research communications
of trirubidium citrate monohydrate from laboratory X-ray powder diffraction data and DFT comparison
aAtlantic International University, Honolulu, HI, USA, and bIllinois Institute of Technology, Chicago, IL, USA
*Correspondence e-mail: kaduk@polycrystallography.com
The +·C6H5O73−·H2O, has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. The hydroxy group participates in an intramolecular hydrogen bond to the deprotonated central carboxylate group with graph-set motif S(5). The water molecule acts as a hydrogen-bond donor to both terminal and central carboxylate O atoms. The three independent rubidium cations are seven-, six- and six-coordinate, with bond-valence sums of 0.84, 1.02, and 0.95, respectively. In the extended structure, their polyhedra share edges and corners to form a three-dimensional network. The hydrophobic methylene groups occupy channels along the b axis.
of the title compound, 3RbKeywords: crystal structure; powder diffraction; density functional theory; citrate; rubidium.
1. Chemical context
In the course of a systematic study of the crystal structures of Group 1 (alkali metal) citrate salts to understand the anion's conformational flexibility, deprotonation, coordination tendencies, and hydrogen bonding, we have determined several new crystal structures. 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 sixteen new compounds and twelve previously characterized structures are being reported separately (Rammohan & Kaduk, 2017a). Seven of the new structures – NaKHC6H5O7, NaK2C6H5O7, Na3C6H5O7, NaH2C6H5O7, Na2HC6H5O7, K3C6H5O7, and Rb2HC6H5O7 – have been published recently (Rammohan & Kaduk, 2016a,b,c,d,f, 2017b; Rammohan et al. (2016)), and two additional structures – KH2C6H5O7 and KH2C6H5O7(H2O)2 – have been communicated to the CSD (Kaduk & Stern, 2016a,b).
2. Structural commentary
The . The root-mean-square deviation of the non-hydrogen atoms in the Rietveld-refined and DFT-optimized structures is 0.127 Å (Fig. 2). The good agreement between the two 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 lengths, bond angles, and torsion angles fall within the normal ranges indicated by a Mercury Mogul geometry check (Macrae et al., 2008). Only the O11—C4—C5—C6 torsion angle involving a terminal carboxylate group is flagged as unusual, but as shown in Rammohan & Kaduk (2017a) these torsion angles exhibit no real preference. The citrate anion occurs in the trans,trans-conformation, which is one of the two low-energy conformations of an isolated citrate trianion. The central carboxylate group and the hydroxyl group occur in the normal planar arrangement. The terminal carboxylate O13 atom and the hydroxy group O16 atom chelate to Rb3. The terminal carboxylate O12 atom and the central carboxylate O15 atom chelate to another Rb3 cation. The terminal carboxylate O12 and central carboxylate O14 chelate to Rb2, and the terminal O10 and central O14 chelate to a third Rb3 atom. The terminal carboxylate O14/O15 acts as a bidentate ligand to Rb1, and the terminal carboxylate O10/O11 chelates to another Rb1.
of the title compound is shown in Fig. 1The Bravais–Friedel–Donnay–Harker (Bravais, 1866; Friedel, 1907; Donnay & Harker, 1937) morphology suggests that we might expect platy morphology for the title compound, with {011} as the principal faces. A 4th-order spherical harmonic texture model was included in the The texture index was 1.014, indicating that was negligible for this rotated flat-plate specimen.
3. Supramolecular features
The three independent Rb+ ions are 7-, 6- and 6-coordinate (upper threshold for Rb—O bond lengths = 3.40 Å), with bond-valence sums of 0.84, 1.02, and 0.95, respectively. These polyhedra share edges and corners to form a three-dimensional network (Fig. 3). Hydrogen bonds (Table 1) between the water molecules and the citrate anions result in chains propagating along the b-axis direction. The hydroxyl group participates in an intramolecular hydrogen bond to the deprotonated central carboxylate group with graph-set motif S(5). The water molecule acts as a hydrogen-bond donor to both the terminal carboxylate atom O13 and the central carboxylate atom O14. The Mulliken overlap populations indicate, by the correlation in Rammohan & Kaduk (2017a), that these hydrogen bonds account for 41.6 kcal mol−1 of crystal energy. A C—H⋯O hydrogen bond also apparently contributes to the crystal energy. The hydrophobic methylene groups occupy channels along the b-axis. This compound is isostructural to K3C6H5O7(H2O) (Carrell et al., 1987; CSD Refcode ZZZHVI01).
4. Database survey
Details of the comprehensive literature search for citrate structures are presented in Rammohan & Kaduk (2017a). A search of the cell of trirubidium citrate monohydrate in the Cambridge Structural Database (Groom et al., 2016) (increasing the default tolerance from 1.5 to 2.0%) yielded 228 hits, but combining the cell search with a citrate fragment yielded Love & Patterson (1960, CSD Refcode ZZZHZC), but no coordinates were reported for this phase. Increasing the tolerance on the cell to 5% yielded K3C6H5O7(H2O) (Burns & Iball, 1954, CSD Refcode ZZZHVI; Carrell et al., 1987, CSD Refcodes ZZZHVI01 and ZZZHVI02).
5. Synthesis and crystallization
H3C6H5O7(H2O) (10.0 mmol, 2.0972 g) was dissolved in 10 ml deionized water. Rb2CO3 (15.0 mmol, 3.4659 g, Sigma–Aldrich) was added to the citric acid solution slowly with stirring. The resulting clear colourless solution was evaporated to dryness at ambient conditions to yield a white powder.
6. Refinement
Crystal data, data collection and structure . The specimen was blended with a NIST SRM 640 Si internal standard (a = 5.43105 Å). The powder pattern (Fig. 4) was indexed using Jade 9.4 (MDI, 2012), which yielded a primitive monoclinic cell having a = 7.44769 (10), b = 11.87554 (16), c = 13.41675 (18) Å, β = 97.8820 (9)°, V = 1175.44 (3) Å3, and Z = 4. The suggested was P21/n, which was confirmed by successful solution and Three intense peaks from a structure solution using as implemented in Jana2006 (Petříček et al., 2014) were used to carry out a Le Bail fit in GSAS (Larson & Von Dreele, 2004). The resulting peak list was imported into Endeavour 1.7b (Putz et al., 1999), which was used to solve the structure with a citrate anion and 3 Rb atoms as fragments. A significant peak in a difference Fourier map in GSAS corresponded to the oxygen atom of a water molecule, indicating that the compound was a monohydrate.
details are summarized in Table 2Pseudo-Voigt profile coefficients were as parameterized in Thompson et al. (1987) with profile coefficients for Simpson's rule integration of the pseudo-Voigt function according to Howard (1982). The asymmetry correction of Finger et al. (1994) was applied, and microstrain broadening by Stephens (1999). The structure was refined by the using GSAS/EXPGUI (Larson & Von Dreele, 2004; Toby, 2001). All C—C and C—O bond lengths were restrained, as were all bond angles. The hydrogen atoms were included at fixed positions, which were recalculated during the course of the using Materials Studio (Dassault Systemes, 2014). The Uiso values of the C and O atoms in the citrate anion were constrained to be equal, and the Uiso values of the hydrogen atoms were constrained to be 1.3 times those of the atoms to which they are attached.
7. DFT calculations
After the CRYSTAL09 (Dovesi et al., 2005). The basis sets for the C, H, and O atoms were those of Gatti et al. (1994), and the basis set for Rb was that of Schoenes et al. (2008). The calculation used 8 k-points and the B3LYP functional, and took about 72 h on a 2.4 GHz PC. The Uiso values from the were assigned to the optimized fractional coordinates.
a density functional geometry optimization (fixed experimental unit cell) was carried out usingSupporting information
3Rb+·C6H5O73−·H2O | c = 13.41675 (18) Å |
Mr = 463.52 | β = 97.8820 (9)° |
Monoclinic, P21/n | V = 1175.44 (4) Å3 |
Hall symbol: -P 2yn | Z = 4 |
a = 7.44769 (10) Å | Dx = 2.619 Mg m−3 |
b = 11.87554 (16) Å | T = 300 K |
x | y | z | Uiso*/Ueq | ||
Rb1 | 0.0102 (2) | 0.1660 (2) | 0.11841 (17) | 0.0456 (4)* | |
Rb2 | 0.1182 (3) | 0.43646 (19) | 0.38731 (17) | 0.0456 (4)* | |
Rb3 | 0.3356 (2) | 0.4349 (2) | 0.11309 (16) | 0.0456 (4)* | |
C4 | 0.886 (2) | 0.9013 (13) | 0.1375 (12) | 0.033 (3)* | |
C5 | 0.8103 (19) | 0.7886 (13) | 0.1665 (13) | 0.033 (3)* | |
C6 | 0.9144 (18) | 0.6786 (13) | 0.1510 (9) | 0.033 (3)* | |
C7 | 0.794 (2) | 0.5780 (14) | 0.1757 (11) | 0.033 (3)* | |
C8 | 0.847 (2) | 0.4649 (15) | 0.1373 (13) | 0.033 (3)* | |
C9 | 1.1021 (17) | 0.6830 (16) | 0.2152 (9) | 0.033 (3)* | |
O10 | 1.0404 (15) | 0.9238 (11) | 0.1753 (9) | 0.0351 (13)* | |
O11 | 0.7895 (15) | 0.9429 (11) | 0.0622 (9) | 0.0351 (13)* | |
O12 | 0.9890 (15) | 0.4210 (10) | 0.1791 (8) | 0.0351 (13)* | |
O13 | 0.7342 (15) | 0.4316 (11) | 0.0691 (10) | 0.0351 (13)* | |
O14 | 1.0988 (13) | 0.6888 (12) | 0.3119 (7) | 0.0351 (13)* | |
O15 | 1.2398 (14) | 0.6654 (9) | 0.1693 (7) | 0.0351 (13)* | |
O16 | 0.9233 (13) | 0.6642 (11) | 0.0459 (8) | 0.0351 (13)* | |
H17 | 0.66841 | 0.77938 | 0.11192 | 0.042 (4)* | |
H18 | 0.76254 | 0.79781 | 0.23982 | 0.042 (4)* | |
H19 | 0.64492 | 0.60516 | 0.15820 | 0.042 (4)* | |
H20 | 0.80258 | 0.57869 | 0.26635 | 0.042 (4)* | |
H21 | 1.06826 | 0.65697 | 0.05902 | 0.0456 (16)* | |
O22 | 0.6164 (13) | 0.2217 (9) | 0.0449 (8) | 0.040 (4)* | |
H23 | 0.54454 | 0.20759 | 0.09843 | 0.052 (5)* | |
H24 | 0.65210 | 0.29614 | 0.04430 | 0.052 (5)* |
Rb1—O10i | 2.976 (12) | C8—O12 | 1.239 (12) |
Rb1—O11i | 3.153 (13) | C8—O13 | 1.221 (13) |
Rb1—O11ii | 3.281 (11) | C9—C6 | 1.539 (8) |
Rb1—O12iii | 3.146 (12) | C9—O14 | 1.302 (11) |
Rb1—O13iii | 3.773 (12) | C9—O15 | 1.285 (10) |
Rb1—O14iv | 2.946 (10) | O10—Rb1viii | 2.976 (12) |
Rb1—O15iv | 3.182 (10) | O10—Rb2ix | 2.789 (11) |
Rb1—O16ii | 3.078 (11) | O10—Rb3ix | 2.866 (12) |
Rb1—O22iii | 3.036 (10) | O10—C4 | 1.222 (12) |
Rb2—O10iv | 2.789 (11) | O11—Rb1viii | 3.153 (13) |
Rb2—O11v | 3.201 (10) | O11—Rb1ii | 3.281 (11) |
Rb2—O11vi | 2.892 (12) | O11—Rb2x | 3.201 (10) |
Rb2—O12iii | 2.833 (11) | O11—Rb2xi | 2.892 (12) |
Rb2—O14iii | 3.160 (13) | O11—C4 | 1.257 (12) |
Rb2—O15iv | 3.504 (11) | O12—Rb1xii | 3.146 (12) |
Rb2—O22vii | 2.830 (10) | O12—Rb2xii | 2.833 (11) |
Rb3—O10iv | 2.866 (12) | O12—Rb3xii | 2.847 (11) |
Rb3—O12iii | 2.847 (11) | O12—C8 | 1.239 (12) |
Rb3—O13 | 3.105 (11) | O13—Rb1xii | 3.773 (12) |
Rb3—O13ii | 2.900 (13) | O13—Rb3 | 3.105 (11) |
Rb3—O14iv | 3.108 (13) | O13—Rb3ii | 2.900 (13) |
Rb3—O15iii | 2.952 (10) | O13—C8 | 1.221 (13) |
Rb3—O16ii | 2.920 (11) | O14—Rb1ix | 2.946 (10) |
Rb3—O22 | 3.485 (11) | O14—Rb2xii | 3.160 (13) |
C4—C5 | 1.522 (8) | O14—Rb3ix | 3.108 (13) |
C4—O10 | 1.222 (12) | O14—C9 | 1.302 (11) |
C4—O11 | 1.257 (12) | O15—Rb1ix | 3.182 (10) |
C5—C4 | 1.522 (8) | O15—Rb2ix | 3.504 (11) |
C5—C6 | 1.548 (8) | O15—Rb3xii | 2.952 (10) |
C6—C5 | 1.548 (8) | O15—C9 | 1.285 (10) |
C6—C7 | 1.555 (8) | O16—Rb1ii | 3.078 (11) |
C6—C9 | 1.539 (8) | O16—Rb3ii | 2.920 (11) |
C6—O16 | 1.431 (8) | O16—C6 | 1.431 (8) |
C7—C6 | 1.555 (8) | O22—Rb1xii | 3.036 (10) |
C7—C8 | 1.511 (8) | O22—Rb2xiii | 2.830 (10) |
C8—C7 | 1.511 (8) | O22—Rb3 | 3.485 (11) |
O10i—Rb1—O11i | 43.0 (3) | O12iii—Rb2—O22xv | 131.2 (3) |
O10i—Rb1—O11ii | 77.4 (3) | O14iii—Rb2—O22xv | 149.8 (3) |
O10i—Rb1—O12iii | 150.3 (3) | O10iv—Rb3—O12iii | 82.6 (3) |
O10i—Rb1—O14iv | 88.3 (4) | O10iv—Rb3—O13 | 90.1 (4) |
O10i—Rb1—O15iv | 75.8 (3) | O10iv—Rb3—O13ii | 148.9 (4) |
O10i—Rb1—O16ii | 143.4 (3) | O10iv—Rb3—O14iv | 67.7 (3) |
O10i—Rb1—O22iii | 109.2 (3) | O10iv—Rb3—O15iii | 81.2 (3) |
O11i—Rb1—O11ii | 76.5 (3) | O10iv—Rb3—O16ii | 142.7 (4) |
O11i—Rb1—O12iii | 145.8 (3) | O12iii—Rb3—O13 | 171.8 (4) |
O11i—Rb1—O14iv | 127.8 (4) | O12iii—Rb3—O13ii | 103.2 (3) |
O11i—Rb1—O15iv | 115.7 (3) | O12iii—Rb3—O14iv | 87.3 (3) |
O11i—Rb1—O16ii | 120.6 (3) | O12iii—Rb3—O15iii | 73.3 (4) |
O11i—Rb1—O22iii | 69.9 (3) | O12iii—Rb3—O16ii | 70.6 (3) |
O11ii—Rb1—O12iii | 127.9 (3) | O13—Rb3—O13ii | 85.0 (4) |
O11ii—Rb1—O14iv | 75.0 (3) | O13—Rb3—O14iv | 86.4 (3) |
O11ii—Rb1—O15iv | 113.0 (3) | O13—Rb3—O15iii | 109.3 (4) |
O11ii—Rb1—O16ii | 66.1 (3) | O13—Rb3—O16ii | 114.1 (3) |
O11ii—Rb1—O22iii | 111.3 (3) | O13ii—Rb3—O14iv | 142.1 (3) |
O12iii—Rb1—O14iv | 84.9 (3) | O13ii—Rb3—O15iii | 71.8 (3) |
O12iii—Rb1—O15iv | 79.3 (3) | O13ii—Rb3—O16ii | 65.2 (4) |
O12iii—Rb1—O16ii | 64.7 (3) | O14iv—Rb3—O15iii | 145.3 (3) |
O12iii—Rb1—O22iii | 78.1 (3) | O14iv—Rb3—O16ii | 85.2 (3) |
O14iv—Rb1—O15iv | 44.3 (2) | O15iii—Rb3—O16ii | 113.7 (3) |
O14iv—Rb1—O16ii | 85.3 (3) | C5—C4—O10 | 116.5 (15) |
O14iv—Rb1—O22iii | 162.1 (3) | C5—C4—O11 | 111.2 (15) |
O15iv—Rb1—O16ii | 120.7 (3) | O10—C4—O11 | 130.4 (16) |
O15iv—Rb1—O22iii | 135.4 (3) | C4—C5—C6 | 119.9 (13) |
O16ii—Rb1—O22iii | 82.4 (3) | C5—C6—C7 | 107.8 (11) |
O10iv—Rb2—O11v | 174.5 (4) | C5—C6—C9 | 109.2 (13) |
O10iv—Rb2—O11xiv | 87.3 (3) | C5—C6—O16 | 109.0 (13) |
O10iv—Rb2—O12iii | 84.3 (3) | C7—C6—C9 | 114.3 (13) |
O10iv—Rb2—O14iii | 87.6 (3) | C7—C6—O16 | 103.0 (11) |
O10iv—Rb2—O22xv | 106.7 (3) | C9—C6—O16 | 113.3 (12) |
O11v—Rb2—O11xiv | 98.2 (3) | C6—C7—C8 | 115.2 (13) |
O11v—Rb2—O12iii | 90.4 (4) | C7—C8—O12 | 117.7 (15) |
O11v—Rb2—O14iii | 92.4 (3) | C7—C8—O13 | 111.0 (14) |
O11v—Rb2—O22xv | 75.9 (3) | O12—C8—O13 | 131.3 (17) |
O11xiv—Rb2—O12iii | 152.2 (3) | C6—C9—O14 | 114.9 (12) |
O11xiv—Rb2—O14iii | 77.6 (3) | C6—C9—O15 | 116.7 (12) |
O11xiv—Rb2—O22xv | 76.7 (3) | O14—C9—O15 | 127.7 (14) |
O12iii—Rb2—O14iii | 75.6 (3) |
Symmetry codes: (i) x−1, y−1, z; (ii) −x+1, −y+1, −z; (iii) x−1, y, z; (iv) −x+3/2, y−1/2, −z+1/2; (v) −x+1/2, y−1/2, −z+1/2; (vi) x−1/2, −y+3/2, z+1/2; (vii) x−1/2, −y+1/2, z+1/2; (viii) x+1, y+1, z; (ix) −x+3/2, y+1/2, −z+1/2; (x) −x+1/2, y+1/2, −z+1/2; (xi) x+1/2, −y+3/2, z−1/2; (xii) x+1, y, z; (xiii) x+1/2, −y+1/2, z−1/2; (xiv) x+1/2, −y+5/2, z+3/2; (xv) x+1/2, −y+3/2, z+3/2. |
3Rb+·C6H5O73−·H2O | a = 5.43105 Å |
Mr = 28.09 | V = 160.20 Å3 |
Cubic, Fd3m | Z = 8 |
Hall symbol: -F 4vw 2vw | T = 300 K |
x | y | z | Uiso*/Ueq | ||
Si1 | 0.125 | 0.125 | 0.125 | 0.01* |
Si1—Si1i | 2.3517 | Si1—Si1iii | 2.3517 |
Si1—Si1ii | 2.3517 | Si1—Si1iv | 2.3517 |
Si1i—Si1—Si1ii | 109.4712 | Si1ii—Si1—Si1iii | 109.4712 |
Si1i—Si1—Si1iii | 109.4712 | Si1ii—Si1—Si1iv | 109.4712 |
Si1i—Si1—Si1iv | 109.4712 | Si1iii—Si1—Si1iv | 109.4712 |
Symmetry codes: (i) x+1/4, y+1/4, −z; (ii) −z, x+1/4, y+1/4; (iii) y+1/4, −z, x+1/4; (iv) −x, −y, −z. |
3Rb+·C6H5O73−·H2O | β = 97.8820° |
Mr = 463.48 | V = 1175.44 Å3 |
Monoclinic, P21/n | Z = 4 |
a = 7.4477 Å | Cu Kα radiation, λ = 1.5418 Å |
b = 11.8755 Å | T = 300 K |
c = 13.4168 Å |
x | y | z | Uiso*/Ueq | ||
Rb1 | 0.00583 | 0.17144 | 0.11496 | 0.04560* | |
Rb2 | 0.11938 | 0.43645 | 0.38752 | 0.04560* | |
Rb3 | 0.33332 | 0.44502 | 0.10955 | 0.04560* | |
C4 | 0.88224 | 0.90099 | 0.13558 | 0.03270* | |
C5 | 0.79490 | 0.79062 | 0.16279 | 0.03270* | |
C6 | 0.90539 | 0.68265 | 0.15421 | 0.03270* | |
C7 | 0.78654 | 0.58443 | 0.18427 | 0.03270* | |
C8 | 0.83169 | 0.47105 | 0.13960 | 0.03270* | |
C9 | 1.09412 | 0.68118 | 0.22083 | 0.03270* | |
O10 | 1.03887 | 0.92354 | 0.18002 | 0.03510* | |
O11 | 0.78874 | 0.96367 | 0.07211 | 0.03510* | |
O12 | 0.97854 | 0.42387 | 0.17390 | 0.03510* | |
O13 | 0.71389 | 0.43264 | 0.07008 | 0.03510* | |
O14 | 1.10018 | 0.68748 | 0.31550 | 0.03510* | |
O15 | 1.22967 | 0.66839 | 0.17504 | 0.03510* | |
O16 | 0.93669 | 0.67035 | 0.05167 | 0.03510* | |
H17 | 0.66841 | 0.77938 | 0.11192 | 0.04250* | |
H18 | 0.76254 | 0.79781 | 0.23982 | 0.04250* | |
H19 | 0.64492 | 0.60516 | 0.15820 | 0.04250* | |
H20 | 0.80258 | 0.57869 | 0.26635 | 0.04250* | |
H21 | 1.06826 | 0.65697 | 0.05902 | 0.04560* | |
O22 | 0.60639 | 0.21834 | 0.03896 | 0.03990* | |
H23 | 0.54454 | 0.20759 | 0.09843 | 0.05180* | |
H24 | 0.65210 | 0.29614 | 0.04430 | 0.05180* |
C4—C5 | 1.530 | C7—H19 | 1.093 |
C4—O10 | 1.264 | C7—H20 | 1.093 |
C4—O11 | 1.266 | C8—O12 | 1.258 |
C5—C6 | 1.536 | C8—O13 | 1.274 |
C5—H17 | 1.093 | C9—O14 | 1.267 |
C5—H18 | 1.096 | C9—O15 | 1.261 |
C6—C7 | 1.551 | O16—H21 | 0.984 |
C6—C9 | 1.559 | O22—H23 | 0.983 |
C6—O16 | 1.434 | O22—H24 | 0.984 |
C7—C8 | 1.530 |
D—H···A | D—H | H···A | D···A | D—H···A |
O16—H21···O15 | 0.984 | 1.838 | 2.552 | 126.9 |
O22—H23···O14i | 0.983 | 1.704 | 2.672 | 168.7 |
O22—H24···O13 | 0.984 | 1.707 | 2.683 | 170.8 |
C5—H17···O22 | 1.093 | 2.674 | 3.749 | 167.4 |
Symmetry code: (i) −x+3/2, y−1/2, −z+1/2. |
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