Dipotassium zinc bis­(di­hydrogendiphosphate) dihydrate, K₂Zn(H₂P₂O₇)₂·2H₂O

The framework of K₂Zn(H₂P₂O₇)₂·2H₂O contains acid diphos­phate–metallate layers linked by K...O interactions and weak hydrogen bonds. Zn²⁺ cations are coordinated octahedrally by O atoms from two bidentate [H₂P₂O₇]²⁻ anions and two water mol­ecules.

Key indicators

• Single-crystal X-ray study
• T = 292 K
• Mean [sigma](P-O) = 0.004 Å
• R factor = 0.056
• wR factor = 0.093
• Data-to-parameter ratio = 18.9

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level C:



REFLT_03
         From the CIF: _diffrn_reflns_theta_max           31.58
         From the CIF: _reflns_number_total               2154
         TEST2: Reflns within _diffrn_reflns_theta_max
         Count of symmetry unique reflns         2376
         Completeness (_total/calc)             90.66%
          Alert C: < 95% complete


 0 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 1 Alert Level C = Please check

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S1. Comment

To our knowledge, no mixed dihydrogendiphosphates of the form (A,T)_x(H₂P₂O₇)_y.zH₂O (A = alkaline earth and T = transition metal) have been reported. Some simple alkali metal dihydrogendiphosphates are known: Na₂H₂P₂O₇·6H₂O (Collin & Willis, 1971), K₂H₂P₂O₇ (Larbot et al., 1983), K₂H₂P₂O₇.1/2H₂O (Dumas et al., 1973), K₃H(H₂P₂O₇)₂ (Dumas, 1978), K₃Na(H₂P₂O₇)₂ (Dumas et al., 1980), Rb₂H₂P₂O₇·0.5H₂O (Averbuch-Pouchart & Durif, 1993a) and Cs₂H₂P₂O₇ (Averbuch-Pouchart & Durif, 1993b). Acidic metal diphosphates have been implicated in some enzyme-catalyzed reaction processes (Haromy et al., 1984) and are used as inhibitors in the formation and dissolution of apatite crystals in vitro (Mathew et al., 1993). We recently reported the structures of two hydrogendiphosphates, KM(HP₂O₇)·2H₂O (M = Mn, Zn) (Assaaoudi et al., 2002). We report here the structure of the dihydrogendiphosphate K₂Zn(H₂P₂O₇)₂·2H₂O.

The structure of K₂Zn(H₂P₂O₇)₂·2H₂O can be described in terms of layers parallel to (001) (Fig. 1). Each layer is built up of [KO₈], [ZnO₆] and [H₂P₂O₇] polyhedra (Fig. 2) sharing corners and edges. The [ZnO₆] polyhedra share four corners with two neighbouring [H₂P₂O₇] anions to form the unit [Zn(H₂P₂O₇)₂·2H₂O], I. The [KO₈] polyhedra share one edge to form the unit [K₂O₁₄], II. Edge-sharing of units I and II results in a layer parallel to (001). Neighbouring layers are connected by K···O interactions and weak hydrogen bonds.

Each of the two unique phosphorus atoms is coordinated by four O atoms, one of which belongs to a hydroxyl group, in a slightly distorted tetrahedral geometry. The two tetrahedra share a corner (O1) to form the [H₂P₂O₇]^2- anion in a roughly eclipsed conformation. The average P—O distance of 1.533 Å is similar to that found in K₂H₂P₂O₇ (1.537 Å) and K₃H(H₂P₂O₇)₂ (1.543 Å). The P—O—P angle of 128.85 (6)° is close to that in Ca₂P₂O₇ (130.0°; Calvo, 1968) and K₄P₂O₇·3H₂O (130.3°; Robertson & Calvo 1967). The Zn²⁺ ions are coordinated in a nearly regular octahedral geometry by two bidentate [H₂P₂O₇]^2- anions and two water molecules. The average Zn—O distance of 2.084 Å is close to that in β-Zn₂P₂O₇ (2.121 Å; Calvo, 1965). The [ZnO₆] polyhedra are isolated, with the shortest Zn···Zn distance being over 6 Å. The K atoms are eightfold coordinated, with K—O distances ranging from 2.757 (3) to 3.339 (4) Å. The average K—O distance of 2.959 Å is slightly longer than those found in K₄P₂O₇·3H₂O (2.812 Å; Dumas & Galigne, 1974) and K₂H₂P₂O₇ (2.908 Å; Larbot et al., 1983).

S2. Experimental

Stoichiometric amounts of ZnCl₂ were dissolved in a K₄P₂O₇ solution in distilled water. After it was stirred for 1 d and allowed to stand for two to three weeks, large prismatic colourless crystals were deposited. The crystals were filtered off and washed with a water–ethanol (20:80) solution.

Computing details

Data collection: SMART (Bruker, 1999); cell refinement: SAINT (Bruker, 1999); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia,1997) and ATOMS (Dowty,1999); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. Projection along the b axis of K2Zn(H2P2O7)2·2H2O. Polyhedra: yellow [H2P2O7], green [ZnO6]; circles: large pink K, small grey H.
	Fig. 2. Coordination polyhedra of [KO8], [ZnO6] and [H2P2O7]. Displacement ellipsoids are at the 50% probability level.

dipotassium zinc bis(dihydrogendiphosphate) dihydrate

Crystal data

K2Zn(H2P2O7)2·2H2O	Z = 1
Mr = 531.51	F(000) = 264
Triclinic, P1	Dx = 2.479 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 6.827 (3) Å	Cell parameters from 1307 reflections
b = 7.333 (3) Å	θ = 2.8–29.8°
c = 7.570 (3) Å	µ = 2.84 mm^−1
α = 80.753 (8)°	T = 292 K
β = 72.547 (8)°	Prism, colourless
γ = 83.442 (8)°	0.33 × 0.12 × 0.04 mm
V = 356.0 (2) Å^3

Data collection

Bruker SMART APEX CCD area-detector diffractometer	2154 independent reflections
Radiation source: fine-focus sealed tube	1244 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.081
ω scans	θmax = 31.6°, θmin = 2.8°
Absorption correction: multi-scan (XPREP; Sheldrick, 1997)	h = −9→9
Tmin = 0.670, Tmax = 0.893	k = −10→10
4313 measured reflections	l = −10→10

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)] = 0.056	Hydrogen site location: difference Fourier map
wR(F^2) = 0.093	H-atom parameters constrained
S = 0.86	w = 1/[σ^2(Fo^2) + (0.001P)^2] where P = (Fo^2 + 2Fc^2)/3
2154 reflections	(Δ/σ)max < 0.001
114 parameters	Δρmax = 1.28 e Å^−3
4 restraints	Δρmin = −0.98 e Å^−3

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
K1	0.89203 (18)	0.26588 (17)	0.70406 (16)	0.0330 (3)
Zn1	0.5000	0.5000	0.5000	0.0172 (2)
O1W	0.5496 (5)	0.7084 (5)	0.2659 (4)	0.0249 (8)
H1W	0.6116	0.6620	0.1712	0.06 (2)*
H2W	0.5971	0.7950	0.2787	0.10 (3)*
P1	0.32331 (18)	0.27285 (18)	0.24797 (16)	0.0165 (3)
P2	0.75109 (18)	0.18972 (18)	0.24168 (16)	0.0157 (3)
O1	0.5623 (4)	0.2317 (5)	0.1528 (4)	0.0222 (8)
O2	0.2936 (5)	0.3926 (4)	0.3967 (4)	0.0189 (7)
O3	0.2376 (4)	0.3499 (5)	0.0907 (4)	0.0216 (8)
O4	0.2362 (5)	0.0815 (5)	0.3359 (5)	0.0246 (8)
H4	0.2492	0.0549	0.4414	0.10 (3)*
O5	0.7418 (5)	0.3276 (5)	0.3708 (4)	0.0223 (8)
O6	0.9303 (5)	0.2144 (5)	0.0615 (4)	0.0220 (8)
H6	1.0168	0.2738	0.0775	0.07 (2)*
O7	0.7467 (5)	−0.0092 (5)	0.3307 (4)	0.0257 (8)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
K1	0.0422 (7)	0.0272 (7)	0.0347 (7)	0.0050 (6)	−0.0193 (6)	−0.0088 (6)
Zn1	0.0218 (4)	0.0135 (4)	0.0199 (4)	−0.0022 (3)	−0.0085 (3)	−0.0069 (3)
O1W	0.034 (2)	0.019 (2)	0.022 (2)	−0.0068 (17)	−0.0057 (16)	−0.0045 (16)
P1	0.0189 (6)	0.0152 (7)	0.0182 (6)	−0.0025 (5)	−0.0077 (5)	−0.0053 (5)
P2	0.0181 (6)	0.0147 (7)	0.0163 (6)	−0.0024 (5)	−0.0055 (5)	−0.0059 (5)
O1	0.0193 (18)	0.031 (2)	0.0200 (18)	−0.0003 (15)	−0.0082 (14)	−0.0106 (15)
O2	0.0205 (17)	0.0159 (18)	0.0261 (18)	−0.0012 (14)	−0.0096 (14)	−0.0135 (14)
O3	0.0223 (18)	0.025 (2)	0.0206 (17)	−0.0045 (15)	−0.0114 (15)	0.0016 (15)
O4	0.039 (2)	0.0161 (19)	0.0243 (19)	−0.0084 (16)	−0.0157 (16)	−0.0006 (15)
O5	0.0259 (18)	0.0209 (19)	0.0261 (18)	−0.0024 (15)	−0.0102 (15)	−0.0144 (15)
O6	0.0221 (18)	0.028 (2)	0.0192 (18)	−0.0107 (16)	−0.0051 (14)	−0.0083 (15)
O7	0.036 (2)	0.020 (2)	0.0218 (18)	−0.0059 (16)	−0.0102 (16)	0.0004 (15)

Geometric parameters (Å, º)

K1—O6^i	2.757 (3)	Zn1—O2	2.080 (3)
K1—O2^ii	2.775 (3)	Zn1—O1W^ii	2.116 (3)
K1—O4^iii	2.874 (4)	Zn1—O1W	2.116 (3)
K1—O7^iv	2.899 (4)	P1—O3	1.485 (3)
K1—O1W^ii	2.941 (4)	P1—O2	1.490 (3)
K1—O5	2.949 (3)	P1—O4	1.556 (3)
K1—O2^v	3.139 (3)	P1—O1	1.589 (3)
K1—O3^ii	3.339 (4)	P2—O7	1.505 (3)
Zn1—O5^ii	2.057 (3)	P2—O5	1.499 (3)
Zn1—O5	2.057 (3)	P2—O6	1.536 (3)
Zn1—O2^ii	2.080 (3)	P2—O1	1.603 (3)
O6^i—K1—O2^ii	114.43 (10)	O2^ii—Zn1—O1W	91.69 (14)
O6^i—K1—O4^iii	104.22 (10)	O2—Zn1—O1W	88.31 (14)
O2^ii—K1—O4^iii	123.60 (10)	O1W^ii—Zn1—O1W	180.000 (1)
O6^i—K1—O7^iv	78.02 (10)	Zn1—O1W—K1^ii	89.76 (11)
O2^ii—K1—O7^iv	150.48 (10)	Zn1—O1W—H1W	109.5
O4^iii—K1—O7^iv	74.48 (10)	K1^ii—O1W—H1W	107.7
O6^i—K1—O1W^ii	107.72 (10)	Zn1—O1W—H2W	114.1
O2^ii—K1—O1W^ii	61.43 (10)	K1^ii—O1W—H2W	118.4
O4^iii—K1—O1W^ii	68.78 (10)	H1W—O1W—H2W	114.7
O7^iv—K1—O1W^ii	143.13 (11)	O3—P1—O2	116.54 (19)
O6^i—K1—O5	165.84 (10)	O3—P1—O4	109.15 (19)
O2^ii—K1—O5	59.76 (9)	O2—P1—O4	109.95 (19)
O4^iii—K1—O5	72.66 (10)	O3—P1—O1	104.89 (17)
O7^iv—K1—O5	113.51 (10)	O2—P1—O1	109.67 (18)
O1W^ii—K1—O5	58.15 (9)	O4—P1—O1	106.05 (19)
O6^i—K1—O2^v	113.36 (9)	O5—P2—O7	114.9 (2)
O2^ii—K1—O2^v	86.82 (9)	O5—P2—O6	112.91 (19)
O4^iii—K1—O2^v	114.10 (10)	O7—P2—O6	110.9 (2)
O7^iv—K1—O2^v	63.75 (9)	O5—P2—O1	110.48 (18)
O1W^ii—K1—O2^v	135.87 (9)	O7—P2—O1	107.20 (19)
O5—K1—O2^v	80.01 (9)	O6—P2—O1	99.19 (17)
O6^i—K1—O3^ii	67.22 (9)	P1—O1—P2	130.8 (2)
O2^ii—K1—O3^ii	47.81 (8)	P1—O2—Zn1	132.41 (19)
O4^iii—K1—O3^ii	146.43 (9)	P1—O2—K1^ii	109.43 (16)
O7^iv—K1—O3^ii	130.45 (9)	Zn1—O2—K1^ii	95.19 (12)
O1W^ii—K1—O3^ii	82.69 (10)	P1—O2—K1^vi	104.84 (15)
O5—K1—O3^ii	107.43 (9)	Zn1—O2—K1^vi	113.98 (12)
O2^v—K1—O3^ii	98.56 (8)	K1^ii—O2—K1^vi	93.18 (9)
O5^ii—Zn1—O5	180.0	P1—O3—K1^ii	86.07 (14)
O5^ii—Zn1—O2^ii	92.71 (12)	P1—O4—K1^iii	150.3 (2)
O5—Zn1—O2^ii	87.29 (12)	P1—O4—H4	109.5
O5^ii—Zn1—O2	87.29 (12)	K1^iii—O4—H4	98.9
O5—Zn1—O2	92.71 (12)	P2—O5—Zn1	130.27 (19)
O2^ii—Zn1—O2	180.000 (1)	P2—O5—K1	126.92 (18)
O5^ii—Zn1—O1W^ii	93.39 (13)	Zn1—O5—K1	90.68 (11)
O5—Zn1—O1W^ii	86.61 (13)	P2—O6—K1^vii	125.17 (18)
O2^ii—Zn1—O1W^ii	88.31 (14)	P2—O6—H6	109.5
O2—Zn1—O1W^ii	91.69 (14)	K1^vii—O6—H6	115.6
O5^ii—Zn1—O1W	86.61 (13)	P2—O7—K1^iv	124.14 (17)
O5—Zn1—O1W	93.39 (13)
O5^ii—Zn1—O1W—K1^ii	−47.92 (12)	O1—P1—O4—K1^iii	−75.1 (4)
O5—Zn1—O1W—K1^ii	132.08 (12)	O7—P2—O5—Zn1	−102.3 (3)
O2^ii—Zn1—O1W—K1^ii	−140.53 (11)	O6—P2—O5—Zn1	129.1 (2)
O2—Zn1—O1W—K1^ii	39.47 (11)	O1—P2—O5—Zn1	19.1 (3)
O3—P1—O1—P2	165.1 (3)	O7—P2—O5—K1	28.7 (3)
O2—P1—O1—P2	39.2 (3)	O6—P2—O5—K1	−99.9 (2)
O4—P1—O1—P2	−79.5 (3)	O1—P2—O5—K1	150.06 (17)
O5—P2—O1—P1	−47.7 (4)	O2^ii—Zn1—O5—P2	−176.4 (3)
O7—P2—O1—P1	78.2 (3)	O2—Zn1—O5—P2	3.6 (3)
O6—P2—O1—P1	−166.5 (3)	O1W^ii—Zn1—O5—P2	95.1 (3)
O3—P1—O2—Zn1	−121.3 (2)	O1W—Zn1—O5—P2	−84.9 (3)
O4—P1—O2—Zn1	113.8 (3)	O2^ii—Zn1—O5—K1	40.72 (11)
O1—P1—O2—Zn1	−2.4 (3)	O2—Zn1—O5—K1	−139.28 (11)
O3—P1—O2—K1^ii	−4.4 (2)	O1W^ii—Zn1—O5—K1	−47.74 (12)
O4—P1—O2—K1^ii	−129.28 (17)	O1W—Zn1—O5—K1	132.26 (12)
O1—P1—O2—K1^ii	114.48 (17)	O6^i—K1—O5—P2	−110.0 (4)
O3—P1—O2—K1^vi	94.44 (18)	O2^ii—K1—O5—P2	−179.3 (2)
O4—P1—O2—K1^vi	−30.4 (2)	O4^iii—K1—O5—P2	−30.7 (2)
O1—P1—O2—K1^vi	−146.65 (15)	O7^iv—K1—O5—P2	33.1 (2)
O5^ii—Zn1—O2—P1	166.5 (3)	O1W^ii—K1—O5—P2	−106.1 (2)
O5—Zn1—O2—P1	−13.5 (3)	O2^v—K1—O5—P2	88.6 (2)
O1W^ii—Zn1—O2—P1	−100.2 (3)	O3^ii—K1—O5—P2	−175.49 (19)
O1W—Zn1—O2—P1	79.8 (3)	O6^i—K1—O5—Zn1	34.8 (5)
O5^ii—Zn1—O2—K1^ii	44.12 (12)	O2^ii—K1—O5—Zn1	−34.43 (10)
O5—Zn1—O2—K1^ii	−135.88 (12)	O4^iii—K1—O5—Zn1	114.12 (12)
O1W^ii—Zn1—O2—K1^ii	137.43 (12)	O7^iv—K1—O5—Zn1	177.92 (10)
O1W—Zn1—O2—K1^ii	−42.57 (12)	O1W^ii—K1—O5—Zn1	38.73 (11)
O5^ii—Zn1—O2—K1^vi	−51.70 (14)	O2^v—K1—O5—Zn1	−126.58 (12)
O5—Zn1—O2—K1^vi	128.30 (14)	O3^ii—K1—O5—Zn1	−30.66 (12)
O1W^ii—Zn1—O2—K1^vi	41.62 (15)	O5—P2—O6—K1^vii	−124.4 (2)
O1W—Zn1—O2—K1^vi	−138.38 (15)	O7—P2—O6—K1^vii	105.1 (2)
O2—P1—O3—K1^ii	3.49 (18)	O1—P2—O6—K1^vii	−7.4 (2)
O4—P1—O3—K1^ii	128.74 (15)	O5—P2—O7—K1^iv	−100.6 (2)
O1—P1—O3—K1^ii	−117.98 (15)	O6—P2—O7—K1^iv	28.9 (3)
O3—P1—O4—K1^iii	37.4 (4)	O1—P2—O7—K1^iv	136.19 (18)
O2—P1—O4—K1^iii	166.4 (3)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O4—H4···O7^iii	0.82	1.71	2.529 (5)	175
O6—H6···O3^v	0.82	1.70	2.503 (5)	165
O1W—H1W···O3^viii	0.82	1.95	2.731 (5)	158
O1W—H2W···O7^ix	0.78	2.00	2.775 (5)	171

Symmetry codes: (iii) −x+1, −y, −z+1; (v) x+1, y, z; (viii) −x+1, −y+1, −z; (ix) x, y+1, z.