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The title complex, K2[Ni2(C6H5O7)2(H2O)4]·4H2O, is a dinuclear centrosymmetric anionic octa­hedral complex, involv­ing citrates as tridentate and bridging ligands, and coordinating water mol­ecules. An extensive network of hydrogen bonds connects the complex anions through the two unique uncoordinating water mol­ecules. The K+ counter cation is surrounded by seven O atoms in the form of an irregular polyhedron and further stabilizes the crystal packing.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536813022630/kp2456sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536813022630/kp2456Isup2.hkl
Contains datablock I

CCDC reference: 963427

Key indicators

  • Single-crystal X-ray study
  • T = 293 K
  • Mean [sigma](C-C) = 0.002 Å
  • R factor = 0.023
  • wR factor = 0.063
  • Data-to-parameter ratio = 14.0

checkCIF/PLATON results

No syntax errors found



Alert level C PLAT220_ALERT_2_C Large Non-Solvent O Ueq(max)/Ueq(min) ... 3.1 Ratio PLAT222_ALERT_3_C Large Non-Solvent H Uiso(max)/Uiso(min) .. 6.2 Ratio PLAT314_ALERT_2_C Check Small Angle for H2O: Metal-O4W -H4WB 87.90 Deg. PLAT911_ALERT_3_C Missing # FCF Refl Between THmin & STh/L= 0.600 6 PLAT975_ALERT_2_C Positive Residual Density at 0.93A from O3W . 0.40 eA-3
Alert level G PLAT002_ALERT_2_G Number of Distance or Angle Restraints on AtSite 3 PLAT004_ALERT_5_G Info: Polymeric Structure Found with Dimension . 3 PLAT005_ALERT_5_G No _iucr_refine_instructions_details in the CIF ? Do ! PLAT042_ALERT_1_G Calc. and Reported MoietyFormula Strings Differ ? Check PLAT045_ALERT_1_G Calculated and Reported Z Differ by ............ 2.00 Ratio PLAT164_ALERT_4_G Nr. of Refined C-H H-Atoms in Heavy-Atom Struct. 4 PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature 293 K PLAT200_ALERT_1_G Check the Reported _diffrn_ambient_temperature 293 K PLAT232_ALERT_2_G Hirshfeld Test Diff (M-X) Ni1 -- O1W .. 5.2 su PLAT232_ALERT_2_G Hirshfeld Test Diff (M-X) Ni1 -- O2W .. 5.8 su PLAT232_ALERT_2_G Hirshfeld Test Diff (M-X) Ni1 -- O3 .. 8.3 su PLAT720_ALERT_4_G Number of Unusual/Non-Standard Labels .......... 8 PLAT764_ALERT_4_G Overcomplete CIF Bond List Detected (Rep/Expd) . 1.20 Ratio PLAT793_ALERT_4_G The Model has Chirality at C3 (Verify) .... R PLAT860_ALERT_3_G Note: Number of Least-Squares Restraints ....... 2 PLAT912_ALERT_4_G Missing # of FCF Reflections Above STh/L= 0.600 8
0 ALERT level A = Most likely a serious problem - resolve or explain 0 ALERT level B = A potentially serious problem, consider carefully 5 ALERT level C = Check. Ensure it is not caused by an omission or oversight 16 ALERT level G = General information/check it is not something unexpected 4 ALERT type 1 CIF construction/syntax error, inconsistent or missing data 7 ALERT type 2 Indicator that the structure model may be wrong or deficient 3 ALERT type 3 Indicator that the structure quality may be low 5 ALERT type 4 Improvement, methodology, query or suggestion 2 ALERT type 5 Informative message, check

Comment top

The construction of metal–organic frameworks (MOFs) is an area of intense research activity due to their intriguing structural diversity and potential applications as zeolitic, optoelectronic, magnetic and conducting materials (Chui et al., 1999; Kiang et al., 1999; Kahn & Martinez, 1998; Lin et al., 1999). Depending on the conformation of carbon chains, the functional group of organic ligands and the type of metal ions, a variety of metal coordination polymers with different topological structures, such as one-dimensional chains (Shin et al., 2003), two-dimensional grids (Kondo et al., 2000), three-dimensional porous motifs (Yao et al., 2007) and helical strands (Wu et al., 2003) were observed. In this paper, we report the synthesis of a dimeric nickel(II) citrate complex by self-assembly under hydrothermal conditions.

In the crystal the centrosymmetric structural unit is a dinuclear NiII anion (Fig. 1) and the two potassium cations, and crystalline water molecules. The crystallographic unit is a half of the structural unit. The NiII ion adopts an octahedral coordination mode. One citrate ligand is bound with an hydroxyl and two carboxylate groups to the NiII ion, whereas one O atom (O6) from a carboxylate group of a symmetry-related citrate ligand occupies another apex, and two water molecules complete the octahedral environment. The Ni—O distances range from 2.0322 (12) Å to 2.0927 (10) Å (Table 1). Neighbouring dimeric complexes are consolidated into a three-dimensional structure by hydrogen bonds (Table 2, Fig. 2). The crystallographically independent potassium cation, K1, is seven-coordinated by O atoms, with an average contact distance of 2.852 Å.

The corresponding nickel–citrate complex with the triclinic space group P1, K2[Ni(C6H5O7)(H2O)2]2.4H2O, has been reported (Baker et al., 1983). The complex exists as centrosymmetric dimers, which has identical structure with the title complex, but a difference is that the potassium ions and water molecules of crystallization occupy the spaces between the nickel–citrate dimers in the two cases, resulting in the different formation of the geometry of potassium ion and hydrogen bonds.

Related literature top

For applications of structures with metal-organic frameworks, see: Chui et al. (1999); Kahn & Martinez (1998); Kiang et al. (1999); Lin et al. (1999). For metal coordination polymers with a variety of topologies, see: Kondo et al. (2000); Shin et al. (2003); Wu et al. (2003); Yao et al. (2007). For the nickel–citrate complex K2[Ni(C6H5O7)(H2O)2]2.4H2O, which crystallized in the triclinic space group P1, see: Baker et al. (1983).

Experimental top

Citric acid monohydrate (0.048 g), NiCl2.6H2O (0.042 g) and KOH (0.027 g) were dissolved in 6 ml mixed solvent of DMF–H20 (2:1 v/v), which were placed in a small vial. The mixture was heated at 351 K for 3 d and then cooled to room temperature. Green block crystals of the product were collected by filtration and washed with ethanol several times (88% based on Ni). This synthetic route allowed us to obtain a pure phase. Elemental analysis, calculated (%) for title compound: C 20.06, H 3.62; found C 20.35, H 3.44.

Refinement top

H atoms were positioned geometrically, with C—H = 0.93 Å, and allowed to ride during subsequent refinement, with Uiso(H) = 1.2Ueq(C).

Computing details top

Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. The structure of the dimeric complex anion, with the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level. H atoms have been omitted for clarity.
[Figure 2] Fig. 2. Dimeric complexes are consolidated into three-dimensional structures by hydrogen bonds. Symmetry code: -x, 1/2 + y, 1/2 - z
Dipotassium tetraaquabis(µ-citrato-κ4O:O',O'',O''')nickelate(II) tetrahydrate top
Crystal data top
K2[Ni2(C6H5O7)2(H2O)4]·4H2OZ = 2
Mr = 717.94F(000) = 736
Monoclinic, P21/cDx = 1.911 Mg m3
Hall symbol: -P 2ybcMo Kα radiation, λ = 0.71073 Å
a = 10.616 (2) ŵ = 1.94 mm1
b = 13.006 (3) ÅT = 293 K
c = 9.0513 (18) ÅBlock, green
β = 93.09 (3)°0.30 × 0.20 × 0.15 mm
V = 1247.8 (4) Å3
Data collection top
Bruker SMART APEXII CCD
diffractometer
3128 independent reflections
Radiation source: fine-focus sealed tube2916 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.017
ϕ and ω scansθmax = 28.4°, θmin = 1.9°
Absorption correction: multi-scan
(SADABS; Sheldrick, 2001)
h = 1412
Tmin = 0.636, Tmax = 0.741k = 1717
9515 measured reflectionsl = 1212
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.023Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.063H-atom parameters constrained
S = 1.02 w = 1/[σ2(Fo2) + (0.0378P)2 + 0.4504P]
where P = (Fo2 + 2Fc2)/3
3128 reflections(Δ/σ)max = 0.001
224 parametersΔρmax = 0.43 e Å3
2 restraintsΔρmin = 0.55 e Å3
Crystal data top
K2[Ni2(C6H5O7)2(H2O)4]·4H2OV = 1247.8 (4) Å3
Mr = 717.94Z = 2
Monoclinic, P21/cMo Kα radiation
a = 10.616 (2) ŵ = 1.94 mm1
b = 13.006 (3) ÅT = 293 K
c = 9.0513 (18) Å0.30 × 0.20 × 0.15 mm
β = 93.09 (3)°
Data collection top
Bruker SMART APEXII CCD
diffractometer
3128 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 2001)
2916 reflections with I > 2σ(I)
Tmin = 0.636, Tmax = 0.741Rint = 0.017
9515 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0232 restraints
wR(F2) = 0.063H-atom parameters constrained
S = 1.02Δρmax = 0.43 e Å3
3128 reflectionsΔρmin = 0.55 e Å3
224 parameters
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
Ni10.243734 (14)0.519202 (13)0.006123 (17)0.01642 (7)
K10.13777 (3)0.90086 (3)0.14726 (4)0.03020 (9)
O10.07698 (9)0.76820 (8)0.19256 (13)0.0290 (2)
O20.12630 (9)0.63014 (8)0.06472 (12)0.0256 (2)
O30.38530 (9)0.63022 (8)0.02002 (10)0.01756 (18)
O40.32413 (10)0.51024 (8)0.20239 (12)0.0247 (2)
O50.43183 (11)0.60531 (8)0.37004 (11)0.0278 (2)
O60.37540 (9)0.41901 (8)0.07541 (12)0.0240 (2)
O70.25885 (11)0.27918 (10)0.11481 (19)0.0503 (4)
O1W0.11765 (10)0.40268 (8)0.03601 (12)0.0235 (2)
O2W0.16893 (11)0.54135 (9)0.21942 (12)0.0238 (2)
O3W0.00587 (17)0.89783 (14)0.11374 (17)0.0549 (4)
O4W0.32069 (13)0.97832 (11)0.06745 (14)0.0336 (3)
C10.15547 (12)0.71310 (10)0.13242 (14)0.0187 (2)
C20.29093 (12)0.75171 (10)0.13945 (16)0.0202 (3)
C30.39866 (11)0.67514 (10)0.12633 (13)0.0160 (2)
C40.38568 (12)0.58926 (10)0.24245 (14)0.0181 (2)
C50.47751 (12)0.26558 (11)0.14594 (16)0.0197 (3)
C60.36067 (12)0.32483 (11)0.11019 (15)0.0212 (3)
H10.444 (2)0.6015 (17)0.036 (2)0.040 (6)*
H2A0.2987 (17)0.8014 (15)0.067 (2)0.030 (5)*
H2B0.3039 (17)0.7872 (16)0.227 (2)0.031 (5)*
H5A0.4817 (18)0.2059 (16)0.090 (2)0.033 (5)*
H5B0.4680 (17)0.2407 (15)0.249 (2)0.029 (5)*
H1WB0.047 (2)0.4026 (18)0.003 (2)0.048 (6)*
H1WA0.152 (2)0.354 (2)0.006 (3)0.065 (8)*
H2WA0.220 (2)0.525 (2)0.290 (3)0.057 (7)*
H2WB0.140 (2)0.601 (2)0.235 (3)0.055 (7)*
H3WC0.003 (3)0.8359 (11)0.141 (4)0.096 (11)*
H3WA0.073 (3)0.906 (4)0.168 (5)0.18 (2)*
H4WA0.372 (2)0.948 (2)0.100 (3)0.041 (6)*
H4WB0.351 (2)1.0134 (19)0.001 (3)0.053 (7)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ni10.01296 (10)0.01699 (11)0.01930 (10)0.00081 (6)0.00068 (6)0.00159 (6)
K10.02800 (17)0.03044 (18)0.03236 (17)0.00154 (13)0.00338 (13)0.00315 (13)
O40.0277 (5)0.0229 (5)0.0230 (5)0.0075 (4)0.0032 (4)0.0043 (4)
O30.0162 (4)0.0189 (4)0.0176 (4)0.0000 (4)0.0014 (3)0.0016 (3)
O60.0158 (4)0.0174 (5)0.0390 (6)0.0003 (4)0.0041 (4)0.0049 (4)
O20.0151 (4)0.0257 (5)0.0358 (5)0.0002 (4)0.0014 (4)0.0107 (4)
O50.0335 (6)0.0305 (6)0.0188 (5)0.0038 (4)0.0047 (4)0.0002 (4)
O10.0182 (5)0.0257 (5)0.0438 (6)0.0019 (4)0.0077 (4)0.0090 (5)
C50.0148 (6)0.0170 (6)0.0273 (7)0.0008 (5)0.0012 (5)0.0021 (5)
C60.0155 (6)0.0201 (6)0.0281 (6)0.0004 (5)0.0018 (5)0.0029 (5)
C20.0152 (6)0.0169 (6)0.0286 (7)0.0014 (5)0.0011 (5)0.0030 (5)
O70.0178 (5)0.0321 (7)0.1024 (12)0.0080 (5)0.0151 (6)0.0266 (7)
C10.0149 (6)0.0201 (6)0.0209 (6)0.0015 (5)0.0006 (4)0.0004 (5)
C30.0136 (5)0.0167 (6)0.0175 (5)0.0004 (4)0.0004 (4)0.0021 (4)
C40.0147 (6)0.0196 (6)0.0201 (6)0.0019 (5)0.0009 (4)0.0005 (5)
O1W0.0150 (5)0.0245 (5)0.0308 (5)0.0034 (4)0.0016 (4)0.0013 (4)
O2W0.0265 (5)0.0223 (5)0.0224 (5)0.0007 (4)0.0003 (4)0.0012 (4)
O3W0.0621 (10)0.0611 (10)0.0421 (8)0.0235 (8)0.0082 (7)0.0023 (7)
O4W0.0313 (6)0.0412 (7)0.0287 (6)0.0052 (5)0.0048 (5)0.0084 (5)
Geometric parameters (Å, º) top
Ni1—O42.0322 (12)O1—C11.2462 (16)
Ni1—O22.0330 (11)C5—C61.5100 (18)
Ni1—O62.0345 (10)C5—C3v1.5259 (18)
Ni1—O2W2.0677 (12)C5—H5B0.984 (18)
Ni1—O1W2.0709 (11)C5—H5A0.93 (2)
Ni1—O32.0927 (10)C6—O71.2320 (17)
K1—O7i2.6796 (13)C2—C11.5213 (18)
K1—O3W2.8108 (17)C2—C31.5259 (17)
K1—O4ii2.8425 (12)C2—H2B0.925 (19)
K1—O4W2.8557 (16)C2—H2A0.926 (19)
K1—O1Wii2.8633 (13)O7—K1i2.6796 (13)
K1—O12.8708 (12)C3—C5v1.5259 (18)
K1—O3Wiii3.053 (2)C3—C41.5449 (18)
O4—C41.2606 (17)O1W—K1iv2.8633 (13)
O4—K1iv2.8425 (12)O1W—H1WB0.79 (3)
O3—C31.4477 (15)O1W—H1WA0.83 (3)
O3—H10.75 (2)O4W—H4WB0.85 (3)
O6—C61.2723 (17)O4W—H4WA0.72 (3)
O2W—H2WB0.84 (3)O3W—K1iii3.053 (2)
O2W—H2WA0.88 (3)O3W—H3WC0.842 (10)
O2—C11.2707 (17)O3W—H3WA0.845 (10)
O5—C41.2475 (17)
O4—Ni1—O288.95 (5)C1—O2—Ni1128.10 (9)
O4—Ni1—O689.34 (5)C1—O1—K1145.86 (10)
O2—Ni1—O6174.20 (4)C6—C5—C3v115.44 (11)
O4—Ni1—O2W174.86 (4)C6—C5—H5B109.1 (11)
O2—Ni1—O2W89.11 (5)C3v—C5—H5B108.7 (11)
O6—Ni1—O2W92.12 (5)C6—C5—H5A109.1 (12)
O4—Ni1—O1W91.73 (5)C3v—C5—H5A110.1 (12)
O2—Ni1—O1W92.74 (5)H5B—C5—H5A103.7 (16)
O6—Ni1—O1W92.85 (5)O7—C6—O6124.63 (13)
O2W—Ni1—O1W93.12 (5)O7—C6—C5118.43 (13)
O4—Ni1—O380.12 (4)O6—C6—C5116.93 (12)
O2—Ni1—O389.07 (5)C1—C2—C3119.47 (11)
O6—Ni1—O385.17 (4)C1—C2—H2B107.3 (12)
O2W—Ni1—O395.08 (4)C3—C2—H2B108.4 (12)
O1W—Ni1—O3171.62 (4)C1—C2—H2A108.7 (11)
O7i—K1—O3W98.82 (5)C3—C2—H2A107.8 (11)
O7i—K1—O4ii98.49 (4)H2B—C2—H2A104.2 (16)
O3W—K1—O4ii143.18 (4)C6—O7—K1i147.10 (10)
O7i—K1—O4W85.94 (5)O1—C1—O2123.20 (12)
O3W—K1—O4W77.54 (5)O1—C1—C2116.40 (12)
O4ii—K1—O4W71.58 (4)O2—C1—C2120.38 (11)
O7i—K1—O1Wii97.26 (5)O3—C3—C2107.32 (10)
O3W—K1—O1Wii145.89 (5)O3—C3—C5v110.58 (10)
O4ii—K1—O1Wii62.15 (4)C2—C3—C5v107.80 (11)
O4W—K1—O1Wii133.61 (4)O3—C3—C4108.84 (10)
O7i—K1—O182.13 (4)C2—C3—C4108.91 (10)
O3W—K1—O171.57 (5)C5v—C3—C4113.21 (11)
O4ii—K1—O1143.15 (3)O5—C4—O4125.05 (13)
O4W—K1—O1144.57 (4)O5—C4—C3117.64 (12)
O1Wii—K1—O181.15 (4)O4—C4—C3117.23 (11)
O7i—K1—O3Wiii167.85 (5)Ni1—O1W—K1iv100.16 (5)
O3W—K1—O3Wiii69.78 (6)Ni1—O1W—H1WB122.5 (17)
O4ii—K1—O3Wiii89.00 (4)K1iv—O1W—H1WB113.6 (16)
O4W—K1—O3Wiii87.41 (5)Ni1—O1W—H1WA99.7 (18)
O1Wii—K1—O3Wiii94.69 (4)K1iv—O1W—H1WA116.3 (18)
O1—K1—O3Wiii97.62 (4)H1WB—O1W—H1WA104 (2)
C4—O4—Ni1113.92 (9)K1—O4W—H4WB87.9 (17)
C4—O4—K1iv129.32 (9)K1—O4W—H4WA123.4 (19)
Ni1—O4—K1iv101.83 (4)H4WB—O4W—H4WA107 (2)
C3—O3—Ni1104.99 (7)K1—O3W—K1iii110.22 (6)
C3—O3—H1109.4 (17)K1—O3W—H3WC107 (2)
Ni1—O3—H1106.2 (17)K1iii—O3W—H3WC140 (2)
C6—O6—Ni1128.00 (9)K1—O3W—H3WA92 (3)
Ni1—O2W—H2WB114.0 (16)K1iii—O3W—H3WA104 (4)
Ni1—O2W—H2WA115.0 (16)H3WC—O3W—H3WA90 (4)
H2WB—O2W—H2WA109 (2)
Symmetry codes: (i) x, y+1, z; (ii) x, y+1/2, z+1/2; (iii) x, y+2, z; (iv) x, y1/2, z+1/2; (v) x+1, y+1, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1W—H1WB···O2i0.79 (3)1.96 (3)2.7322 (16)167 (2)
O2W—H2WB···O1vi0.84 (3)1.93 (3)2.7638 (16)170 (2)
O4W—H4WB···O5ii0.85 (3)1.91 (3)2.7459 (17)171 (2)
O2W—H2WA···O4Wvii0.88 (3)1.83 (3)2.7064 (18)174 (2)
O4W—H4WA···O5viii0.72 (3)2.20 (2)2.8714 (19)155 (2)
O3—H1···O6v0.75 (2)2.13 (2)2.7152 (15)135 (2)
O3W—H3WA···O2Wix0.85 (1)2.25 (4)2.912 (2)135 (5)
Symmetry codes: (i) x, y+1, z; (ii) x, y+1/2, z+1/2; (v) x+1, y+1, z; (vi) x, y+3/2, z1/2; (vii) x, y1/2, z1/2; (viii) x1, y+3/2, z1/2; (ix) x, y+1/2, z1/2.
Selected bond lengths (Å) top
Ni1—O42.0322 (12)Ni1—O2W2.0677 (12)
Ni1—O22.0330 (11)Ni1—O1W2.0709 (11)
Ni1—O62.0345 (10)Ni1—O32.0927 (10)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1W—H1WB···O2i0.79 (3)1.96 (3)2.7322 (16)167 (2)
O2W—H2WB···O1ii0.84 (3)1.93 (3)2.7638 (16)170 (2)
O4W—H4WB···O5iii0.85 (3)1.91 (3)2.7459 (17)171 (2)
O2W—H2WA···O4Wiv0.88 (3)1.83 (3)2.7064 (18)174 (2)
O4W—H4WA···O5v0.72 (3)2.20 (2)2.8714 (19)155 (2)
O3—H1···O6vi0.75 (2)2.13 (2)2.7152 (15)135 (2)
O3W—H3WA···O2Wvii0.845 (10)2.25 (4)2.912 (2)135 (5)
Symmetry codes: (i) x, y+1, z; (ii) x, y+3/2, z1/2; (iii) x, y+1/2, z+1/2; (iv) x, y1/2, z1/2; (v) x1, y+3/2, z1/2; (vi) x+1, y+1, z; (vii) x, y+1/2, z1/2.
 

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