Structural and spectroscopic studies of nickel(II) complexes with a library of bis(oxime)amine-containing ligands

Article abstract of DOI:10.1021/ic025860q

A library of tripodal amine ligands with two oxime donor arms and a variable coordinating or noncoordinating third arm has been synthesized, including two chiral ligands based on L-phenylalanine. Their Ni(II) complexes have been synthesized and characterized by X-ray crystallography, UV-vis absorption, circular dichroism, and FTIR spectroscopy, mass spectrometry, and room-temperature magnetic susceptibility. At least one crystal structure is reported for all but one Ni/ligand combination. All show a six-coordinate pseudo-octahedral coordination geometry around the nickel center, with the bis(oxime)amine unit coordinating in a facial mode. Three distinct structure types are observed: (1) for tetradentate ligands, six-coordinate monomers are formed, with anions and/or solvent filling out the coordination sphere; (2) for tridentate ligands, six-coordinate monomers are formed with Ni^II(NO₃)₂, with one monodentate and one bidentate nitrate filling the remaining coordination positions; (3) for tridentate ligands, six-coordinate, bis(μ-Cl) dimers are formed with Ni^IICl₂, with one terminal and two bridging chlorides filling the coordination sphere. The UV-vis absorption spectra of the complexes show that the value of 10 Dq varies according to the nature of the third arm of the ligand. The trend based on the third arm follows the order alkyl/aryl < amide < carboxylate < alcohol < pyridyl < oxime.

Full text of DOI:10.1021/ic025860q

Inorg. Chem. 2003, 42, 717−728
Structural and Spectroscopic Studies of Nickel(II) Complexes with a
Library of Bis(oxime)amine-Containing Ligands
Michael J. Goldcamp, Sara E. Edison, Leah N. Squires, Dell T. Rosa, Neil K. Vowels,
Nathan L. Coker, Jeanette A. Krause Bauer, and Michael J. Baldwin*
Department of Chemistry, UniVersity of Cincinnati, Cincinnati, Ohio 45221-0172
Received July 9, 2002
A library of tripodal amine ligands with two oxime donor arms and a variable coordinating or noncoordinating third
arm has been synthesized, including two chiral ligands based on L-phenylalanine. Their Ni(II) complexes have
been synthesized and characterized by X-ray crystallography, UV−vis absorption, circular dichroism, and FTIR
spectroscopy, mass spectrometry, and room-temperature magnetic susceptibility. At least one crystal structure is
reported for all but one Ni/ligand combination. All show a six-coordinate pseudo-octahedral coordination geometry
around the nickel center, with the bis(oxime)amine unit coordinating in a facial mode. Three distinct structure types
are observed: (1) for tetradentate ligands, six-coordinate monomers are formed, with anions and/or solvent filling
out the coordination sphere; (2) for tridentate ligands, six-coordinate monomers are formed with NiII(NO ) , with
3 2
one monodentate and one bidentate nitrate filling the remaining coordination positions; (3) for tridentate ligands,
six-coordinate, bis(µ-Cl) dimers are formed with NiIICl2, with one terminal and two bridging chlorides filling the
coordination sphere. The UV−vis absorption spectra of the complexes show that the value of 10 Dq varies according
to the nature of the third arm of the ligand. The trend based on the third arm follows the order alkyl/aryl < amide
< carboxylate < alcohol < pyridyl < oxime.
Introduction
metal complex, the environment around the metal center
(steric, hydrophobic or polar properties, hydrogen bonding
propensity, etc.), and the solubility properties. All of these
properties are useful in optimizing potential catalysts. From
a bioinorganic viewpoint, oximes are not known to be present
as ligands in metalloproteins, although oxime-containing
tetrapeptides with antibacterial, cytotoxic, or anti-inflamma-
tory activity have been found in marine sponges.1 Also, the
enzyme ammonia monooxygenase produces hydroxylamine,2
which forms oximes upon reaction with aldehydes or ketones.
Thus, incorporation of oximes in post-translationally modi-
fied proteins is not unreasonable from a biosynthetic
standpoint. However, an exact match of the donor groups is
not necessary for useful bioinorganic modeling, as has been
shown on numerous occasions by the use of pyridyl,
pyrazolyl, and macrocyclic polyamine ligands in place of
the imidazole group of histidine in bioinorganic model
complexes.
The development of new polydentate ligands is important
for the discovery of new transition metal catalysts, for the
advancement of bioinorganic chemistry both in its role of
understanding the chemistry of metallobiomolecules and in
producing useful new biomimetic and bioinspired reactions,
and for the continuing development of basic coordination
chemistry. In particular, the design of a series of polydentate
ligands combining a common unit with a systematically
variable feature provides the opportunity to examine the
effect of that variation on the chemistry and spectroscopy
of the metal complexes of the ligand series and to optimize
any useful chemistry that is observed in those complexes.
The series of new polydentate ligands described here uses a
“tripodal amine” type motif. The common unit is an “N3”
donor set consisting of an amine with a pair of oxime-
containing arms, and the third arm off the tertiary amine
provides the variable feature. It may contribute a strong
donor, weak donor, or nondonor group. Variation of the third
arm may be used to modify the electronic structure of the
(1) Franklin, M. A.; Penn, S. G.; Lebrilla, C. B.; Lam, T. H.; Pessah, I.
N.; Molinski, T. F. J. Nat. Prod. 1996, 59, 1121-1127.
(2) (a) Hollocher, T. C.; Tate, M. E.; Nicholas, D. J. D. J. Biol. Chem.
1981, 256, 10834-10836. (b) Hooper, A. B.; Vannelli, T.; Bergmann,
D. J.; Arciero, D. M. Antoine Van Leeuwenhoek 1997, 71, 59-67.
* Author to whom correspondence should be addressed. E-mail:
michael.baldwin@uc.edu.
10.1021/ic025860q CCC: $25.00 © 2003 American Chemical Society
Published on Web 01/04/2003
Inorganic Chemistry, Vol. 42, No. 3, 2003 717

Goldcamp et al.
is reported on bulk solids for those complexes for which X-ray
crystallographic structural characterization is reported to demon-
strate that the structures are representative of the bulk material.
For all others, mass spectral data are used to confirm the complex
formulation.
The protonation state of the oximes significantly alters their
ligand properties, and deprotonation is easily accomplished
by addition of hydroxide or some weaker bases. Ligands
containing multiple oximate (deprotonated oxime) donor
groups have been shown to stabilize unusually highly valent
transition metals, such as Ni(III) and Ni(IV).3 We have
recently reported the structural and electrochemical charac-
terization and reactivity of the Ni(II) complexes of the tris-
(oxime) containing ligand tris(1-propan-2-onyl oxime)amine
(herein designated TRISOXH3, previously designated Ox3H3)
in various protonation states.4 The Ni(II)-oximate complex
reacts with O2 to oxidize Ph3P to Ph3PO, with incorporation
of oxygen from O2. This unusual reactivity between Ni(II)
and O2 is due in part to the significant lowering of the
Ni(II) oxidation potentials by the polyoximate donor set. It
is anticipated that variation of the third arm of the ligand,
while maintaining the basic bis(oxime)amine donor set, will
allow the O2 reactivity of the Ni(II) complexes to be
optimized by modulation of the electronic structure of the
metal through variation of the donor properties of the ligand
and by modifying the interaction of the active metal complex
with potential oxidation substrates.
In this paper, we report the synthesis and characterization
of a series of new tripodal amine ligands containing two
oxime arms and a variable third arm. We also report the
structural characterization of the Ni(II) complexes of these
ligands in the neutral oxime protonation state. The structures
obtained to date allow prediction of additional structures as
the ligand library is expanded. For the tridentate ligands in
particular (those in which the third ligand arm is a nondonor
alkyl or aryl group), complexes derived from NiCl2 and Ni-
(NO3)2 have very different but predictable structure types.
Spectroscopic studies of the series of complexes show that
the ligand variation produces a reasonably predictable
spectrochemical series for the Ni(II) ligand field transitions,
based on the nature of the group on the third arm.
Ligand Syntheses. N-n-Propyl-N,N-bis(1-propan-2-onyl oxime)-
amine (PRABOH2). TACO (3.4 g, 1.6 × 10-2 mol) and n-
propylamine (0.48 g, 8.1 × 10-3 mol) were combined in acetonitrile
(125 mL), and the mixture was heated to reflux. After approximately
30 min, almost all TACO had dissolved. The reaction was heated
an additional 30 min, and the small amount of unreacted TACO
was filtered from the mixture. The filtrate solvent was removed by
rotary evaporation to give an orange crude solid. The crude solid
was extracted with diethyl ether (200 mL), and the ether was
removed by rotary evaporation to give a gold-colored oil. The oil
was washed with hexanes (100 mL) and dried under vacuum, giving
a pale orange solid, which was washed with three 10 mL portions
of cold water to give the off-white solid product (0.97 g, 4.8 ×
10-3 mol, 59% yield). 1H NMR (d6-DMSO): 0.81 (t, 3H), 1.41 (q,
2H), 1.76 (s, 6H), 2.26 (t, 2H), 2.94 (s, 4H), 10.50 (s, 2H) ppm.
13C NMR (d6-DMSO): 11.60, 12.07, 19.20, 54.80, 57.76, 154.05
ppm. FTIR (KBr): 2965 (s), 2926 (s), 2876 (s), 2827 (s), 1664 (w),
1463 (m), 1442 (m), 1386 (w), 1366 (m), 1269 (m), 1256 (w), 1176
(w), 1137 (w), 1046 (m), 1022 (m), 966 (s), 937 (m), 913 (w), 858
(w), 827 (w), 750 (w), 677 (w) cm-1. Mp 69-73 °C. MS: (M +
Na)+ at m/z ) 224.1 (100%), (M + H)+ at m/z ) 202.2 (30%).
N,N-Bis(1-propan-2-onyl oxime) Glycine N′-Methylamide
(GLABOH3). TACO (3.8 g, 1.8 × 10-2 mol) and glycine N′-meth-
ylamide (0.80 g, 9.1 × 10-3 mol) were combined in acetonitrile
(50 mL), and the mixture was heated to reflux. After approximately
1 h, almost all TACO had dissolved. The reaction was heated for
an additional 2 h at approximately 40 °C, resulting in a pale orange
solution. The solvent was removed by rotary evaporation to yield
a crude orange solid. The solid was extracted with diethyl ether
(100 mL), and the ether was allowed to slowly evaporate to give
an off-white solid. Washing with THF (<10 mL) removed some
color to give a nearly white solid (0.32 g, 1.4 × 10-3 mol, 16%
1
yield). H NMR (d6-DMSO): 1.78 (s, 6H), 2.60 (d, 3H), 2.96 (s,
2H), 3.08 (s, 4H), 7.54 (q, 1H), 10.59 (s, 2H) ppm. 13C NMR (d6-
DMSO): 12.32, 25.32, 56.19, 58.14, 153.58, 170.24 ppm. FTIR
(KBr): 3276 (s, br), 3082 (m, br), 2878 (s), 2838 (s), 1651 (vs),
1548 (m), 1489 (m), 1435 (m), 1405 (m), 1366 (m), 1340 (w),
1265 (m), 1164 (w), 1131 (w), 1031 (m), 962 (m), 913 (m), 890
(m), 821 (w) cm-1. Mp 119-124 °C (dec). MS: (M + Na)+ at
m/z ) 253.1 (100%), (M + H)+ at m/z ) 231.1 (15%).
Experimental Section
Materials. All chemicals were obtained from Fisher/Acros or
Aldrich and used without further purification. The preparations of
the TACO reagent (the triethylamine adduct of chloroacetone
oxime),5 glycine N′-methylamide,6 L-phenylalanine N′-methyl-
amide,7 bromoacetophenone oxime,8 tris(1-propan-2-onyl oxime)-
amine,4,9 and nickel(II) (tris(1-propan-2-onyl oxime)amine) nitrate4
have been previously reported. Purity of the synthesized ligands is
demonstrated by their 1H NMR spectra. Elemental analysis (CHN)
N-Phenethyl-N,N-bis(1-propan-2-onyl oxime)amine (PEA-
BOH2). PEABOH2 was prepared similarly to PRABOH2 using
TACO (10.0 g, 4.79 × 10-2 mol) and phenethylamine (2.9 g, 2.4
× 10-2 mol). The product (4.9 g, 1.9 × 10-2 mol, 79% yield) was
further purified by recrystallization from boiling water, with
methanol added dropwise until all of the solid dissolved, followed
by slow cooling to room temperature. 1H NMR (d6-DMSO): 1.67
(s, 6H), 2.56 (t, 2H), 2.71 (t, 2H), 3.03 (s, 4H), 7.13-7.29 (m,
5H), 10.53 (s, 2H) ppm. 13C NMR (CDCl3): 12.28, 32.87, 55.59,
57.90, 125.98, 128.31, 128.77, 140.08, 157.15 ppm. FTIR (KBr):
2951 (s), 2830 (s), 1939 (w), 1863 (w), 1798 (w), 1660 (w), 1600
(w), 1443 (s), 1369 (s), 1259 (m), 1130 (m), 1022 (s), 962 (s), 935
(s), 829 (m), 748 (s), 695 (s), 582 (m) cm-1. Mp 94-98 °C. MS:
(M + H)+ at m/z ) 264 (100%).
(3) (a) Baucom, E. I.; Drago, R. S. J. Am. Chem. Soc. 1971, 93, 6469-
6475. (b) Korvenranta, J.; Saarinen, H.; Nasakkala, M. Inorg. Chem.
1982, 21, 4296-4300. (c) Singh, A. N.; Singh, R. P.; Mohanty, J. G.;
Chakravorty, A. Inorg. Chem. 1977, 16, 2597-2601. (d) Singh, A.
N.; Chakravorty, A. Inorg. Chem. 1980, 19, 969-971. (e) Sproul, G.;
Stucky, G. D. Inorg. Chem. 1973, 12, 2898-2901.
(4) Goldcamp, M. J.; Robison, S. E.; Krause Bauer, J. A.; Baldwin, M. J.
Inorg. Chem. 2002, 41, 2307-2309.
(5) Goldcamp, M. J.; Rosa, D. T.; Landers, N. A.; Mandel, S. M.; Krause
Bauer, J. A.; Baldwin, M. J. Synthesis 2000, 14, 2033-2038.
(6) Marvel, C. S.; Elliott, J. R.; Boettner, F. E.; Yuska, H. J. Am. Chem.
Soc. 1946, 68, 1681-1686.
(7) Nowick, J. S.; Holmes, D. L.; Noronha, G.; Smith, E. M.; Nguyen, T.
M.; Huang, S.-L. J. Org. Chem. 1996, 61, 3929-3934.
(8) Barton, D. H. R.; Crich, D.; Kretzschmar, G. J. Chem. Soc., Perkin
Trans. 1 1986, 39-54.
(9) (a) Matthaiopoulos, G. Chem. Ber. 1898, 31, 2396. (b) Ogloblin, K.
A.; Potekhin, A. A. J. Org. Chem. USSR (Engl. Transl.) 1965, 1, 399-
405. (c) Goldcamp, M. J.; Krause Bauer, J. A.; Baldwin, M. J. Acta
Crystollogr., Sect. E. 2002, E58, 1354-1355.
718 Inorganic Chemistry, Vol. 42, No. 3, 2003

Ni(II) Complexes of Bis(oxime)amine Ligands
N-Phenyl-N,N-bis(1-propan-2-onyl oxime)amine (ABOH2).
ABOH2 was prepared similarly to PRABOH2, using aniline (2.2 g,
2.4 × 10-2 mol) and TACO (10 g, 4.8 × 10-2 mol) in 150 mL of
acetonitrile. The product was purified by dropwise rinsing with
dichloromethane to give white solid ABOH2 (0.82 g, 4.2 × 10-3
mol, 18% yield). Further purification can be achieved by dissolution
in a minimal volume of ethyl acetate, followed by slow diffusion
of a layer of hexane (about four times the volume of ethyl acetate)
31.43, 43.74, 54.32, 62.23, 64.22, 125.85, 126.82, 127.63, 127.92,
128.12, 128.46, 128.89, 129.32, 132.48, 135.64, 139.69, 152.85,
154.51, 170.75 ppm. FTIR (KBr): 3057 (s), 2968 (s), 2880 (s),
1957 (w), 1891 (w), 1814 (w), 1655 (vs), 1537 (m), 1495 (s), 1441
(s), 1412 (s), 1300 (m), 1258 (m), 1159 (w), 1125 (m), 1073 (w),
1001 (s), 936 (s), 751 (s), 699 (vs), 643 (m), 540 (w) cm-1. Mp
72-78 °C. MS: (M + Na)+ at m/z ) 467.2 (100%).
N-n-Octyl-N,N-bis(1-propan-2-onyl oxime)amine (OBOH2).
OBOH2 was prepared in a manner similar to PRABOH2, using
TACO (10.1 g, 4.82 × 10-2 mol) and n-octylamine (3.1 g, 2.4 ×
10-2 mol). OBOH2 is a golden oil (2.1 g, 7.7 × 10-3 mol, 32%
1
in a closed test tube for several days. H NMR (d6-DMSO): 1.70
(s, 6H), 4.02 (s, 4H), 6.61 (t, 1H), 6.79 (d, 2H), 7.11 (t, 2H), 10.61
(s, 2H) ppm. 13C NMR (d6-DMSO): 11.81, 54.85, 112.90, 116.57,
128.98, 148.85, 154.13 ppm. FTIR (KBr): 3273 (s), 2913 (m), 1935
(w), 1832 (w), 1600 (s), 1504 (s), 1391 (s), 1260 (w), 1226 (s),
1187 (m), 1011 (s), 958 (m), 825 (m), 756 (s), 675 (s), 571 (m),
508 (m), 420 (w) cm-1. Mp 138-146 °C. MS: (M + Na)+ at m/z
) 258.1 (100%), (M + H)+ at m/z ) 236.1 (10%).
N-(Pyridin-2-yl)methyl-N,N-bis(1-propan-2-onyl oxime)amine
(PYRABOH2). PYRABOH2 was prepared similarly to PRABOH2,
using TACO (4.3 g, 2.1 × 10-2 mol) and 2-(aminomethyl)-pyridine
(1.0 g, 9.2 × 10-3 mol). The product (0.71 g, 2.8 × 10-3 mol,
34% yield) was purified by recrystallization from boiling water,
with methanol added dropwise until all of the solid dissolved,
followed by slow cooling to room temperature. 1H NMR (d6-
acetone): 1.87 (s, 6H), 3.07 (s, 4H), 3.66 (s, 2H), 7.23 (t, 1H),
7.51 (d, 1H), 7.76 (t, 1H), 8.49 (d, 1H), 9.77 (s, 2H) ppm. 13C
NMR (d6-acetone): 12.29, 58.62, 60.14, 122.87, 123.73, 137.18,
149.67, 155.28, 160.26 ppm. FTIR (KBr): 2926 (s), 2874 (s), 2828
(s), 2816 (s), 2708 (m), 1681 (w), 1638 (w), 1617 (w), 1596 (s),
1573 (m), 1476 (s), 1438 (s), 1368 (s), 1267 (m), 1246 (m), 1054
(m), 1034 (s), 1003 (m), 989 (m), 973 (m), 960 (m), 925 (s) 820
(m), 777 (m), 735 (m), 669 (m), 623 (m) cm-1. Mp 96-102 °C.
MS: (M + Na)+ at m/z ) 273 (100%).
N,N-Bis(1-propan-2-onyl oxime) L-Phenylalanine N′-Meth-
ylamide (PAMBOH3). TACO (3.5 g, 1.7 × 10-2 mol) and
L-phenylalanine N′-methylamide (1.4 g, 7.9 × 10-3 mol) were
combined in 100 mL of 2-propanol, and the reaction mixture was
heated to reflux and stirred for 4 h, after which the solvent was
removed by rotary evaporation. The crude product was extracted
with two 200 mL portions of diethyl ether, and the ether was
evaporated to yield an oil, which was dried under vacuum to yield
a white solid (0.49 g, 1.5 × 10-3 mol, 19% yield). The solid
PAMBOH3 can be further purified by slow diffusion of hexane
into an ethyl acetate solution of PAMBOH3. 1H NMR (d6-
DMSO): 1.58 (s, 6H), 1.71 (m, 2H), 2.55 (d, 3H), 2.68 (m, 1H),
2.90 (s, 4H), 7.20-7.24 (m, 5H), 7.56 (d, 1H), 10.56 (s, 2H) ppm.
13C NMR (d6-DMSO): l2.19, 25.56, 32.66, 54.26, 64.17, 126.02,
128.13, 129.28, 139.40, 154.40, 183.12 ppm. FTIR (KBr): 2923
(m), 1955 (w), 1654 (vs), 1550 (s), 1451 (s), 1412 (s), 1379 (s),
1260 (m), 1157 (m), 1128 (m), 1034 (m), 954 (m), 747 (m), 701
(m), 494 (w) cm-1. Mp 44-52 °C. MS: (M + H)+ at m/z ) 321
(100%).
1
yield). H NMR (CDCl3): 0.80 (3H, t), 1.18 (m, br, 10H), 1.35
(m, br, 2H), 1.83 (s, 6H), 2.30 (t, 2H), 2.96 (s, 4H), 9.53 (s, br,
2H) ppm. 13C NMR (CDCl3): 12.08, 13.75, 18.61, 22.32, 26.50,
26.96, 29.15, 31.52, 53.72, 57.72, 156.91 ppm. FTIR (KBr): 3160
(s), 2926 (s), 2855 (m), 1511 (vs), 1346 (vs), 1265 (s), 1076 (m),
1020 (m), 688 (m) cm-1. MS: (M + Na)+ at m/z ) 294.2 (90%),
(M + H)+ at m/z ) 272.2 (100%).
Potassium N,N-Bis(1-propan-2-onyl oxime) Glycinate
(GLYBOH2K). TACO (3.50 g, 1.68 × 10-2 mol) and glycine ethyl
ester hydrochloride (1.00 g, 7.16 × 10-3 mol) were added together
in 200 mL of 2-propanol, and the mixture was heated to reflux
and stirred. A solution of triethylamine (0.725 g, 7.16 × 10-3 mol)
in 20 mL of 2-propanol was added dropwise over a period of about
30 min. The reaction was heated an additional 1.5 h, after which
the solvent was removed by rotary evaporation to yield a crude
solid. A 200 mL portion of diethyl ether was added to the crude
solid, and the mixture was stirred for 1 h. The mixture was then
filtered, and the ether was evaporated to yield an oil, which was
washed with hexane and dried under vacuum. The oil was then
dissolved in a minimal amount of ethyl acetate, and the solution
was run through a 6 cm long silica gel column. The orange-colored
materials did not move from the top of the column, and the pale
yellow and colorless fractions were collected and dried to yield
1.41 g of a white solid, N,N-bis(1-propan-2-onyl oxime) glycine
ethyl ester. A portion of this product (0.20 g, 8.1 × 10-4 mol) was
dissolved in 15 mL of 50/50 methanol/water, and 0.80 mL of a 1.0
M KOH (in methanol) solution was added dropwise over 30 min.
The solution was heated at 50 °C for several hours and then stirred
overnight at room temperature. The solvent was then removed by
rotary evaporation, yielding an off-white solid. This solid was
washed with 200 mL of diethyl ether (to remove any unreacted
ester starting material) to give a white solid, GLYBOH2K (0.137
g, 5.4 × 10-4 mol, 66% yield). The product was used without
1
further purification. H NMR (D2O): 1.73 (s, 6H), 2.07 (s, 4H),
2.69 (s, 2H), 10.45 (s, br, 2H) ppm. 13C NMR (D2O): 12.69, 58.00,
58.33, 159.35, 178.88 ppm. FTIR (KBr): 2909 (s), 1580 (vs), 1497
(w), 1457 (w), 1394 (m), 1310 (m), 1263 (w), 1156 (w), 1124 (w),
1044 (m), 959 (w), 928 (m), 743 (m), 678 (w) cm-1. Mp 196-206
°C (dec). MS: (M - K)- at m/z ) 216 (85%).
N-2-Hydroxyethyl-N,N-bis(1-propan-2-onyl oxime)amine
(EABOH3). EABOH3 was prepared similarly to PRABOH2, using
TACO (5.0 g, 2.4 × 10-2 mol) and ethanolamine (0.70 g, 1.1 ×
10-2 mol). EABOH3 (1.6 g, 7.9 × 10-3 mol, 72% yield) was further
purified by dissolution in a minimal volume of ethyl acetate,
followed by slow diffusion of a layer of hexane (about four times
the volume of ethyl acetate) in a closed test tube for several days.
1H NMR (d6-DMSO): 0.82 (s, 6H), 1.49 (t, 2H), 2.08 (s, 4H), 2.51
(m, 2H), 9.56 (s, 2H) ppm. 13C NMR (d6-DMSO): 12.36, 55.59,
58.61, 59.15, 154.54 ppm. FTIR (KBr): 2919 (s), 2875 (s), 2815
(s), 1675 (w), 1493 (m), 1445 (m), 1380 (m), 1272 (m), 1219 (w),
1135 (w), 1081 (m), 1039 (s), 966 (s), 780 (m), 671 (m) cm-1. Mp
N,N-Bis(1-acetophenone oxime) L-Phenylalanine N′-Meth-
ylamide (PAMABPOH3). TABO (vide infra) (0.724 g, 2.30 × 10-3
mol) and L-phenylalanine N′-methylamide (0.207 g, 1.16 × 10-3
mol) were combined in 50 mL of 2-propanol, and the mixture was
heated to reflux and stirred for 3 h. The solvent was then removed
by rotary evaporation to yield a crude solid, which was extracted
with two 40 mL portions of diethyl ether. The ether extracts were
then evaporated to give a yellow oil, which was dried under vacuum
to yield a white solid, PAMABPOH3 (0.154 g, 3.47 × 10-4 mol,
1
30% yield). H NMR (d6-DMSO): 2.28 (d, 3H), 3.03 (m, 1H),
3.61 (m, 4H), 3.91 (m, 2H), 6.38 (m, 1H), 7.03-7.41 (m, 15H),
11.05 (s, 1H), 11.63 (s, 1H) ppm. 13C NMR (d6-DMSO): 25.35,
Inorganic Chemistry, Vol. 42, No. 3, 2003 719

Goldcamp et al.
120-128 °C. MS: (M2 + Na)+ at m/z ) 429.2 (60%), (M + Na)+
at m/z ) 226.1 (100%), (M + H)+ at m/z ) 204.1 (10%).
1456 (vs), 1423 (s), 1373 (m), 1240 (m), 1109 (m), 1073 (s), 1024
(m), 934 (m), 850 (m), 750 (m), 702 (m), 680 (m), 610 (m), 590
(m), 512 (m) cm-1. MS: [Ni(PEABOH2)]2Cl3 at m/z ) 749.1
+
N,N,N-Trimethyl-N-(1-acetophenone oxime)ammonium Bro-
mide (TABO). A solution of triethylamine (0.20 g, 2.0 × 10-3
mol) in diethyl ether (10 mL) was added to a stirring solution of
bromoacetophenone oxime (0.37 g, 1.7 × 10-3 mol) in diethyl ether
(10 mL). A white precipitate immediately formed, and after 10 min
of stirring, the mixture was filtered to yield a white solid, N,N,N-
trimethyl-N-(1-acetophenone oxime)ammonium bromide (0.42 g,
1.3 × 10-3 mol, 76% yield), which was used without further
purification. 1H NMR (d6-DMSO): 1.11 (t, 9H), 3.21 (q, 6H), 4.43
(s, 2H), 7.46 (m, 4H), 7.63 (d, 1H), 7.75 (s, 1H) ppm. FTIR
(KBr): 3086 (s), 2994 (s), 2811 (m), 1622 (w), 1481 (s), 1406 (s),
1294 (m), 1158 (m), 1074 (w), 1028 (s), 1003 (s), 949 (m), 902
(100%). Anal. Calcd for Ni(C14H21N3O2)Cl2 (368.91): C, 42.79;
H, 5.39; N, 10.69. Found: C, 42.61; H, 5.24; N, 10.60.
Nickel(II) (N-Phenethyl-N,N-bis(1-propan-2-onyl oxime)-
amine) Nitrate (Ni(PEABOH2)(NO3)2). Ni(PEABOH2)(NO3)2 was
prepared similarly to Ni(PRABOH2)(NO3)2 in methanol, yielding
a blue solid (57% yield). FTIR (KBr): 3161 (w), 2929 (w), 1494
(m), 1454 (m), 1384 (vs), 1338 (w), 1272 (m), 1243 (w), 1106
(w), 1077 (w), 1020 (w), 929 (w), 855 (w), 748 (m), 688 (m), 519
+
(m) cm-1. MS: Ni(PEABOH2)NO3 at m/z ) 383.1 (95%).
Nickel(II) (N-n-Octyl-N,N-bis(1-propan-2-onyl oxime)amine)
Chloride ([Ni(OBOH2)Cl]2(µ-Cl)2). [Ni(OBOH2)Cl]2(µ-Cl)2 was
prepared similarly to Ni(TRISOXH3)Cl2 in acetonitrile, yielding a
green solid (55% yield). Green crystals for X-ray crystallography
were obtained by slow evaporation of an acetone/diethyl ether
solution of [Ni(OBOH2)Cl]2(µ-Cl)2 in a test tube. FTIR (KBr): 2954
(m), 2927 (s), 2855 (s), 1628 (w), 1464 (s), 1432 (m), 1373 (m),
1343 (w), 1288 (w), 1241 (m), 1232 (m), 1113 (m), 1078 (m), 1052
(m), 1035 (m), 994 (w), 932 (m), 851 (m), 724 (w), 689 (m), 680
(w), 793 (s), 766 (s), 702 (s), 531 (w) cm-1
.
Nickel(II) Complexes. Nickel(II) (Tris(1-propan-2-onyl oxime)-
amine) Chloride (Ni(TRISOXH3)Cl2). Tris(1-propan-2-onyl oxime)-
amine (TRISOXH3, 0.20 g (8.7 × 10-4 mol) ) and 0.21 g (8.8 ×
10-4 mol) nickel(II) chloride hexahydrate were added together in
about 15 mL of methanol and stirred to yield a blue solution, which
gave a blue solid (0.26 g, 7.2 × 10-4 mol, 82% yield) after slow
evaporation of the solvent. Blue crystals for X-ray crystallography
were obtained by slow evaporation of a methanol/ethyl acetate
solution of Ni(TRISOXH3)Cl2 in a test tube. FTIR (KBr): 1662
(w), 1632 (w), 1466 (s), 1434 (s), 1387 (s), 1292 (w), 1237 (m),
1117 (w), 1072 (s), 1029 (s), 940 (m), 872 (w), 848 (w) 656 (m)
cm-1. MS: Ni(TRISOXH3)Cl+ at m/z ) 323 (100%). Anal. Calcd
for Ni(C9H18N4O3)Cl2 (359.86): C, 30.04; H, 5.04; N, 15.57.
Found: C, 30.12; H, 4.63; N, 15.41.
+
(m), 661 (m), 588 (m) cm-1. MS: [Ni(OBOH2)]2Cl3 at m/z )
763 (30%), Ni(OBOH2)Cl+ at m/z ) 364 (100%). Anal. Calcd for
Ni(C14H29N3O2)Cl2 (401.00): C, 41.93; H, 7.29; N, 10.48. Found:
C, 42.06; H, 7.17; N, 10.38.
Nickel(II) (N-n-Octyl-N,N-bis(1-propan-2-onyl oxime)amine)
Nitrate (Ni(OBOH2)(NO3)2. Ni(OBOH2)(NO3)2 was prepared
similarly to Ni(PRABOH2)(NO3)2 in methanol, yielding a blue solid
(48% yield). FTIR (KBr): 2956 (s), 2926 (s), 2855 (m), 1678 (w),
1612 (w), 1508 (s), 1439 (s), 1385 (s), 1346 (s), 1265 (s), 1111
(w), 1076 (m), 1058 (m), 1020 (m), 926 (w), 852 (w), 814 (w),
753 (w), 723 (w), 688 (m), 581 (w) cm-1. MS: [Ni(OBOH1)]2-
Nickel(II) (N-n-Propyl-N,N-bis(1-propan-2-onyl oxime)amine)
Nitrate (Ni(PRABOH2)(NO3)2). N-n-Propyl-N,N-bis(1-propan-2-
onyl oxime)amine (0.20 g (9.9 × 10-4 mol)) (PRABOH2) and 0.29
g (1.0 × 10-3 mol) of nickel(II) nitrate hexahydrate were added
together in about 15 mL of methanol and stirred to yield a blue
solution, which after evaporation of the solvent yielded a blue solid
(0.16 g, 4.2 × 10-4 mol, 62% yield). Blue crystals for X-ray
crystallography were obtained by slow evaporation of a methanol/
ethyl acetate/acetone solution of Ni(PRABOH2)(NO3)2. FTIR
(KBr): 2970 (m), 2938 (m), 1500 (s), 1464 (s), 1448 (s), 1375 (s),
1318 (s), 1265 (m), 1110 (w), 1072 (m), 1043 (m), 941 (m), 851
(w), 814 (w), 750 (w), 685 (w), 579 (w) cm-1. MS: Ni-
(PRABOH1)+ at m/z ) 258.1 (50%), Ni(PRABOH1)(CH3OH)+ at
+
+
NO3 at m/z ) 718.3 (30%), Ni(OBOH2)NO3 at m/z ) 391.1
(100%).
Nickel(II) (N-Phenyl-N,N-bis(1-propan-2-onyl oxime)amine)
Nitrate (Ni(ABOH2)(NO3)2). Ni(ABOH2)(NO3)2 was prepared
similarly to Ni(PRABOH2)(NO3)2 in methanol. Blue crystals (70%
yield) for X-ray crystallography were obtained by slow evaporation
of an acetone solution of Ni(ABOH2)(NO3)2 in a flask. FTIR
(KBr): 2932 (m), 1595 (m), 1500 (s), 1456 (s), 1374 (s), 1317 (s),
1269 (s), 1235 (m), 1183 (m), 1078 (m), 1045 (m), 1023 (m), 924
(m), 859 (w), 823 (w), 789 (m), 756 (m), 681 (m), 550 (w) cm-1
.
+
+
+
m/z ) 290.1 (65%), Ni(PRABOH2)NO3 at m/z ) 321.1 (90%).
MS: [Ni(ABOH1)]2NO3 at m/z ) 646 (30%), Ni(ABOH2)NO3
at m/z ) 355 (50%), Ni(ABOH1)+ at m/z ) 292 (30%). Anal. Calcd
for Ni(C12H17N3O2)(NO3)2 (417.99): C, 34.48; H, 4.10; N, 16.75.
Found: C, 34.45; H, 3.87; N, 16.32.
Anal. Calcd for Ni(C9H19N3O2)(NO3)2 (208.73): C, 28.15; H, 4.99;
N, 18.24. Found: C, 28.19; H, 4.55; N, 18.10.
Nickel(II) (N-n-Propyl-N,N-bis(1-propan-2-onyl oxime)amine)
Chloride ([Ni(PRABOH2)Cl]2(µ-Cl)2). [Ni(PRABOH2)Cl]2(µ-Cl)2
was prepared similarly to Ni(TRISOXH3)Cl2 in methanol. Green
crystals (73% yield) for X-ray crystallography were obtained by
slow evaporation of an acetone solution of [Ni(PRABOH2)Cl]2(µ-
Cl)2 in a test tube. FTIR (KBr): 2961(m), 2876 (m), 1660 (m),
1604 (w), 1465 (s), 1371 (s), 1292 (w), 1245 (m), 1235 (m), 1112
Nickel(II) (N-Phenyl-N,N-bis(1-propan-2-onyl oxime)amine)
Chloride (Ni(ABOH2)Cl2). Ni(ABOH2)Cl2 was prepared similarly
to Ni(TRISOXH3)Cl2 in methanol, yielding a green solid (71%
yield). FTIR (KBr): 2912 (m), 1599 (m), 1497 (s), 1466 (s), 1428
(m), 1377 (m), 1221 (s), 1099 (m), 1072 (s), 1038 (m), 972 (s),
909 (m), 875 (m), 810 (m), 756 (m), 695 (m), 670 (m), 602 (m),
530 (m) cm-1. MS: [Ni(ABOH2)]2Cl3+ at m/z ) 693.1 (5%), [Ni-
(ABOH1)]2Cl+ at m/z ) 621.1 (25%), [Ni(ABOH2)][Ni(ABOH1)]+
at m/z ) 583.1 (15%), Ni(ABOH2)Cl+ at m/z ) 328.0 (15%), Ni-
(ABOH1)+ at m/z ) 292.1 (100%).
Nickel(II) (N,N-Bis(1-propan-2-onyl oxime) Glycine N′-
Methylamide) Chloride (Ni(GLABOH3)Cl2). Ni(GLABOH3)Cl2
was prepared similarly to Ni(TRISOXH3)Cl2 in methanol. Blue-
green crystals (79% yield) for X-ray crystallography were obtained
by slow evaporation of a methanol/ethyl acetate solution of Ni-
(GLABOH3)Cl2 in a test tube. FTIR (KBr): 2956 (m), 2916 (m),
1643 (vs), 1568 (m), 1459 (s), 1405 (s), 1382 (s), 1316 (m), 1272
(m), 1064 (s), 1033 (m), 992 (w), 939 (m), 852 (m), 674 (m), cm-1
.
+
MS: [Ni(PRABOH2)]2Cl3 at m/z ) 623 (35%), Ni(PRABOH2)-
Cl+ at m/z ) 294 (100%) Anal. Calcd for Ni(C9H19N3O2)Cl2‚1H2O
(348.88): C, 30.98; H, 6.07; N, 12.04. Found: C, 31.46; H, 5.86;
N, 11.73.
Nickel(II) (N-Phenethyl-N,N-bis(1-propan-2-onyl oxime)-
amine) Chloride ([Ni(PEABOH2)Cl]2(µ-Cl)2). [Ni(PEABOH2)-
Cl]2(µ-Cl)2 was prepared similarly to Ni(TRISOXH3)Cl2 in metha-
nol. Green crystals (71% yield) for X-ray crystallography were
obtained by slow evaporation of a methanol/ethyl acetate solution
of [Ni(PEABOH2)Cl]2(µ-Cl)2 in a test tube. FTIR (KBr): 2901 (m),
720 Inorganic Chemistry, Vol. 42, No. 3, 2003

Ni(II) Complexes of Bis(oxime)amine Ligands
(w), 1231 (m), 1161 (m), 1131 (m), 1052 (m), 1027 (m), 988 (m),
911 (m), 857 (m), 734 (w), 703 (m), 651 (m), 595 (m), 556 (m)
cm-1. MS: Ni(GLABOH3)Cl+ at m/z ) 323.0 (100%), Ni-
(GLABOH3)(CH3COO)+ at m/z ) 347.1 (95%), [Ni(GLABOH2)]2-
a purple solid (45% yield). FTIR (KBr): 2920 (m), 1472 (s), 1458
(s), 1431 (s), 1383 (vs), 1333 (s), 1291 (s), 1244 (m), 1236 (m),
1106 (m), 1069 (m), 1040 (m), 997 (w), 967 (w), 904 (m), 877
(m), 815 (m), 683 (m), 661 (m) cm-1. MS: Ni(EABOH3)NO3+ at
m/z ) 323 (65%).
+
Cl+ at m/z ) 609.1 (15%), Ni(GLABOH2)Ni(GLABOH3)Cl2 at
m/z ) 645.1 (15%), [Ni(GLABOH3)]2Cl3 at m/z ) 681.1 (15%).
Anal. Calcd for Ni(C9H18N4O3)Cl2 (359.86): C, 30.05; H, 5.04;
N, 15.57. Found: C, 30.15; H, 4.59; N, 15.36.
Nickel(II) (N,N-Bis(1-propan-2-onyl oxime) Glycine N′-
Methylamide) Nitrate (Ni(GLABOH3)(NO3)2). Ni(GLABOH3)-
(NO3)2 was prepared similarly to Ni(PRABOH2)(NO3)2 in methanol,
yielding a blue solid (60% yield). FTIR (KBr): 2979 (m), 2931
(m), 1648 (vs), 1578 (m), 1456 (s), 1361 (vs), 1311 (s), 1229 (s),
1169 (m), 1135 (m), 1110 (w), 1083 (m), 1048 (s), 997 (m), 920
Nickel(II) (N-(Pyridin-2-yl)methyl-N,N-bis(1-propan-2-onyl
oxime)amine) Chloride (Ni(PYRABOH2)Cl2). Ni(PYRABOH2)-
Cl2 was prepared similarly to Ni(TRISOXH3)Cl2 in methanol. Blue
crystals (66% yield) for X-ray crystallography were obtained by
slow evaporation of a ethanol/methanol solution of Ni(PYRABOH2)-
Cl2 in a closed flask. FTIR (KBr): 2929 (m), 1667 (w), 1608 (m),
1574 (w), 1467 (s), 1437 (s), 1379 (s), 1314 (m), 1287 (m), 1235
(m), 1162 (w), 1125 (m), 1107 (m), 1060 (s), 1032 (s), 995 (m),
926 (m), 864 (m), 851 (m), 773 (s), 741 (w), 673 (m), 602 (m),
540 (m), 513 (m) cm-1. MS: Ni(PYRABOH2)Cl+ at m/z ) 343.0
(100%). Anal. Calcd for Ni(C12H18N4O2)Cl2 (379.90): C, 37.94;
H, 4.78; N, 14.75. Found: C, 37.66; H, 4.65; N, 14.90.
(m), 859 (m), 812 (m), 738 (w), 687 (m), 597 (m), 558 (m) cm-1
.
MS: Ni(GLABOH3)NO3+ at m/z ) 350.0 (75%), Ni(GLABOH2)+
at m/z ) 287.1 (35%).
Nickel(II) (N,N-Bis(1-propan-2-onyl oxime)-L-phenylalanine
N′-Methylamide) Nitrate (Ni(PAMBOH3)(NO3)2). Ni(PAMBOH3)-
(NO3)2 was prepared similarly to Ni(PRABOH2)(NO3)2 in methanol.
Blue crystals (68% yield) for X-ray crystallography were obtained
by slow diffusion of ethyl acetate into an ethanol solution of Ni-
(PAMBOH3)(NO3)2 in a test tube. FTIR (KBr): 1737 (m), 1629
(s), 1550 (m), 1384 (s), 1304 (s), 1157 (m), 1043 (s), 861 (m), 827
(m), 756 (m), 702 (m), 537 (m) cm-1. MS: [Ni(PAMBOH2)]2-
NO3+ at m/z ) 816 (25%), Ni(PAMBOH2)Ni(PAMBOH1)+ at m/z
Nickel(II) (N-(Pyridin-2-yl)methyl-N,N-bis(1-propan-2-onyl
oxime)amine) Nitrate (Ni(PYRABOH2)(NO3)2). Ni(PYRABOH2)-
(NO3)2 was prepared similarly to Ni(PRABOH2)(NO3)2 in methanol.
Purple crystals (82% yield) were obtained by slow diffusion of a
layer of ethyl acetate into a methanol solution of Ni(PYRABOH2)-
(NO3)2 in a closed flask. FTIR (KBr): 2923 (m), 1608 (m), 1470
(s), 1449 (s), 1384 (vs), 1326 (s), 1241 (m), 1159 (w), 1105 (w),
1067 (m), 1048 (m), 1025 (m), 998 (w), 922 (w), 889 (w), 867
(w), 852 (w), 770 (m), 737 (w), 673 (w) cm-1. MS: Ni-
(PYRABOH1)Ni(PYRABO)+ at m/z ) 613 (60%), Ni(PYRABOH2)-
+
) 753 (15%), Ni(PAMBOH3)NO3 at m/z ) 440 (100%). Anal.
+
Calcd for Ni(C16H24N4O3)(NO3)2‚0.25 CH3COOCH2CH3 + 1.25H2O
(547.64): C, 37.29; H, 5.25; N, 15.35. Found: C, 36.96; H, 5.01;
N, 14.86.
NO3 at m/z ) 370 (100%).
Nickel(II) (N,N-Bis(1-propan-2-onyl oxime)glycinate) Chlo-
ride (Ni(GLYBOH2)Cl). Potassium N,N-bis(1-propan-2-onyl oxime)-
glycinate (0.20 g, 7.8 × 10-4 mol) (GLYBOH2K) and 0.19 g (8.0
× 10-4 mol) of nickel(II) chloride hexahydrate were combined in
15 mL of methanol and stirred to yield a blue solution, which was
reduced in volume by slow evaporation in a test tube. KCl
precipitate was filtered from the solution, and further evaporation
yielded a blue solid (39% yield). FTIR (KBr): 2925 (m), 1590
(vs), 1431 (s), 1403 (s), 1325 (m), 1290 (w), 1235 (m), 1124 (w),
1067 (m), 1034 (m), 995 (w), 926 (w), 895 (w), 858 (w), 731 (m),
680 (m) cm-1. MS: Ni(GLYBOH2)Ni(GLYBOH1)+ at m/z ) 547.1
(100%).
Nickel(II) (N,N-Bis(1-propan-2-onyl oxime)glycinate) Nitrate
(Ni(GLYBOH2)NO3). Ni(GLYBOH2)NO3 was prepared similarly
to Ni(GLYBOH2)Cl, using acetonitrile as the solvent and filtering
off KNO3 precipitate to yield a blue solid (32% yield). FTIR
(KBr): 2930 (m), 1606 (s), 1382 (vs), 1357 (vs), 1234 (m), 1120
(w), 1071 (m), 1035 (m), 996 (w), 930 (w), 896 (w), 826 (m), 737
(m), 678 (m) cm-1. MS: Ni(GLYBOH2)Ni(GLYBOH1)+ at m/z )
547.1 (100%), Ni(GLYBOH2)+ at m/z ) 274.0 (65%).
Experimental Methods. NMR spectra were obtained using a
Bruker AC250 spectrometer as d6-DMSO, CDCl3, d6-acetone, or
D2O solutions and referenced to TMS (or CH3OH for 13C NMR
spectra in D2O solutions). FTIR spectra were collected on a Bio-
Rad Excalibur spectrometer as KBr pellets. UV-vis absorption
spectra were collected on a Hewlett-Packard 8453 spectrometer
using a 2 cm path length cell as H2O, CH3OH, or CH3CN solutions.
Circular dichroism spectra were collected on a Jasco J-715
spectropolarimeter (interfaced with a PC) using a 2 cm path length
cell as DMF solutions. Mass spectra were collected by the
University of Cincinnati Mass Spectrometry Facility on a Micro-
mass QTOF-II or an IonSpec FT-ICR mass spectrometer with
electrospray sample introduction. Samples were prepared by
dissolution in CH3OH, with NaCl added to neutral ligands to induce
charge in some cases. Magnetic susceptibility data of solid samples
Nickel(II) (N,N-Bis(1-propan-2-onyl oxime)-L-phenylalanine
N′-Methylamide) Chloride (Ni(PAMBOH3)Cl2). Ni(PAMBOH3)-
Cl2 was prepared similarly to Ni(TRISOXH3)Cl2 in methanol,
yielding a blue solid (74% yield). FTIR (KBr): 1625 (vs), 1554
(w), 1447 (m), 1410 (m), 1382 (m), 1237 (w), 1156 (w), 1066 (m),
859 (w), 748 (m), 687 (s), 553 (s) cm-1. MS: [Ni(PAMBOH3)]2-
Cl3+ at m/z ) 861 (25%), Ni(PAMBOH3)Cl+ at m/z ) 413 (100%).
Nickel(II) (N,N-Bis(1-acetophenone oxime)-L-phenylalanine
N′-Methylamide) Chloride (Ni(PAMABPOH3)Cl2). Ni(PAMAB-
POH3)Cl2 was prepared similarly to Ni(TRISOXH3)Cl2 in methanol.
Blue-green crystals (79% yield) for X-ray crystallography were
obtained by slow diffusion of diethyl ether into a 50/50 methanol/
ethanol solution of Ni(PAMABPOH3)Cl2 in a test tube. FTIR
(KBr): 2932 (m), 1620 (vs), 1550 (m), 1433 (s), 1288 (m), 1253
(m), 1162 (m), 1057 (s), 1026 (s), 841 (w), 760 (m), 687 (s), 567
(m), 534 (m) cm-1. MS: Ni(PAMABPOH3)Cl+ at m/z ) 537
(100%). Anal. Calcd for Ni(C26H28N4O3)Cl2‚1H2O (592.14): C,
52.74; H, 5.11; N, 9.46. Found: C, 52.77; H, 4.80; N, 9.30.
Nickel(II) (N-2-Hydroxyethyl-N, N-bis(1-propan-2-onyl oxime)-
amine) Chloride (Ni(EABOH3)Cl2). Ni(EABOH3)Cl2 was pre-
pared similarly to Ni(TRISOXH3)Cl2 in methanol. Blue-green
crystals (72% yield) for X-ray crystallography were obtained by
slow diffusion of a layer of acetone into a methanol solution of
Ni(EABOH3)Cl2 in a closed flask. FTIR (KBr): 2922 (s), 1628
(m), 1462 (s), 1439 (s), 1397 (s), 1380 (s), 1303 (w), 1242 (m),
1111 (m), 1065 (s), 1034 (s), 996 (m), 968 (m), 905 (m), 873 (m),
680 (s), 626 (m), 527 (m) cm-1. MS: Ni(EABOH3)Cl+ at m/z )
296 (100%), Ni(EABOH2)+ at m/z ) 260 (35%). Anal. Calcd for
Ni(C8H17N3O3)Cl2 (332.84): C, 28.87; H, 5.15; N, 12.62. Found:
C, 29.03; H, 4.79; N, 12.57.
Nickel(II) (N-2-Hydroxyethyl-N,N-bis(1-propan-2-onyl oxime)-
amine) Nitrate (Ni(EABOH3)(NO3)2). Ni(EABOH3)(NO3)2 was
prepared similarly to Ni(PRABOH2)(NO3)2 in methanol, yielding
Inorganic Chemistry, Vol. 42, No. 3, 2003 721

Goldcamp et al.
ground to a fine powder were collected at room temperature using
a Johnson Matthey MSB-1 balance, which was calibrated with a
powder sample of recrystallized HgCo(SCN)4. Elemental analyses
(CHN) of all samples were performed by Quantitative Technologies,
Inc. (Whitehouse, NJ). Samples submitted for CHN analysis were
crystalline solids prepared similarly to X-ray crystallographic
samples and were ground to a powder and dried under vacuum
before submission for CHN analysis.
X-ray Crystallography. Intensity data for Ni(GLABOH3)Cl2,
Ni(PRABOH2)(NO3)2, Ni(PAMABPOH3)Cl2, [Ni(PEABOH2)Cl]2-
(µ-Cl)2, Ni(TRISOXH3)Cl2, and Ni(ABOH2)(NO3)2 were collected
at 150 K on a standard SMART 1K CCD diffractometer using
graphite-monochromated Mo KR radiation, λ ) 0.71073 Å, while
Ni(PAMBOH3)(NO3)2 was collected at 298 K. The detector was
set at a distance of 4.5-5.0 cm from the crystal. A series of
10-30 s data frames measured at 0.3° increments of ω were
collected to calculate a unit cell. For data collection, frames were
measured for a duration of 10-30 s at 0.3° intervals of ω, with a
maximum θ value of approximately 28°.
Intensity data for Ni(PYRABOH2)Cl2 and Ni(EABOH3)Cl2 were
collected at 150 K on a standard SMART 6000 CCD diffractometer
using graphite-monochromated Mo KR radiation, λ ) 0.71073 Å,
while [Ni(OBOH2)Cl]2(µ-Cl)2 was collected at 295 K. The detector
was set at a distance of 4.5-6.5 cm from the crystal. A series of
20-30 s data frames measured at 0.3° increments of ω were
collected to calculate a unit cell. For data collection, frames were
measured for a duration of 20-35 s at 0.3° intervals of ω, with a
maximum θ value ranging from 28 to 32°.
displacement parameters indicative of disorder; their displacement
parameters were set to be equivalent to their better behaved
neighbors (O8, C9, and C11). The large displacement parameter
for C14 was left where it refined. The ethyl acetate solvent of
crystallization occupancy was set at 0.5 for Ni(PAMBOH3)(NO3)2.
The disorder in the displacement parameters was left where refined,
since a suitable disorder model was not realized. Ni(PAMABOH3)-
Cl2 crystallized as an ethanol solvate. Two molecules of acetone
crystallize in the lattice of Ni(ABOH2)(NO3)2. Some disorder is
observed, but separation of conformers was not achieved. Two
molecules of water are present in the lattice for Ni(PYRABOH2)-
Cl2. Additionally, some disorder is observed for C2-C5, as
indicated by the enlarged displacement parameters, but these were
left where they refined. The octyl group in [Ni(OBOH2)Cl]2-
(µ-Cl)2 shows disorder. The anisotropic displacement parameter for
C14 was held equivalent to C13. The PRABO ligand in [Ni-
(PRABOH2)Cl2](µ-Cl)2 is disordered in both the backbone, C1, and
the propyl group, C9. The refined occupancies for the major
conformer of C1 and C9 are 53% and 54%, respectively. The
refinement converged smoothly with crystallographic agreement
factors as given in Tables 1-3.
Results and Discussion
Ligand Synthesis. The synthesis of the general bis(oxime)
tripodal amine ligand is achieved by reaction of the oxime-
containing alkylation reagent TACO5 with a primary amine
containing the third donor “arm” of choice (Scheme 1). This
synthetic method allows for facile isolation of pure ligands,
Intensity data for [Ni(PRABOH2)Cl]2(µ-Cl)2 were collected at
150 K on a standard SMART 2K CCD diffractometer using
graphite-monochromated Ag KR radiation, λ ) 0.56086 Å. The
detector was set at a distance of 5 cm from the crystal. A series of
20 s data frames measured at 0.3° increments of ω were collected
to calculate a unit cell. For data collection, frames were measured
for a duration of 20 s at 0.3° intervals of ω, with a maximum θ
value of 21.94°. The data frames were processed using the program
SAINT.10 The data were corrected for decay, Lorentz, and polariza-
tion effects. An absorption correction based on the multiscan
technique and beam corrections were applied using SADABS.10
The structures were solved by a combination of direct methods
or Patterson (SHELXTL10) and the difference Fourier technique
and refined by full-matrix least squares on F2. Non-hydrogen atoms
were refined with anisotropic displacement parameters. Weights
1
as is evidenced in the H NMR spectra, with incorporation
of nearly any functional group into the bis(oxime) tripodal
amine ligand framework. Ligands reported here include a
variety of noncoordinating, weakly coordinating, and strongly
coordinating functional groups on the third arm of the tripod.
The ligands PRABOH2, PEABOH2, OBOH2, and ABOH2
all contain noncoordinating third arms. Ligands such as
GLABOH3, PAMBOH3, and PAMABPOH3 can provide a
weakly coordinating donor group such as an amide oxygen.
-
EABOH3, GLYBOH2 , PYRABOH2, and TRISOXH3 pro-
vide stronger donor groups such as alcohol, carboxylate,
pyridyl, and oxime groups, respectively (Figure 1).
In addition to variability in the donor set, this facile
synthetic method allows for incorporation of other structural
features into the ligands and complexes. Chirality can be
introduced by the use of natural amino acids as the primary
amine starting materials. Chiral metal complexes offer several
advantages over their nonchiral counterparts, such as the
possibility of catalyzing stereospecific reactions11 and the
availability of circular dichroism (CD) spectroscopy as an
additional tool for the characterization of the complexes and
their reactivity. We have previously reported the chiral
L-methionine based MABO ligand (along with its nickel(II)
and zinc(II) complexes),12 and two ligands based on L-
phenylalanine, PAMBOH3, and PAMABPOH3 are reported
here. With PAMABPOH3, the capability to change the steric
and solubility properties of the oxime donor arms is also
2
were assigned as w-1 ) [σ2(Fo ) + (aP)2 + bP] where P )
2
0.33333Fo + 0.66667Fc2. Hydrogen atoms were either located
directly from the difference map or calculated based on geometric
criteria. -OH or -NH hydrogens were held fixed where located.
All remaining hydrogens were treated with a riding model in
subsequent refinements. The isotropic temperature factors for the
H-atoms were defined as U(H) ) aUeq of the adjacent atom where
a ) 1.5 for -CH3 and -OH and 1.2 for all others. In the case of
Ni(TRISOXH3)Cl2, all hydrogens were located directly and the
positions and Uiso refined.
Methyl groups are disordered in Ni(GLABOH3)Cl2 and Ni-
(TRISOXH3)Cl2, the hydrogen occupancies were set at 0.5. Several
atoms in Ni(PAMBOH3)(NO3)2 (O9, C10, C11, and C12) have large
(10) (a) SMART and SAINT programs were used for data collection and
data processing (Siemens Analytical X-ray Instruments, Inc., Madison,
WI). (b) SADABS was used for the application of semiempirical
absorption and beam corrections (G. M. Sheldrick, University of
Goettingen, Germany, 1996). (c) SHELXTL was used for the structure
solution and generation of figures and tables (G. M. Sheldrick,
University of Goettingen, Germany and Siemens Analytical X-ray
Instruments, Inc., Madison, WI).
(11) Palucki, M.; Finney, N. S.; Pospisil, P. J.; Gu¨ler, M. L.; Ishida, T.;
Jacobsen, E. N. J. Am. Chem. Soc. 1998, 120, 948-954.
(12) Rosa, D. T.; Krause Bauer, J. A.; Baldwin, M. J. Inorg. Chem. 2001,
40, 1606.
722 Inorganic Chemistry, Vol. 42, No. 3, 2003

Ni(II) Complexes of Bis(oxime)amine Ligands
Table 1. X-ray Crystallography Parameters and Factors for the Complexes Ni(TRISOXH3)Cl2, Ni(PYRABOH2)Cl2, Ni(EABOH3)Cl2,
Ni(GLABOH3)Cl2, and Ni(PAMABPOH3)Cl2
Ni(TRISOXH3)Cl2
Ni(GLABOH3)Cl2
Ni(PYRABOH2)Cl2
Ni(EABOH3)Cl2
Ni(PAMABPOH3)Cl2
emp form
fw
C9H18Cl2N4O3Ni
359.88
150(2)
monoclinic
P21/n
C9H18Cl2N4O3Ni
359.88
150(2)
monoclinic
P21
C12H18Cl2N4O2Ni‚2H2O
415.95
150(2)
orthorhombic
P212121
C8H17Cl2N3O3Ni
332.86
150(2)
monoclinic
P21/n
C26H28Cl2N4O3Ni‚ C2H6O
620.20
150(2)
monoclinic
P21
temp (K)
crystal system
space group
unit cell dimens
a (Å)
8.9006(4)
18.2483(8)
8.9406(4)
90
94.357(1)
90
1447.94(11), 4
1.651
1.717
8.094(3)
11.710(3)
8.319(2)
90
114.982(14)
90
714.7(3), 2
1.672
1.740
8.0043(2)
14.7734(3)
14.9036(3)
90
90
90
1762.36(7), 4
1.568
1.427
8.4430(3)
12.1399(4)
12.8157(4)
90
91.081(1)
90
1313.34(8), 4
1.683
1.884
7.9618(3)
16.6749(6)
11.0062(4)
90
100.2490(10)
90
1437.89(9), 2
1.432
0.901
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
vol (Å3), Z
density (calcd) (Mg/m3)
abs coeff (mm-1
Flack param
)
N/A
0.055(10)
0.013(9)
N/A
0.018(11)
final R indices [I > 2σ(I)]
R1
0.0295
0.0685
0.0248
0.0579
0.0337
0.0691
0.0305
0.0757
0.0366
0.0917
wR2
R indices (all data)
R1
wR2
0.0332
0.0699
0.0272
0.0586
0.0362
0.0699
0.0339
0.0773
0.0429
0.0949
Table 2. X-ray Crystallography Parameters and Factors for the Complexes Ni(PAMBOH3)(NO3)2, Ni(ABOH2)(NO3)2, and Ni(PRABOH2)(NO3)2
Ni(PAMBOH3)(NO3)2
Ni(PRABOH2)(NO3)2
Ni(ABOH2)(NO3)2
emp form
fw
C16H24N6O9Ni‚1/2 (C4H8O2)
547.17
C9H19N5O8Ni
384.00
C12H17N5O8Ni‚2 (C3H6O)
534.17
temp (K)
crystal system
space group
unit cell dimens
a (Å)
298(2)
orthorhombic
P212121
150(2)
monoclinic
P21/n
150(2)
monoclinic
P21/n
12.727(2)
12.970(2)
16.683(2)
90
90
90
2753.8(7), 4
1.320
0.761
8.3181(2)
19.4089(5)
9.9222(1)
90
94.897(1)
90
1596.04(6), 4
1.598
1.264
12.0935(8)
15.3388(10)
13.7565(9)
90
b (Å)
c (Å)
R (deg)
â (deg)
106.808(1)
γ (deg)
vol (Å3), Z
dens (calcd) (Mg/m3)
2442.8(3), 4
1.452
0.854
abs coeff (mm-1
Flack paramr
)
0.00(2)
N/A
N/A
final R indices [I > 2σ(I)]
R1
0.0637
0.1479
0.0342
0.0839
0.0647
0.1100
wR2
R indices (all data)
R1
wR2
0.1559
0.2048
0.0457
0.0884
0.0763
0.1132
shown, as the typical methyl groups of most of the ligands
in the series are replaced by phenyl groups. The acetophe-
none-based reagent TABO, similar to TACO, provides an
easy method for addition of oxime donor arms with phenyl
groups to amines. While incorporation of the third donor
arm can be easily achieved by choice of the amine starting
material, addition of carboxylate donor groups by reaction
of amino acids with TACO does not proceed as easily, likely
due to relatively low nucleophilicity of the zwitterion form
of the amino acids. This problem can be overcome by
conversion of the amino acid to its ester derivative, followed
by reaction with TACO to give the ester bis(oxime) tripodal
amine and then saponification of the ester with KOH to give
the potassium carboxylate salt.
crystallization from a variety of high and medium polarity
solvents. With the exception of the GLYBOH2K ligand, at
least one X-ray crystal structure of a Ni(II) complex has been
obtained for each ligand. In these crystal structures, the
polydentate ligands all bind in a manner similar to nickel-
(II), with the oxime nitrogens and the central amine forming
a general N3 donor unit, which always coordinates in a facial
mode. The third arm may or may not provide additional
donor atoms, depending on the type of functional group on
that arm. All of these complexes have six-coordinate, pseudo-
octahedral geometry at the nickel center, with similar
Ni-N(amine) and Ni-N(oxime) bond lengths and N-Ni-N
bond angles for the common bis(oxime)amine N3 donor set
(Table 4). However, some notable differences in structure
result from both the nature of the ligand’s third arm and the
anion of the Ni(II) salt which is used. Three major crystal
structure types are observed in the Ni(II) complexes of this
series of ligands. (Type 1) For the tetradentate ligands
Synthesis and Structure of Ni(II) Complexes. The
nickel(II) complexes of this series of polyoxime tripodal
amine ligands can be easily obtained by addition of 1 equiv
of the ligand to the Ni(II) salt of choice, followed by
Inorganic Chemistry, Vol. 42, No. 3, 2003 723

Goldcamp et al.
Table 3. X-ray Crystallography Parameters and Factors for the Complexes [Ni(PRABOH2)Cl]2(µ-Cl)2, [Ni(PEABOH2)Cl]2(µ-Cl)2, and
[Ni(OBOH2)Cl]2(µ-Cl)2
[Ni(PRABOH2)Cl]2(µ-Cl)2
[Ni(PEABOH2)Cl]2(µ-Cl)2
[Ni(OBOH2)Cl]2(µ-Cl)2
emp form
fw
C18H38Cl4N6O4Ni2
661.76
C28H42Cl4N6O4Ni2
785.90
C28H58Cl4N6O4Ni2
802.02
temp (K)
crystal system
space group
unit cell dimens
a (Å)
150(2)
monoclinic
P21/n
150(2)
triclinic
P-1
295(2)
monoclinic
C2/c
8.5525(3)
15.9383(6)
10.5236(4)
90
103.847(1)
90
1392.81(9), 2
1.578
0.923
8.4695(2)
10.2688(3)
10.5412(2)
111.407(1)
100.985(1)
94.575(1)
826.64(3), 1
1.579
23.8527(1)
14.0684(6)
11.7874(5)
90
90.715(1)
90
3955.2(3), 4
1.347
1.260
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
vol (Å3), Z
density (calcd) (Mg/m3)
abs coeff (mm-1
Flack param
)
1.506
N/A
N/A
N/A
final R indices [I > 2σ(I)]
R1
0.0459
0.1074
0.0234
0.0589
0.0595
0.1205
wR2
R indices (all data)
R1
wR2
0.0783
0.1162
0.0285
0.0602
0.0776
0.1278
Scheme 1. General Reaction Scheme for the Synthesis of Bis(oxime)
Tripodal Amine Ligands
(TRISOXH3, GLABOH3, PAMBOH3, PAMABPOH3,
EABOH3, and PYRABOH2), monomeric, six-coordinate,
pseudo-octahedral geometries are observed (Figure 2 and
Figure 3). In these structures, the two “free” nickel coordina-
-
tion positions are occupied by monodentate anions (NO3
or Cl-) (In previously reported structures of these types,
solvent molecules may coordinate in the place of nitrate
anions.4,12) (Type 2) For the tridentate ligands (ABOH2,
OBOH2, PEABOH2, and PRABOH2), the complexes with
NiII(NO3)2 form monomeric, pseudo-octahedral structures
(Figure 4). The coordination sphere of the nickel is completed
by one nitrate anion acting as a bidentate ligand in the two
free equatorial positions and a second nitrate acting as a
monodentate ligand in the free axial position (defined as trans
to the amine donor). (Type 3) For the same tridentate ligands
with NiIICl2, bis(µ-Cl) bridged dimers are formed, in which
the neighboring chlorides fill the coordination sphere of the
nickel (Figure 5). There are multiple examples, with no
exceptions, of each crystal structure type, strongly indicating
that these are generalized structural phenomena controlled
by both the ligand donor set and coordination properties of
the anions in the complex. Thus, of the complexes which
have not been structurally characterized by X-ray crystal-
lography, it might be expected that Ni(GLABOH3)-
(NO3)2, Ni(PAMBOH3)Cl2, Ni(PYRABOH2)(NO3)2, and
Ni(EABOH3)(NO3)2 will assume structure type 1, Ni-
(PEABOH2)(NO3)2 and Ni(OBOH2)(NO3)2 will assume
structure type 2, and Ni(ABOH2)Cl2 will assume structure
type 3. The Ni(GLYBOH2)Cl and Ni(GLYBOH2)(NO3) com-
plexes, with their tetradentate N3O donor set, may be
Figure 1. Library of tripodal amine ligands containing at least two oxime
donor groups.
expected to form structures of type 1. However, the negative
-
charge of the GLYBOH2 ligand will likely result in the
coordination of only one anion, with solvent occupying the
sixth coordination position. Also, it is conceivable that the
carboxylate donor arm could bridge to other metal centers,
forming dimeric structures. Room-temperature magnetic
724 Inorganic Chemistry, Vol. 42, No. 3, 2003

Ni(II) Complexes of Bis(oxime)amine Ligands
Figure 2. X-ray crystal structures (ORTEP views) of Ni(TRISOXH3)Cl2 (top left), Ni(GLABOH3)Cl2 (top right), Ni(EABOH3)Cl2 (bottom left), and
Ni(PYRABOH2)Cl2 (bottom right). These tetradentate ligands form six-coordinate, monomeric complexes with Ni(II).
Table 4. X-ray Crystallographic Nickel-Ligand Bond Lengths
bond lengths (Å)
complex
Ni-N(oxime)
Ni-N(amine)
Ni-(third arm)
bond type
Ni(TRISOXH3)(NO3)2 (ref 4)
2.051(2)
2.099(2)
2.085(2)
2.078(2)
Ni-N(oxime)
Ni(TRISOXH3)Cl2
2.0485(14)
2.0957(14)
2.1198(15)
2.0628(15)
2.0410(12)
2.0496(12)
2.062(2)
2.034(2)
2.050(2)
2.030(2)
2.024(5)
2.061(5)
2.042(3)
2.060(3)
2.0429(12)
2.0584(12)
2.040(3)
2.1131(13)
2.1110(15)
2.1189(12)
2.115(2)
2.0367(14)
2.0811(16)
2.1565(10)
2.069(2)
2.062(2)
2.062(4)
n/a
Ni-N(oxime)
Ni-N(pyridyl)
Ni-O(alcohol)
Ni-O(amide)
Ni-O(amide)
Ni-O(amide)
Ni(PYRABOH2)Cl2
Ni(EABOH3)Cl2
Ni(GLABOH3)Cl2
Ni(PAMABPOH3)Cl2
Ni(PAMBOH3)(NO3)2
[Ni(PRABOH2)Cl]2(µ-Cl)2
[Ni(PEABOH2)Cl]2(µ-Cl)2
[Ni(OBOH2)Cl]2(µ-Cl)2
Ni(PRABOH2)(NO3)2
Ni(ABOH2)(NO3)2
2.140(2)
2.134(5)
2.186(3)
2.2068(12)
2.201(3)
n/a
n/a
2.044(3)
1.9917(17)
2.0311(16)
2.011(2)
2.1088(17)
2.168(2)
n/a
n/a
2.024(3)
susceptibility measurements for all of the nickel(II) com-
plexes reported here are consistent with values for six-
coordinated, pseudo-octahedral nickel(II).13 Values of µeff
measured for the complexes range from 2.62 to 3.33 (µspin only
) 2.83), which are in agreement with a spin of S ) 1 at the
metal center (See Table S1 in the Supporting Information).
The crystal structures of the nickel(II) complexes show
that the hydrogens from one or more of the oxime hydroxyl
Inorganic Chemistry, Vol. 42, No. 3, 2003 725

Goldcamp et al.
Figure 3. X-ray crystal structures (ORTEP views) of Ni(PAMBOH3)(NO3)2 (left, noncoordinating nitrate atoms omitted for clarity) and Ni(PAMABPOH3)-
Cl2 (right). As with the other tetradentate ligands, six-coordinate, monomeric complexes are formed. In addition, these L-phenylalanine derived ligands
incorporate a chiral center into the complex, which allows for the use of CD spectroscopy.
Figure 4. X-ray crystal structures (ORTEP views) of Ni(ABOH2)(NO3)2 (left) and Ni(PRABOH2)(NO3)2 (right). The tridentate ligands form six-coordinate,
monomeric complexes when bound to NiII(NO3)2.
groups form intramolecular hydrogen bonds with the anion
bound to the nickel center in the axial position. For example,
in the crystal structure of Ni(TRISOXH3)Cl2 (see Figure 2),
H1 and H3 of two of the oxime groups form hydrogen
bonds to the axial chloride (Cl1) with distances of 2.35(3)
and 2.50(3) Å, respectively. The ability of these polyoxime
ligands to form hydrogen bonds with ligands or substrates
bound to the metal center may provide stabilization of other-
wise reactive species or enhanced reactivity with substrates.
Similar intramolecular hydrogen bonding effects have been
designed into polydentate ligands by others. Berreau and co-
workers have reported a zinc complex in which the ligand
forms a hydrogen bond to a coordinated methanol or DMF
molecule as a structural model for liver alcohol dehydroge-
nase.14 Similarly, Borovik and co-workers have shown that
tripodal amine ligands with urea type donor groups can form
hydrogen bonds to stabilize terminal hydroxide ligands in
various metal complexes.15 Metal-bound active oxygen
intermediates may also be activated by hydrogen bonding,
as is suggested for the vanadium haloperoxidases. Vanadium-
peroxo complexes of tripodal and bipodal amine ligands
reported by Butler and co-workers show intramolecular
hydrogen bonds between the ligands and the metal-bound
peroxide.16 Thus, these polydentate ligands containing oxime
groups may be useful for designing metal complexes with
the strong potential for hydrogen bonding with and stabiliza-
tion of exogenous ligands.
UV-vis Spectroscopic Characterization. The UV-vis
absorption spectra of the series of tripodal amine-containing
(14) (a) Garner, D. K.; Allred, R. A.; Tubbs, K. J.; Arif, A. M.; Berreau,
L. M. Inorg. Chem. 2002, 41, 3533-3541. (b) Berreau, L. M.;
Makowska-Grzyska, M. M.; Arif, A. M. Inorg. Chem. 2001, 40,
2212-2213.
(15) Macbeth, C. A.; Hammes, B. S.; Young, V. G.; Borovik, A. S. Inorg.
Chem. 2001, 40, 4733-4741.
(16) Kimblin, C.; Bu, X.; Butler, A. Inorg. Chem. 2002, 41, 161-163.
(13) Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M. In
AdVanced Inorganic Chemistry, 6th ed.; John Wiley and Sons: New
York, 1999; pp 838-839.
726 Inorganic Chemistry, Vol. 42, No. 3, 2003

Ni(II) Complexes of Bis(oxime)amine Ligands
Figure 5. X-ray crystal structures (ORTEP views) of [Ni(PRABOH2)Cl]2(µ-Cl)2 (top left), [Ni(PEABOH2)Cl]2(µ-Cl)2 (top right), and [Ni(OBOH2)Cl]2-
(µ-Cl)2. The tridentate ligands, when coordinated to NiIICl2, form bis(µ-Cl) bridged dimers.
Ni(II) complexes are consistent with other six-coordinate,
pseudo-octahedral Ni(II) complexes.17 Each contains three
absorption bands in the ligand field region (300-1200 nm),
although for some, the highest energy of these is buried under
the tail of intense high energy absorbance bands. The lowest
energy transition in an octahedral d8 complex corresponds
to 10 Dq. The value of 10 Dq varies according to the nature
of the third arm of the ligand, producing a reasonable
spectrochemical series for the Ni(II) ligand field transitions.
In acetonitrile, a relatively weakly coordinating solvent, the
trend based on the third arm follows the order alkyl/aryl <
amide < carboxylate < alcohol < pyridyl < oxime, which
is consistent with expectations based on the donor strength
of the third arm. The spectra of the nitrate salts in acetonitrile
are shown in Figure 6 and values of 10 Dq are listed in Table
5. The value of 10 Dq is lower for the ABOH2 complex
than for complexes of the other tridentate ligands due to
modulation of the donor ability of the coordinated central
amine nitrogen, which is directly bound to the phenyl ring,
unlike in the other aliphatic amines (PRABOH2, PEABOH2,
OBOH2).
Figure 6. UV-vis absorption spectra of NiII nitrate complexes in
CH3CN solution.
(For UV-vis spectra, see Figures S1 to S4 in Supporting
Information.) It appears that in water, weakly coordinating
third arms (such as an amide oxygen) are displaced by the
more strongly coordinating solvent molecule,12 which slightly
shifts the order of the spectrochemical series. In methanol,
both the chloride and the nitrate containing complexes follow
the order observed in acetonitrile. Values of 10 Dq for all
the complexes in acetonitrile, methanol, and water are
compiled in Table 5.
The effects of solvent and counterions on the value of 10
Dq were also investigated. Complexes containing either
chloride or nitrate ions were examined in methanol and water
The spectroscopic properties of the compounds can be
further explored if a chiral center is designed into the
complex. Natural chiral amino acids can be used as starting
(17) Lever, A. B. P. In Inorganic Electronic Spectroscopy; Elsevier:
Amsterdam, 1984.
Inorganic Chemistry, Vol. 42, No. 3, 2003 727

Goldcamp et al.
Table 5. Values of 10 Dq (cm-1) for the Ni(II) Complexes in Different Solventsa
CH3OH
CH3OH
(X ) NO3
H2O
H2O
(X ) NO3
CH3CN
(X ) NO3
-
-
-
complex
(X ) Cl-)
)
(X ) Cl-)
)
)
Ni(TRISOXH3)X2
Ni(PYRABOH2)X2
Ni(EABOH3)X2
Ni(GLYBOH2)X
Ni(GLABOH3)X2
Ni(PAMBOH3)X2
Ni(PRABOH2)X2
Ni(OBOH2)X2
10260
10200
10100
10000
9900
9800
9430
9760
9430
10990
10930
10750
10640
10420
10420
10100
10100
10100
n/a
10990
10990
10750
10530
10530
10420
10100
10750
10420
n/a
10990
10930
10640
10580
10470
10310
10310
10310
10310
n/a
11360
11240
10870
10640
10530
10420
10310
10200
10310
9710
Ni(PEABOH2)X2
Ni(ABOH2)X2
< 9600
a Complexes that are insoluble in a solvent are listed as n/a.
lography. Three generalized structure types are formed,
which are determined by the ligand donor set and the anion
coordination properties. In these crystal structures, interesting
intramolecular hydrogen bonding is observed between the
hydrogens of the oxime hydroxyl groups and the axially
coordinated anions. Analysis of the UV-vis absorption
spectra of this series of Ni(II) complexes shows that variance
of the donor ability of the third arm of the ligand tripod can
tune the ligand field energy of the metal complexes, with a
spectrochemical series of alkyl/aryl < amide < carboxylate
< alcohol < pyridyl < oxime for third arm donor types. It
is anticipated that this variation in electronic properties and
other attributes of the ligands will allow optimization of
interesting reactivity for the metal complexes of these ligands.
Figure 7. UV-vis (no marker) and CD (circle markers) spectra of the
chiral complexes Ni(PAMBOH3)Cl2 (solid line) and Ni(PAMABPOH3)-
Cl2 (dashed line) in DMF.
materials in order to synthesize chiral derivatives of the
tripodal amine polyoxime ligands. The metal complexes of
these ligands can be probed by circular dichroism to give
electronic information that is complementary to that obtained
by UV-vis spectroscopy, similarly to the previously reported
spectroscopic study of the Ni(II) and Zn(II) complexes of a
bis(oxime) containing ligand based on L-methionine N′-
methylamide.12 A descent in symmetry model was used to
analyze the ligand field spectra of the Ni(II) complexes, and
the electronic transitions were used to examine deviations
from Oh symmetry. The CD and UV-vis spectra of two
new chiral complexes, Ni(PAMBOH3)(NO3)2 and Ni-
(PAMABPOH3)(NO3)2, are shown in Figure 7, demonstrating
that these chiral complexes are conducive to the use of CD
spectroscopy as an analytical tool in future studies of the
reactivity of the complexes.
Acknowledgment. Funding was provided by the Petro-
leum Research Fund administered by the American Chemical
Society (ACS-PRF 37653-AC3) and the University of
Cincinnati. N.K.V. was supported by NSF-REU award
#CHE-0097726. Crystallographic data were collected on the
SMART 1K diffractometer by J.A.K.B. through the Ohio
Crystallographic Consortium located at the University of
Toledo, Toledo, OH 43606 (Ohio Board of Regents 1995
Investment Fund CAP-075), and on the SMART 2K and
SMART 6000 diffractometers through Dr. Alan Pinkerton,
Department of Chemistry, University of Toledo, Toledo, OH.
The University of Cincinnati Mass Spectrometry Facility is
part of the Ohio Mass Spectrometry Consortium. We also
thank Professor Apryll Stalcup at the University of Cincinnati
for the use of her CD spectrometer.
Summary and Conclusions
Supporting Information Available: 1H NMR, 13C NMR, and
mass spectra of the ligands, mass spectra of the nickel complexes,
UV-vis absorption spectra of the nickel complexes in CH3OH and
H2O, room-temperature magnetic susceptibility values, and crystal-
lographic data in CIF format. This material is available free of
charge via the Internet at http://pubs.acs.org.
We have synthesized a library of novel tripodal amine
ligands with at least two oxime donor groups and a variable
third donor arm. Incorporation of steric and chiral features
can be easily achieved without significant modification of
the synthetic route. The nickel(II) complexes of these ligands
have been structurally characterized by X-ray crystal-
IC025860Q
728 Inorganic Chemistry, Vol. 42, No. 3, 2003