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Synthesis and characterization of the first organosulfur electron donor intercalates of the metal dichalcogenides and dihalides
Synthetic Metals, 55-57 (1993) 2019-2022
2019
SYNTHESIS AND CHARACTERIZATION OF THE FIRST ORGANOSULFUR ELECTRON DONOR INTERCALATES OF THE METAL DICHALCOGENIDES AND DIHALIDES
T. E. SUTTO,t B. A. AVERILLJ and J.-M. FABRE:1: ~Department of Chemistry U n i v e r s i t y of Virginia Charlottesville, VA 22601,USA l:I,abovatoire (te Chimie Organique Struclurale Universit6 Mrmtpelliev II Place Eugbne V,ataillon 34060 Montpellier Cedex 5 Franco
ABSTRACT New intercalates based on metal dichalcogenides and dihalides as host matrices and electron donors of T T F type as guest molecules are p r e p a r e d . T h e i r electrical c o n d u c t i v i t y and their structure are d e t e r m i n e d and discussed. INTRODUCTION A variety of strategies have been developed in recent years for the preparation of new low-dimensional conductors, ranging from the ssrnthesi§ of new organic electron donors related to tetrathia- or tetraselenaf~l¥,aleneI to methods for preparing stacks of oxidizable metall~macrocycleg.~ ' ' Our laboratories have focussed on an alternative approach" that Involveg the use of inorganic layered materials as macroanionic electron acceptorg that enfbrce a particular structural arranffgment u p o n lntercala.ted electron donors sucO as tetrathiafulvalene (TTF),a tetraselenafulvalene, '~ and related molecules." To date, this approach has been used successfully only with the strongly oxidizing host FeOCI, which has resulted in the formation of intercalated radical cations due to the occurrence of complete eleTctron transfer from guest to host for all guests except BEDT-TTF (ET). We report herein that this strategy can be extended to other layered materJalsj including the transition metal dichalcogenides and the previously intractable layered metal halides, for the T'I'F analogs dibenzotetrathlafulvalene (DBTTF) and tetracyanotetrnthiafulvalene (TCNTTF).
I /
bBlqF
Nc~
~
icN
TCNTTF
Elsevier Sequoia
2020 EXPF, RIMENTAL
The intercalates were prepared by suspending the metal dlcha]cogenides (TBS2 was the 2H modification) or halides (150 r a g ) i n i0 ml acetonitrile or-xylenes, respectively~ sonlcation with an Uitrasonic~ Model W-380 sonicator at full power for one mlnute~ addition of excess DBTTF or TCNTTF, and sonication for another minute at full power. The ~ampIes were then evacuated, flushed with argon, and allowed to react at 60°C for I week. The ~olids were collected by filtration, washed with benzene, and dried in vacuo for 2 hours. Microanalyses wei~e carried out by Galbraith Laboratories, Knoxville, TN, USA. X-ray powder patterns were obtained on a Scintag powder diffractometer over a 2(9 range of ,]-70° at 0.01° intervals and Indexed and flt using a Fortran IV X-ray fitting program. Resistivity data were measured using a four-probe arrangement with a 10+0.01 mA constant current sourer; temperatures over the 8-300K range were measured with a Lake Shore calibrated Si diode. Samples were pressed at 5000 psi in a 0.25 Inch die~ and electrodes were attached with silver paint. RESULTS AND DISCUSSION The compositions of the new materials prepared are listed in Table I, along with their unit ceil parameters and c-axls expansions. Table I. Compositions, unit cell parameters, and c-axls expansions of the new intercalates; Ac values are derived from data in Ref. 8.
Mater|al .,,
x I
.
.
a (~) .
.
.
b (~) i
c (~)
Ac (~)
.
DBTTFxTiS2
0.541
6.824
5.903
25.30
19.60
DBTTFxTiSe2
0.545
6.984
6.147
25.75
19.65
DBTTFxTaS2
0.551
6.497
5.770
25.91
20.00
DBTTFxTaSe2
0.665
6.898
6.1"79
26.35
20.07
TCNTTFxCUCI2
0.323
6.577
5.711
16.49
9.4g
TCNTTFxCUBr2
0.332
6.861
6.151
16.79
10.84
TCNTTFxNIBr2
0.330
7.212
6.408
16.6l
10.51
TCNTTFxCdBr2
0.333
7.842
6.77l
16.39
10.06
TCNTTFxCdl2
0.739
8.467
7.18l
16.62
9.76
For the DBTTF-intercnlates, the X-ray data Indicate the presence of an orthorhomblc unit cell, with a ~ 2a*, b - ,/3a*, and an expanded _o-axis (a* is the a-axis of the uninte-rcalated ]lost). The observed interlayer spacing of ca. 19.5A is greater than the length of the DBTTF molecule (15.1A), suggesting a bilayer structure In which the planar Intercalants are canted from the perpendicular to the layers; one possible arrangement Is shown schematically in Figure la. A tilt angle of 49±20 ts consistent with
2021
the observed stotchiometries and c-axis expansions, if the fntsrcalants are assumed to stack at a ca. 3 . 6 A - d i s t a n c e in the bilayer and are not in r e g i s t e r with the chalcogenide a r r a y in the a - b plane. This s t r u c t u r e is analogous to those observed for a suertes of aromatic hydrocarbon intercalates of the metal dichalcogenides." This observation and the fact that DBTTF is the only TTF analog that has been found to Intercalate into the dichalcogenides suggest that the aromatic character of DBTTF is sufficiently great that in this regard it behaves as an aromatic hydrocarbon analogous to tetracene. Resistivity data for the DBTTF-TaS 2 and TaSe 2 intercalates are shown in Figure 2a, along with data for TaS and TaSe 2 c6ntrois treated exactly (3
b
////'/ Figure 1. (a) Schematic view of the canted bilayer s t r u c t u r e proposed for the DBTTF-MY2intercalates. The chalcogen atoms (Y) are shown as circles with crosses, the M atoms as larger open circles, and the DBTTF is shown in a view p e r p e n d i c u l a r to its long axis. (b) Schematic view of the orlentatton proposed for the TCNTTF-MX 2 intercalates. The hagdes (X) are shown as circles with cresses and the M-atoms as open circles. as for the intercalation reactions, but in the absence of guests. These data s u g g e s t that the guest molecules are simply r e d u c i n g the i n t e r l a y e r i n t e r a c tions without significantly p e r t u r b i n g the host layers. In particular, there is no evidence for enhanced conductivity s u g g e s t i n g that significant guesthost electron t r a n s f e r has occurred. No evidence for s u p e r c o n d u c t i v i t y above 4K was observed. Similar results were observed for the Tt systems, but the measured reststivities were significantly higher. The X - r a y data for the TCNTTF-MX 2 intercalates are readily fit with an orthorhombtc unft cell analogous to that observed for the DBTTF-MY2 systems, again with a significant c-axis expansion. The observed i n t e r l a y e r distances of 10_+0.SA and the stoTchtometry are consistent with a Btructure in which the TCNTTF molecules are oriented with their molecular planes p e r p e n d i c u l a r to the host, but with the long axes tilted b y ca. 300 to allow one nitrile on each end to interact with the metal ions of the host lattice, as illustrated in Figure l b . For all materials except the Cdl 2 intercalate, the observed stoichiometry s u g g e s t s that the short distance between metals in the 010 direction results in occupancy of only e v e r y other row of metals by TCNTTF molecules. In the case of CdIT., the metal ions of the lattice are sufficiently far apart (hm to the ~izo of-the larger iodide ions to allow occupation of e v e r y row by TCNTTF, r e s u l t i n g in a doubling of the i n t e r calant content.
2022 31.0
a
b
5.0
~ 21.0
¢J
\
E ~,3.0
k~$>
e Oo°
%'0
0
11,0 e 'e -° -o -O ,O m _o _e O-o.e~ -~
1.0
1.0 010
100.0 200.0 Temp. in K
500.0
o.o
lOO.O 200.0 Temp. In )~
l.~igure 2. (a) Resistivity data vs. temperature for pressed pellets of TaS~ ( A ) , DBTTFn 55.TAS2 (o), TaSe,/ (E{), and DBTTF n 66.TaSe~. (o). (b)" Resistivity cra'ta vs. temperatur6 for pressed pelY6ts of the TCNTTF intercalates of CuCl 2 ( o ) , CuBr 2 ( ~ ) , CdI 2 (A), and NiBr 2 (o). Resistivity data as a function of temperature are shown for selected TCNTTF-MX 2 intercalates in Fi6q*re 2b. All of the intercalates except that with CuBr 2 exhibit semiconducting behavior comparable to that measured for the p a t e n [ metal halides. In distinct c o n t r a s t , TCNTTF0 3.1.CuBrl vQ exhibits decreasing r e s i s t i v i t y all the way to 4K, consistent "~rIth met&lll~ behavior. The origin of this phenomenon is not clear at p r e s e n t , but may be due to some degree of charge t r a n s f e r from TCNTTF (a r a t h e r poor electron donor) to the CuRr 2 host. Alternatively, the B r : C u ratio of 1.79 may indicate that some degree of reduction of copper, accompanied b y loss of bromide, is o c c u r r i n g d u r i n g the intercalation reaction to form a mixedvalence metal halide. ACKNOWLEDGEMENTS Th]s research was supported in part by the office of Naval Research Materials Division (N00014-91-J-1962) and by NATO (0727/87). REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9.
D. O. Cowan end F. M. Wiygul, Chem. Eng. News 64:28 (1986). T. J. Marks, Science 227:881 (1985). B. M. Hoffman and J. A. Ibers, Acc. Chem. Res. 16:15 (1983). B. A. Averill and S. M. Kauzlarich, Mol. Cryst. Lkl. Cryst. 107:55 (1984). S. M. Kauzlarich, J. F. gllena, P. D . Stupik, W. M. Reiff, and B. A. Averill, J. Am. Chem. Soc. I09:456l (1987). J. F. Bringley, J.-M. l"abre, and B. A. Averill, Chem. Mater, 4:522 (1992). J. F. Bringley, J.-M. Fabre, and B. A. Averlll, J. Am. Chem, Soc. 112:4577 (1990). T. Hibma, in "intercalation Chemistry", M. S. Whittingham and A. J. Jacobsen, eds., Academic Press, New York, 1982, p. 292. T. E. Sutto and B. A. Averill, to be submitted for publication.
300.0
2019
SYNTHESIS AND CHARACTERIZATION OF THE FIRST ORGANOSULFUR ELECTRON DONOR INTERCALATES OF THE METAL DICHALCOGENIDES AND DIHALIDES
T. E. SUTTO,t B. A. AVERILLJ and J.-M. FABRE:1: ~Department of Chemistry U n i v e r s i t y of Virginia Charlottesville, VA 22601,USA l:I,abovatoire (te Chimie Organique Struclurale Universit6 Mrmtpelliev II Place Eugbne V,ataillon 34060 Montpellier Cedex 5 Franco
ABSTRACT New intercalates based on metal dichalcogenides and dihalides as host matrices and electron donors of T T F type as guest molecules are p r e p a r e d . T h e i r electrical c o n d u c t i v i t y and their structure are d e t e r m i n e d and discussed. INTRODUCTION A variety of strategies have been developed in recent years for the preparation of new low-dimensional conductors, ranging from the ssrnthesi§ of new organic electron donors related to tetrathia- or tetraselenaf~l¥,aleneI to methods for preparing stacks of oxidizable metall~macrocycleg.~ ' ' Our laboratories have focussed on an alternative approach" that Involveg the use of inorganic layered materials as macroanionic electron acceptorg that enfbrce a particular structural arranffgment u p o n lntercala.ted electron donors sucO as tetrathiafulvalene (TTF),a tetraselenafulvalene, '~ and related molecules." To date, this approach has been used successfully only with the strongly oxidizing host FeOCI, which has resulted in the formation of intercalated radical cations due to the occurrence of complete eleTctron transfer from guest to host for all guests except BEDT-TTF (ET). We report herein that this strategy can be extended to other layered materJalsj including the transition metal dichalcogenides and the previously intractable layered metal halides, for the T'I'F analogs dibenzotetrathlafulvalene (DBTTF) and tetracyanotetrnthiafulvalene (TCNTTF).
I /
bBlqF
Nc~
~
icN
TCNTTF
Elsevier Sequoia
2020 EXPF, RIMENTAL
The intercalates were prepared by suspending the metal dlcha]cogenides (TBS2 was the 2H modification) or halides (150 r a g ) i n i0 ml acetonitrile or-xylenes, respectively~ sonlcation with an Uitrasonic~ Model W-380 sonicator at full power for one mlnute~ addition of excess DBTTF or TCNTTF, and sonication for another minute at full power. The ~ampIes were then evacuated, flushed with argon, and allowed to react at 60°C for I week. The ~olids were collected by filtration, washed with benzene, and dried in vacuo for 2 hours. Microanalyses wei~e carried out by Galbraith Laboratories, Knoxville, TN, USA. X-ray powder patterns were obtained on a Scintag powder diffractometer over a 2(9 range of ,]-70° at 0.01° intervals and Indexed and flt using a Fortran IV X-ray fitting program. Resistivity data were measured using a four-probe arrangement with a 10+0.01 mA constant current sourer; temperatures over the 8-300K range were measured with a Lake Shore calibrated Si diode. Samples were pressed at 5000 psi in a 0.25 Inch die~ and electrodes were attached with silver paint. RESULTS AND DISCUSSION The compositions of the new materials prepared are listed in Table I, along with their unit ceil parameters and c-axls expansions. Table I. Compositions, unit cell parameters, and c-axls expansions of the new intercalates; Ac values are derived from data in Ref. 8.
Mater|al .,,
x I
.
.
a (~) .
.
.
b (~) i
c (~)
Ac (~)
.
DBTTFxTiS2
0.541
6.824
5.903
25.30
19.60
DBTTFxTiSe2
0.545
6.984
6.147
25.75
19.65
DBTTFxTaS2
0.551
6.497
5.770
25.91
20.00
DBTTFxTaSe2
0.665
6.898
6.1"79
26.35
20.07
TCNTTFxCUCI2
0.323
6.577
5.711
16.49
9.4g
TCNTTFxCUBr2
0.332
6.861
6.151
16.79
10.84
TCNTTFxNIBr2
0.330
7.212
6.408
16.6l
10.51
TCNTTFxCdBr2
0.333
7.842
6.77l
16.39
10.06
TCNTTFxCdl2
0.739
8.467
7.18l
16.62
9.76
For the DBTTF-intercnlates, the X-ray data Indicate the presence of an orthorhomblc unit cell, with a ~ 2a*, b - ,/3a*, and an expanded _o-axis (a* is the a-axis of the uninte-rcalated ]lost). The observed interlayer spacing of ca. 19.5A is greater than the length of the DBTTF molecule (15.1A), suggesting a bilayer structure In which the planar Intercalants are canted from the perpendicular to the layers; one possible arrangement Is shown schematically in Figure la. A tilt angle of 49±20 ts consistent with
2021
the observed stotchiometries and c-axis expansions, if the fntsrcalants are assumed to stack at a ca. 3 . 6 A - d i s t a n c e in the bilayer and are not in r e g i s t e r with the chalcogenide a r r a y in the a - b plane. This s t r u c t u r e is analogous to those observed for a suertes of aromatic hydrocarbon intercalates of the metal dichalcogenides." This observation and the fact that DBTTF is the only TTF analog that has been found to Intercalate into the dichalcogenides suggest that the aromatic character of DBTTF is sufficiently great that in this regard it behaves as an aromatic hydrocarbon analogous to tetracene. Resistivity data for the DBTTF-TaS 2 and TaSe 2 intercalates are shown in Figure 2a, along with data for TaS and TaSe 2 c6ntrois treated exactly (3
b
////'/ Figure 1. (a) Schematic view of the canted bilayer s t r u c t u r e proposed for the DBTTF-MY2intercalates. The chalcogen atoms (Y) are shown as circles with crosses, the M atoms as larger open circles, and the DBTTF is shown in a view p e r p e n d i c u l a r to its long axis. (b) Schematic view of the orlentatton proposed for the TCNTTF-MX 2 intercalates. The hagdes (X) are shown as circles with cresses and the M-atoms as open circles. as for the intercalation reactions, but in the absence of guests. These data s u g g e s t that the guest molecules are simply r e d u c i n g the i n t e r l a y e r i n t e r a c tions without significantly p e r t u r b i n g the host layers. In particular, there is no evidence for enhanced conductivity s u g g e s t i n g that significant guesthost electron t r a n s f e r has occurred. No evidence for s u p e r c o n d u c t i v i t y above 4K was observed. Similar results were observed for the Tt systems, but the measured reststivities were significantly higher. The X - r a y data for the TCNTTF-MX 2 intercalates are readily fit with an orthorhombtc unft cell analogous to that observed for the DBTTF-MY2 systems, again with a significant c-axis expansion. The observed i n t e r l a y e r distances of 10_+0.SA and the stoTchtometry are consistent with a Btructure in which the TCNTTF molecules are oriented with their molecular planes p e r p e n d i c u l a r to the host, but with the long axes tilted b y ca. 300 to allow one nitrile on each end to interact with the metal ions of the host lattice, as illustrated in Figure l b . For all materials except the Cdl 2 intercalate, the observed stoichiometry s u g g e s t s that the short distance between metals in the 010 direction results in occupancy of only e v e r y other row of metals by TCNTTF molecules. In the case of CdIT., the metal ions of the lattice are sufficiently far apart (hm to the ~izo of-the larger iodide ions to allow occupation of e v e r y row by TCNTTF, r e s u l t i n g in a doubling of the i n t e r calant content.
2022 31.0
a
b
5.0
~ 21.0
¢J
\
E ~,3.0
k~$>
e Oo°
%'0
0
11,0 e 'e -° -o -O ,O m _o _e O-o.e~ -~
1.0
1.0 010
100.0 200.0 Temp. in K
500.0
o.o
lOO.O 200.0 Temp. In )~
l.~igure 2. (a) Resistivity data vs. temperature for pressed pellets of TaS~ ( A ) , DBTTFn 55.TAS2 (o), TaSe,/ (E{), and DBTTF n 66.TaSe~. (o). (b)" Resistivity cra'ta vs. temperatur6 for pressed pelY6ts of the TCNTTF intercalates of CuCl 2 ( o ) , CuBr 2 ( ~ ) , CdI 2 (A), and NiBr 2 (o). Resistivity data as a function of temperature are shown for selected TCNTTF-MX 2 intercalates in Fi6q*re 2b. All of the intercalates except that with CuBr 2 exhibit semiconducting behavior comparable to that measured for the p a t e n [ metal halides. In distinct c o n t r a s t , TCNTTF0 3.1.CuBrl vQ exhibits decreasing r e s i s t i v i t y all the way to 4K, consistent "~rIth met&lll~ behavior. The origin of this phenomenon is not clear at p r e s e n t , but may be due to some degree of charge t r a n s f e r from TCNTTF (a r a t h e r poor electron donor) to the CuRr 2 host. Alternatively, the B r : C u ratio of 1.79 may indicate that some degree of reduction of copper, accompanied b y loss of bromide, is o c c u r r i n g d u r i n g the intercalation reaction to form a mixedvalence metal halide. ACKNOWLEDGEMENTS Th]s research was supported in part by the office of Naval Research Materials Division (N00014-91-J-1962) and by NATO (0727/87). REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9.
D. O. Cowan end F. M. Wiygul, Chem. Eng. News 64:28 (1986). T. J. Marks, Science 227:881 (1985). B. M. Hoffman and J. A. Ibers, Acc. Chem. Res. 16:15 (1983). B. A. Averill and S. M. Kauzlarich, Mol. Cryst. Lkl. Cryst. 107:55 (1984). S. M. Kauzlarich, J. F. gllena, P. D . Stupik, W. M. Reiff, and B. A. Averill, J. Am. Chem. Soc. I09:456l (1987). J. F. Bringley, J.-M. l"abre, and B. A. Averill, Chem. Mater, 4:522 (1992). J. F. Bringley, J.-M. Fabre, and B. A. Averlll, J. Am. Chem, Soc. 112:4577 (1990). T. Hibma, in "intercalation Chemistry", M. S. Whittingham and A. J. Jacobsen, eds., Academic Press, New York, 1982, p. 292. T. E. Sutto and B. A. Averill, to be submitted for publication.
300.0