*O—A049 183 NORTHWtSTCRN LmIV EVANSTON IU. OUT OF CICMISTRY CLECTRZCM.ZICNSIONAL MO4.LCULAR PtTALSI

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~~~~!O. 2 v7~5 ’r ~ ~/Single Crystal Electrical Conductivity of Nickel Phthalocyanine Iodide~ (

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Northwestern UniversityDepartn~nt of Ch emistry 2?Evanston, Illinois 60201 ..

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New Lov-Dlmena tona l Molecular Metals :Single Crystal Electrical Conductivity of ~t~tei~m, 1977Nicke l Phtha locyanine Iodide s . PERFORM INOORG . REPORT NUMSER

7 AUTHOR(.) S. CONTRACT OR GRANT NUkI B ER(a)

C.J. Schranun, D. R. Stojakovic , B.M. Hoffman ,and T. 3. Marks NOOO1l~-77-C-0231 V

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I?. QISTRISUTION STATEMENT (of ho .b.Sr.cS onf.r.d Sn DI.ck 20. if dSll.r.n S Sr.., R.p.rS) Jfr~ .‘)7 j~7~3

FIS. SUPPLEMENTARY NOTES

*5. KEY WORDS (Cinllnu . on r.o.va. old. If n.c..wv ond Sd•nlIly bj. bIoc~ ,nonb..)

PbthalocyanineMolecular metalElectrical conductivityResonance Raman

ao. AS IT RACT (ConShwi. .Sd. If n..... ~~v id IdsnSSb b~ W.ck n. .b.r)

(see page 1)

DO ~~~~~~

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unc lassified. . SICU RITY CLAI ~~P,CATI0N OF tH IS PA SS ~~~ on D a ~~~~~~~~

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NEW LOW-DIMENSIONAL MOLECULAR METALS: SINGLE CRYSTAL

ELECTRICAL CONDUCTIVITY OF NICKEL PHTHALOCYANINE IODIDE.

~~~~~~~~~~ -:

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____ -

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—‘t .Abstract

Single crystals of NiPcI1•0 (Pc = phthalocyanine), which are composed

of one-dimensional stacks of (NIP c)~° ~ molecules and chains of I~

molecules , exhibit metallic electrical conductivity in the stacking direc-

tion. At room temperature the carrier mean free path Is 3.3 - 8. 2A.

~~~~~ i~-~ii~ -~~~~~~~~~~~~~~~~~~~ —~~~~~~—

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~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~

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The highly anisotropic and sometimes spectacular electrical , magnetic ,

and optical charateristics of molecular materials with strongl y one-dimensional

interactions have made them of great current interest to chemists and physi-

cists ~1~ fr). As part of our efforts to obtain a better understanding of , and

chemical control over , the fundamental properties of such materials, we

recently synthesized an extensive new class of highly conductive molecular

solids, containing stacks of metallophthalocyanine (MPc) molecules (Figui’e-

4#)-(e). These were made via a preparative procedure which utilizes iodine

oxidation to afford lattices composed of one-dimensional array s of planar donor

molecules (in this case MPc units) with fractionally occupied electronic valence

shells (tpartial oxidation PorP mixed valences) and chains of polyiodk~ coun-

terions ~€ k ~7. The general structural pattern of such lattice~ is schematized

in Figure lB.

Our initial studies of the partially oxidized phthalocyanlnes revealed

a greater chemical flexibility in terms of metal-ion constituents and range

of stoichiometries than in any previously reported class of conductive

molecular materials. Electrical conductivitie s of pressed microcrystalline

powder samples were comparable to those of other “molecular metals” (1-5),

and we predicted that single crystal conductivities would be metal-like in

the MPc stacking direction. We here report the synthesis and physical pro-

perties of single crystals of one member of this new series of highly con-

ductive compounds: NiPcI1~ ~~. The earlier predictions about such materials

1’

~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~ ~~~~~~~~~ - —- — — .

2

are confirmed: At room temperature the mobilit ies of the individual charge

carriers in NiPcI10 , expressed as the mean free path , are comparable to or

greater than any previously known stacked molecular conductor (1-5) and the

temperature dependence of the electrical conductivity is indeed metallic.

Needle-like crystals of NIPCI1 0 , exhibiting a silver-gold metallic lustre

in reflection , were prepared by slowly diffusing together solutions of 12 and

sublimed NiPc (12). The resonance Raman spectrum of the crystals with

5145 A Alt excitation exhibits the characteristic symmetric stretching funda-

mentals of 13 - at ‘~~~~ 107 cm ‘ along with the expected nv (n = 2, 3, 4, 5. . .)

overtone progression (6, 7, 14). These data confirm the partially oxidized

formulation NiPc(13 ~~~~. shown in Figure lb. Single crystal electron paramag-

netic resonance studies of NiPcI1 ~ provide evidence that the partial oxidation

is predominant ly ligand-centered, rather than metal-ion centered (12). Further

metrical details of the crystal structure , provided by single crystal X-ray

diffraction and diffuse scattering measurements, will be presented elsewhere (12).

Figure 2 presents typical electrical conductivity data , c~1(T) , data (four-

probe, phase-locked 27 Hz. ac apparatus (15)) for NiPC 11 0 along the NiPc

stacking direction (crystallographic c-axis). At room temperature, conductivities

in the r ange 250-650 ohm 1 cm~~ are observed. These values are comparable to

those for the well known “organic metal” TTF-TCNQ (1-5, 16). However,

because of the very large cross-sectional area of the NiPc molecules, when

- -

—.~- .,.

.-.—— — —“-.-———-—

3

comparing NiPcI1 ~ to other materials, it is important to consider the pro-

perties of the individual charge carriers (10). Within the framework of one-

electron band theory (3, 17), the conductivity can be related to A, the mean

free path of a carrier along the stacking direction (the average distance tra-

veiled between scattering events) and to A, the cross-sectional area per con-

ducting stack , by the equation

=

(1)

For NiPcI1~0 at room temperature , we find values for A to be in the range 3. 3-

8. 2 1 or 1. 0-2. 3 intermolecular spacings. This result can be compared to

values in other highly conductive stacked molecular systems of 2. 1-2.8 spacings

for TTT2 I3 (18), 1. 6-2 . 5 spacings for HMTSF-TCNQ (19), 0.4-0. 6 spacings

for TTF-TCNQ (16), — 0. 6 spacings for K2 Pt(CN)4 Br0 ~~. 3H~O (2) 0. 15

spacings for Qn (TCNQ)2 (20) and ~0. 06 spacings for the related macrocyclic

system Ni(octamethyitetrabenzporphyrin) 110 (10, 11). The mean free path for

the most highly conductive NiPcI1 ~ crystals still, however , is less than that

in Ni metal, Ca. 60 A or ca. 26 interatomic spacings (21).

Figure 2 shows that as the temperature is decreased from ambient values

the conductivity is metallic , increasing with decreasing temperature until

a maximum is reached at a temperature Tm fn~90°K which varies somewhat

from crystal to crystal. At the maxim um , calculated values of A are in

the range 4-9 spacings which maybe compared with \ of 10-15 spacings for

TTF-TCNQ at its temperature of maximum conduc tivity ( 60°K).

For T > Tm there is no hysteresis in the conduc-

I

4

tivity- temperature curves and ‘11(T) obeys the relationship (1, 3, 18, 19)

1/ 1( T ) = a + b T ~

.

(2)

For all crystals examined , a least-squares fitting to equation (2) yields

= 1. 9 ~0. 1 and a plot of log J 1-( ~(295 K)/c~(T)1 versus T yields a super-

imposable family of curves : this has been show to provide assurance of the relia-

bility of the meas urements and of a well-defined scattering mechanism(18). The

value of y obtained is distinctly different from the value ‘y = 1 found for simple

metals and is similar to that found for several other molecular metals, 2 .0 -

2.4 (18, 19).

Upon cooling below Tm the conductivity abruptly decreases and then con-

tinues to slowly decrease with further cooling (Figure 2). This behavior sug-

gests an interpretation in terms of a Peierls transition (1-5) or a first-order

phase transition. Raman spectral studies down to 4°K do indicate that the

lattice charge distribution , i. e., the average degree of NiPc partial oxidation,

remains unaltered through this transition. Pronounced hysteresis in dc con-

ductivity observed upon passage through Tm is suggestive of contributions

from stress at the contacts , and indeed microwave conductivity studies in

collaboration with Prof. T. Poehier suggest that the transition IS at lower

temperatures in unstressed crystals .

Thus , the temperature dependence of the conductivity of NiP c11 ~ is

metal-like and the room temperature mean free path compares favorably

with that of the most highly conductive materials composed of molecular

stacks. On a broader plane , this study and related

_ _ _ _ - --

.

-.. -

-

~

..

• 5

work (10) confirm the idea that the partial oxidation of metallomacro-

cycles is a chemically versatile synthetic route to a wide array of new

molecular metals.

C. J. Schramm , D. B. Stojakovic , B. M. Hoffman , and T. J. Marks

Department of Chemistry andThe Materials Research Center

Northwestern UniversityEvanston , Illinois 60201

- — • •-~-

—-~~~~

• 6

References and Notes

• 1. H. J. Keller , ed., “Chemistry and Physics of One-dimensional Metals, ”

Plenum Press, New York , 1977.

2. J. S. Miller and A. J. Epstein , Prog. Inorg. Chem., 20, 1 (1976).

3. A. J. Berlinsky, Contemp. Phys. , 17 , 331 (1976).

4. Z. G. Soos and D. J. Klein in “Molecular Associations, ” B. Foster, ed.,

Academic Press, New York, 1975, Chapter 1.

5. W. D. Metz, Science, 190, 450 (1975).

6. J. L. Peterson , C.J. Schratnm , B. M. Hoffman , and T. J. Marks, J .

Amer.Chem . Soc., 99, 286 (1977).

• 7. T.J. Marks, ATrn .N. Y. Acad .Sci., in press.

8. A. Gleizes, T. J. Marks , and J.A. Ibers , J. Amer .Chem.Soc., 97, 3545

(1975).

9. M. A . Cowie A. Gleizes, G. W. Grynkewich, D. W. Kalina, M. S. McClure,

B. P. Scaringe, B. C. Teite lbaum , S. L. Ruby, J. A. !bers , C. R. Kannewurf,

and T. J. Marks, submU±ed for publication .

10. T. E. Phillips and B. M. Hoffman , J. Amer . Chem. Soc. , 99 , 7734(1977).

• 11. T. E. Phillips, H. P. Scaringe, B. M. Hoffman, and .1. A. Ibers , manuscript

in preparation.

12. C.J. Schramm , H. P. Scaringe , D. R. Stojakovi c, B. M. Hoffman , T.J.

Marks, and J . A. Ibers , manuscript in preparation.

13. T. J. Marks, D. F. Webster , S. L. Ruby , and S. Schultz , J. Chem. Soc.,

Chern. Comm., 444 (1975).

—~~~~~~~ ~~~~~~ — -• • . .• •

- ..• -—•—-—- •~~~~ ---

7

14. D. W. Kalina, D. R. Stojakovic, B. C. Teitelbaum, and T. J. Marks,

manuscript in preparation.

15. T. E. Phillips, J. B. Anderson , and B. M. Hoffman ,

manuscript in preparation. Measurements were made with the• precautions suggested in , D. E. Schafer , F. Wudi , G.A. Thomas ,

J.P. Ferrar is, and D.O. Cowan , Solid State Commun., 14 , 347 (1974).

16. G. A. Thomas, et . al. , Phys. Rev. , B, 13, 5105 (1976).

17. N. F. Mott and E.A . Davis, “Electronic Processes in Noncrystalline

Mat erials, “ Clarendon Press, Oxford, 1971.

18. L. C. rsett and E. A. Perez-Albuerne , Solid State. Commun., 21, 433 (1977).

TTT = tetrathiotetracene.

19. A.N. Bloch, D.O. Cowan, K. Beckgaard, H .E. Pyle, R.H. Bands, and

T.O. Poehler, Phys.Rev.Lett., 34, 1561 (1975).

20. V. Walatka, Jr., and J. H. Peristein, Mol. cryst . Liq. Cryst., 15, 269

(1971). Qn = quinolinium.

21. CRC Handbook of Chemistry and Physics, 58th ed ., CRC Press, Inc.,

Cleveland, 1977, p. F-170.

22 . This research was supported by grants from the Northwestern Materials

Research Center (NSF DMR~ 72-0319A06), the Paint Research Institute

(53Co to T.J. M. ),and the U. S. Office of Naval Research (to T.J. M .).

T. J M . is a Camille and Henry Dreyfus Foundation Teacher-Scholar.

- -- -. --- . - - -

-.

- rr ~~~~~~ .. . ________________________________________________________

8

Figure Captions

Fig. 1A. The molecular structure of a metal phthalocyafli lle. B. Schematic

representation of the crystal structure of NiPcI1~0 and similar materials.

The view is perpendicular to the stacking direction.

Fig. 2. Plot of the conductivity ratio, a~ (T)/u 11 (295K), versus temperature

for a typical crystal of NiPcI1 ~ in which ~ (295K) 350 (0cm)- ’.

I .

- - • . . . • . ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - -

- A

A.

• MPc

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B. MI

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M II

MI

M II

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30 120 210 300TEMPERATURE ( K)

•~~ • . - ~~~~~~~~ ~ ~~~~~~~~~~ ~~~~~~~~~~ .-. 4

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