The two-dimensional coordination polymer tetra­aqua­mesaconatobarium(II), [Ba(C₅H₄O₄)(OH₂)₄]_n

The structure of [Ba(C₅H₄O₄)(OH₂)₄]_n consists of two-dimensional rectangular grid layers, built up from the self-assembly of zigzag chains of edge-sharing {BaO₉} polyhedra linked by bridging bidendate mesaconate anions (C₅H₄O₄²⁻) through different coordination modes of the carboxyl­ate groups. The polymer layers form a three-dimensional network via O—H...O hydrogen-bond interactions between the coordinated water mol­ecules and the O atoms of the carboxyl­ate groups.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.007 Å
• H-atom completeness 34%
• R factor = 0.046
• wR factor = 0.132
• Data-to-parameter ratio = 19.0

checkCIF results

No syntax errors found


 Alert Level B:



PLAT_110  Alert B ADDSYM detects potential lattice centering or halving   ?

Author response: See text for explanation of substructure-superstructure

PLAT_112  Alert B ADDSYM Detects Additional (Pseudo) Symm. Elem.          B

Author response: See text for explanation of substructure-superstructure.

PLAT_113  Alert B ADDSYM suggests Pseudo/New Spacegroup ........       P21/m

Author response: See text for explanation of substructure-superstructure

General Notes



FORMU_01  There is a discrepancy between the atom counts in the
          _chemical_formula_sum and the formula from the _atom_site* data.
          Atom count from _chemical_formula_sum:C5 H12 Ba1 O8
          Atom count from the _atom_site data:  C5 H4 Ba1 O8

CELLZ_01
         From the CIF: _cell_formula_units_Z    4
         From the CIF: _chemical_formula_sum  C5 H12 Ba O8
         TEST: Compare cell contents of formula and atom_site data

         atom    Z*formula  cif sites diff
         C         20.00     20.00    0.00
         H         48.00     16.00   32.00
         Ba         4.00      4.00    0.00
         O         32.00     32.00    0.00
          Difference between formula and atom_site contents detected.
          WARNING: H atoms missing from atom site list. Is this intentional?

CHEMW_03
         From the CIF: _cell_formula_units_Z                    4
         From the CIF: _chemical_formula_weight           337.49
         TEST: Calculate formula weight from _atom_site_*
         atom     mass    num     sum
         C        12.01    5.00   60.06
         H         1.01    4.00    4.03
         O        16.00    8.00  127.99
         Ba      137.33    1.00  137.33
         Calculated formula weight              329.41
          The ratio of given/expected molecular weight as calculated
          from the _atom_site* data lies outside
          the range 0.99 <> 1.01


 0 Alert Level A = Potentially serious problem

 3 Alert Level B = Potential problem

 0 Alert Level C = Please check

---

S1. Comment

Unsaturated carboxylic acids and their derivatives display interesting reactivity patterns when they are heated and/or irradiated in the solid state (Díaz de Delgado et al., 1991; Case et al., 1994; Vela et al., 2000; Xiao et al., 2000; Odani et al., 2001). The nature of the reactions in the solid state is determined by the control that the crystalline lattice exerts. In general, the preorganization of molecules and the orientation of double bonds in the crystal determine the nature of the reaction products. For example, we have reported that when heating barium hydrogen itaconate monohydrate at about 473 K, an unusual isomerization to barium citraconate in the solid state occurs as a consequence of the arrangement of the molecules in the starting material (Briceño et al., 1999).

In this work, we report the X-ray diffraction study of barium mesaconate tetrahydrate, (I), and its thermal behavior. This study is part of a systematic investigation on the structure–reactivity relationships in the solid state of metal complexes of α,β-unsaturated carboxylic acids. In spite of the simplicity of mesaconic acid (methylmaleic acid), and of its similarity with maleic and fumaric acids (cis and trans butenedioic acids, respectively), the structural chemistry of its salts and complexes is unknown. Only the structure of potassium mesaconate (Gupta & Yadav, 1975) has been reported, as indicated by a search in the Cambridge Structural Database (Allen & Kennard, 1993).

In the structure of (I), the Ba atoms are coordinated to nine O atoms, as shown in Fig. 1. Five of these O atoms come from four different mesaconate anions and four O atoms come from water molecules. The Ba—O distances range from 2.683 (3) to 2.967 (4) Å. The disposition of the O atoms around the Ba atom can be described as a distorted monocapped rectangular antiprism. Edge-sharing polyhedra form unidimensional zigzag chains along the b axis, which are linked through bridging bidendate mesaconate anions (Fig. 2). The carboxylate groups display different coordination modes. The O1/C1/O2 carboxylate acts as monodentade group through the O2 atom, while O3/C4/O4 displays a combination of symmetrical chelating and monoatomic anti–anti bridging modes, allowing the coordination to three different Ba atoms. The dihedral angle between the planes containing the carboxylate groups is approximately 89.8 (1)°. These coordination modes induce self-assembly of the chains of barium polyhedra with the mesaconate anions, as well as their arrangement in a parallel and alternate head-to-tail fashion, and produce two-dimensional rectangular grid layers parallel to the bc plane (Fig. 3). The polymer layers interact through extensive hydrogen bonds between water molecules and carboxylate O atoms: O1W···O3Wⁱ 2.836 (3) Å, O1W···O2Wⁱⁱ 2.833 (2) Å and O2W···O1ⁱⁱⁱ 2.807 (3) Å [symmetry codes: (i) 1/2 − x, 1/2 + y, 1/2 − z; (ii) 1/2 − x, −1/2 + y, 1/2 − z; (iii) −1 + x, y, z], among others, along the c direction.

The disposition of the double bonds in neighboring molecules is parallel, and a series of infinite contacts along the b direction is observed. An analysis of the distances among such contacts indicates that there exist a group of infinite contacts between the atoms C2···C2^iv [symmetry code: (iv) −x + 1, −y + 1, −z + 1] along this direction at a distance of 4.168 (2) Å. In spite of these avorable structural characteristics for reactivity in the solid state, thermal analysis (TGA and DSC) and FT–IR spectra indicate that the material does not react upon heating. It is stable between 473 and 613 K, which corresponds to the temperature range between dehydration and decomposition of the organic ligand.

It is worth noting that the analysis of the results using PLATON (Spek, 1990) suggested the existence of a unit cell (2) with half of the volume of the experimentally determined cell, (1). They are related by the following transformation matrix: [a,b,c]₂ = [1/2,0,1/2/0,1,0/-1,0,0][a,b,c]₁. The dimensions of the proposed smaller cell are: a = 8.323 (1), b = 7.478 (1), c = 8.893 (1) Å, β = 105.92 (1)°, space group P2₁/m. PLATON also indicated pseudo-B centering and the possibility of maintaining cell 1 but in space group P2₁/m. Solution and refinement of the structure in cell 1 using space groups P2₁/m and P2/m were not successful.

A careful examination of the data set collected showed that 1125 out the 2446 unique reflections, can only be accounted for using the larger cell. Even though the majority of the superstructure reflections are rather weak, 376 of those reflections have F_o > 4σF_o. It may be noticed that the majority of the atoms have y coordinates equal or close to 1/4, and that only a few of the O atoms are clearly distant from such a position. After the reduction of the unit cell proposed by PLATON, the atoms with y coordinates equal or close to 1/4 are assigned to special positions with y = 1/4. In the ase of the Ba atom, the value obtained for its y-coordinate in the structure refinement carried out in the larger cell [y = 0.24927 (2)] is statistically different from 1/4. Also, after the reduction, in order to accomodate the number of O atoms in the small unit cell in general positions, they should have half of the occupancy factors indicated by the multiplicity of their positions.

Because of the substructure–superstructure relationship that exists between cells 1 and 2, we believe that the experimentally determined unit cell (cell 1) should used in order to properly describe the structure of the compound under study. Sub-superstructure relationships have been observed in other metal dicarboxylates, for example lithium hydrogen maleate dihydrate (Díaz de Delgado et al., 1993).

S2. Experimental

The title compound was prepared by reaction of mesaconic acid (C₅H₆O₄) and BaCO₃ in a 1:1 ratio in water. The mixture was maintained under continuous stirring for 24 h. The resulting solution was filtered and allowed to evaporate slowly at ambient temperature. After 2–3 weeks, colorless crystals suitable for X-ray analysis formed. The IR spectra were recorded from KBr discs, using a PE-1725X FT—IR spectrometer. IR (cm⁻¹): υ(br, O—H) 3495, υ(w, C═C) 1627, υ(s, C═O_asym) 1501, υ(s, C═O_sym) 1389–1335. In order to study the reactivity in solid state, samples of approximately 80 mg of the material were placed in a reactor connected to a vacuum line an heated at 473, 543, 613 and 823 K. In each case, once the desired temperature was reached, the temperature was kept constant for 10 min. Thermogravimetric analyses (TG and DTG) and differential scanning calorimetry measurements (DSC) were perfomed in a Dupont 951 Thermal Analyzer and a Dupont 990 cell, under a dynamic dry nitrogen atmosphere at a flow rate of 50 ml seg⁻¹ and a heating rate of 20 K min⁻¹. The temperatue range was 298–873 K. TGA and DSC data: weight loss to step 1: 21.29% (calculated 21.34%), 343–443 K, endo; step 2: 20.20% (calculated 20.16%), 673–783 K, endo.

S3. Refinement

Two unassigned extremes of residual density, positive 2.06 e/A³ (0.17, 1/4, 1/5) and negative −2.88 e/A³ (0.13, 1/4, 0.12), were observed approximately 0.7 and 0.9 Å from atom Ba1.

Computing details

Data collection: COLLECT in UCLA Crystallographic Package (Strouse, 1988); cell refinement: LEAST in UCLA Crystallographic Package; data reduction: REDUCE in UCLA Crystallographic Package; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 1998); software used to prepare material for publication: SHELXL97 and PLATON (Spek, 1990).

Figures

	Fig. 1. Coordination enviroment of the Ba atom in [Ba(C5H4O4)(OH2)4]n. Displacement ellipsoids are shown at the 50% probability level.
	Fig. 2. Zigzag chains of {BaO9} polyhedra in the structure of [Ba(C5H4O4)(OH2)4]n.
	Fig. 3. Projection of the structure of [Ba(C5H4O4)(OH2)4]n onto the bc plane.

tetraaquomesaconatebarium(II)

Crystal data

[Ba(C5H4O4)(H2O)4]	F(000) = 648
Mr = 337.49	Dx = 2.106 Mg m^−3 Dm = 2.07 (2) Mg m^−3 Dm measured by Neutral buoyancy in CHCl3/CH3I
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71070 Å
Hall symbol: -P 2yn	Cell parameters from 25 reflections
a = 8.893 (1) Å	θ = 20.0–35.0°
b = 7.478 (1) Å	µ = 3.75 mm^−1
c = 16.582 (2) Å	T = 293 K
β = 105.13 (1)°	Prism, colorless
V = 1064.5 (2) Å^3	0.60 × 0.35 × 0.28 mm
Z = 4

Data collection

Nicolet P3/F (Crystal Logic) diffractometer	1478 reflections with I > 2σ(I)
Radiation source: normal-focus sealed tube	Rint = 0.026
Graphite monochromator	θmax = 27.5°, θmin = 2.4°
τ–2τ scans	h = −11→11
Absorption correction: ψ scan (North et al., 1968)	k = −9→9
Tmin = 0.220, Tmax = 0.350	l = 0→21
4858 measured reflections	3 standard reflections every 97 reflections
2446 independent reflections	intensity decay: <0.5

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.046	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.133	w = 1/[σ^2(Fo^2) + (0.0728P)^2 + 0.0708P] where P = (Fo^2 + 2Fc^2)/3
S = 1.18	(Δ/σ)max = 0.001
2446 reflections	Δρmax = 2.06 e Å^−3
129 parameters	Δρmin = −2.88 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.045 (2)

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
Ba1	0.21293 (2)	0.249273 (16)	0.166617 (10)	0.0224 (2)
C1	0.5437 (5)	0.2496 (3)	0.0509 (3)	0.0286 (8)
C2	0.5626 (6)	0.2498 (3)	−0.0361 (3)	0.0321 (9)
C3	0.7056 (5)	0.2502 (3)	−0.0504 (3)	0.0286 (8)
H3	0.7933	0.2500	−0.0052	0.034*
C4	0.7258 (5)	0.2509 (3)	−0.1369 (2)	0.0268 (8)
C5	0.4164 (7)	0.2510 (5)	−0.1085 (4)	0.057 (2)
H5A	0.4454	0.2471	−0.1604	0.074*
H5B	0.3581	0.3581	−0.1063	0.074*
H5C	0.3537	0.1486	−0.1046	0.074*
O1	0.6636 (5)	0.2501 (2)	0.1134 (3)	0.0380 (10)
O2	0.4076 (5)	0.2492 (2)	0.0587 (3)	0.0384 (10)
O3	0.7329 (4)	0.1041 (4)	−0.17209 (17)	0.0386 (7)
O4	0.7329 (4)	0.3971 (4)	−0.17193 (17)	0.0391 (7)
O1W	0.5357 (4)	0.2496 (2)	0.2489 (2)	0.0351 (7)
O2W	−0.0654 (3)	0.4583 (5)	0.1388 (2)	0.0471 (8)
O3W	−0.0659 (3)	0.0409 (4)	0.1385 (2)	0.0446 (8)
O4W	0.1060 (5)	0.2506 (3)	−0.0185 (2)	0.0481 (10)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ba1	0.0237 (3)	0.0231 (3)	0.0207 (3)	0.00033 (7)	0.00595 (14)	0.00038 (6)
C1	0.0261 (18)	0.035 (2)	0.026 (2)	−0.0022 (12)	0.0098 (15)	−0.0018 (11)
C2	0.027 (2)	0.043 (2)	0.027 (2)	−0.0024 (13)	0.0090 (17)	−0.0008 (12)
C3	0.033 (2)	0.030 (2)	0.0236 (17)	0.0010 (12)	0.0095 (15)	0.0001 (10)
C4	0.0279 (19)	0.0275 (19)	0.0262 (18)	0.0001 (11)	0.0089 (15)	−0.0006 (10)
C5	0.031 (3)	0.109 (6)	0.029 (3)	−0.0013 (19)	0.006 (2)	−0.0004 (17)
O1	0.0252 (19)	0.059 (3)	0.0308 (19)	0.0013 (10)	0.0098 (15)	−0.0009 (9)
O2	0.0265 (19)	0.063 (3)	0.0277 (19)	−0.0013 (10)	0.0106 (16)	0.0015 (9)
O3	0.064 (2)	0.0233 (13)	0.0357 (14)	0.0038 (13)	0.0254 (13)	−0.0012 (10)
O4	0.064 (2)	0.0234 (13)	0.0376 (14)	−0.0031 (13)	0.0259 (14)	0.0012 (10)
O1W	0.0333 (17)	0.0457 (19)	0.0266 (16)	0.0013 (9)	0.0084 (13)	0.0015 (8)
O2W	0.0363 (16)	0.0426 (17)	0.059 (2)	−0.0006 (13)	0.0071 (14)	−0.0077 (14)
O3W	0.0240 (14)	0.0429 (17)	0.064 (2)	0.0004 (12)	0.0069 (13)	0.0095 (14)
O4W	0.0342 (18)	0.077 (3)	0.0333 (17)	0.0012 (11)	0.0089 (14)	0.0005 (10)

Geometric parameters (Å, º)

Ba1—O3^i	2.683 (3)	C2—C3	1.352 (6)
Ba1—O4^ii	2.685 (3)	C2—C5	1.523 (6)
Ba1—O2	2.796 (4)	C3—C4	1.492 (5)
Ba1—O1W	2.838 (4)	C3—H3	0.9300
Ba1—O3^iii	2.853 (3)	C4—O4	1.248 (4)
Ba1—O4^iii	2.855 (3)	C4—O3	1.253 (4)
Ba1—O2W	2.861 (3)	C4—Ba1^vi	3.231 (4)
Ba1—O3W	2.862 (3)	C5—H5A	0.9600
Ba1—O4W	2.967 (4)	C5—H5B	0.9600
Ba1—C4^iii	3.231 (4)	C5—H5C	0.9600
Ba1—Ba1^iv	4.5946 (5)	O3—Ba1^i	2.683 (3)
Ba1—Ba1^v	4.5946 (5)	O3—Ba1^vi	2.853 (3)
C1—O2	1.250 (6)	O4—Ba1^ii	2.685 (3)
C1—O1	1.278 (6)	O4—Ba1^vi	2.855 (3)
C1—C2	1.495 (7)
O3^i—Ba1—O4^ii	160.00 (15)	O2—Ba1—Ba1^iv	111.71 (6)
O3^i—Ba1—O2	83.44 (8)	O1W—Ba1—Ba1^iv	75.03 (5)
O4^ii—Ba1—O2	83.43 (8)	O3^iii—Ba1—Ba1^iv	32.75 (5)
O3^i—Ba1—O1W	80.48 (9)	O4^iii—Ba1—Ba1^iv	77.50 (6)
O4^ii—Ba1—O1W	80.40 (9)	O2W—Ba1—Ba1^iv	68.57 (6)
O2—Ba1—O1W	65.80 (11)	O3W—Ba1—Ba1^iv	121.55 (7)
O3^i—Ba1—O3^iii	112.34 (6)	O4W—Ba1—Ba1^iv	125.23 (4)
O4^ii—Ba1—O3^iii	67.91 (8)	C4^iii—Ba1—Ba1^iv	55.35 (4)
O2—Ba1—O3^iii	134.64 (11)	O3^i—Ba1—Ba1^v	35.11 (5)
O1W—Ba1—O3^iii	75.00 (10)	O4^ii—Ba1—Ba1^v	141.75 (6)
O3^i—Ba1—O4^iii	67.91 (8)	O2—Ba1—Ba1^v	111.68 (6)
O4^ii—Ba1—O4^iii	112.34 (6)	O1W—Ba1—Ba1^v	75.12 (5)
O2—Ba1—O4^iii	134.64 (11)	O3^iii—Ba1—Ba1^v	77.55 (6)
O1W—Ba1—O4^iii	75.04 (10)	O4^iii—Ba1—Ba1^v	32.80 (5)
O3^iii—Ba1—O4^iii	45.15 (10)	O2W—Ba1—Ba1^v	121.58 (7)
O3^i—Ba1—O2W	133.12 (11)	O3W—Ba1—Ba1^v	68.73 (6)
O4^ii—Ba1—O2W	66.89 (10)	O4W—Ba1—Ba1^v	125.61 (4)
O2—Ba1—O2W	123.45 (10)	C4^iii—Ba1—Ba1^v	55.31 (4)
O1W—Ba1—O2W	143.20 (8)	Ba1^iv—Ba1—Ba1^v	108.935 (12)
O3^iii—Ba1—O2W	77.34 (10)	O2—C1—O1	122.8 (4)
O4^iii—Ba1—O2W	101.55 (10)	O2—C1—C2	117.1 (4)
O3^i—Ba1—O3W	67.03 (10)	O1—C1—C2	120.1 (4)
O4^ii—Ba1—O3W	132.98 (11)	C3—C2—C1	121.1 (4)
O2—Ba1—O3W	123.41 (10)	C3—C2—C5	120.6 (5)
O1W—Ba1—O3W	143.46 (8)	C1—C2—C5	118.2 (5)
O3^iii—Ba1—O3W	101.61 (10)	C2—C3—C4	121.6 (4)
O4^iii—Ba1—O3W	77.49 (10)	C2—C3—H3	119.2
O2W—Ba1—O3W	66.09 (12)	C4—C3—H3	119.2
O3^i—Ba1—O4W	92.55 (7)	O4—C4—O3	122.4 (4)
O4^ii—Ba1—O4W	92.12 (7)	O4—C4—C3	119.0 (3)
O2—Ba1—O4W	54.75 (12)	O3—C4—C3	118.6 (3)
O1W—Ba1—O4W	120.54 (10)	O4—C4—Ba1^vi	61.5 (2)
O3^iii—Ba1—O4W	153.30 (8)	O3—C4—Ba1^vi	61.5 (2)
O4^iii—Ba1—O4W	153.67 (8)	C3—C4—Ba1^vi	171.4 (3)
O2W—Ba1—O4W	78.53 (9)	C2—C5—H5A	109.5
O3W—Ba1—O4W	78.64 (9)	C2—C5—H5B	109.5
O3^i—Ba1—C4^iii	90.39 (7)	H5A—C5—H5B	109.5
O4^ii—Ba1—C4^iii	90.48 (7)	C2—C5—H5C	109.5
O2—Ba1—C4^iii	141.32 (13)	H5A—C5—H5C	109.5
O1W—Ba1—C4^iii	75.52 (10)	H5B—C5—H5C	109.5
O3^iii—Ba1—C4^iii	22.69 (6)	C1—O2—Ba1	147.6 (4)
O4^iii—Ba1—C4^iii	22.60 (6)	C4—O3—Ba1^i	151.4 (2)
O2W—Ba1—C4^iii	87.95 (10)	C4—O3—Ba1^vi	95.9 (2)
O3W—Ba1—C4^iii	88.01 (10)	Ba1^i—O3—Ba1^vi	112.14 (9)
O4W—Ba1—C4^iii	163.93 (12)	C4—O4—Ba1^ii	151.4 (2)
O3^i—Ba1—Ba1^iv	141.70 (6)	C4—O4—Ba1^vi	95.9 (2)
O4^ii—Ba1—Ba1^iv	35.16 (6)	Ba1^ii—O4—Ba1^vi	112.03 (9)

Symmetry codes: (i) −x+1, −y, −z; (ii) −x+1, −y+1, −z; (iii) x−1/2, −y+1/2, z+1/2; (iv) −x+1/2, y+1/2, −z+1/2; (v) −x+1/2, y−1/2, −z+1/2; (vi) x+1/2, −y+1/2, z−1/2.