.I. Phys. Chem. 1990, 94, 4832-4835
4832
An ab Initio Characterization of the Tetraphosphorus Oxide P,O Lawrence L. Lohr Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109 (Received: October 16, 1989; In Final Form: January 9, 19901
The gaseous tetraphosphorus oxide P40 has been characterized by ab initio electronic structure calculations. Four stationary points have been located at the HF/3-21G* and HF/6-31G* levels by using analytic gradients and the GAUSSIANX~program. Vibrational frequencies were calculated from analytic second derivatives at each stationary point, with three of these points corresponding to local minima and the fourth to a transition state. Isomerization energies were calculated at the correlated MP2/6-3 IC*//HF/6-31G* and MP4SDQ/6-31G*//HF/6-31G* levels. At every level considered the most stable structure is the cyclic planar form (C2usymmetry); less stable is the nonplanar bridge-bonded structure (C2"symmetry), and least stable is the terminally bonded structure (C,, symmetry). Comparisons of calculated vibrational frequencies to those observed by Andrews and Withnall [ J . Am. Chemi. Soc. 1988, 1 I O , 56051 support their identification of the terminally bonded isomer but suggest that spectral bonds assigned to the bridge-bonded isomer may belong instead to another species, possibly the cyclic isomer.
Introduction In a recent publication' we reported the results of an ab initio computational study of the structures, isomerization energies, and vibrational frequencies of the series of diphosphorus oxides P20, ( x = 1-5). That study, like our earlier studies2*, of monophosphorus oxides and oxyacids, was inspired by the continuing experimental interest in the combustion of phosphorus and phosphorus-containing compounds. Some recent experimental developments include matrix isolation studies of the PH3-03 a d d ~ c tof, ~the products H,PO, H,POH, (HO),HPO, and HPO , ~ of the products PO, HPO, PO2, from the PH, 0, r e a ~ t i o nand PO,, HOPO, P205,H 2 P 0 , and HOPH from the PH, + 0 reaction.6 The laser-induced fluorescence of gaseous PO, has also been recently inve~tigated.~ A particularly important studyx involved the IR characterization in an argon matrix of the products P 4 0 , PO, and PO2 formed by the reaction of 0 atoms with P4. This was the first identification of the species P40, with IR absorptions being assigned to both the C,,terminally bonded and C2, bridge-bonded isomers. Since the intensity of the spectral peaks associated with the bridgebonded isomer increased upon short-wavelength irradiation, while those associated with the terminally bonded isomer did not, the former is assumed to be the more stable isomer, a conclusion consistent with the known structure9of the tetraphosphorus oxide P406(all oxygens bridging). More recently, a studylo of the matrix reaction of P2 with O3 has led to the identification of PO, PO,, PO2-, P 2 0 , P202,P203, PZO4, P205,and possibly planar cyclic P40. Also recently studied" are the vis-UV absorption spectra of PO, and PO, in solid Ar. In our present computational study we report ab initio results for the geometries, energies, and vibrational frequencies for three isomers of P,O, namely, terminally bonded, bridge-bonded, and cyclic, as well as for a transition qtate. The suggestion to consider a cyclic structure mas made to us b) Andrewsi2 following the computational ~ t u d i e sof ' ~ McCluskey and Andrews and the ex-
+
( 1 ) Lohr, L. L. J . Phys. Chem. 1990, 94, 1807; citation of refs 7 and I8 for PO, vibrational frequencies should have included citation of ref 4. (2) Lohr. L. L. J . Phys. Chem. 1984, 88, 5569. (3) Lohr, L. L.; Boehm, R . C. J . Phys. Chem. 1987, 91, 3203. (4) Withnall. R.; Hawkins, M.; Andrews, L. J . Phys. Chem. 1986. 90. 575. (5) Withnall, R.; Andrews, L. J . Phys. Chem. 1987, 91, 784. (6) Withnall, R.; Andrews, L. J . Phys. Chem. 1988, 92, 4610. (7) Hamilton, P. A. J . Chem. Phys. 1987, 86, 33. (8) Andrews, L.; Withnall, R . J . Am. Chem. SOC.1988, 110, 5605. (9) Beagley, E.:Cruickshank. D. W. J.; Hewitt, 7.G.: Jost, K. H . Trans. Faraday SOC.1969, 65, 1219.
(IO) Mielke, Z.; McCluskey. M.; Andrews, L. Chem. Phy.r. Lett. 1990, 165, 146. ( I I ) Withnail. R.; McCluskey, M.; Andrews. L. J . Phys. Chem. 1989. 93. 126. ( 1 2) Andrews. L. Private communication.
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periments of Mielke et a1.I0 Comparisons are made to our earlier results[ for diphosphorus oxides, especially P,O. Other recent computational studies of phosphorus compounds i n ~ l u d e l in~-~~ vestigations of H3P0, of H2PXYH (X, Y = 0,s),and of HPPH and H2PP and investigations" of monophosphorus and diphosphorus acids as well as methylated phosphates. Method ,411 calculations were made with the GAUSSIANB~program," with molecular geometries being initially optimized at the S C F (HF) level by using analytic gradients and the split-valence basis set 3-21G*, which contains polarization functions (all six second-order Gaussians were employed) for the second-row atom (P) only. This computational level is designated HF/3-21G*. In order to distinguish local minima from saddle points, vibrational frequencies were calculated at this level by using analytic second derivatives. Geometries were then reoptimized, and vibrational frequencies were recalculated at the HF/6-3 1G* level (split valence plus polarization functions for both P and 0 atoms). Correlation energies were initially calculated at the MP2, MP3, and MP4SDTQ levels by using the 3-21G* basis and HF/3-21G* geometries; these calculations are designated as MPn/3-21G*/ /HF/3-21G*. Correlation energies were also calculated at the MP2, MP3, and MP4SDQ levels by using the 6-31G* basis and HF/6-3 1G* geometries: the latter calculations are designated as MPn/6-31G*//HF/6-31G*. Although generally adequate for rough characterization of geometries, the HF/3-21G* level does not adequately describe P - U P linkages in the oxo-bridged isomers of P203,P20,, and P20,, or as in the acids H4P202rh( n = 1-4) studiedi7cby Ewig and Van Wazer, and thus would be suspect for the bridge-bonded isomers of P40. Results and Discussion Molecular Structures. Figure 1 shows the HF/3-21G* and HF/6-3 IC* (in parentheses) geometries for the four stationary points which we have located for P,O. The order is in terms of decreasing energy (increasing stability), with the saddle point of ( I 3) McCluskey, M.; Andrews, L. To be submitted for publication. (14) Boatz, J. A: Schmidt. M. W.; Gordon, M. S. J . Phys. Chem. 1987, 91, 1743. (15) Boatz, J . A.; Gordon, M. S. J . Comput. Chem. 1986, 7, 306. (16) Schmidt, M .W.; Gordon, M . S. Inorg. Chem. 1986, 25, 248. ( 1 7 ) (a) Ewig, C. S.; Van Wazer, J. R. J . Am. Chem. Soc. 1985, 107, 1965. (b) J . Am. Chem. SOC.1986, 108,4354. (c) J . Am. Chem. SOC.1988, 110. 79. (18) Frisch, M. J.; Binkely, J . S.; Schlegel, H. B.; Raghavachari, K.; Melius. C. F.; Martin, R . L.; Stewart, J. J . P.; Bobrowitz, F. W.; Rohlfing, C. M.: Kahn, L. R.; DeFrees, D. J.; Seeger, R.; Whiteside, R. A,; Fox, D. J . ; Fluder, E. M.; Pople, J. A. GAUSSIAN86; Carnegie-Mellon Quantum Chemistry Publishing Unit: Pittsburgh, PA, 1986.
C 1990 American Chemical Society
The Journal of Physical Chemistry, Vol. 94, No. 12, 1990 4833
Tetraphosphorus Oxide P 4 0
TABLE I: Ab Initio Energies" and Energy Differencesbfor P,O structure TS
symmetry
HF
MP2
MP4SDQ
ZPEe
cs
-1437.666 56 (19 590) -1437.702 96 (1 1601) -1437.74284 (2849) -1437.755 82 (0)
-1438.307 77 (13772) -1438.32383 ( 1 0 247) -1438.345 57 (5476) -1438.37052
-1438.328 00 (16 151) -1438.349 14 (1 1512) -1438.37921 (49 12) -1438.401 59
0.009 62 (-262) 0.01 1 22 (90) 0.01 I 04 (50) 0.01081
(0)
(0)
(0)
I
C3"
11
C2"
111
C2"
"Energies in au at designated level with 6-31G' basis and HF/6-31G* geometries from Figure I . bEnergy difference in cm-' in parentheses. 'Zero-point energy at HF/6-31G* level.
' \2271 ( 2 288)
P-P
2 157 ( 2 164)
Figure 1. Stationary-point geometries at the HF/3-21G* and (in parentheses) HF/6-31G* levels for P40. Bond distances in angstroms and angles in degrees. The structures are in the order of decreasing energy (increasing stability). For structure I (CJ the three basal P-P bonds are 2.232 and 2.245 A at the HF/3-21G1 and HF/6-31G* levels, respectively.
C,symmetry (labeled TS for "transition state" as it is characterized by having one imaginary vibrational frequency) being the least stable, followed by the terminally bonded structure ( I ) with C3" symmetry, then the bridge-bonded structure (11) of C, symmetry, and finally the cyclic structure (111) of C2, symmetry as the most stable. This energy ordering (Table I) is found to be the same at all computational levels considered with either basis set, although the energy differences are certainly dependent on the level and basis. The P-P bond distances are somewhat longer than those in the parent P4 molecule with Td symmetry, the latter being found to be 2.162 and 2.076 8, at the HF/3-21G* and HF/6-31G* levels, respectively. Specifically, the basal P-P bonds in the terminally bonded C,,structure I are 2.245 8, at the HF/6-3lG* level, while the basal bond in the bridge-bonded C2, structure I1 is 2.206 A at the same level, both values being comparable to the value of 2.214 8, for P2H4. The experimental value19 (electron diffraction) for P4 itself is 2.21 A, in line with the general tendency of HF/6-31G* bond distances to be too short. The nominal double and single bonds in the cyclic structure (111) differ somewhat from each other, being 2.030 and 2.164 A, respectively, at the HF/631G* level. In our earlier study] of P20, (x = 1-5), we reported the result that P-O-P bond angles are unusually sensitive to the inclusion of oxygen polarization functions in the basis set, with bond angle (19) Maxwell, L. R.; Hendricks, S. B.; Mosley, V. M . J . Chem. Phys. 1935, 3, 699.
reductions in going from HF/3-21G* to HF/6-3 1G* computational levels of 164.0' to 138.0' for P203, 164.4' to 130.6' for P204, and 180.0' to 131.6' for P205. A similar reduction in P-0-P angles was r e p ~ r t e d "by ~ Ewig and Van Wazer in their theoretical study of the oxo-bridged acids H4P202n-1( n = 1-4). Thus, the near-consistency of the bridge angle in P 4 0 with structure 11, namely, 98.6' and 97.6' at the HF/3-21G* and HF/6-3 1G* levels (Figure IC),respectively, may seem surprising. However, this angle is already constrained to be rather small by the P4 tetrahedron, much as there is a very small and insensitive P-0-P angle in cyclic P20, also of C2,symmetry, with bridge angles of 67.7' and 68.3' at these respective levels. Similarly constrained, though to a larger value, is the P U P angle in cyclic P 4 0 (structure HI),which has values of 131.7' and 130.3' at the HF/3-21G* and HF/6-3 1G* levels, respectively. Even the P-P-O angle in the TS structure is nearly constant at 112.2' and 109.8' for the HF/3-21G* level, as is the related angle in the P 2 0 TS structure, namely, 96.9' and 94.1' at these respective levels. Our value of 98' for the P-0-P angle in bridge-bonded P 4 0 (structure 11) is thus smaller than the 1 10' value estimateds by Andrews and Withnall from the I8O shifts in the stronger antisymmetric and weaker symmetric stretching modes and much smaller than the 126.4 f 0.7' value (electron diffraction) found9 for P406, which is a not nearly so constrained molecule. By contrast, our value of 130' for the P-0-P angle in cyclic P 4 0 (structure 111) is larger than the estimate of Andrews and Withnall. Our P-0 distances of 1.676 and 1.635 8, (Figure 1 c and d, HF/6-31G*) is rather close, however, to the observed distance of 1.638 f 0.003 A for P406. an X-ray crystallographic study9 of P408,with six bridging and two terminal 0 atoms per molecule, found averaged brid ing angles of 130.1 f 0.9' and P-O distancesof 1.633 f 0.010 (bridging 0) and 1.412 f 0.015 8, (terminal 0),the latter being comparable to our HF/6-31G* value of 1.462 8, in the terminally bridged C30isomer of P 4 0 (Figure l b ) . Molecular Energies. From the ab initio energies (in au) and energy differences (in cm-I) in Table I, we see that the stability of the bridge-bonded isomer I1 relative to the terminally bonded isomer I and the TS structure is reduced by inclusion of correlation corrections, although as stated above, the bridged isomer I1 is still the energetically preferred of the two. Similar results are found with the smaller 3-21G* basis but are not tabulated. For P 2 0 we earlier found that the preferred collinear isomer is stabilized by correlation corrections relative to the bridged and TS forms. The consistency here is that correlation appears to be more important for the terminally bonded form of P,O than for the bridge-bonded form; for P 2 0 , where the terminally bonded form is the more stable at the H F level because of the large strain in the alternative cyclic form, correlation increases the stabilization of the terminally bonded form, but for P 4 0 , where the bridgebonded form, not nearly so strained as its P 2 0 analogue, is more stable at the H F level than the terminally bonded form, correlation decreases the stabilization of the bridged-bonded form, but not sufficiently to change the qualitative energy ordering of the isomers. It is presumably low-lying excitations into vacant T * MO's associated with the terminal P - 0 group which account for the larger correlation energy of molecules containing this grouping as compared to the higher lying excitations associated with P-0-P bridges.
A
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Lohr
The Journal of Physical Chemistry, Vol. 94, No. 12, I990
TABLE 11: Vibrational Frequencies and IR Intensities for P,O structure symmetry mode calc v" obs Y,+ calc intC 319.3 5.0 12.7 1.4 7.8 2.0 10.2 13.4 7.6
I320 647 55 I 46 1 455 388
203 197 344id 1357 645 574 463 381 275 836 734 623 517 498 48 1 392 384 382
855 713 656 626 518 470 35 1 3 29 228
1241 603
so1
441 393 243 856 ( 1 ) 553 (?)
244. I 0.2 33.6 1.7 1 .o 40.2 79.1 28.8 6.5 9.2 1.9 8.6
0 10.4 0.3 826 (?)
42.2 53.2 14.4 4.3 14.9 5.8
1.7 6. I
0
"HF/6-31G* values in cm-I. bobserved values in cm-l from ref 8; the 826-cm-' value for structure 111 is from ref IO. 'IR intensities in km mol-! at HF/6-31G* level. dImaginary frequency.
Somewhat surprisingly, the planar cyclic isomer (structure 111) is the most stable structure considered, being approximately 5000 level cm-l lower in energy at the MP4SDQ/6-3lG*//HF/6-31G* than the nonplanar bridge-bonded isomer (structure 11). Electron correlation enhances this stability, again presumably because of low-energy excitations to a* MO's, this time associated with the nominal P-P double bonds. The P-0-P angle in the ring is of low strain, with a value virtually identical with that we computed for the unconstrained P2O4 and P 2 0 5 molecules, namely, approximately 130'. We explore below the question as to whether the species assigned by Andrews and Withnall as nonplanar bridge-bonded P 4 0 might be planar cyclic P 4 0 instead. Although we find (Table I) the terminally bonded C3cisomer 1 to be less stable than the bridge-bonded isomer I1 by at least 6000 cm-I and less stable than the cyclic isomer 111 by at least 1 1 000 cm-l, the transition state has an energy about 5000 cm-' still higher (MP4SDQ/6-31G*//HF/6-31G* values). About all we can say is that this result appears to be consistent with the result8 of Andrews and Withnall cited in the Introduction that the IR intensity of the terminally bonded isomer does not increase upon irradiation of the matrix containing the reaction products, suggesting that although it is not the most stable isomer, it is nonetheless stabilized against isomerization by a significant barrier. Vibrational Frequencies. Table I 1 list the HF/6-31G* vibrational frequencies (in cm-I) and IR intensities (in km mol-,) for each of the P 4 0 stationary points. The smaller basis HF/3-21G* values are similar but not tabulated. Also listed are the observed values8 of Andrews and Withnall; in line with common experience these are 88-95% of our calculated values. An exception is the intermediate e mode ( q )of the terminally bonded isomer, with the observed value of 393 cm-I. Overall, however, the excellent agreement between our (scaled) frequencies and the observed values lends strong support to Andrews and Withnall's identifications of the terminally bonded species. By contrast. we do not
1 0
1P,O(C,)
Terminal
P,(T,)
P40(C2,) Bridged
P,O(C2,) Cyclic
I
Figure 2. Correlation of the HF/6-31G* vibrational frequencies (in cm-I) for P,O structure I (C,,, terminally bonded) and I1 (C,,, bridgebonded) with the frequencies of P, (Td). Frequencies for the cyclic P 4 0 structure 111 (C2J are shown at the right.
have computational evidence which supports their identification of the (nonplanar) bridge-bonded isomer. Their highest frequency associated with this isomer is at 856 cm-l and is known from the I8O isotope shift to be antisymmetric; our highest (unscaled) frrequency mode of that (b,) symmetry is at 734 cm-I, while our highest overall ( a l ) is at 836 cm-I. Their assignment of the symmetric P-0-P stretch is to a mode at 553 cm-l, so that their assignments parallel those for P40s, for which there is a consensus20~21 that there is an antisymmetric P-0-P stretch at 953 cm-' and a symmetric stretch at 640 cm-l in solid Ar. However, Mielke et al. have very recently identifiedi0a sharp I6O, l 8 0 IR doublet at 826 and 790 cm-', respectively, as arising from a new P 4 0 species which is produced in a photolyzed Ar matrix presumably by the reaction of P 2 0 with P2. They suggested a cyclic structure for this species, which is different from the presumably bridge-bonded species formed from the reaction of P4 with 0 atoms. Our calculated frequency (Table 11) of 855 cm-' for the b2 mode of cyclic P 4 0 is consistent with this assignment; we are uncertain as to the identity and structure of the species earlier8 assigned to brige-bonded P 4 0 . One possibility is that our computational level (HF/6-31G*) seriously underestimates both the P-0-P angle and the antisymmetric P-0-P stretching frequency in nonplanar bridge-bonded P40. Since the angle and frequency are certainly correlated, with the HF/6-3 1G* frequency being, only 270 cm-I for cyclic P 2 0 with a tightly constrained P-0-P angle of 68.3', this possibility warrants further study. If the species exhibiting the 856-cm-, antisymmetric stretch is nonplanar bridge-bonded P 4 0 after all, then we should have obtained a calculated frequency of approximately 950 cm-I rather than 734 cm-' (Table 11) for the higher b2 mode. An unreported species which conceivably may be responsible for the observed 856-cm-' absorption is P402 with Dzd symmetry; the antisymmetric P-0-P stretches transform as a degenerate e representation so that only one fundamental in this spectral region would be seen. Figure 2 shows the calculated HF/6-31G* frequencies for the terminally bonded and bridge-bonded isomers of P 4 0 together with similarly calculated frequencies for P4. When an 0 atom is added terminally to P4, a high frequency a, stretching mode and a very low frequency e bending mode appear, with the t2 framework mode splitting into a , and e components. When an 0 atom forms a (20) Chapman, A. C. Specfrochim.Arlo, Part A 1969, 24, 1687. ( 21) Beattie, I . R.; Livingstone, K . M. S.; Ozin, G. A,; Reynolds, D. J. J . Chem SOC 1970. 449
J . Phys. Chem. 1990, 94, 4835-4838 bridge, moderately high frequency a, and b2 stretching modes and a low frequency bl bending mode are formed, with the t2 and e framework modes splitting as shown.
Summary Our ab initio characterization of the tetraphosphorus oxide P 4 0 supports the conclusion* of Andrews and Withnall that the terminally bonded isomer of C3, symmetry is less stable than the bridge-bonded isomer of C2, symmetry. In addition, we have located a more stable structure, the cyclic planar isomer, also with C2, symmetry, which may possibly be the form responsible for the 856- and 553-cm-' IR absorptions which they associated6 with the bridge-bonded form but is more likely the newly reportedlo species formed from P 2 0 and P2 and having an 826-cm-' IR absorption. The computed value of 130° for the P-0-P bridging
4835
angle in the cyclic isomer is virtually identical with the computed values we have recently reported1 for the oxo-bridged isomers of Pz03,P204, and P20s, while the angle computed for the nonplanar bridge-bonded isomer of P 4 0 is a much smaller and presumably strained value of 98'. The structural integrity of the P-0-P grouping is thus found to be the unifying theme of our computational studies of diphosphorus and tetraphosphorus oxides, as it was in Ewig and Van Wazer's of the diphosphorus acids H4P202n-
I,
Acknowledgment. The author thanks Professor Lester Andrews of the University of Virginia for the suggestion of this research problem and for numerous very helpful telephone conversations. He also thanks the University of Michigan Computing Center for a special allocation of computing funds which made this project possible.
Simulation of Crystal Field Effect in Monoclinic Rare Earth Oxyhydroxides Doped with Trivalent Europium Jorma Holsa Department of Chemical Engineering, Helsinki University of Technology, SF-021 50 Espoo, Finland (Received: Ocrober 27, 1989) The visible luminescence spectra of the monoclinic form of the Eu3+-dopedrare earth oxyhydroxides, REOOH:Eu3+ (RE = La, Gd, Y,and Lu), recorded at 77 K are reported and analyzed. The 'FW experimental energy level schemes were simulated with the aid of the phenomenological crystal field (cf) theory. The sets of the nine nonzero cf parameters for the C, symmetry reproduce the experimental energy level schemes in a satisfactory manner (with rms deviations between 5.7 and 11.5 cm-I) in spite of the real symmetry of the RE site being lower, C,. The parameter values as well as the strength of the cf effect vary only slightly within the structurally isomorphic REOOH series. The cf effect is weak when compared to that in rare earth oxyhalides, oxysulfates, and oxymolybdates/oxytungstates studied previously.
Introduction Rare earth oxyhydroxides, REOOH (RE = La-Lu and Y), have been under keen interest since they were first prepared and characterized some 50 years ago.' These compounds have different physical, e.g., optical and magnetic, properties depending on the host cation-a fact inherent in the nature of the chemically so similar rare earth elements. Even the structure of rare earth oxyhydroxides, though remaining the same through the rare earth series, can be modified without difficulty by using elevated pressure and temperature in preparatiom2 As a result of such versatile properties, rare earth oxyhydroxides have been subject to a considerable amount of studies dealing with the preparation3s4and crystal structure determination, by both and neutron diffraction7 techniques. Their as well as opticallo,'' properties have been described, and infraredI2 and MBssbauerI3 studies have been carried out with these materials. Finally, the (I) (2) 239. (3) (4)
Weiser, H. B.; Milligan, W. 0. J . Phys. Chem. 1938, 42, 669. Gondrand, M.; Norlund Christensen, A. Mafer. Res. Bull. 1971, 6,
Norlund Christensen, A. Acfa Chem. Scand. 1966, 20, 896. Holsa, J.; Leskela, T.; Leskela, M. Proc. Symp. Inorg. Anal. Chem. 1984, 68. (5) Klevtsova, R. F.; Klevtsov, P. V. J . Sfruct. Chem. 1964, 5 , 795. (6) Norlund Christensen, A. Acfa Chem. Scand. 1965, 19, 1504. (7) Norlund Christensen, A.; von Heidestam, 0.Acfa Chem. Scand. 1966, 20. 2658. (8) Norlund Christensen, A.; Quezel, S . J . SolidSfate Chem. 1974, 9, 234. (9) Norlund Christensen, A.; Quezel, S . Solid State Commun. 1972, IO, 765. (IO) Chateau, C.; Holsa, J.; Leskela, T.; Leskela, M. Inf. Symp. Rare Earfh Specfrosc. 1984, 49. ( I I ) Holsa, J.; Leskela, T.; Leskela, M. Inorg. Chem. 1985, 24, 1539. (12) Klevtsov, P. V.; Klevtsova, R. F.;Sheina, L. P. J . Strucr. Chem. 1967, 8, 229. (13) Katila, T.E.; Typpi, V. K.; Shenoy, G. K.; Niinisto, L. Solid State Commun. 1972, 1 1 , 1147.
0022-3654/90/2094-4835$02.50/0
effect of the phase transition with increased external pressure and temperature on the optical luminescence of the trivalent Eu3+ion has been investigated. I 4 ~ 1 The aim of this paper is to extend the study of the optical luminescence properties of the monoclinic form of rare earth oxyhydroxides doped with trivalent europium to the analysis of the cf effect on the 7Fw levels. The phenomenological simulation of the cf splittings of these levels was carried out with the aid of a phenomenological cf model. The evolution of the cf effect as a function of the host cation and the correlation to the properties of the other rare earth oxysalts studied previously16-20are also reported.
Experimental Section Preparation of RE Oxyhydroxides. Monoclinic R E oxyhydroxides can be obtained by two different methods: either by the thermal decomposition of the corresponding trihydroxides2I or hydrothermally.6 Especially the lighter members of the whole RE series can be prepared with the former method whereas the latter method gives only trihydroxides or mixed-phase products. In order to prepare oxyhydroxides extending over the whole RE series, both methods were used this work. In general, the hydrothermal method was found to give products of better crystallinity. (14) Chateau, C.; Holsa, J.; Leskela, T.; Leskela, M. Proc. 11th Scand. Sfruc. Chem. Meet. 1984, 52. (1 5 ) Holsa, J.; Chateau, C.;Leskela, T.; Leskela, M. Acfa Chem. Scand., A 1985, 39, 415. (16) Holsa, J.; Porcher, P. J . Chem. Phys. 1981, 75, 2108. (17) Holsa, J.; Porcher, P. J . Chem. Phys. 1982, 76, 2790. (18) Porcher, P.; Svoronos, D. R.; Leskela, M.; HBlsa, J. J . Solid State Chem. 1983, 46, 101. (19) Sovers, 0. J.; Yoshioka, T. J . Chem. Phys. 1968, 49, 4945. (20) Huang, J.; Loriers, J.; Porcher, P. J . Solid S f a f eChem. 1982, 43, 87. (21) Klevtsov, P. V.; Sheina, L. P. Inorg. Mafer. 1965, I , 2006.
0 1990 American Chemical Society
