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Vibrational spectra of partially debenzenated analogues in some en-Td-type clathrates
Journal of
MOLECULAR STRUCTURE ELSEVIER
Journal of Molecular
Vibrational
Structure 408/409 (997) 43 I-434
spectra of partially debenzenated en-ird-type clathrates
analogues in some
L. Andreeva, B. Minceva-Sukarova* Institute of Chemistry, Facully of Science, University “3s Cyril and Merhodius”, Arhimedova 5. P.O. Box 162, 91001 Skopje, Republic of Macedonia Received 8 October
1996; accepted 21 October
1996
Abstract The en-T,,-type coordinated metal, The influence of a studied by infrared
clathrates are host-guest compounds with the general formula M(en)M’(CN),.2G; M is octahedrally M’ is tetrahedrally coordinated metal (Hg, Cd or Zn) and G is a guest molecule (in our case benzene). graduai loss of the benzene molecules from the host lattice in these partially debenzenated clathrates was spectroscopy. For this purpose, a series of partially debenzenated en-T&ype clathrates was prepared and
their infrared spectra recorded. The loss of the benzene from the host lattice did not cause any changes in the frequency of the bands due to the vibrations of the benzene molecules. However, considerable changes in the bands due to the vibrations of the host lattice, M(en)M’(CN)4, were detected. These changes are most evident in the region of the stretching and out-of-plane bending NH2 vibrations. Most of the bands due to these vibrations are no longer present in the vibrational spectra of the “empty clathrates” (clathrates in which the benzene has left the host lattice). One explanation for this behaviour could be the existence of an interaction between the guest molecules and the host lattice. 0 1997 Elsevier Science B.V. Keywords:
Clathrates;
Benzene; en-T&ype
clathrates;
Infrared spectra
1. Introduction The compounds named clathrates are host-guest compounds, where the guest molecules are enclosed in a cavity formed by the host lattice. A great impetus to the chemistry of clathrates was given by the determination of the crystal structure of the first Hofmann’s benzene compound, Ni(NH3)2Ni(CN)4.2C6H6, by Powell and Rayner [ 1,2]. Since then numerous analogues of these clathrates have been prepared by replacing the octahedral Ni by other bivalent metals, * Corresponding
author.
and the square-planar Ni by tetrahedral coordinated metals. However, only for four of those analogues, has the crystal structure been determined [3-51. The family of clathrates can be extended by replacing two ammonia molecules in the Hofmanntype clathrate by a bidentate ligand, such as ethylendiamine (en). This results in a series of en-type clathrates [6,7]. Among them are the clathrates named en-Td type with the general formula Cd(en)M’(CN)4.2G (en is CzHsNz; M’ is Cd or Hg; G is CbH6). The crystal structure of only two of these clathrates, Cd(en)Ni(CN)4.2ChHh [8] and Cd(en)Cd(CN)4.2ChH6 [9], is known. The powder
0022.2860/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved PI/ SOO22-2860(96)09716-5
432
L. Andreeva, B. Minceva-Sukarova/Journal of Molecular Structure 408/409 (1997) 431-434
diffraction data have suggested that the ethylendiamine molecules in these compounds bridge two cadmium atoms, as a result of which a polymeric three-dimensional network is formed. The guest molecules are enclathrated in the cavities formed by this three-dimensional network. There is no direct chemical bond between the guest molecules and the host lattice. However, previous infrared studies [ 10, I l] suggested the presence of weak interactions (of a hydrogen-bonding type) between the guest molecules and the host lattice. In order to examine this more thoroughly, we recorded the infrared spectra of the clathrates, in which the amount of benzene molecules progressively (step by step) decreases until eventually, pure host lattice remains.
2. Experimental The en-Td type clathrates, Cd(en)M’(CN)4.2C6H6 (M’ is Cd or Hg), were prepared by methods reported previously [6,7]. The benzene clathrates are unstable compounds and the guest molecules tend to escape from the host lattice. Because of this, the samples must be kept in a desiccator full of benzene vapour. In this way, the mean-life of the clathrates is significantly prolonged. This property of the clathrates has been used to prepare the partially debenzenated analogues: the clathrate was kept in air for about 15 minutes, during which time a certain amount of benzene left the host lattice. After that time, the infrared spectrum was recorded. The next spectrum (again after a decrease in benzene) was recorded after another 15 minutes, and so on. Judging by the infrared spectra, after less then an hour virtually all the benzene molecules had abandoned the host lattice. The infrared spectra were recorded on the IT-IR interferometer, Perkin-Elmer System 2000. The samples were measured from KBr pellets (4 cm-’ resolution, 16 scans).
Cd(en)Cd(CN)4 (Cd-en-Cd), are shown in Fig. 1. The bands due to the vibrations of the benzene molecules are marked with an asterisk. The differences between these two infrared spectra are obvious: the spectrum due to the clathrate has more bands then the “empty clathrate”. When the benzene molecules were completely removed from the clathrate, only the bands due to the host lattice remained in the spectrum. However, on removal of the guest molecules from the clathrates, notable changes can be detected in the infrared spectra of ethylendiamine molecules, in the region of the stretching NH:! and bending NH2 vibrations. 3.1. The region of stretching NH2 vibrations The gradual loss of the benzene molecules in one of the studied clathrates, Cd(en)Hg(CN)4.2C6H6, in the region of v(NH~) is shown in Fig. 2a. There are two main changes in this part of the spectrum. First, the three bands in the clathrate transform into four in the “empty clathrate”; three of them remain at the same frequency, while the fourth band appears at the highfrequency side. Second, there are evident changes in the intensity (increasing or decreasing) of some of the bands due to the vibrations of ethylendiamine when the the benzene molecules have left. 3.2. The region of the antisymmetric deformational vibrations
NH2
The gradual loss of the benzene molecules in for the vibration region of &NHz) Cd(en)Hg(CN)4.2C,sHs clathrate, see Fig. 2b. On the removal of the benzene molecules from the host
3. Results and discussion IO
The infrared spectra of one of the investigated clathrates, Cd(en)Cd(CN)4.2C6H6 (Cd-en-Cd-Bz), clathrate”, corresponding “empty and its
3000
2000
1000
cm'
Fig. 1. The infrared spectra of (a) Cd(en)Cd(CN)4.2C6H6 (Cd-enCd-Bz) and (b) its corresponding “empty clathrate” Cd(en)Cd(CN), (Cd-en-Cd).
L. Andreeva.
B. Mincevu-Sukarova/Journal
of Molecular
Structure
408/409
(1997) 431-434
433
and = 625 cm-‘) appear, while at the same time the band at 520 cm-’ gradually disappears.
4. Conclusion
W 1150
IO50
950
650
550
450
Wavenumber I cm-r Fig. 2. (a) The infrared spectra of debenzenated analogues in Cd-enHg-Bz clathrates in the region of (a) stretching NH*, (b) wagging NH*, (c) twisting NH2 and (d) rocking NH2 vibrations. The first and the last spectrum belong to the clathrate Cd(en)Cd(CN)4.2CbHh and to the “empty clathrate” Cd(en)Cd(CN)4, respectively. The vibrations due to the benzene molecules are marked with an asterisk.
lattice, a new band appears on the high-frequency side of the main band (Fig. 2b). The frequency of this new band is about 10 cm-’ higher, while its intensity is about the same as the intensity of the main band. 3.3. The region vibrations
ofwagging, twisting and rocking NH2
The changes in the infrared spectra of the studied clathrates, upon gradual loss of the benzene molecules, in the region of w(NH2) and r(NH2) for Cd(en)Hg(CN)4.2C6H6 are shown in Fig. 2c. The band at about 1076 cm-‘, assigned to the wagging NH? mode, disappears from the infrared spectrum. On the other hand, the band at around 1002 cm-‘, assigned to the twisting NH2 mode, shifts to = 20 At the same time, two cm-’ lower frequency. additional side bands (from both sides of the main band) appear in the spectrum of the “empty clathrate” (Fig. 2~). The spectral evidence for the gradual loss of the benzene molecules from the host lattice is more complicated in the region of rocking NH2 vibrations than in other regions. In the spectrum of the clathrate, the band around 520 cm-’ is assigned to p(NH2). During “debenzenation”, several new bands on the high-frequency side of this band (at = 540, = 574
The evident changes in the infrared spectra of the studied debenzenated analogous of en-Td type clathrates indicate the existence of some kind of interaction between the host lattice and the guest molecules. In our previous studies of Hofmann-type [ 10,111 as well as Hofmann-Td type [ 121 clathrates, we have offered an explanation in terms of proton-proton interactions which most probably originate from the H atoms (from the NH3 group) in the host lattice and the H atoms (from the benzene molecules) from the guest molecules. An alternative explanation may be given on the basis of the results of theoretical studies on Hofmann-type clathrates, using the INDO method [ 131, which suggested that this interaction actually arises between the a electrons from the rings of benzene molecules and H atoms from the NH3 groups. The crystal structure of en-T,, type clathrates is almost the same as that of Hofmann-Td type clathrates (except that instead of NH3 groups in the host lattice, ethylendiamnine -NH*-CH2-CH2--NH?-groups are present). Therefore, similar interaction(s) between the host lattice and the guest molecules can cause the observed changes in the infrared spectra of en-Td type clathrates in the region of v(NH~) and &NH& and in particular in the region of w(NH?), r(NH2) and p(NH2). The fact that these changes are more evident in the region of w(NH& r(NH2) and p(NH2) supports the suggestion [13] that these interactions are due to the weak hydrogen bonds formed between the benzene r electrons and the NH2 groups from the ethylendiamine in the host lattice.
References [I] H.M. Powell and J.H. Rayner, Nature (London), 163 (1949) 556. [2] J.H. Rayner and H.M. Powell, J. Chem. Sot., (1952) 319. [3] R. Kuroda and Y. Sasaki, Acta Crystallogr., 830 (1974) 687. [4] Y. Sasaki, Bull. Chem. Sot. Jpn., 42 (1969) 2412. [S] H.G. Buttner, F. Fillaux, C.J. Howard and G.J. Kearley, Acta Crystallogr., BSO (I 994) 43 I.
434
L. Andreeva, B. Minceva-Sukarova/Journal of Molecular Structure 408/409 (1997) 431-434
[6] T. Iwamoto, Inorg. Chim. Acta, 2 (1968) 269. [7] T. Miyoshi, T. Iwamoto and Y. Sasaki, Inorg. Chim. Acta, 6 (1972) 59. [8] T. Miyoshi, T. Iwamoto and Y. Sasaki, Inorg. Nucl. Chem. Len., 6 (1970) 21. [9] S. Nishikiori and T. Iwamoto, J. Inclusion Phenom., 3 (1985) 283.
[lo] B. Minceva-Sukarova, L. Andreeva and V. Petrusevski, J. Mol Struct., 219 (1990) 111. [ 1 I] L. Andreeva and B. Minceva-Sukarova, Bull. Chem. Technol. Macedonia, 8 (1990) 269. [ 121 B. Minceva-Sukarova, L. Andreeva, Cl. Ivanovski and V Petrusevski, Vestn. Slav. Kern. Drus., 37 (I 990) 12 1. [ 131 I. Uemasu, Polyhedron, 2 (1983) 115.
MOLECULAR STRUCTURE ELSEVIER
Journal of Molecular
Vibrational
Structure 408/409 (997) 43 I-434
spectra of partially debenzenated en-ird-type clathrates
analogues in some
L. Andreeva, B. Minceva-Sukarova* Institute of Chemistry, Facully of Science, University “3s Cyril and Merhodius”, Arhimedova 5. P.O. Box 162, 91001 Skopje, Republic of Macedonia Received 8 October
1996; accepted 21 October
1996
Abstract The en-T,,-type coordinated metal, The influence of a studied by infrared
clathrates are host-guest compounds with the general formula M(en)M’(CN),.2G; M is octahedrally M’ is tetrahedrally coordinated metal (Hg, Cd or Zn) and G is a guest molecule (in our case benzene). graduai loss of the benzene molecules from the host lattice in these partially debenzenated clathrates was spectroscopy. For this purpose, a series of partially debenzenated en-T&ype clathrates was prepared and
their infrared spectra recorded. The loss of the benzene from the host lattice did not cause any changes in the frequency of the bands due to the vibrations of the benzene molecules. However, considerable changes in the bands due to the vibrations of the host lattice, M(en)M’(CN)4, were detected. These changes are most evident in the region of the stretching and out-of-plane bending NH2 vibrations. Most of the bands due to these vibrations are no longer present in the vibrational spectra of the “empty clathrates” (clathrates in which the benzene has left the host lattice). One explanation for this behaviour could be the existence of an interaction between the guest molecules and the host lattice. 0 1997 Elsevier Science B.V. Keywords:
Clathrates;
Benzene; en-T&ype
clathrates;
Infrared spectra
1. Introduction The compounds named clathrates are host-guest compounds, where the guest molecules are enclosed in a cavity formed by the host lattice. A great impetus to the chemistry of clathrates was given by the determination of the crystal structure of the first Hofmann’s benzene compound, Ni(NH3)2Ni(CN)4.2C6H6, by Powell and Rayner [ 1,2]. Since then numerous analogues of these clathrates have been prepared by replacing the octahedral Ni by other bivalent metals, * Corresponding
author.
and the square-planar Ni by tetrahedral coordinated metals. However, only for four of those analogues, has the crystal structure been determined [3-51. The family of clathrates can be extended by replacing two ammonia molecules in the Hofmanntype clathrate by a bidentate ligand, such as ethylendiamine (en). This results in a series of en-type clathrates [6,7]. Among them are the clathrates named en-Td type with the general formula Cd(en)M’(CN)4.2G (en is CzHsNz; M’ is Cd or Hg; G is CbH6). The crystal structure of only two of these clathrates, Cd(en)Ni(CN)4.2ChHh [8] and Cd(en)Cd(CN)4.2ChH6 [9], is known. The powder
0022.2860/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved PI/ SOO22-2860(96)09716-5
432
L. Andreeva, B. Minceva-Sukarova/Journal of Molecular Structure 408/409 (1997) 431-434
diffraction data have suggested that the ethylendiamine molecules in these compounds bridge two cadmium atoms, as a result of which a polymeric three-dimensional network is formed. The guest molecules are enclathrated in the cavities formed by this three-dimensional network. There is no direct chemical bond between the guest molecules and the host lattice. However, previous infrared studies [ 10, I l] suggested the presence of weak interactions (of a hydrogen-bonding type) between the guest molecules and the host lattice. In order to examine this more thoroughly, we recorded the infrared spectra of the clathrates, in which the amount of benzene molecules progressively (step by step) decreases until eventually, pure host lattice remains.
2. Experimental The en-Td type clathrates, Cd(en)M’(CN)4.2C6H6 (M’ is Cd or Hg), were prepared by methods reported previously [6,7]. The benzene clathrates are unstable compounds and the guest molecules tend to escape from the host lattice. Because of this, the samples must be kept in a desiccator full of benzene vapour. In this way, the mean-life of the clathrates is significantly prolonged. This property of the clathrates has been used to prepare the partially debenzenated analogues: the clathrate was kept in air for about 15 minutes, during which time a certain amount of benzene left the host lattice. After that time, the infrared spectrum was recorded. The next spectrum (again after a decrease in benzene) was recorded after another 15 minutes, and so on. Judging by the infrared spectra, after less then an hour virtually all the benzene molecules had abandoned the host lattice. The infrared spectra were recorded on the IT-IR interferometer, Perkin-Elmer System 2000. The samples were measured from KBr pellets (4 cm-’ resolution, 16 scans).
Cd(en)Cd(CN)4 (Cd-en-Cd), are shown in Fig. 1. The bands due to the vibrations of the benzene molecules are marked with an asterisk. The differences between these two infrared spectra are obvious: the spectrum due to the clathrate has more bands then the “empty clathrate”. When the benzene molecules were completely removed from the clathrate, only the bands due to the host lattice remained in the spectrum. However, on removal of the guest molecules from the clathrates, notable changes can be detected in the infrared spectra of ethylendiamine molecules, in the region of the stretching NH:! and bending NH2 vibrations. 3.1. The region of stretching NH2 vibrations The gradual loss of the benzene molecules in one of the studied clathrates, Cd(en)Hg(CN)4.2C6H6, in the region of v(NH~) is shown in Fig. 2a. There are two main changes in this part of the spectrum. First, the three bands in the clathrate transform into four in the “empty clathrate”; three of them remain at the same frequency, while the fourth band appears at the highfrequency side. Second, there are evident changes in the intensity (increasing or decreasing) of some of the bands due to the vibrations of ethylendiamine when the the benzene molecules have left. 3.2. The region of the antisymmetric deformational vibrations
NH2
The gradual loss of the benzene molecules in for the vibration region of &NHz) Cd(en)Hg(CN)4.2C,sHs clathrate, see Fig. 2b. On the removal of the benzene molecules from the host
3. Results and discussion IO
The infrared spectra of one of the investigated clathrates, Cd(en)Cd(CN)4.2C6H6 (Cd-en-Cd-Bz), clathrate”, corresponding “empty and its
3000
2000
1000
cm'
Fig. 1. The infrared spectra of (a) Cd(en)Cd(CN)4.2C6H6 (Cd-enCd-Bz) and (b) its corresponding “empty clathrate” Cd(en)Cd(CN), (Cd-en-Cd).
L. Andreeva.
B. Mincevu-Sukarova/Journal
of Molecular
Structure
408/409
(1997) 431-434
433
and = 625 cm-‘) appear, while at the same time the band at 520 cm-’ gradually disappears.
4. Conclusion
W 1150
IO50
950
650
550
450
Wavenumber I cm-r Fig. 2. (a) The infrared spectra of debenzenated analogues in Cd-enHg-Bz clathrates in the region of (a) stretching NH*, (b) wagging NH*, (c) twisting NH2 and (d) rocking NH2 vibrations. The first and the last spectrum belong to the clathrate Cd(en)Cd(CN)4.2CbHh and to the “empty clathrate” Cd(en)Cd(CN)4, respectively. The vibrations due to the benzene molecules are marked with an asterisk.
lattice, a new band appears on the high-frequency side of the main band (Fig. 2b). The frequency of this new band is about 10 cm-’ higher, while its intensity is about the same as the intensity of the main band. 3.3. The region vibrations
ofwagging, twisting and rocking NH2
The changes in the infrared spectra of the studied clathrates, upon gradual loss of the benzene molecules, in the region of w(NH2) and r(NH2) for Cd(en)Hg(CN)4.2C6H6 are shown in Fig. 2c. The band at about 1076 cm-‘, assigned to the wagging NH? mode, disappears from the infrared spectrum. On the other hand, the band at around 1002 cm-‘, assigned to the twisting NH2 mode, shifts to = 20 At the same time, two cm-’ lower frequency. additional side bands (from both sides of the main band) appear in the spectrum of the “empty clathrate” (Fig. 2~). The spectral evidence for the gradual loss of the benzene molecules from the host lattice is more complicated in the region of rocking NH2 vibrations than in other regions. In the spectrum of the clathrate, the band around 520 cm-’ is assigned to p(NH2). During “debenzenation”, several new bands on the high-frequency side of this band (at = 540, = 574
The evident changes in the infrared spectra of the studied debenzenated analogous of en-Td type clathrates indicate the existence of some kind of interaction between the host lattice and the guest molecules. In our previous studies of Hofmann-type [ 10,111 as well as Hofmann-Td type [ 121 clathrates, we have offered an explanation in terms of proton-proton interactions which most probably originate from the H atoms (from the NH3 group) in the host lattice and the H atoms (from the benzene molecules) from the guest molecules. An alternative explanation may be given on the basis of the results of theoretical studies on Hofmann-type clathrates, using the INDO method [ 131, which suggested that this interaction actually arises between the a electrons from the rings of benzene molecules and H atoms from the NH3 groups. The crystal structure of en-T,, type clathrates is almost the same as that of Hofmann-Td type clathrates (except that instead of NH3 groups in the host lattice, ethylendiamnine -NH*-CH2-CH2--NH?-groups are present). Therefore, similar interaction(s) between the host lattice and the guest molecules can cause the observed changes in the infrared spectra of en-Td type clathrates in the region of v(NH~) and &NH& and in particular in the region of w(NH?), r(NH2) and p(NH2). The fact that these changes are more evident in the region of w(NH& r(NH2) and p(NH2) supports the suggestion [13] that these interactions are due to the weak hydrogen bonds formed between the benzene r electrons and the NH2 groups from the ethylendiamine in the host lattice.
References [I] H.M. Powell and J.H. Rayner, Nature (London), 163 (1949) 556. [2] J.H. Rayner and H.M. Powell, J. Chem. Sot., (1952) 319. [3] R. Kuroda and Y. Sasaki, Acta Crystallogr., 830 (1974) 687. [4] Y. Sasaki, Bull. Chem. Sot. Jpn., 42 (1969) 2412. [S] H.G. Buttner, F. Fillaux, C.J. Howard and G.J. Kearley, Acta Crystallogr., BSO (I 994) 43 I.
434
L. Andreeva, B. Minceva-Sukarova/Journal of Molecular Structure 408/409 (1997) 431-434
[6] T. Iwamoto, Inorg. Chim. Acta, 2 (1968) 269. [7] T. Miyoshi, T. Iwamoto and Y. Sasaki, Inorg. Chim. Acta, 6 (1972) 59. [8] T. Miyoshi, T. Iwamoto and Y. Sasaki, Inorg. Nucl. Chem. Len., 6 (1970) 21. [9] S. Nishikiori and T. Iwamoto, J. Inclusion Phenom., 3 (1985) 283.
[lo] B. Minceva-Sukarova, L. Andreeva and V. Petrusevski, J. Mol Struct., 219 (1990) 111. [ 1 I] L. Andreeva and B. Minceva-Sukarova, Bull. Chem. Technol. Macedonia, 8 (1990) 269. [ 121 B. Minceva-Sukarova, L. Andreeva, Cl. Ivanovski and V Petrusevski, Vestn. Slav. Kern. Drus., 37 (I 990) 12 1. [ 131 I. Uemasu, Polyhedron, 2 (1983) 115.