Synthesis and characterization of nickel(II) bis(alkylthio)salen complexes

Article abstract of DOI:10.1021/ic990950p

NiX₂(2-RSC₆H₄CH=NCH₂CH₂N=CHC₆H₄SR-2) (NiX₂L; L = 5) (1a, X = Br, R = C₆H₁₃; 1b, X = Cl, R = C₁₂H₂₅) and NiX₂(2-C

Full text of DOI:10.1021/ic990950p

712
Inorg. Chem. 2000, 39, 712-718
Synthesis and Characterization of Nickel(II) Bis(alkylthio)salen Complexes
D. Scott Bohle,* Abdullah Zafar, Patricia A. Goodson, and David A. Jaeger
Department of Chemistry, University of Wyoming, Laramie, Wyoming 82071-3838
ReceiVed August 6, 1999
NiX2(2-RSC6H4CHdNCH2CH2NdCHC6H4SR-2) (NiX2L; L ) 5) (1a, X ) Br, R ) C6H13; 1b, X ) Cl, R )
C12H25) and NiX2(2-C6H13SC6H4CH2NHCH2CH2NHCH2C6H4SC6H13-2) (NiX2L; L ) 6) (2a, X ) Br; 2b, X )
Cl; 2c, X ) OClO3) were prepared from ligands 5 and 6, respectively. The 1:2 metal-ligand complex Ni(OClO3)2(2-
RSC6H4CH2NHCH2CH2NHCH2C6H4SR-2)2 3, was obtained from an EtOH solution of 2c. The characterization
of paramagnetic 1-3 included single-crystal X-ray diffraction studies of 1a and 3. Complex 2c converted into 3
in the presence of excess ligand 6 in CHCl3.
Introduction
As a part of our evaluation of Ni(II) bis(alkylthio)salen and
related complexes as templates for Diels-Alder reactions, we
have studied several unfunctionalized complexes. Our interest
in such complexes also extends to their potential surfactant
character. Surfactant transition metal complexes are anticipated
to have a wide range of interesting stereochemical, redox, and
physical properties. But there have been only a few reports6 of
the synthesis, isolation, and characterization of surfactant
transition metal complexes, in contrast to many reports of the
formation and study of such surfactants in solution without
isolation.7 Herein we report the synthesis and characterization
of Ni(II) complexes 1 and 2, which contain several ligands and
counterions. Interestingly, 2c was found to interconvert with
1:2 complex 3. In contrast to Ni(II) thiosalen and related
complexes, 1-3 exhibit octahedral coordination with its con-
comitant paramagnetism.
There have been numerous reports of transition metal
complexes containing thiosalen1,2 and other ligands1,2a with two
sulfur and two nitrogen donor atoms but only a few reports of
complexes containing related ligands in which both sulfur atoms
are alkylated.1,3,4 In particular, in its thiosalen and similar
complexes, Ni(II) typically adopts a four-coordinate square
planar geometry.1,2a-d Alkylation of the sulfur atoms can give
dipositively charged complexes in which Ni(II) remains four-
coordinate3 or neutral octahedral complexes containing coor-
dinated counterions.1,3,4a-c In both geometries, the S-alkyl groups
are in a cisoid relationship. With two functionalized S-alkyl
chains incorporated into Ni(II) bis(alkylthio)salen and related
complexes, one containing a 1,3-diene unit and the other a
dienophile unit, their cisoid disposition is appropriate for
controlling the regioselectivity of Diels-Alder cycloaddition
between them. Namely, the 1,3-diene and dienophile units can
interact intramolecularly only in one relative orientation due to
the fixed side-by-side alignment of the S-alkyl chains. As a
result, only one of two possible regioisomeric cycloadducts
should be formed, in an application of the coordination template
hypothesis.4d In related studies,5 we have used the alignment
of functionalized surfactant monomers within their aqueous
micelles to control the regioselectivity of Diels-Alder reactions.
* Corresponding author. Telephone: 307-766-2795. Fax: 307-766-2807.
E-mail: Bohle@uwyo.edu.
(1) Holm, R. H.; Everett, G. W., Jr. Prog. Inorg. Chem. 1966, 7, 83.
(2) For examples, see: (a) Yamamura, T.; Tadokoro, M.; Tanaka, K.;
Kuroda, R. Bull. Chem. Soc. Jpn. 1993, 66, 1984. (b) Yamamura, T.;
Tadokoro, M.; Kuroda, R. Chem. Lett. 1989, 1245. (c) Bertini, I.;
Sacconi, L.; Speroni, G. P. Inorg. Chem. 1972, 11, 1323. (d) Coombes,
R. C.; Costes, J.-P.; Fenton, D. E. Inorg. Chim. Acta 1983, 77, L173.
(e) Fallon, G. D.; Gatehouse, B. M.; Marini, P. J.; Murray, K. S.;
West, B. O. J. Chem. Soc., Dalton Trans. 1984, 2733.
(3) Sacconi, L.; Mani, F.; Bencini, A. In ComprehensiVe Coordination
Chemistry; Wilkinson, G., Gillard, R. D., McCleverty, J. A., Eds.;
Pergamon: New York, 1987; Vol. 5, Chapter 50.
Experimental Section
General Procedures and Materials. 1H (400 MHz) and 13C (100.6
MHz) NMR spectra were recorded in CDCl3 unless noted otherwise
with Me4Si and CHCl3 (center line at δ 77.00 relative to Me4Si) as
(4) (a) Lindoy, L. F.; Smith, R. J. Inorg. Chem. 1981, 20, 1314. (b)
Drummond, L. A.; Hendrick, K.; Kanagasundaram, M. J. L.; Lindoy,
L. F.; McPartlin, M.; Tasker, P. A. Inorg. Chem. 1982, 21, 3923. (c)
Busch, D. H.; Jicha, D. C.; Thompson, M. C.; Wrathall, J. W.; Blinn,
E. J. Am. Chem. Soc. 1964, 86, 3642. (d) Thompson, M. C.; Busch,
D. H. J. Am. Chem. Soc. 1964, 86, 3551. (e) Nation, D. A.; Taylor,
M. R.; Wainwright, K. P. J. Chem. Soc., Dalton Trans. 1992, 1557.
(f) Nation, D. A.; Taylor, M. R.; Wainwright, K. P. J. Chem. Soc.,
Dalton Trans. 1996, 3001.
(5) (a) Jaeger, D. A.; Su, D. Tetrahedron Lett. 1999, 40, 257. (b) Su, D.;
Jaeger, D. A. Tetrahedron Lett. 1999, 40, 7871. (c) Jaeger, D. A.;
Wang, J. Tetrahedron Lett. 1992, 33, 6515. (d) Jaeger, D. A.; Wang,
J. J. Org. Chem. 1993, 58, 6745. (e) Jaeger, D. A.; Wang, J.; Goodson,
P. A. J. Crystallogr. Spectrosc. Res. 1993, 23, 955.
10.1021/ic990950p CCC: $19.00 © 2000 American Chemical Society
Published on Web 02/02/2000

Nickel(II) Bis(alkylthio)salen Complexes
Inorganic Chemistry, Vol. 39, No. 4, 2000 713
1
internal standards, respectively. H and 13C NMR spectra recorded in
anhydrous NiBr2 (0.17 g, 0.78 mmol) in absolute EtOH (20 mL) at 25
°C was added rapidly a solution of 5a (0.37 g, 0.79 mmol) in EtOH
(10 mL). The resulting mixture was heated to reflux (CaCl2 drying
tube) for 15 h, concentrated by rotary evaporation to ca. 12 mL, and
then held at 5 °C for 15 h. No crystallization occurred until the mixture
sat at 25 °C for 30 min. Thereafter the mixture was held at 5 °C for 2
h, followed by filtration to give dark green crystals of 1a (0.26 g, 48%).
After the mother liquor was held at 25 °C for a few weeks, X-ray-
quality crystals were obtained: mp 175-177 °C dec; 1H NMR (CDCl3;
only broad signals were observed due to 1a’s paramagnetic character)
δ 11.60 (br s), 10.63 (br s), 7.08 (br s), 5.58 (br s), 2.44 (br s), 1.25-
1.80 (br m), 0.98 (br s); 13C NMR (CDCl3; only a few signals were
observed due to 1a’s paramagnetic character) δ 159.82, 32.50, 24.25,
12.17. Anal. Calcd for C28H40N2S2NiBr2: C, 48.93; H, 5.87. Found:
C, 48.95; H, 5.88.
2-(Dodecylthio)benzaldehyde (4b). A mixture of 2-nitrobenzalde-
hyde (1.00 g, 6.62 mmol), 1-dodecanethiol (2.39 g, 11.9 mmol)
(Aldrich), K2CO3 (1.00 g, 7.23 mmol), and DMF (5 mL) was held at
110 °C for 24 h under N2. Then, at 25 °C, it was poured into H2O (70
mL) and extracted with Et2O (4 × 25 mL), and the combined extracts
were dried over MgSO4. Rotary evaporation left a dark brown
amorphous solid, which was chromatographed on a 3 cm × 25 cm
column of silica gel packed in hexane and eluted with hexane to give
4b (0.59 g, 29%): 1H NMR (CDCl3) δ 10.39 (s, 1 H, CHO), 7.83 (dd,
J ) 1.5, 7.7, 1 H, Ar H), 7.49-7.53 (m, 1 H, Ar H), 7.40-7.42 (m, 1
H, Ar H), 7.29 (dt, J ) 0.7, 7.9, 1 H, Ar H), 2.95 (t, J ) 7.4, 2 H,
SCH2), 1.66-1.72 (m, 2 H, SCH2CH2), 1.43-1.47 (m, 2 H, SCH2-
CH2CH2), 1.26 (m, 16 H, (CH2)8), 0.88 (t, J ) 6.9, 3 H, CH3); 13C
NMR (CDCl3) δ 191.71, 142.53, 134.13, 134.06, 132.15, 128.29,
125.36, 33.48, 32.11, 29.82, 29.77, 29.67, 29.54, 29.37, 29.17, 28.75,
22.89, 14.32. Anal. Calcd for C19H30OS: C, 74.45; H, 9.87. Found:
C, 74.49; H, 9.80.
N,N′-Bis[(2-(dodecylthio)phenyl)methylene]-1,2-ethanediamine (5b).
A solution of 4b (1.96 g, 6.39 mmol) and ethylenediamine (0.183 g,
3.04 mmol) in C6H6 (40 mL) was heated to reflux under a Dean-
Stark trap for 6 h and then allowed to stand at 25 °C for 15 h over
MgSO4. Thereafter the mixture was filtered and rotary-evaporated to
give a yellow solid, which was dried for 2 h (25 °C, 0.001 mmHg)
and recrystallized twice from hexane (-20 °C) to give yellow flakes
of 5b (0.86 g, 44%): mp 42-43 °C; 1H NMR (CDCl3) δ 8.87 (s, 2 H,
2 ArCHN), 7.91 (dd, J ) 1.4, 7.7, 2 H, 2 Ar H), 7.35-7.39 (m, 2 H,
2 Ar H), 7.31 (dt, J ) 1.6, 7.5, 2 H, 2 Ar H), 7.21 (br t, J ) 7.1, 2 H,
2 Ar H), 4.02 (s, 4 H, NCH2CH2N), 2.80 (t, J ) 7.4, 4 H, 2 SCH2),
1.52-1.56 (m, 4 H, 2 SCH2CH2), 1.24-1.37 (m, 36 H, 2 (CH2)9), 0.88
(t, J ) 6.8, 6 H, 2 CH3); 13C NMR (CDCl3) δ 161.30, 137.81, 136.20,
130.81, 130.67, 128.17, 126.65, 62.00, 35.15, 32.14, 29.86, 29.82, 29.73,
29.58, 29.39, 29.23, 29.01, 22.91, 14.35. Anal. Calcd for C40H64N2S2:
C, 75.41; H, 10.13. Found: C, 75.60; H, 9.99.
DMSO-d6 employed CD3S(O)CD2H (δ 2.50 relative to Me4Si) and
CD3S(O)CD3 (δ 39.52 relative to Me4Si) as internal standards,
respectively. J values are in hertz. Vis-NIR spectra were recorded on
a Perkin-Elmer Lambda 9 spectrophotometer with quartz cuvettes (1
cm path length). Magnetic susceptibility was determined on a Johnson
Mathey magnetic susceptibility balance (MSB-1). Flash chromatography
was performed on silica gel (ICN 02776, 60 Å, 32-63 µm). All melting
points were taken in open capillary tubes and are uncorrected. Ratios
describing the compositions of solvent mixtures represent relative
volumes. Elemental analyses were performed by Atlantic Microlab,
Norcross, GA.
2-(Hexylthio)benzaldehyde (4a). A modified literature procedure8
was used. A mixture of 2-nitrobenzaldehyde (Aldrich) (3.00 g, 19.9
mmol), 1-hexanethiol (3.52 g, 29.8 mmol) (Aldrich), K2CO3 (3.01 g,
21.8 mmol), and DMF (20 mL) was held at 110 °C for 18 h, cooled to
25 °C, and diluted with Et2O (125 mL), and the resulting mixture was
filtered. Rotary evaporation left a brown oil, which was dried for 15 h
(25 °C, 0.001 mmHg) and flash-chromatographed on a 3 cm × 35 cm
column of silica gel packed in hexane and eluted with hexane to give
4a (2.37 g, 54%): 1H NMR (CDCl3) δ 10.39 (s, 1 H, CHO), 7.83 (dd,
J ) 1.5, 7.7, 1 H, Ar H), 7.51 (m, 1 H, Ar H), 7.41 (m, 1 H, Ar H),
7.29 (dt, J ) 0.9, 7.4, 1 H, Ar H), 2.95 (t, J ) 7.4, 2 H, SCH2), 1.66-
1.73 (m, 2 H, SCH2CH2), 1.45-1.47 (m, 2 H, SCH2CH2CH2), 1.28-
1.32 (m, 4 H, (CH2)2), 0.89 (t, 3 H, CH3); 13C NMR (CDCl3) δ 191.77,
142.52, 134.15, 134.08, 132.18, 128.31, 125.39, 33.50, 31.55, 28.85,
28.72, 22.71, 14.21. Anal. Calcd for C13H18OS: C, 70.23; H, 8.16.
Found: C, 70.53; H, 8.21.
N,N′-Bis[(2-(hexylthio)phenyl)methylene]-1,2-ethanediamine (5a).
A solution of 4a (2.54 g, 11.4 mmol) and ethylenediamine (0.33 g, 5.6
mmol) in C6H6 (50 mL) was heated to reflux under a Dean-Stark trap
for 2 h and allowed to stand at 25 °C for 12 h over MgSO4. Thereafter
the mixture was filtered and rotary-evaporated to give a yellow oil from
which ethylenediamine and 4a were removed by Kugelrohr distillation
(ca. 100 °C) to leave 5a (2.42 g, 93%): 1H NMR (CDCl3) δ 8.87 (s,
2 H, 2 ArCHN), 7.91 (dd, J ) 1.5, 7.7, 2 H, Ar H), 7.36-7.38 (m, 2
H, Ar H), 7.31 (dt, J ) 1.5, 7.3, 2 H, Ar H), 7.21 (br t, J ) 7.4, 2 H,
Ar H), 4.03 (s, 4 H, NCH2CH2N), 2.80 (t, J ) 7.3, 4 H, 2 SCH2),
1.50-1.58 (m, 4 H, 2 SCH2CH2), 1.23-1.38 (m, 12 H, 2 (CH2)3), 0.87
(t, J ) 7.1, 6 H, 2 CH3); 13C NMR (CDCl3) δ 161.31, 137.80, 136.20,
130.83, 130.68, 128.16, 126.66, 62.01, 35.16, 31.56, 29.18, 28.67, 22.74,
14.25. Anal. Calcd for C28H40N2S2: C, 71.74; H, 8.60. Found: C, 71.76;
H, 8.58.
[N,N′-Bis[(2-(hexylthio)phenyl)methylene]-1,2-ethanediamine]-
nickel(II) Bromide (1a). A modified literature procedure2a,b was used
for the syntheses of 1a and the complexes below. To a suspension of
(6) For examples, see: (a) Yashiro, M.; Matsumoto, K.; Yoshikawa, S.
Chem. Lett. 1989, 985. (b) Yashiro, M.; Matsumoto, K.; Yoshikawa,
S. Chem. Lett. 1992, 1429. (c) Yashiro, M.; Matsumoto, K.; Seki, N.;
Yoshikawa, S. Bull. Chem. Soc. Jpn. 1993, 66, 1559. (d) Behm, C.
A.; Creaser, I. I.; Korybut-Daszkiewicz, B.; Geue, R. J.; Sargeson, A.
M.; Walker, G. W. J. Chem. Soc., Chem. Commun. 1993, 1844. (e)
Fallis, I. A.; Griffiths, P. C.; Griffiths, P. M.; Hibbs, D. E.; Hursthouse,
M. B.; Winnington, A. L. J. Chem. Soc., Chem. Commun. 1998, 665.
(f) Behm, C. A.; Boreham, P. F. L.; Creaser, I. I.; Korybut-
Daszkiewicz, B.; Maddalena, D. J.; Sargeson, A. M.; Snowdon, G.
M. Aust. J. Chem. 1995, 48, 1009. (g) Arumugam, M. N.; Arunacha-
lam, S. Indian J. Chem. 1997, 36A, 84. (h) Bruce, D. W.; Denby, I.
R.; Tiddy, G. J. T.; Watkins, J. M. J. Mater. Chem. 1993, 3, 911. (i)
Mun˜oz, S.; Gokel, G. W. Inorg. Chim. Acta 1996, 250, 59. (j)
Sprintschnik, G.; Sprintschnik, H. W.; Kirsch, P. P.; Whitten, D. G.
J. Am. Chem. Soc. 1977, 99, 4947. (k) Menger, F. M.; Lee, J.-J.;
Hagen, K. S. J. Am. Chem. Soc. 1991, 113, 4017. (l) Sakai, S.;
Fuginami, T. Hyomen 1990, 28, 644 and references therein.
(7) For examples, see: (a) Lu, X.; Zhang, Z.; Liang, Y. Langmuir 1997,
13, 533. (b) Ghirlanda, G.; Scrimin, P.; Tecilla, P.; Toffolettii, A.
Langmuir 1998, 14, 1646. (c) Hampl, F.; Liska, F.; Mancin, F.; Tecilla,
P.; Tonellato, U. Langmuir 1999, 15, 405. (d) Kofman, V.; Shane, J.
J.; Dikanov, S. A.; Bowman, M. K.; Libman, J.; Shanzer, A.; Goldfarb,
D. J. Am. Chem. Soc. 1995, 117, 12771. (e) Bhattacharya, S.;
Snehalatha, K.; George, S. K. J. Org. Chem. 1998, 63, 27 and
references therein.
[N,N′-Bis[(2-(dodecylthio)phenyl)methylene]-1,2-ethanediamine]-
nickel(II) Chloride (1b). To a solution of NiCl2‚6H2O (0.20 g, 0.82
mmol) in EtOH (15 mL) at 50 °C was added during 4 min a solution
of 5b (0.52 g, 0.82 mmol) in EtOH (10 mL). The mixture was then
heated to reflux for 3 h and rotary-evaporated. The resultant crude
product was recrystallized from MeOH (25 °C) under a swift current
of N2 to give 1b (0.15 g, 25%): mp 145-146 °C dec; 1H NMR (CDCl3;
broad signals were observed due to 1b’s paramagnetic character) δ
16.35 (br s), 11.71 (br s), 11.03 (br s), 6.82 (br s), 5.28 (br s), 2.54 (br
s), 1.80 (br s), 1.00-1.70 (br m), 0.90 (br m); 13C NMR (CDCl3; only
alkyl chain signals were observed due to 1b’s paramagnetic character)
δ 33.18, 32.29, 30.94, 29.39, 28.92, 28.77, 28.40, 21.70, 13.16. Anal.
Calcd for C40H64N2S2NiCl2: C, 62.66; H, 8.41. Found: C, 62.82; H,
8.43.
N,N′-Bis[(2-(hexylthio)phenyl)methyl]-1,2-ethanediamine (6). A
solution of NaBH4 (0.117 g, 3.09 mmol) in MeOH (5 mL) was added
to a solution of 5a (0.28 g, 0.60 mmol) in MeOH (5 mL) at 0 °C during
5 min, and the resultant mixture was stirred for 20 min at 0 °C. Another
portion of solid NaBH4 (0.050 g, 1.3 mmol) was then added, and the
reaction mixture was stirred at 25 °C for 6 h. After the addition of
H2O (30 mL), the resultant mixture was extracted with Et2O (15 mL).
The extract was dried over MgSO4 and rotary-evaporated, and the
residue was dried for 12 h (25 °C, 0.001 mmHg) to give 6 as an oil
(8) Meth-Cohn, O.; Tarnowski, B. Synthesis 1978, 56.

714 Inorganic Chemistry, Vol. 39, No. 4, 2000
Bohle et al.
Table 1. Crystallographic Data and Refinement Parameters
(0.25 g, 88%): 1H NMR (CDCl3) δ 7.28-7.33 (m, 4 H, Ar H), 7.20
(dt, J ) 1.5, 7.5, 2 H, Ar H), 7.11-7.15 (m, 2 H, Ar H), 3.87 (s, 4 H,
ArCH2), 2.89 (t, J ) 7.4, 4 H, 2 SCH2), 2.78 (s, 4 H, NCH2CH2N),
1.78 (br s, 2 H, 2 NH), 1.63 (m, J ) 7.5, 4 H, 2 SCH2CH2), 1.36-1.48
(m, 4 H, 2 SCH2CH2CH2), 1.21-1.33 (m, 8 H, 2 (CH2)2), 0.88 (t, J )
6.9, 6 H, 2 CH3); 13C NMR (CDCl3) δ 139.68, 136.33, 129.31, 128.40,
127.63, 125.70, 51.98, 48.90, 33.67, 31.59, 29.23, 28.88, 22.76, 14.25.
Anal. Calcd for C28H44N2S2: C, 71.13; H, 9.38. Found: C, 71.09; H,
9.25.
1a
3
empirical formula
C28H40Br2N2NiS2
687.27
21.173(4)
14.287(3)
10.053(2)
90
C56H88Cl2N4NiO8S4
1203.15
10.377(1)
11.911(1)
26.008(3)
91.296(7)
97.868(9)
104.767(9)
3073.6(6)
P1h
mass (g mol-1
a (Å)
)
b (Å)
c (Å)
R (deg)
â (deg)
98.79(2)
90
γ (deg)
[N,N′-Bis[(2-(hexylthio)phenyl)methyl]-1,2-ethanediamine]nickel-
(II) Bromide (2a). To a suspension of anhydrous NiBr2 (0.11 g, 0.50
mmol) in absolute EtOH (10 mL) was added during 5 min a solution
of 6 (0.24 g, 0.50 mmol) in EtOH (10 mL) at 50 °C. Then the mixture
was heated to reflux for 5 h, concentrated to 10 mL by rotary
evaporation, and held at 5 °C for 12 h. The resultant crystals were
collected by filtration and dried for 12 h (25 °C, 0.001 mmHg) to give
V (Å3)
3005.3(10)
P21/c
space group
temp (°C)
-100
-50
wavelength (Å)
0.71073
1.519
0.71073
1.300
F
calcd (g cm-3
)
abs coeff, µ (mm-1
)
3.463
0.592
R1a
0.062
0.065
1
wR2b
0.15
0.16
blue 2a (0.25 g, 73%): mp 163-164 °C dec; H NMR (DMSO-d6;
aR1
)
∑||Fo|
-
|Fc||/∑|Fo|. b wR2
)
{∑[w(Fo
-
Fc2)2]/
2
only broad signals were observed due to 2a’s paramagnetic character)
δ 9.77 (br m), 5.64 (br s), 1.69 (br s), 1.07-149 (br m), 0.81 (br s).
Anal. Calcd for C28H44N2S2NiBr2: C, 48.65; H, 6.42. Found: C, 48.83;
H, 6.47.
∑[w(Fo )2]}1/2
.
2
Crystallographic Structure Determinations. X-ray diffraction data
were collected for single crystals of complexes 1a and 3 on a Siemens
P4 diffractometer equipped with a molybdenum tube (λ ) 0.71073 Å)
and a graphite monochromator. In each case, the diffraction data were
measured using ω scans. The intensities of three standard reflections
monitored every 100 reflections during the respective data collections
indicated negligible crystal decomposition.
The structures were solved by direct methods and refined by full-
matrix least-squares techniques on F2 for all data for both 1a and 3
using structure solution programs from the SHELXTL system.9 For
1a, non-hydrogen atoms were refined anisotropically, while all hydrogen
atoms were placed in calculated positions (0.96 Å) and refined with
fixed isotropic thermal parameters. For 3, hydrogen atoms on the
nitrogen atoms were located in successive Fourier maps and refined
isotropically, while all other hydrogen atoms were placed in calculated
positions and refined with fixed isotropic thermal parameters set to
1.2 times those of the atoms to which they were attached. The non-
hydrogen atoms were refined anisotropically. Crystallographic param-
eters for 1a and 3 are collected in Table 1.
[N,N′-Bis[(2-(hexylthio)phenyl)methyl]-1,2-ethanediamine]nickel-
(II) Chloride (2b). To a solution of NiCl2‚6H2O (0.068 g, 0.29 mmol)
in EtOH (20 mL) at 25 °C was added during 3 min a solution of 6
(0.136 g, 0.287 mmol) in EtOH (5 mL). The mixture was then heated
to reflux for 4 h and rotary-evaporated. The residue was recrystallized
from EtOH (25 °C) to give green 2b (0.075 g, 44%): mp 179-182 °C
1
dec; H NMR (DMSO-d6; only broad signals were observed due to
2b’s paramagnetic character) δ 9.21-9.86 (br m), 7.72 (br s), 5.75 (br
m), 2.01 (br s), 1.67 (br s), 1.16 (br s), 0.76 (br s); 13C NMR (DMSO-
d6; only a few alkyl group signals were observed due to 2b’s
paramagnetic character) δ 30.28, 21.79, 13.38. Anal. Calcd for
C28H44N2S2NiCl2‚0.5H2O: C, 55.01; H, 7.42. Found: C, 55.13; H, 7.25.
The presence of water was confirmed by IR analysis of 2b (KBr pellet);
an O-H stretch was found (3460 cm-1).
[N,N′-Bis[(2-(hexylthio)phenyl)methyl]-1,2-ethanediamine]nickel-
(II) Perchlorate (2c). Caution! Perchlorates are potentially explosive.
Although we have had no explosions in our work with 2c or 3 (see
below), appropriate precautions should be taken in working with them.
A mixture of Ni(ClO4)2‚6H2O (0.19 g, 0.51 mmol), 6 (0.24 g, 0.51
mmol), and anhydrous EtOH (16 mL) was heated to reflux for 4 h and
rotary-evaporated. The residue was washed with hexane, and CH2Cl2
(15 mL) was added. The resultant mixture was filtered, the filtrate was
rotary-evaporated, and the residue was dried for 12 h (25 °C, 0.001
mmHg) to give pink 2c (0.22 g, 60%): mp 222-227 °C dec; 1H NMR
(CDCl3; only broad signals were observed due to 2c’s paramagnetic
character) δ 83.37 (br s), 57.79 (br s), 32.34 (br s), 15.67 (br s), 14.13
(br s), 12.77 (br s), 9.67 (br s), 6.77 (br s), 3.07 (br s), 2.76 (br s), 2.49
(br s), 2.00 (br s), 1.70 (br s), 0.89-1.40 (br m); 13C NMR (CDCl3;
only a few signals were observed due to 2c’s paramagnetic character)
δ 146.92, 121.49, 35.71, 27.88, 14.98. Anal. Calcd for C28H44N2S2-
NiCl2O8: C, 46.05; H, 6.07. Found: C, 46.30; H, 6.04.
Results and Discussion
Syntheses. Complexes 1 were prepared as outlined in Scheme
1. 2-Nitrobenzaldehyde was converted into 2-(alkylthio)benz-
aldehydes 4 according to a modified literature procedure8 by
reaction with the indicated alkanethiols. The condensation of 4
with ethylenediamine gave ligands 5, followed by their
reactions2a,b with NiX2 to give complexes 1.
Scheme 1a
[Bis[N,N′-bis[(2-(hexylthio)phenyl)methyl]-1,2-ethanediamine]]-
nickel(II) Perchlorate (3). Complex 3 was isolated as blue crystals
from an EtOH solution of 2c held at 25 °C for 36 h: mp 119-121 °C
1
dec; H NMR (CDCl3; only broad signals were observed due to 3’s
paramagnetic character) δ 10.16-10.29 (br m), 8.11-9.00 (br m), 6.33
(br m), 5.85-6.19 (br m), 3.71 (br s), 0.90-2.11 (br m), 0.75 (br m);
13C NMR (CDCl3) δ 151.05, 150.58, 141.48, 140.93, 140.01, 139.08,
132.76, 132.42, 132.14, 131.27, 37.91, 37.51, 31.64, 31.47, 30.46, 29.03,
22.75, 22.70, 22.61, 14.18, 14.10. Anal. Calcd for C56H88N4S4-
NiCl2O8: C, 55.90; H, 7.37. Found: C, 55.75; H, 7.18.
Spectrophotometric Titration. A CHCl3 solution of complex 2c
(3.00 mL, 11.63 mM) was placed in a 1 cm quartz cell and its spectrum
recorded between 200 and 800 nm against a CHCl3 blank. Then a CHCl3
solution of ligand 6 (85.66 mM) was added in portions. Spectra were
recorded after the addition of a total of 0.10, 0.20, 0.30, 0.40, 0.60,
and 0.80 mL of the ligand solution. Absorbance was corrected for
dilution: Acor ) Aobs[(Vi + Va)/Vi], where Acor ) corrected absorbance,
Vi ) initial volume of 2c solution, and Va ) total volume of 6 solution
added.
a Key: (a) C6H13SH or C12H25SH, K2CO3, DMF, 110 °C; (b)
H2NCH2CH2NH2, C6H6, Dean-Stark; (c) NiX2 (X ) Br, Cl), EtOH,
reflux.
Complexes 2 were prepared as outlined in Scheme 2. The
reduction of the carbon-nitrogen double bonds of 5a gave
(9) Sheldrick, G. M. SHELXTL Crystallographic System, Version 5.03/
Iris; Siemens Analytical X-ray Instruments Inc.: Madison, WI, 1994.

Nickel(II) Bis(alkylthio)salen Complexes
Inorganic Chemistry, Vol. 39, No. 4, 2000 715
Scheme 2a
a Key: (a) NaBH4, MeOH, 25 °C; (b) NiX2 (X ) Br, Cl, ClO4),
EtOH, reflux.
ligand 6, followed by its reactions2a,b with NiX2 to give
complexes 2. Complex 3 was isolated from an EtOH solution
of 2c.
Characterization. Complexes 1-3 were characterized by
combustion analyses and 1H and 13C NMR spectroscopy.
Additionally, they were characterized by Vis-NIR spectroscopy,
and 1a and 3 were also characterized by single-crystal X-ray
diffraction.
Figure 1. Change in absorbance at 575 nm for a solution of 2c in
CHCl3 upon the addition of ligand 6 in CHCl3. Absorbance was
corrected for dilution.
General Characteristics. The complexes were initially
determined to be paramagnetic on the basis of their 1H and 13
C
NMR spectra. For 1a, 1b, 2c, and 3 in CDCl3 and 2a and 2b in
DMSO-d6, large paramagnetic shifts and extensive broadening
1
were observed in their H NMR spectra, and generally only a
few signals were observed, mainly for aliphatic carbon atoms,
in their 13C NMR spectra. The solid-state magnetic moment of
2a is 2.91 µB at 25 °C, consistent with two unpaired electrons.10
Both 1a and 1b are insoluble in H2O and very soluble in
organic solvents such as CH2Cl2 and CHCl3. They dissociate
completely in DMSO, as evidenced by the presence of only
sharp signals corresponding to the free ligand 5 in their 1H NMR
spectra; they dissociate partially in MeOH, as indicated by sharp
signals corresponding to the free ligand and broad signals
Figure 2. Visible spectra (uncorrected for dilution) obtained in the
spectrophotometric titration of 2c with 6 in CHCl3. From top to bottom,
the spectra correspond to the points of Figure 1 on going from 0 to 2.0
equiv of added ligand 6.
1
corresponding to the paramagnetic complex in their H NMR
spectra. Both 1a and 1b decompose in aqueous suspensions to
give the corresponding 2-(alkylthio)benzaldehydes, as indicated
1
by H NMR. Coordination of the Schiff base nitrogens with
equilibrium between 2c and 3 in MeOH/EtOH may be associated
with the poor coordination properties of ClO4-, which result in
replacement of the weaker thioether donors in 2c by the stronger
secondary amine donors in 3. This hypothesis is supported by
the facts that 2a and 2b, with better coordinating halide ligands,
recrystallize from EtOH to give only 2a and 2b and that they
Ni(II) activates the carbon-nitrogen double bonds toward
hydrolysis.11
Complexes 2a-c are insoluble in H2O and soluble in organic
solvents such as CH2Cl2 and CHCl3. The colors of the
complexes are sensitive to the axial ligands; 2a is blue, 2b is
green, and 2c is pink. Complex 2c exhibits striking solvato-
chromism and ranges from a very light pink in noncoordinating
1
do not display solvatochromism. Furthermore, by H NMR
analysis, 2a and 2b do not dissociate in DMSO-d6.
solvents such as CHCl3 (λmax ) 564 nm, ꢀ ) 16.2 cm-1 M-1
)
Complex 2c in CHCl3 converts into complex 3 in the presence
of excess ligand 6. Titration of a solution of 2c in CHCl3with
a concentrated solution of 6 in CHCl3 gave a visual change
from pink to green, concomitant with a decrease in absorption.
The change in (corrected) absorbance of the system at 575 nm
upon the addition of 6 is shown in Figure 1. The absorbance
decreased almost linearly upon addition of the first equivalent
of 6 and began to level off thereafter, consistent with the
conversion of 1:1 complex 2c into 1:2 complex 3. The apparent
lesser absorbance by the 1:2 complex, as shown in Figure 2,
may be due to its higher local symmetry as compared to that of
the 1:1 complex.12 The final (bottom) spectrum of Figure 2
displays λmax at 595 nm, which closely corresponds to that of 3
in CHCl3 (λmax ) 597 nm).
to green in coordinating solvents such as EtOH (λmax ) 618
nm, ꢀ ) 5.62 cm-1 M-1).
Complex 2c dissociates in coordinating solvents such as
DMSO and MeOH/EtOH. The 1H NMR spectra of 2c in DMSO-
d6 and CD3OD display sharp signals for free ligand 6 in addition
to broad contact-shifted signals. Presumably, in these coordinat-
ing solvents there are multiple equilibria among the 1:1 complex
2c, the 1:2 complex 3, the free ligand 6, and [Ni(solvent)n]2+
.
Equilibrium constants were unobtainable because the signals
in the 1H NMR spectrum could not be assigned unambiguously.
There are a couple of factors that lead to the formation and
isolation of both 2c and 3. Presumably, the very low solubility
of 3 in EtOH causes its preferential crystallization. The
The insolubility and, in some cases, instability of complexes
1 and 2 in H2O limit their scope as surfactants. However, it is
possible that they aggregate to form reversed micelles13 in
(10) Selwood, P. W. Magnetochemistry, 2nd ed.; Interscience: New York,
1956; Chapter 10.
(11) (a) Eichhorn, G. L.; Bailar, J. C., Jr. J. Am. Chem. Soc. 1953, 75,
2905. (b) Eichhorn, G. L.; Trachtenberg, I. M. J. Am. Chem. Soc.
1954, 76, 5183. (c) Harris, C. M.; Lenzer, S. L.; Martin, R. L. Aust.
J. Chem. 1961, 14, 420. (d) Collman, J. P. In Transition Metal
Chemistry; Carlin, R. L., Ed.; Marcel Dekker: New York, 1966; Vol.
2, p 1.
(12) Gerloch, M.; Constable, E. C. Transition Metal Chemistry; VCH: New
York, 1994.
(13) Fendler, J. H. Membrane Mimetic Chemistry; Wiley-Interscience: New
York, 1982; Chapter 3.

716 Inorganic Chemistry, Vol. 39, No. 4, 2000
Bohle et al.
Table 2. Visible Spectral Data for Transitions and Crystal Field Parameters of 1 and 2 in CHCl3
transitionsa
crystal field parameters
complex
3T2g r 3A2g
1Eg r 3A2g
3T1g r 3A2g
3T1g r 3A2g
Bb (cm-1
)
∆
b (cm-1
)
o
1a
1b
2a
2b
2c
1093, 8.41
1044, 7.62
1166, 7.89
1088, 9.30
1204, 3.59
961, 6.21
912, 9.06
945, 9.16
906, 12.8
865, 9.83
794, 12.0
818, 12.4
844, 13.8
861, 13.7
d
570,c 15.2
594, 14.6
609, 14.9
611, 15.6
564, 16.2
584
615
606
629
656
9068
9474
8678
8925
8356
a λ (nm), ꢀ (cm-1 M-1). b Calculated using the two lowest energy bands. c Shoulder observed at ca. 626, 12.12. d Unassignable.
relatively nonpolar solvents such as CH2Cl2 and CHCl3. In any
event, aggregation should not be a requirement for operation
of the chain alignment effect noted above for the control of
Diels-Alder regioselectivity.
Vis-NIR Absorption Spectroscopy. Visible and near-IR
spectra for complexes 1 and 2 were recorded in CHCl3, and
their results are summarized in Table 2. All three spin-allowed
transitions typical of d8 high-spin complexes were observed. In
addition, a sharp band corresponding to the spin-forbidden
transition 1Eg
overlapped with the T1g r A2g band.
r
3A2g was observed at ca. 626 nm, which
3
3
Complexes 1a and 1b display interesting trends in the energies
of various electronic transitions. The two lower energy transi-
tions undergo a blue shift of 49 nm upon changing the axial
ligand from bromide to chloride, as predicted by the spectro-
chemical series. In contrast, the two higher transitions undergo
a red shift of 24 nm with the same change. Presumably, the
higher energy states interact more with the larger and more
polarizable bromide ligand in 1b than with the chloride in 1a.
Similar trends were observed with 2a and 2b. However, for 2c
the spectrum was more complex and contained at least six bands.
Thus the 3T1g r 3A2g band was not assigned. The crystal field
parameters B and ∆o were calculated using the two lowest
energy transitions. In general, the ∆o values are higher for
complexes 1 compared to complexes 2 and follow a trend based
on the spectrochemical series 1b > 1a > 2b > 2a > 2c.
X-ray Diffraction Studies. X-ray-quality crystals of 1a were
obtained from an EtOH solution at 25 °C. The compound
crystallized in the monoclinic space group P21/c (Z ) 4). The
metal center adopts an octahedral geometry as shown in Figure
3 with the bromides occupying the axial positions with Ni-Br
distances of 2.5602(8) and 2.5912(8) Å. The bis(alkylthio)salen
ligand chelates the metal center with the donor nitrogen and
sulfur atoms occupying the four equatorial positions. The Ni-N
distances are 2.035(4) and 2.039(4) Å, longer than the Ni-N
distances (1.85 and 1.86 Å) in Ni(thiosalen),2a which has a
square planar geometry. The origin of these trends can be
Figure 3. X-ray crystal structure of 1a: (a) view showing octahedral
geometry around Ni; (b) view illustrating opposed orientation of the
alkyl side chains. Important metric parameters: Ni(1)-Br(1) 2.5602-
(8), Ni(1)-Br(2) 2.5912(8), Ni(1)-N(1) 2.039(4), Ni(1)-N(2) 2.035-
(4), Ni(1)-S(1) 2.3987(13), Ni(1)-S(2) 2.4045(13) Å; Br(1)-Ni(1)-
Br(2) 178.69(3), S(1)-Ni(1)-S(2) 93.00(4), N(1)-Ni(1)-N(2) 83.8(2),
N(1)-Ni(1)-S(1) 92.85(11), N(2)-Ni(1)-S(2) 90.84(12)°.
2
2
attributed either to the occupation of the dx -y orbitals in the
paramagnetic complexes or possibly to the distortion of ligand
1a. Both 1a and Ni(thiosalen) contain bent N-C-C-N units
with dihedral angles of |53.2| and |44|°,2a respectively. However,
we note that the N-C-C-N dihedral angle is |47.3|° in the
crystal structure of a related Cu(I) complex,4e and given the
similar ligand geometries in these complexes, the differences
in the Ni-N bond lengths are most likely due to occupation of
2.52 Å were observed for diamagnetic and paramagnetic Ni-
SR2 complexes, respectively. Thus, Ni-S bond lengths of 2.39
and 2.40 Å within 1a are in agreement with those for
paramagnetic complexes.
Another interesting feature of 1a’s crystal structure is that
both sulfur atoms have the same configuration (R in Figure 3).
As a result, the two hexyl chains extend in opposite directions,
thereby precluding the possibility of intramolecular hydrophobic
interaction between them in the solid state; see Figure 3b. Also
note that the hexyl chains are not in a fully extended all-trans
conformation.
2
2
the dx -y orbitals in the paramagnetic derivatives. These trends
in metal-ligand bond lengths are also observed for the Ni-S
bonds, 2.399(1) and 2.405(1) Å in 1a, which are in turn
significantly longer than the Ni-S bonds (2.14 and 2.17 Å) in
Ni(thiosalen).2a These values are consistent with general trends
for Ni-S bond lengths within Ni-SR and Ni-SR2 groups; an
examination of the Cambridge Crystallographic Database gave
a mean value of 2.18 Å for Ni-SR and a bifurcated distribution
for Ni-SR2. Bond lengths in the ranges 2.12-2.28 and 2.32-

Nickel(II) Bis(alkylthio)salen Complexes
Inorganic Chemistry, Vol. 39, No. 4, 2000 717
Figure 4. X-ray crystal structure of 1a showing the bilayer packing
arrangement (hydrogen atoms not shown).
Figure 4 shows the bilayer packing arrangement for 1a, which
is typical for solid-state surfactants.14 Molecules are packed in
a zigzag manner with the benzene ring of one molecule partially
stacked over the benzene ring and associated aldimino carbon
of another molecule. The shortest face-to-face stacking distance
between the two π-systems is 3.5 Å. Another interesting feature
is the presence of a weak hydrogen-bonding interaction between
Br(2) of one molecule and H at C(8) of the adjacent stacked
benzene ring; the Br‚‚‚HAr distance is 2.73 Å. Weakly acidic
protons are known to engage in hydrogen bonding with
electronegative atoms such as oxygen and the halogens.15 For
example, this type of intermolecular hydrogen bonding is
observed for acetic acid between a hydrogen of the methyl group
and the carbonyl oxygen (CH‚‚‚OC; 2.4 Å).15b
It is interesting to compare the solid-state structure of 1a with
that of the Ni(II) complex of ligand 7,16 in which both oxygens
Figure 5. X-ray crystal structure of 3 showing the two independent
molecules. Important metric parameters: Ni(1)-N(1) 2.131(4), Ni(1)-
N(2) 2.131(4), Ni(1)-O(1) 2.157(4), Ni(2)-N(3) 2.140(5), Ni(2)-N(4)
2.121(4), Ni(2)-O(5) 2.124(4) Å; N(1)-Ni(1)-N(2) 83.9(2), N(1)-
Ni(1)-N(2A) 96.1(2), N(1)-Ni(1)-O(1) 87.9(2), N(3)-Ni(2)-N(4)
83.4(2), N(3)-Ni(2)-N(4A) 96.6(2), N(3)-Ni(2)-O(5) 88.3(2)°.
which invert on going to N(1A) and N(2A), respectively; within
the other molecule, the nitrogen atoms have analogous con-
figurations. In the final refinement, there were no correlation
coefficients greater than 0.1. The Ni-N bond lengths range from
2.121(4) to 2.140(5) Å, which are longer than those of 1a. A
weaker Ni-N interaction for secondary amine ligands relative
to Schiff base ligands is typical. The two axial positions are
occupied by two perchlorate counterions with Ni-O distances
of 2.157(4) and 2.124(4) Å for the center and the corner
molecules, respectively. The oxygen atoms on the perchlorate
ions of the corner molecules are disordered.
Figure 6 shows the two-dimensional packing of 3’s crystal
lattice. The molecules form linear arrays with hydrophobic
carbon-carbon contacts (shortest 3.59 Å) between the benzene
ring edge of one molecule and the ethylene group of the
ethylenediamine unit of another molecule. Every molecule
makes such contacts on either side to form a linear array. The
linear arrays pack together in a bilayer arrangement presumably
stabilized by hydrophobic interactions between the hexyl chains.
The interacting chains run antiparallel to each other with a
distance of 4.0-4.2 Å between intermolecular carbon atoms.
Every molecule uses two of its four hexyl chains, one on each
are alkylated. In the latter complex, the oxygen atoms do not
coordinate with Ni(II); thus 7 behaves as a bidentate ligand
utilizing only its nitrogen atoms.
X-ray-quality crystals of 3 were grown from an EtOH solution
of 2c; the crystal structure of 3 is shown in Figure 5. The
compound crystallized in the centrosymmetric triclinic space
group P1h (Z ) 2) with two independent half-molecules in the
asymmetric unit. One occupies the center of the unit cell, and
the other occupies a corner. Within each molecule, Ni lies on
a crystallographic inversion center. The molecules have octa-
hedral geometry at Ni with two chelated ligands in a trans
relationship; the chelate rings have a λ,δ-configuration. Within
one molecule, N(1) and N(2) have opposite configurations,
(14) For example, see: Pascher, I.; Lundmark, M.; Nyholm, P.-G.; Sundell,
S. Biochim. Biophys. Acta 1992, 1113, 339 and references therein.
(15) (a) Desiraju, G. R. Angew. Chem., Int. Ed. Engl. 1995, 34, 2311. (b)
Jo¨nsson, P.-G. Acta Crystallogr., Sect. B 1971, 27, 893. (c) Mehta,
G.; Uma, R. J. Chem. Soc., Chem. Commun. 1998, 1735. (d) Zafar,
A. Ph.D. Dissertation, University of Pittsburgh, 1997.
(16) Sacconi, L.; Bertini, I. Inorg. Chem. 1968, 7, 1178.

718 Inorganic Chemistry, Vol. 39, No. 4, 2000
Bohle et al.
Summary
Paramagnetic bis(alkylthio)salen complexes 1 and 2 were
prepared from NiX2 and ligands 5 and 6, respectively. Com-
plexes 1 are soluble and stable in solvents such as CH2Cl2 and
CHCl3 but are unstable in coordinating solvents. Complexes 2
are also soluble and stable in solvents such as CH2Cl2 and
CHCl3; 2a and 2b are stable in coordinating solvents, but 2c is
unstable. Complex 3 crystallized from a solution of 2c in EtOH.
The transformation in CHCl3 of 2c into 3 in the presence of
excess ligand 6 was investigated. The X-ray crystal structure
of 1a displays quadridentate binding of Ni by ligand 5a and a
bilayer packing arrangement that is typical of surfactants. The
X-ray crystal structure of 3 shows an octahedral geometry at
Ni with two trans ethylenediamine chelates, uncoordinated
thioether groups, and a bilayer packing arrangement.
Acknowledgment. D.S.B. and D.A.J. acknowledge the
Department of Energy (Contract DE-FC02-91ER) and the
National Science Foundation (Grant CHE-9526188), respec-
tively, for the support of this research.
Figure 6. X-ray crystal structure of 3 showing the packing of linear
arrays.
Supporting Information Available: Tables of positional param-
eters, bond distances and angles, anisotropic displacement parameters,
and hydrogen atom coordinates. This material is available free of charge
via the Internet at http://pubs.acs.org.
side, to pack into linear arrays, while the other two chains are
disposed above and below the plane of the linear bilayer array
to form a three-dimensional lattice. As with 1a, the hexyl chains
are not in an all-trans conformation. The most striking feature
of the crystal structure is the absence of any binding interaction
between Ni and the thioether groups. Uncoordinated donor
groups such as OH, OR2, and pyridyl have been observed in
the X-ray crystal structures of related octahedral Ni(II) com-
plexes.17
IC990950P
(17) (a) Brooker, S.; McKee, V. J. Chem. Soc., Dalton Trans. 1990, 3183.
(b) Bailey, N. A.; Fenton, D. E.; Kitchen, S. J.; Lilley, T. H.; Williams,
M. G.; Tasker, P. A.; Leong, A. J.; Lindoy, L. F. J. Chem. Soc., Dalton
Trans. 1991, 627.