A new layered Ca–succinate coordination polymer, poly[μ
3-succinato-calcium(II)], [Ca(C
4H
5O
4)]
n, was synthesized by reaction of CaCl
2·2H
2O and succinic acid in an aqueous medium under hydrothermal microwave conditions. The structure contains infinite layers of edge-sharing calcium pentagonal–bipyramidal polyhedra forming six-membered rings connected through succinate ligands. Such an assembly of inorganic building units is unique for calcium metal–organic framework-type structures. Adjacent layers are packed into a final pseudo-three-dimensional structure through weak C—H
O hydrogen bonds.
Supporting information
CCDC reference: 866739
CaCl2.2H2O (0.68 g, 4.6 mmol) and succinic acid (0.82 g, 6.9 mmol) were
dissolved in demineralized water (10 ml) prior to the addition of KOH (1.04 g,
18.5 mmol). The reaction mixture was placed in a Teflon-lined autoclave and
hydrothermally treated by microwave heating [Power?] at 453 K for 3 h.
The colourless X-ray quality crystals obtained were filtered off and washed
repeatedly with distilled water. Elemental composition obtained by
energy-dispersive X-ray analysis (EDAX) was found to be 25.3 wt.% Ca, 31.5
wt.% C and 43.2 wt.% O, which correspond to the theoretical values for
Ca[O2C(CH2)2CO2] (25.7 wt% Ca, 30.8 wt.% C and 41.0 wt.% O).
All H atoms were located from a difference Fourier map and refined
isotropically.
Data collection: COLLECT (Bruker Nonius, 2000); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997); data reduction: DENZO-SMN (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2010); software used to prepare material for publication: publCIF (Westrip, 2010).
poly[µ
3-succinato-calcium(II)]
top
Crystal data top
[Ca(C4H4O4)] | F(000) = 640 |
Mr = 156.15 | Dx = 1.851 Mg m−3 |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2ybc | Cell parameters from 2705 reflections |
a = 5.8860 (1) Å | θ = 1.0–27.5° |
b = 11.2117 (3) Å | µ = 1.05 mm−1 |
c = 17.0754 (4) Å | T = 293 K |
β = 95.9450 (15)° | Plate-like, colourless |
V = 1120.78 (4) Å3 | 0.30 × 0.30 × 0.02 mm |
Z = 8 | |
Data collection top
Nonius KappaCCD area-detector diffractometer | 2567 independent reflections |
Radiation source: fine-focus sealed tube | 2096 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.014 |
ϕ and ω scans | θmax = 27.5°, θmin = 3.0° |
Absorption correction: multi-scan (DENZO-SMN; Otwinowski & Minor, 1997) | h = −7→7 |
Tmin = 0.744, Tmax = 0.979 | k = −14→14 |
4997 measured reflections | l = −22→22 |
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)] = 0.035 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.109 | All H-atom parameters refined |
S = 0.99 | w = 1/[σ2(Fo2) + (0.0808P)2 + 0.1895P] where P = (Fo2 + 2Fc2)/3 |
2567 reflections | (Δ/σ)max < 0.001 |
195 parameters | Δρmax = 0.95 e Å−3 |
0 restraints | Δρmin = −0.56 e Å−3 |
Crystal data top
[Ca(C4H4O4)] | V = 1120.78 (4) Å3 |
Mr = 156.15 | Z = 8 |
Monoclinic, P21/c | Mo Kα radiation |
a = 5.8860 (1) Å | µ = 1.05 mm−1 |
b = 11.2117 (3) Å | T = 293 K |
c = 17.0754 (4) Å | 0.30 × 0.30 × 0.02 mm |
β = 95.9450 (15)° | |
Data collection top
Nonius KappaCCD area-detector diffractometer | 2567 independent reflections |
Absorption correction: multi-scan (DENZO-SMN; Otwinowski & Minor, 1997) | 2096 reflections with I > 2σ(I) |
Tmin = 0.744, Tmax = 0.979 | Rint = 0.014 |
4997 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.035 | 0 restraints |
wR(F2) = 0.109 | All H-atom parameters refined |
S = 0.99 | Δρmax = 0.95 e Å−3 |
2567 reflections | Δρmin = −0.56 e Å−3 |
195 parameters | |
Special details top
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are
estimated using the full covariance matrix. The cell s.u.'s are taken into
account individually in the estimation of s.u.'s in distances, angles and
torsion angles; correlations between s.u.'s in cell parameters are only used
when they are defined by crystal symmetry. An approximate (isotropic)
treatment of cell s.u.'s is used for estimating s.u.'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 >
2σ(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 | |
Ca1 | 0.21306 (5) | 0.56909 (3) | 0.185162 (19) | 0.01560 (14) | |
Ca2 | 0.28839 (5) | 0.27309 (3) | 0.316014 (19) | 0.01573 (14) | |
O1 | 0.1722 (2) | 1.09158 (12) | 0.37734 (8) | 0.0241 (3) | |
O2 | 0.5089 (2) | 0.99948 (13) | 0.38864 (8) | 0.0274 (3) | |
O3 | −0.0738 (2) | 0.87384 (12) | 0.29840 (8) | 0.0282 (3) | |
O4 | 0.0504 (2) | 0.69623 (11) | 0.27102 (7) | 0.0205 (3) | |
O5 | 1.0192 (2) | 0.34454 (13) | 0.39387 (8) | 0.0294 (3) | |
O6 | 0.6808 (2) | 0.25373 (12) | 0.37624 (7) | 0.0225 (3) | |
O7 | 0.5521 (2) | 0.64704 (11) | 0.27198 (7) | 0.0199 (3) | |
O8 | 0.4234 (2) | 0.47090 (12) | 0.30160 (8) | 0.0276 (3) | |
C1 | 0.3024 (3) | 1.00470 (15) | 0.39902 (10) | 0.0177 (4) | |
C2 | 0.2035 (3) | 0.89929 (16) | 0.43968 (10) | 0.0201 (4) | |
C3 | 0.2142 (4) | 0.78654 (17) | 0.39078 (12) | 0.0239 (4) | |
C4 | 0.0550 (3) | 0.78576 (15) | 0.31555 (10) | 0.0173 (4) | |
C5 | 0.8109 (3) | 0.33934 (15) | 0.40094 (10) | 0.0173 (3) | |
C6 | 0.7070 (3) | 0.44431 (16) | 0.44085 (10) | 0.0193 (4) | |
C7 | 0.7159 (3) | 0.55767 (16) | 0.39201 (11) | 0.0209 (4) | |
C8 | 0.5549 (3) | 0.55807 (15) | 0.31726 (10) | 0.0174 (4) | |
H61 | 0.798 (4) | 0.457 (2) | 0.4890 (14) | 0.029 (6)* | |
H62 | 0.553 (4) | 0.423 (2) | 0.4489 (12) | 0.032 (6)* | |
H71 | 0.690 (4) | 0.629 (2) | 0.4236 (14) | 0.031 (6)* | |
H21 | 0.297 (3) | 0.8905 (17) | 0.4894 (12) | 0.015 (5)* | |
H31 | 0.357 (5) | 0.771 (3) | 0.3772 (16) | 0.051 (9)* | |
H22 | 0.055 (4) | 0.917 (2) | 0.4484 (12) | 0.026 (5)* | |
H32 | 0.173 (4) | 0.716 (2) | 0.4210 (15) | 0.037 (6)* | |
H72 | 0.863 (5) | 0.573 (2) | 0.3799 (14) | 0.039 (7)* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Ca1 | 0.0120 (2) | 0.0131 (2) | 0.0215 (2) | −0.00025 (11) | 0.00086 (14) | 0.00022 (12) |
Ca2 | 0.0122 (2) | 0.0130 (2) | 0.0219 (2) | −0.00021 (11) | 0.00093 (15) | −0.00055 (12) |
O1 | 0.0212 (7) | 0.0174 (6) | 0.0324 (7) | −0.0011 (5) | −0.0026 (5) | 0.0047 (5) |
O2 | 0.0187 (7) | 0.0292 (7) | 0.0351 (7) | −0.0021 (5) | 0.0070 (6) | 0.0049 (6) |
O3 | 0.0287 (7) | 0.0195 (7) | 0.0335 (7) | 0.0091 (5) | −0.0112 (6) | −0.0050 (6) |
O4 | 0.0183 (6) | 0.0173 (6) | 0.0256 (6) | 0.0018 (5) | 0.0006 (5) | −0.0041 (5) |
O5 | 0.0192 (7) | 0.0285 (7) | 0.0416 (8) | 0.0006 (5) | 0.0087 (6) | −0.0075 (6) |
O6 | 0.0202 (7) | 0.0165 (6) | 0.0299 (7) | 0.0014 (5) | −0.0012 (5) | −0.0039 (5) |
O7 | 0.0178 (6) | 0.0168 (6) | 0.0248 (6) | −0.0013 (5) | 0.0006 (5) | 0.0048 (5) |
O8 | 0.0266 (7) | 0.0200 (7) | 0.0336 (7) | −0.0087 (5) | −0.0092 (6) | 0.0044 (5) |
C1 | 0.0178 (9) | 0.0180 (8) | 0.0169 (8) | −0.0025 (7) | −0.0002 (6) | −0.0020 (7) |
C2 | 0.0234 (9) | 0.0192 (9) | 0.0173 (8) | −0.0038 (7) | 0.0012 (7) | 0.0013 (7) |
C3 | 0.0255 (10) | 0.0166 (9) | 0.0273 (10) | 0.0004 (7) | −0.0082 (8) | 0.0002 (7) |
C4 | 0.0142 (8) | 0.0154 (8) | 0.0220 (9) | −0.0007 (6) | 0.0010 (7) | 0.0013 (6) |
C5 | 0.0164 (8) | 0.0158 (8) | 0.0194 (8) | 0.0029 (6) | 0.0004 (6) | −0.0006 (7) |
C6 | 0.0205 (9) | 0.0184 (8) | 0.0188 (8) | 0.0019 (7) | 0.0016 (7) | −0.0007 (7) |
C7 | 0.0217 (10) | 0.0143 (9) | 0.0256 (9) | −0.0013 (7) | −0.0028 (7) | 0.0011 (7) |
C8 | 0.0141 (8) | 0.0142 (8) | 0.0236 (9) | 0.0004 (6) | 0.0004 (6) | −0.0008 (6) |
Geometric parameters (Å, º) top
Ca1—O2i | 2.3027 (13) | O4—C4 | 1.258 (2) |
Ca1—O4 | 2.3215 (12) | O4—Ca2vi | 2.5126 (12) |
Ca1—O3ii | 2.3646 (13) | O5—C5 | 1.245 (2) |
Ca1—O1ii | 2.4171 (13) | O5—Ca2viii | 2.3144 (13) |
Ca1—O6iii | 2.4312 (13) | O6—C5 | 1.273 (2) |
Ca1—O8 | 2.4876 (13) | O6—Ca1i | 2.4312 (13) |
Ca1—O7 | 2.5162 (12) | O7—C8 | 1.261 (2) |
Ca1—C8 | 2.8655 (18) | O7—Ca2iii | 2.3300 (12) |
Ca2—O5iv | 2.3144 (13) | O8—C8 | 1.258 (2) |
Ca2—O7i | 2.3300 (12) | C1—C2 | 1.517 (2) |
Ca2—O8 | 2.3774 (13) | C2—C3 | 1.520 (3) |
Ca2—O1v | 2.4197 (13) | C2—H21 | 0.97 (2) |
Ca2—O6 | 2.4387 (13) | C2—H22 | 0.93 (2) |
Ca2—O3ii | 2.4855 (13) | C3—C4 | 1.510 (3) |
Ca2—O4ii | 2.5126 (13) | C3—H31 | 0.92 (3) |
Ca2—C4ii | 2.8654 (18) | C3—H32 | 0.99 (3) |
O1—C1 | 1.271 (2) | C4—Ca2vi | 2.8654 (18) |
O1—Ca1vi | 2.4171 (13) | C5—C6 | 1.520 (2) |
O1—Ca2vii | 2.4197 (13) | C6—C7 | 1.524 (2) |
O2—C1 | 1.248 (2) | C6—H61 | 0.94 (2) |
O2—Ca1iii | 2.3027 (13) | C6—H62 | 0.96 (2) |
O3—C4 | 1.260 (2) | C7—C8 | 1.509 (2) |
O3—Ca1vi | 2.3646 (13) | C7—H71 | 0.98 (2) |
O3—Ca2vi | 2.4855 (13) | C7—H72 | 0.93 (3) |
| | | |
O2i—Ca1—O4 | 156.46 (5) | C1—O2—Ca1iii | 145.06 (12) |
O2i—Ca1—O3ii | 91.48 (5) | C4—O3—Ca1vi | 154.85 (12) |
O4—Ca1—O3ii | 108.83 (5) | C4—O3—Ca2vi | 94.07 (10) |
O2i—Ca1—O1ii | 118.75 (5) | Ca1vi—O3—Ca2vi | 111.09 (5) |
O4—Ca1—O1ii | 77.61 (4) | C4—O4—Ca1 | 152.55 (11) |
O3ii—Ca1—O1ii | 80.10 (5) | C4—O4—Ca2vi | 92.86 (10) |
O2i—Ca1—O6iii | 79.84 (5) | Ca1—O4—Ca2vi | 101.01 (5) |
O4—Ca1—O6iii | 83.73 (4) | C5—O5—Ca2viii | 141.15 (12) |
O3ii—Ca1—O6iii | 161.30 (5) | C5—O6—Ca1i | 127.77 (11) |
O1ii—Ca1—O6iii | 89.54 (5) | C5—O6—Ca2 | 125.73 (11) |
O2i—Ca1—O8 | 87.96 (5) | Ca1i—O6—Ca2 | 99.69 (5) |
O4—Ca1—O8 | 88.32 (5) | C8—O7—Ca2iii | 153.47 (11) |
O3ii—Ca1—O8 | 69.24 (4) | C8—O7—Ca1 | 92.61 (10) |
O1ii—Ca1—O8 | 139.96 (5) | Ca2iii—O7—Ca1 | 100.29 (4) |
O6iii—Ca1—O8 | 126.34 (4) | C8—O8—Ca2 | 155.18 (12) |
O2i—Ca1—O7 | 82.82 (5) | C8—O8—Ca1 | 94.04 (11) |
O4—Ca1—O7 | 76.61 (4) | Ca2—O8—Ca1 | 110.58 (5) |
O3ii—Ca1—O7 | 121.01 (4) | O2—C1—O1 | 124.18 (16) |
O1ii—Ca1—O7 | 150.98 (4) | O2—C1—C2 | 117.01 (16) |
O6iii—Ca1—O7 | 74.62 (4) | O1—C1—C2 | 118.81 (15) |
O8—Ca1—O7 | 51.98 (4) | C1—C2—C3 | 110.89 (15) |
O2i—Ca1—C8 | 86.30 (5) | C1—C2—H21 | 105.6 (12) |
O4—Ca1—C8 | 80.28 (5) | C3—C2—H21 | 110.0 (12) |
O3ii—Ca1—C8 | 95.19 (5) | C1—C2—H22 | 108.3 (14) |
O1ii—Ca1—C8 | 154.43 (5) | C3—C2—H22 | 111.2 (15) |
O6iii—Ca1—C8 | 100.68 (5) | H21—C2—H22 | 110.6 (18) |
O8—Ca1—C8 | 25.97 (5) | C4—C3—C2 | 114.50 (15) |
O7—Ca1—C8 | 26.08 (4) | C4—C3—H31 | 107.4 (17) |
O5iv—Ca2—O7i | 157.82 (5) | C2—C3—H31 | 112.5 (18) |
O5iv—Ca2—O8 | 89.57 (5) | C4—C3—H32 | 105.8 (15) |
O7i—Ca2—O8 | 109.74 (5) | C2—C3—H32 | 110.7 (15) |
O5iv—Ca2—O1v | 78.55 (5) | H31—C3—H32 | 105 (2) |
O7i—Ca2—O1v | 85.40 (4) | O4—C4—O3 | 120.67 (16) |
O8—Ca2—O1v | 160.39 (5) | O4—C4—C3 | 119.44 (15) |
O5iv—Ca2—O6 | 117.61 (5) | O3—C4—C3 | 119.89 (16) |
O7i—Ca2—O6 | 77.92 (4) | O4—C4—Ca2vi | 61.14 (9) |
O8—Ca2—O6 | 79.31 (5) | O3—C4—Ca2vi | 59.91 (9) |
O1v—Ca2—O6 | 92.32 (4) | C3—C4—Ca2vi | 173.06 (13) |
O5iv—Ca2—O3ii | 88.38 (5) | O5—C5—O6 | 124.61 (16) |
O7i—Ca2—O3ii | 88.55 (5) | O5—C5—C6 | 116.96 (16) |
O8—Ca2—O3ii | 69.07 (4) | O6—C5—C6 | 118.43 (15) |
O1v—Ca2—O3ii | 125.38 (4) | C5—C6—C7 | 111.23 (14) |
O6—Ca2—O3ii | 138.94 (5) | C5—C6—H61 | 106.7 (14) |
O5iv—Ca2—O4ii | 84.83 (5) | C7—C6—H61 | 107.8 (14) |
O7i—Ca2—O4ii | 76.03 (4) | C5—C6—H62 | 107.8 (14) |
O8—Ca2—O4ii | 120.80 (4) | C7—C6—H62 | 111.6 (14) |
O1v—Ca2—O4ii | 74.04 (4) | H61—C6—H62 | 111.6 (19) |
O6—Ca2—O4ii | 151.38 (4) | C8—C7—C6 | 114.24 (15) |
O3ii—Ca2—O4ii | 51.92 (4) | C8—C7—H71 | 109.8 (13) |
O5iv—Ca2—C4ii | 87.94 (5) | C6—C7—H71 | 111.3 (13) |
O7i—Ca2—C4ii | 79.80 (5) | C8—C7—H72 | 109.4 (15) |
O8—Ca2—C4ii | 95.09 (5) | C6—C7—H72 | 111.6 (15) |
O1v—Ca2—C4ii | 99.96 (5) | H71—C7—H72 | 100 (2) |
O6—Ca2—C4ii | 153.55 (5) | O8—C8—O7 | 121.04 (17) |
O3ii—Ca2—C4ii | 26.03 (4) | O8—C8—C7 | 119.76 (16) |
O4ii—Ca2—C4ii | 26.00 (4) | O7—C8—C7 | 119.19 (15) |
C1—O1—Ca1vi | 123.96 (11) | O8—C8—Ca1 | 59.99 (9) |
C1—O1—Ca2vii | 125.57 (11) | O7—C8—Ca1 | 61.31 (9) |
Ca1vi—O1—Ca2vii | 101.01 (5) | C7—C8—Ca1 | 173.89 (13) |
Symmetry codes: (i) −x+1, y−1/2, −z+1/2; (ii) −x, y−1/2, −z+1/2; (iii) −x+1, y+1/2, −z+1/2; (iv) x−1, y, z; (v) x, y−1, z; (vi) −x, y+1/2, −z+1/2; (vii) x, y+1, z; (viii) x+1, y, z. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
C3—H31···O7 | 0.91 (4) | 2.63 (3) | 3.370 (3) | 139 (3) |
C2—H21···O2ix | 0.97 (2) | 2.59 (2) | 3.424 (2) | 144 (2) |
C2—H21···O6x | 0.97 (2) | 2.79 (2) | 3.584 (2) | 140 (2) |
C7—H72···O4viii | 0.92 (3) | 2.67 (3) | 3.376 (3) | 135 (2) |
Symmetry codes: (viii) x+1, y, z; (ix) −x+1, −y+2, −z+1; (x) −x+1, −y+1, −z+1. |
Experimental details
Crystal data |
Chemical formula | [Ca(C4H4O4)] |
Mr | 156.15 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 293 |
a, b, c (Å) | 5.8860 (1), 11.2117 (3), 17.0754 (4) |
β (°) | 95.9450 (15) |
V (Å3) | 1120.78 (4) |
Z | 8 |
Radiation type | Mo Kα |
µ (mm−1) | 1.05 |
Crystal size (mm) | 0.30 × 0.30 × 0.02 |
|
Data collection |
Diffractometer | Nonius KappaCCD area-detector diffractometer |
Absorption correction | Multi-scan (DENZO-SMN; Otwinowski & Minor, 1997) |
Tmin, Tmax | 0.744, 0.979 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 4997, 2567, 2096 |
Rint | 0.014 |
(sin θ/λ)max (Å−1) | 0.649 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.035, 0.109, 0.99 |
No. of reflections | 2567 |
No. of parameters | 195 |
H-atom treatment | All H-atom parameters refined |
Δρmax, Δρmin (e Å−3) | 0.95, −0.56 |
Selected bond lengths (Å) topCa1—O2i | 2.3027 (13) | Ca2—O5iv | 2.3144 (13) |
Ca1—O4 | 2.3215 (12) | Ca2—O7i | 2.3300 (12) |
Ca1—O3ii | 2.3646 (13) | Ca2—O8 | 2.3774 (13) |
Ca1—O1ii | 2.4171 (13) | Ca2—O1v | 2.4197 (13) |
Ca1—O6iii | 2.4312 (13) | Ca2—O6 | 2.4387 (13) |
Ca1—O8 | 2.4876 (13) | Ca2—O3ii | 2.4855 (13) |
Ca1—O7 | 2.5162 (12) | Ca2—O4ii | 2.5126 (13) |
Symmetry codes: (i) −x+1, y−1/2, −z+1/2; (ii) −x, y−1/2, −z+1/2; (iii) −x+1, y+1/2, −z+1/2; (iv) x−1, y, z; (v) x, y−1, z. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
C3—H31···O7 | 0.906 (35) | 2.632 (34) | 3.370 (3) | 139 (3) |
C2—H21···O2vi | 0.973 (22) | 2.588 (22) | 3.424 (2) | 144 (2) |
C2—H21···O6vii | 0.973 (22) | 2.786 (23) | 3.584 (2) | 140 (2) |
C7—H72···O4viii | 0.915 (32) | 2.669 (30) | 3.376 (3) | 135 (2) |
Symmetry codes: (vi) −x+1, −y+2, −z+1; (vii) −x+1, −y+1, −z+1; (viii) x+1, y, z. |
The design of new metal–organic framework (MOF) materials with useful structural properties by combining various metal cations with heteropolyfunctional organic linkers such as polycarboxylates, polyphosphonates or polyamines has become a great challenge in the last decade (Yaghi, 2004; Eddaoudi, 2007; Kuppler et al., 2009; Farrusseng et al., 2009). Calcium-based polycarboxylates can be used in bioapplications due to the nontoxic nature and biocompatability of calcium cations. However, the number of known Ca-based polycarboxylate structures is relatively low compared with more frequently investigated MOFs based on transition metal cations. Several structures are known to date with aromatic polycarboxylic ligands (Platers et al., 1997; Groeneman & Atwood, 1999; Zhu et al., 2005; Volkringer et al., 2007; Dale & Elsegood, 2003) and some with alkylpolycarboxylates (De Lill et al., 2005; Mathew & Takagi, 1995; Mathew et al., 1994). We report here the synthesis and structural characterization of a new layered Ca–succinate compound, the title compound, (I).
The crystal structure of (I) is built from infinite layers of edge-sharing calcium polyhedra. Each polyhedron shares three of its edges with neighbouring polyhedra, generating inorganic layers with six-membered rings (Fig. 1). Fig. 2 shows a view of adjacent inorganic layers connected via weak C—H···O hydrogen bonds along the a axis. Ca atoms in the centres of these polyhedra occupy two different crystallographic sites (Ca1 and Ca2) in general positions and both are coordinated to seven different O atoms, all coming from dicarboxylate groups. This sevenfold coordination defines slightly distorted pentagonal–bipyramidal polyhedra with Ca—O distances in the range 2.3027 (13)–2.5162 (12) Å (Table 1), which is similar to the coordination environment in some other known seven-coordinate Ca carboxylates (Williams et al., 2008; Mathew & Takagi, 1995; Mathew et al., 1994). The Ca1 atoms are coordinated by four O atoms in a monodentate bridging mode from three different succinate dianions (O1ii, O3ii, O4 and O6iii) and by atom O2i in a monodentate manner (symmetry codes are as in Table 1). The remaining two O atoms (O7 and O8) are connected to Ca1 in chelating and bridging modes. The Ca2 atoms have similar O atom coordination modes. Four O atoms from three different succinate dianions are coordinated to Ca2 in a monodentate bridging mode (O1v, O6, O7i and O8). Atom O5 coordinates in a monodentate fashion and the remaining two O atoms (O3ii and O4ii) in a chelating mode. Edge-sharing CaO7 polyhedra forming six-membered rings are further connected to succinate species from both sides of the inorganic layers (Fig. 1). Structures with edge-sharing metal-based polyhedra forming layers of multi-membered rings are already known in manganese and magnesium glutarates (Vaidhyanathan et al., 2003; Hulvey & Cheetham, 2007) and cobalt succinate (Livage et al., 1998). Ca-based polyhedra in MOF-type structures show a low degree of crystal structure flexibility and are usually arranged through common edges or faces into one-dimensional chain-like inorganic units. The assembly of Ca-based polyhedral units into layers forming six-membered rings in the structure of (I) is, to our knowledge, unique and described in this contribution for the first time.
There are two symmetry-independent succinate ligands which are fully deprotonated, with C—O distances in the range 1.246 (2)–1.271 (2) Å. C—C bonds in the succinate chain are within the range of 1.518 (3)–1.524 (3) Å typical for distances between C atoms in aliphatic chains (Livage et al., 1998; Hulvey & Cheetham, 2007). The succinate ligands connect to the inorganic layers from both sides. Selected bond lengths and angles are shown in Table 1. Two dicarboxylate groups from two different succinate ligands chelate one Ca2+ centre and also bridge a second Ca2+ centre. The remaining two dicarboxylate anions bridge three Ca2+ centres in a monodentate manner with one O atom and in a bidentate manner with the second O atom. The coordination geometries of the Ca2+ centres and succinate ligands are shown in Fig. 3.
There are no classical hydrogen-bond donors (O—H···O) in (I) and consequently no such hydrogen bonds in the structure. However, two potential weak C—H···O contacts (C2—H21···O2 and C2—H21···O6) between metal-coordinated carboxylate O atoms from one layer and C-chain-bonded H atoms from a neighbouring layer connect the Ca–succinate units into a hydrogen-bonded network. Despite the relatively long C—H···O contacts between these layers [C2···O2 = 3.432 (2) Å and C2···O6 = 3.584 (2) Å], the C—H···O angles tend towards linearity [144 (2) and 140 (2)°], which indicates the existence of weak hydrogen-bonding interactions between neighbouring layers (Desiraju, 1991). There are also two weak intra-layer C—H···O interactions between coordinated O atoms and the H atoms bonded to atoms C3 and C7 (Table 2).