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The present form of barium acetate, formulated as [Ba(C2H3O2)2(H2O)3]n, is the largest reported hydrate of the salt and this leads to a distinct structural behaviour setting it apart from the rest of the family. The compound is a linear polymer with a nine-coordinate Ba(Oaqua)3(Oacetate)6 mono­mer unit. The non-H part of the structure is ordered according to C2/m symmetry, while the disordered water H atoms only abide by this symmetry in a statistical sense. Each mol­ecule is halved by a mirror plane bis­ecting the Ba centre, one water mol­ecule and one acetate ligand, while containing the other acetate ligand. The chains are inter­connected by a disordered water-water/acetate O-H...O hydrogen-bonding network involving all water H atoms. The structure and stability of this phase are compared with the other known acetates of barium which differ in the degree of hydration.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270108006057/sq3131sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270108006057/sq3131Isup2.hkl
Contains datablock I

CCDC reference: 686418

Comment top

Barium acetate is known to present a variety of hydration states. For three of them, their X-ray crystal structures have been reported (Cambridge Structural Database, Version?; Allen 2002), viz. a monohydrate, Ba(C2H3O2)2·H2O, (II) (Groombridge et al. 1985), an anhydrous form, Ba(C2H3O2)2, (III) (Gautier-Luneau & Mosset, 1988), and a partially hydrated form, [Ba(C2H3O2)2]6·3.5H2O, (IV) (Leyva et al., 2007). We report here the crystal structure of the title trihydrate, Ba(C2H3O2)2·3H2O, (I), which although characterized by a thorough vibrational study 20 years ago (Maneva & Nikolova, 1988) has not been studied so far from a crystallographic point of view.

Fig. 1 shows a schematic view of the (linear) polymeric structure of (I), built up of a Ba centre, three water molecules and two acetate ligands, one of them (acetate 2) acting in a simple chelating mode and the second (acetate 1) in a µ3κ4O,O' chelating double-bridging mode. This leads to a Ba···Ba distance along the chain of 4.608 (1) Å, comparable with the separation in the monohydrate, (II) [4.586 Å], but longer than those in the less hydrated forms [4.330 Å in the semihydrate, (III) [Should this be (IV) as defined in first paragraph?], and 4.338 Å in the anhydrate, (IV) [Should this be (III) as defined in first paragraph?]].

Each Ba(C2H3O2)2(H2O)3 unit in (I) is halved by a mirror plane which passes through the Ba1 centre and one water molecule (O2W), while bisecting both perpendicular acetate ligands: acetate 2, through all four non-H atoms (C12, C22, O12 and O22, which thus lie on special positions in the mirror plane), and acetate 1, through atoms C11 and C21.

Due to chelation, the BaO9 polyhedron is rather deformed, with a wide range of coordination angles [45.69 (11)–152.83 (14)°], which makes the resulting geometry difficult to describe in terms of a regular model. The water molecules are more loosely bound to Ba than are the carboxylate O atoms, as inferred from the coordination distances (Table 1). Total bond valence (Brown & Altermatt, 1985) on Ba1 amounts to 2.283, with a mean value of 0.277 for Oac and 0.206 for Owater.

As explained in the Refinement section, only the non-H part of the structure follows a strict C2/m symmetry. The H atoms follow it only on average, and to accommodate them in a non-colliding way, the local symmetry must be lowered to 1, as shown in Fig. 2. The possible centrosymmetric H-atom arrays give rise to non-colliding H-atom distributions and sensible hydrogen-bonding schemes (Table 2), while providing an `average' model compatible with the electron-density map. The polymeric structure consists of ribbons (Fig. 1) which run along b and are in turn interconnected by the disordered set of (O—H)water···Owater/ac hydrogen bonds, where all Hwater atoms take part. The first entry in Table 2 corresponds to an intrachain contact, while the remaining ones are the interchain interactions along the a and c axis directions (Fig. 3)

As expected, the four structurally characterized barium acetates present a predictable inverse relationship between water content and crystal density (Table 3). In addition, all but (I) present a stable three-dimensional structure at room temperature. It might be concluded that, in the particular case of the structure reported here, the large number of coordinated water molecules has the effect of reducing the covalent links between the Ba polyhedra, thus `opening' the three-dimensional structure into the one-dimensional one displayed by (I), a fact presumably associated with its intrinsic instability.

Related literature top

For related literature, see: Allen (2002); Brown & Altermatt (1985); Gautier-Luneau & Mosset (1988); Groombridge et al. (1985); Leyva et al. (2007); Maneva & Nikolova (1988).

Experimental top

Crystals of (I) were obtained through a two-step low-temperature recrystallization procedure. A concentrated aqueous solution of the as-purchased monohydrated salt was initially left at 255 K until chilled, and taken to 268 K afterwards. After 10–15 d, and with the solution almost dry, very large colourless blocks of (I) appeared all of a sudden. Thermogravimetric analysis suggested a water content of three molecules per formula unit, a fact confirmed by the structural analysis. The specimens are unstable at room temperature: if dry, they decompose in a few hours, losing crystalline character; if left in a drop of mother liquor, they are digested and the stable monohydrate grows.

Refinement top

Crystals of (I) are unstable at room temperature and decompose easily in the X-ray beam. After several unsuccessful attempts, a complete data set was finally collected on a single specimen under a soft N2 cooling stream (ca 260 K). The non-H part of the structure could be easily solved and refined in centrosymmetric C2/m, with the molecule halved by a mirror plane, but H-atom assignment posed a problem because the positions from the Fourier synthesis were unacceptable due to collision/superposition, e.g. the electron-density maxima, and their symmetry-related images generated by the full space-group symmetry, generated around each OW atom an almost perfect CH3-like umbrella which was sterically incompatible with their neighbours.

An analysis of the possible hydrogen-bonding interactions and the scheme which they suggested led to an acceptable centrosymmetric H-atom configuration, not abiding by the full space-group symmetry (see Fig. 2 for a typical example), but which could explain the lost `2' and `m' symmetries and the electron-density maps, when overlapped. Thus, C2/m should be considered as the `non-H' space group, but when H atoms are taken into account this is true only in an `average' sense. The refinement was accordingly performed in C2/m with this disordered H-atom distribution. Acetate methyl H atoms were included at calculated positions, with O—C—C—H torsion angles left free to refine, a procedure which also resulted in rotationally disordered CH3 sets. O—H distances were restrained to 0.85 (2) Å. In all cases, Uiso(H) was set to 1.5Ueq(X), where X = C or O, as appropriate.

Computing details top

Data collection: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1988); cell refinement: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1988); data reduction: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1988); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL-NT (Sheldrick, 2008); software used to prepare material for publication: SHELXTL-NT (Sheldrick, 2008) and PLATON (Spek, 2003).

Figures top
[Figure 1] Fig. 1. A molecular diagram of (I), showing the way in which chains are formed along the b axis. Independent atoms are drawn as octant shaded displacement ellipsoids at the 40% probability level, connected by solid bonds, while symmetry-related atoms are shown as open ellipsoids connected by hollow bonds. H atoms have been omitted for clarity. [Symmetry codes: (i) x, -y + 1, z; (ii) -x + 1/2, -y + 1/2, -z; (iii) -x + 1/2, y + 1/2, -z.]
[Figure 2] Fig. 2. A schematic representation of one of the possible locally centrosymmetric Hwater dispositions leading (on average) to a C2/m distribution compatible with the heavy-atom space group. The figure is built up around the symmetry centre at (1/2, 1/2, 0), giving rise to the symmetry operation (i). [Symmetry codes: (i) -x + 1, -y + 1, -z; (ii) -x + 1, y, -z; (iii) x, -y + 1, z; (iv) -x + 1, -y + 1, -z + 1; (v) x,y,1 + z; (vi) -x + 1/2, -y + 1/2, -z; (vii) -x + 1/2, y + 1/2, -z; (viii) x + 1/2, -y + 1/2, z; (ix) x + 1/2, y + 1/2, z.]
[Figure 3] Fig. 3. A schematic packing view of (I), projected down b, the chain direction. Disordered H atoms have been omitted for clarity. Short O···O contacts resulting from the hydrogen-bonding are shown as dashed lines.
catena-Poly[[(acetato-κ2O,O')triaquabarium(II)]- µ3-acetato-κ4O:O,O':O'] top
Crystal data top
[Ba(C2H3O2)2(H2O)3]F(000) = 592
Mr = 309.48Dx = 2.044 Mg m3
Monoclinic, C2/mMo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yCell parameters from 25 reflections
a = 16.020 (3) Åθ = 10–15°
b = 7.4892 (15) ŵ = 3.95 mm1
c = 9.1211 (18) ÅT = 263 K
β = 113.23 (3)°Block, colourless
V = 1005.6 (4) Å30.28 × 0.18 × 0.14 mm
Z = 4
Data collection top
Rigaku AFC-6
diffractometer
1006 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.066
Graphite monochromatorθmax = 26.0°, θmin = 2.4°
ω/2θ scansh = 319
Absorption correction: ψ scan
(North et al., 1968.)
k = 99
Tmin = 0.39, Tmax = 0.58l = 1110
2492 measured reflections3 standard reflections every 150 reflections
1069 independent reflections intensity decay: <2%
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.032H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.085 w = 1/[σ2(Fo2) + (0.0521P)2 + 0.0465P]
where P = (Fo2 + 2Fc2)/3
S = 1.12(Δ/σ)max < 0.001
1069 reflectionsΔρmax = 2.00 e Å3
85 parametersΔρmin = 1.75 e Å3
15 restraintsExtinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.0061 (8)
Crystal data top
[Ba(C2H3O2)2(H2O)3]V = 1005.6 (4) Å3
Mr = 309.48Z = 4
Monoclinic, C2/mMo Kα radiation
a = 16.020 (3) ŵ = 3.95 mm1
b = 7.4892 (15) ÅT = 263 K
c = 9.1211 (18) Å0.28 × 0.18 × 0.14 mm
β = 113.23 (3)°
Data collection top
Rigaku AFC-6
diffractometer
1006 reflections with I > 2σ(I)
Absorption correction: ψ scan
(North et al., 1968.)
Rint = 0.066
Tmin = 0.39, Tmax = 0.583 standard reflections every 150 reflections
2492 measured reflections intensity decay: <2%
1069 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.03215 restraints
wR(F2) = 0.085H atoms treated by a mixture of independent and constrained refinement
S = 1.12Δρmax = 2.00 e Å3
1069 reflectionsΔρmin = 1.75 e Å3
85 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Ba10.338393 (19)0.50000.09767 (3)0.0232 (2)
C110.1413 (4)0.50000.1858 (7)0.0255 (11)
C210.0396 (5)0.50000.2807 (12)0.056 (2)
H21A0.02550.43010.37570.084*0.50
H21B0.01900.62030.30940.084*0.50
H21C0.00990.44960.21730.084*0.50
O110.1820 (2)0.3532 (4)0.1458 (4)0.0354 (7)
C120.2630 (4)0.50000.3771 (7)0.0296 (12)
C220.2239 (6)0.50000.5024 (10)0.054 (2)
H22A0.16940.57050.46620.081*0.50
H22B0.26730.54970.59950.081*0.50
H22C0.20990.37970.52140.081*0.50
O120.3471 (3)0.50000.4152 (6)0.0423 (11)
O220.2069 (3)0.50000.2300 (5)0.0319 (9)
O1W0.40795 (19)0.2802 (5)0.0933 (4)0.0352 (7)
H1WC0.4585 (18)0.234 (6)0.033 (3)0.053*0.50
H1WB0.3697 (18)0.199 (4)0.140 (5)0.053*
H1WA0.416 (4)0.346 (3)0.163 (4)0.053*0.50
O2W0.5308 (3)0.50000.2786 (6)0.0374 (11)
H2WB0.542 (2)0.50000.3781 (16)0.056*
H2WA0.5541 (19)0.4070 (14)0.255 (3)0.056*0.50
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ba10.0235 (3)0.0145 (2)0.0305 (3)0.0000.00954 (18)0.000
C110.035 (3)0.019 (2)0.026 (3)0.0000.015 (3)0.000
C210.033 (4)0.056 (5)0.062 (5)0.0000.000 (4)0.000
O110.0393 (16)0.0193 (13)0.0415 (17)0.0011 (13)0.0095 (14)0.0008 (13)
C120.029 (3)0.025 (3)0.032 (3)0.0000.009 (3)0.000
C220.041 (4)0.086 (6)0.037 (4)0.0000.017 (4)0.000
O120.033 (2)0.061 (3)0.030 (2)0.0000.009 (2)0.000
O220.028 (2)0.0280 (18)0.036 (2)0.0000.0077 (19)0.000
O1W0.0341 (17)0.0301 (13)0.0401 (18)0.0062 (13)0.0133 (16)0.0046 (13)
O2W0.035 (2)0.040 (3)0.033 (2)0.0000.010 (2)0.000
Geometric parameters (Å, º) top
Ba1—O11i2.722 (3)C21—H21B0.9600
Ba1—O11ii2.722 (3)C21—H21C0.9600
Ba1—O222.810 (4)C12—O121.252 (8)
Ba1—O112.833 (3)C12—O221.287 (8)
Ba1—O11iii2.833 (3)C12—C221.504 (10)
Ba1—O122.845 (5)C22—H22A0.9600
Ba1—O2W2.866 (5)C22—H22B0.9600
Ba1—O1W2.918 (3)C22—H22C0.9600
Ba1—O1Wiii2.918 (3)O1W—H1WC0.85 (2)
C11—O11iii1.257 (4)O1W—H1WB0.85 (2)
C11—O111.257 (4)O1W—H1WA0.85 (2)
C11—C211.513 (9)O2W—H2WB0.85 (2)
C21—H21A0.9600O2W—H2WA0.85 (2)
O11i—Ba1—O11ii152.70 (15)O2W—Ba1—O1Wiii76.50 (10)
O11i—Ba1—O2276.87 (7)O1W—Ba1—O1Wiii68.68 (13)
O11ii—Ba1—O2276.87 (7)O11iii—C11—O11122.0 (6)
O11i—Ba1—O11112.22 (7)O11iii—C11—C21119.0 (3)
O11ii—Ba1—O1167.90 (11)O11—C11—C21119.0 (3)
O22—Ba1—O1175.86 (11)C11—C21—H21A109.5
O11i—Ba1—O11iii67.90 (11)C11—C21—H21B109.5
O11ii—Ba1—O11iii112.22 (7)H21A—C21—H21B109.5
O22—Ba1—O11iii75.86 (11)C11—C21—H21C109.5
O11—Ba1—O11iii45.68 (11)H21A—C21—H21C109.5
O11i—Ba1—O1278.27 (7)H21B—C21—H21C109.5
O11ii—Ba1—O1278.27 (7)C11—O11—Ba1ii144.6 (3)
O22—Ba1—O1246.11 (13)C11—O11—Ba194.9 (3)
O11—Ba1—O12118.10 (11)Ba1ii—O11—Ba1112.10 (11)
O11iii—Ba1—O12118.10 (11)O12—C12—O22121.4 (6)
O11i—Ba1—O2W94.44 (7)O12—C12—C22120.9 (6)
O11ii—Ba1—O2W94.44 (7)O22—C12—C22117.6 (6)
O22—Ba1—O2W124.81 (13)C12—C22—H22A109.5
O11—Ba1—O2W150.35 (9)C12—C22—H22B109.5
O11iii—Ba1—O2W150.35 (9)H22A—C22—H22B109.5
O12—Ba1—O2W78.70 (15)C12—C22—H22C109.5
O11i—Ba1—O1W137.97 (10)H22A—C22—H22C109.5
O11ii—Ba1—O1W69.29 (10)H22B—C22—H22C109.5
O22—Ba1—O1W141.58 (7)C12—O12—Ba195.9 (4)
O11—Ba1—O1W74.99 (9)C12—O22—Ba196.6 (3)
O11iii—Ba1—O1W100.31 (9)Ba1—O1W—H1WC109.3 (19)
O12—Ba1—O1W136.96 (8)Ba1—O1W—H1WB109.6 (18)
O2W—Ba1—O1W76.50 (10)H1WC—O1W—H1WB110 (3)
O11i—Ba1—O1Wiii69.29 (10)Ba1—O1W—H1WA108.9 (19)
O11ii—Ba1—O1Wiii137.97 (9)H1WC—O1W—H1WA109 (3)
O22—Ba1—O1Wiii141.58 (7)H1WB—O1W—H1WA109 (3)
O11—Ba1—O1Wiii100.31 (9)Ba1—O2W—H2WB110 (2)
O11iii—Ba1—O1Wiii74.99 (9)Ba1—O2W—H2WA109.4 (19)
O12—Ba1—O1Wiii136.96 (8)H2WB—O2W—H2WA109 (2)
Symmetry codes: (i) x+1/2, y+1/2, z; (ii) x+1/2, y+1/2, z; (iii) x, y+1, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1W—H1WB···O22ii0.85 (2)1.90 (2)2.744 (4)174 (5)
O1W—H1WC···O1Wiv0.85 (2)2.02 (3)2.763 (6)145 (5)
O1W—H1WA···O2Wv0.85 (2)1.97 (2)2.800 (5)164 (5)
O2W—H2WA···O1Wiv0.85 (2)2.04 (2)2.800 (5)147 (2)
O2W—H2WB···O12vi0.85 (2)2.02 (2)2.705 (7)137 (3)
Symmetry codes: (ii) x+1/2, y+1/2, z; (iv) x+1, y, z; (v) x+1, y+1, z; (vi) x+1, y+1, z+1.

Experimental details

Crystal data
Chemical formula[Ba(C2H3O2)2(H2O)3]
Mr309.48
Crystal system, space groupMonoclinic, C2/m
Temperature (K)263
a, b, c (Å)16.020 (3), 7.4892 (15), 9.1211 (18)
β (°) 113.23 (3)
V3)1005.6 (4)
Z4
Radiation typeMo Kα
µ (mm1)3.95
Crystal size (mm)0.28 × 0.18 × 0.14
Data collection
DiffractometerRigaku AFC-6
diffractometer
Absorption correctionψ scan
(North et al., 1968.)
Tmin, Tmax0.39, 0.58
No. of measured, independent and
observed [I > 2σ(I)] reflections
2492, 1069, 1006
Rint0.066
(sin θ/λ)max1)0.617
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.032, 0.085, 1.12
No. of reflections1069
No. of parameters85
No. of restraints15
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)2.00, 1.75

Computer programs: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1988), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), SHELXTL-NT (Sheldrick, 2008) and PLATON (Spek, 2003).

Selected bond lengths (Å) top
Ba1—O11i2.722 (3)Ba1—O122.845 (5)
Ba1—O222.810 (4)Ba1—O2W2.866 (5)
Ba1—O112.833 (3)Ba1—O1W2.918 (3)
Symmetry code: (i) x+1/2, y+1/2, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1W—H1WB···O22ii0.85 (2)1.90 (2)2.744 (4)174 (5)
O1W—H1WC···O1Wiii0.85 (2)2.02 (3)2.763 (6)145 (5)
O1W—H1WA···O2Wiv0.85 (2)1.97 (2)2.800 (5)164 (5)
O2W—H2WA···O1Wiii0.85 (2)2.04 (2)2.800 (5)147.4 (19)
O2W—H2WB···O12v0.85 (2)2.02 (2)2.705 (7)137 (3)
Symmetry codes: (ii) x+1/2, y+1/2, z; (iii) x+1, y, z; (iv) x+1, y+1, z; (v) x+1, y+1, z+1.
Water content versus density for all known Ba(C2H3O2)2(H2O)n top
Structurenρ (Mg m-3)Structure typeR.T. stability
(III)02.533DStable
(IV)0.5832.3283DStable
(II)12.263DStable
(I)32.0441DUnstable
 

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