Ⅲ-2. Atomic & Solid State Physics (Muon)

RIKEN Accel. Prog. Rep. 48 (2015)

Studdy of couppling bettween eleectron coonductionn and spiin fluctuaation
in novel organiic chargee transferr complexes withh TANC
*1,*2
*1
*1
*1
*2
M. Enomoto,*1,*2
Y. Furuya,*1
K
K. Isoda,*1
M. Tadokoro,*1and I. Watanaabe*2

＊1
＊1
＊2
＊2

Department of C
Chemistry, Tokyoo University of Sccience
RIKEN Nishinaa CenterNNNN

Figuure 1(b)(a)(c)

Fig. 2. Crysstal structures oof {[Cu(TANCC)](NO33)0.50.5}nn
10.0Depolarization rate (μs-11)

We have suucceeded to synthesize
sorrganic conducctors
wiithanovel
electronnaccepeptor,
5,6
6,11,12-tetraaazanaphthacenne (TANC; seee Figure 1). TheTA
ANC moleculle forms highhly conductiv
ve compoundds invaarious combinnations with metalmions. In particular, sevveral
Cu
u-TANC systeems are highlyy attractive coomplexes in teerms
off formation oof both π-electron condu
uctive bands andoordinating strructure betweeen the accep
ptor molecule andcoco
opper spin ssites. Employying these properties
piss animmportant approach to consstruct π-d intteraction systeems,
suuch as the (DCCNQI)22Cu syystem,1)1) wheree DCNQI dennotes
N,,N’-dicyanoquuinodiimine.
1.5+
In the case of [Cu1.5+(TTANC)](NO33)0.5
00.5
0 , Cu ions andTA
ANC radicalss are alternateely linked thhrough coordiinate
intteraction betw
ween Cu-N atooms along thee b-axis, as shhown
in Fig. 2(a). These flat-ribbbon structuress stack with eachher to form 22D layers in thet ab-plane, while NO33 aanion
othlayyers are segreegated from eaach Cu-TANC
C layers (see FFigs.
1(bb) and (c)). W
While the condductivity of th
his complex shhows
semiconductingg behavior, thee single crysttal exhibits a highonductivity off 50 S cm-1-1 at 300 K along the a-axis, w
whichcois the stacking ddirection of thhe TANC molecules. Moreoover,onductivity shows highly annisotropic behhavior, that is,, σ||aco/ σ||bσ ~ 8.3, whhich correspoonds to the seegregated staccked
strructure of CCu-TANC 2DD layers. Intterestingly, X
X-rayphhotoelectron sspectroscopy resultsrindicatte the coexisttence2+off Cu++ and the Cu2+
at a 1 : 1 ratio in the Cu-TANC layyers.
Moreover,M
the innfrared reflectivity measureement revealss thateleectrons fluctuuate betweenn these two valence statees at
coopper ion sitess in both the directions off stacking (a-aaxis)annd flat-ribbon (b-axis) structtures.
tTANC complex fam
mily,
On the othher hand, theAgg(TANC), alsoo forms a simmilar conductiv
ve layer withoout aco
ounter anionn layer, succh as the NO33 layerr in1.5+[CCu1.5+(TANC)]](NO33)0.5
Thhe anisotrop
pic conducttivity
0.5.
meeasurement ffor the Ag complex
cat room
rtemperaature
shhows that σσ||a / σ||b ~ 13, whiich reflects thelow
w-dimensionaal character ofo the Ag coomplex compparedwiith the Cu onne. Infrared reflectivity
rstu
udy supports thisobbservation. Thhe reflectivity component, whichw
is norm
mal tothee stacking ddirection, is negligible,nwhilew
the parrallel
coomponent cann be observeed similar too that in thee Cucoomplex.
To understannd how electtron conduction occurs inn theTAANC complexxes, we carried out μSR measurementss on
1.5+[CCu1.5+(TANC)]](NO33)0.5
t depolarizaation
0.5. We found that the1/2-1/2
ratte at 300 K iis proportionaal to -H1/2, whichw
suggestss theex
xistence of thee 1D diffusionn behavior of spin-excitedssttates

1.0

100

1000

10000
00.1

0.0

Longituudinal field (OOe)Fig.
F 3. The fieeld dependencce of the depolarization rateeata 300 K.
(thee solid line in Fig. 2) rather than 2D diffuusion (the brokkenlinee in Fig. 2). This behavior w
was also obseerved at 200 anda1000 K. Since we have prediccted from ou
ur previous ligght
experiments thaat electrons are conducctive in thesehighh-temperaturee regions, thee present μSR
R results suppport
our prediction. AtA this momentt, we are not sureswhether thist2+
t Cu++ and Cu
C 2+1D diffusion behavior occurs iin the line of thennection or in the direection of TANCTstacking.
conCommparison betw
ween the μSSR data of thetCu and Agcommplexes will an
nswer this queestion.
Refferences

1) A.
A Aumüller et all.: Angew. Chemm., Int. Ed. Engll. 25, 740 (19866).
2) F.
F L. Pratt et al.: Synth. Met., 855, 1747 (1997).
3) F.
F L. Pratt et al.: Hyperfine Inteeract., 104, 357 (1997).
4) N.
N Kojima et al.: Solid State Coommun., 120, 165
1 (2001).
5) N.
N Kida et al.: Phhys. Rev. B, 777, 14427 (2008)).

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