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
CCDC reference: 963427
Key indicators
- Single-crystal X-ray study
- T = 293 K
- Mean
(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
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.
H atoms were positioned geometrically, with C—H = 0.93 Å, and allowed to
ride during subsequent refinement, with Uiso(H) = 1.2Ueq(C).
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).
Dipotassium tetraaquabis(µ-citrato-
κ4O:
O',
O'',
O''')nickelate(II) tetrahydrate
top
Crystal data top
K2[Ni2(C6H5O7)2(H2O)4]·4H2O | Z = 2 |
Mr = 717.94 | F(000) = 736 |
Monoclinic, P21/c | Dx = 1.911 Mg m−3 |
Hall symbol: -P 2ybc | Mo Kα radiation, λ = 0.71073 Å |
a = 10.616 (2) Å | µ = 1.94 mm−1 |
b = 13.006 (3) Å | T = 293 K |
c = 9.0513 (18) Å | Block, 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 tube | 2916 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.017 |
ϕ and ω scans | θmax = 28.4°, θmin = 1.9° |
Absorption correction: multi-scan (SADABS; Sheldrick, 2001) | h = −14→12 |
Tmin = 0.636, Tmax = 0.741 | k = −17→17 |
9515 measured reflections | l = −12→12 |
Refinement top
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.023 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.063 | H-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 parameters | Δρmax = 0.43 e Å−3 |
2 restraints | Δρmin = −0.55 e Å−3 |
Crystal data top
K2[Ni2(C6H5O7)2(H2O)4]·4H2O | V = 1247.8 (4) Å3 |
Mr = 717.94 | Z = 2 |
Monoclinic, P21/c | Mo Kα radiation |
a = 10.616 (2) Å | µ = 1.94 mm−1 |
b = 13.006 (3) Å | T = 293 K |
c = 9.0513 (18) Å | 0.30 × 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 = 0.741 | Rint = 0.017 |
9515 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.023 | 2 restraints |
wR(F2) = 0.063 | H-atom parameters constrained |
S = 1.02 | Δρmax = 0.43 e Å−3 |
3128 reflections | Δρmin = −0.55 e Å−3 |
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 | x | y | z | Uiso*/Ueq | |
Ni1 | 0.243734 (14) | 0.519202 (13) | −0.006123 (17) | 0.01642 (7) | |
K1 | −0.13777 (3) | 0.90086 (3) | 0.14726 (4) | 0.03020 (9) | |
O1 | 0.07698 (9) | 0.76820 (8) | 0.19256 (13) | 0.0290 (2) | |
O2 | 0.12630 (9) | 0.63014 (8) | 0.06472 (12) | 0.0256 (2) | |
O3 | 0.38530 (9) | 0.63022 (8) | −0.02002 (10) | 0.01756 (18) | |
O4 | 0.32413 (10) | 0.51024 (8) | 0.20239 (12) | 0.0247 (2) | |
O5 | 0.43183 (11) | 0.60531 (8) | 0.37004 (11) | 0.0278 (2) | |
O6 | 0.37540 (9) | 0.41901 (8) | −0.07541 (12) | 0.0240 (2) | |
O7 | 0.25885 (11) | 0.27918 (10) | −0.11481 (19) | 0.0503 (4) | |
O1W | 0.11765 (10) | 0.40268 (8) | 0.03601 (12) | 0.0235 (2) | |
O2W | 0.16893 (11) | 0.54135 (9) | −0.21942 (12) | 0.0238 (2) | |
O3W | −0.00587 (17) | 0.89783 (14) | −0.11374 (17) | 0.0549 (4) | |
O4W | −0.32069 (13) | 0.97832 (11) | −0.06745 (14) | 0.0336 (3) | |
C1 | 0.15547 (12) | 0.71310 (10) | 0.13242 (14) | 0.0187 (2) | |
C2 | 0.29093 (12) | 0.75171 (10) | 0.13945 (16) | 0.0202 (3) | |
C3 | 0.39866 (11) | 0.67514 (10) | 0.12633 (13) | 0.0160 (2) | |
C4 | 0.38568 (12) | 0.58926 (10) | 0.24245 (14) | 0.0181 (2) | |
C5 | 0.47751 (12) | 0.26558 (11) | −0.14594 (16) | 0.0197 (3) | |
C6 | 0.36067 (12) | 0.32483 (11) | −0.11019 (15) | 0.0212 (3) | |
H1 | 0.444 (2) | 0.6015 (17) | −0.036 (2) | 0.040 (6)* | |
H2A | 0.2987 (17) | 0.8014 (15) | 0.067 (2) | 0.030 (5)* | |
H2B | 0.3039 (17) | 0.7872 (16) | 0.227 (2) | 0.031 (5)* | |
H5A | 0.4817 (18) | 0.2059 (16) | −0.090 (2) | 0.033 (5)* | |
H5B | 0.4680 (17) | 0.2407 (15) | −0.249 (2) | 0.029 (5)* | |
H1WB | 0.047 (2) | 0.4026 (18) | 0.003 (2) | 0.048 (6)* | |
H1WA | 0.152 (2) | 0.354 (2) | −0.006 (3) | 0.065 (8)* | |
H2WA | 0.220 (2) | 0.525 (2) | −0.290 (3) | 0.057 (7)* | |
H2WB | 0.140 (2) | 0.601 (2) | −0.235 (3) | 0.055 (7)* | |
H3WC | −0.003 (3) | 0.8359 (11) | −0.141 (4) | 0.096 (11)* | |
H3WA | −0.073 (3) | 0.906 (4) | −0.168 (5) | 0.18 (2)* | |
H4WA | −0.372 (2) | 0.948 (2) | −0.100 (3) | 0.041 (6)* | |
H4WB | −0.351 (2) | 1.0134 (19) | 0.001 (3) | 0.053 (7)* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Ni1 | 0.01296 (10) | 0.01699 (11) | 0.01930 (10) | −0.00081 (6) | 0.00068 (6) | −0.00159 (6) |
K1 | 0.02800 (17) | 0.03044 (18) | 0.03236 (17) | 0.00154 (13) | 0.00338 (13) | −0.00315 (13) |
O4 | 0.0277 (5) | 0.0229 (5) | 0.0230 (5) | −0.0075 (4) | −0.0032 (4) | 0.0043 (4) |
O3 | 0.0162 (4) | 0.0189 (4) | 0.0176 (4) | 0.0000 (4) | 0.0014 (3) | −0.0016 (3) |
O6 | 0.0158 (4) | 0.0174 (5) | 0.0390 (6) | 0.0003 (4) | 0.0041 (4) | −0.0049 (4) |
O2 | 0.0151 (4) | 0.0257 (5) | 0.0358 (5) | 0.0002 (4) | 0.0014 (4) | −0.0107 (4) |
O5 | 0.0335 (6) | 0.0305 (6) | 0.0188 (5) | −0.0038 (4) | −0.0047 (4) | −0.0002 (4) |
O1 | 0.0182 (5) | 0.0257 (5) | 0.0438 (6) | 0.0019 (4) | 0.0077 (4) | −0.0090 (5) |
C5 | 0.0148 (6) | 0.0170 (6) | 0.0273 (7) | −0.0008 (5) | 0.0012 (5) | −0.0021 (5) |
C6 | 0.0155 (6) | 0.0201 (6) | 0.0281 (6) | −0.0004 (5) | 0.0018 (5) | −0.0029 (5) |
C2 | 0.0152 (6) | 0.0169 (6) | 0.0286 (7) | 0.0014 (5) | 0.0011 (5) | −0.0030 (5) |
O7 | 0.0178 (5) | 0.0321 (7) | 0.1024 (12) | −0.0080 (5) | 0.0151 (6) | −0.0266 (7) |
C1 | 0.0149 (6) | 0.0201 (6) | 0.0209 (6) | 0.0015 (5) | 0.0006 (4) | 0.0004 (5) |
C3 | 0.0136 (5) | 0.0167 (6) | 0.0175 (5) | 0.0004 (4) | 0.0004 (4) | −0.0021 (4) |
C4 | 0.0147 (6) | 0.0196 (6) | 0.0201 (6) | 0.0019 (5) | 0.0009 (4) | 0.0005 (5) |
O1W | 0.0150 (5) | 0.0245 (5) | 0.0308 (5) | −0.0034 (4) | 0.0016 (4) | −0.0013 (4) |
O2W | 0.0265 (5) | 0.0223 (5) | 0.0224 (5) | −0.0007 (4) | −0.0003 (4) | 0.0012 (4) |
O3W | 0.0621 (10) | 0.0611 (10) | 0.0421 (8) | 0.0235 (8) | 0.0082 (7) | −0.0023 (7) |
O4W | 0.0313 (6) | 0.0412 (7) | 0.0287 (6) | −0.0052 (5) | 0.0048 (5) | −0.0084 (5) |
Geometric parameters (Å, º) top
Ni1—O4 | 2.0322 (12) | O1—C1 | 1.2462 (16) |
Ni1—O2 | 2.0330 (11) | C5—C6 | 1.5100 (18) |
Ni1—O6 | 2.0345 (10) | C5—C3v | 1.5259 (18) |
Ni1—O2W | 2.0677 (12) | C5—H5B | 0.984 (18) |
Ni1—O1W | 2.0709 (11) | C5—H5A | 0.93 (2) |
Ni1—O3 | 2.0927 (10) | C6—O7 | 1.2320 (17) |
K1—O7i | 2.6796 (13) | C2—C1 | 1.5213 (18) |
K1—O3W | 2.8108 (17) | C2—C3 | 1.5259 (17) |
K1—O4ii | 2.8425 (12) | C2—H2B | 0.925 (19) |
K1—O4W | 2.8557 (16) | C2—H2A | 0.926 (19) |
K1—O1Wii | 2.8633 (13) | O7—K1i | 2.6796 (13) |
K1—O1 | 2.8708 (12) | C3—C5v | 1.5259 (18) |
K1—O3Wiii | 3.053 (2) | C3—C4 | 1.5449 (18) |
O4—C4 | 1.2606 (17) | O1W—K1iv | 2.8633 (13) |
O4—K1iv | 2.8425 (12) | O1W—H1WB | 0.79 (3) |
O3—C3 | 1.4477 (15) | O1W—H1WA | 0.83 (3) |
O3—H1 | 0.75 (2) | O4W—H4WB | 0.85 (3) |
O6—C6 | 1.2723 (17) | O4W—H4WA | 0.72 (3) |
O2W—H2WB | 0.84 (3) | O3W—K1iii | 3.053 (2) |
O2W—H2WA | 0.88 (3) | O3W—H3WC | 0.842 (10) |
O2—C1 | 1.2707 (17) | O3W—H3WA | 0.845 (10) |
O5—C4 | 1.2475 (17) | | |
| | | |
O4—Ni1—O2 | 88.95 (5) | C1—O2—Ni1 | 128.10 (9) |
O4—Ni1—O6 | 89.34 (5) | C1—O1—K1 | 145.86 (10) |
O2—Ni1—O6 | 174.20 (4) | C6—C5—C3v | 115.44 (11) |
O4—Ni1—O2W | 174.86 (4) | C6—C5—H5B | 109.1 (11) |
O2—Ni1—O2W | 89.11 (5) | C3v—C5—H5B | 108.7 (11) |
O6—Ni1—O2W | 92.12 (5) | C6—C5—H5A | 109.1 (12) |
O4—Ni1—O1W | 91.73 (5) | C3v—C5—H5A | 110.1 (12) |
O2—Ni1—O1W | 92.74 (5) | H5B—C5—H5A | 103.7 (16) |
O6—Ni1—O1W | 92.85 (5) | O7—C6—O6 | 124.63 (13) |
O2W—Ni1—O1W | 93.12 (5) | O7—C6—C5 | 118.43 (13) |
O4—Ni1—O3 | 80.12 (4) | O6—C6—C5 | 116.93 (12) |
O2—Ni1—O3 | 89.07 (5) | C1—C2—C3 | 119.47 (11) |
O6—Ni1—O3 | 85.17 (4) | C1—C2—H2B | 107.3 (12) |
O2W—Ni1—O3 | 95.08 (4) | C3—C2—H2B | 108.4 (12) |
O1W—Ni1—O3 | 171.62 (4) | C1—C2—H2A | 108.7 (11) |
O7i—K1—O3W | 98.82 (5) | C3—C2—H2A | 107.8 (11) |
O7i—K1—O4ii | 98.49 (4) | H2B—C2—H2A | 104.2 (16) |
O3W—K1—O4ii | 143.18 (4) | C6—O7—K1i | 147.10 (10) |
O7i—K1—O4W | 85.94 (5) | O1—C1—O2 | 123.20 (12) |
O3W—K1—O4W | 77.54 (5) | O1—C1—C2 | 116.40 (12) |
O4ii—K1—O4W | 71.58 (4) | O2—C1—C2 | 120.38 (11) |
O7i—K1—O1Wii | 97.26 (5) | O3—C3—C2 | 107.32 (10) |
O3W—K1—O1Wii | 145.89 (5) | O3—C3—C5v | 110.58 (10) |
O4ii—K1—O1Wii | 62.15 (4) | C2—C3—C5v | 107.80 (11) |
O4W—K1—O1Wii | 133.61 (4) | O3—C3—C4 | 108.84 (10) |
O7i—K1—O1 | 82.13 (4) | C2—C3—C4 | 108.91 (10) |
O3W—K1—O1 | 71.57 (5) | C5v—C3—C4 | 113.21 (11) |
O4ii—K1—O1 | 143.15 (3) | O5—C4—O4 | 125.05 (13) |
O4W—K1—O1 | 144.57 (4) | O5—C4—C3 | 117.64 (12) |
O1Wii—K1—O1 | 81.15 (4) | O4—C4—C3 | 117.23 (11) |
O7i—K1—O3Wiii | 167.85 (5) | Ni1—O1W—K1iv | 100.16 (5) |
O3W—K1—O3Wiii | 69.78 (6) | Ni1—O1W—H1WB | 122.5 (17) |
O4ii—K1—O3Wiii | 89.00 (4) | K1iv—O1W—H1WB | 113.6 (16) |
O4W—K1—O3Wiii | 87.41 (5) | Ni1—O1W—H1WA | 99.7 (18) |
O1Wii—K1—O3Wiii | 94.69 (4) | K1iv—O1W—H1WA | 116.3 (18) |
O1—K1—O3Wiii | 97.62 (4) | H1WB—O1W—H1WA | 104 (2) |
C4—O4—Ni1 | 113.92 (9) | K1—O4W—H4WB | 87.9 (17) |
C4—O4—K1iv | 129.32 (9) | K1—O4W—H4WA | 123.4 (19) |
Ni1—O4—K1iv | 101.83 (4) | H4WB—O4W—H4WA | 107 (2) |
C3—O3—Ni1 | 104.99 (7) | K1—O3W—K1iii | 110.22 (6) |
C3—O3—H1 | 109.4 (17) | K1—O3W—H3WC | 107 (2) |
Ni1—O3—H1 | 106.2 (17) | K1iii—O3W—H3WC | 140 (2) |
C6—O6—Ni1 | 128.00 (9) | K1—O3W—H3WA | 92 (3) |
Ni1—O2W—H2WB | 114.0 (16) | K1iii—O3W—H3WA | 104 (4) |
Ni1—O2W—H2WA | 115.0 (16) | H3WC—O3W—H3WA | 90 (4) |
H2WB—O2W—H2WA | 109 (2) | | |
Symmetry codes: (i) −x, −y+1, −z; (ii) −x, y+1/2, −z+1/2; (iii) −x, −y+2, −z; (iv) −x, y−1/2, −z+1/2; (v) −x+1, −y+1, −z. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
O1W—H1WB···O2i | 0.79 (3) | 1.96 (3) | 2.7322 (16) | 167 (2) |
O2W—H2WB···O1vi | 0.84 (3) | 1.93 (3) | 2.7638 (16) | 170 (2) |
O4W—H4WB···O5ii | 0.85 (3) | 1.91 (3) | 2.7459 (17) | 171 (2) |
O2W—H2WA···O4Wvii | 0.88 (3) | 1.83 (3) | 2.7064 (18) | 174 (2) |
O4W—H4WA···O5viii | 0.72 (3) | 2.20 (2) | 2.8714 (19) | 155 (2) |
O3—H1···O6v | 0.75 (2) | 2.13 (2) | 2.7152 (15) | 135 (2) |
O3W—H3WA···O2Wix | 0.85 (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, z−1/2; (vii) −x, y−1/2, −z−1/2; (viii) x−1, −y+3/2, z−1/2; (ix) −x, y+1/2, −z−1/2. |
Selected bond lengths (Å) topNi1—O4 | 2.0322 (12) | Ni1—O2W | 2.0677 (12) |
Ni1—O2 | 2.0330 (11) | Ni1—O1W | 2.0709 (11) |
Ni1—O6 | 2.0345 (10) | Ni1—O3 | 2.0927 (10) |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
O1W—H1WB···O2i | 0.79 (3) | 1.96 (3) | 2.7322 (16) | 167 (2) |
O2W—H2WB···O1ii | 0.84 (3) | 1.93 (3) | 2.7638 (16) | 170 (2) |
O4W—H4WB···O5iii | 0.85 (3) | 1.91 (3) | 2.7459 (17) | 171 (2) |
O2W—H2WA···O4Wiv | 0.88 (3) | 1.83 (3) | 2.7064 (18) | 174 (2) |
O4W—H4WA···O5v | 0.72 (3) | 2.20 (2) | 2.8714 (19) | 155 (2) |
O3—H1···O6vi | 0.75 (2) | 2.13 (2) | 2.7152 (15) | 135 (2) |
O3W—H3WA···O2Wvii | 0.845 (10) | 2.25 (4) | 2.912 (2) | 135 (5) |
Symmetry codes: (i) −x, −y+1, −z; (ii) x, −y+3/2, z−1/2; (iii) −x, y+1/2, −z+1/2; (iv) −x, y−1/2, −z−1/2; (v) x−1, −y+3/2, z−1/2; (vi) −x+1, −y+1, −z; (vii) −x, y+1/2, −z−1/2. |
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.