Molecular Second-Order Optical Nonlinearity of Push-Pull Bisdithiolene Nickel Complexes
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(diamine)(maleonitrildithiolato)Ni(II) was synthesized by mixing disodium maleonitrildithiolate[9] and nickel(II) chloride in concentrated ammonia solution. The synthetic schemes for 1-7 are shown in Scheme 1. Scheme I
a) ex. P4 Slo, CH 2 CI 2 , reflux 4h, RT, 12 h, R = 2-ethylhexyl 69%, R = cyclododecyl, 72%; b) CH 2 Cl 2/CH 3 CN, reflux 10 min, RT 24 h, R = 2-ethylhexyl, 59%, R = cyclododecyl, 60%; c) CH 2 C12 , RT 3 h, 62% d) CH 2 CI 2 , RT 3 h, 89%. e) CH 2 C12 , RT 3 h, 56%. H3N( S X CN NiX H3N" •Oa.
R
b
RON~ =
F3CS, F .-
H3CO
OCH3
H3co•ý
4
OCH3
X
OCH3 HaCOrek
0d0 1-OC1
~
CF3 S CF SN"S 3
F Fab
,' ocFý
d
".•"t~
*CF
H3Cg:430 H C 3
Hcor"-
6
OCI-4
F3 ~0
NQ'
v
5
R
OC-1
'
cyclododecyl 4
CN
S N"X CF 2-ethylhexyl
C-
OCI30
O\I
H3C
R= 2-ethylhexyl 3
x[CN
"
,a CF3
cyclododecyl I 2-ethylhexyl 2 H3C
Sr N!"
Rs' Ni(tdf)2
•R•S
0
R
1"1 CN
"NSNI
F, &Sý
S
CF 3 e CF C FS 33
N
i
0N0
F
7
Compounds 1-7 gave IH NMR, FTIR, UV-Vis, and FABMS fully consistent with the proposed structure and satisfactory elemental analyses were obtained for complexes 5-9. Transition dipole moments (Weg) were calculated from the area of the absorption band, taking twice the numerical integral of the low-energy half of the absorption band. Ground-state dipole moment were determined from an analysis of the solution dielectric constant and refractive index versus concentration (10-3-10-5 M) of the solute, using chloroform as the solvent except dichloromethane was used for 9. All solvents used in gg measurement were dried over 4-A molecular sieves. The equation adopted for calculating gg was based on that of Osipov-Onsager for the solute dissolved in polar solvents[12,13]. Excited-state dipole moments (ges) of 3 and 5-9 were determined using solvatochromic method as previously described[14]. The dipole moment change, ge - jig, was calculated from the coefficient, obtained from a least-squares fitting of McRae expression to the Xnax of ICT band in 10-20 different solvents. The most uncertain quantity of solvatochromic method is the poorly defined Onsager radius a. We took the sum of spherical radius of solute and
166
solvent for a [ 15]. The spherical radii of solutes were calculated from measured density values of compounds 3 and 5-9. RESULTS AND DISCUSSION X-ray single crystal structures [16] of 1, 4, and 6 were obtained in order to elucidate differences in ground-state bonding structures, i.e., 3-5 of one type and 6-7 of the other. Selected bond distances are listed in Table 1. Table I
Selected bond distances
(A) of 1, 4, and 6 from X-ray single crystal structures 3- .cacceptor 3
donorc 1S'
I donor
Cl-C2 1 4
1.522(9) 1.34(2)
6
1.410(5)
C -S1 C2-S2 1.654(4) 1.661(10) 1.688(11) 1.713(4) 1.696(4)
\ /1 Ni
/ $2
S4
Ni-S I Ni-S 2 .... 2.178(3) 2.151(3) 2.124(1) 2.113(1)
-'acceptor
Ni-S 3 Ni-S 4 2.145(3) 2.145(3) 2.122(1) 2.118(1)
C3 -S3 C4-84 1.745(12) 1.718(11) 1.717(4) 1.706(4)
C3-C4
1.50(2) 1.366(6)
For the central Ni(S 2 C2 )2 moiety of 4, all bond distances of 4 are consistent w
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