ton Exchange in Crystalline Zirconium Phosphates
243
-200 a,
B
also, a solid adduct poly-L-proline-LiBr has been isolat- . ed.19 On the other hand, studies of the nmr21,22 and thermodynamic proper tie^^^-^^ of solutions of various electrolytes in methanol have indicated that, under these conditions, the C1- anion is extensively solvated.
+
-CO-NH-
LiCl F=
OI
-C(O--Li)=NH-
P
+-
4- C1-
(1)
-600 Po
C10
2 4 LiCl conc. ( M I
8
Figure 1. Conformational changes of PHBG in the LiCI-methanol
solvent system, as foliawed by (0)ORD and ( 0 )viscosity.
ion is strongly solvated (eq 2). Indeed, experimental evidence has accumulated to indicate that both requirements are met. Thus, complex formation between Li+ and the amide group has been inferred from measurements of viscosity,14 heats of r e a c t i ~ n , ' ~rate of proton exchange,16 and 7Li spin-lattice relaxation tirne.l? Moreover, a crystalline N-methylacetamide-LiC1 complex has been obtained and its structure determined by X-ray analysis;18
4- nMeOH
.--L
CI-(MeOB),
(2)
(14) J. Bello and H. R . Bello, Nature (London), 194, 681 (1962). (15) J. Bello, D. J. Haas, and H. R. Bello, Biochemistry, 5, 2539 (1966). (16) T. Schleich, B. Rollefson, and P. H. von Hippel, J. Amer. Chem. SOC.,93, 7070 (1971) (17) T. Schleich, R. Gentzier. and P. H. von Hippel, J , Amer. Chem. SOC.,90, 5954 (1968). (18) D. J. Haas, Nature (London), 201, 64 (1964). (19) W. F. Harrington and J. Kurtz, J. Mol. Biol., 17, 440 (1966). (20) J. Engel, J. Kurtz, E. Katchalski, and A. Berger, J. Mol. Biol., 17, 255 (1966). (21) R. D. Green, J. S. Martin, W. B. McG.Cassie, and J. 8. Hayne, Can. J. Chem., 47, 1639 (1969). (22) R. N. Butler and M. C. R. Symons, Chem. Commun., 71 (1969). (23) C . V. Krishnan and H. L. Friedman, J. Phys Chem., 75, 3606 (1971). (24) I. M. Kolthoff and M, K. Chantooni, Jr., J. Phys. Chem., 76, 2024 (1972). (25) T. Kenjo, S. Brown, E. Held, and R . M. Diamond, J. Phys. Chem., 76, 1775 (1972).
On the Wlechariisrn of Ion Exchange in Crystalline Zirconium Phosphates. V I I. The Crystal Structure mi Bis(arnmonium orthophosphate) Monohydrate' A. Clearfield" and J. M. Troup Contribution from the Clippinger Graduate Research Laboratories, Departmentof Chemistry, Ohio University, Athens, Ohio 45701 (Received June 28, 7972) Publication costs assisted by the Ohio University Research Institute
The crystal structure of the ammonium ion exchanged phase of a-zirconium phosphate, Zr(NH4POdz. H20, has been determined. The space group is P21/c with a = 9.131(5) A, b = 5.417(5) i\, c = 19.19(1) A, and @ = 102.7(1)". There are four molecules per unit cell. The structure is essentially that of a-zirconium phosphate with the layers spread apart to accommodate the ammonium ions. Each ammonium ion is surrounded by four P-0--type oxygen atoms. Each such oxygen atom has in turn four ammonium ion near neighbors. The water molecule resides between the ammonium ions and is sufficiently close to hydrogen bond to them.
The crystalline compound a-zirconium bis( monohydrogen orthophosphate) monohydrate, Zr(HPO&HzO, hereafter referred to as a-ZrPbehaves as an ion exchanger.2 Both hydrogen ions of the orthophosphate groups are exchangeable. wit]? sodium, potassium, and ammonium ions the prckons are replaced by the cations in two stagThe first exchange reaction leads to the formation of the half-exchanged phase. This is followed by conversion of
the half-exchanged phase to a phase containing 2 mol of cation per formula weight. Since the crystal structure of a-ZrP fs known,? a knowledge of the structures of the exchanged phases would greatly aid in clarifying the nature of the (1) Acknowledgment for support of this work is made to the National
Science Foundation under Grants No. GP-10150 and GP-26050. Portions of this paper were taken from the M.S. thesis of J. M. Troup presented to the Chemistry Department, Ohio University, August 1971. The Journal of Physical Chemistry, Vo!. 77, No. 2, 1973
A. Clearfield and J. M. Troup
exchange sites and the mechanism of the exchange reactions. In this paper we report on the structure of the fully exchanged arnmonium ion phase. Experimental Section
Preparation of Crystals. Microcrystalline a-ZrP was prepared and analyzed as described previously.2 Single crystals were grown in sealed quartz tubes from a mixture of a-ZrPpowder and 12 M phosphoric acid. Several weeks at temperatures of 170-180" were required for the growth of suitable crystals. The ammonium ion exchange was accomplished by lidding concentrated ammonia dropwise to 0.6 g of a-ZrP crystals in 200 ml of water until a final pH of 11 was achieved. The mixture was allowed to stand for 40 hr to ensure complete exchange. A powder pattern of the crystals, !shown in Table I,* was identical with that of the ammonium ion exchanged phase prepared from microcrystalline a-ZrP,2 Analysis gave 8.39% N , 2.70% H, and 20.43% loss on ignition. Calculated for Zr(NH4POh.. 0 gave 8.36% N, 2.98% M, and 20.91% loss on ignin. The end product of the ignition was ZrP207 as shown by its X-ray powder pattern, X-Ray Data. The crystals are flat platelets similar in morphology to a-ZrPe7It was necessary to mount and seal the crystals in tinderliann glass capillaries along with a drop of mother liquor t o ensure that they did not change composition during data gathering. One crystal of dimensions 0.25 0.25 x i) 02 mm was mounted about the a axis and another of dimensions 0.12 X 0.12 x 0.03 mm about the b axis. S U K V photographs ~~ using the Weissenberg and precession techniques were taken with Cu K a (A 1.5408 A) andl Mo K a (A 0.7107 A), respectively. The unit cell was found t o be monoclinic with systematic absences h01 for 1 = 2rt 1 and Olio for k = 2n -+ 1. These results indicate space group ?&/e. Preliminarj unit cell dimensions were obtained from zer5 layer line precession and Weissenberg photographs which were corrected fix shrinkage by exposing a pair of fiducial spots along the horizontal and verticle directions. ccurate cell dimensions were not obtained from these . p h o ~ ~ ~ r because a ~ h s cf streaking of the spots (see subsequent Discussion). Bnstead the preliminary cell dimensions were refined by a least-squares fit9 to an X-ray powder pattern, which had been calibrated with NaCl as internal standard. The results were a = 9.131 0.005 A, b -- 5.417 bt: 0.005 kB, c == 23.50 & 0.01 A, and p = 126.85 0.10".Table I gives the indexed powder pattern. The density was ~ e t ~ r by m flotation ~ ~ e ~in a mixed solution of iod ~ ~ e t h a nand e lxdxabromoethane and found to be 2.36 f 0.04 g cm8. T h k compares to a calculated density ( V = 326.0 of 2-40gJcm3 with = 4. ~ n t e n s ~ tdata y were collected by the equi-inclination ~ , e c ~ ~ using ~ i multiple ~ ? ~ ~ ifilms and Cu K a ta were obtained about the a axis, nkl ( n = b axis, I d (pz =: 0-1). The intensities were measured by ( ~ 0 ~ ~ ~ ~ with 3 a an r i intensity s~~ strip using eye ~ s ~ ~ mThe a t ~~) h~ o.t o ~ r a pshowed ~s some streaking and ~ ~ ~ )of~spots g along a ~ the ~ direction o ~ parallel to the spinof the camera, These effects were also observed in crystwls.7 However, with a-ZrP it was possible to stals (by ~ x ~ ~ ~ ~in~polarized a t i o light) n in which very little or no disorder was evident. Not so with the amm [ ~ ~ i uemx c ~ ~ x :crystals. ~ e ~ The two crystals used for innsity m e a s u r e ~ i e were ~ ~ , ~the best of about 20 examined but still showed a ~ ~ ~ n i ~amount ~ c a noft streaking. To partially ~ o ~ n for~ this e the ~ intensities ~ ~ ~ oft the ~ spots ~ on
+
*
1:")
z
*
each film were read and the values of equivalent reflections averaged. The elongation and contraction of the spots on the top and bottom halves of the films were accounted for by multiplying the observed density of a spot by the ratio of its length to that of the standard spot. A total of 513 nonequivalent reflections were recorded. The linear absorption coefficient was calculated to be 58.2 cm-l for Cu Ka. From this value it was estimated that the transmittance varied from 25 to 75% in our experiments. Thus, it was necessary to correct for absorption effects and this was done using a locally written program suitable for thin platelets.lOa The data were then corrected for Lorentz and polarization factorslob and placed on the same scale by a locally modified version of the least-squares procedure of Monahan, Shiffer, and Shiffer .I1 Solution and Refinement of the Structure A three-dimensional Patterson function was calculated12a and the positional parameters of zirconium and the two phosphorus atoms obtained from the map. These positions were partially refined and a Fourier map prepared based only on these heavy atom positions. This map revealed the positions of the remaining atoms except for two oxygens. The positional parameters were then refined (five cycles) by the block-diagonal least-squares method.I2b Initial isotropic temperature factors were assigned as 1.5 for zirconium, 2.0 for phosphorus, 2.5 for oxygen, and 3.0 for nitrogen. A second electron density map was now prepared based on the refined parameters and this revealed the locations of the two missing atoms. All positional and isotropic temperature parameters were refined and in five cycles the residual, R -.- 2(11Fol - lFcl~~/Z\Fol, was reduced to 0.155. The data were now examined for systematic errors.12d No errors due to extinction were observed but it appeared that small errors in merging the film data had occurred. When these were corrected R was further reduced to 0.138. A difference map now revealed that the zirconium and phosphorus atoms were vibrating anisotropically. These atoms were therefore refined anisotropically
(2) A. Clearfieid and J. A. Stynes, J. lnorg. Nuci. Cham., 28, 117 (1964). (3) (a) A. Clearfield, W. L. Duax. A. S. Medina, 6. D. Smith, and J. R. Thomas, J . Phys. Chem., 73, 3424 (1969); (b) G. Alberti, E. Torracca, and A. Conte, J. Inorg. Nucl. Chem., 28, 607 (1966). (4) F. Mounier and L. Winand, Bull. SOC.Chim. Fr., 1829 (1968). (5) A. Clearfield, W. L. Duax, J. M. Garces, and A. S. Medina. J. Inory. Nucl. Chern., 34, 329 (1972). (6) A. Clearfield and J. M. Kalnins, manuscript in preparation. (7) A. Clearfield and G. D. Smith, lnorg. Chem., 8 , 431 (1969). (8) Tables I, IiI, and I V will appear following these pages in the microfilm edition of this volume of the journal. Single copies may be obtained from the Business Operations Office, Books and Journals Division, American Chemical Society, 1155 Sixteenth St., N.W., Washington, D. C. 20036. Remit check or money order for $3.00 for photocopy or $2.00 for microfiche, referriig to code number JPC-73-243. (9) W. L. Duax, Ohio University, Athens, Ohio. (10) (a) G. D. Smith, "Absorption Correction for Thin Piateiets," Ohio University, Athens, Ohio. 1965. (b) F. R . Ahrned and C. P. Saunderson, "NRC-2 Data Process,," National Research Council, Ottawa, Ont., Canada, 1966. (11) J. E. Monahan, M. Shiffer, and J. P. Shiffer, Acta Crystallogr., 22, 322 (1967). Program modified by G. D. Smith and R. W . Blessing, Ohio University, Athens, Ohio 1968. (12) Programs used in the calculation were (a) F. R. Ahrned. "NRC-8 Fourier Program," 1966; (b) "NRC-10 Structure $'Factor Least Squares," 1967: (c) M. E. Pippy and F.,,R. Ahrned, NRC-12 Scan of interatomic Distances and Angles, 1967; (d) C.,,P. Huber, "NRC-14 Error Analysis and the Agreement Summary. 1967. All programs are from National Research Council, Ottawa, Ont., Canada.
Ion Exchange in Crystalline Zirconium Phosphates
245
while all others were refined isotropically. After five cycles no further significant changes in the parameters occurred. The final R was 0,124 and the weighted residual, R‘ = [Zw(lFol -- lFcl)2/Zw(Fo)2]1/z, was 0.116. The function minimized in the least-squares procedure was Zw( lPo1 - IFk1)2.For the initial cycles of refinement the weights were U J = 1 if lFoI 5 P I ; or P1/IFoJ if IF,, > PI where PI = 25 X scale factor. Near the end of the refinement the weighting scheme was changed to w = 1/(1 + [(IF01-. f $ b / P ~ ]where ~ ) ~ PI ’ ~= 20 and PZ = 70. Neutral atom scattering factors were used in the calculation.13a The stornic scattering factor for zirconium was corrected (real part only) for the effects of dispersion.13b A final difference Fourier map showed ripples around the zirconium atom with maxima up to 2.5 e/A3. Other randomly dibtributed positive regions of up to 2 e/A3 were observed. These maxima were about twice the value of the positive regions present in the final difference map for aZrP.7 Thus, in the present case this residual density must arise not only from the usual series termination, thermal vibration, and absorption errors but also from the disorder reflected in the ~ i , r ~ ? a ~ofi nthe g diffraction maxima. Other manifestations of the disorder are the lower observed out 20%) electron densities for the atoms of this structure as coimpared LO a-ZrP and the higher estimated standard deviations. However, the correctness of the present structure Y.Sindicated by the fact that the layers duplicate the layer arrmgeiment in a-ZrP and the average bond distances in thr! Iayens of the two crystals are nearly identical.
Results and Discu:ssion The final positional parameters and isotropic temperature factors tire given in Table II. Anisotropic thermal paTABLE ll: x - R a y Positional and Thermal Parameters with Estimated Sltandard Deviations Atom
X
Y
z
a, A2
0.2504(50) 0.252(9) 0.235(10) 0.251 (43) 0.019(7) -0.023(12) 0.253(79) -0.014(7) 0.020(11) 0.248(66) 0.247(38) 0.230(27) 0.283(14) 0.238(34)
0.5142(3) 0.0845(7) 0.4050(8) 0.082(2) 0.040(1) 0.444(3) 0.163(2) 0.087(2) 0.424(2) 0.327(2) 0.453(2) 0.338(2) 0.295(3) 0.212(3)
1.4(1) 1.7(3) 1.9(4) 2.2(9j 0.9(7) 3.8(12) 1.5(7) 0.8(7) 3.2(11) 3.8(9) 3.3(10) 4.2(9) 2.3(11) 6.0(15)
-._-I___
Zv(1) P(2)
0.7717(71
P(3)
0.:?83(2) o 053(4)
(4) (5) S(6) O(7) O(9) Q(10) Q(l1) Q(12) N(1) N(2)
0.231(2)
0.202(5)
0.:’33(7) O.404(4) 3d5) 0.;!10(7) 0 793(5) 0.49615) O.WS(6) 0.471(6)
O,fIt1(7)
e zirconium and phosphorus atoms are listed in Table I l l 8 The estimated standard deviations in the least significant figures are given in parentheses. Table IV8lists the observed and calculated structure factors. As was the structure of Zr(NH4PO.&H20 is essentially that of a-ZrP with the layers moved apart to accommodatfa the aminonium ions. However, this is not evident from the positional parameters given in Table I1 because they are based on a unit cell which is different than the one used to describe a-ZrP. The relationship between
the two unit cells only became apparent at the Conclusion of this work and was confirmed by examination of zero layer line precession and Weissenberg photographs. If $he przsent cell (cell 1) is represented by a, b, c and the a-ZrP cell (cell 2) by A , B, C then A = -a, B = - b, C = c + 2a. The new cell dimensions are A = 9.131(5) A, B = 5.417(5) A, C = 19.19(1) A, and p = 102.7(1)”. The transformation matrix then gives the new positional coordinates in terms of the old as X = - x -I-22, Y = -y, and Z = + 2 . Positional parameters of the atoms for cell 2 are given in Table V and the indexing of the powder pattern based on the new ceil is shown
TABLE \I: X-Ray Positional Parameters Based on Monoclinic Cell 2a ___I_
Atom
X
0.7433 -0.062 0.474 0.111 -0.122 0.844 -0.077 0.382 0.362 0.539 0.409 0.169 0.118 -0.387
Y
0.2504 0.752 0.265 0.751 0.519 0.977 0.753 0.014
0.480 0.253 0.747 0.270 ~0.284 -0.23
z 0.4858 0.5845 0.0955 0.582 0.540 0.556 0.663 0.088 0.078 0.173 0.952 0,162 0.295 0.212
aThe positional parameters have been a!se transformed to other equivalent positions in P21/c to facilitate easy comparison to the oc-ZrP structure.
in Table I. Comparison of the values in Table V with the corresponding data for a-ZrP7 imnaediately shows the similarity between the two structures. The a-ZrP layer consists of zirconium atoms very nearly in a planar hexagonal array. Any three metal atoms form a slightly distorted equilatoral triangle and two adjacent triangles (four metal atoms) form an approximate equisid. ed parallelogram. One of the phosphorus atoms is located near the center of a triangle approximately 1.2 A above the metal atom plane. The other phosphorus atom is located near the center of the other triangle of the parallelogram but 1.2 A below the plane. Three oxygen atoms of each phosohate group are bonded to the three zirconium atoms of the triangles. Thio produces an octahedral coordination of oxygen atoms about the metal atoms. The fourth oxygen of each phosphate group points away from the plane of the layer toward an adjacent layer. These oxygens presumably bear the protons and are identified as P(2)O(7) and P(3)-0(10). An ORTEP drmwing14 of et portion of the layer in Z r ~ N ~ ~ P is ~shown ~ ~ in z Figure * ~ z1 ~ and it is seen to closely resemble the layer just described. Bond distances and angles within the layer are givkn in Tables V I and CaI.12C The average metal oxygen bond distance in the present case is quite close to the average observed in a-ZrP but the larger spread in values for (13) J. A. lbers, “International Tables for X-Ray Crystallography,” Val. Ill, Kynoch Press, Birmingham, England. 1962, (a) p 202, (b) p 213. (14) C . K. Johnson, Thermal-Ellipsoid Plot Program, ORNL-3794. The Journal of Physical Chemistry, Vol. 77, No. 2, 1973
A. Clearfield and J. M. Troup
246
TABLE VI: Interatomic Distances in
Zr (1 )-0(4)
2.06(4) 2.C4(5) 2.07(6) 2.15 (4)
o(5) O(6)
ob31 O(9)
l.Sg(6) 2.02 (5)
O(11)
Av
2.055
(A)
Zr(NH4P04)2"20
P(2)-0(4)
o(5) 0 (6) o(7)
Av P ( 3 ) - 0 (8)
O(9) O(10) O(11)
Av ,TABLE VI!:
Bond angles in Z r ( N H 4 P 0 4 ) 2 " 2 0
0(4)-Zr-0(5)
M(4)
0(4)-Zr-0(6) 0(4)-Zr-0(8) 0(4)-Zr-0(9) 0(4)-Zr-0( 11 ) O(5)-Zr-0(6)
99 (4)
0(5)-Zr-0(8) 0(6)-Zr-Q(9) 0(8)-Zr-0(9)
05(4) 85 (4)
177 (5) 93 ( 2 ) 92(31 87(:3j 89(39
1.59(5) 1.56(6) 1.52(8) 1.55(3) 1.555 1.59(7) 1.54(8) 1.49(5) 1.56(6) 1.545
(Degrees)
0(4)--P(2)-0(5) 0 (4)-P(2)-0 (6) 0(4)-P(2)-0(7) 0 (5)-P(2)-0(6) 0 (5)-P( 2 ) - 0 (7) 0 ( 6 ) - P ( 2 ) - 0 (7)
Av 0(8)-P(3)-0(9) 0(8)-P(3)-0(10) 0(8)-P(3)-0(11) 0 ( 9 ) - P ( 3 ) - 0 ( 10) 0(9)-P(3)-0(11) Q (10)-P( 3 ) - 0 (11)
Av
102(6) 118(6) 109( 11) llO(3) 116(9) lOl(10) 109.3 109(3) 98(8) 109(5) 112(9) 114(6) 114(9) 109.3
p3 Figure 2. Idealized picture of a cavity formed by two adjacent layers showing the approximate locations of the ammonium ions. The primed atoms are related to the unprimed atoms of the same number by one unit cell translation.
d
Q
Figure 3. Ammonium ion coordination and positioning in the Zr(NH4P04)2.H20 crystal. The water molecule is O(12). The number in parentheses refers to the symmetry position of the atom. Figure 1. A portion of the layer at z = in Z I ( N H ~ P O ~ ) ~ . H ~ O . The arrows indicate the A and B directions in unit cell 2. The dashed lines refer lo the psuedohexagonal cell as described in surrounded by five oxygen atoms, four arising from P-Oref 7. Qnly the nitrogen atoms below the layer are shown. groups and the fifth from the water molecule. N(1) has as near neighbors two O(7) atoms from the same layer and one O(7) and one O(10) from an adjacent layer, i.e., if the Zr( NH4P04)2.H20 reflects the poorer quality of the intwo O(7) atoms come from the topside of layer 1, then the tensity data. This is also evident in the values of the latter two atoms point down from the bottomside of the 0-P-0 bond angles which were found to range from 98 to layer above layer 1. This is shown in Figure 2 where the 118". However. the average of these angles is 109.3" for ammonium ions are placed in a cavity formed by two adboth phosohate groups. Thus, the deviations from tetrahejacent layers.7 Nitrogen-oxygen interatomic distances are dral bond angle value8 are random and reflect the errors given. in Table VIII. The N(2)-0(7)(4) distance is rather in the intensity data. long and another contact N(2)-0(8)(1) is equally close The ammonium ions occupy two different sites within but probably not involved in bonding. the crystal as shown in Figure 1. Each ammonium ion i s The Journalof Physical Chemistry, Vol. 77, No. 2, 1973
Ion Exchange in Crystalline Zirconium Phosphates
247 TABLE VIII: Interatomic Distances Involving Ammonium Ion
*O?'
!
,
/--. Y
N ( 1 ) - 0 ( 7 ) (2)' 0(7)(4) 0(7)(2) 0(10)(3) O(12) (3) N (2)-O( 12) (3) 0 (1 0) (1) O(10) (3) ' 0(10)(1)' 0(7)(4) 0(8)(1)
I
ZRI
2.72(9) 2.76(7) 3.03(41) 3.05(9) 2.94(9) 2.77(7) 2.80(38) 2.85(8) 2.90(38) 3.17(8) 3.13(10)
N(1) (1)-N(2) (3)' N(1)(3) N(1)(3)' N(2)(3) N(2) (1) - N ( l ) (3) N(l)(3)' N(2)(3)' ~(2)(3)"
3.49 3.65 3.65 3.86 3.49 3.86 3.88 3.88
@Thesecond parenthasized number for the oxygen and nitrogen atoms refers to the 4c symmetry positions for P 2 , / c as given in "International Tables for X-Ray Crystallography," Vol. I, Kynoch Press, Birmingham, England, 1952, p 99. Primed atoms are related to unprimed atoms of the same designation by a unit cell translation. N(2) (3)" is one cell translation away from N ( 2 ) (3) and two cell translations from N 12) ( 3 ) ' .
04
TABLE IX: Interatomic Distances and Possible Hydrogen Bonds Involving the Water Molecule
NI
Figure 4. A portion of the Z r ( N H 4 P 0 4 ) 2 " 2 0 structure showing the coordination of the zirconium atom, two of the six phosphate groups bonded to the metal atom, and the arrangement of ammonium ions
