Inorganic Chemistry, Vol. 12, No. 11,1973 2721
Dehydration of Zirconium Oxide Halide Octahydrates P F 2 0 C r skeleton is varied from 0 to 3 is now known, as is the series of adducts, excluding the adduct of PFzO-t-Bu. The basicity order of the series24 predicts the electron-releasing order i-Pr > Et > Me. This order is in agreement with previous work' and with the classical electron-releasing ability."-23 The effect of substituting a methyl group for a hydrogen upon the basicity of these difluorophosphites is additive. A plot of the number of attached methyls us. J p B is linear. The relationship of JPB us. the number of attached methyls can be used to predict a JPB coupling constant for PF2O-tBu.BH3 of 74.7 Hz. See Figure 1. Foester and Cohns have reported that a 1: 1 correlation between displacement base strength and J p B is not possible in a series of the type PF2X (X = Me, MeO, Me2N, MeS). However, Rudolph and Schultz4 indicated that for a series of smoothly varying phosphine ligands [Le., PF2X (X = F, C1, Br) or PF3-,H,] the relationship between the magnitude of JPBand the dative bond strength is a general one. The relationship between J ~ and B the displacement base strength of the smooth series PF20C(CH3)3-,H, is essentially quantitative. See Table 111. Verkade and White' have recently correlated the relative stability of borane adducts with BH stretching frequencies. Coyle and Stone26 originally suggested that BH ir stretching frequencies could be related to boron-ligand bond strength in boron adducts, but Cohn' found no simple relationships (24) Steric effects on the basicity are assumed t o be small in rela tion to (p-d)n electron drift from the oxygen system since the order of basicity is not that expected for steric requirements, PF,OMe > PF,OEt > PF,O-i-Pr. See ref 1, 3, and 5 . See also H. C. Brown, J . Amer. Chem. Soc., 7 5 , 16 (1953). (25) D . W. White and J. G. Verkade, Phosphorus, 3 , 9 (1973). (26) T. P. Coyle and F. G. A . Stone, Progr. Boron Chem., 1 , 83 ( 1 964).
Table 111
Ligand
Adduct JPB, Hz
PF, 0-i-Pr
72.5
PF,OEt
70.4c
PF,OMe
68.2d
AJPB, Hz
A(av % Av % dis- displaceplacementa ment)b
2.1
60.5
10.5
2.2
60.5C
10.5
a See Table I. Average per cent displacement is calculated by averaging the two per cent displacements obtained from the pairs of exchange reactions. b Change in per cent displacement is calculated by subtracting 50% from the average per cent displacement. Per cent displacement for the reaction PF,OEt + PF,OEt.BH, PF,OEt + PF,OEt.BH, is 50% ( K e g = 1). See Table I. C See ref 1. d See ref 3.
in a series of similar fluorophosghine-boranes. Although the differences in frequencies (cm-') are small in the series PF20R [R = i-Pr (2438, 2378), Et (2448,2382),' Me (2452, 2383),' Tfet (2456, 2382)'], a trend similar to that suggested by Coyle and Stone and demonstrated by Verkade and White is evident.
Acknowledgment. The authors are grateful for the assistance of John Gray with some of the "F nmr spectra, Goji Kodama with "B nmr spectra, and David Goldsmith with the mass spectrometer. We also thank the Air Force for the use of a Jeol60-MHz nmr instrument at Robins Air Force Base and thank John Dubose for the sample of galvinoxyl. We gratefully acknowledge the donors of Petroleum Research Fund, administered by the American Chemical Society, for support of this work. Registry No. PF, 0-t-Bu, 4 1380-08-9 ;PF ,0-i-Pr , 17 37-8 3-3; PF,O-i-Pr.BH,, 41380-10-3; B,H,, 19287-45-7.
Contribution No. 4675 from the Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91 109
Characterization of the Thermal Dehydration of Zirconium Oxide Halide Octahydrates D. A. POWERS and HARRY B. GRAY* Received April 16, 1972
The compounds ZrOX,.8H,O (X = C1, Br) dehydrate thermally in a stepwise manner t o the respective hexahydrates, tetrahydrates, and finally ZrO,. Dehydration is complete at 700". The intermediate hydrates have been isolated and characterized. Several regions of the infrared spectra of the various hydrates have been assigned with the aid of analogous deuterated compounds. The experimental evidence may be interpreted in terms of the structural formulations [Zr,(OH),(H20),,]X,~12H,0, [Zr,(OH),(H,O),,]X,.4HZO, and [Zr,(OH),(H,O),,]X,, for the octahydrates, hexahydrates, and tetrahydrates, respectively. The last tetrameric cation is proposed to contain seven-coordinate Zr(1V).
Constant-temperature dehydration of zirconium oxide chloride octahydrate, ZrOC12.8H20, at varying humidities has been investigated previously. The inconsistencies among the results reported in these studies are indicative of the difficulty of establishing equilibrium in the experimental system. Furthermore, dynamic thermal dehydration studies have employed rapid heating rates on bulk samples in stagnant atmospheres and have produced varying results.3s4 We unl2
( 1 ) T. P. Spasibenko and S. A. Kobycheva, Rum. J. Inorg. Chem., 15, 181 (1970). ( 2 ) W. A. Castor, J r . , and F. Basolo, J . Amer. Chem. SOC.,7 5 , 4 8 0 4 (1953).
dertook the present investigation with the principal objective of clarifying the thermal behavior of the octahydrates of both ZrOC12 and ZrOBr2. X-Ray crystallographic studies have shown' 9 6 that the correct structural formulation of ZrOCl2.8Hz0 is [Zr,(OH),(3) (a) S. Takagi, J . Cnem. Soc. Jap., 7 5 , 637 (1954); Chem. Abstr., 4 9 , 7651'(1954); (b) J . H . Canterford and R. Colton, "Halides of the Second and Third Row Transition Metals," Wiley, London, 1968, p 132. (4) L. N. Komissarova, V. E. Plyuschehev, and I. N. Kremenskaya, Rum J. Inorg. Chem., 5 , 281 (1960). (5) A. Clearfield and P. A. Vaughan, Acta Crystallogr., 9, 5 5 5 (1 9 5 6). (6) T. C. W. Mak, Can. J. Chem., 46, 3491 ( 1 9 6 8 ) .
2722 Inorganic Chemistry, Vol. 12, No. 11, 19 73 (Hz0)16]C18~12Hz0.In the tetrameric complex cation the four Zr(1V) atoms form a slightly distorted square arrangement held together by dihydroxo bridges. Four H 2 0 molecules are bound to each Zr(1V) to complete a distorted dodecahedral, eight-coordinate geometry.6 The fact that [Zr4(0Hj8(Hz0j16]C18.12Hz0 is one of the very few structurally well-characterized compounds containing both lattice and coordinated H20, as well as bridging OH-, prompted us t o carry out parallel infrared spectroscopic studies with the intent of locating the characteristic vibrational modes of these three components of many hydrated solids. Experimental Section Zirconium oxide chloride octahydrate was prepared from reagent grade zirconium tetrachloride (Alfa) according to the procedure of Brauer.' The material was recrystallized three times from 1 N hydrochloric acid. Since solutions of zirconium oxide chloride octahydrate readily supersaturate, recrystallization was greatly speeded by addition of seed crystals. Crystals used in the study were white, wellseparated needles about 0.5 cm in length. Clumps and mats of poorly separated crystals were found t o give irreproducible results. ZrOCl, 8H,O effloresces significantly only in dry air. The crystals could be collected without decomposition by suction filtration. The material was best washed with an ice-cold mixture of equal volumes of ethanol and concentrated hydrochloric acid. Washing with acetone, pure ethanol, or ether results in serious decomposition of the crystals. The compound was found t o be free of ferric ion when tested with potassium thiocyanate solution. Anal. Calcd: Zr, 28.30; C1, 22.00. Found: Zr, 28.46; C1, 22.22. The crystals were further characterized by their X-ray powder diffraction pattern which showed a tetragonal unit cell of dimensionsa = 17.11 ?: 0.02 and c = 7.71 f 0.02 A, in good agreement with published results. s,6 The deuterio analog was prepared by a similar procedure using 99.8% D,O (Columbia) and gaseous DC1 (Merck). Rapid exchange of D,O with atmospheric water made recovery of a perfectly deuterated compound impossible. Infrared spectra indicated the product was about 80% deuterated. Zirconium oxide bromide octahydrate was prepared by dissolving 10 g of zirconium tetrachloride in 25 ml of iced water. Seventyfive milliliters of concentrated hydrobromic acid (Allied) was added to precipitate the crude product. This product was collected, redissolved, and reprecipitated three times to eliminate chloride ion. The material was dissolved in 15 ml of water containing 2 ml of concentrated hydrobromic acid. The solution was concentrated at 70" until crystallization began. The compound was recrystallized three times. As in the case of ZrOC1,.8H,O, seeding the solutions increased the rate of recrystallization significantly. White, well-separated needles 0.5 cm in length were selected and washed by decantation with an ice-cold mixture of equal volumes of ethanol and hydrobromic acid. Zirconium oxide bromide octahydrate effloresces somewhat even in room air. The crystals were picked from the wash, quickly pressed between absorbent filter paper, and then bottled. The compound was found to be free of ferric ion when tested with potassium thiocyanate solution. Anal. Calcd: Zr, 22.19; Br, 38.87. Found: Zr, 22.19; Br, 39.11;Cl,
