Structural investigations of unsubstituted polymethylenediphosphonic

Mar 1, 1977 - Ravi Shankar , Nisha Singla , Meenal Asija , Gabriele Kociok-Köhn , and Kieran C. Molloy ... Crystal A. Merrill and Anthony K. Cheetham...
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Structural Investigations of Unsubstituted Polymethylenediphosphonic Acids. 1. The Crystal and Molecular Structure of Methylenediphosphonic and Ethane-I ,2-diphosphonic Acids' $. W. Peterson,* E. Gebert, A. H. Reis, Jr.,' M. E. Druyan,' 0. W. Mason, and D. F. Peppard Chemistry Division, Argonne National Laboratoty, Argonne, Illinols 60439 (Received May 24, 1976; Revised Manuscript Received December 20, 1976) Publication costs assisted by Argonne National Laboratory

A previously discussed correlation between an increase in hydrogen-bond strength with a decrease in P-O(H) distance in methylene-substituted diphosphonic acids is not upheld for hydrogen bonding in unsubstituted polymethylenediphosphonic acids. Strong asymmetric hydrogen bonds link -(OH)P(=O)OH moieties into infinite chains spiralling about 21 axes and cross linking the molecules to form three-dimensionalmolecular chains in both methylenediphosphonic acid (PCP), CH2(P03H2)2,and ethane-1,2-diphosphonicacid (PC2P), (CH2)2(P03H2)2.PCP and PC2P show short P-C bond distances (1.793(2) and 1.786(2) A, respectively) as compared with substituted diphosphonic acids (- 1.83 A). PCP crystallizes in the monoclinic space group, Pl/c, with unit cell dimensions a = 7.836(4), b = 5.497(3),c = 13.766(7)A, P = 103.60(2)', and 2 = 4. PC2P crystallizes in the monoclinic space group P21/c with unit cell dimensions, a = 5.856(2),b = 5.272(2), c = 11.665(4) A, /3 = 100.69(2)O, and 2 = 2. Three-dimensionalx-ray data were collected for both compounds using a GE XRD-490 automated diffractometer. Full-matrix least-squares refinement of PCP gave a final RF = 0.036 for a total of 1017 unique reflections, while a similar refinement of PCZP gave a final RF = 0.046 for 1019 unique reflections. Implications for cation coordination and liquid-liquid extraction chelation sites are discussed for ionized PCP and PC2P.

Introduction Considerable interest has been focused on methylenesubstituted and unsubstituted diphosphonic acids, because of their favorable binding characteristics toward metal cation^.^ Recently, structural investigations of both types of diphosphonic acids have appeared within this J o ~ n a l ? 1 ~ Ethane-1-hydroxy-1,l-diphosphonic acid monohydrate, (CH3)C(OH)(P03Hz)z.H20,4 gave evidence for what the authors believed to be a correlation in disphosphonic acids between hydrogen bond strength and phosphorus-oxygen bond length. The authors noted that a decrease in the P-O(H) bond length correlated with a decrease in hydrogen bond distance and a lengthening of the related P=O distance. They explained these effects in terms of a delocalization and buildup of negative charge density on the phosphonyl oxygens due to attraction of the phosphonic protons to their hydrogen-bond acceptor. However, we believe what the authors were observing was the P-O(H) bond shortening and P=O bond lengthening which occurs in very strong hydrogen bonds due to the formation of a more symmetrical hydrogen bond, not a general correlation. A recent structural study of CH2(PO3H& PCP; showed that the above correlation does not hold for a molecule where longer hydrogen bonds are involved, however, an earlier determination of PCP showed somewhat different bond distancesS6Therefore, we wish to report the very precisely determined molecular and crystal structures of CH2(P03H2)2, PCP, and (CH&(PO3HzP)z, PC2P. The recently completed structural determination of (CH2)3(P03H2)2, PC3P, will be published shortly. Highly accurate structural data on a number of diphosphonic acids will be necessary in order to further evaluate the small (0.01 A) differences in bond lengths involved in the above correlation. Experimental Section Collection and Reduction of X - R a y Data. Samples of PCP and PC2P were prepared by the method of Moedritzer and Irani.7 Recrystallization from methanol reThe Journal of Physical Chemistty, Vol. 81, No. 5, 1977

TABLE I: Experimental Details for PCP Cell constants: T = 27 O C , a = 7.836(4) A , b = 5.497(3) A , c = 13.766(7) A , p = 103.60(2)

O

Cell volume: 576.33 A 3 Molecular weight of asymmetric unit: 176.001

g/mol Calculated density: 2.026 g ~ r n - ~ Measured density: 2.026(2) g cm-3by flotation in CH3C1 t CH,Br 2=4 Space group: P2,lc (C:h ;no. 1 4 ) Radiation: Mo K a , h = 0.71069 (Ross 1 filter) Attenuator: Cu foil at 1 0 000 Hz Take-off angle: 2.0 Maximum 20 : 50.0 (+hkZ) Scan type: coupled e-2e Scan width: 1.6 Scan speed: 0.1 steps Counting time: 4 s/step (background 16 s each side of peak) O

Crystal:

b axis mounted Volume = 0.859 X loF5cm3 (-0.01 x 0.01 x 0.0176 cm) Absorption coefficient = 7.165 cm-' Maximum transmission factor = 0.89 Minimum transmission factor = 0.86 Number of reflections collected = 1017 R F for all reflections = 3.60% (1017) R F for reflections where F , > l u F , = 3.39% (965) WRFZ

r-

8.96%

sulted in the formation of clear triangular-prism crystals. (a) PCP. A crystal with approximate dimensions 0.010 x 0.010 x 0.013 cm was mounted along the b axis for study. Preliminary oscillation, Weissenberg, and precession photographs revealed 2/m Laue symmetry and the systematic absences h01 for 1 = 2n + 1and OkO for k = 2n + 1. This is consistent with the centrosymmetric monoclinic space group R 1 / c [Cq,; no. 141. A GE XRD-490 automated x-ray diffractometer was used for data collection. Accurate unit-cell parameters were obtained by least-squares from the angular coordinates of 14 reflections measured in a 20 range of 27-33'.

Structural Investigations of Unsubstituted PolymethylenediphosphonicAcids

TABLE 11: Experimental Details for PC,P Cell constants: T = 25 ‘C, a = 5.856(2)A , b = 5.272(2) A , c = 11.665(4) A , p = 100.69(2) ’ Cell volume: 353.88A3 Molecular weight of asymmetric unit: 190.28 g/mol Calculated density: 1.783 g cm-3 Measured density: 1.757g cmm3 by flotation in CH3Cl t CH,I,

2=4 Space group = P2,/c(C:, ; no. 14) Radiation: Mo Kcu, h = 0.71069(Ross 1 filter) Attenuator: Cu foil at 10 000 Hz Take-off angle: 2 Maximum 20:60.0’ (khkl) Scan type: coupled e -28 Scan width: 1.6 Scan speed: 0.1 steps Counting time: 4 s/step (background 16 s each side of peak) Crystal: b axis mounted cm3 Volume = 0.144x (0.036X 0.032X 0.013cm) Absorption coefficient = 11.874cm-’ Maximum transmission factor = 0.86 Minimum transmission factor = 0.67 Number of reflections collected = 1064 R F for all reflections = 4.58% (1017) R F for reflections where F , > l o F , = 4.36% (980) WRF= Z 12.6% O

O

Details specific to data collection and analysis are given in Table I. A description of the instrumentation used in this data collection has been given previously.s (b) PC2P. A clear parallellopiped crystal with dimensions 0.035 X 0.032 X 0.012 cm was mounted along the b axis. Preliminary x-ray photographs established the space group P21/c also for PC2P. The techniques for obtaining space group information, unit cell constants, and data collection and reduction were similar to those described above. Details specific for PC2P data collection are given in Table 11. Solution and Refinement of the Structures. (a) PCP. The structure was independently solved; the positions of the phosphorus atoms were determined from a three-dimensional Patterson map. A Fourier map based on the phosphorus positions (RF = 0.68) revealed the positions of the six oxygen and the one carbon atom (RF= 0.37). The positions and isotropic thermal parameters were refined by full-matrix least-squares techniques converging at an RF = 0.139. Four cycles of anisotropic least-squares refinement converged at RF = 0.060. A difference Fourier map clearly revealed the positions of all six hydrogen atoms. Anisotropic least-squares refinement of all heavy atoms and isotropic least-squares refinement of all hydrogen atoms converged after three cycles to RF = 0.036 for 1017 unique reflections, Rwp = 0.089, and E2 = 1.38, where RF = Z: IIFoI- IFc~I/Z:Fo RwF2 =

[Z: w(FO2 - F:)’/Z:

WF:]~”

Z: 2 = [I:w(F2 - F:)2/(No - N R ) ] ’ I 2

No is the number of independent observations and NRis the number of parameters varied. A final difference Fourier map revealed no peaks above 0.55 e/A3. No parameter varied more than A/u = 0.03 in the last cycle of the refinement. Table I11 is a listing of the final positional parameters of all atoms and isotropic thermal parameters for hydrogen atoms in PCP. Table IV gives the anisotropic thermal parameters for non-hydrogen atoms in PCP.

467

TABLE 111: Final Positional Parameters and Isotopic Thermal Parameters for PCPa Atom

x

Y

B

z

P ( l ) 0.23569(7) 0.34786(10) 0.27013(4) P(2) 0.28647(8) 0.36825(11) 0.05649(4) C 0.2105(4) 0.5128(5) 0.15509(17) 0.32868(14) 0(1) 0.4299(2) 0.3581(3) 0.32815(12) O(2) 0.1120(2) 0.4498(3) 0.24482(13) O(3) 0.2099(3) 0.0742(3) 0.08854(12) O(4) 9.4706(2) 0.2766(3) 0.02100(15) O(5) 0.1488(2) 0.1647(4) O(6) 0.2604(3) 0.5575(4) -0.02907(13) H(l) 0.267(3) 0.650(5) 0.167(2) H(2) 0.097(4) 0.546(5) 0.134(2) H(3). 0.346(4) 0.595(6) -0.042(2) H(4) 0.460(4) 0.493(6) 0.349(2) H(5) 0.120(5) 0.051(7) 0.223(2) H(6) 0.148(4) 0.124(5) -0.029(2) a

2.2(7) 2.4(6) 3.1(8) 3.6(8) 4.0(9) 2.6(7)

Estimated standard deviations are given in parentheses.

TABLE IV : Anisotropic Thermal Parametersa ( x 10“)for P C P ~ B2,

114(2) 137(2) 123(8) 149(7) 194(6) 137(6) 156(6) 266(8) 267(8)

B33

15(1) 15(1) 22(1) 31(1) 18(1) 26(1) 30(1) 20(1) 27(1)

The anisotropic thermal parameter is in the form: expi-(Bllh2 t BZ2kZ t BJ2 t 2B,,hk t 2B,,hl t Standard deviations are given in parentheses. 2B,,kl)]. TABLE V: Final Positional Parameters and Isotropic Thermal Parameters for PC,Pa Atom

X

V

z

0.24003(8) 0.19065(9) 0.14087(4) 0.1312(3) 0.0284(4) 0.00754(17) 0.2103(3) 0.0394(3) 0.24619(14) 0.4968(3) 0.2354(4) 0.13254(17) 0.1215(3) 0.4546(3) 0.13885(15) 0.233(4) -0.113(5) 0.002(2) 0.173(4) 0.117(4) -0.056(2) -0.032(5) -0.013(6) 0.327(2) 0.448(7) -0.150(7) 0.320(3) a

B

2.2(5) 1.4(4) 2.8(6) 4.9(9)

Estimated standard deviations are given in parentheses.

(b) PC2P. The phosphorus, carbon, and oxygen atoms were located from a Patterson map (RF= 0.48). Three cycles of isotropic full-matrix least-squares refinement converged at an RF = 0.13. Four additional cycles of anisotropic least-squares refinement converged at an RF = 0.053. The hydrogen atoms were located quite easily at this stage from a difference Fourier map. Anisotropic (non-hydrogen atom) and isotropic (hydrogen atom) least-squares refinement converged after four cycles to a final RF = 0.046 for 1019 reflections, R,p = 0.126, and E2 = 2.04. A final difference Fourier revealed no electron density above 0.68 e/A3. No parameter varied by more than A/u = 0.10 in the last cycle of refinement. Table V is a listing of the final positional parameters of all atoms and isotropic thermal parameters for hydrogen atoms on PC2P, while Table VI lists the anisotropic thermal parameters of all non-hydrogen atoms of PC2P. A comparison of the observed and calculated structure-factor amplitudes is available as supplementary material (see paragraph at end of text regarding suppleThe Journal of Physlcal Chemlstv, Vol. 81, No. 5, 1977

Peterson et al.

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TABLE VI: Anisotropic Thermal Parameters4 (X io4)for PC,P* Atom P C 0(1) O(2) O(3)

'11

111(2) 121(5) 162(4) 132(4) 260(6)

'33

,2'

148(2) 188(6) 215(5) 359(7) 150(5)

'1,

,2'

B13

H4

32(1) -11(1) 13(1) -10(1) 34(1) -10(5) 13(2) -14(2) 39(1) 32(4) 13(2) 17(2) 66(2) -84(5) 34(2) -76(3) 51(1) 33(4) 50(2) 7(2)

a The form of the anisotropic thermal parameter is exp{-(Bl,h2 + B,,hZ + B3,ZZ+ 2B,,hk + 2B,,hl t Estimated standard deviations are given in 2B,,kZ)]. parentheses.

TABLE VII: Interatomic Distances for PCP4 Distance,

Distance,

Bond (a) Intramolecular Distances P(1)-0(1) 1.547(2) P(2)-0(4) P(1)-0(2) 1.502(2) P(2)-0(5) P(1)-0(3) 1.546(2) P(2)-0(6) P( 1)-c 1.795(3) P(2)-C C-H( 1) 0.87(3) C-H(2)

1.493( 2) 1.551(2) 1.549(2) 1.791(2) 0.88(3)

Bond

a

a

Figure 1. The PCP molecule showing atom labels and bond distances.

(b) Non-Hydrogen Bonding Interactions to 3.3 a O(1)- - - 0 ( 2 ) 2.540(3) O(5)- - 0 ( 6 ) 2.487(3)

-

-O(5)- - - -0(3) O(3)- - - - 0 ( 6 ) P(1)- - - -P(2)

O(1)-- - -0(3) 2.409( 3 ) O(5)- - - -0(5)' O(2)- - - - 0 ( 3 ) 2.578(3) O(4)- - - - 0 ( 6 ) 2.549(3) O(4)- - - - 0 ( 6 ) 2.599(3)

2.902(4) 3.046(3) 3.129(3) 3.061(2)

Estimated standard deviations are given in parentheses. TABLE VIII: Interatomic and Torsion Andes for PCP4 (a) Interatomic Angles 112.9(1) 0(4)-P(2)-0(5) 114.6( 1 ) O(4)-P( 2)-0(6) 0(1)-P(1)-0(3) 102.3( 1) O(5)-P( 2)-0(6) c-P( 1)-O( 1) 109.4(1) C-P(2)-0(4) c-P( 1)-O( 2) 109.3(1) C-P(2)-0( 5) C-P( 1)-O( 3) 108.1(1) C-P(2)-0(6) P(1)-c-P( 2) 117.2(1) H(l)-C-H(2)

O(1)-P( 1)-O( 2) O(2)-P( 1)-0(3)

113.7(1) 113.4(1) 106.7(1) 113.3(1) 103.2( 1) 105.7(1) 108(21)

(b) Torsion Angles O(4)-P( 2)-P(1)-0(3) 22.3( 1) 0(6)-P(2)-P(1)-0(2) 34.5(2) O(5)-P( 2)-P( 1)-O( 1) 34.9( 1 ) a

Estimated standard deviations are given in parentheses.

mentary material) for both PCP and PC2P. Scattering factors for neutral atoms were taken from the compilation of Cromer and Wabe~-.~The values for phosphorus, oxygen, and carbon atoms were corrected for anomalous dispersion using the values of Cromer.lo Computational programs used for these structural de~ collection and reduction; terminations were R T M O N , ~data DATA LIB,^^ absorption, Lorentz, and polarization corrections; S5xFLs,l3 least-squares refinement; S5FOUR,13 Fourier ~ and angles calculation; and synthesis; O R F F E , ~distances ORTEP,14 molecular drawing. All calculations were carried out on the Xerox Sigma V Computer of the Chemistry Division, ANL, and the IBM 370/195 of the Applied Mathematics Division, ANL. T h e Molecular and Crystal Structures. (a) PCP. Intramolecular bond distances are given in Table VII; the corresponding interatomic angles and torsion angles are given in Table VIII. The hydrogen bond distances are given in Table IX. Figure 1 is a drawing of the PCP molecule indicating atom labeling. Molecular packing and hydrogen bonding are shown in Figure 2. The non-hydrogen positions and the bond distances and angles derived here for PCP are in good agreement with those of Calv~S,~ The Journal of Physical Chemistw, Vol. 8 1, No. 5, 1977

Figure 2. The unit cell of the PCP crystal showing molecular packing and hydrogen bonding.

TABLE IX: Hydrogen-Bonded Distances and Bond Angles in PCP4 Bond 0(6)-H(3)-0(4) 0(6)-W3) o ( 4 j - ~ ( j3 0(1)-H(4)-0(4) 0(1)-H(4)

Distance, A

Angle, deg

2.54 2( 3) 0.75(4) 1.85(4j 2.604(3) 0.81(4) i.80(4j 2.565(3) 0.71(4) 1.87(4) 2.677(3) 0.73(3) 1.95(4)

170(4) 172(4) 173(4) 170(3)

Estimated standard deviations are given in parentheses.

but differ substantially from the earlier report! Therefore, our present discussion will focus only on hydrogen bonding involving the PCP molecule. Every phosphonyl hydrogen of PCP is asymmetrically bonded to two oxygen atoms to form an extensive three-dimensional network of hydrogen bonds involving all molecules of the unit cell. Each P=O oxygen is an acceptor for two intermolecular hydrogen bonds while each P-O(H) oxygen is bonded to a single hydrogen. Three distinctive hydrogen bonded configurations are found (a) 16-memberedrings sitting at an inversion center containing

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Structural Investlgations of Unsubstituted Polymethylenediphosphonic Acids

TABLE X: Interatomic Distances and Hydrogen-Bonded Distances and Angles in PC,Pa Bond Distance, A Angle, deg (a) Interatomic Distances P-O( 1) 1.501(2) 1.543(2) P-O( 2) 1.553( 2) P-0(3) P-c 1.786(2) C-H( 1) 0.97(3) C-H( 2) 0.94( 2) 1.544(4) C-C' p. - -p 4.395(3)

-

(b) Hydrogen Bonds 0(3)-H(3)-O( 1) 2.527(2) 174(4) 0(3)-H(31 0.74(4) 0(1)-H(3) 1.86(4) O(2)-H( 4)-O( 1) 2.543(3) 152(4) 0.85(4) O( 2 )-H(4 1 1.79(4) 0(1)-H(4) Estimated standard deviations are given in parentheses.

Figure 3. A 16-membered hydrogen bonded-ring formed by several PCP molecules.

TABLE XI: Interatomic Angles in PC,Pa Angle O(1)-P-0(2) O(l)-P-O( 3) O(2)-P-O( 3) C-P-O( 1) c-P-O( 2) C-P-O( 3) C'-c-P

Figure 4. An eight-membered hydrogen-bonded rlng formed by two PCP molecules.

a H4

Figure 5. The PCpPmolecule showing atom labels and bond distances.

four hydrogen bonds involving H(4) and H(6) where 0(1)-H(4)-0(4) = 2.604(3) A, and 0(5)-H(6)-0(2) = 2.677(3) A (see Figure 3); (b) eight-membered rings sitting a t an inversion center containing two hydrogen bonds involving H(3) where 0(6)-H(3)-0(4) = 2.542(3) A (see Figure 4); (c) hydrogen-bonded chains which spiral around the b axis (the 21 screw axis) and contain hydrogen bonds involving H(5) where 0(2)-H(5)-0(3) = 2.565(3) A. The lengths of the various hydrogen bonds probably reflect the constraints of the system of which they are a part, ie., the hydrogen bonds of the 16-membered ring are longer than

Deg 113.3(1) 111.6(1) 107.5(1 ) 112.4(1) 102.3( 109.2(1) 1) 112.3(2)

Estimated standard deviations are given in parentheses.

those of the more constrained eight-membered ring and spiral configurations. We have recently shown8J6that di-tert-butylphosphinic acid exists in the solid state as a distinct phosphinic acid dimer composed of an eightmembered asymmetrically h drogen-bonded ring with an 0-H-0 distance of 2.486(9) In PCP, no intramolecular hydrogen bonding exists even though many intramolecular 0-0' interactions are within 2.4-3.0 A. (See Table VII.) (b) PCzP. Table X contains intramolecular bond distances and hydrogen bond distances and angles; bond angles and torsion angles are given in Table XI. Figure 5 is a drawing of the PC2P molecule with the atoms identified. Molecule packing and hydrogen bonding within the unit cell are shown in Figure 6. Molecules of PCzP pack within the unit cell such that the center of the C-C' bond is located at a center of in-

1.

Figure 6. The unit cell of the PCpP crystal showlng molecular packlng and hydrogen bonding. The Journal of Physbal Chemistry, Vol 81, No. 5, 1977

Peterson et al.

470

bond angle of 112.3(2)O in PC2Pmay be compared to the P(l)-C-P(2) bond angle of 117.2(1)' in PCP indicating reduced repulsion due to substitution of the less polar CH2 group. From previous NMR and IR results? a significant amount of P-P coupling is shown for n I3 in this diphosphonic acid series.

Figure 7. An 18-membered hydrogen-bonded ring formed by several PCpP molecules.

version (i), thus the asymmetric unit is half of the PC2P molecule. For n odd, molecules within the series (CH2)JP03HJ2 cannot have an inversion center; however, when n is even, as in the present case, an inversion center is possible. The presence of the center largely determines the conformation of PC2P. Thus the CH2 groups are staggered when viewed down the C-C bond as are the O=P(OH)OH moieties when viewed down the P-P vector. In addition, the C-C(H)H is staggered with respect to O=P(OH)OH when viewed down the C-P bond although this is not required by symmetry. This latter configuration must be determined by packing and hydrogen bonding in which each phosphonyl oxygen is-an acceptor for two hydrogen bonds involving OH groups from two separate PC2P molecules. Infinite hydrogen bond spirals centered on each 21 axis (parallel to b) extend throughout the lattice similar to those previously observed for a number of substituted phosphoric and phosphinic acids16

- -HO\ \ I

0-H-0

I

P

I \

P

I \

0- -

In addition, there are large 18membered hydrogen-bonded rings (see Figure 7) formed in which two PC2Pmolecules are linked through hydrogen bonding to two phosphonyl-oxygen acceptors from another pair of molehles. In effect, the infinite spirals cross link PC2P molecules in forming the large rings (see Figure 7). There is no intramolecular hydrogen bonding even though it is a steric possibility. Each hydrogen is asymmetrically bound to two oxygens with P 4 oxygens bonding to two hydrogens as in the PCP case. The hydrogen bond lengths are: 0(3)-H(3)-0(1) = 2.527(2) A where 0(3)-H(3) = 0.74(4) A while 0(1)-H(3) = 1.86(4) 8,and 0(2)-H(4)-0(1) = 2.543(3) A where 0(2)-H(4) = 0.85(4) A while 0(1)-H(4) = 1.79(4) A. These hydrogen bonds are somewhat shorter than those found for the PCP molecule. The shortening probably results from the better packing which the molecules can achieve because of the inherent center of symmetry of the PC2P molecule. The phosphorus atom is tetrahedrally coordinated to three oxygen atoms and one carbon atom with bond distances of P-O(1) = 1.501(2) A, P-O(2) = 1.543(2) A, P-0(3) = 1.553(2) A, P-C = 1.786(2) A, and bond angles of O(l)-P-O(2) = 113.3(1)', O(l)-P-O(3) = 111.6(1)', 0(2)-P4(3) = 107.5(1)', C-P-0(3) = 109.2(1)'. The bond length of P-0(1), the phosphonyl group, shows considerable double bond character while P-0(2) and P-0(3) have normal lengths for P-OH bonds. The 'lr character of O(1) is also reflected in the bond angles involving O(1) which are seen to be large. The P-C-C-P chain is planar due to the inversion center on the GC' bond. The P-C-C' The Journal of Physical Chemistry, Vol. 81, No. 5, 1977

Discussion The possible correlation between hydrogen bond strength, decreased P-O(H) distance, and increased P 4 distance is not upheld for the PCP and PC2P materials. Our structural findings support Calvo et al.6on the PCP structure and we extend the information about the phosphonic acids with the PCzP study. In PCP, P a ( - H ) distances are shown to be equal within errors of the estimated standard deviations; however, hydrogen-bonding distances varied from 2.542(3) to 2.677(3) A. Also, each P=O is involved in two hydrogen bonds of different length. In PC2P, P-O(H) distances differ by 0.01 A with the longer hydrogen bond associated with the shorter P-O(H) distance in direct conflict with the above correlation. As in PCP, the P=O group also bonds to two different hydrogen atoms. A correlation between P-O(H) distances and hydrogen-bonded distances for all diphosphonic acids is thus inappropriate. In the ethane1-hydroxy-1,l-diphosphonicacid material4 very short hydrogen bonds (2.450(4) and 2.479(4) A) exist compared to 2.527(2) A in PC2P and 2.542(2) A in PCP. It seems likely that the correlation observed in the case of ethane-1-hydroxyl-1,l-diphosphonic acid is appropriate for very strong hydrogen bonds and merely reflects the formation of more symmetrical hydrogen bonds at these short spacings causing the P-O(H) and P=O groups to become more nearly equivalent. In the PC2P molecule, a slight decrease in the average P-C distance is observed compared to the PCP molecule, 1.786(2) and 1.793(2) A,respectively. This small difference resulting from the introduction of an additional CH2group probably stems from weaker repulsive forces between the methylene hydrogens and the phosphonic acid groups. These P-C distances are substantially shorter than those in the substituted methylenediphosphonic acids; for example, in the ethane-1-hydroxy case, P-C bond distances of 1.832 and 1.840 A are The longer distances in the latter example are probably due to the presence of electron-withdrawing substituents on the methylene carbon. Ionized forms of PCP and PC2P will have up to six chelation sites where actinide and lanthanide cations may be bound. Assuming a chelation involving intra diphosphonic coordination, varying the size of the carbon chain will cause the bite of the ligand to change, therefore varying the size of the metal-ligand chelation rings which can be formed, their conformation, and stability. Cation extraction characteristics of these materials will be discussed in a subsequent report. Supplementary Material Available: A listing of calculated and observed structure factor amplitudes (16 pages). Ordering information is given on any- current masthead page.

References and Notes (1) Work performed under the auspices of the U.S. Energy Research and Development Administration. (2) Department of Biochemistry, Loyoia Unhrersity School of Dentistry, Maywood, Ill. 60153. (3) (a) D. F. Peppard, Annu. Rev. NucL Sci., 21, 365-398 (1971); (b) E. K. Hulet and D. D. Bode, MTP Int. Rev. Sci, Inofg. Chem., Ser. One 7 , 1-45 (1972); (c) C. F. Cailis, A. F. Kerst, and J. W. Lyons,

47 1

Structural Investigation of Methylenediphosphonic Acids

(4) (5) (6)

(7) (8) (9)

“Coordination Chemistry”, S. Kirschner, Ed., Plenum Press, New York, N.Y., 1969, pp 223-247; (d) V. A. Uchtman, J Phys. Chem., 76, 1304 (1972). V. A. Uchtman and R. A. Gloss, J. Phys. C h h , 78, 1298 (1972). D. De La Matter, J. J. McCullough, and C. Calvo, J Phys. Chem., 77, 1146 (1973). F. M. Lovell, Abstracts of the American Crystallographic Association, July 26-31, 1964, J-11, Bozeman, Mont. K. Moedritzer and R. R. Irani, J Inorg. Nucl. Chem., 22, 297 (1961). M. E. Druyan, A. H. Rels, Jr., E. Gebert, S. W. Peterson, G. Mason, and D. F. Peppard, J. Am. Chern. SOC.,98, 4801 (1976). “International Tables for X-ray Crystallography”, Vol. IV, Kynoch Press, Birmingham, England, 1974, p 71.

(10) “International Tables for X-ray Crystallography”, Vol. IV, Kynoch Press, Blrmlngham, England, 1974, p 148. (1 1) An IBM 1130 program written by J. Scherer at ANL. (12) An IBM 3701195 program written by H. A. Levy. (13) SSFOUR, SSXFLS, and SSFFE are Sigma 5 versions of the programs: FOURIER by R. J. Dellaca and W. T. Robinson, ORXFLSB written by W. R. Busing and H. A. Levy, and ORFFEB written by W. R. Busing and H. A. Levy. (14) ORTEP written by c. Johnson. (15) A. H. Reis, Jr., S. W. Peterson, M. E. Druyan, E. Gebert, 0. W. Mason, and D. F. Peppard, Inorg. ..Chem, 15, 2748 (1976). (16) D. Fenske, R. Mattes, J. Lons, and K. F. Tebbe, Chern. Ber., 106, 1139 (1973), and references therein.

Structural Investigations of Methylenediphosphonic Acids. 2. The Molecular and Crystal Structure of Propane-I,3-diphosphonic Acid’ E. Gebert, A. H. Reis, Jr.,* M. E. Druyan,2 S. W. Peterson,* 0. W. Mason, and D. F. Peppard Chemistry Division, Argonne National Laboratory, Argonne, Illlnols 60439 (Received May 24, 1976; Revlsed Manuscript Received December 20, 1976) Publication costs assisted by Argonne National Laboratory

Propane-1,3-diphosphonicacid, (CH2)3(P03H2)z, PCsP, crystallizes in the noncentrosymmetric, monoclinic, space group Pc [Ct, no. 71 with unit cell constants a = 9.540(2), b = 9.964(2), c = 9.705(2) A, p = 118.90(1)’, and 2 = 4. The asymmetric unit of PC3Pconsists of two crystallographically unique molecules. The structure was solved by a combination of direct methods, Fourier, and least-squares refinement techniques; the final RF = 0.024 for 1412 independent unique reflections. The two PC3P molecules within the asymmetric unit have quite different conformations. Hydrogen-bonded rings of differing size shape the P-C-C-C-P backbone of one PC3P molecule into an almost planar conformation,while the backbone of the other molecule is distorted into a distinctive nonplanar conformation. Eight intermolecularhydrogen bonds of lengths varying from 2.579(8) to 2.711(5) 8, are involved in four rings of 10,12,14, and 16 members. The hydrogen bond length appears to be correlated with the size of the hydrogen bonded ring in which it participates.

Introduction Chemical and physical properties have been measured for the series of methylenediphosphonic acids,. (CH2)n(P03H2)2, where n = 1-6.3 The observed melting points, IR spectra, and NMR spectra show interesting changes as n increases. In a previous paper? we have discussed the molecular and crystal structures of (CH2)(P03H2)2,PCP, and (CHz)z(P03H2)2, PC2P. Each of these materials contains an interwoven network of strong intermolecular hydrogen bonds formed between phosphonic acid groups. The two halves of P-C-C-P are related by a center of symmetry hence the backbone is precisely planar. The planar conformations affect both the physical and chemical properties of each material. Planarity of the backbone is not required for (CH,),(PO3Hz)2, PC3P, hence this molecule is likely to be structurally quite different than PCP or PC2P. An x-ray structural investigation of PC3P was undertaken in order to investigate the correlation of structure with chemical and physical properties and to better define the potential binding sites for metal ions. Experimental Section Collection and Reduction of X-Ray Data. Propane1,3-diphosphonicacid, PC3P, was prepared by the method of Moedritzer and 11-ani.~ Crystals of sufficient size and quality were grown from a benzene solution by slow evaporation. A diamond shaped plate (0.038 X 0.038 X 0.025 cm) was selected for data collection. Preliminary oscillation, Weissenberg, and precession photographs showed 2/m Laue symmetry and gave the systematic

TABLE I: Experimental Details for PC,P Formula: (CH,),(PO,H,), Formula weight: 204.06 g equiv Space group: Pc [C,’,no. 71 Extinctions: h01,l = 2n + 1 Cell constants: a: = 9.540 (2), b = 9.964 (2), c = 9.705 (2) A, p = 118.90 (1)” Cell volume: 807.67 A 3 Calculated density: 1.68 g cm” Measured density: 1.66 g cm-, [by flotation in HCCl, + HCBr, ] Number of molecules in the asymmetric unit: 2 (2= 4) Radiation: (data collection) M o Ka, k = 0.71073, 2” take-off angle Absorption coefficient: 5.214 cm-’ Maximum 28 : 50” Scan width: 1.6” Scan speed: 0.1” steps Counting time: 4 s/step (background 1 6 s each side of Peak) Crystal: b axis mounted Volume = 0.296 x cm3 (0.038 x 0.038 x 0.025 cm) Maximum transmission factor = 0.90 Minimum transmission factor = 0.86 Number of reflections above u = 1391 Number of independent reflections = 1412 RF factor for all reflections = 0.024 RF factor for all reflections above 1 u = 0.024 W R F Z= 0.057

absences as hO1 for 1 = 2n + 1,which is consistent with the two monoclinic space groups, Pc [Cf, no. 71 and P 2 / c [C&, no 131. Accurate unit-cell lattice constants were determined by least-squares analysis of x-ray powder diffraction The Journal of Physlcal Chemlstv, Vol 81, No. 5, 1977