1146
D. DeLaMatter, J. J. McCullough, and C. Calvo
Crystal Structure of Methylenediphosphonic Acid D. DeLaMatter, J. J. McCullough, and C. Calvo* Department of Chemistry, McMaster University, Hamilton. Ontario, Canada (Received September 27, 7972) Publication costs assisted by The National Research Council of Canada
Methylenediphosphonic acid is monoclinic with space group p 2 1 / c and has lattice parameters a = 7.840(9), b = 5.494(3), c = 13.746(6) A'and p = 103.69(7)", with Z = 4. The structure was refined by fullmatrix least squares to a final R value of 0.032 with 1173 reflections measured with a Syntex automatic diffractometer. The P-C bonds are 1.790(3) and 1.794(3) A in length with a P-C-P angle of 117.2(1)". The P-0 bond lengths are 1.494(2) and 1.500(2) A while the average P-0(-H) bond length is 1.546 A. Each of the oxygen atoms involved in the former bonds is an acceptor for two hydrogen bonds.
Introduction The study of the structure of a substantial number of diphosphates has as its goal the understanding of the nature of the bonding in this anion. The role and the nature of the T bonding within the anion still remains obscure. In addition the nature of the motion of the bridging atom remains unresolved.' The study of the methylenediphosphonates was undertaken because the bridging bonds, since they involve P-C, should be devoid of r bonding and because the motion of the bridging group can be studied over a large temperature range by nmr techniques. The crystal structure of the acid has been resolved as the first step in this study, although a recent report on the structure of ethane-1-hydroxy-1,l-diphosphonicacid monohydrate2 uses some unpublished results on an early study of the structure of methylene diphosphonic acid by Lovell.3 Experimental Section Methylenediphosphonic acid was prepared by hydrolysis of the tetraisopropyl ester with hydrochloric acid, according to the method of Roy.4 The acid gave colorless crystals from 1-butanol, which melted in the range 192-204" (lit. m p 203-206"). The nmr spectrum of the acid was obtained at 100 MHz in DzO, and showed a triplet for the methylene group at 5.16 ppm withJPH= 21 Hz. Crystals large enough for a structure determination were obtained by the slow evaporation of a saturated solution of isopropyl alcohol. One of these was ground into a sphere having a diameter of 0.25 mm and used to collect all the data. The unit cell parameters were determined by least squares from 15 values of 20 determined with a Syntex Pi automatic diffractometer using graphite monochromatized Mo K a radiation (A 0.71069 A). Crystal Data. The formula weight was 176.01; a = 7.840(9), b = 5.494(3), c = 13.74(6) A, p = 103.69(7)", unit cell volume 575.26 A3, Z = 4, space group E l / c , calculated density = 2.03 g/cm3, experimental density = 2.05 g/cm3(3). Data were collected in a quadrant up to a 28 angle of 50" with a standard reflection measured after every 50 reflections. Peaks were scanned a t a rate varying from 2 to 24"/min, depending upon the peak intensity, and backgrounds were measured at fixed angles a t either side of the peak and for the same time interval as used to scan the peak. Intensities whose measure after background correction were negative were dropped from the refinement to save computational time. Those whose intensity exThe Journal of Physical Chem/stry. Vol. 77. No. 9. 1973
ceeded 3a were regarded as observed and the remainder as unobserved with a maximum possible value of 3a. The data set contained 1170 symmetry independent reflections with 898 of these regarded as observed. These data were corrected for Lorentz, polarization, extinction, and absorption ( p R = 0.1). A trial structure was generated using the sign determination routines in X-ray 67. The phosphorus positions were readily identified in the subsequently prepared electron density maps and the oxygen atom positions resolved by the use of difference syntheses. The structure was refined using full-matrix least squares utilizing a program written for the CDC-6400 by J. S. Stephens. Atomic scattering curves were obtained from the "International Tables for x-Ray Crystallography."s Weights, w , were chosen so that W A F , with AF the difference between the observed and calculated structure factor, was independent of F,. Those unobserved reflections with F, less than the assigned maximum possible structure factor were given zero weight in the refinement. When convergence had been obtained with isotropic temperature factors, anisotropic components were allowed to vary. An R value of 0.042 was obtained, a t this stage, with wR = 0.052. Finally hydrogen atoms were assigned to the carbon atom, and to those oxygen atoms with the longer P-0 bond lengths. Although these atoms seemed to appear in the difference synthesis their positions were assigned as lying 1 A removed from its nearest neighbors and with idealized angular geometry. The refinement was carried to convergence, with all shifts less than 1/5a, with isotropic thermal parameters for the hydrogen atoms. The final H value is 0.032 and wR = 0.035. The final atomic parameters are in Table I and the thermal parameters are in Table II.6 Description of the Structure, Methylenediphosphonic acid deviates by about 30" from an eclipsed configuration 8. E. Robertson and C. Calvo, Can. J. Chem., 46, 605 (1968). V. A . Uchtman and R . A. Gloss, J. Phys. Chem.. 76, 1298 (1972). F. M. Loveli, Abstracts of the American Crystallographic Association Meeting, July, 1964. C. H. Roy, U. S. Patent No. 3,251,907; Chem Abstr., 65, 3908d (1966). "International Tables for X-Ray Crystallography." Vol. Ill, Kynoch Press, Birmingham, 1963. The final atomic parameters and the thermal parameters, Tables i and 1 1 , respectively, as well as a listing of the observed and calculated structure factors will appear following these pages in the mlcrofilm 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, referring to code number JPC-73-1146.
1147
Crystal Structure of Methylenediphosphonic Acid TABLE I I I: Interatomic Distances and Angles with Standard Errorsa for MethylenediphosphonicAcid Length, Bond
P (1a)-C (a)
-2;
1.790(3) 1.546(2) 1.547(2)
P (2a)-C (a)
1.794 (3) 1.545(2)
1.494(2)
1.548(2) 1.500(2)
C(a)-O(1a) -0(3a) -0(5a)
2.656(3) 2.631 (3) 2.749 (3)
C (a)-0 (2a) -0 (4a) -0(6a)
2.728 (3) 2.715(3) 2.685 (3)
0 (1a)-0 (3a) -0(5a) 0 (3a)-0 (5a)
2.486(3) 2.539 (3) 2.544 (3)
0 (2a)-0 (4a) -0(6a) 0 (4a)-0 (6a)
2.406(3) 2.542 (3) 2.562(3)
H (1a)-0 (1a) -0(5C) 0(1a)-0(5c)
0.73 (6) 1.87(6) 2.605(3)
H (2a)-0 (2a) -0(5b) 0 (2a)-0 (5b)
0.68(6) 1.93(6) 2.603 (3)
H(3a)-0(3a) -0(6d) 0 (3a)-0(6d)
0.73(4) 1.95(4) 2.675(3)
H (4a)-0 (4a)
0.85(5) 1.74(5) 2.577(3)
C(a)-H(5a) -H (6a)
0.91 (4) 0.93(4)
Angle
Degree
C (a)-P(la)-0 (1a) -0 (3a) -0 (5a) 0 (1a)-0 (3a) -0 (5a) 0 (3a)-0 (5a)
105.4(1) 103.2(1) 113.6(1) 107.0(1) 113.3(1) 113.5(1)
C(a)-P(2a)-O (2a) -0(4a) -0 (sa) O(2a) -0(4a) -0(6a) O(4a) -0(6a)
109.1(1) 108.2(1) 109.3(1) 102.2(1) 113.2(1) 114.5(1)
P (1a)-C (a)-P (2a)
117.2(1)
H (5a)-C (a)-H (6a)
112(3)
0 (5c)-H (1a)-O( 1a) 0 (5b)-H (2a)-0 (2a)
177(6) 178 (6)
0 (3a)-H (3a)-0 (6d) 0 (4a)-H (4a)-0 (6d)
172(4) 171 (4)
a Includes errors in the
= X , -y,
Bond
-0(2a) -0(4a) -0(6a)
-0(la) -0 (3a) -0(5a)
C
A
d = X,
'12
-0(6b) 0 (4a)-0 (6b)
Angle
Degree
unlt cell lengths. Atom position X(ln) is derived from those in Table I by the transformations a = x, y, z; b = - x , '/z -k y,
- y, '12 -tZ.
when viewed along the P-P vector. The carbon atom is bonded to two phosphorus atoms and two hydrogen atoms and these atoms are distributed nearly tetrahedrally about the carbon atom. The P-C-P angle is 117.2(2)".The carbon atom is displaced from colinearity with the two phosphorus atoms such that it lies nearly equidistant from all the oxygen atoms in the molecule. These distances range from 2.621 to 2.750 A. Table I11 contains the pertinent bond distances and angles. Each molecule is bonded through hydrogen atoms to eight neighbors, four a t each end. Groups of four molecules hydrogen bond to form rings about the inversion center, e.g., $O$ in Figure 1, by the bonding of O(6) to O(3) and O(4) through H(3) and H(4), respectively. These rings then form ribbons running parallel to the - b c direction with adjacent ribbons joined by means of a centrosymmetrically related pair sharing H(1) and H(2) between O(5) and O(1) and O(2). The structure shows chains 0 H-0-P-0-H- 0 at each end running parallel to the - a b direction with the acceptor oxygen atoms in a trans arrangement. The individual P-C bond lengths, at 1.790(3) and 1.794(3) A, differ insignificantly. The P-0 bond lengths fall into two distinct classes. The shorter ones involve
+
+
--
-
'/2 - 2 ;
Figure 1
O(5) and O(6) and are 1.494(2) and 1.500(2) A long while the remaining ones, which in fact are POH groups, all lie between 1.545(2) and 1.548(2) A. All the C-P-0 bond angles on side 2 lie with 1.5" of the ideal tetrahedral value while those on side 1 range from 103.2 to 113.6". Two alf the three 0-P-0 bond angles on each side are larger than ideal and one is smaller. The smallest of these lies on side The Journal of Physical Chemistry, Voi. 77, No. 9, 1973
R . A. Work, I l l , and R . L. McDonald
2 and has a value of 102.2(1)”. Each tetrahedra has as its shortest 0-0 edge that one containing the two OH groups.
Discussion Uchtman and Gloss2 indicated that in C(CHs)(OH)(P03H2h (I), N H + ( C H ~ P O Z H Z ) ~ ( C H Z P O(111, ~ H ) and Lovell’s results on CH2(P02H2)2 (111) that as the P-0(-H) bond strengthened, as measured by its bond length, so does the hydrogen bond, as measured by the donor-acceptor 0-0 contact. In addition these authors noted that a decrease in the P - 0 bond length paralleled a decrease in the P-0(-H) bond length which shared a common P atom. The present refinement breaks the pattern since the P-O( -H) bond lengths differ insignificantly while the 0-Ha. - 0 distances are different. The second effect does not seem universal either since the average P-0(-H) bonds in I and I11 are identical while 111 has the shorter P - 0 bonds. I has a nearly eclipsed configuration when viewed down the P-P axis, with C-P-0 and 0-0 bond angles on one
side of the molecule (side 1) consistent with a displacement of the P from an ideal tetrahedron toward the plane of the oxygen atoms. On the other side of the P atom (side 2 ) the P is also displaced away from the edge containing the two OH groups. In contrast methylenediphosphonic acid distorts in a manner consistent with a displacement of the phosphorus atom away from the edge containing the two OH groups. A further difference between I and I11 concems the P-C bond lengths (1.832 and 1.840 A in I) although the P-C-P bond angles (115” in I) are similar. As indicated by Uchtman and Gloss2 this difference is not consistent with a steric effect. Careful molecular orbital calculations might sort out the various effects leading to these differences and reflect on Uchtman and Gloss2 suggestion that the dihedral angle collapses because of the repulsion arising when functional groups replace the hydrogen atoms on the carbon atom. Acknowledgment. This research was supported through a grant from the National Research Council of Canada.
A Far-Infrared Study of the Association of Benzoic Acid with Substituted Ammonium Halides in Benzene R. A. Work, Ill, and R. L. McDonald* Department of Chemistry. University of Hawaii, Honolulu, Hawaii 96822 (Received December 27. 1972)
Tetraheptyl- and tri-n-octylammonium chlorides and bromides were studied by far-infrared techniques in benzene solutions containing small amounts of benzoic acid. Both cation-anion and anion-acid stretching vibrations can be observed simultaneously in the region below 400 cm -1. An ,internal OCO deformation mode of benzoic acid which absorbs in the far-infrared was used to estimate anion-acid association constants. Although ion pair-ion pair association of the tetraheptylammonium salts is decreased by benzoic acid solvation of the anion. in no case was any evidence of cation-anion separation observed.
Several recent papersl-3 have described the interaction of ion pairs with hydrogen-bonding molecules .in aprotic organic solvents. Taylor and Kuntzlb used nmr and midinfrared techniques to study the interaction of various ion pairs with phenol in several different solvents. Phenolanion association constants were computed from “free” VOH intensities, and it was suggested that solvent separation of the ion pairs occurs on addition of phenol. Martin, et a l . , 2 c used similar nmr and infrared techniques to study the association of tetra-n-butylammonium halides with various alcohols in CC14. They concluded that 1:l alcohol-anion complexes were formed in solution. Diamond, et al.,3 studied the coordination of water-insoluble phenols and alcohols with tetraalkylammonium fluoride and chloride in toluene by extraction techniques. Up to four alcohol or phenol molecules were found to coordinate to the halide ion in the organic phase. Although far-infrared instruments have been commercially available for more than a decade, surprisingly few The Journal of Physical Chemistry, Vol. 77,No. 9,1973
far-infrared studies of ion pair-molecule interactions in solution have been reported. We have found that in favorable cases both cation-anion and anion-molecule stretching vibrations can be observed simultaneously in the region below 400 cm-1 for systems consisting of an ion pair and a hydrogen-bonding molecule in an “inert” diluent. Most polar solvents are unsuitable as diluents because they exhibit intense, broad absorptions in the far-infrared region due to dipole-dipole interactions.“ On the other hand, benzene is an excellent solvent. It is transparent, it (1) (a) R. P. Taylor and I. D. Kuntz, Jr., J. Amer. Chem. Soc., 92,4813 (1970);(b) J. Phys. Chem.. 74, 4573 (1970). (2) (a) R. D. Green and J. S. Martin, J. Amer. Chem. SOC., 89, 5549 (1967);(b) J. S. Martin, J-l.’Hayami, and R. U. Lemieux. Can. J. Chem., 46, 3263 (1968);(c) R. D. Green, J. S. Martin, W. E. McG. Cassie, and J. E. Hyne, Can. J. Chem., 47, 1639 (1969). (3) D. J. Turner, A. Beck, and R. M. Diamond, J. Phys. Chem., 72, 2831 (1968);T. Kenjo, S. Brown, E. Held, and R. M. Diamond, J. Phys. Chem., 76,1775 (1971). (4) R. J. Jakobsen and J. W. Brasch, J. Amer. Chem. Soc., 86, 3571 (1964).
