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Spectroscopic properties and structure of the Holmium perchlorate-1,10 phenanthroline complexes in non-aqueous solvents
SPECTROSCOPIC PROPERTIES AND STRUCTURE OF THE HOLMIUM PERCHLORATE-1,lO PHENANTHROLINE COMPLEXES IN NON-AQUEOUS SOLVENTS KRYSTYNA BUKIETYRSKA*
and
PHAM NGOC THUYf
Institute of Chemistry, University of Wroclaw, 50-383 Wroclaw, 14 Joliot-Curie, Poland (Received 3 August 1987 ; accepted after revision 25 November 1987)
Abstract-Absorption spectroscopy studies of the anhydrous Ho(ClO& in CH30H and CH&N solutions with different concentrations of 1,lO-phenanthroline are reported. Analysis of the intensities of the&-transitions (in terms of Judd-Ofelt parameters and oscillator strengths of the “hypersensitive” transition) indicates that stable complex species with the N-donor ligand are formed. The species with four molecules of l,lO-phenanthroline in acetonitrile solution is characterized by one of the highest known P,, values observed for the heavy lanthanide compounds in solution. Studies of this species mixed CH,CN-solv. solutions (where solv.-H,O and CH,OH) showed the first coordination sphere of holmium as [Ho(phen), - (CH3CN)13+. The spectral characteristics of these systems are particularly suitable for studies of the “hypersensitivity” mechanisms.
In our recent paper’ we have studied the spectroscopic properties of anhydrous and hydrated neodymium perchlorates in methanol solutions with 2,2’-bipyridine (bipy) and 1, lo-phenanthroline (phen). It was found, that in non-aqueous solutions, species with N-donor ligand molecules in the direct environment of the lanthanide ion can exist. It is interesting then, to compare the behaviours of heavy and light lanthanide ion complexes. Some structural differences between them can be expected-because the lanthanide contraction may be responsible for some difficulties in the packing of relatively large ligand molecules in the first coordination sphere of the smaller (rNd3+= 0.995 A, r&+ = 0.894 A) holmium ion. The more interesting aspect of this paper, however, appeared in the influence of the solvents and N-donor ligand on the intensities of the f-f transitions of the heavy lanthanide ion. A particular role of CH3CN is clearly seen from results presented in this paper. We have investigated anhydrous holmium perchlorates with 1, lo-phenanthroline in CH30H and CH$N solutions. Solvates of some anhydrous lanthanide perchlorates in these solvents were *Author to whom correspondence should be addressed. TPermanent Vietnam.
address:
University
of Hanoi,
Hanoi,
studied recently by different methods, which were helpful in our studies.‘-’
EXPERIMENTAL Hydrated Ho(ClO,), was prepared from 99.9% Hoz03 (Merck), by the method given by Forsberg.6 Anhydrous Ho(ClO& was prepared by the slow heating of the hydrated holmium perchlorate, for at least 120 h. All salts used were fully analysed. 1 , 10-phenanthroline was dehydrated in vacua (1 mm Hg) for at least one week. All anhydrous reagents were checked for water contamination. Only samples with no O-H stretching bands in their IR spectra, were used for spectral measurements. The solvents used were also dried carefully. CH30H was dried using molecular sieves (A-4). Acetonitrile was doubly distilled over P4010, then dehydrated using CaH, and redistilled. In freshly prepared solvent, no O-H stretching bands were observed in the IR. The solutions in mixed solvents were prepared from an anhydrous solution of Ho(ClO& in anhydrous acetonitrile with 1, lo-phenanthroline (molar ratio Ho3+ : phen = 1: 4), with CH3CN diluted with an appropriate amount of water or methanol, respectively. All solutions for the spectroscopic measurements were stored under a dry nitrogen atmosphere.
641
642
K. BUKIETYfiSKA
MEASUREMENTS
AND CALCULATIONS
Spectral measurements were made on a Cary 14spectrophotometer at 293 K, over the spectral range available (11,00&30,000 cm-‘). UV bands of the Ho3+ ion have not been used in the intensity parameter calculations, because basic lines of the absorption bands were not well determined due to the strong absorption of the ligand in this spectral region. Experimental oscillator strengths of solution absorption bands were obtained by graphical integration of the area under the absorption curves after the appropriate correction of the base line. Q, parameters were calculated from the experimental oscillator strength values by applying the Judd-Ofelt equation in the form :
where : X-refraction index x = (n”+ 2)2/9n ; @--matrix elements of the unit tensor operator calculated by Carnal1 et al.’ from the free ion state eigenvectors J-total quantum number.
;
Calculations were performed for the different sets of levels, however, sets of levels with minimal mean square error were the same for all the considered systems. Absorption spectra of Ho3+-l,lO-phen-
A
H&Phe
(a)
-l:o
A
and P. N. THUY
anthroline complexes in CH30H and CH,CN were measured for different M: L ratios (from M:L= 1:0.5 to M:L= 1:5). The spectra with M : L = 1: 0 are the spectra of pure holmium perchlorate dissolved in the appropriate solvent. The spectra of anhydrous hohnium perchlorate with phen (M : L = 1: 4) in CH,CN, with different molar ratios of H20 and CH30H were also measured. RESULTS
AND DISCUSSION
As was proved previously for Nd3+ with phen,’ the most significant differences for different Ho3+. . phen molar ratios are observed for the “hypersensitive” transition. This is illustrated in Fig. l(a), where the influence of the increasing 1, lo-phenanthroline concentration on the ‘G6 c ‘Z8Ho3+ transition is presented. The Judd-Ofelt parameter values RAof the Ho(ClO,),-phen system in methanol solutions are collected in Table 1. Among the three Q parameters (Table l), as can be expected, Q2 exhibits the most significant changes, whereas Sk,and Q6 remain almost constant within the limit of experimental error. Detailed analysis of the influence of the increasing metal to ligand ratios on the oscillator strength values of the “hypersensitive” transition (PhYP)and the R1 parameter values, is presented in Figs 2(a) and 3(a),
A (b)
-
H&Phe l:o
-___ 0.7
iy: ii p/J
0.6
1:1
-.-a_-1:2 -.-_._1:3 -a-.,1:4 .........1:s
!.+:! i_fI ?@Y I, i! j /' ;/ ;/[,,.~~~~j~~
0.5
0.4
0.3
450
460
x[nm)
450
460
h(nm)
Fig. 1. Effect of the increasing phen concentration on the “hypersensitive” transition ‘Gs t ‘I8 of the Ho3+ ion in the absorption spectrum of the anhydrous holmium perchlorate in: (a) CH,OH (c&l+ = 1.60 x 10m2 M, d = 5 cm), (b) CH,CN (cHo3+= 1.75 x lo-* M, d = 2 cm).
Holmium perchlorate- I,1 0 phenanthroline complexes
643
respectively. The results of spectral measurements on the anhydrous Ho(ClO&-phen system in acetonitrile solutions are also collected in Table 1 and in Figs l(b), 2(b) and 3(b). In this case, generally, higher intensities are observed. PhyP and !& parameter values again exhibit the strongest increase in their values with increasing 1,lo-phenanthroline concentration. A more detailed inspection of these data provided us with the conclusion that ligand influence is even more distinct on the intensities of other f-f transitions. A small, but systematic decrease of the R, parameter values is also observed. To make a comparison of the spectral properties of the Ho(ClO&-phen system in both solvents more realistic, we have expressed the intensity parameters in Sz, values. It seems, however, that we should be very careful, when applying the unified formula of the refractive index function to all calculations. Taking into account the rather undoubtful fact that the spectroscopic mechanism of the “hypersensitive” transition is different from that for other f-f transitions,’ we can not expect very good correspondence amongst the measurements in CH30H and CH,CN solutions. The general picture of the spectral changes, however, in CH@H and CH&!N is rather different and presumably different complex species can form in solutions of these solvents. Moreover, it seems very probable that no species higher than [Ho(phen),13+can exist in significant amounts in CH30H solution. It is also very characteristic that for metal to ligand ratios higher than 1: 4, a solid complex compound precipitates out from the solution. On the other hand, for the acetonitrile solutions, both the shape of the P = f (M/L) and the very high intensity [Figs l(b), 2(b)], together with the good solubilities of the solutions with high M : L ratios (up to 1: 5), suggest that the highest stable species which exists in CH$N solution is the species containing four 1, IO-phenanthroline molecules. A very high intensity of this species in the acetonitrile solution suggests that besides four phen molecules, some solvent molecules are present in the first coordination sphere of the lan~a~de ion. Recently, however, Bunzli et al.” proved that in acetonitrile solution some perchlorate ions are preserved in the first coordination sphere of the lanthanide solvate. We decided to check the influence of other solvents (H,O, CH,OH) on the spectral intensity of the 1: 4 species in CH3CN solution. Results are presented in Fig. 4 and Table 2. In Fig. 4, relations between P hyp=f(Hoc a+/so) c IV are P resented and quite striking differences can be seen between the influence of H,O and CH30H on the intensity of the “hypersensitive”
644
K. BUKIETYNSKA
and P. N. THUY A
P.106
(b)
34,.
t
* 1:l
1:2
1:3
1:1
1:4 Ho%Phe
1:2
1:3
l:r, 1:s Ho3:+Phe
Fig. 2. Oscillator strength values (P) of the “hypersensitive” transition ‘G, + 5Z, of the Ho3+ ion as a function of the molar ratio of Ho3+ . phen : (a) for the anhydrous holmium perchlorate in CHSOH (cH03+= 1.60 x lo-’ M), (b) for the anhydrous holmium perchlorate in CH$N (cH03+= 1.75 x lo-’ M).
e-
(b)
Q2
A
Q&O
(a)
6,
c 1:1
1:2
1:3
c 1:1
1% H&Phe
1:2
1:3
1:4
1:s HaPhe
Fig. 3. Q, parameter values of the anhydrous hohnium perchlorate in: (a) CH30H (c,,~‘+= 1.60x lo-’ M), (b) CH,CN (cHo3+= 1.75x lo-* M) as a function of the molar ratio of Ho3+ : phen.
parameter values (0,) of Ho(ClO& +four phen solutions in CH&N for different cH03+: csolv. ratios where solv.-H,O and CH,OH x +,,a+ = 2.22 x lo-’ M
Table 2. Judd-Ofelt
Ho3+ : solv. Solv.
Hz0
n, x 1020 a2
2 CH,OH
a2
Q, Q,
1:o
1:l
1:2
1:4
1:8
8.33 +0.30
8.24kO.28
10.60+ 0.36
8.93 Ifr0.33
8.67f 0.33
4.18kO.38 5.34+ 0.57 10.63f0.46 5.34f0.57 4.18kO.38
4.45 3.93 f+ 0.33 0.50 10.52kO.42 5.05 f0.64 4.45 f 0.43
4.62+ 3.88 +0.34 0.50
4.5OkO.46 3.85kO.31
4.48f0.41 3.84k0.34
10.67kO.42 5.13f0.62 4.28 &-0.42
10.6OkO.43 5.08kO.63 4.23 + 0.42
10.4lkO.42 5.2OkO.62 4.25 + 0.43
Holmium perchlorate-I,10
L
*
1:2
13,
1:6
‘:’
Ho3tSolv.
Fig. 4. Oscillator strength values of the “hypersensitive” transition ‘Gs +- ‘Is of the Ho3* ion as a function of the Ho3+ : solv. (where Ho 3+ :H,O 0, Ho’+ :CH,OH 0) for llJo@hen),](ClO,), phen solutions in CH&N (cH03+= 1.75 x lo-’ M).
transition of the [Ho~p~en~~13~species in CHQ?. In the case of H&S--one water molecule added per
one Ho3+ ion caused a significant decrease of the PbW The addition of the next two water molecules caused only slight intensity changes, and practically no further changes in intensity were observed when an additional amount of water was added, In the case of CH,OH, addition of this solvent up to a Ho3+ : Solv, molar ratio of 3 : 8 does not cause any change of the PhYp value. These results can be explained in terms of differences between the solvation ability of the [Ho(phen)4]3+ species in CH&N by these two solvents. If we assume the [Ho(pherQ4J3’ species in CH3CN has a coordination number of nine, with eight of the coordination positions occupied by four l,lO-phenanthroline molecules and one position occupied by CHCN or CIO;, a significant decrease in intensity should be observed when one Hz0 molecule is exchanged for CH3CN or ClO; in the first coordination sphere of Ho3+. CH30H has lower polarity and its size is significantly larger than H,O. It seems that the presence of a CH,CN molecule is more probable in the first coordination sphere than a ClOi ion, which should be exchanged by the large chelating 1, 10-phenanthroline molecule, when a large excess of this ligand is added. In our opinion, coordination numbers higher than nine seem to be rather doubtful for this system,
phenanthroline
compfexes
645
in the case of such large ligands as 1,lO-phenanthroline. These data are particularly interesting from the point of view of the spectral properties of systems with Ln3+-N bonding. The species [Ho(phen), * {CH3CN)]3+ gave higher values of all the parameters, even in comparison with the mixed Ln3+-phen-CHSOH species. It should be pointed out that & parameter values [Fig. 3(b)] decrease slightly but systematically, when 1, IO-phenanthroline exchanges with CH,CN molecules in the first coordination sphere of the Ho3+ ion. It suggests that this solvent is more tightly bonded to the Ln3’ ion, and complexation with 1,l O-phenanthroline is due mainly to the entropy effect. Very high intensities of [Ho(phen), * (CH3CN)]3’ may be the result of the very significant anisotropy of this species.* Unfort~ately, since we were unable to prepare crystals good enough for X-ray and spectroscopic analysis, studies of the luminescence and absorption spectroscopy of Ln3+--phen systems with different anions and solvents should be very helpful in unders~nding their properties and will be the subject of forthcoming papers. The Ln3+-phen--CH,CN system, however, seems to be particularly interesting from the point of view of the “hypersensitivity” mechanism.
REFERENCES 1. K. Bu~ety~ska
and Pham Ngoc Thuy, horg. C&n. Actu 1987,132,21. 2. B. Keller, J. Legendtiewicz and G. Oczko, Bull. Acud. Pd. Sci. 1986, 34,257. 3. J. C. G. Bunzli and M. M, Vuckovic, Inorg. Chitn. Actu 1983,73,53. 4. J. C. G. Bun&, J. R. Yersin and C. Mabillard, Inorg. Chem. 1982,21,1471. 5. J. C. G. Bun& and C, Mabi~ard, Znorg. Chem 1986, 25,2750. 6. J. H. For&g and T. Moeller, Inorg. Chem. 1969, 8, 883. 7. W. T. Carnal& P. R. Field and K. Rajnak, J. Chem. Phys. 1968,49,4437. 8. S. F. Mason, S&&are and Bo~~~~g 1980,39,43.
and
PHAM NGOC THUYf
Institute of Chemistry, University of Wroclaw, 50-383 Wroclaw, 14 Joliot-Curie, Poland (Received 3 August 1987 ; accepted after revision 25 November 1987)
Abstract-Absorption spectroscopy studies of the anhydrous Ho(ClO& in CH30H and CH&N solutions with different concentrations of 1,lO-phenanthroline are reported. Analysis of the intensities of the&-transitions (in terms of Judd-Ofelt parameters and oscillator strengths of the “hypersensitive” transition) indicates that stable complex species with the N-donor ligand are formed. The species with four molecules of l,lO-phenanthroline in acetonitrile solution is characterized by one of the highest known P,, values observed for the heavy lanthanide compounds in solution. Studies of this species mixed CH,CN-solv. solutions (where solv.-H,O and CH,OH) showed the first coordination sphere of holmium as [Ho(phen), - (CH3CN)13+. The spectral characteristics of these systems are particularly suitable for studies of the “hypersensitivity” mechanisms.
In our recent paper’ we have studied the spectroscopic properties of anhydrous and hydrated neodymium perchlorates in methanol solutions with 2,2’-bipyridine (bipy) and 1, lo-phenanthroline (phen). It was found, that in non-aqueous solutions, species with N-donor ligand molecules in the direct environment of the lanthanide ion can exist. It is interesting then, to compare the behaviours of heavy and light lanthanide ion complexes. Some structural differences between them can be expected-because the lanthanide contraction may be responsible for some difficulties in the packing of relatively large ligand molecules in the first coordination sphere of the smaller (rNd3+= 0.995 A, r&+ = 0.894 A) holmium ion. The more interesting aspect of this paper, however, appeared in the influence of the solvents and N-donor ligand on the intensities of the f-f transitions of the heavy lanthanide ion. A particular role of CH3CN is clearly seen from results presented in this paper. We have investigated anhydrous holmium perchlorates with 1, lo-phenanthroline in CH30H and CH$N solutions. Solvates of some anhydrous lanthanide perchlorates in these solvents were *Author to whom correspondence should be addressed. TPermanent Vietnam.
address:
University
of Hanoi,
Hanoi,
studied recently by different methods, which were helpful in our studies.‘-’
EXPERIMENTAL Hydrated Ho(ClO,), was prepared from 99.9% Hoz03 (Merck), by the method given by Forsberg.6 Anhydrous Ho(ClO& was prepared by the slow heating of the hydrated holmium perchlorate, for at least 120 h. All salts used were fully analysed. 1 , 10-phenanthroline was dehydrated in vacua (1 mm Hg) for at least one week. All anhydrous reagents were checked for water contamination. Only samples with no O-H stretching bands in their IR spectra, were used for spectral measurements. The solvents used were also dried carefully. CH30H was dried using molecular sieves (A-4). Acetonitrile was doubly distilled over P4010, then dehydrated using CaH, and redistilled. In freshly prepared solvent, no O-H stretching bands were observed in the IR. The solutions in mixed solvents were prepared from an anhydrous solution of Ho(ClO& in anhydrous acetonitrile with 1, lo-phenanthroline (molar ratio Ho3+ : phen = 1: 4), with CH3CN diluted with an appropriate amount of water or methanol, respectively. All solutions for the spectroscopic measurements were stored under a dry nitrogen atmosphere.
641
642
K. BUKIETYfiSKA
MEASUREMENTS
AND CALCULATIONS
Spectral measurements were made on a Cary 14spectrophotometer at 293 K, over the spectral range available (11,00&30,000 cm-‘). UV bands of the Ho3+ ion have not been used in the intensity parameter calculations, because basic lines of the absorption bands were not well determined due to the strong absorption of the ligand in this spectral region. Experimental oscillator strengths of solution absorption bands were obtained by graphical integration of the area under the absorption curves after the appropriate correction of the base line. Q, parameters were calculated from the experimental oscillator strength values by applying the Judd-Ofelt equation in the form :
where : X-refraction index x = (n”+ 2)2/9n ; @--matrix elements of the unit tensor operator calculated by Carnal1 et al.’ from the free ion state eigenvectors J-total quantum number.
;
Calculations were performed for the different sets of levels, however, sets of levels with minimal mean square error were the same for all the considered systems. Absorption spectra of Ho3+-l,lO-phen-
A
H&Phe
(a)
-l:o
A
and P. N. THUY
anthroline complexes in CH30H and CH,CN were measured for different M: L ratios (from M:L= 1:0.5 to M:L= 1:5). The spectra with M : L = 1: 0 are the spectra of pure holmium perchlorate dissolved in the appropriate solvent. The spectra of anhydrous hohnium perchlorate with phen (M : L = 1: 4) in CH,CN, with different molar ratios of H20 and CH30H were also measured. RESULTS
AND DISCUSSION
As was proved previously for Nd3+ with phen,’ the most significant differences for different Ho3+. . phen molar ratios are observed for the “hypersensitive” transition. This is illustrated in Fig. l(a), where the influence of the increasing 1, lo-phenanthroline concentration on the ‘G6 c ‘Z8Ho3+ transition is presented. The Judd-Ofelt parameter values RAof the Ho(ClO,),-phen system in methanol solutions are collected in Table 1. Among the three Q parameters (Table l), as can be expected, Q2 exhibits the most significant changes, whereas Sk,and Q6 remain almost constant within the limit of experimental error. Detailed analysis of the influence of the increasing metal to ligand ratios on the oscillator strength values of the “hypersensitive” transition (PhYP)and the R1 parameter values, is presented in Figs 2(a) and 3(a),
A (b)
-
H&Phe l:o
-___ 0.7
iy: ii p/J
0.6
1:1
-.-a_-1:2 -.-_._1:3 -a-.,1:4 .........1:s
!.+:! i_fI ?@Y I, i! j /' ;/ ;/[,,.~~~~j~~
0.5
0.4
0.3
450
460
x[nm)
450
460
h(nm)
Fig. 1. Effect of the increasing phen concentration on the “hypersensitive” transition ‘Gs t ‘I8 of the Ho3+ ion in the absorption spectrum of the anhydrous holmium perchlorate in: (a) CH,OH (c&l+ = 1.60 x 10m2 M, d = 5 cm), (b) CH,CN (cHo3+= 1.75 x lo-* M, d = 2 cm).
Holmium perchlorate- I,1 0 phenanthroline complexes
643
respectively. The results of spectral measurements on the anhydrous Ho(ClO&-phen system in acetonitrile solutions are also collected in Table 1 and in Figs l(b), 2(b) and 3(b). In this case, generally, higher intensities are observed. PhyP and !& parameter values again exhibit the strongest increase in their values with increasing 1,lo-phenanthroline concentration. A more detailed inspection of these data provided us with the conclusion that ligand influence is even more distinct on the intensities of other f-f transitions. A small, but systematic decrease of the R, parameter values is also observed. To make a comparison of the spectral properties of the Ho(ClO&-phen system in both solvents more realistic, we have expressed the intensity parameters in Sz, values. It seems, however, that we should be very careful, when applying the unified formula of the refractive index function to all calculations. Taking into account the rather undoubtful fact that the spectroscopic mechanism of the “hypersensitive” transition is different from that for other f-f transitions,’ we can not expect very good correspondence amongst the measurements in CH30H and CH,CN solutions. The general picture of the spectral changes, however, in CH@H and CH&!N is rather different and presumably different complex species can form in solutions of these solvents. Moreover, it seems very probable that no species higher than [Ho(phen),13+can exist in significant amounts in CH30H solution. It is also very characteristic that for metal to ligand ratios higher than 1: 4, a solid complex compound precipitates out from the solution. On the other hand, for the acetonitrile solutions, both the shape of the P = f (M/L) and the very high intensity [Figs l(b), 2(b)], together with the good solubilities of the solutions with high M : L ratios (up to 1: 5), suggest that the highest stable species which exists in CH$N solution is the species containing four 1, IO-phenanthroline molecules. A very high intensity of this species in the acetonitrile solution suggests that besides four phen molecules, some solvent molecules are present in the first coordination sphere of the lan~a~de ion. Recently, however, Bunzli et al.” proved that in acetonitrile solution some perchlorate ions are preserved in the first coordination sphere of the lanthanide solvate. We decided to check the influence of other solvents (H,O, CH,OH) on the spectral intensity of the 1: 4 species in CH3CN solution. Results are presented in Fig. 4 and Table 2. In Fig. 4, relations between P hyp=f(Hoc a+/so) c IV are P resented and quite striking differences can be seen between the influence of H,O and CH30H on the intensity of the “hypersensitive”
644
K. BUKIETYNSKA
and P. N. THUY A
P.106
(b)
34,.
t
* 1:l
1:2
1:3
1:1
1:4 Ho%Phe
1:2
1:3
l:r, 1:s Ho3:+Phe
Fig. 2. Oscillator strength values (P) of the “hypersensitive” transition ‘G, + 5Z, of the Ho3+ ion as a function of the molar ratio of Ho3+ . phen : (a) for the anhydrous holmium perchlorate in CHSOH (cH03+= 1.60 x lo-’ M), (b) for the anhydrous holmium perchlorate in CH$N (cH03+= 1.75 x lo-’ M).
e-
(b)
Q2
A
Q&O
(a)
6,
c 1:1
1:2
1:3
c 1:1
1% H&Phe
1:2
1:3
1:4
1:s HaPhe
Fig. 3. Q, parameter values of the anhydrous hohnium perchlorate in: (a) CH30H (c,,~‘+= 1.60x lo-’ M), (b) CH,CN (cHo3+= 1.75x lo-* M) as a function of the molar ratio of Ho3+ : phen.
parameter values (0,) of Ho(ClO& +four phen solutions in CH&N for different cH03+: csolv. ratios where solv.-H,O and CH,OH x +,,a+ = 2.22 x lo-’ M
Table 2. Judd-Ofelt
Ho3+ : solv. Solv.
Hz0
n, x 1020 a2
2 CH,OH
a2
Q, Q,
1:o
1:l
1:2
1:4
1:8
8.33 +0.30
8.24kO.28
10.60+ 0.36
8.93 Ifr0.33
8.67f 0.33
4.18kO.38 5.34+ 0.57 10.63f0.46 5.34f0.57 4.18kO.38
4.45 3.93 f+ 0.33 0.50 10.52kO.42 5.05 f0.64 4.45 f 0.43
4.62+ 3.88 +0.34 0.50
4.5OkO.46 3.85kO.31
4.48f0.41 3.84k0.34
10.67kO.42 5.13f0.62 4.28 &-0.42
10.6OkO.43 5.08kO.63 4.23 + 0.42
10.4lkO.42 5.2OkO.62 4.25 + 0.43
Holmium perchlorate-I,10
L
*
1:2
13,
1:6
‘:’
Ho3tSolv.
Fig. 4. Oscillator strength values of the “hypersensitive” transition ‘Gs +- ‘Is of the Ho3* ion as a function of the Ho3+ : solv. (where Ho 3+ :H,O 0, Ho’+ :CH,OH 0) for llJo@hen),](ClO,), phen solutions in CH&N (cH03+= 1.75 x lo-’ M).
transition of the [Ho~p~en~~13~species in CHQ?. In the case of H&S--one water molecule added per
one Ho3+ ion caused a significant decrease of the PbW The addition of the next two water molecules caused only slight intensity changes, and practically no further changes in intensity were observed when an additional amount of water was added, In the case of CH,OH, addition of this solvent up to a Ho3+ : Solv, molar ratio of 3 : 8 does not cause any change of the PhYp value. These results can be explained in terms of differences between the solvation ability of the [Ho(phen)4]3+ species in CH&N by these two solvents. If we assume the [Ho(pherQ4J3’ species in CH3CN has a coordination number of nine, with eight of the coordination positions occupied by four l,lO-phenanthroline molecules and one position occupied by CHCN or CIO;, a significant decrease in intensity should be observed when one Hz0 molecule is exchanged for CH3CN or ClO; in the first coordination sphere of Ho3+. CH30H has lower polarity and its size is significantly larger than H,O. It seems that the presence of a CH,CN molecule is more probable in the first coordination sphere than a ClOi ion, which should be exchanged by the large chelating 1, 10-phenanthroline molecule, when a large excess of this ligand is added. In our opinion, coordination numbers higher than nine seem to be rather doubtful for this system,
phenanthroline
compfexes
645
in the case of such large ligands as 1,lO-phenanthroline. These data are particularly interesting from the point of view of the spectral properties of systems with Ln3+-N bonding. The species [Ho(phen), * {CH3CN)]3+ gave higher values of all the parameters, even in comparison with the mixed Ln3+-phen-CHSOH species. It should be pointed out that & parameter values [Fig. 3(b)] decrease slightly but systematically, when 1, IO-phenanthroline exchanges with CH,CN molecules in the first coordination sphere of the Ho3+ ion. It suggests that this solvent is more tightly bonded to the Ln3’ ion, and complexation with 1,l O-phenanthroline is due mainly to the entropy effect. Very high intensities of [Ho(phen), * (CH3CN)]3’ may be the result of the very significant anisotropy of this species.* Unfort~ately, since we were unable to prepare crystals good enough for X-ray and spectroscopic analysis, studies of the luminescence and absorption spectroscopy of Ln3+--phen systems with different anions and solvents should be very helpful in unders~nding their properties and will be the subject of forthcoming papers. The Ln3+-phen--CH,CN system, however, seems to be particularly interesting from the point of view of the “hypersensitivity” mechanism.
REFERENCES 1. K. Bu~ety~ska
and Pham Ngoc Thuy, horg. C&n. Actu 1987,132,21. 2. B. Keller, J. Legendtiewicz and G. Oczko, Bull. Acud. Pd. Sci. 1986, 34,257. 3. J. C. G. Bunzli and M. M, Vuckovic, Inorg. Chitn. Actu 1983,73,53. 4. J. C. G. Bun&, J. R. Yersin and C. Mabillard, Inorg. Chem. 1982,21,1471. 5. J. C. G. Bun& and C, Mabi~ard, Znorg. Chem 1986, 25,2750. 6. J. H. For&g and T. Moeller, Inorg. Chem. 1969, 8, 883. 7. W. T. Carnal& P. R. Field and K. Rajnak, J. Chem. Phys. 1968,49,4437. 8. S. F. Mason, S&&are and Bo~~~~g 1980,39,43.