Solid State Sciences 4 (2002) 979–983www.elsevier.com/locate/ssscie

Synthesis and single crystal structure of HSmP2O7.4H2O

Fathia Chehimi-Moumena,∗, Mokhtar Féridb, Dalila Ben Hassen-Chehimia,Malika Trabelsi-Ayadia

a Laboratoire de Physico-Chimie Minérale, Faculté des Sciences de Bizerte, 7021 Zarzouna-Bizerte, Tunisiab Laboratoire des Procédés Chimiques, Institut National de Recherche Scientifique et Technique, B.P. 95 Hammam-Lif, Tunisia

Received 1 October 2001; received in revised form 15 April 2002; accepted 23 April 2002

Abstract

Synthesis, IR absorption and single crystal structure are reported for a new diphosphate HSmP2O7.4H2O. This salt crystallizes in amonoclinic cell, space group P21/n with: a = 6.635(2), b = 11.529(4), c = 11.7581(9) Å, β = 92.02(2)◦; Z = 4. The crystal structurewas refined toR = 0.0174 using 2918 reflections withI > 2σ(I). Crystal structure of HSmP2O7.4H2O is built up by corrugated layersof HP2O3−

7 anions parallel to the(101) plane. Inside a layer the diphosphate anions are interconnected by water molecules as to form achain parallel to theb direction. The cohesion between the layers is provided by water molecules and SmO8 dodecahedra. 2002 Éditionsscientifiques et médicales Elsevier SAS. All rights reserved.

Keywords:Diphosphate; Chemical synthesis; Crystal structure

1. Introduction

The synthesis of acidic lanthanide diphosphates of gen-eral formula HLnP2O7.xH2O (Ln = La–Lu,x = 3; 3.5; 3–4)has been reported since 1967 [1–4]. The authors have setin evidence, from the X-ray powder diffraction, the exis-tence of two groups: HLnP2O7.xH2O (Ln = La–Sm) [1,2,4] crystallizing in the orthorhombic system (type I) [4] andHLnP2O7.xH2O (Ln = Sm–Lu) [2–4] crystallizing in thetriclinic system (type II) [4]. It was found that the samar-ium compound can adopt both structures. No crystal datawere available for these compounds. The study of this typeof phosphates has been undertaken in our laboratory in orderto study their crystalline structure.

In a previous paper we have reported the synthesis and thesingle crystal structure of HGdP2O7.3H2O [5]. This com-pound is found to be isostructural with the HLnP2O7.xH2O(Ln = Sm–Lu) mentioned above. It crystallizes in the P1̄space group.

In this paper we report the characterization and the singlecrystal structure of a new variety of samarium compoundno mentioned before: HSmP2O7.4H2O, crystallizing in themonoclinic system with space group P21/n (type III).

* Correspondence and reprints.E-mail address:fathia.chehimi@fsb.rnu.tn (F. Chehimi-Moumen).

2. Experimental

2.1. Chemical preparation

Single crystals of HSmP2O7.4H2O suitable for X-raydata collection, were obtained by mixing 10 ml of an acidicsamarium chloride solution SmCl3.6H2O (5 × 10−2 M,pH = 1) with 20 ml of a sodium diphosphate Na4P2O7.10H2-O aqueous solution (10−1 M). The mixture was slowly evap-orated at room temperature. The crystallization of prismaticcrystals of HSmP2O7.4H2O started from the solution after afew days. The single crystals are then, isolated and washedwith distilled water.

2.2. Crystal data, intensity data collection and structuredetermination

The main crystallographic features of HSmP2O7.4H2Oand the experimental parameters used for the X-ray datacollection are given in Table 1.

The determination of the structure was performed us-ing the Patterson-heavy atom method for the location of thesamarium atom. Successive difference-Fourier syntheses re-veal the positions of the phosphorus and oxygen atoms. Aftersome refinement cycles theR factor was 0.033. Introductionof the anisotropic thermal factors leads to 0.0216 for theR

1293-2558/02/$ – see front matter 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.PII: S1293-2558(02 )01348-1

980 F. Chehimi-Moumen et al. / Solid State Sciences 4 (2002) 979–983

Table 1Crystal data and experimental parameters for the X-ray intensity datacollection

Crystal data

Chemical formula HSmP2O7.4H2OFormula weight 397.36Crystal system MonoclinicSpace group P21/na (Å) 6.635(2)b (Å) 11.529(4)c (Å) 11.7581(9)β (deg) 92.02 (2)V (Å3) 898.9(4)Z 4ρcal (g cm−3) 2.93F(000) 358Absorption coefficientµ (mm−1) 1.84Crystal size (mm3) 0.08× 0.075× 0.09

Intensity measurement

Temperature (K) 293Wavelength AgKα (0.56087 Å)Diffractometer Enraf Nonius MACH 3Scan mode ω/2θScan speed (◦s−1) 0.02Scan width (deg) 1.20Monochromator GraphiteTheta range (deg) 2–25Measurement area −9< h< 8

0< k < 170< l < 17

Total number of scanned refl. 3326Total number of independent refl. 3201

Structure determination

No absorption correctionProgram used WINGX [6]

Structure resolution SHELXS 97 [7]Structure refinement SHELXL 97 [7]

Unique reflection include 2918 forI > 2σ(I )Weighting scheme WGHT= 1/[σ2(F2

o )+ (0.0261P )2

+ 0.8564P ]whereP = (F2

o + 2F2c )/3

Goodness of fit 1.077Unweighted agreement factorR 0.0174Weighted agreement factorwR 0.0450

value. The hydrogen atoms were localised by geometry. Af-ter some refinement cycles, using anisotropic thermal factorsfor the non hydrogen atoms and isotropic thermal factors forthe hydrogen ones, which positions were not refined, the fi-nalR value is 0.0174 for 2918 reflections withI > 2σ(I).

2.3. Infra-red spectroscopy

The FTIR spectrum was recorded in the 4000–400 cm−1

range, on a Perkin–Elmer FTIR 1000 spectrophotometer.The powder was finely ground and pressed into KBr pellets.

3. Results and discussion

3.1. Structure description

The final atomic positions and anisotropic thermal para-meters for the non-hydrogen atoms in the HSmP2O7.4H2Ostructure are given, respectively, in Tables 2 and 3. The cor-responding atomic arrangement is built by corrugated layersof HP2O3−

7 anions parallel to the(1 0 1) plane and contain-ing the W4 water molecule. In Fig. 1 a projection on the(1 01̄) plane shows the arrangement of these layers and howare intercalated between them the samarium atoms and thewater molecules.

3.1.1. The diphosphoric groupThe diphosphoric group observed in the present arrange-

ment has no internal symmetry and is so built by two non-equivalent PO4 tetrahedra. The projection of a P2O7 groupalong the phosphorus atoms P(1)–P(2) direction shows thatit has a slightly staggered conformation. The correspondingdistortion angles are: O(E13)–P(1)–P(2)–O(E23)= 20.12◦;O(E11)–P(1)–P(2)–O(E22)= 9.29◦; O(E12)–P(1)–P(2)–O(E21)= 10.64◦.

The main geometrical features in this entity are reportedin Table 4. The P–O average values observed in the twoindependent tetrahedra: 1.537 Å for P(1)O4 and 1.538 Åin the P(2)O4, as well the P–P value (2.9337(9) Å) andthe P(1)–O(L)–P(2) angle (130.82◦) are in good accordancewith previous investigations in diphosphates [8–11].

The oxygen–acidic hydrogen O–H distance (0.770 Å) andthe H–O–P angle (113.43◦) are slightly smaller than thoseobserved in HGdP2O7.3H2O [5] and MnHP2O7 [8].

Fig. 1. Projection on the(101) plane of the atomic arrangement inHSmP2O7.4H2O. Dotted circles represent the samarium atoms, the openones the oxygen atoms of water molecules and the black ones the hydrogenatoms.

F. Chehimi-Moumen et al. / Solid State Sciences 4 (2002) 979–983 981

Table 2Final atomic coordinates for HSmP2O7.4H2O,Ueq (Å2) for non-hydrogen atoms andUiso (Å2) for hydrogen atoms

Atom x(σ) y(σ ) z(σ ) Ueq(σ )

Sm 0.75586(1) 0.416462(9) 0.836115(9) 0.00862(4)P1 1.25552(7) 0.54867(5) 0.85658(4) 0.00869(9)P2 0.47917(8) 0.63207(5) 0.66190(4) 0.00887(9)O(E11) 1.4190(2) 0.4586(1) 0.8741(1) 0.0137(3)O(E12) 1.0654(2) 0.5006(2) 0.8016(1) 0.0171(3)O(E13) 1.2144(3) 0.6167(1) 0.9636(1) 0.0169(3)O(E21) 0.3421(3) 0.5755(1) 0.5666(2) 0.0175(3)O(E22) 0.6546(2) 0.5560(1) 0.6941(1) 0.0148(3)O(E23) 0.5245(2) 0.7532(1) 0.6267(1) 0.0147(3)O(L) 0.3391(2) 0.6451(1) 0.7698(1) 0.0128(3)O(W1) 0.7687(3) 0.6207(2) 0.9355(1) 0.0186(3)O(W2) 0.8236(3) 0.3393(2) 0.6448(2) 0.0250(4)O(W3) 0.5520(3) 0.2385(2) 0.8257(2) 0.0349(5)O(W4) 0.2647(4) 0.3622(2) 0.6010(3) 0.0436(7)

UisoH 0.3250 0.5101 0.5754 0.06(1)H(11) 0.8895 0.6393 0.9556 0.04(1)H(12) 0.7129 0.6242 0.9962 0.03(1)H(21) 0.7880 0.2748 0.6217 0.03(1)H(22) 0.7564 0.3724 0.5923 0.08(2)H(31) 0.6009 0.1799 0.8178 0.04(1)H(32) 0.4331 0.2443 0.8046 0.05(1)H(41) 0.2840 0.3057 0.5606 0.04(1)H(42) 0.1661 0.3633 0.6527 0.10(2)

Table 3Anisotropic thermal parameters (Å2) for HSmP2O7.4H2O

Atom U11(σ ) U22(σ ) U33(σ ) U23(σ ) U13(σ ) U12(σ )

Sm 0.00756(5) 0.00841(5) 0.00992(5) 0.00046(3) 0.00059(3) 0.00076(3)P1 0.0074(2) 0.0098(2) 0.0090(2) 0.0004(2) 0.0017(2) 0.0005(2)P2 0.0092(2) 0.0084(2) 0.0091(2) 0.00131(2) 0.0003(2) −0.0008(2)O(E11) 0.0098(6) 0.0137(7) 0.0178(7) 0.0038(6) 0.0029(5) 0.0039(5)O(E12) 0.0099(7) 0.0201(8) 0.0211(8) 0.0001(6) −0.0009(6) −0.0041(6)O(E13) 0.0240(8) 0.0171(7) 0.0099(7) −0.0015(6) 0.0038(6) 0.0044(6)O(E21) 0.0224(8) 0.0138(7) 0.0157(8) −0.0002(6) −0.0053(6) −0.0029(6)O(E22) 0.0112(7) 0.0174(7) 0.0159(7) 0.0044(6) 0.0019(6) 0.0036(6)O(E23) 0.0163(7) 0.0100(6) 0.0178(7) 0.0034(6) 0.0017(5) −0.0040(6)O(L) 0.0138(7) 0.0112(7) 0.0137(7) 0.0021(5) 0.0046(5) −0.0001(5)O(W1) 0.0191(8) 0.0200(8) 0.0167(8) 0.0018(6) 0.0003(6) −0.0019(6)O(W2) 0.042(1) 0.0169(8) 0.0155(8) −0.0024(7) −0.0053(8) 0.0050(8)O(W3) 0.0166(9) 0.0162(9) 0.072(2) −0.011(1) −0.0005(9) −0.0034(7)O(W4) 0.057(2) 0.017(1) 0.060(2) −0.008(1) 0.029(1) −0.010(1)

3.1.2. The samarium coordinationThe samarium atom has eightfold oxygen coordination

forming a distorted dodecahedron with Sm–O distancesranging from 2.320 to 2.629 Å (Table 5).

Fig. 2 shows that each SmO8 dodecahedron shares threeoxygen atoms with water molecules and five oxygen atomswith four adjacent P2O7 groups belonging to two differentlayers. The SmO8 dodecahedra provide then the cohesionbetween the phosphoric layers.

The SmO8 dodecahedra in the HSmP2O7.4H2O arrange-ment share no corner contrary to what is found in theHGdP2O7.3H2O structure. The shortest Sm–Sm distance isfound to be 6.1095 Å.

3.1.3. The hydrogen bond networkIn all previously reported atomic arrangements including

acidic diphosphate groups, the acidic anions are found to beconnected to each others by strong hydrogen bonds involv-ing the acidic hydrogen and external oxygen atoms of adja-cent P2O7 groups as to build infinite networks. Four types ofgeometrical configurations are known: infinite chains as ob-served in MnHP2O7 [8], infinite ribbons in Ag2H2P2O7 [9],infinite layers in Cs2H2P2O7 [10] and infinite tridimensionalnetwork in Cs2H2P2O7.Te(OH)6 [11]. Recently an originalassociation of HP2O3−

7 anions is reported by the authors forthe HGdP2O7.3H2O structure [5]. These anions assemblethemselves by pairs as to build finite clusters.

982 F. Chehimi-Moumen et al. / Solid State Sciences 4 (2002) 979–983

Table 4Main interatomic distances (Å) and bond angles (deg) in the P2O7 group

Tetrahedron around P1〈P–O〉 = 1.537 Å

P1 O(E11) O(E12) O(E13) O(L)i

O(E11) 1.510(2) 2.515(2) 2.524(2) 2.522(2)O(E12) 113.2(1) 1.503(2) 2.503(2) 2.509(2)O(E13) 113.1(1) 112.0(1) 1.515(2) 2.473(2)O(L)i 107.33(9) 106.4(1) 104.1(1) 1.620(2)

Tetrahedron around P2〈P–O〉 = 1.538 Å

P2 O(E21) O(E22) O(E23) O(L)

O(E21) 1.561(2) 2.525(2) 2.470(2) 2.521(2)O(E22) 111.4(1) 1.495(2) 2.548(2) 2.522(2)O(E23) 108.1(1) 117.2(1) 1.490(2) 2.459(2)O(L) 105.5(1) 108.78(9) 105.07(9) 1.606(2)

Symmetry operation:i x + 1, y, z.

Fig. 2. The coordination of the samarium atom.

The examination of the hydrogen bond network in HSm-P2O7.4H2O, shows that the acidic hydrogen of the HP2O3−

7group is engaged in H-bond with the oxygen of the W4 watermolecule, and not with any oxygen of adjacent diphosphategroup. This H-bond is a strong one, since the O(W4)–O(E21) distance (2.54 Å) is comparable to the O–O distanceobserved inside a PO4 tetrahedron. The hydrogens of the W4water molecule, H(41) and H(42), are engaged in weak H-bonds with two oxygens of two adjacent HP2O3−

7 groups,

Fig. 3. Projection of an isolated layer of diphosphoric anions.

since the corresponding donor–acceptor distances are 2.936and 3.175 Å. A view of an isolated layer of HP2O3−

7 anions(Fig. 3) shows that the latters are interconnected throughthese hydrogen bonds as to form infinite chains parallel totheb direction.

It can be noted from Table 6 that H(42) form a bifurcatedH-bond, since it is also connected to O(W2) through a weakhydrogen bond (O(W2)· · ·O(W4)= 3.002 Å).

The W2 water molecule forms two hydrogen bonds, onefor each H atom; H(21) is connected to O(W1) and H(22) toan external oxygen atom of the diphosphoric group.

The hydrogens of W1 are connected to O atoms ofthree different P2O7 groups belonging to the same layer.H(11) forms a bifurcated hydrogen bond with O(E13) andO(E23)iii , whereas H(12) forms a single and strong hydrogenbond with O(E21)iii . The W3 water molecule provides theconnection between the layers thought week H-bond withacceptor–donor distances of 2.881 and 2.991 Å.

Table 5Main interatomic distances (Å) and bond angles (deg) in the SmO8 dodecahedron

Sm O(E11)ii O(E12) O(E13)iii O(E22) O(E23)iv O(W1) O(W2) O(W3)

O(E11)ii 2.346(2) 2.515(2) 4.757(3) 5.541(3) 3.777(2) 4.780(3) 4.900(3) 6.295(3)O(E12) 143.31(6) 2.320(2) 3.642(2) 3.031(2) 3.040(3) 2.914(3) 3.037(3) 4.570(3)O(E13)iii 83.75(6) 101.36(7) 2.387(2) 4.847(3) 4.592(3) 2.964(3) 5.506(3) 6.360(3)O(E22) 75.42(6) 79.93(6) 143.68(6) 2.398(2) 4.566(2) 3.006(3) 2.808(3) 4.042(3)O(E23)iv 134.51(6) 79.95(6) 70.59(6) 143.42(6) 2.411(2) 4.211(3) 5.170(3) 6.379(3)O(W1) 75.27(6) 71.83(6) 72.81(6) 73.29(6) 127.50(6) 2.458(2) 4.736(3) 4.798(3)O(W2) 116.91(7) 78.52(7) 145.87(6) 70.36(6) 75.89(6) 141.16(7) 2.475(2) 3.065(3)O(W3) 69.89(7) 146.02(7) 86.65(8) 112.67(8) 71.65(7) 76.81(8) 136.23(6) 2.629(2)

Symmetry operations:ii x − 1, y, z; iii −x + 2,−y + 1,−z + 2; iv −x + 3/2, y − 1/2,−z + 3/2.

F. Chehimi-Moumen et al. / Solid State Sciences 4 (2002) 979–983 983

Table 6Main interatomic distances (Å) and bond angles (deg) in the hydrogenbonds

O–H· · ·O O–H O· · ·H O–H· · ·O O· · ·OO(E21)–Ha· · ·O(W4) 0.770 1.779 174.93 2.547(3)O(W1)–H11· · ·O(E13) 0.855 2.170 154.40 2.964(3)O(W1)–H11· · ·O(E23)i 0.855 2.502 130.70 3.1273(3)O(W1)–H12· · ·O(E11)ii 0.816 2.024 148.90 2.755(3)O(W2)–H21· · ·O(W1)i 0.823 1.932 174.50 2.753(3)O(W2)–H22· · ·O(E21)iii 0.841 2.047 161.37 2.857(3)O(W3)–H31· · ·O(E22)i 0.757 2.169 157.01 2.881(3)O(W3)–H32· · ·O(L)iv 0.821 2.285 144.34 2.991(3)O(W4)–H41· · ·O(E13)i 0.819 2.198 149.96 2.936(3)O(W4)–H42· · ·O(E12)v 0.909 2.470 134.59 3.175(4)O(W4)–H42· · ·O(W2)v 0.909 2.288 135.13 3.002(3)H(11)–O(W1)–H(12) 101.3(2)H(21)–O(W2)–H(22) 91.7(2)H(31)–O(W3)–H(32) 116.5(2)H(41)–O(W4)–H(42) 121.9(2)

Symmetry operations:i −x + 3/2, y − 1/2,−z+ 3/2; ii −x+ 2,−y + 1,−z+ 2; iii −x +

1,−y + 1,−z + 1; iv −x + 1/2, y − 1/2,−z + 3/2; v x − 1, y, z.

Fig. 4. IR spectrum of HSmP2O7.4H2O.

3.2. Infra-red spectroscopy

The IR spectrum of HSmP2O7.4H2O is illustrated inFig. 4. The different frequencies ranges can be assigned asfollows [12,13]:

• The 3600–1500 cm−1 range corresponds to the OH/H2O vibration modes. The three bands at 3594, 3450and 3240 cm−1, corresponding to H2O stretching vibra-tion confirm the existence of hydrogen bonds of dif-ferent strengths in the HSmP2O7.4H2O arrangement.The two large bands of weak intensity between 2800and 2300 cm−1 can be attributed to the P–O–H vibra-tion modes. Around 1600 cm−1 appear two bands cor-responding to H2O bending modes.

• The 1300–400 cm−1 range shows the different diphos-phate vibration modes. The characteristics bands of theP2O7 group,νas(POP) andνs(POP) appear, respectively,at 973–917 and 776 cm−1.

Acknowledgement

The authors thank Professor M. Rzaigui for the datacollection.

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