—O16—Na19110.5 (7)O14viii—K20—O15i78.9 (2)
C6—O16—Na19v90.1 (4)O14viii—K20—O16ix71.2 (3)
C6—O16—K20vi164.8 (7)O14viii—K20—O17vii139.0 (3)
Na19—O16—Na19v102.2 (3)O15i—K20—O16ix80.8 (2)
Na19—O16—K20vi83.8 (3)O15i—K20—O17vii104.6 (3)
Na19v—O16—K20vi92.0 (3)O16ix—K20—O17vii149.7 (3)
C3—O17—H18108.0 (4)
Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) x+1, y, z; (iii) −x+1, −y+1, −z+2; (iv) x+1, y+1, z; (v) −x+1, −y+2, −z+1; (vi) x, y+1, z; (vii) x−1, y, z; (viii) x−1, y−1, z; (ix) x, y−1, z.
(ramm093_DFT) top
Crystal data top
NaKHC6H5O7c = 10.1419 Å
Mr = 252.17α = 74.8964°
Triclinic, P1β = 76.0187°
Hall symbol: -P 1γ = 71.4496°
a = 5.9993 ÅV = 451.27 Å3
b = 8.2277 ÅZ = 2
Data collection top
Density functional calculation
Crystal data top
NaKHC6H5O7α = 74.8964°
Mr = 252.17β = 76.0187°
Triclinic, P1γ = 71.4496°
a = 5.9993 ÅV = 451.27 Å3
b = 8.2277 ÅZ = 2
c = 10.1419 Å
Data collection top
Density functional calculation
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
C10.584730.474610.690080.02150*
C20.588400.562650.803150.00260*
C30.774910.666910.770240.00260*
C40.742880.742840.899350.00260*
C50.904580.855460.890440.02150*
C60.740200.819020.641540.02150*
H70.627190.460440.894390.00340*
H80.412020.651220.827300.00340*
H90.772820.635570.989120.00340*
H100.558900.823080.922110.00340*
O110.490770.582910.584330.02150*
O120.655910.314550.699390.02150*
O130.883920.902571.006230.02150*
O141.040720.897380.781760.02150*
O150.908920.816000.538210.02150*
O160.547040.938500.648840.02150*
O171.004090.544190.748300.02150*
H181.109800.606230.681050.02790*
Na190.260240.876400.550430.05110*
K200.175110.205850.714800.04060*
H210.500000.500000.500000.03000*
H221.000001.000001.000000.03000*
Bond lengths (Å) top
C1—C21.515C4—H101.095
C1—O111.318C5—O131.297
C1—O121.234C5—O141.244
C2—C31.543C6—O151.268
C2—H71.092C6—O161.259
C2—H81.090O11—H211.207
C3—C41.540O13—H221.200
C3—C61.558O17—H180.971
C3—O171.430H21—O11i1.207
C4—C51.515H22—O13ii1.200
C4—H91.095
Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) −x+2, −y+2, −z+2.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O13—H22···O131.2001.2002.400180.0
O11—H21···O111.2071.2072.414180.0
O17—H18···O150.9712.1792.676110.3
O17—H18···O110.9712.2273.060143.1
Hydrogen-bond geometry (Å, °, e) top
D—H···AD—HH···AD···AD—H···AOverlap
O11—H21···O11i1.2071.2072.414180.00.138
O13—H22···O13ii1.2001.2002.400180.00.142
O17—H18···O150.9712.1792.676110.30.033
O17—H18···O11iii0.9712.2273.060143.10.028
Symmetry codes: (i) 1 - x, 1 - y, 1 - z; (ii) 2 - x, 2 - y, 2 - z; (iii) 1 + x, y, z.

Experimental details

(RAMM093_publ)(ramm093_DFT)
Crystal data
Chemical formulaNaK(C6H6O7)NaKHC6H5O7
Mr252.19252.17
Crystal system, space groupTriclinic, P1Triclinic, P1
Temperature (K)300?
a, b, c (Å)5.99933 (18), 8.2277 (2), 10.1419 (3)5.9993, 8.2277, 10.1419
α, β, γ (°)74.8964 (19), 76.019 (2), 71.4496 (14)74.8964, 76.0187, 71.4496
V (Å3)451.27 (3)451.27
Z22
Radiation type Kα1, Kα2, λ = 1.540629, 1.544451 Å?, λ = ? Å
µ (mm−1)–?
Specimen shape, size (mm)Flat sheet, 24 × 24 × ×
Data collection
DiffractometerBruker D2 PhaserDensity functional calculation
Specimen mountingStandard holder–
Data collection modeReflection–
Data collection methodStep?
Absorption correction–?
No. of measured, independent and
observed reflections		–?, ?, ?
Rint–?
θ values (°)2θmin = 4.908 2θmax = 99.914 2θstep = 0.020θmax = ?
Refinement
R factors and goodness of fitRp = 0.034, Rwp = 0.046, Rexp = 0.024, R(F2) = 0.08172, χ2 = 4.040R[F2 > 2σ(F2)] = ?, wR(F2) = ?, S = ?
No. of parameters98–
No. of restraints29?
H-atom treatmentOnly H-atom displacement parameters refined?
Δρmax, Δρmin (e Å−3)–?

Computer programs: DIFFRAC.Measurement (Bruker, 2009), PowDLL (Kourkoumelis, 2013), FOX (Favre-Nicolin & Černý, 2002), GSAS (Larson & Von Dreele, 2004), EXPGUI (Toby, 2001), DIAMOND (Putz & Brandenburg, 2015), publCIF (Westrip, 2010).

 

References

First citationBravais, A. (1866). Etudes Cristallographiques. Paris: Gauthier Villars, Paris.  Google Scholar
 First citationBruker (2009). DIFFRAC. Bruker AXS Inc., Madison, Wisconsin, USA.  Google Scholar
 First citationDonnay, J. D. H. & Harker, D. (1937). Am. Mineral. 22, 446–467.  CAS Google Scholar
 First citationDovesi, R., Orlando, R., Civalleri, B., Roetti, C., Saunders, V. R. & Zicovich-Wilson, C. M. (2005). Z. Kristallogr. 220, 571–573.  Web of Science CrossRef CAS Google Scholar
 First citationDovesi, R., Roetti, C., Freyria-Fava, C., Prencipe, M. & Saunders, V. R. (1991). Chem. Phys. 156, 11–19.  CrossRef CAS Web of Science Google Scholar
 First citationFavre-Nicolin, V. & Černý, R. (2002). J. Appl. Cryst. 35, 734–743.  Web of Science CrossRef CAS IUCr Journals Google Scholar
 First citationFinger, L. W., Cox, D. E. & Jephcoat, A. P. (1994). J. Appl. Cryst. 27, 892–900.  CrossRef CAS Web of Science IUCr Journals Google Scholar
 First citationFriedel, G. (1907). Bull. Soc. Fr. Mineral. 30, 326–455.  Google Scholar
 First citationGatti, C., Saunders, V. R. & Roetti, C. (1994). J. Chem. Phys. 101, 10686–10696.  CrossRef CAS Web of Science Google Scholar
 First citationGroom, C. R. & Allen, F. H. (2014). Angew. Chem. Int. Ed. 53, 662–671.  Web of Science CSD CrossRef CAS Google Scholar
 First citationICDD (2015). PDF-4+ 2015 and PDF-4 Organics 2016 (Databases), edited by Dr. Soorya Kabekkodu. International Centre for Diffraction Data, Newtown Square PA, USA.  Google Scholar
 First citationKourkoumelis, N. (2013). Powder Diffr. 28, 137–48.  Google Scholar
 First citationLarson, A. C. & Von Dreele, R. B. (2004). GSAS. Report LAUR 86-748. Los Alamos National Laboratory, New Mexico, USA.  Google Scholar
 First citationMacrae, C. F., Bruno, I. J., Chisholm, J. A., Edgington, P. R., McCabe, P., Pidcock, E., Rodriguez-Monge, L., Taylor, R., van de Streek, J. & Wood, P. A. (2008). J. Appl. Cryst. 41, 466–470.  Web of Science CSD CrossRef CAS IUCr Journals Google Scholar
 First citationMDI. (2012). Jade 9.5. Materials Data Inc., Livermore CA, USA.  Google Scholar
 First citationPutz, H. & Brandenburg, K. (2015). DIAMOND. Crystal Impact GbR, Bonn, Germany.  Google Scholar
 First citationRammohan, A. & Kaduk, J. A. (2015). Acta Cryst. B72. Submitted.  Google Scholar
 First citationStephens, P. W. (1999). J. Appl. Cryst. 32, 281–289.  Web of Science CrossRef CAS IUCr Journals Google Scholar
 First citationStreek, J. van de & Neumann, M. A. (2014). Acta Cryst. B70, 1020–1032.  Web of Science CrossRef IUCr Journals Google Scholar
 First citationThompson, P., Cox, D. E. & Hastings, J. B. (1987). J. Appl. Cryst. 20, 79–83.  CrossRef CAS Web of Science IUCr Journals Google Scholar
 First citationToby, B. H. (2001). J. Appl. Cryst. 34, 210–213.  Web of Science CrossRef CAS IUCr Journals Google Scholar
 First citationWestrip, S. P. (2010). J. Appl. Cryst. 43, 920–925.  Web of Science CrossRef CAS IUCr Journals Google Scholar

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Journal logoCRYSTALLOGRAPHIC
COMMUNICATIONS
ISSN: 2056-9890
Volume 72| Part 2| February 2016| Pages 170-173
doi:10.1107/S2056989016000232
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