Ag₂PdP₂O₇

Disilver(I) palladium(II) diphosphate, Ag₂PdP₂O₇, is isotypic with Na₂PdP₂O₇. It consists of infinite diphosphato-pallad­ate(II) [Pd(P₂O₇)_2/2]²⁻ ribbons with the Pd^II ion in an almost square-planar coordination ( symmetry) and the P₂O₇ group exhibiting 2 symmetry. The [Pd(P₂O₇)_2/2]²⁻ ribbons are linked by distorted [AgO₆] octa­hedra. ³¹P-MAS NMR studies on Ag₂PdP₂O₇ are in accordance with one independent site for phospho­rus; its isotropic chemical shift δ_iso = 21.5 p.p.m. is similar to that of Pd₂P₂O₇.

Related literature

For related literature on palladium oxo-compounds, see: Arndt & Wickleder (2007); Dahmen et al. (1994); Laligant et al. (1991); Palkina et al. (1978); Panagiotidis et al. (2005b); Waser et al. (1953). For related literature on polynary palladium phosphates, see: El Maadi et al. (2003); Laligant (1992a,b); Lii et al. (2004); For related literature on noble metal phosphates, see: Panagiotidis et al. (2005a, 2008). For background on chemical shift parameters, see: Moreno et al. (2002); Griffiths et al. (1986); Hayashi & Hayamizu (1989). For details of software used, see: Bak et al. (2000); Soose & Meyer (1980); Vosegaard et al. (2002).

Experimental

Crystal data

• Ag₂PdP₂O₇

• M_r = 496.10

• Monoclinic, C 2/c

• a = 15.739 (2) Å

• b = 5.7177 (7) Å

• c = 8.187 (1) Å

• β = 116.75 (1)°

• V = 657.91 (15) ų

• Z = 4

• Mo Kα radiation

• μ = 9.08 mm⁻¹

• T = 293 (2) K

• 0.08 × 0.05 × 0.05 mm

Data collection

• Enraf–Nonius CAD-4 diffractometer

• Absorption correction: ψ scan (North et al., 1968) T_min = 0.551, T_max = 0.631

• 1890 measured reflections

• 947 independent reflections

• 591 reflections with I > 2σ(I)

• R_int = 0.080

• 3 standard reflections frequency: 60 min intensity decay: none

Refinement

• R[F² > 2σ(F²)] = 0.035

• wR(F²) = 0.074

• S = 0.97

• 947 reflections

• 58 parameters

• Δρ_max = 1.30 e Å⁻³

• Δρ_min = −1.14 e Å⁻³

Data collection: CAD-4 EXPRESS (Enraf–Nonius, 1994); cell refinement: CAD-4 EXPRESS; data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2008); software used to prepare material for publication: WinGX (Farrugia, 1999).

Supporting information

S1. Comment

With the synthesis and crystal structure refinement of the first gold phosphate Au^IIIPO₄ (Panagiotidis et al., 2005a) and two modifications of Ir^III(PO₃)₃ (Panagiotidis et al., 2008) we have widened the crystal chemical knowledge on anhydrous phosphates of the noble metals. Investigations in the ternary system Pd/P/O provided, apart from the already existing phosphates Pd(PO₃)₂ (Palkina et al., 1978) and Pd₂P₂O₇ (Panagiotidis et al., 2005b), no evidence for further thermodynamically stable palladium phosphates. Due to our interest in network structures built from square-planar units [MO₄] (M = Pd^II, Au^III) and phosphate tetrahedra we focused therefore our search on polynary palladium phosphates. Polynary phosphates of divalent palladium are rare in literature. Up to now, only the compositions M^I₂PdP₂O₇ (M = Li (Laligant, 1992a), Na (Laligant, 1992b), K (El Maadi et al., 2003), K_3.5Pd_2.25(P₂O₇)₂ (El Maadi et al., 2003) and Cs₂Pd₃(P₂O₇)₂ (Lii et al., 2004) were reported. In Pd₂P₂O₇ itself, Li₂PdP₂O₇, and Na₂PdP₂O₇ infinite ribbons [Pd(P₂O₇)_2/2]^2- are the characteristic structural motif. K₂PdP₂O₇ adopts a layer structure with the crystal chemical composition [Pd(P₂O₇)_4/4]^2-. The structures of K_3.5Pd_2.25(P₂O₇)₂ and Cs₂Pd₃(P₂O₇)₂ consist of [Pd^IIO₄] and [P₂O₇] groups generating a three-dimensional framework.

According to our X-ray single-crystal study Ag₂PdP₂O₇ is isotypic to Na₂PdP₂O₇. The unit cell contains four formula units Ag₂PdP₂O₇ with one crystallographically independent site for silver, palladium and phosphorus (Fig. 1). As in the crystal structures of PdO (Waser et al., 1953), M-Pd^IISO₄ (Dahmen et al., 1994), Pd^II(NO₃)₂(H₂O)₂ (Laligant et al., 1991), and Pd₂P₂O₇ the Pd²⁺ ions show a square-planar coordination by oxygen. In Ag₂PdP₂O₇ palladium is coordinated in a chelating way by two [P₂O₇] groups. This coordination mode, with a, for such diphosphates typically observed, bridging angle 〈(P—O2—P) = 124.9°, leads to the formation of corrugated ribbons [Pd(P₂O₇)_2/2]^2- (Fig. 2). These ribbons are linked by significantly distorted [Ag^IO₆] octahedra. Due to different crystal chemical environment of the four independent oxygen atoms, with O1 forming one bond to P and two to Ag, O2 forming two bonds to P and O3 and O4 forming one bond each to P, Pd and Ag, a radial distortion of the phosphate groups with one very short, two medium long and one elongated distance d(P—O) is observed. In accordance with the crystal structure of Ag₂PdP₂O₇ ³¹P-MAS-NMR investigations (Varian Infinity Plus, 9.4 tesla-magnet, 2.5-mm MAS double resonance NMR probe, rotation frequency 3.0 kHz) show the presence of just one phosphorus site. Chemical shift parameters were determined by means of numerically calculated spectra (programme SIMPSON (Bak et al., 2000), MINUIT routine in SIMPSON (Vosegaard et al., 2002)) to δ_iso = 21.5 p.p.m., δ_aniso = 79.0 p.p.m. and η = 0.87. The chemical shifts are reported in parts per million (p.p.m.) from the external standard 85% H₃PO₄. As in Pd₂P₂O₇ (η = 0.86) and in contrast to other diphosphates (Moreno et al., 2002; Griffiths et al., 1986; Hayashi & Hayamizu, 1989) a remarkably high value for η is observed. The isotropical chemical shift of Ag₂PdP₂O₇ which is similar to the one observed for Pd₂P₂O₇ (δ_iso = 28.3 p.p.m.) is exceptionally high in comparison to δ_iso values of diphosphates of the alkaline and alkaline earth metals (Moreno et al., 2002; Griffiths et al., 1986; Hayashi & Hayamizu, 1989). We attribute this observation to significant covalency in the Pd—O interaction.

Related literature

For related literature on palladium oxo-compounds, see: Arndt & Wickleder (2007); Dahmen et al. (1994); Laligant et al. (1991); Palkina et al. (1978); Panagiotidis et al. (2005b); Waser et al. (1953). For related literature on polynary palladium phosphates, see: El Maadi et al. (2003); Laligant (1992a,b); Lii et al. (2004); For related literature on noble metal phosphates, see: Panagiotidis et al. (2005a, 2008b). For background on chemical shift parameters, see: Moreno et al. (2002); Griffiths et al. (1986); Hayashi & Hayamizu (1989). For details of software used, see: Bak et al. (2000); Soose & Meyer (1980); Vosegaard et al. (2002).

S2. Experimental

Microcrystalline Ag₂PdP₂O₇ was synthesized via a solid state reaction by heating an amorphous precursor for 24 h at T = 773 K in air. The precursor was obtained by drying a mixture of 100.0 mg (0.94 mmol) palladium powder (99.99%, UMICORE AG, Hanau–Wolfgang) with an excess of conc. nitric acid and stoichiometric amounts of 319.2 mg AgNO₃ (1.88 mmol) (p.A., Merck) and 18.8 ml H₃PO₄ (0.1 M) at 423 K as a brownish powder.

Isothermal heating of 100.0 mg (0.82 mmol) PdO, 189.3 mg (0.82 mmol) Ag₂O (p.A. Merck) and 116.0 mg (0.41 mmol) P₄O₁₀ (99%, Riedel de Häen) (addition of 8.0 mg PdCl₂ as mineralizer) carried out in sealed and evacuated silica tubes at 773 K for seven days gave besides microcrystalline, single-phase Ag₂PdP₂O₇ (eq. 1) also small amounts of yellow plate-like single crystals which were distributed over the whole ampoule.

PdO_s + Ag₂O_s + 1/2 P₄O_10,s → Ag₂PdP₂O_7,s (eq. 1)

Computing details

Data collection: CAD-4 EXPRESS (Enraf–Nonius, 1994); cell refinement: CAD-4 EXPRESS (Enraf–Nonius, 1994); data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2008); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

	Fig. 1. Projection of the crystal structure of Ag2PdP2O7 along [010] with tetrahedral [PO4] units (yellow), Pd^2+ (red) and Ag^+ grey (DIAMOND v3.1f).
	Fig. 2. Diphosphato-palladate(II) ribbon [Pd(P2O7)2/2]^2- along [001]. Thermal elipsoids with 50% probability (DIAMOND, v3.1f).

Disilver(I) palladium(II) diphosphate

Crystal data

Ag2PdP2O7	F(000) = 904
Mr = 496.10	The lattice parameters given were refined with the program SOS (Soose & Meyer, 1980), using 40 reflections from a Guinier IP photograph.
Monoclinic, C2/c	Dx = 5.008 Mg m^−3
Hall symbol: -C 2yc	Mo Kα radiation, λ = 0.71073 Å
a = 15.739 (2) Å	Cell parameters from 40 reflections
b = 5.7177 (7) Å	θ = 6.3–34.3°
c = 8.187 (1) Å	µ = 9.08 mm^−1
β = 116.75 (1)°	T = 293 K
V = 657.91 (15) Å^3	Prism, yellow
Z = 4	0.08 × 0.05 × 0.05 mm

Data collection

Enraf–Nonius CAD-4 diffractometer	591 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.080
Graphite monochromator	θmax = 29.9°, θmin = 2.9°
Nonprofiled ω scans	h = −22→22
Absorption correction: ψ scan (North et al., 1968)	k = −8→0
Tmin = 0.551, Tmax = 0.631	l = −11→11
1890 measured reflections	3 standard reflections every 60 min
947 independent reflections	intensity decay: none

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.035	w = 1/[σ^2(Fo^2) + (0.0245P)^2] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.074	(Δ/σ)max < 0.001
S = 0.97	Δρmax = 1.30 e Å^−3
947 reflections	Δρmin = −1.14 e Å^−3
58 parameters	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.00104 (17)
0 constraints

Special details

Geometry. All e.s.d.'s 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 and angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry.

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
Pd1	0	0	0	0.0145 (2)
Ag1	0.23426 (5)	0.85894 (13)	0.79398 (9)	0.0217 (2)
P1	0.10116 (14)	0.3445 (4)	0.8422 (3)	0.0137 (4)
O1	0.8200 (4)	0.5226 (10)	0.5959 (7)	0.0177 (13)
O2	0	0.4744 (14)	0.75	0.0139 (16)
O3	0.8949 (4)	0.1859 (11)	0.8057 (7)	0.0220 (14)
O4	0.6031 (4)	0.2953 (11)	0.5045 (8)	0.0213 (14)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Pd1	0.0103 (4)	0.0178 (5)	0.0135 (4)	−0.0012 (4)	0.0036 (3)	0.0055 (4)
Ag1	0.0197 (4)	0.0247 (4)	0.0171 (3)	−0.0044 (3)	0.0050 (3)	−0.0017 (3)
P1	0.0111 (9)	0.0152 (11)	0.0146 (9)	−0.0028 (9)	0.0055 (8)	0.0003 (10)
O1	0.016 (3)	0.016 (3)	0.019 (3)	0.011 (3)	0.006 (2)	0.005 (3)
O2	0.014 (4)	0.011 (4)	0.015 (4)	0	0.006 (3)	0
O3	0.018 (3)	0.027 (4)	0.019 (3)	−0.003 (3)	0.007 (3)	0.010 (3)
O4	0.011 (3)	0.026 (4)	0.023 (3)	0.004 (3)	0.004 (2)	−0.012 (3)

Geometric parameters (Å, º)

Pd1—O4^i	1.987 (5)	P1—O4^x	1.539 (6)
Pd1—O4^ii	1.987 (5)	P1—O2	1.605 (4)
Pd1—O3^iii	2.007 (6)	O1—P1^vii	1.505 (6)
Pd1—O3^iv	2.007 (6)	O1—Ag1^xi	2.321 (5)
Ag1—O1^v	2.321 (5)	O1—Ag1^vii	2.436 (6)
Ag1—O4^vi	2.368 (6)	O2—P1^xii	1.605 (4)
Ag1—O1^vii	2.436 (6)	O3—P1^vii	1.537 (6)
Ag1—Ag1^viii	3.0427 (6)	O3—Pd1^xiii	2.007 (6)
Ag1—Ag1^ix	3.0427 (6)	O4—P1^xiv	1.539 (6)
P1—O1^vii	1.505 (6)	O4—Pd1^xv	1.987 (5)
P1—O3^vii	1.537 (6)	O4—Ag1^xvi	2.368 (5)
O4^i—Pd1—O4^ii	180.0 (4)	Ag1^viii—Ag1—Ag1^ix	139.96 (5)
O4^i—Pd1—O3^iii	94.5 (2)	O1^vii—P1—O3^vii	110.2 (3)
O4^ii—Pd1—O3^iii	85.5 (2)	O1^vii—P1—O4^x	111.6 (3)
O4^i—Pd1—O3^iv	85.5 (2)	O3^vii—P1—O4^x	112.4 (4)
O4^ii—Pd1—O3^iv	94.5 (2)	O1^vii—P1—O2	109.8 (4)
O3^iii—Pd1—O3^iv	180.0 (6)	O3^vii—P1—O2	106.6 (3)
O1^v—Ag1—O4^vi	159.7 (2)	O4^x—P1—O2	106.0 (3)
O1^v—Ag1—O1^vii	88.23 (19)	P1^vii—O1—Ag1^xi	123.5 (3)
O4^vi—Ag1—O1^vii	87.5 (2)	P1^vii—O1—Ag1^vii	141.5 (3)
O1^v—Ag1—Ag1^viii	116.60 (15)	Ag1^xi—O1—Ag1^vii	91.77 (19)
O4^vi—Ag1—Ag1^viii	77.30 (15)	P1^xii—O2—P1	124.9 (5)
O1^vii—Ag1—Ag1^viii	57.82 (14)	P1^vii—O3—Pd1^xiii	128.7 (3)
O1^v—Ag1—Ag1^ix	84.21 (15)	P1^xiv—O4—Pd1^xv	126.2 (3)
O4^vi—Ag1—Ag1^ix	93.96 (16)	P1^xiv—O4—Ag1^xvi	127.8 (3)
O1^vii—Ag1—Ag1^ix	161.97 (14)	Pd1^xv—O4—Ag1^xvi	105.4 (2)

Symmetry codes: (i) x−1/2, −y+1/2, z−1/2; (ii) −x+1/2, y−1/2, −z+1/2; (iii) x−1, y, z−1; (iv) −x+1, −y, −z+1; (v) x−1/2, −y+3/2, z+1/2; (vi) x−1/2, y+1/2, z; (vii) −x+1, y, −z+3/2; (viii) −x+1/2, y−1/2, −z+3/2; (ix) −x+1/2, y+1/2, −z+3/2; (x) x−1/2, −y+1/2, z+1/2; (xi) x+1/2, −y+3/2, z−1/2; (xii) −x, y, −z+3/2; (xiii) x+1, y, z+1; (xiv) x+1/2, −y+1/2, z−1/2; (xv) −x+1/2, y+1/2, −z+1/2; (xvi) x+1/2, y−1/2, z.