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Possible existence of a (pyridine-H-pyridine)+ cation in some lanthanide chelates and tetraphenylboron compounds
348
Notes
analysis (found: 8.7 per cent N2H4, 60.6 per cent Cd and 29.6 per cent F; calcd: 8.6 per cent N2H,,, 60.3 per cent Cd and 30.6 per cent F). The i.r. spectrum is shown in Table 4 and has all the vibrations, characteristic for the NzH62÷ ions. The spectrum was assigned by comparing it with the spectra of N2H6F2, N2H6CI2121], and N2,H6SO4122 ]. Three endothermic peaks (160°, 202 ° and 262°C) indicate a compound, different from the two hydrazinium fhiorides[23]. The isolated compound is related to the magnesium complex, N2H6(MgF3) 2 [24]. No reaction was observed between CdF 2 and N2HsF in aqueous solutions.
"'Jo~ef Stefan'" Institute P. GLAVI(~ Faculty of Natural Sciences and Technology J. SLIVNIK University of Ljubljana A. BOLE Ljubljana Yugoslavia Acknowledgements---The present work was carried out with the financial supports of the "Boris Kidri~" Foundation and of the National Bureau of Standards, Washington, which are gratefully acknowledged. The authors wish to thank Miss B. Sedej for the chemical analysis and Mr. M. Milojevi~ for the thermal analysis.
REFERENCES I. P. Glavi~ and J. Slivnik, J. inorg, nucl. Chem. 32, 2939 (1970). 2. P. Glavi~ and A. Bole, J. inorg, nucl. Chem. 34, 2959 (1972). 3. P. Glavit3, J. Slivnik and A. Bole, J. inorg, nucl. Chem. 35, 427 (1973). 4. P. Glavi~, J. Slivnik and A. Bole, J. inorg, nucl. Chem. 35, 427 (1973). 5. H. Franzen and O. von Mayer, Z. anorg, allg. Chem. 60, 247 (1908).
6. H. Franzen and H. L. Lucking, Z. anorg. Chem. 70, 145 (1911). 7. P. R~.y and P. V. Sacker, J. chem, Soc. 117, 321 (1920). 8. A. Braibanti, G. Bigliardi, A. M. Lanfredi and M. Camellini, Z. Kristallogr. 120, 261 (1964). 9. A. Braibanti, G. Bigliardi, R. Canalli Padovani and F. Dallavalle, Gazz. chim. ital. 95, 1212 (1965). 10. S. P. Kozerenko. S. A. Polishchuk and N. I. Sigula, Dokl. Akad. Nauk SSSR 205, 1104 (1972). 11. P. J. Aliev, M. N. Guseinov and N. G. Kluchnikov, Zh. neorg. Khim. 17, 85 (1972). 12. P. Glavi~, Thesis, Ljubljana 1968. 13. M. Trontelj and P. Glavi~, J. chem. Thermodynamics 1, 339 (1969). 14. T. Curtius and F. Schrader, J. prakt. Chem. 50/2, 311 (1894). 15. These results were reported together with some other transition-metal fluorides (ZrFa, HfF 4, CeF4, NiF2, ZnF2) on the 4th European Symposium on Fluorine Chemistry, Ljubljana, 28 Aug.-I Sept., 1972; IJS Report R-613, November 1972. 16. H. M. Haendler and W. J. Bernard, J. Am. chem. Soc. 73, 5218 (1951). 17. T. S. West, Complexometry with EDTA and Related Agents, BDH Chemicals Ltd., Poole, 1969. 18. L. Sacconi and A. Sabatini, J. inorg, nucl. Chem. 25, 1389 (1963). 19. A. Braibanti, F. Dallavale, M. A. PeUinghelli and E. Leporati, Inorg. Chem. 7, 1430 (1968). 20. A. Ferrari, A. Braibanti and A. M. Lanfredi, Ann. chim. Roma 418/11, 1238 (1958). 21. R.G. Snyder and J. C. Decius, Spectrochim. Acta 13, 280 (1959). 22. A. V. R. Warrier and P. S. Narayanan, Indian J. Pure appl. Phys. 5, 216 (1967). 23. M. Milojevi6 and J. Slivnik, Thermal analysis, Vol. 3, p. 19. Proceedings Third ICTA, Davos, 1971. 24. J. Slivnik, M. ~vanut and B; $edej, Mh. Chem. 99, 1713 (1968).
J. inorg, nucL Chem., 1975,Vol. 37, pp. 348-350. Pergamon Press. Printedin Great Britain.
Possible existence of a (pyridine-H-pyridine) ÷ cation in some lanthanide chelates and tetraphenylboron compounds (Received 10 May 1974)
LANTHANIDE complexes of stoichiometry, Ln(hfaa)~. L. LH [L = 3- or 4-methyl pyridine, hfaa = (CF3COCHCOCF3)- ] have been prepared. The isolation of a series of compounds, BPh4. L. LH, suggests that the neutral L is not coordinated to the metal ion in the lanthanide complexes. It is proposed that these compounds may contain a hydrogen bonded (L2H) + unit. A similar hydrogen bonded unit may be present in other solvated tetrakis(fl-diketoenolato)lanthanide complexes. A number of tetrakis(fl-diketoenolato)lanthanide com-
plexes, Ln(hJaa)4 cation, [hfaa = (CF3COCHCOCF3)] with a range of cations including pyridinium have been reported by Melby et al.[1]. These compounds probably contain an 8-coordinate Ln 3÷ ion similar to that found in Y~hJaa)4Cs where the eight carbonyl oxygens are coordinated to the metal ion[2]. More recently, complexes containing an additional molecule of neutral amine, Ln(hfaa)4.4Mepy. 4MepyH, where Ln = Tb and Gd, and 4Mepy and 4MepyH = 4-methylpyridine and the 4-methylpyridinium cation respectively, have been isolated[3]. The possibility
349
Notes of the neutral amine molecule being loosely held in the crystal is not supported by our observation that the compounds may be sublimed with only partial loss of the neutral amine. An alternative explanation is that the 4Mepy molecule is coordinated to the lanthanide ion giving it a 9-coordinate stereochemistry. Nine-coordination is unusual in lanthanide chelates and most established examples of this coordination number involve monodentate ligands. For example, the [Ln(H20)~] 3÷ ion occurs in crystalline Ln(EtSOg)39H20[4] and Ln(BrO3)39H20[5] and the [Ln(OH)9] 6- ion in crystalline lanthanide trihydroxides[6]. Similar stereochemistries have been reported for various lanthanide halides[7] and oxyhalides[8]. Ninecoordination has been established in the chelates, M[Ln(edta)(H20)315H20[9], where M = K ÷, ,Na + and NH~ and edta = ethylenediaminetetraceticacid tetraanion, and has been suggested as the possible stereochemistry of some water and dimethylformamide adducts of tetrakisIfldiketoenolato)-lanthanide complexes[10]. We report below the preparation of other tetrakis(fldiketoenolato)lanthanide complexes containing a molecule of neutral amine and also compounds of similar composition containing the anion BPh2.
EXPERIMENTAL
Typical synthetic procedures are given below. The lanthanide halides were prepared from the respective oxides (Koch-Light). The pyridine and substituted pyridines were distilled before use. Hexafluoroacetylacetone and trifluoroacetylacetone (Koch-Light) were used without any further purification.
Preparation of Eu(hfaa)4. 4Mepy. 4MepyH A solution of 0.26g EuCI 3 (0-001 mole) in 10ml 50:50 aqueous ethanol was added dropwise to a solution of 0.94g hexafluoroacetylacetone (0.0045mole) and 0.93g 4-methylpyridine (0.01 mole) in 20 ml ethanol. The crystalline product was washed with 50:50 aqueous ethanol and dried in vaeuo,
Preparation of BPh4.4Mepy. 4MepyH A solution of 0.30g 4MepyHCl (0.0023mole) in 15ml water was added to a solution of 0.68 g NaBPh4 (0"002 mole) in 15 ml 4-methylpyridine. The crystalline product was washed with water and dried in vacuo. 4MepyHCl was
prepared by bubbling HCI through a dry benzene solution of 4-methylpyridine.
Preparation of BPh 4 . BufNH3. DMF BPh 4 . ButNHa was obtained by mixing equimolar solutions of NaBPh 4 and ButNHaCI in acetonitrile. 0-5g BPh 4 . ButNH3 was dissolved in ca. 10 ml dimethylformamide. On standing, crystals separated which were washed with light petroleum and dried in vacuo. Only the 1 : 1 species, BPh~. LH, were obtained for L = NH3, EtaN, quinuclidine [N(CH2CH2)aCH ], and 2,6lutidine. 1 : 1 species 4MepyHX, were also the sole product for X = ClO~, BF~ and PF 6. No homogeneous salts of 4MepyH were obtained using the anions: NCS-, p-CH 3C6H4SO3-, CO~ 2, $203"2, N(SO3)~ 3 or fl-naphthol 2,6disulphonate. RESULTS AND DISCUSSION
The complexes, Ln(hfaa)4. L . LH (Ln = Eu, Gd and Tb, L = 4Mepy and Ln = Eu, L = 3Mepy), have been prepared in the presence of excess heterocyclic amine (see Experimental). Attempts to prepare analogous compounds with L = NH3, Me3N, ButNH2, quinoline and piperidine were not successful, the products in each case being either the ~'normal" tetrakis compounds, Ln(hfaa)4. LH, or a hydrated form of this compound, Ln(hfaa)4, L H . (H20), (n ~< 1). The inclusion of an additional heterocyclic amine molecule is not restricted to tetrakis hexafluoroacetylacetonate chelates as we have also prepared Eu(tfaa)4.4Mepy,4MepyH [tfaa = (CFaCOCHCOCHa)- ]. The complexes, Ln(hfaa)4. L. LH, may be vacuum sublimed with only partial loss of the neutral amine which suggests that the additional amine molecule is not simply occluded in the crystal structure. It is significant that the inclusion of a neutral amine molecule in these complexes occurs with substituted pyridines but has not been observed with aliphatic amines or larger heterocyclic amines such as quinoline. It is unlikely that steric and/or electronic effects would particularly favour coordination to the Ln a + ion of the pyridines rather than any of the other amines examined. These arguments against the pyridines being clathrated or coordinated to give a nine-coordinate Ln 3+ ion led us to consider the possibility of a hydrogen bonding interaction between the protonated and neutral amines such as that shown in (I). A similar type of structure was predicted by Had,~i[ll] in the case of ~t-picoline-N-oxide(II) and has been confirmed by X-ray work[12]. No analogous pyridine system has been reported [ 13].
Table 1. Microanalytical results Compound
Eu(hfaa) 4 . 4Mepy. 4MepyH Gd(hfaa)4.4Mepy. 4MepyH Tb(hfaa)4.4Mepy. 4MepyH Eu(hfaa) 4 . 3Mepy. 3MepyH Eu(tfaa)4.4Mepy. 4MepyH BPh 4 . 4Mepy. 4MepyH BPh 4 . 3Mepy. 3MepyH BPh 4 . 2Mepy. 2MepyH BPh4. py. pyH BPh 4 . Bu'NH 3 . DMF
C
Found (70) H
N
C
Calcd (~) H
N
32.7 32.6 32.7 33.0 39.9 85.3 85.7 85.7 85.5 79.4
1.7 1.6 1.6 1.6 3.4 7.0 7.1 6.6 6.4 8.6
2.3 2-5 2.4 2.4 2.9 5.4 5.4 5.3 5.7 5.9
32.9 32.8 32.7 32.9 40.4 85.4 85.4 85.4 85'4 79.8
1.6 1.6 1.6 1.6 3-3 7.0 7.0 7.0 6.5 8.4
2.4 2.4 2-4 2.4 2.9 5.5 5-5 5.5 5"9 6.0
350
Notes
~ - - H - - N ~ I
+
(I) CHa
7+
--O--H--O--N~) (II)
CH3
We have examined the ~H NMR spectra of mixtures of 4Mepy and 4MepyH in acetonitrile solution at 37 C and did not obtain any evidence of the existence of the cation (I) in these solutions. On the basis that this cation may be stabilized in the solid state by the large lanthanide complex anion the behaviour of another large anion BPh2, was examined under similar conditions. The compounds, BPh4. L. LH, were isolated where L = py, 2Mepy, 3Mepy and 4Mepy. These compounds can be vacuum sublimed with only partial loss of L. The view that the molecule of neutral amine is not clathrated in the crystal is supported by the observation that BPh 4 . 4MepyH, at least, does not occlude non-donor molecules such as benzene. All of the other amines investigated (see Experimental) gave either the normal 1:1 salts BPh 4. LH, or inhomogeneous products. However, recrystallization of the 1:1 complex BPh 4 . Bu'NH 3 from dimethylformamide {DMF), gave BPh,. Bu~NH3. DMF; it is notable that the hydrochlorides of the pyridines, and of Bu'NH2, are extremely hygroscopic, giving LH{OH2),,CI. None of the other anions examined each of which was smaller than either BPhg or LnthJaa)-, gave a 2:1 compound. The correlation between the behaviour of the Ln(hjaa)g and BPh,~ ions suggests strongly that the Ln 3+ ion is not 9-coordinate in the salts Ln(hJaa)4. L. LH and that a discrete cationic unit, probably of type ~1), is present in both these and the B P h 4 . L . L H salts. Similarly, the formation of a DMF adduct of BPh 4 . Bu'NH 3 suggests, by analogy with the L. LH salts, the formation of a cation of type IIll):
CHa)3CNH2--H...O==C
Illl)
\
Neither DMF nor water adducts[10] of tetrakisCfl-diketoenolato)lanthanide complexes need be formulated as containing 9-coordinate Ln3~; instead the DMF or H20 may be weakly bonded to the cation, as in (II1). The bonding interactions in cations such as (1) and (111) are likely to be relatively weak: the occurrence of type/I) only with pyridines and not with aliphatic amines or larger heterocycles indicates that the molecular size and shape of the amine is particularly important. I.R. spectroscopy and mass spectrometry at low ionizing energies (ca. 10 eV) have not provided unambiguous evidence for the proposed structure. This will require X-ray structural investigations CHRISTOPHER GLIDEWELL T. MAURICE SHEPHERD Department of Chemistry The University St. Andrews Scotland
REFERENCES
1. L. R. Melby, N. J. Rose, E. Abramson and J. C. Caris, J. Am. chem. Soc. 86, 5117 (1964). 2. M. J. Bennett, F. A. Cotton, P. Legzdins and S. J. Lippard, Inorg. Chem. 7, 1770 (1968); J. H. Burns and M. D. Danford, ibid. 8, 1780 (1969). 3. T. D. Brown and T. M. Shepherd, J. chem. Soc. Dalton 336 (1973). 4. J. A. A. Ketelaar, Physica 4, 619 (1937); D. R. Fitzwater and R. E. Rundle, Z. Kristallogr. 112, 362 (1959). 5. L. Helmholz, J. Am. chem. Soc. 61, 1544 (1939). 6. K. Schubert and A. Seitz, Z. anorg, allg. Chem. 254, 116 (1947). 7. W. H. Zachariasen, Acta crystallogr. 1, 265 (1948); A. Zalkin and D. H. Templeton, J. Am. chem. Soc. 75, 2453 (1953); D. H. Templeton and G. F. Carter, J. phys. Chem. 58, 940 (1954); J. H. Burns, Inorg. Chem. 4, 881 (1965); A. Zalkin, D. H. Templeton and T. E. Hopkins, lnorg. Chem. 5, 1466 (1966). 8. W. H. Zachariasen, Acta crystallogr. 9, 1015 (1956); I. Mayer, S. Zolotov and F. Kassierer, lnorg. Chem. 4, 1637 (1965). 9. J. L. Hoard, B. Lee and M. D. Lind, J. Am. chem. Soc. 87, 1612 (1965). 10. M. O. Workman and J. H. Burns, Inorg. Chem. 8, 1542 (1969). 11. D. Had~i, J. chem. Soc. 5128 (1962). 12. H. H. Mills and J. C. Speakman, Proc. chem. Soc. 216 (1963). 13. J. C. Speakman, Structure and Bonding 12, 141 (1972).
Notes
analysis (found: 8.7 per cent N2H4, 60.6 per cent Cd and 29.6 per cent F; calcd: 8.6 per cent N2H,,, 60.3 per cent Cd and 30.6 per cent F). The i.r. spectrum is shown in Table 4 and has all the vibrations, characteristic for the NzH62÷ ions. The spectrum was assigned by comparing it with the spectra of N2H6F2, N2H6CI2121], and N2,H6SO4122 ]. Three endothermic peaks (160°, 202 ° and 262°C) indicate a compound, different from the two hydrazinium fhiorides[23]. The isolated compound is related to the magnesium complex, N2H6(MgF3) 2 [24]. No reaction was observed between CdF 2 and N2HsF in aqueous solutions.
"'Jo~ef Stefan'" Institute P. GLAVI(~ Faculty of Natural Sciences and Technology J. SLIVNIK University of Ljubljana A. BOLE Ljubljana Yugoslavia Acknowledgements---The present work was carried out with the financial supports of the "Boris Kidri~" Foundation and of the National Bureau of Standards, Washington, which are gratefully acknowledged. The authors wish to thank Miss B. Sedej for the chemical analysis and Mr. M. Milojevi~ for the thermal analysis.
REFERENCES I. P. Glavi~ and J. Slivnik, J. inorg, nucl. Chem. 32, 2939 (1970). 2. P. Glavi~ and A. Bole, J. inorg, nucl. Chem. 34, 2959 (1972). 3. P. Glavit3, J. Slivnik and A. Bole, J. inorg, nucl. Chem. 35, 427 (1973). 4. P. Glavi~, J. Slivnik and A. Bole, J. inorg, nucl. Chem. 35, 427 (1973). 5. H. Franzen and O. von Mayer, Z. anorg, allg. Chem. 60, 247 (1908).
6. H. Franzen and H. L. Lucking, Z. anorg. Chem. 70, 145 (1911). 7. P. R~.y and P. V. Sacker, J. chem, Soc. 117, 321 (1920). 8. A. Braibanti, G. Bigliardi, A. M. Lanfredi and M. Camellini, Z. Kristallogr. 120, 261 (1964). 9. A. Braibanti, G. Bigliardi, R. Canalli Padovani and F. Dallavalle, Gazz. chim. ital. 95, 1212 (1965). 10. S. P. Kozerenko. S. A. Polishchuk and N. I. Sigula, Dokl. Akad. Nauk SSSR 205, 1104 (1972). 11. P. J. Aliev, M. N. Guseinov and N. G. Kluchnikov, Zh. neorg. Khim. 17, 85 (1972). 12. P. Glavi~, Thesis, Ljubljana 1968. 13. M. Trontelj and P. Glavi~, J. chem. Thermodynamics 1, 339 (1969). 14. T. Curtius and F. Schrader, J. prakt. Chem. 50/2, 311 (1894). 15. These results were reported together with some other transition-metal fluorides (ZrFa, HfF 4, CeF4, NiF2, ZnF2) on the 4th European Symposium on Fluorine Chemistry, Ljubljana, 28 Aug.-I Sept., 1972; IJS Report R-613, November 1972. 16. H. M. Haendler and W. J. Bernard, J. Am. chem. Soc. 73, 5218 (1951). 17. T. S. West, Complexometry with EDTA and Related Agents, BDH Chemicals Ltd., Poole, 1969. 18. L. Sacconi and A. Sabatini, J. inorg, nucl. Chem. 25, 1389 (1963). 19. A. Braibanti, F. Dallavale, M. A. PeUinghelli and E. Leporati, Inorg. Chem. 7, 1430 (1968). 20. A. Ferrari, A. Braibanti and A. M. Lanfredi, Ann. chim. Roma 418/11, 1238 (1958). 21. R.G. Snyder and J. C. Decius, Spectrochim. Acta 13, 280 (1959). 22. A. V. R. Warrier and P. S. Narayanan, Indian J. Pure appl. Phys. 5, 216 (1967). 23. M. Milojevi6 and J. Slivnik, Thermal analysis, Vol. 3, p. 19. Proceedings Third ICTA, Davos, 1971. 24. J. Slivnik, M. ~vanut and B; $edej, Mh. Chem. 99, 1713 (1968).
J. inorg, nucL Chem., 1975,Vol. 37, pp. 348-350. Pergamon Press. Printedin Great Britain.
Possible existence of a (pyridine-H-pyridine) ÷ cation in some lanthanide chelates and tetraphenylboron compounds (Received 10 May 1974)
LANTHANIDE complexes of stoichiometry, Ln(hfaa)~. L. LH [L = 3- or 4-methyl pyridine, hfaa = (CF3COCHCOCF3)- ] have been prepared. The isolation of a series of compounds, BPh4. L. LH, suggests that the neutral L is not coordinated to the metal ion in the lanthanide complexes. It is proposed that these compounds may contain a hydrogen bonded (L2H) + unit. A similar hydrogen bonded unit may be present in other solvated tetrakis(fl-diketoenolato)lanthanide complexes. A number of tetrakis(fl-diketoenolato)lanthanide com-
plexes, Ln(hJaa)4 cation, [hfaa = (CF3COCHCOCF3)] with a range of cations including pyridinium have been reported by Melby et al.[1]. These compounds probably contain an 8-coordinate Ln 3÷ ion similar to that found in Y~hJaa)4Cs where the eight carbonyl oxygens are coordinated to the metal ion[2]. More recently, complexes containing an additional molecule of neutral amine, Ln(hfaa)4.4Mepy. 4MepyH, where Ln = Tb and Gd, and 4Mepy and 4MepyH = 4-methylpyridine and the 4-methylpyridinium cation respectively, have been isolated[3]. The possibility
349
Notes of the neutral amine molecule being loosely held in the crystal is not supported by our observation that the compounds may be sublimed with only partial loss of the neutral amine. An alternative explanation is that the 4Mepy molecule is coordinated to the lanthanide ion giving it a 9-coordinate stereochemistry. Nine-coordination is unusual in lanthanide chelates and most established examples of this coordination number involve monodentate ligands. For example, the [Ln(H20)~] 3÷ ion occurs in crystalline Ln(EtSOg)39H20[4] and Ln(BrO3)39H20[5] and the [Ln(OH)9] 6- ion in crystalline lanthanide trihydroxides[6]. Similar stereochemistries have been reported for various lanthanide halides[7] and oxyhalides[8]. Ninecoordination has been established in the chelates, M[Ln(edta)(H20)315H20[9], where M = K ÷, ,Na + and NH~ and edta = ethylenediaminetetraceticacid tetraanion, and has been suggested as the possible stereochemistry of some water and dimethylformamide adducts of tetrakisIfldiketoenolato)-lanthanide complexes[10]. We report below the preparation of other tetrakis(fldiketoenolato)lanthanide complexes containing a molecule of neutral amine and also compounds of similar composition containing the anion BPh2.
EXPERIMENTAL
Typical synthetic procedures are given below. The lanthanide halides were prepared from the respective oxides (Koch-Light). The pyridine and substituted pyridines were distilled before use. Hexafluoroacetylacetone and trifluoroacetylacetone (Koch-Light) were used without any further purification.
Preparation of Eu(hfaa)4. 4Mepy. 4MepyH A solution of 0.26g EuCI 3 (0-001 mole) in 10ml 50:50 aqueous ethanol was added dropwise to a solution of 0.94g hexafluoroacetylacetone (0.0045mole) and 0.93g 4-methylpyridine (0.01 mole) in 20 ml ethanol. The crystalline product was washed with 50:50 aqueous ethanol and dried in vaeuo,
Preparation of BPh4.4Mepy. 4MepyH A solution of 0.30g 4MepyHCl (0.0023mole) in 15ml water was added to a solution of 0.68 g NaBPh4 (0"002 mole) in 15 ml 4-methylpyridine. The crystalline product was washed with water and dried in vacuo. 4MepyHCl was
prepared by bubbling HCI through a dry benzene solution of 4-methylpyridine.
Preparation of BPh 4 . BufNH3. DMF BPh 4 . ButNHa was obtained by mixing equimolar solutions of NaBPh 4 and ButNHaCI in acetonitrile. 0-5g BPh 4 . ButNH3 was dissolved in ca. 10 ml dimethylformamide. On standing, crystals separated which were washed with light petroleum and dried in vacuo. Only the 1 : 1 species, BPh~. LH, were obtained for L = NH3, EtaN, quinuclidine [N(CH2CH2)aCH ], and 2,6lutidine. 1 : 1 species 4MepyHX, were also the sole product for X = ClO~, BF~ and PF 6. No homogeneous salts of 4MepyH were obtained using the anions: NCS-, p-CH 3C6H4SO3-, CO~ 2, $203"2, N(SO3)~ 3 or fl-naphthol 2,6disulphonate. RESULTS AND DISCUSSION
The complexes, Ln(hfaa)4. L . LH (Ln = Eu, Gd and Tb, L = 4Mepy and Ln = Eu, L = 3Mepy), have been prepared in the presence of excess heterocyclic amine (see Experimental). Attempts to prepare analogous compounds with L = NH3, Me3N, ButNH2, quinoline and piperidine were not successful, the products in each case being either the ~'normal" tetrakis compounds, Ln(hfaa)4. LH, or a hydrated form of this compound, Ln(hfaa)4, L H . (H20), (n ~< 1). The inclusion of an additional heterocyclic amine molecule is not restricted to tetrakis hexafluoroacetylacetonate chelates as we have also prepared Eu(tfaa)4.4Mepy,4MepyH [tfaa = (CFaCOCHCOCHa)- ]. The complexes, Ln(hfaa)4. L. LH, may be vacuum sublimed with only partial loss of the neutral amine which suggests that the additional amine molecule is not simply occluded in the crystal structure. It is significant that the inclusion of a neutral amine molecule in these complexes occurs with substituted pyridines but has not been observed with aliphatic amines or larger heterocyclic amines such as quinoline. It is unlikely that steric and/or electronic effects would particularly favour coordination to the Ln a + ion of the pyridines rather than any of the other amines examined. These arguments against the pyridines being clathrated or coordinated to give a nine-coordinate Ln 3+ ion led us to consider the possibility of a hydrogen bonding interaction between the protonated and neutral amines such as that shown in (I). A similar type of structure was predicted by Had,~i[ll] in the case of ~t-picoline-N-oxide(II) and has been confirmed by X-ray work[12]. No analogous pyridine system has been reported [ 13].
Table 1. Microanalytical results Compound
Eu(hfaa) 4 . 4Mepy. 4MepyH Gd(hfaa)4.4Mepy. 4MepyH Tb(hfaa)4.4Mepy. 4MepyH Eu(hfaa) 4 . 3Mepy. 3MepyH Eu(tfaa)4.4Mepy. 4MepyH BPh 4 . 4Mepy. 4MepyH BPh 4 . 3Mepy. 3MepyH BPh 4 . 2Mepy. 2MepyH BPh4. py. pyH BPh 4 . Bu'NH 3 . DMF
C
Found (70) H
N
C
Calcd (~) H
N
32.7 32.6 32.7 33.0 39.9 85.3 85.7 85.7 85.5 79.4
1.7 1.6 1.6 1.6 3.4 7.0 7.1 6.6 6.4 8.6
2.3 2-5 2.4 2.4 2.9 5.4 5.4 5.3 5.7 5.9
32.9 32.8 32.7 32.9 40.4 85.4 85.4 85.4 85'4 79.8
1.6 1.6 1.6 1.6 3-3 7.0 7.0 7.0 6.5 8.4
2.4 2.4 2-4 2.4 2.9 5.5 5-5 5.5 5"9 6.0
350
Notes
~ - - H - - N ~ I
+
(I) CHa
7+
--O--H--O--N~) (II)
CH3
We have examined the ~H NMR spectra of mixtures of 4Mepy and 4MepyH in acetonitrile solution at 37 C and did not obtain any evidence of the existence of the cation (I) in these solutions. On the basis that this cation may be stabilized in the solid state by the large lanthanide complex anion the behaviour of another large anion BPh2, was examined under similar conditions. The compounds, BPh4. L. LH, were isolated where L = py, 2Mepy, 3Mepy and 4Mepy. These compounds can be vacuum sublimed with only partial loss of L. The view that the molecule of neutral amine is not clathrated in the crystal is supported by the observation that BPh 4 . 4MepyH, at least, does not occlude non-donor molecules such as benzene. All of the other amines investigated (see Experimental) gave either the normal 1:1 salts BPh 4. LH, or inhomogeneous products. However, recrystallization of the 1:1 complex BPh 4 . Bu'NH 3 from dimethylformamide {DMF), gave BPh,. Bu~NH3. DMF; it is notable that the hydrochlorides of the pyridines, and of Bu'NH2, are extremely hygroscopic, giving LH{OH2),,CI. None of the other anions examined each of which was smaller than either BPhg or LnthJaa)-, gave a 2:1 compound. The correlation between the behaviour of the Ln(hjaa)g and BPh,~ ions suggests strongly that the Ln 3+ ion is not 9-coordinate in the salts Ln(hJaa)4. L. LH and that a discrete cationic unit, probably of type ~1), is present in both these and the B P h 4 . L . L H salts. Similarly, the formation of a DMF adduct of BPh 4 . Bu'NH 3 suggests, by analogy with the L. LH salts, the formation of a cation of type IIll):
CHa)3CNH2--H...O==C
Illl)
\
Neither DMF nor water adducts[10] of tetrakisCfl-diketoenolato)lanthanide complexes need be formulated as containing 9-coordinate Ln3~; instead the DMF or H20 may be weakly bonded to the cation, as in (II1). The bonding interactions in cations such as (1) and (111) are likely to be relatively weak: the occurrence of type/I) only with pyridines and not with aliphatic amines or larger heterocycles indicates that the molecular size and shape of the amine is particularly important. I.R. spectroscopy and mass spectrometry at low ionizing energies (ca. 10 eV) have not provided unambiguous evidence for the proposed structure. This will require X-ray structural investigations CHRISTOPHER GLIDEWELL T. MAURICE SHEPHERD Department of Chemistry The University St. Andrews Scotland
REFERENCES
1. L. R. Melby, N. J. Rose, E. Abramson and J. C. Caris, J. Am. chem. Soc. 86, 5117 (1964). 2. M. J. Bennett, F. A. Cotton, P. Legzdins and S. J. Lippard, Inorg. Chem. 7, 1770 (1968); J. H. Burns and M. D. Danford, ibid. 8, 1780 (1969). 3. T. D. Brown and T. M. Shepherd, J. chem. Soc. Dalton 336 (1973). 4. J. A. A. Ketelaar, Physica 4, 619 (1937); D. R. Fitzwater and R. E. Rundle, Z. Kristallogr. 112, 362 (1959). 5. L. Helmholz, J. Am. chem. Soc. 61, 1544 (1939). 6. K. Schubert and A. Seitz, Z. anorg, allg. Chem. 254, 116 (1947). 7. W. H. Zachariasen, Acta crystallogr. 1, 265 (1948); A. Zalkin and D. H. Templeton, J. Am. chem. Soc. 75, 2453 (1953); D. H. Templeton and G. F. Carter, J. phys. Chem. 58, 940 (1954); J. H. Burns, Inorg. Chem. 4, 881 (1965); A. Zalkin, D. H. Templeton and T. E. Hopkins, lnorg. Chem. 5, 1466 (1966). 8. W. H. Zachariasen, Acta crystallogr. 9, 1015 (1956); I. Mayer, S. Zolotov and F. Kassierer, lnorg. Chem. 4, 1637 (1965). 9. J. L. Hoard, B. Lee and M. D. Lind, J. Am. chem. Soc. 87, 1612 (1965). 10. M. O. Workman and J. H. Burns, Inorg. Chem. 8, 1542 (1969). 11. D. Had~i, J. chem. Soc. 5128 (1962). 12. H. H. Mills and J. C. Speakman, Proc. chem. Soc. 216 (1963). 13. J. C. Speakman, Structure and Bonding 12, 141 (1972).