J O U R N A L O F C H E M I S T R Y Materials Synthesis and structural characterization of a novel tin(II ) oxyphosphate, [NH4+]2[Sn3O(PO4)2]2-·H2O, containing one-dimensional chains constructed from tin phosphate cages Srinivasan Natarajan* Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur P.O., Bangalore 560 064, India. E-mail: raj@jncasr.ac.in Received 13th August 1998, Accepted 30th September 1998 The hydrothermal synthesis and single crystal structure of a novel tin(II) oxyphosphate, [NH4+]2[Sn3O(PO4)2]2-·H2O, made from the networking of distorted square-pyramidal SnO4 and tetrahedral PO4 moieties, is presented.Crystal data: a=7.240(1), b=19.552(3), c=8.438(1) A° ; V=1194.5(3) A° 3; space group Cmc21 (no. 36) and Z=2. The structure, dominated by the presence of a large number of three-coordinated oxygen atoms and SnKOKSn linkages, creating an oxy-phosphate unit, consists of capped three-membered rings (cages) connected to each other via phosphate groups forming infinite one-dimensional chains. These chains are related to each other via multipoint hydrogen bonding involving the protonated ammonium and water molecules.atoms. The structure of this material consists of capped three- Introduction membered rings (cages) connected to each other via phosphate The design and synthesis of new open-framework materials groups forming infinite chains. These chains are held together having micro- and meso-porosity is a challenge to the synthetic via multipoint hydrogen bonding involving the protonated chemist, as such materials are being used in the areas of ammonium and water molecules.catalysis and separation processes.1 The synthesis under hydro/solvo-thermal conditions provides a facile route for Experimental making materials with new open architectures as well as complex organic–inorganic composites. This methodology Synthesis leads to the development of new classes of materials that can The title compound, synthesized hydrothermally employing exploit the ability of polar organic molecules to direct the guanidium carbonate as the structure directing agent, is crystallization of inorganic frameworks through multipoint described below.In a typical experiment, 2.0671 g of tin hydrogen bonding.2 The hydrogen bonded interactions oxalate (Aldrich) was dispersed in 10 ml of water.To this between the inorganic and organic moieties of a framework mixture 1.153 g of phosphoric acid (Aldrich) was added drop- structure are all the more important when dealing with low wise and the mixture stirred vigorously. Then 1.262 g of dimensional materials as is becoming more apparent by the guanidium carbonate was added to the above very slowly large number of available literature dealing with such materials.under continuous stirring. The final mixture was transferred The chemistry of bivalent tin and its related compounds, and sealed in a PTFE-lined stainless steel autoclave (Parr, especially the phosphates and oxalates, synthesized in the USA), and heated at 175 °C for 3 days under autogeneous presence of organic structure directing agents (amines) pressure.The final composition of the mixture was continues to yield unexpected results with the isolation of 1 SnC2O451H3PO450.7 guadinium carbonate555H2O. The materials having one- [Sn2(PO4) (C2O4)0.5]3 (chain), tworesulting product, which contained a few single crystals along {[Sn2(PO4)2]2-[C2N2H10]2+·H2O}4 ( layer) and threewith some white powder, was filtered oV and washed thor- {[Sn4P3O12]-0.5[NH3(CH2)2NH3]2+, [Sn4 P3O12]-0.5- oughly with de-ionized distilled water (yield ca. 50%). The [NH3(CH2)4NH3]2+}5,6 dimensionally extended networks. powder X-ray diVraction pattern of both the crushed single The basic building unit, four-membered rings constructed by crystals as well as the white powder, taken independently, two Sn atoms and two P atoms (Sn2P2O4 unit), present in all were found to be identical and indicated that the product was these materials, has also been isolated.7 All these compounds homogeneous and a new material; the pattern is entirely contain either trigonal pyramidal SnO3 or distorted square consistent with the structure determined by single crystal X-ray pyramidal SnO4 units, vertex linked with tetrahedral PO4 units diVraction.Thermogravimetric analysis (TGA) was carried to form the network. These solids, based on Sn(II ), in addition out in nitrogen atmosphere from room temperature up to to having novel architectures also provide a basis for evaluating 600 °C. the influence of the Sn(II) lone pair of electrons on the structural features as well as the importance of multipoint hydrogen Structure determination bonding in the stability of such phases.The synthesis and structure of a novel tin(II ) oxyphosphate A suitable colorless single crystal was carefully selected under material having a 10-membered star shaped channel8 has a polarizing microscope and glued to the tip of a glass fiber been reported recently.In the present work, the synthesis using Superglue (cyanoacrylate). Crystal structure determiand structure of another novel tin(II) oxyphosphate, nation by X-ray diVraction was performed at room-tempera- [NH4+]2[Sn3O(PO4)2]2-·H2O, made by the networking of ture on a Siemens Smart-CCD diVractometer equipped with distorted square-pyramidal SnO4 and tetrahedral PO4 units is a normal focus, 2.4 kW sealed tube X-ray source (Mo-Ka presented.This is the first report of a Sn(II ) phosphate material radiation, l=0.71073 A° ) operating at 50 kV and 40 mA. A formed entirely by four-coordinate Sn(II) atoms; all the pre- hemisphere of intensity data were collected in 1321 frames viously reported Sn(II ) phosphate3–8 and phosphonate9,10 with v scans (width of 0.30° and exposure time of 40 s per frame).The final unit-cell constants were determined by a materials contain both three- and four-coordinated Sn(II) J. Mater. Chem., 1998, 8, 2757–2760 2757Table 1 Summary of crystal data, intensity measurements and structure refinement parameters for [NH4+]2[Sn3O(PO4)2]2-·H2O Empirical formula Sn3P2O10N2H10 Crystal system Orthorhombic Space group Cmc21 (no. 36) Crystal size/mm 0.04×0.04×0.125 a/A° 7.240(1) b/A° 19.552(3) c/A° 8.438(1) V/A° 3 1194.5(3) Z 2 Formula mass 616.1(1) Dc/g cm-3 1.713 l(Mo-Ka)/A° 0.71073 m/mm-1 3.27 Temperature of 298 measurement/K h range/° 2.08–23.28° Total data collected 4995 Index ranges -7h7, -21k20, -6l9 Unique data 2299 Observed data [s>2s(I )] 749 Rint 4.68 Refinement method Full-matrix least-squares on |F 2| R indices [s>2s(I )] R=3.67; Rw=7.83 R (all data) R=4.79; Rw=8.47 Goodness of fit/S 1.13 No.of variables 103 Largest diVerence map peak 0.699, -0.975 and hole/e A° -3 least-squares fit of 1379 reflections in the range 42h46.5° and are presented in Table 1. A total of 4995 reflections were collected in the range -7h7, -21k20, -6l9 and these were merged to give 2299 unique reflections (Rint.= 0.0468) of which 749 were considered to be observed [I>2s(I )].The pertinent experimental conditions for the structure determination are listed in Table 1. The structure was solved by direct methods using SHELXS-8611 and diVerence Fourier syntheses. Hydrogen atoms of the water and ammonia molecules were found in the diVerence Fourier map and held in the riding mode.Refinement of the Flack parameter to ca. 1.0 indicated that the incorrect absolute structure had been established in the initial model. The polarity of the model was reversed by changing the sign of the polar-axis z coordinate for all the atoms and re-refining the model, which resulted in a final value for the Flack parameter of-0.05(8) and residuals of R=0.0367 and Rw=0.0783. Re-refinement of this transformed coordinate set with the Flack parameter set to 1.00 led to residuals of R=0.0382 and Rw=0.0902.The last cycles of refinement included atomic positions and anisotropic thermal parameters for all non-hydrogen atoms and isotropic thermal parameters for all the hydrogen atoms. Full-matrixleast- squares structure refinement against |F2| was carried out using the SHELXTL-PLUS12 package of programs.The final Fourier map had a minimum and maximum peaks of -0.975 and 0.699 e A° -3, respectively. Further details of the crystal structure investigation may be obtained from the Fig. 1 (a) Asymmetric unit of [NH4+]2[Sn3O(PO4)2]2-·H2O. Thermal Fachinformationszentrum, Karlsruhe, 76344 Eggensteinellipsoids are shown at 50% probability.(b) The basic building block Leopoldshafen (Germany), on quoting the depository number showing the cage-like structure with the terminal phosphate groups. CSD-408705. Full crystallographic details, excluding structure (c) View showing the connectivity between the cages, forming factors, have been deposited at the Cambridge six-membered rings along the b axis, through the phosphate groups.Crystallographic Data Centre (CCDC). See Information for Authors, J. Mater. Chem., 1998, Issue 1. Any request to the CCDC for this material should quote the full literature citation new anionic tin(II) oxyphosphate structure built up from the vertex linking between distorted square pyramidal SnO4 and and the reference number 1145/125.tetrahedral PO4 building blocks. The framework has the formula [Sn3O(PO4)2]2- and charge neutrality is achieved by Results and discussion the incorporation of protonated ammonium molecules; there are two [NH4]+ ions per framework formula unit. The entire The asymmetric unit consists of 13 non-hydrogen atoms [Fig. 1(a)] and final atomic coordinates for all the non- architecture is constructed by four-coordinate Sn(II) atoms and tetrahedral PO4 units.To our knowledge, this is the first hydrogen atoms are given in Table 2. This materials forms a 2758 J. Mater. Chem., 1998, 8, 2757–2760Table 2 Atomic coordinates (×104) and equivalent isotropic displacement parameters (A° 2×103) for [NH4+]2[Sn3O(PO4)2]2-·H2O Atom x y z Ueq a Sn(1) 10000 8675(1) 9852(2) 26(1) Sn(2) 7568(1) 7410(1) 7759(4) 22(1) P(1) 10000 8627(3) 5938(8) 17(2) P(2) 10000 6357(3) 5104(10) 18(2) O(1) 10000 7696(6) 8954(16) 16(3) O(2) 10000 9070(6) 7469(15) 22(4) O(3) 8237(13) 6574(4) 4197(12) 22(3) O(4) 8249(12) 8167(4) 5937(11) 18(2) O(5) 10000 6724(7) 6741(14) 20(4) O(6) 10000 9128(7) 4533(19) 27(5) O(7) 10000 5581(6) 5379(18) 26(4) N(100) 7697(28) 5155(11) 8001(43) 59(8) O(100) 10000 5932(10) 625(32) 73(7) aEquivalent isotropic U defined as one third of the trace of the orthogonalized Uij tensor.Fig. 3 Structure of [NH4+]2[Sn3O(PO4)2]2-·H2O showing the chains and the interactions between the ammonium and water molecules time an open-framework tin phosphate material is constructed along the c axis (hydrogens on the ammonium and water molecules by four-coordinated Sn(II) atoms alone.The exclusive presence are omitted). of four-coordinate Sn(II), in the current material, leads to the presence of a large number of SnKOKSn type linkages. These linkages create a situation where more than one type of oxygen Decomposition of amine molecules during hydrothermal atom has three-coordination. Oxygen atom O(1) bonds to reactions has been observed before.8 three tin atoms and two other oxygens, O(3) and O(5), are The SnKO bond lengths are in the range 2.058–2.457 A° (av.also three coordinate but bonded to two tin atoms and one 2.276 A ° ), and the OKSnKO bond angles lie between 72.7 and phosphorus atom. However, it should be noted that the three- 146.2° (av. 91.7°). These values are in excellent agreement with coordinate oxygen atoms do not create a situation where those for other tin phosphate materials where Sn atoms are PKOKP bondings occur, in accord with the principle that lies four coordinate3,4 with respect to oxygen.However, the at the heart of Lo� wenstein’s rule.13 longest bond distance [Sn(1)KO(3) 2.460 A ° ] and the largest The entire framework is constructed from a cage-like unit bond angles [O(3)KSn(1)KO(3) 145.1° and O(5)KSn(2)KO(3) as shown in Fig. 1(b). This unit, viz., the capped three-ring, 146.2°] are observed for linkages involving the three-coordiseen for the first time, is built up from three two-membered nate oxygen atoms. The PKO distances are in the range rings formed by the SnKOKSn linkages creating a bowl with 1.536–1.555 A ° (av. 1.546 A ° ) and the OKPKO bond angles are the oxygen [O(1)], bonding to three tin atoms, forming the in the range 106.7–111.6° (av. 109.5°). These values are comparbase of the bowl. The bowl is closed with a capping phosphate able to those observed in other phosphate materials. Important group forming a cage [Fig. 1(b)]. The individual cages, in bond distances and angles are presented in Table 3.turn, are connected to each other through another phosphate Thermogravimetric analysis (TGA) of the title compound group [Fig. 1(c)]. The linkage between the capped three- was carried out in the presence of nitrogen from room temperamembered rings and the phosphate groups occurs via a three- ture to 600 °C. Only one weight loss was observed in the coordinate oxygen atom [Fig. 1(b) and (c)]. This type of region of 300–400 °C, which corresponds to about 11.5% of bonding creates a heavily distorted six-membered ring along the total mass of the sample and can be directly correlated to the b axis [Fig. 1(c)]. the decomposition of very strongly hydrogen bonded water The linkages between the cage and the phosphate groups and ammonium molecules (calc. ca. 10%).The powder X-ray create zigzag infinite one dimensional chains along the a axis (Fig. 2). Along the c axis the structure presents continuous Table 3 Selected bond distances (A° ) and angles (°) for ribbons made of the caged three-rings and phosphate groups [NH4+]2[Sn3O(PO4)2]2-·H2Oa (Fig. 3). The ammonium and water molecules occupy spaces in between these ribbons/chains held together by strong multi- Sn(1)KO(1) 2.058(11) Sn(1)KO(2) 2.153(13) Sn(1)KO(3)a 2.457(10) Sn(1)KO(3)b 2.457(10) point hydrogen bonded interactions (Fig. 2 and 3). The Sn(2)KO(1) 2.104(8) Sn(2)KO(4) 2.190(10) ammonium molecules arise from the decomposition of the Sn(2)KO(5) 2.375(9) Sn(2)KO(3)b 2.400(9) starting amine used for the synthesis, viz., guanidium carbonate. P(1)KO(6) 1.54(2) P(1)KO(2) 1.555(14) P(1)KO(4) 1.554(9) P(1)KO(4)c 1.554(9) P(2)KO(7) 1.536(13) P(2)KO(3) 1.547(10) P(2)KO(3)c 1.547(10) P(2)KO(5) 1.56(2) O(1)KSn(1)KO(2) 89.4(5) O(1)KSn(1)KO(3)a 74.5(2) O(2)KSn(1)KO(3)a 82.0(2) O(1)KSn(1)KO(3)b 74.5(2) O(2)KSn(1)KO(3)b 82.0(2) O(3)aKSn(1)KO(3)b 145.1(4) O(1)KSn(2)KO(4) 88.2(4) O(1)KSn(2)KO(5) 72.7(3) O(4)KSn(2)KO(5) 87.8(4) O(1)KSn(2)KO(3)b 75.0(4) O(4)KSn(2)KO(3)b 81.4(3) O(5)KSn(2)KO(3)b 146.2(3) O(6)KP(1)KO(2) 106.7(8) O(6)KP(1)KO(4) 111.6(5) O(2)KP(1)KO(4) 108.8(5) O(6)KP(1)KO(4)c 111.6(5) O(2)KP(1)KO(4)c 108.8(5) O(4)KP(1)KO(4)c 109.3(7) O(7)KP(2)KO(3) 110.2(6) O(7)KP(2)KO(3)c 110.2(6) O(3)KP(2)KO(3)c 111.2(9) O(7)KP(2)KO(5) 108.8(10) O(3)KP(2)KO(5) 108.3(5) O(3)cKP(2)KO(5) 108.3(5) aSymmetry transformations used to generate equivalent atoms: Fig. 2 Structure of [NH4+]2[Sn3O(PO4)2]2-·H2O showing the ax-1/2, -y+1/2, z+1/2; b-x+1/2, -y+1/2, z+1/2; c-x, y, z. one-dimensional chains along the a axis. J. Mater. Chem., 1998, 8, 2757–2760 2759diVraction pattern of the decomposed sample indicates a poorly References crystalline phase, for which all the lines correspond to those 1 D. W. Breck, Zeolite Molecular Sieves: Structure, Chemistry and of the crystalline phase Sn2P2O7 (JCPDS: 35-28); it seems Use, Wiley and Sons, London, 1974; R. M.Barrer, Hydrothermal likely that an amorphous phase with a Sn5P ratio greater than Chemistry of Zeolites, Academic Press, London, 1982; R. Szostak, 352 is also present. Molecular Sieves: Principles of Synthesis and Identification, Van The synthesis of a novel tin oxyphosphate material Nostrand Reinhold, New York, 1989.containing one-dimensional chains constructed from capped 2 M. E. Davis and R. F. Lobo, Chem. Mater., 1992, 4, 759. 3 S. Natarajan, J. Solid State Chem., 1998, 139, 200. tin phosphate cages is accomplished. The exclusive presence 4 S. Natarajan and A. K. Cheetham, J. Solid State em., 1998, of four-coordinate SnII atoms along with a large number of in press.three-coordinate oxygens makes this material unique amoung 5 S. Natarajan, M. P. Attfield and A. K. Cheetham, Angew. Chem., framework tin phosphates. This new phase, together with Int. Ed. Engl., 1997, 36, 978. previously reported Sn(II) phosphate solids, illustrates pro- 6 S. Natarajan and A. K. Cheetham, Chem. Commun., 1997, 1089. found structural influences of relatively minor modifications 7 S.Ayyappan, A. K. Cheetham, S. Natarajan and C. N. R. Rao, in reaction conditions and/or changes in the starting source J. Solid State Chem., 1998, 139, 207. 8 S. Natarajan and A. K. Cheetham, J. Solid State Chem., 1997, for the tin. While the isolation of a one-dimensional solid with 134, 207. a [SnO4] distorted-square pyramidal core along with three- 9 G. H. Bonavia, R. C. Haushalter, S. Lu, C. J. O’Conner and coordinate oxygen provides information about the stereochem- J. Zubieta, J. Solid State Chem., 1997, 132, 144 . ical consequences of the Sn(II ) lone pair electrons, further 10 P. J. Zapf, D. J. Rose, R. C. Haushalter and J. Zubieta, J. Solid evaluation is required to exploit the structure-directing influ- State Chem., 1996, 125, 182; 1997, 132, 438 and references therein. ences of this unit in the presence of other organic amines in 11 G. M. Sheldrick, SHELXS-86 Program for Crystal Structure Determination, University of Go� ttingen, 1986; Acta. Crystallogr., the synthesis of potentially open-framework phosphate Sect. A, 1990, 35, 467. materials. 12 G. M. Sheldrick, SHELXS-93 Program for Crystal Structure solution and refinement, University of Go� ttingen, 1993. 13 W. Lo� wenstein, Am. Mineral., 1954, 39, 92. Acknowledgments The author thanks Professor C.N.R. Rao, FRS for his keen interest, help and encouragement. Paper 8/06412A 2760 J. Mater. Chem., 1998, 8, 2757&ndas