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Addition compounds of HfCl4 and ZrCl4 with organic ligands
J, inorg, nucl. ('hem., 1969, Vol. 31, pp. 1743 to 1748.
Pergamon Press.
Printed in Gte:Lt Britain
A D D I T I O N C O M P O U N D S OF HfCI4 A N D ZrCl4 WITH ORGANIC LIGANDS W. M. GRAVEN and R. V. PETERSON Materials Sciences Laboratory Aerospace Corporation, FJ Segundo, Calif. 9(/245 (First received 29 May 1968; in r e v i s e d j o r m 31 October 1968)
Abstract-Addition compounds of HfC14 and ZrCI4 with eight organic ligands have been prepared and analyzed. Infrared spectra and thermal decomposition measurements have demonstrated the similarity of properties between addition compounds of these two metal tetrahalides.
SINCE the first r e p o r t e d [ I ] i n t e r a c t i o n of o r g a n i c ligands with ZrCl4, a v a r i e t y of a d d i t i o n c o m p o u n d s h a v e b e e n p r e p a r e d by n u m e r o u s i n v e s t i g a t o r s . In c o n t r a s t . v e r y few a d d i t i o n c o m p o u n d s of HfC14 h a v e b e e n reported. In the few cases w h e r e c o m p a r i s o n s are possible, it a p p e a r s that small, b u t significant, differences exist in c e r t a i n p r o p e r t i e s of HfCI4 a n d ZrC14 a d d i t i o n c o m p o u n d s . In view of the close c h e m i c a l similarities of the two e l e m e n t s , it is significant to note the r e l e n t o b s e r v a t i o n [ 2 ] t h a t o n e - s t e p s e p a r a t i o n of HfC]4 a n d ZrCI4 is feasible b y utilization of the difference in rates of p r e c i p i t a t i o n of their complexes with o - p h e n y l e n e b i s d i m e t h y l a r s i n e (diarsine): T h i s work was u n d e r - t a k e n to o b t a i n c o m p a r a t i v e data for a r e p r e s e n t a t i v e g r o u p of o r g a n i c a d d i t i o n c o m p o u n d s of ZrC14 a n d HfCI4. With only a single e x c e p t i o n , the HfC14 c o m p o u n d s h a v e not b e e n p r e v i o u s l y reported. T h e r e f o r e , the p r e p a r a t i o n a n d c h a r a c t e r i z a t i o n of these c o m p o u n d s will also be reported. EXPERIMENTAL Materials. Hafnium tetrachloride was obtained from Electronic Space Products, Inc., and ZrCI4
was obtained from Alfa Inorganics, Inc. Both compounds were purified by sublimation prior to their use,
An X-ray fluorescence analysis showed the presence of 4-5 wt-% Zr in the HfCI4 and 2-3 wt-% Hf in the ZrCI4. These results, as well as the demonstrated absence of impurities in amounts greater than 0-1 percent, were confirmed by emission spectrographic analyses. In order to correct for the presence of the elemental analogs, effective atomic weights for 171.44 of Hf and 92.17 for Zr were used for computation of the analytical results. Vapor pressures of HfCI4, measured by a transpiration method between 200° and 250°, agreed well with data found in the literature[3]. All the organic ligands and solvents were Matheson, Coleman; and Bell spectroquality reagents. Each was dried with a suitable agent, distilled, and stored under an atmosphere of dry argon prior to its use. Preparative procedure. Since both metal tetrahalides and their addition compounds are susceptible to hydrolytic decomposition upon exposure to moisture, all operations involving transfer of solid materials were carried out in a glove box under an inert atmosphere. Reactions were carried out in flasks stoppered with rubber serum caps through which the liquid reagents were introduced with hypodermic syringes. I. J. M. M a t t h e w s , J . Arn. chem. Soc. 20, 815 (1898). 2. R.J.H. Clark, W. Errington, J. Lewis and R. S. Nyholm, J. chem. Soc. (A), 989 (1966). 3. A. A. Palko, A. D. Ryon and D. W. Kuhn,J. phys, Chem. 62, 319 (1958). 1743
1744
W . M . G R A V E N and R. V. PETERSON
In a typical preparation, 1-2 g of sublimed HfC4 was weighed out in a round-bottom flask. Approximately 20 ml of CC14 was added and the flask was stoppered and pressurized with dry argon. A volume of the organic ligand corresponding to 2-4 times the expected stoichiometric amount, was added with a hypodermic syringe. The reaction flask was then placed in a mechanical shaker for 16-48 hr. After the flask was transferred to the glove box, the liquid portion of the contents was decanted, the solid product was washed several times with dry hexane, and the flask was equipped with a stopcock adaptor for attachment to the vacuum line. The product was dried by evacuation to 10-3 torr. Analytical procedure. Hafnium and Zr were determined gravimetrically as their oxides by hydrolysis of the sample in an alcohol-water mixture followed by evaporation and ignition of the residue to constant weight in a Vycor crucible. Chlorine was determined gravimetrically as AgCI by using standard procedures which were modified (a) to avoid loss of HCI during hydrolysis by immersing the weighed sample immediately in NaOH solution (followed by careful acidification) and (b) to remove the suspension of hydrous metal oxide by filtration prior to the precipitation of AgCI. The i.r. spectra were obtained with a Beckman IR 4 spectrophotometer using NaC1 and CsBr prism interchange units. For the 1350-5000 cm -1 region, samples were mounted as Fluorolube mulls held between NaCI plates. For the 290-1350 cm -1 region, Nujol was used as the mulling agent, and for the 290-680 cm -1 region, the samples were held between Csl plates. The sample-mounting operations were carried out in a glove box. Melting points or decomposition temperatures were determined with a Hoover capillary melting point apparatus. Samples were transferred to capillary melting point tubes in the glove box and were sealed off before introduction to the apparatus.
RESULTS AND
DISCUSSION
It is evident from the elemental analytical data listed in Table 1 that with each ligand used, except p-dioxane, a di-addition product was obtained. Since in each case a two- to six-fold excess of ligand was employed, these compositions should correspond to the maximum ligand/metal ratios which are stable under the reaction conditions. In general, these compositions are in agreement with those reported in the literature, although two groups of investigators have prepared addition compounds with different stoichiometric formulas. A monoacetonate of ZrCI4 was obtained[4] when the reaction was carried out a t - 5 °, and 3:1 pyridine adducts were observed[5] with both ZrCI4 and HfC14 when the reactions were carried out in benzene with an excess of ligand present. Presently available data are insufficient to distinguish between a structure in which the two oxygens ofp-dioxane are attached to adjacent octahedral positions around the metal[6] and an alternative structure consisting of polymeric chains of metal atoms linked by p-dioxane molecules [7]. Each of the addition compounds dissolved completely in anhydrous methanol. Qualitative analyses of the methanol solutions using gas chromatography showed that each of the compounds had decomposed, thereby releasing the organic ligand. In several cases, rough calibrations indicated quantitative recovery of the ligands. Each of the addition compounds is a white solid which is stable at ambient temperature, but is rapidly decomposed by moisture. Some of the compounds exhibit characteristic melting points, although there is evidence of decomposition 4. 5. 6. 7.
P. T. Joseph and W. B. Blumenthal, J. org. Chem. 24, 1371 (1959). T. C. Ray and A. D. Westland, lnorg. Chem. 4, 1501 (1965). R. F. Rolsten and H. H. Sisler, J. A m . chem. Soc. 79, 1819 (1957). P.J. Hendra and D. B. Powell,J. chem. Soc. 5105 (1960).
Addition compounds of HfC]4 and ZrCl 4
1745
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1746
W . M . G R A V E N and R. V. PETERSON
of the molten liquid. Others appear to undergo decomposition without melting, also at fairly reproducible temperatures. Table 1 shows these data, together with corresponding values from the literature for several of the ZrC14 addition compounds. It is evident that for each pair of addition compounds, the ZrC14 compound melts and/or decomposes at a lower temperature than the HfC14 analog. This is to be expected for covalent compounds of metallic elements which are members of the same periodic family. It is also in agreement with the observation that HfCI4 compounds with phosphorus oxyhalides melted at slightly higher temperatures than did the corresponding ZrCI4 compounds [11]. The principal i.r. absorption bands of the HfCI4 and ZrC4 addition compounds are given in Table 2. Not included are very weak bands and bands at frequencies greater than 2400 cm -1, the former to avoid inclusion of bands due to trace impurities, such as solvents or free ligands, and the latter because of the inaccuracy of placement of the C - - H stretching frequencies for samples mulled with Fluorolube. For comparison, the absorption bands of the free ligands, obtained from thin films of the liquids or, in the case of dimethyl ether, from a Nujol solution, are also listed. In addition, the absorption bands observed for N ujol mulls of the freshly sublimed metal tetrahalides are included. It is apparent that no significant differences between the spectra of the HfCI4 and ZrCI4 compounds are to be found at frequencies greater than 600 cm -1. This is not unexpected, since metal-ligand fundamental stretching frequencies should be found at frequencies lower than 600 cm -1, and overtones which might occur at higher frequencies would probably have been eliminated from the compilation because of their low intensities. Only in the addition products with methyl formate are differences observed at frequencies higher than about 365 cm -~. For these two compounds, the differences in the 365-600 cm -1 region may result from the coupling of ligand vibrational modes with metal-ligand stretching modes. In the region above 600 cm -~, frequency shifts from ligand to addition compound are quite apparent. Without attempting an assignment of all of the absorption bands, one may note the shift to lower frequencies of the carbonyl stretching bands: from 1670 to 1654 cm -1 for the dimethylformamide compounds, from 1722 to 1635 cm -1 for the methyl formate compounds, and from 1725 to 1660 cm -~ for the acetone compounds. The C - - O - - C stretching bands in the ethers have been lowered from 1093 to 1003 cm -~ in the dimethyl ether compounds, from 1120 to 1000 cm -~ in the diethyl ether compounds, and from 1120 to 1035 cm -1 in the dioxane products. In contrast, the (3~N stretching band has been raised from 2248 cm -1 in acetonitrile to 2271 cm -1 in its addition compounds. Similarly, the coupled ~C and ~ N stretching band at 1580 cm -a in pyridine has been raised to 1602 cm -~ in its addition compounds. Although the weakening of the C - - O bonds, as indicated by the lower stretching frequencies in the addition compounds, can be readily understood in terms of the electron withdrawal resulting from coordinate bonding of the oxygen atom to 11. E. M. Larsen, J. Howatson, A. M. Gammill and L. Wittenberg, J. A m . chem. Soc. 74, 3489 (1952).
Addition compounds of HfCI~and ZrCI4
1747
Table 2. I.R. absorption bands of HfC14and ZrCI4 addition compounds HfCI4 2dimethylformamide ZrCl4 2dimethylformamide Dimethylformamide HfCI4"2pyridine ZrCI~.2pyridine Pyridine HfCI4"2acetonitrile ZrC14.2acetonitrile Acetonitrile HfCI4'2methyl formate ZrCl4.2methyl formate Methyl formate HfCL" 2acetone ZrCI4'2acetone Acetone HfCI4'2dimethyl ether ZrCI.~.2dimethyl ether Dimethyl ether HfCI¢ 2diethyl ether ZrCI4"2diethyl ether Diethyl ether HfCI4-dioxane ZrClcdioxane Dioxane HfCI4 ZrCI4
1658s, 1481s, 1420s, 1352s, 1236m, 1124m, 1053m, 1007w, 701s, 420s, 366s, 319s, 309s, 298s 1650s, 1480s, 1420s, 1342s, 1232m, 1122m, 1052m, 1005w, 699s, 421s, 366s, 333s, 321s, 311s, 299s 1670s, 1500s, 1438s, 1388s, 1255s, 1091s, 864rn, 664s, 406m. 359s, 349s, 321s 1601s, 1536m, 1478s, 1441s, 1210m, 1059s, 104Is, 1010s, 754s, 686s, 642s, 424s, 335s, 309s, 298s 1602s, 1532m, 1482s, 1439s, 1212m, 1061s, 1043s, 1012s, 754s, 687s, 643s, 424s, 339s, 332s, 322s, 310s, 299s 1983m, 1920m, 1870m, 1580s, 1481s, 1439s, 1216s, 1145s, 1068s, 1029s, 990s, 747vs, 704vs, 604s, 407s 2305s, 2270s, 1020s, 942s, 356s. 339s, 315s, 300m 2303s, 2272s, 1022s, 942s, 362s, 343s, 314s,'298m 2290rn, 2248s, 1444s, 1375s, 1038s, 917s, 748m, 380m 1637s, 1607s, 1308s, 1173m, 973m, 881s, 872s, 800s, 683s, 612m, 510m, 452w, 368s, 338s, 332s, 319s, 310s, 298s 1632s, 1610s, 1303s, 1172m,971m, 881s, 873s, 798s, 678m, 613s. 576s, 494m, 392s, 366s, 347s, 332s, 320s, 309s, 299s 1722s, 1431s, 1378m, 1208s, 1157s, 1027m,909s, 766s, 335vs, 322s 1660s, 1630s, 1251s, 1082s. 828m, 538s, 432s, 341s, 320s, 311s, 300s 1661s, 1631s, 1253s, 1084s, 827m, 537s, 431s, 349s, 339s, 332s, 322s, 31 Is, 300m 1725s, 1428s, 1365s, 1223s, 1093m,902m, 531m, 393w 1593w, 1448s, 1421w, 1253m, 1144m, 1002s, 868s, 857s, 478m, 347s. 321rn, 309s, 301m 1594m, 1445s, 1419w, 1250m. 1143m, 1004s, 867s, 859s, 475m, 347s. 338s, 331m, 308s, 300m 1452m, 1165s, 1093s, 921m, 426m 1600m, 1187m, 1143m, 1087m, 1000s, 983s, 866s, 826s, 739s, 514s. 456s, 338s, 320s, 309s, 298s 1600m, 1187m, 1144m, 1087m, 1001s, 98 Is, 867s, 824m, 739s. 515s, 456s, 348m, 340s, 334s, 321s, 31 Is, 300s 1442m, 1381s. 1348s, 1295m, l l20vs, 1075s, 1041m, 932m, 844s, 498w, 442s 1298m, 1256s. 1090m, 1076m, 1035s, 881s, 849s, 829s, 610s, 357s. 339s, 319s, 309s, 301s 1293m, 1251s, 1089m, 1072m, 1034s, 880s, 849s, 828s, 609s, 363s, 347s, 339s, 333s, 321s, 309s, 299s 1450m, 1362m, 1286m, 1253s, l120s, 1081m, 1046m,873s, 617s, 289m 41 lm, 382s, 368s, 310m, 297s 405s. 392s, 309m, 297s
the metal, it is more difficult to explain the apparent strengthening of the C - - N bonds. A coupling of the T i - - N and C ~ N stretching frequencies has been suggested[12] to account for the increase in the C-~-~N stretching frequency observed when acetonitrile forms a 3 : 1 adduct with TiCI~. 12. M . W . Duckworth, G. W. A. Fowles and R. A. Hoodless, J. chem. Soc. 5665 (1963).
1748
W . M . G R A V E N and R. V. PETERSON
The spectral region below 365cm -1 is not easily interpreted for the addition compounds, as others have observed previously[13]. Although some differences between the spectra of the HfCI4 addition compounds and their ZrCI4 analogs are observed, no systematic variation is apparent. I n the spectra of the acetonitrile, methyl formate, dimethyl ether and dioxane products, there is evidence of band shifts to slightly higher frequencies in the ZrC14 compounds than in their respective HfCI4 analogs. In the remaining compounds, as well as the dimethyl ether and dioxane products, one or more bands present in the spectra of the ZrCI4 compounds are missing from the spectra of their respective HfCI4 analogs. Bands at 299 and 309 cm -1 appear in the spectra of all of the addition compounds, as well as in the spectra of freshly sublimed HfC14 and ZrCI4 dispersed in Nujol. The spectrum of each of the metal tetrahalides also exhibits a pair of bands in the region from 365 to 405 cm -1, with the ZrCI4 pair shifted by 24 cm -~ toward higher frequencies. The band at 411 cm -1 for HfCI4 has a much lower intensity and may result from the presence of approximately 5% ZrCL. The absence of bands in this region in the spectra of the addition compounds, except for the methyl formate compounds, demonstrates that substantial alterations in the metal-halogen stretching frequencies accompany the rearrangements resulting from the formation of two additional coordinate bonds to the metals. In the spectra of the gaseous tetrachlorides, the asymmetric stretching vibration has been observed[14] at 423 cm -1 for ZrC14 and at 393 cm -1 for HfCh. Although the positions of these bands and their separation compare rather well with the higher frequency doublets in the spectra of the solids, band splitting and the appearance of additional bands at lower frequencies accompany the transition from the vapor to the solid phase. Acknowledgement-The authors wish to thank J. H. Richardson for making the X-ray fluorescence analyses and W. D. Albright, Jr. for preparing and analyzing one of the addition compounds. 13. 1. R. Beattie and M. Webster, J. chem. Soc. 3507 (1964). 14. A. Biichler, J. B. Berkowitz-Mattuck and D. H. Dugre, J. chem. Phys. 34, 2202 (1961).
Pergamon Press.
Printed in Gte:Lt Britain
A D D I T I O N C O M P O U N D S OF HfCI4 A N D ZrCl4 WITH ORGANIC LIGANDS W. M. GRAVEN and R. V. PETERSON Materials Sciences Laboratory Aerospace Corporation, FJ Segundo, Calif. 9(/245 (First received 29 May 1968; in r e v i s e d j o r m 31 October 1968)
Abstract-Addition compounds of HfC14 and ZrCI4 with eight organic ligands have been prepared and analyzed. Infrared spectra and thermal decomposition measurements have demonstrated the similarity of properties between addition compounds of these two metal tetrahalides.
SINCE the first r e p o r t e d [ I ] i n t e r a c t i o n of o r g a n i c ligands with ZrCl4, a v a r i e t y of a d d i t i o n c o m p o u n d s h a v e b e e n p r e p a r e d by n u m e r o u s i n v e s t i g a t o r s . In c o n t r a s t . v e r y few a d d i t i o n c o m p o u n d s of HfC14 h a v e b e e n reported. In the few cases w h e r e c o m p a r i s o n s are possible, it a p p e a r s that small, b u t significant, differences exist in c e r t a i n p r o p e r t i e s of HfCI4 a n d ZrC14 a d d i t i o n c o m p o u n d s . In view of the close c h e m i c a l similarities of the two e l e m e n t s , it is significant to note the r e l e n t o b s e r v a t i o n [ 2 ] t h a t o n e - s t e p s e p a r a t i o n of HfC]4 a n d ZrCI4 is feasible b y utilization of the difference in rates of p r e c i p i t a t i o n of their complexes with o - p h e n y l e n e b i s d i m e t h y l a r s i n e (diarsine): T h i s work was u n d e r - t a k e n to o b t a i n c o m p a r a t i v e data for a r e p r e s e n t a t i v e g r o u p of o r g a n i c a d d i t i o n c o m p o u n d s of ZrC14 a n d HfCI4. With only a single e x c e p t i o n , the HfC14 c o m p o u n d s h a v e not b e e n p r e v i o u s l y reported. T h e r e f o r e , the p r e p a r a t i o n a n d c h a r a c t e r i z a t i o n of these c o m p o u n d s will also be reported. EXPERIMENTAL Materials. Hafnium tetrachloride was obtained from Electronic Space Products, Inc., and ZrCI4
was obtained from Alfa Inorganics, Inc. Both compounds were purified by sublimation prior to their use,
An X-ray fluorescence analysis showed the presence of 4-5 wt-% Zr in the HfCI4 and 2-3 wt-% Hf in the ZrCI4. These results, as well as the demonstrated absence of impurities in amounts greater than 0-1 percent, were confirmed by emission spectrographic analyses. In order to correct for the presence of the elemental analogs, effective atomic weights for 171.44 of Hf and 92.17 for Zr were used for computation of the analytical results. Vapor pressures of HfCI4, measured by a transpiration method between 200° and 250°, agreed well with data found in the literature[3]. All the organic ligands and solvents were Matheson, Coleman; and Bell spectroquality reagents. Each was dried with a suitable agent, distilled, and stored under an atmosphere of dry argon prior to its use. Preparative procedure. Since both metal tetrahalides and their addition compounds are susceptible to hydrolytic decomposition upon exposure to moisture, all operations involving transfer of solid materials were carried out in a glove box under an inert atmosphere. Reactions were carried out in flasks stoppered with rubber serum caps through which the liquid reagents were introduced with hypodermic syringes. I. J. M. M a t t h e w s , J . Arn. chem. Soc. 20, 815 (1898). 2. R.J.H. Clark, W. Errington, J. Lewis and R. S. Nyholm, J. chem. Soc. (A), 989 (1966). 3. A. A. Palko, A. D. Ryon and D. W. Kuhn,J. phys, Chem. 62, 319 (1958). 1743
1744
W . M . G R A V E N and R. V. PETERSON
In a typical preparation, 1-2 g of sublimed HfC4 was weighed out in a round-bottom flask. Approximately 20 ml of CC14 was added and the flask was stoppered and pressurized with dry argon. A volume of the organic ligand corresponding to 2-4 times the expected stoichiometric amount, was added with a hypodermic syringe. The reaction flask was then placed in a mechanical shaker for 16-48 hr. After the flask was transferred to the glove box, the liquid portion of the contents was decanted, the solid product was washed several times with dry hexane, and the flask was equipped with a stopcock adaptor for attachment to the vacuum line. The product was dried by evacuation to 10-3 torr. Analytical procedure. Hafnium and Zr were determined gravimetrically as their oxides by hydrolysis of the sample in an alcohol-water mixture followed by evaporation and ignition of the residue to constant weight in a Vycor crucible. Chlorine was determined gravimetrically as AgCI by using standard procedures which were modified (a) to avoid loss of HCI during hydrolysis by immersing the weighed sample immediately in NaOH solution (followed by careful acidification) and (b) to remove the suspension of hydrous metal oxide by filtration prior to the precipitation of AgCI. The i.r. spectra were obtained with a Beckman IR 4 spectrophotometer using NaC1 and CsBr prism interchange units. For the 1350-5000 cm -1 region, samples were mounted as Fluorolube mulls held between NaCI plates. For the 290-1350 cm -1 region, Nujol was used as the mulling agent, and for the 290-680 cm -1 region, the samples were held between Csl plates. The sample-mounting operations were carried out in a glove box. Melting points or decomposition temperatures were determined with a Hoover capillary melting point apparatus. Samples were transferred to capillary melting point tubes in the glove box and were sealed off before introduction to the apparatus.
RESULTS AND
DISCUSSION
It is evident from the elemental analytical data listed in Table 1 that with each ligand used, except p-dioxane, a di-addition product was obtained. Since in each case a two- to six-fold excess of ligand was employed, these compositions should correspond to the maximum ligand/metal ratios which are stable under the reaction conditions. In general, these compositions are in agreement with those reported in the literature, although two groups of investigators have prepared addition compounds with different stoichiometric formulas. A monoacetonate of ZrCI4 was obtained[4] when the reaction was carried out a t - 5 °, and 3:1 pyridine adducts were observed[5] with both ZrCI4 and HfC14 when the reactions were carried out in benzene with an excess of ligand present. Presently available data are insufficient to distinguish between a structure in which the two oxygens ofp-dioxane are attached to adjacent octahedral positions around the metal[6] and an alternative structure consisting of polymeric chains of metal atoms linked by p-dioxane molecules [7]. Each of the addition compounds dissolved completely in anhydrous methanol. Qualitative analyses of the methanol solutions using gas chromatography showed that each of the compounds had decomposed, thereby releasing the organic ligand. In several cases, rough calibrations indicated quantitative recovery of the ligands. Each of the addition compounds is a white solid which is stable at ambient temperature, but is rapidly decomposed by moisture. Some of the compounds exhibit characteristic melting points, although there is evidence of decomposition 4. 5. 6. 7.
P. T. Joseph and W. B. Blumenthal, J. org. Chem. 24, 1371 (1959). T. C. Ray and A. D. Westland, lnorg. Chem. 4, 1501 (1965). R. F. Rolsten and H. H. Sisler, J. A m . chem. Soc. 79, 1819 (1957). P.J. Hendra and D. B. Powell,J. chem. Soc. 5105 (1960).
Addition compounds of HfC]4 and ZrCl 4
1745
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1746
W . M . G R A V E N and R. V. PETERSON
of the molten liquid. Others appear to undergo decomposition without melting, also at fairly reproducible temperatures. Table 1 shows these data, together with corresponding values from the literature for several of the ZrC14 addition compounds. It is evident that for each pair of addition compounds, the ZrC14 compound melts and/or decomposes at a lower temperature than the HfC14 analog. This is to be expected for covalent compounds of metallic elements which are members of the same periodic family. It is also in agreement with the observation that HfCI4 compounds with phosphorus oxyhalides melted at slightly higher temperatures than did the corresponding ZrCI4 compounds [11]. The principal i.r. absorption bands of the HfCI4 and ZrC4 addition compounds are given in Table 2. Not included are very weak bands and bands at frequencies greater than 2400 cm -1, the former to avoid inclusion of bands due to trace impurities, such as solvents or free ligands, and the latter because of the inaccuracy of placement of the C - - H stretching frequencies for samples mulled with Fluorolube. For comparison, the absorption bands of the free ligands, obtained from thin films of the liquids or, in the case of dimethyl ether, from a Nujol solution, are also listed. In addition, the absorption bands observed for N ujol mulls of the freshly sublimed metal tetrahalides are included. It is apparent that no significant differences between the spectra of the HfCI4 and ZrCI4 compounds are to be found at frequencies greater than 600 cm -1. This is not unexpected, since metal-ligand fundamental stretching frequencies should be found at frequencies lower than 600 cm -1, and overtones which might occur at higher frequencies would probably have been eliminated from the compilation because of their low intensities. Only in the addition products with methyl formate are differences observed at frequencies higher than about 365 cm -~. For these two compounds, the differences in the 365-600 cm -1 region may result from the coupling of ligand vibrational modes with metal-ligand stretching modes. In the region above 600 cm -~, frequency shifts from ligand to addition compound are quite apparent. Without attempting an assignment of all of the absorption bands, one may note the shift to lower frequencies of the carbonyl stretching bands: from 1670 to 1654 cm -1 for the dimethylformamide compounds, from 1722 to 1635 cm -1 for the methyl formate compounds, and from 1725 to 1660 cm -~ for the acetone compounds. The C - - O - - C stretching bands in the ethers have been lowered from 1093 to 1003 cm -~ in the dimethyl ether compounds, from 1120 to 1000 cm -~ in the diethyl ether compounds, and from 1120 to 1035 cm -1 in the dioxane products. In contrast, the (3~N stretching band has been raised from 2248 cm -1 in acetonitrile to 2271 cm -1 in its addition compounds. Similarly, the coupled ~C and ~ N stretching band at 1580 cm -a in pyridine has been raised to 1602 cm -~ in its addition compounds. Although the weakening of the C - - O bonds, as indicated by the lower stretching frequencies in the addition compounds, can be readily understood in terms of the electron withdrawal resulting from coordinate bonding of the oxygen atom to 11. E. M. Larsen, J. Howatson, A. M. Gammill and L. Wittenberg, J. A m . chem. Soc. 74, 3489 (1952).
Addition compounds of HfCI~and ZrCI4
1747
Table 2. I.R. absorption bands of HfC14and ZrCI4 addition compounds HfCI4 2dimethylformamide ZrCl4 2dimethylformamide Dimethylformamide HfCI4"2pyridine ZrCI~.2pyridine Pyridine HfCI4"2acetonitrile ZrC14.2acetonitrile Acetonitrile HfCI4'2methyl formate ZrCl4.2methyl formate Methyl formate HfCL" 2acetone ZrCI4'2acetone Acetone HfCI4'2dimethyl ether ZrCI.~.2dimethyl ether Dimethyl ether HfCI¢ 2diethyl ether ZrCI4"2diethyl ether Diethyl ether HfCI4-dioxane ZrClcdioxane Dioxane HfCI4 ZrCI4
1658s, 1481s, 1420s, 1352s, 1236m, 1124m, 1053m, 1007w, 701s, 420s, 366s, 319s, 309s, 298s 1650s, 1480s, 1420s, 1342s, 1232m, 1122m, 1052m, 1005w, 699s, 421s, 366s, 333s, 321s, 311s, 299s 1670s, 1500s, 1438s, 1388s, 1255s, 1091s, 864rn, 664s, 406m. 359s, 349s, 321s 1601s, 1536m, 1478s, 1441s, 1210m, 1059s, 104Is, 1010s, 754s, 686s, 642s, 424s, 335s, 309s, 298s 1602s, 1532m, 1482s, 1439s, 1212m, 1061s, 1043s, 1012s, 754s, 687s, 643s, 424s, 339s, 332s, 322s, 310s, 299s 1983m, 1920m, 1870m, 1580s, 1481s, 1439s, 1216s, 1145s, 1068s, 1029s, 990s, 747vs, 704vs, 604s, 407s 2305s, 2270s, 1020s, 942s, 356s. 339s, 315s, 300m 2303s, 2272s, 1022s, 942s, 362s, 343s, 314s,'298m 2290rn, 2248s, 1444s, 1375s, 1038s, 917s, 748m, 380m 1637s, 1607s, 1308s, 1173m, 973m, 881s, 872s, 800s, 683s, 612m, 510m, 452w, 368s, 338s, 332s, 319s, 310s, 298s 1632s, 1610s, 1303s, 1172m,971m, 881s, 873s, 798s, 678m, 613s. 576s, 494m, 392s, 366s, 347s, 332s, 320s, 309s, 299s 1722s, 1431s, 1378m, 1208s, 1157s, 1027m,909s, 766s, 335vs, 322s 1660s, 1630s, 1251s, 1082s. 828m, 538s, 432s, 341s, 320s, 311s, 300s 1661s, 1631s, 1253s, 1084s, 827m, 537s, 431s, 349s, 339s, 332s, 322s, 31 Is, 300m 1725s, 1428s, 1365s, 1223s, 1093m,902m, 531m, 393w 1593w, 1448s, 1421w, 1253m, 1144m, 1002s, 868s, 857s, 478m, 347s. 321rn, 309s, 301m 1594m, 1445s, 1419w, 1250m. 1143m, 1004s, 867s, 859s, 475m, 347s. 338s, 331m, 308s, 300m 1452m, 1165s, 1093s, 921m, 426m 1600m, 1187m, 1143m, 1087m, 1000s, 983s, 866s, 826s, 739s, 514s. 456s, 338s, 320s, 309s, 298s 1600m, 1187m, 1144m, 1087m, 1001s, 98 Is, 867s, 824m, 739s. 515s, 456s, 348m, 340s, 334s, 321s, 31 Is, 300s 1442m, 1381s. 1348s, 1295m, l l20vs, 1075s, 1041m, 932m, 844s, 498w, 442s 1298m, 1256s. 1090m, 1076m, 1035s, 881s, 849s, 829s, 610s, 357s. 339s, 319s, 309s, 301s 1293m, 1251s, 1089m, 1072m, 1034s, 880s, 849s, 828s, 609s, 363s, 347s, 339s, 333s, 321s, 309s, 299s 1450m, 1362m, 1286m, 1253s, l120s, 1081m, 1046m,873s, 617s, 289m 41 lm, 382s, 368s, 310m, 297s 405s. 392s, 309m, 297s
the metal, it is more difficult to explain the apparent strengthening of the C - - N bonds. A coupling of the T i - - N and C ~ N stretching frequencies has been suggested[12] to account for the increase in the C-~-~N stretching frequency observed when acetonitrile forms a 3 : 1 adduct with TiCI~. 12. M . W . Duckworth, G. W. A. Fowles and R. A. Hoodless, J. chem. Soc. 5665 (1963).
1748
W . M . G R A V E N and R. V. PETERSON
The spectral region below 365cm -1 is not easily interpreted for the addition compounds, as others have observed previously[13]. Although some differences between the spectra of the HfCI4 addition compounds and their ZrCI4 analogs are observed, no systematic variation is apparent. I n the spectra of the acetonitrile, methyl formate, dimethyl ether and dioxane products, there is evidence of band shifts to slightly higher frequencies in the ZrC14 compounds than in their respective HfCI4 analogs. In the remaining compounds, as well as the dimethyl ether and dioxane products, one or more bands present in the spectra of the ZrCI4 compounds are missing from the spectra of their respective HfCI4 analogs. Bands at 299 and 309 cm -1 appear in the spectra of all of the addition compounds, as well as in the spectra of freshly sublimed HfC14 and ZrCI4 dispersed in Nujol. The spectrum of each of the metal tetrahalides also exhibits a pair of bands in the region from 365 to 405 cm -1, with the ZrCI4 pair shifted by 24 cm -~ toward higher frequencies. The band at 411 cm -1 for HfCI4 has a much lower intensity and may result from the presence of approximately 5% ZrCL. The absence of bands in this region in the spectra of the addition compounds, except for the methyl formate compounds, demonstrates that substantial alterations in the metal-halogen stretching frequencies accompany the rearrangements resulting from the formation of two additional coordinate bonds to the metals. In the spectra of the gaseous tetrachlorides, the asymmetric stretching vibration has been observed[14] at 423 cm -1 for ZrC14 and at 393 cm -1 for HfCh. Although the positions of these bands and their separation compare rather well with the higher frequency doublets in the spectra of the solids, band splitting and the appearance of additional bands at lower frequencies accompany the transition from the vapor to the solid phase. Acknowledgement-The authors wish to thank J. H. Richardson for making the X-ray fluorescence analyses and W. D. Albright, Jr. for preparing and analyzing one of the addition compounds. 13. 1. R. Beattie and M. Webster, J. chem. Soc. 3507 (1964). 14. A. Biichler, J. B. Berkowitz-Mattuck and D. H. Dugre, J. chem. Phys. 34, 2202 (1961).