The water-insoluble title compound,
catena-poly[palladium(II)-di-
-acetato-
4O:
O'], [Pd(C
2H
3O
2)
2]
n, was obtained from a nitratopalladium solution and acetic acid as a pale-pink powder.
Ab initio crystal structure determination was carried out using X-ray powder diffraction techniques. Patterson and Fourier syntheses were used for atom location and the Rietveld technique was applied for the final structure refinement. The structure consists of palladium acetate complexes connected into polymeric chains running along
b, in which two Pd atoms are bridged by two acetate groups that are in a
cis configuration with respect to one another. The unique Pd atom lies on a site with 2/
m symmetry and the acetate moieties have imposed
m symmetry; these are joined into infinite chains running along the
b direction. The shortest Pd
Pd distance in the row is 2.9192 (1) Å. The planes of adjacent palladium complexes are inclined towards each other, the angle between the planes being approximately 30°.
Supporting information
CCDC reference: 251295
The synthesis of (I) was carried out either by adding acetic acid to a solution of palladium dissolved in nitric acid, or from a solution of [Pd3(CH3COO)6] in acetic acid by adding nitric acid. The solution was heated at 393 K. The precipitated pale-pink product was filtered, washed with water and dried in air. The chemical composition of the obtained precipitate corresponds to Pd(CH3COO)2.
X-ray powder diffraction data are deposited in JCPDS-ICDD PDF2 database. Cell parameters were obtained from d-spaces by indexing and refining using programs described in (Visser, 1969, Kirik et al., 1979). The space group was determined from the analysis of systematic absences. The structural investigations were carried out using a full-profile structure analysis package based on a modified version of the Rietveld refinement program DBWS– 9006PC (Wiles & Young, 1981). The intensities of 120 reflections were estimated from the powder pattern by means of the full- profile fitting procedure (Le Bail et al., 1988) and used in the Patterson synthesis. Pd atoms were located directly from a Patterson map, and the positions of O and C atoms were defined from difference Fourier syntheses. H atoms were not located but were included in the refined structure model, rigidly connected to their C atoms and taking into account special positions of C atoms. The final refinement was carried out by the Rietveld (1969) method. The obtained crystal structure data are presented in Table 1 and Table 2.
Data collection: DRON-4 data collection software; cell refinement: POWDER (Kirik et al., 1979); data reduction: ?; program(s) used to solve structure: Modified DBWM (Wiles & Young, 1981); program(s) used to refine structure: Modified DBWM; molecular graphics: XP (Siemems, 1989).
catena-poly[palladium(II)-di-µ-acetato-
κ4O:
O']
top
Crystal data top
[Pd(C2H3O2)2] | F(000) = 216.0 |
Mr = 224.51 | Cell parameters are obtained from the Rietveld refinement |
Monoclinic, P21/m | Dx = 2.15 Mg m−3 |
Hall symbol: -P 2yb | Cu Kα radiation, λ = 1.54056 Å |
a = 7.4467 (1) Å | T = 293 K |
b = 5.8383 (1) Å | Particle morphology: thin powder |
c = 7.9900 (1) Å | pale yellow |
β = 93.46 (1)° | circular flate plate, 20.0 × 20.0 mm |
V = 346.74 (1) Å3 | Specimen preparation: Prepared at 293 K and 101 kPa, cooled at 0 K min−1 |
Z = 2 | |
Data collection top
DRON-4 powder diffractometer | Specimen mounting: packed powder pellet |
Radiation source: conventional sealed tube | Data collection mode: reflection |
Graphite monochromator | 2θmin = 5.0°, 2θmax = 90.0°, 2θstep = 0.02° |
Refinement top
Refinement on F2 | Excluded region(s): none |
Least-squares matrix: full | Profile function: Pearson VII |
Rp = 0.108 | 41 parameters |
Rwp = 0.152 | 0 restraints |
Rexp = 0.117 | 0 constraints |
RBragg = 0.047 | H-atom parameters constrained |
R(F2) = 0.040 | Weighting scheme based on measured s.u.'s |
χ2 = 1.904 | (Δ/σ)max = 0.1 |
? data points | Preferred orientation correction: March-Dollase correction |
Crystal data top
[Pd(C2H3O2)2] | β = 93.46 (1)° |
Mr = 224.51 | V = 346.74 (1) Å3 |
Monoclinic, P21/m | Z = 2 |
a = 7.4467 (1) Å | Cu Kα radiation, λ = 1.54056 Å |
b = 5.8383 (1) Å | T = 293 K |
c = 7.9900 (1) Å | circular flate plate, 20.0 × 20.0 mm |
Data collection top
DRON-4 powder diffractometer | Data collection mode: reflection |
Specimen mounting: packed powder pellet | 2θmin = 5.0°, 2θmax = 90.0°, 2θstep = 0.02° |
Refinement top
Rp = 0.108 | ? data points |
Rwp = 0.152 | 41 parameters |
Rexp = 0.117 | 0 restraints |
RBragg = 0.047 | H-atom parameters constrained |
R(F2) = 0.040 | (Δ/σ)max = 0.1 |
χ2 = 1.904 | |
Special details top
Experimental. Structure determination was carried out by the X-ray powder diffraction method. The experimental data were collected on a DRON-4 automatic diffractometer, equipped with a secondary flat graphite monochromator in conjunction with a scintillation detector. Cu Kα radiation was used (λ1=1.54056 Å, λ2=1.54439 Å). The sample was prepared by top-loading the standard quartz sample holder with cutting the excess of well grained substance. The diffraction pattern was scanned with the step of 0.02° 2θ and counting time of 10 sec./step in the most informative angular range from 5° to 90% 2θ at ambient temperature. Corundum was used as the external standard. X-ray powder diffraction data are deposited in JCPDS-ICDD PDF2 database. Cell parameters were obtained from d-spaces by indexing and refining using programs described in (Visser, 1969, Kirik et al., 1979). The space group was determined from the analysis of systematic absences. The structural investigations were carried out using a full-profile structure analysis package based on a modified version of the Rietveld refinement program DBWS– 9006PC (Wiles & Young, 1981). The intensities of 120 reflections were estimated from the powder pattern by means of the full- profile fitting procedure (Le Bail et al., 1988) and used in the Patterson synthesis. |
Refinement. R_prof-backgr = 0.147 |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
Pd | 0.0000 | 0.5 | 0.5 | 0.0095* | |
O11 | 0.255 (1) | 0.559 (2) | 0.602 (1) | 0.0381* | |
C11 | 0.343 (3) | 0.75 | 0.634 (3) | 0.0377* | |
C12 | 0.524 (3) | 0.75 | 0.708 (2) | 0.0279* | |
O21 | 0.084 (1) | 0.569 (1) | 0.270 (1) | 0.0194* | |
C21 | 0.111 (3) | 0.75 | 0.185 (3) | 0.0300* | |
C22 | 0.182 (2) | 0.75 | 0.026 (2) | 0.0262* | |
H12A | 0.5168 | 0.75 | 0.8263 | 0.08* | |
H12B | 0.5842 | 0.8844 | 0.6744 | 0.08* | |
H22A | 0.3094 | 0.75 | 0.0344 | 0.08* | |
H22B | 0.1446 | 0.8807 | −0.0370 | 0.08* | |
Geometric parameters (Å, º) top
Pd—O11 | 2.050 (8) | C11—C12 | 1.44 (3) |
Pd—O21 | 2.017 (8) | C21—C22 | 1.41 (3) |
O11—C11 | 1.31 (2) | Pd—Pdi | 2.9192 (1) |
O21—C21 | 1.28 (2) | | |
| | | |
O21—Pd—O11 | 89.9 (3) | O21—C21—O21ii | 111.5 (4) |
O11—Pd—O21 | 90.1 (3) | Pdiii—Pd—O11 | 80.3 (3) |
O11ii—C11—O11 | 116.6 (7) | Pdiii—Pd—O21 | 78.5 (2) |
Symmetry codes: (i) −x, y−1/2, −z+1; (ii) x, −y+3/2, z; (iii) −x, y+1/2, −z+1. |
Experimental details
Crystal data |
Chemical formula | [Pd(C2H3O2)2] |
Mr | 224.51 |
Crystal system, space group | Monoclinic, P21/m |
Temperature (K) | 293 |
a, b, c (Å) | 7.4467 (1), 5.8383 (1), 7.9900 (1) |
β (°) | 93.46 (1) |
V (Å3) | 346.74 (1) |
Z | 2 |
Radiation type | Cu Kα, λ = 1.54056 Å |
Specimen shape, size (mm) | Circular flate plate, 20.0 × 20.0 |
|
Data collection |
Diffractometer | DRON-4 powder diffractometer |
Specimen mounting | Packed powder pellet |
Data collection mode | Reflection |
Scan method | ? |
2θ values (°) | 2θmin = 5.0 2θmax = 90.0 2θstep = 0.02 |
|
Refinement |
R factors and goodness of fit | Rp = 0.108, Rwp = 0.152, Rexp = 0.117, RBragg = 0.047, R(F2) = 0.040, χ2 = 1.904 |
No. of data points | ? |
No. of parameters | 41 |
H-atom treatment | H-atom parameters constrained |
(Δ/σ)max | 0.1 |
Selected geometric parameters (Å, º) topPd—O11 | 2.050 (8) | C11—C12 | 1.44 (3) |
Pd—O21 | 2.017 (8) | C21—C22 | 1.41 (3) |
O11—C11 | 1.31 (2) | Pd—Pdi | 2.9192 (1) |
O21—C21 | 1.28 (2) | | |
| | | |
O21—Pd—O11 | 89.9 (3) | O21—C21—O21ii | 111.5 (4) |
O11—Pd—O21 | 90.1 (3) | Pdiii—Pd—O11 | 80.3 (3) |
O11ii—C11—O11 | 116.6 (7) | Pdiii—Pd—O21 | 78.5 (2) |
Symmetry codes: (i) −x, y−1/2, −z+1; (ii) x, −y+3/2, z; (iii) −x, y+1/2, −z+1. |
Palladium acetate complexes have been well investigated because they have some useful properties, especially for catalyst preparation (Stephenson et al., 1965; Romm et al., 1992; Pandey & Henry, 1974.). Crystal data have been reported for palladium acetate and some adducts, for example [Pd3(CH3COO)6] (Lyalina et al., 1993), [Pd3(CH3COO)6]·0.5H2O (Scapski & Smart, 1970), [Pd3(CH3COO)6]·0.5CH2Cl2 (Cotton & Han, 1985) and [Pd3(CH3COO)6]·0.5C6H6 (Cotton & Han, 1983). In all of these compounds, palladium forms a triangular cluster, with two acetate groups in bridging positions on every side of the triangle. In the present work, a polymeric form of palladium acetate, (I), was investigated. We did not find any mention of this form in the literature, including the Cambridge Structural Database (Allen, 2002). However, it seems to be the most easily obtained form, although it has not yet been characterized because of the absence of a single-crystal sample. We have obtained the structure solution using X-ray powder diffraction techniques. The X-ray powder diffraction data are presented in Fig. 1 and the obtained crystal structure is shown in Fig. 2.
The main structural units of (I) are the [Pd(CH3COO)4/2] complexes. Pd atoms occupy the special position (0,1/2,1/2) and form rows along b, with a Pd···Pd distance of 2.9192 (1) Å; this distance is less than that reported for in the triangular clusters, where these distances range from 3.098 to 3.196 Å (Lyalina et al., 1993). All acetate groups in (I) are of the bridging type. Each Pd···Pd contact is served by two acetate groups in cis positions with respect to one another. In spite of the bridging character of the acetate groups, the palladium coordination is square planar, since Pd is located on an inversion centre; by constrast, [Pd3(CH3COO)6] (Lyalina et al., 1993) is only approximately planar. Because of the tension in the chemical bonding, the coordination planes of the neighboring Pd atoms are not parallel, being inclined towards each other with an angle between the planes of approximately 30°. In contrast, the angle between the [PdO4] planes in the trimer cluster is about 60° (Lyalina et al., 1993). The larger angle in the trimer is complemented by a longer Pd···Pd distance. The differences in these two geometrical features can be attributed to the higher thermodynamic stability of the polymeric form of palladium acetate. A similar chain arrangement was previously found in some acetate-containing palladium compounds with additional donor ligands. In particular, [Pd3(CH3COO)4(S(CH2CH(CH3)2))2(C8H10}2] (Fuchita et al., 1996), [Pd3(CH3COO)4((SbPh3)2Ph2)] (Barton et al., 1990) and [Pd3(CH3COO)4(C13O4H21)2] (Ukhin et al., 1981) demonstrate planar palladium coordination with acetate groups in cis positions. The Pd···Pd distances are 2.98 (2), 3.01 (8) and 2.9 (2) Å, respectively.
In summary, palladium acetate can form at least two isomers, viz. trimeric and polymeric. The Pd atoms in both forms have square-planar coordination. The higher thermodynamic stability of the polymeric form is related to the mutual orientation of the [PdO4] planes of adjacent complexes, which provides stronger Pd···Pd interactions.