Hydrogen bonding

Journal

of Molecular

Structure,

82

(1982)

213-219

Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands

HYDROGEN

BONDING

Part 14. Hydrogen bonding in the tetrahedral

KENNETH Department

(Received

M. HARMON, of

Chemistry,

7 December

JULIE Oahland

M. GABRIELE University.

04Hi-

cluster in hydrogrossular

and ANNE Rochester,

S. NUTTALL

Michigan

48063

(U.S.A.)

1981)

ABSTRACT Infrared spectra of hydrogrossular, Ca,AI,(O,H,),, and hydrogrossularxf,, show that hydrogen bonding occurs in the O,H”,- cluster found in this garnetoid mineral. Revsluation of published crystallographic data shows that bond lengths in the cluster are consonant with the presence of bifurcated hydrogen bonds. This cluster, which is very similar to the face-protonated, tetrahedral H,O,F:and H,O,CI:clusters proposed for tetraalkylammonium halide monohydrates, is distorted to S, in hydrogrossular through interaction with the lattice cations. INTRODUCTION

The isomorphous substitution of four OH- for ions such as SiO”,- , PO:-, and SO:- has been observed in a wide variety of natural and synthetic minerals, and in biological materials such as bones and teeth [ 1, 21 . For example, in the series of hydrogarnets ranging from grossular, Ca,Al,(SiO,),, to hydrogrossular, Ca3A12(03Hg)3, the positions of the 96 osygens in the unit cell are unaffected by successive replacements of SiOj by OJHJ [3]. In 1942 McConnell [4] proposed that such substitutions could be accounted for by a face-protonated “tetrahedral hydrosyl unit”. The tetrahedral arrangement of the osygens in the O,H, unit has been confirmed by X-ray and neutron diffraction studies of hydrogrossular [5-71, and the

precise positions

of the hydrogens

on the tetrahedral

faces has been deter-

mined in a neutron diffraction study [ 2, S] of hydrogrossular-cl,,. This “tetrahedral hydrosyl unit ” is of particular interest to us, since it closely resembles the hydrogen bonded face-protonated tetrahedral structures that we have proposed [9-131 for the discrete water-halide cluster ions in tetraalkylammonium halide monohydrates. Our assigned structures have been based on spectroscopic and theoretical considerations, since diffraction data are not yet available; however, in the absence of such data, the esistence of the O,Hiunit of known structure in hydrogrossular is strong support for our basic tenet - that a tetrahedron of electronegative atoms with protons in bifurcated hydrogen bonds on the faces is a reasonable arrangement for a cluster of four protons and four electronegative atoms. 0022-2860/82/0000-0000/$02.75

@ 1982 Elsevier Scientific

Publishing

Company

214

There have been several reports of infrared studies of hydrogrossular [7, 14,15]_ These have not been in complete agreement with one another, and have failed

to resolve

adequately

the question

of whether

hydrogen

bonding

is present in the O,Hi- cluster. Consequently, we have reexamined the infrared spectral properties of hydrogrossular and hydrogrossulard , z to determine whether the 04H:- cluster contains bifurcated hydrogen bonds, as we have proposed for the H402F;- and H402C1:- clusters. EXPERIMENTAL

Hydrogrossular was prepared by the hydrothermal method of Cohen-Addad et al. [6] from Alfa Inorganics fluoride-free calcium oxide and Alfa Inorganics aluminum powder (325 mesh) in a stainless steel Paar bomb at 100°C. Hydrogrossular is the only component of the Ca0-A120,-H20 system to form at this temperature [ 151. Hydrogrossular-d ,? was prepared in a similar manner using 99.7% deuterium oxide. The infrared spectra of the products showed the complete absence of carbonate or silicate. (Silicate contamination occurs if glass apparatus is used.) Sargent reagent grade calcium hydroxide was used as supplied. Infrared spectra were recorded on a Perkin-Elmer 283 spectrophotometer as Nujol mulls on CsI plates. All operations were carried out in a glove box under dry nitrogen. RESULTS Infrared

AND DISCUSSION spectra

The infrared spectrum of a Td H4X4 face-protonated cluster would show three infrared active T2 vibrations; these are an X-H stretching mode, an X-H bending mode, and an X --*X cage deformation [9, lo] _ These bands are observed for the H,O,Ff- and H_,OzClz- clusters in tetraalkylammonium halide monohydrates. Although band splitting occurs with increasing bias of the cluster toward CzV [ 10, 121, in all cases the only absorptions observed are those derived from the three T2 vibrations, which have large intrinsic transition moments in the free ions. All of these absorptions show isotope shifts in the deuterated clusters. Like the halide monohydrates, hydrogrossular (Fig. 1) shows three strong infrared absorptions which shift on deuterium substitution (Table 1). The O-H stretching band is extraordinarily broad and intense, and is unlike those of simple metal hydroxides. This band has a maximum absorption at 3660 cm-‘, and the similarity of this to the absorption maximum of calcium hydroxide at 3650 cm-* was taken by Cohen-Addad et al. [7] as evidence for lack of hydrogen bonding in the O,Hi- unit. However, comparison of the spectra of hydrogrossular and calcium hydroxide (Fig. 1) demonstrates that there is little similarity in the O-H stretching region. Calcium hydroxide

215

I

~I,r

,

..

I.

r/_---------7_

. \

-

!._

_./-\--‘-lr’

r

--.

._ .. . .

!a

L.

I

B ._ -. I

I..

.\-.

.,.--._ -/

-. ‘.

1

II 3600

II~~l,I,I,I,I,I,I,I,I,IIII 2600

2000

1600

1200

800

Fig. 1. Infrared spectra (Nujol mulls on CsI plates) of (A) hydrogrossular, hydroxide. Units are cm-‘, ‘%T; peaks marked (N) are from Nujol.

TABLE

1

Infrared

spectral

bands of hydrogrossular

and hydrogrossular-d,

cr

-I

and (B) calcium

~a*b*c

Regiond

Ca,AlJO,H,),

Ca,Al,(O,D,),

O-H Stretch O-H Bend O.--O Deform. Lattice mode

3660( bs) 780(bs) 380( bs) 525( vs)

ZiOO( s) ; 580( m)e 53O(vs)

400

VHIUD 1.36 x 1.34 1.01

“Nujol mulls on CsI plates. bValues in cm-‘. CSymhols used: broad, h; strong, s; medium. m; very, v. dO-H refers to hydrogen motions recognizing more than one 0 involved lvith of 0, polyhedron. CPartially masked by lattice band. each H; 0-m. 0 refers to deformation ‘Band shifts out of range.

shows a narrow, sharp band which spans about 70 cm-‘, while the stretching band of hydrogrossular spans nearly 1700 cm-‘, from 3750 cm-’ to about 2000 cm-’ _ The integrated intensity of the O-H stretching absorption in hydrogrossular is immensely greater than that of calcium hydroxide, and is of a magnitude consonant with the presence of significant hydrogen bonding. The O-H bending band of hydrogrossular is also broad, and is found at

216

considerably higher frequency (770 cm-‘) than in calcium hydroxide (below 600 cm-‘), where no hydrogen bonding occurs, or in lithium hydroxide monohydrate [16], where the hydroxyls are acting as acceptors in two hydrogen bonds, and are also complexed to two lithium ions. Thus, the position of the O-H bending band in hydrogrossular indicates significant restraint of the hydrogen bending motion. Figure 2 compares the O-H stretching region of the O,H4,- unit in hydrogrossular with the corresponding stretching region of the hydrogen -bonded H402C1~- cluster in tetraethylammonium chloride monohydrate. The similarity in intensity and band shape of the absorptions of the two clusters is apparent. At room temperature, the H402C!l:- O-H stretching region shows the splitting of the T2 band into three components, At + B, + B?,, through bias to C!,, symmetry; at 10 K these are clearly resolved [ 121 _ The cluster in hydrogrossular is essentially D 2drwith a minimal distortion toward S4 (see below). Under DZd or So a T:! band should split intoB* + E(D?d) or B + E(S4); thus two bands would be expected. We cannot resolve the O-H stretching band of hydrogrossular at 10 K; however, Cohen-Addad et al. [ 71 have shown that the O-H band of hydrogrossular is resolved at 4 K into two absorptions, as predicted. They obtained similar results with hydrogrossularii 12at 4 K. The spectrum of hydrogrossular in potassium bromide pellets was reported by Cohen-Addad et al. [7] and by Hunt [14] _ These spectra, though not as

3600

2800

2ooc

Fig. 2. Infrared spectra (Nujol mulls on CsI plates) of the X-H stretching bands (X = Cl and/or 0) of the cluster species in (A) tetraethylammonium chloride monohydrate, and (B) hydrogrossular. Units are cm-‘, ST; peaks marked (N) are from Nujol.

217

well developed, agree with our mull spectra, which shows that ion exchange does not occur in the pressed pellet. Majumdar and Roy [ 151 also report the KBr pellet spectrum of hydrogrossular; however, their spectrum is totally different from the other reported spectra. In one preparation we inadvertently added an excess of aluminum powder, and obtained a material whose infrared spectrum was identical to that reported by Majumdar and Roy for hydrogrossular. Analysis of this substance showed a lower Ca:Al ratio, 1.782, than that obtained for our hydrogrossular, where the Ca:Al ratio is 2.237 (theory 2.228). Thus the material giving the anomalous spectrum apparently contains excess A1(OH)3.

Structure

and bond

lengths

The structure of the O,D”,- cluster in hydrogrossulard 12 [ 2, 81 is shown in Fig. 3. The oxygen polyhedron is nearly tetrahedral, although formally DZd, with two O---O distances of 302 pm and four of 321 pm. The deuteriums lie above the faces and are each located at a distance of 94.6 pm from one of the oxygens. This short O-D bond almost bisects the face; the two longer D.--O distances in a face are 243 pm and 246 pm. Thus the cluster is very close to Dzd sy mmetry, with a slight bias towards Sq. The critical distance in defining an A-H---B interaction as hydrogen bonding is the H.--B distance [ 171. The long D...O distances in the face are 14 and 17 pm shorter than the sum of the Pauling radii of D and 0; both the D..*O and O.--O distances in the face of the cluster fall within the range of values for interactions classified [18,19] as weak bifurcated hydrogen bonds.

Fig. 3. (A) Schematic of oxygen polyhedron of O,D;to define faces; the two short O.-.O cluster in hydrogrossular-cf ,~ edges are parallel with the page. (B) Bonding in the O,D:(from refs. 2, 8). The deuteriums are respectively above and below the polyhedral faces arranged as in (A). For bond distances see text.

218

It is important to note that the distances above are for the 04Di- structure. The infrared spectrum of hydrogrossular+-Iiz shows weaker hydrogen bonding effects than are seen in hydrogrossular. In hydrogrossular [ 53 the O---O distances in the cluster are shortened to 301 pm (two distances) and 302 pm. If the geometry of the oxygen-hydrogen interactions is presumed to be the same as in the O,D”,- cluster, the long H---O interactions would be about 230 pm and 233 pm, which are respectively 30 and 27 pm shorter than the sum of the Pauling radii. This is in the range observed for wellestablished bifurcated hydrogen bonds [ 191 .

Intrinsic

nature

of the 0x4-

cluster

It is not clear whether the Dzd symmetry of the O,Hi- cluster in hydrogrossular is the intrinsic, stable spatial arrangement for this group of atoms, or whether we are observing a Td cluster distorted by lattice effects. The ion departs from the Td symmetry that we have postulated for clusters of this type in two ways: (1) the oxygen polyhedron has two shorter and four longer O.--O distances, and (2) each hydrogen is significantly closer to one of the face oxygens than to the others. Abrahams and Geller [ 203 have determined the structure of grossular, Ca,Al,(SiO,),. The four oxygens of the SiO”,- ion are related by two short (256 pm) and four long (273 pm) distances. The ratio of long to short O---O distances in grossular (1.07) is about the same as in hydrogrossulard I* (1.06 j, and larger than in hydrogrossular (1.00). Thus the intrinsically Td SiO”,- ion is distorted by the garnet lattice to a configuration essentially identical to that of the oxygen polyhedron in hydrogrossular. The hydrogens in hydrogrossular do not occupy central pcsitions on the faces of the O4 polyhedron, but reflect the symmetry of the S4 lattice site. As Cohen-Addad et al. have observed [7], the position of the hydrogens minimizes the electrostatic potential with respect to the surrounding cations. However, this does not preclude the bifurcated hydrogen bonds from being symmetrical at a site of higher symmetry; Williams and Schneemeyer [ 211 have shown that even the strong, centrosymmetric hydrogen bond in hydrogen difluoride ion wiil distort to an unsymmetrical (and weaker [ 22, 231) hydrogen bond to track an unsymmetrical crystal environment. If an O,Hi- cluster of pure Td symmetry were placed in the S, site of hyclrogrossular, one would predict that the oxygen polyhedron would distort in the same manner as the SiO”,- ion does in that site, and that the hydrogens would move from the centers of the faces in the manner observed. Therefore, there is no reason to presume that the 04H:- cluster is intrinsically DZd rather than Td_ It would be of great interest to us to identify a mineral where the O,H:- unit occupies a Td or Oh site. We are initiating a search for such a substance, and any information on possible candidate materials would be appreciated.

219 CONCLUSION

Infrared spectral characteristics and bond lengths attest to the presence of hydrogen bonding in the O,Hi- cluster in hydrogrossular. We believe the cluster is distorted from Td to Did symmetry by lattice effects. The similarity of the O,Hicluster to the H,O,F;and HJ02Ci~- clusters found in tetraalkylammonium halide monohydrates suggests that these water-halide clusters may also substitute for tetrahedral MX, ions, such as SO:-, in minerals, bones and teeth. ACKNOWLEDGEMENT

Acknowledgement is gratefully made to the Donors of the Petroleum Research Fund, administered by the American Chemical Society, for a grant in support of this work. REFERENCES 1 D. McConnell

and F. H. Verhoek, J. Chem. Educ., -10 (1963) 512, and references therein _ 2 D. W. Foreman, Jr., J. Chem. Phys., 48 (1968) 3037, and references therein. 3 E. P. Flint, H. McMurdle and L. S. Wells, J. Res. Nat. Bur. Std., 26 (1941) 13. 4 D. McConnell, Am. Mineral., 27 (1942) 452. 5 R. Weiss and D. Grandjean, Acta Crystallogr., 17 (1964) 1329. 6 C. Cohen-Addad, P. Ducros, A. Durif, E. F. Bertaut and A. Delepalme, J. Phys. Fr., 25 (1964) 478. 7 C. Cohen-Addad, P. Ducros and E. F. Bertaut, Acta Crystallogr., 23 (1967) 220. 8 D. W. Foreman, Jr., Ph.D. Thesis, Ohio State University, 1966; University Microfilms, Ann Arbor, MI 48106 (U.S.A.) “66-15,087. 9 K. M. Harmon and I. Gennick, Inorg. Chem., 14 (1975) 1840. 10 K. M. Harmon and I. Gennick, J. NIol. Struct., 39 (197’7) 39. 11 I. Gennick, K. M. Harmon and J. Hartwig, Inorg. Chem., 16 (1977) 2231. 12 K. M. Harmon and J. M. Gabrieie, Inorg. Chem., 20 (1961) -2013. 13 K. M. Harmon and J. Harmon, J. Mol. Struct.,78 (1982) 33. 14 C. M. Hunt, Ph.D. Thesis, University of Maryland, 1959; University hIicrofilms, Ann Arbor, MI 48106 (U.S.A.) $592793. 15 A. J. Majumdar and R. Roy, J. Am. Ceram. Sot., 40 (1956) -13-l. 16 I. Gennick and K. M. Harmon, Inorg. Chem., 14 (1975) 2214. 17 W. C. Hamilton

18 19 20 21 22 23

and

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in Solids,

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A.

Benjamin,

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York, 1968, pp. 14-16. Ref. 17, p_ 211. J. Donahue, in A. Rich and N. Davidson (Eds.), Structural Chemistry and Molecular Biology, W. H. Freeman, San Francisco, 1968, p. 450 ff. S. C. Abrahams and S. Geller, Acta Crystallogr., 11 (1958) 437. J. M. Williams and L. F. Schneemeyer, J. Am. Chem. Sot., 95 (1973) 5790. K. M. Harmon, S. L. Madeira and R. W. Carling, Inorg. Chem., 13 (197-i) 1260. K. M. Harmon and R. R. Lovelace, J. Phys. Chem., 86 (1982) 900.