Copper(II) and Nickel(II) Complexes of Dianionic and Tetraanionic Dinucleating Macrocycles

Article abstract of DOI:10.1021/ic9712434

With nickel(II) or copper(II) acetate, 2,6-bis(acetoximato)-4-methylphenol (H₂Damox) and 2,6-bis(acetoximato)-4-tert-butylphenol (H₂Dabox) afford molecular dinuclear complexes [Cu₂(Damox)₂] (1), [Ni₂(Damox)₂(MeOH)₂]· MeOH (2), [Cu₂(Dabox)₂] (5) and [Ni₂(Dabox)₂(H₂O)₂] (6). Salts of the macrocyclic tetraimine copper chelates from diacetylcresol with 1,3-diaminopropane and 1,4-diaminobutane, [Cu₂(Dampn)]₂₊ and [Cu₂(Dampn)]²⁺, were also examined. Pyridine solutions of 2 yielded pink crystals of [Ni₂(Damox)₂(Py)₄]·(Py)₂ (3a), which effloresce pyridine to form [Ni₂(Damox)₂(Py)₂]·Py (3). The pseudomacrocyclic complexes 1, 5, and 6 react with BF₃·Et₂O to form BF₂-bridged macrocyclic complexes [Cu₂(Damfb)] (4), [Cu₂(Dabfb)]·H₂O (7), and [Ni₂(Dabfb)] (8). Crystals of [Ni₂(Damox)₂(Py)₄]·(Py)₂ (3a) are monoclinic (space group P2₁ln), with a = 13.297(5) A?, b = 11.240-(5) A?, c = 17.396(6) A?, β= 109.03°, V = 2458(3) A?³, Z = 2, R = 0.050, and R_w = 0.052. The [Ni₂(Dabfb] (8) crystals are orthorhombic (space group Pnma), with a = 11.558(6) A?, b = 17.200(5) A?, c = 16.058(2) A?, V = 3192(3) A?³, Z = 4, R = 0.057, and R_w = 0.057. The saddle-shaped molecules of 8 contain low-spin Ni(II). The copper(II) centers in 1, 5, 6, etc., are strongly antiferromagnetically coupled with -2J values in the range 550-800 cm^-1. The nickel(II) centers in 2 and 3 are weakly (-2J = 3.2 cm^-1) or moderately (-27 = 19.5 cm^-1) antiferromagnetically coupled, whereas 6 shows a moderate ferromagnetic interaction with -2J = -5.1 cm^-1. All the complexes are electrochemically reducible in two 1-electron steps. In CH₃CN, the mixed-valence complexes [Cu₂Dampn)]₊ and [Cu₂(Dambn)]⁺ are valence-localized. The nature of the carbon monoxide interactions with the M(I) centers is clearest for [Cu₂(Dambn)]^+/0, which in dimethylformamide solution binds two molecules of CO in a cooperative fashion.

Full text of DOI:10.1021/ic9712434

1028
Inorg. Chem. 1998, 37, 1028-1036
Copper(II) and Nickel(II) Complexes of Dianionic and Tetraanionic Dinucleating
Macrocycles
Kausik K. Nanda,† Anthony W. Addison,*,† Neil Paterson,‡ Ekkehard Sinn,‡,§
Laurence K. Thompson,| and Ushio Sakaguchi
Departments of Chemistry, Drexel University, Philadelphia, Pennsylvania 19104-2875,
The University, Hull, England HU6 7RX, U.K., Memorial University, St. John’s, NF, Canada A1B 3X7,
and Kumamoto Gakuen University, Kumamoto 862, Japan
ReceiVed October 1, 1997
With nickel(II) or copper(II) acetate, 2,6-bis(acetoximato)-4-methylphenol (H2Damox) and 2,6-bis(acetoximato)-
4-tert-butylphenol (H2Dabox) afford molecular dinuclear complexes [Cu2(Damox)2] (1), [Ni2(Damox)2(MeOH)2]‚
MeOH (2), [Cu2(Dabox)2] (5) and [Ni2(Dabox)2(H2O)2] (6). Salts of the macrocyclic tetraimine copper chelates
from diacetylcresol with 1,3-diaminopropane and 1,4-diaminobutane, [Cu2(Dampn)]2+ and [Cu2(Dambn)]2+, were
also examined. Pyridine solutions of 2 yielded pink crystals of [Ni2(Damox)2(Py)4]‚(Py)2 (3a), which effloresce
pyridine to form [Ni2(Damox)2(Py)2]‚Py (3). The pseudomacrocyclic complexes 1, 5, and 6 react with BF3‚Et2O
to form BF2-bridged macrocyclic complexes [Cu2(Damfb)] (4), [Cu2(Dabfb)]‚H2O (7), and [Ni2(Dabfb)] (8).
Crystals of [Ni2(Damox)2(Py)4]‚(Py)2 (3a) are monoclinic (space group P21/n), with a ) 13.297(5) Å, b ) 11.240-
(5) Å, c ) 17.396(6) Å, â ) 109.03°, V ) 2458(3) Å3, Z ) 2, R ) 0.050, and Rw ) 0.052. The [Ni2(Dabfb] (8)
crystals are orthorhombic (space group Pnma), with a ) 11.558(6) Å, b ) 17.200(5) Å, c ) 16.058(2) Å, V )
3192(3) Å3, Z ) 4, R ) 0.057, and Rw ) 0.057. The saddle-shaped molecules of 8 contain low-spin Ni(II). The
copper(II) centers in 1, 5, 6, etc., are strongly antiferromagnetically coupled with -2J values in the range 550-
800 cm-1. The nickel(II) centers in 2 and 3 are weakly (-2J ) 3.2 cm-1) or moderately (-2J ) 19.5 cm-1
)
.
antiferromagnetically coupled, whereas 6 shows a moderate ferromagnetic interaction with -2J ) -5.1 cm-1
All the complexes are electrochemically reducible in two 1-electron steps. In CH3CN, the mixed-valence complexes
[Cu2(Dampn)]+ and [Cu2(Dambn)]+ are valence-localized. The nature of the carbon monoxide interactions with
the M(I) centers is clearest for [Cu2(Dambn)]+/0, which in dimethylformamide solution binds two molecules of
CO in a cooperative fashion.
Introduction
magneto-structural relations and selective activation of sub-
strates. A common feature of all these macrocycles is that they
Since the initial reports of dinuclear copper(II) complexes
with ligands derived from the condensation of 2,6-diformyl-4-
methylphenol1 or 2,6-diacetyl-4-methylphenol2 and N,N′-diami-
noalkanes or hydroxylamine, there have been extensive studies
on phenoxo-bridged dinuclear macrocyclic complexes.3-13 The
focus of attention has been on probing of their redox potentials,
are dianionic and hence form dicationic dinuclear complexes
of metal ions in the +2 oxidation state. Nag et al. have recently
investigated the chemistry of trivalent metal ions with phenoxo-
bridged tetraaza macrocycles which resulted in tricationic mixed-
valence (+2, +3)14,15 and heterodinuclear (MII-MIII)16 com-
plexes. Tetraanionic macrocycles with similar donors should
yield uncharged molecular dinuclear complexes with dipositive
metal ions and offer the eventual possibility of stabilizing
complexes with tripositive metals. Here we report on the
properties of some macrocyclic dinuclear molecular complexes
of copper(II) and nickel(II), including tetraanionic pseudo-
macrocyclic and macrocyclic ligands (see Chart 1).
* To whom correspondence should be addressed. E-mail:
addisona@dunx1.ocs.drexel.edu.
† Drexel University.
‡ The University of Hull.
§ E-mail: E.Sinn@chem.hull.ac.uk; http://www.hull.ac.uk/chemistry/
homepage.html.
| Memorial University. E-mail: lthomp@morgan.ucs.mun.ca.
Kumamoto Gakuen University. E-mail: sakaguchi@kumagaku.ac.jp.
(1) Pilkington, N. H.; Robson, R. Aust. J. Chem. 1970, 23, 2225.
(2) Addison, A. W. Inorg. Nucl. Chem. 1976, 12, 899.
(3) Nanda, K. K.; Das, R.; Venkatsubramanian, K.; Nag, K. Proc. Indian
Acad. Sci. (Chem. Sci.) 1994, 106, 673.
Experimental Section
Reagents from commercial sources were used as received. 2,6-
Diacetyl-4-methylphenol was synthesized according to a published
(4) Atkins, A. J.; Black, D.; Blake, A. J.; Martin-Becerra, A.; Parsons,
S.; Ramirez, L.; Schroeder, M. Chem. Commun. 1996, 457.
(5) Nag, K. Proc. Indian Acad. Sci. (Chem. Sci.) 1990, 102, 269.
(6) Vigato, P. A.; Tamburini, S.; Fenton, D. E. Coord. Chem. ReV. 1990,
106, 25.
(7) Casellato, U.; Vigato, P. A.; Fenton, D. E.; Vidali, M. Chem. Soc.
ReV. 1978, 8, 199.
(8) Groh, S. E. Isr. J. Chem. 1976/77, 15, 277.
(9) Bell, M.; Edwards, A. J.; Hoskins, B. F.; Kachab, E. H.; Robson, R.
J. Am. Chem. Soc. 1989, 111, 3603.
(11) Sakayama, H.; Matoda, K.; Okawa, H.; Kida, S. Chem. Lett. 1991,
1133.
(12) Tandon, S. S.; McKee, V. J. Chem. Soc., Chem. Commun. 1988, 385.
(13) Yonemura, M.; Matsumura, Y.; Furutachi, H.; Ohba, M.; Okawa, H.
Inorg. Chem. 1997, 36, 2711.
(14) Das, R.; Nanda, K. K.; Paul, I.; Baitalik, S.; Nag, K. Polyhedron 1994,
13, 2639.
(15) Dutta, S. K.; Ensling, J.; Werner, R.; Floerke, U.; Haase, W.; Gu¨tlich,
P.; Nag, K. Angew. Chem., Int. Ed. Engl. 1997, 36, 152.
(16) Dutta, S. K.; Werner, R.; Floerke, U.; Mohanta, S.; Nanda, K. K.;
Haase, W.; Nag, K. Inorg. Chem. 1996, 35, 2292.
(10) Tandon, S. S.; Thompson, L. K.; Bridson, J. N. J. Chem. Soc., Chem.
Commun. 1992, 911.
S0020-1669(97)01243-3 CCC: $15.00 © 1998 American Chemical Society
Published on Web 02/20/1998

CuII and NiII Complexes of Dinucleating Macrocycles
Inorganic Chemistry, Vol. 37, No. 5, 1998 1029
The solution was refluxed for 1 h and concentrated (rotary evaporator).
The product was filtered off, recrystallized from aqueous ethanol, and
dried over P4O10. Yield: 1.6 g (70%), white needles. Mp: 170 °C.
Anal. Calcd for C11H14N2O3: C, 59.5; H, 6.4; N, 12.6. Found: C,
59.3; H, 6.3; N, 12.3. MS: m/z ) 222, [M+]. 1H NMR (acetone-d6):
δ 1.55 (s, 3H, Ar-Me), 2.25 (s, 6 H, COMe), 7.17 (s, 2 H, Ar), 10.25
(s, 2 H, NOH), 11.70 (s, 1 H, Ar-OH).
Chart 1
2,6-Bis(acetoximato)-4-tert-butylphenol (H2Dabox). This com-
pound was synthesized using a procedure similar to that for H2Damox.
Yield: 85%, white needles. Mp: 150 °C. Anal. Calcd for
C14H20N2O3: C, 63.6; H, 7.6; N, 10.6. Found: C, 63.3; H, 7.5; N,
10.8. MS (FAB): m/z ) 265, [M + H]+.
[Cu2(Damox)2] (1). A solution of 0.6 g (2.7 mmol) of H2Damox
in 15 mL of warm acetic acid was added to 0.65 g (3.2 mmol) of Cu-
(CH3COO)2‚H2O in 15 mL of the same solvent. The green solution
obtained was diluted to 200 mL with ethanol. After 5 days, the green-
black prisms were filtered off, washed with ethanol, and dried over
P4O10 in vacuo. Yield: 0.63 g (82%). Anal. Calcd for C22H24-
Cu2N4O6: C, 46.6; H, 4.2; N, 9.9; Cu, 22.4. Found: C, 46.6; H, 4.3;
N, 9.8; Cu, 22.1. MS (FAB): m/z ) 567, [M]+.
[Ni2(Damox)2(MeOH)2]‚MeOH (2). A solution of Ni(CH3COO)2‚
4H2O (0.5 g, 2 mmol) in 30 mL of warm MeOH was added to a stirred
solution of H2Damox (0.44 g, 2 mmol) in 50 mL of MeOH. The
initially dark blue color changed to green in ∼5 min, and an apple-
green precipitate formed. After 1 h the solid was filtered off, washed
thoroughly with MeOH, and dried over CaCl2 in vacuo. Yield: 0.52
g (80%). Anal. Calcd for C25H36N4Ni2O9: C, 45.9; H, 5.5; N, 8.6.
Found: C, 46.1; H, 5.4; N, 8.8.
[Ni2(Damox)2(Py)2]‚Py (3). Pink crystals were deposited when a
saturated solution of 2 in warm pyridine was cooled. These were
filtered off, washed with ether, and dried in vacuo over H2SO4. The
crystals lose their luster upon desiccation. Anal. Calcd for C37H39N7-
Ni2O6: C, 55.9; H, 4.9; N, 12.3. Found: C, 55.7; H, 4.8; N, 12.3.
[Cu2(Damfb)] (4). Complex 1 (1.36 g, 2.4 mmol) was dissolved
in the minimum volume of redistilled boron trifluoride ethyl etherate.
The green solution was poured onto crushed ice, and the precipitate
was filtered off, washed with water, recrystallized from acetone as
greenish-black prisms, and air-dried. Anal. Calcd for acetone mono-
solvate: C25H28B2Cu2F4N4O7: C, 41.7; H, 3.9; N, 7.8; Cu, 19.2.
Found: C, 41.7; H, 4.2; N, 7.6. This was subsequently dried at 160
°C in vacuo to yield 1.0 g (70%) of the unsolvated green product. Anal.
Calcd for C22H22B2Cu2F4N4O6: C, 39.8; H, 3.3; N, 8.5; Cu, 19.2.
Found: C, 39.8; H, 3.4; N, 8.4; Cu, 18.7. MS (FAB): m/z ) 663, [M
+ H]+.
[Cu2(Dabox)2] (5). A solution of Cu(CH3COO)2‚H2O (0.4 g, 2
mmol) in 25 mL of MeOH was added to a MeOH solution (30 mL) of
H3L,2 and the mixture was stirred for 3 h. The brownish green
precipitate was filtered off, washed with MeOH and recrystallized from
CH2Cl2-MeOH as olive green microcrystals. Yield: 0.42 g (65%).
Anal. Calcd for C28H36Cu2N4O6: C, 51.6; H, 5.5; N, 8.6. Found: C,
51.6; H, 5.5; N, 8.7. MS (FAB): m/z ) 651, [M + H]+.
[Ni2(Dabox)2(H2O)2] (6). This compound was synthesized in 75%
yield from Ni(CH3COO)2‚4H2O and H2Dabox using a procedure similar
to that for 5. Insolubility in common solvents prevented recrystalli-
zation. Anal. Calcd for C28H40N4Ni2O8: C, 49.6; H, 5.9; N, 8.3.
Found: C, 50.0; H, 5.7; N, 8.1.
[Cu2(Dabfb)]‚H2O (7). Complex 5 (0.3 g) in redistilled BF3‚Et2O
(10 mL) was heated on a steam bath for 15 min. The resulting dark
green solid was filtered off, washed with ether, and recrystallized from
CH3CN-MeOH. Yield: 0.25 g (70%). Anal. Calcd for C28H36-
B2Cu2F4N4O7: C, 43.9; H, 4.7; N, 7.3. Found: C, 43.6; H, 4.7; N,
7.2. MS (FAB): m/z ) 747, [M + H]+.
procedure.17 Acetonitrile, dichloromethane, and N,N-dimethylform-
amide (DMF) were purified by distillation off P4O10, K2CO3, or CaH2,
respectively, under an N2 atmosphere or in vacuo (DMF). Elemental
microanalyses were performed by Robertson Microanalytical Labora-
tories (Madison, NJ) and Galbraith Laboratories Inc. (Knoxville, TN).
2,6-Diacetyl-4-tert-butylphenol. CH3COCl (55 mL, 0.72 mol) was
added dropwise over a period of 3 h to a chilled, stirred mixture of
AlCl3 (192 g, 1.44 mol), 4-tert-butylphenol (36 g, 0.24 mol), and dry
nitrobenzene (250 mL) in a 2 L flask in an ice-water bath. The
temperature was then raised to 65- 70 °C, and the reaction was allowed
to continue overnight, following which the reaction mixture was cooled
with ice and ice-cold aqueous HCl (6 M, 500 mL) was added slowly
with vigorous stirring. The contents of the flask were allowed to
separate overnight, and most of the nitrobenzene in the organic phase
was then steam-distilled off. The phenolics were extracted with aqueous
KOH, and the extract was acidified with 6 M HCl and back-extracted
with ether (3 × 100 mL). After the ether extract was dried over Na2-
SO4 and the ether was rotary evaporated off, the brown viscous liquid
residue was vacuum-distilled. The yellow liquid product crystallized
after refrigeration and was recrystallized from hexane. Yield: 25 g
(45%), yellow prisms. Mp: 53-54 °C. Anal. Calcd for C14H18O3:
C, 71.8; H, 7.7. Found: C, 71.7; H, 7.7. MS (FAB): m/z ) 235, [M
+ H]+. 1H NMR (CDCl3): δ 1.38 (s, 9 H, t-bu), 2.72 (s, 6 H, COMe),
8.02 (s, 2 H, Ar), 13.11 (s, 1 H, OH).
[Ni2(Dabfb)] (8). Using the same procedure as for 7, this compound
was synthesized from 6 and recrystallized from CH2Cl2-toluene as
dark red crystals in 65% yield. Anal. Calcd for C28H34B2F4N4Ni2O6:
C, 45.6; H, 4.6; N, 7.6. Found: C, 45.4; H, 4.7; N, 7.7. MS (FAB):
m/z ) 717, [M - F]+. 1H NMR (CDCl3): δ 1.30 (s, 9 H, t-Bu), 2.32
(s, 6 H, Me), 7.37 (s, 2 H, Ar).
The cationic macrocyclic chelates [Cu2(Dampn)]2+ and [Cu2-
(Dambn)]2+ were prepared by addition of 1,3-diaminopropane (0.78 g,
10.5 mmol) or 1,4-diaminobutane (0.92 g, 10.5 mmol), respectively,
2,6-Bis(acetoximato)-4-methylphenol (H2Damox). A solution of
NaOH (1.6 g, 40 mmol) in 15 mL of H2O was added slowly to a
refluxing solution of 2,6-diacetyl-4-methylphenol (1.92 g, 10 mmol)
and hydroxylamine hydrochloride (3.1 g, 45 mmol) in 25 mL of ethanol.
(17) Rosenmund, K. W.; Schulz, H. Arch. Pharm. (Weinheim, Ger.) 1927,
265, 308.

1030 Inorganic Chemistry, Vol. 37, No. 5, 1998
Nanda et al.
to copper(II) acetate (2.0 g, 10 mmol) in 20 mL ethanol, followed by
sodium acetate (ca. 4 g, 50 mmol) and diacetylcresol (1.92 g, 10 mmol)
in 10 mL of ethanol. After 10 h of reflux, the ethanol was (rotary)
evaporated off and replaced by water. The green complexes were
precipitated by addition of NaNO3, and the nitrate salts, recrystallized
from water and air-dried, were quantitatively metathesizable in aqueous
methanol into the ClO4- or CF3SO3- salts, which were dried over P4O10.
The nitrates release water of crystallization when desiccated, yielding
hygroscopic products.
[Cu2(Dampn)](NO3)2‚4H2O (9) (Green Prisms). Anal. Calcd for
C28H34Cu2N6O8‚4H2O: C, 44.8; H, 5.44; N, 10.8; Cu, 16.3. Found:
C, 44.4; H, 4.98; N, 10.8; Cu, 16.2. MS (FAB): m/z ) 584, [M -
2NO3]+.
[Cu2(Dampn)](ClO4)2 (10) (Green Needles). Anal. Calcd for C28-
H34Cl2Cu2N4O10: C, 42.8; H, 4.37; N, 7.14; Cu, 16.2. Found: C, 42.4;
H, 4.46; N, 6.83; Cu, 16.2. MS (FAB): m/z ) 584, [M - 2ClO4]+.
[Cu2(Dambn)](NO3)2‚2H2O (11) (Green Crystals). Anal. Calcd
for C30H38Cu2N6O8‚2H2O: C, 46.7; H, 5.43; N, 10.9; Cu, 16.4.
Found: C, 46.7; H, 5.51; N, 10.6; Cu, 16.4. MS (FAB): m/z ) 613,
[M - 2NO3]+.
[Cu2(Dambn)](ClO4)2‚CH3OH (12). Anal. Calcd for C31H42-
Cl2Cu2N4O11: C, 44.1; H, 5.01; N, 6.63; Cu, 15.0. Found: C, 44.0;
H, 4.95; N, 6.60; Cu, 14.6. MS (FAB): m/z ) 713, [M - ClO4]+
[Cu2(Dambn)](CF3SO3)2 (13) (Green Powder). Anal. Calcd for
C32H38Cu2F6N4O8S2: C, 42.2; H, 4.17; N, 6.15. Found: C, 42.5; H,
4.28; N, 5.88. MS (FAB): m/z ) 763, [M - CF3SO3]+.
[Cu(Apmpn)] (14). This neutral Schiff base chelate, a mononuclear
analogue of [Cu2(Dampn)]2+, was prepared by refluxing Cu(OAc)2‚H2O
(5 mmol) with the stoichiometric amounts of o-hydroxyacetophenone,
1,3-diaminopropane (2:1), and NEt3 (10 mmol) in MeOH (40 mL) for
2 h. The precipitate was recrystallized from MeCN and dried in vacuo
over P4O10 to give 1.2 g (3 mmol, 60%) of deep green prisms. Anal.
Calcd for C19H20CuN2O2: C, 61.4; H, 5.42; N, 7.53. Found: C, 61.6;
H, 5.57; N, 7.58.
Table 1. Crystallographic Data for [Ni2(Damox)2(Py)4]‚2Py (3a)
and [Ni2(Dabfb)] (8)
3a
8
formula
fw
cryst system
cryst size, mm
space group
a, Å
C52H54N10O6Ni2
1032.5
monoclinic
0.42 × 0.40 × 0.23
P21/n
13.297(5)
11.240(5)
17.396(6)
109.03(3)
2458(3)
2
C28H34B2F4N4O6Ni2
737.6
orthorhombic
0.40 × 0.10 × 0.10
Pnma
11.558(6)
17.200(5)
16.058(2)
90
3192(3)
4
b, Å
c, Å
â, deg
V, Å3
Z
D
calc, g cm-3
1.39
1.54
F(000)
1076
8.27
0.710 69
293
0.050, 0.052
1520
12.53
0.710 69
293
0.057, 0.057
µ, cm-1
λ(Mo KR), Å
T, K
R,a Rw
b
a R ) ∑||Fo| - |Fc||/∑|Fo|. a Rw ) [∑w(|Fo| - |Fc|)2/∑w(Fo)2]1/2
.
(8) were obtained by diffusing ether into a 1,1,2,2-tetrachloroethane
solution of the complex.
All measurements were made as previously described18 on a Rigaku
AFC6S diffractometer with graphite-monochromated Mo KR radiation.
Pertinent crystallographic data are summarized in Table 1. Cell
constants and an orientation matrix for data collection were obtained
from a least-squares refinement of setting angles of 25 reflections. The
intensities of three standard reflections measured after every 150
reflections showed no greater fluctuations than expected from Poisson
statistics. Lorentz-polarization and absorption corrections were ap-
plied. A total of 6079 and 7135 reflections were collected for [Ni2-
(Damox)2(Py)4]‚2Py (3a) and [Ni2(Dabfb)] (8), respectively, of which
5400 (Rint ) 0.152) and 3568 (Rint ) 0.110) were unique; equivalent
reflections were averaged. Of these, 2494 reflections for 3a and 1374
Physical Measurements. Infrared spectra were recorded on a
Perkin-Elmer 1610 FT-IR using KBr disks. EPR spectra were obtained
with a Varian E-12 X-band spectrometer calibrated near g ) 2 with
2
2
2
reflections for 8 had Fo > 3σF , where 3σF was estimated from
o
o
counting statistics.18,19
diphenylpicrylhydrazyl radical. g-values are (0.005 (g ) and (0.01
||
(g ); isotropic g-values ((0.005) are designated go. Electronic spectra
are from a Perkin-Elmer 330 spectrophotometer, equipped with an
integrating sphere for diffuse reflectance. Mass spectra were obtained
either on a Finnigan-4500 or a ZABHF mass spectrometer. 1H NMR
spectra were obtained on a Bruker AC 250 spectrometer using CDCl3
or acetone-d6 solutions with TMS as the internal standard. Variable-
temperature magnetic susceptibility data were collected in the range
4-300 K by using an Oxford Instruments superconducting Faraday
magnetic susceptibility system with a Sartorius 4432 microbalance. A
main solenoid field of 1.5 T and a gradient field of 10 T m-1 were
employed. Susceptibility data were corrected for diamagnetism using
Pascal’s constants. HgCo(NCS)4 was used as a calibration standard.
Data were analyzed using SAS Institute’s JMP-3.1 or MathSoft’s
MathCad Plus-6 least-squares procedures on a Macintosh 603e platform.
Electrochemical measurements were made at 25 °C in deoxygenated
CH3CN, pyridine, or DMF solutions using a BAS 100A electrochemical
analyzer or a PAR-173/175/176 system incorporating an MPI MP-1012
integrator. The three-electrode assembly comprised the working
electrode, an Ag+ (0.01 M, 0.1 M NEt4ClO4, CH3CN)/Ag reference
electrode, and a Pt auxiliary electrode. The working electrodes were
Pt disk, beads, or wires for voltammetry at scan rates from 20 to 2000
mV s-1 and a Pt disk for rotating electrode (rde) polarography (wherein
the E1/2’s are defined as the potential at which i ) iL/2). The supporting
electrolyte was 0.1-0.2 M NEt4ClO4, and solutions for voltammetry
and polarography were ca. 1 mM in complex. Coulometry was
performed on analytes at the 10-2 M level at a Pt-gauze electrode with
the Pt counter electrode separated in a compartment of permeable
Vycor.
The metal atoms were located from 3-D Patterson maps and the
rest of the non-hydrogen atoms emerged from successive Fourier
synthesis. In the case of [Ni2(Damox)2(Py)4]‚2Py (3a), 6-fold positional
disorder around the pyridine hexagon in the pyridine molecules of
solvation makes the six sites equivalent so that each of the H-locations
in the hexagon corresponds to 5/6 of a full H. In [Ni2(Dabfb)] (8), the
molecule lies on a symmetry plane with the two halves on either side
of the O(1)-O(2) line of bridging oxygens. One of the two tert-butyl
groups in 8 exhibits rotational disorder. The structures were refined
by full-matrix least-squares methods using the TEXRAY20 program
set. Neutral atom scattering factors were taken from Cromer and
Waber.21 All the non-hydrogen atoms were refined anisotropically
except for the disordered tert-butyl carbons, while the hydrogen atoms
were placed at the geometrically calculated positions with fixed isotropic
thermal parameters. The highest residues were 0.38 e Å-3 (3a) and
0.54 e Å-3 (8). Atomic coordinates for the most important atoms of
3a and 8 are given in Tables 2 and 3, respectively.
Results and Discussion
Synthesis. The oximes of the diacetyl phenols (H2Damox
and H2Dabox) are prepared in good yields via their reaction
with excess NH2OH. H2Damox is a photosensitive compound.
The dicopper(II) complex, [Cu2(Damox)2] (1), is stable enough
to be prepared in glacial acetic acid using equivalent amounts
(18) Backhouse, J. R.; Lowe, H. M.; Sinn, E.; Suzuki, S.; Woodward, S.
J. Chem. Soc., Dalton Trans. 1995, 1489.
(19) Corfield, P. W. P.; Doedens, R. J.; Ibers, J. A. Inorg. Chem. 1967, 6,
197.
(20) TEXSAN-TEXRAY Structure Analysis Package; Molecular Structure
Corp: The Woodlands, TX, 1985.
(21) Cromer, D. T.; Waber, J. T. International Tables for X-ray Crystal-
lography; The Kynoch Press: Birmingham, England, 1974; Vol. IV.
X-ray Crystallography. Single crystals of [Ni2(Damox)2(Py)4]‚
2Py (3a) were obtained from a saturated solution of [Ni2(Damox)2-
(MeOH) ]‚MeOH (2) in pyridine. These crystals are unstable when
2
dry, so the one used for the X-ray crystallographic study was sealed in
a capillary tube with mother liquor. Single crystals of [Ni2(Dabfb)]

CuII and NiII Complexes of Dinucleating Macrocycles
Inorganic Chemistry, Vol. 37, No. 5, 1998 1031
Table 2. Positional Parameters for Selected Atoms of
[Ni2(Damox)2(Py)4]‚2Py (3a)
atom
x
y
z
Ni
-0.07599(7)
-0.0806(3)
-0.2839(4)
0.1399(4)
-0.0404(4)
0.0501(4)
-0.2354(4)
-0.1278(4)
-0.1564(5)
-0.2642(5)
-0.1369(5)
-0.2998(5)
-0.0327(5)
-0.178(2)
-0.10621(7)
0.0725(3)
-0.2140(4)
0.3463(4)
-0.1457(4)
0.2777(4)
-0.1074(5)
-0.0816(4)
0.1448(5)
0.1022(6)
0.2675(5)
-0.0189(6)
0.3274(5)
0.259(2)
-0.01774(5)
0.0018(2)
-0.0614(3)
0.0594(3)
0.1095(3)
0.0399(3)
-0.0363(3)
-0.1544(3)
0.0052(3)
-0.0154(3)
0.0278(3)
-0.0403(4)
0.0505(4)
0.379(1)
O(1)
O(2)
O(3)
N(1)
N(2)
N(3)
N(4)
C(1)
C(2)
C(6)
C(8)
C(10)
N(41)a
a Occupancy 0.420.
Table 3. Positional Parameters for Selected Atoms of [Ni2(Dabfb)]
(8)
atom
x
y
z
occ
Ni
0.18314(8)
0.2673(6)
0.0984(6)
0.3011(5)
0.1308(5)
0.2810(6)
0.0866(6)
0.257(1)
0.16771(5)
0.04537(6)
0.0001(5)
0.0883(5)
0.0321(4)
0.1155(4)
-0.0059(5)
0.0962(4)
0.1183(8)
-0.0778(8)
-0.1180(5)
-0.0756(6)
0.0994(6)
0.1071(5)
0.1159(5)
1
1
O(1)
O(2)
O(3)
O(4)
N(1)
N(2)
B
C(1)
C(2)
C(5)
C(11)
C(12)
C(15)
/
/
/
/
4
2
1
1
4
2
0.0244(3)
0.0233(3)
0.0962(3)
0.0946(4)
Figure 1. ORTEP representation (H’s omitted for clarity of presenta-
tion) of [Ni2(Damox)2(Py)4] in [Ni2(Damox)2(Py)4]‚(Py)2 (3a).
0.0191(7)
the transitions 3A2g f 3T2g, 3A2g f 3T1g, and 3A2g f 3T1g(P).23
Furthermore, the spectrum of [Ni2(Damox)2(Py)2]‚Py (3) in the
solid state is similar to that of solid [Ni2(Damox)2(MeOH)2]‚
MeOH (2) and solid [Ni2(Dabox)2(H2O)2] (6), for which six-
coordination is implausible. The bands observed are of energy
similar to those of other well-characterized square-pyramidal
high-spin nickel(II) complexes,1,23,24 while [Ni2(Dabfb)] (8) in
CH2Cl2 solution exhibits a single intense d-d band at 540 nm,
characteristic of diamagnetic square-planar nickel(II) com-
plexes.25,26 This complex’s unexpected resistance to adopting
hexacoordination is evidenced by its optical spectrum in neat
γ-picoline, which again appears to be that of a pentacoordinate
nickel system rather than of a tetrakis(picoline) adduct.
All of the copper(II) complexes show a d-d transition around
600 nm, which is typical of square-planar N2O2-ligated copper-
(II), and a shoulder in the 405-435 nm range which can be
assigned to O-(phenolate) f Cu(II) charge transfer.27 Intense
absorption in the ultraviolet region is a feature common to all
the copper(II) and nickel(II) complexes and is attributed to
intraligand charge-transfer transition.
Description of the Structure of [Ni2(Damox)2(Py)4]‚(Py)2
(3a). The ORTEP representation of 3a is given in Figure 1,
and interatomic distances and angles relevant to the coordination
sphere are given in Table 5. The centrosymmetric structure
contains two nickel centers bridged by two phenoxide oxygen
atoms with two imine nitrogen donors completing the NiN2O2
equatorial plane. The center of inversion is between the two
nickel ions. Each of the metal centers achieves a pseudo-
octahedral configuration through the axial coordination of
1
1
0.306(1)
/
/
4
2
0.3326(6)
0.3361(7)
-0.019(1)
-0.0778(6)
-0.0216(7)
0.1798(4)
0.1050(5)
1
1
/
/
4
2
0.1799(5)
0.1044(5)
of H2Damox and Cu(CH3COO)2‚H2O. This compound is
insoluble in common organic solvents, but obtained as pure
microcrystals by diluting the reaction mixture with EtOH. All
the other dicopper(II) and dinickel(II) complexes of the oximes
were obtained from the reaction of the corresponding oxime
and metal(II) acetate in MeOH. Pyridine solutions of [Ni2-
(Damox)2(MeOH)2]‚MeOH (2) afford pink crystals of [Ni2-
(Damox)2(Py)4]‚2Py (3a). These crystals effloresce coordinated
as well as solvent of crystallization pyridine molecules to form
[Ni2(Damox)2(Py)2]‚Py (3). For comparative purposes, a cop-
per(II) N2O2 chelate was prepared from the mononucleating
Schiff base ligand (ApmpnH2) prepared from condensing 1,3-
diaminopropane in 1:2 ratio with the singly acetylated phenol,
o-hydroxyacetophenone. Macrocyclization of the dioximato
complexes was effected by treating them with boron trifluoride
ethyl etherate.22 In the case of [Ni2(Damox)2(MeOH)2]‚MeOH
(2), we were unable to isolate the pure BF2-bridged macrocyclic
complex. Compounds of the M2(Damox)2 type are relatively
insoluble in most common solvents unless they are strongly
coordinating (such as pyridine). Although this insolubility can
be significantly ameliorated by using the tert-butyl rather than
the methyl derivatives, some difficulties remained for solution
studies.
Electronic Spectra. The electronic spectral data for the
complexes are summarized in Table 4. The spectrum of [Ni2-
(Damox)2(Py)4]‚2Py, generated by dissolving [Ni2(Damox)2-
(Py)2]‚Py in pyridine, exhibits three d-d bands at 900, 595,
and 470 nm. These are attributed in an octahedral model to
(23) Lever, A. B. P. Inorganic Electronic Spectroscopy, 2nd ed.; Elsevier:
New York, 1984.
(24) Nanda, K. K.; Das, R.; Newlands, M. J.; Hynes, R.; Gabe, E. J.; Nag,
K. J. Chem. Soc., Dalton Trans. 1992, 897.
(25) Streeky, J. A.; Pillsbury, D. G.; Busch, D. H. Inorg. Chem. 1980, 19,
3148
(26) Nanda, K. K.; Das, R.; Venkatsubramanian, K.; Paul, P.; Nag, K. J.
Chem. Soc., Dalton Trans. 1993, 2515.
(27) Amundsen, A. R.; Whelan, J.; Bosnich, B. J. Am. Chem. Soc. 1977,
99, 6730.
(22) Addison, A. W.; Carpenter, M.; Lau, L. K.-M.; Wicholas, M. Inorg.
Chem. 1978, 17, 1545: CO-binding constant estimates from KI ) (1/
a
CO)(e0.03892∆E - 1), ∆E in mV.

1032 Inorganic Chemistry, Vol. 37, No. 5, 1998
Nanda et al.
Table 4. Electronic Spectrala Data for the Complexes
complex
medium
λ )
max, nm (ꢀ, M-1 cm-1
[Cu2(Damox)2] (1)
[Cu2(Damox)2]
[Ni2(Damox)2(MeOH)2]‚MeOH (2)
[Ni2(Damox)2(Py)2]‚Py (3)
[Ni2(Damox)2(Py)2]‚Py
[Cu2(Damfb)] (4)
solid state
pyridine
solid state
solid state
pyridine
CH2Cl2
620, 430 (sh), 370 (sh)
625 (650), 355 (15 900), 307 (19 300)
1250 (br), 1000 (br), 600, 410 (sh), 360
1600, 980, 625, 470 (sh), 380
900 (20), 595 (52), 470 (180)
600 (125, sh), 405 (1,070, sh),
340 (11 200)
[Cu2(Damfb)]
[Cu2(Damfb)]
[Cu2(Damfb)]
[Cu2(Dabox)2] (5)
[Ni2(Dabox)2(H2O)2] (6)
[Cu2(Dabfb)]‚H2O (7)
[Ni2(Dabfb)] (8)
acetone
pyridine
DMF
solid state
CH2Cl2
CH2Cl2
DMF
610 (100), 344 (12,100)
635 (390), 353 (11 300), 305 (5900)
598 (290), 420 (1,700, sh), 348 (14 200)
1175, 600 (br), 430 (sh), 345 (sh)
615 (135, sh), 435 (1,360, sh), 390 (11 400)
540 (320), 348 (7,750)
[Ni2(Dabfb)]
1060 (87), 495 (sh, 114), 355 (9830)
[Ni2(Dabfb)]
γ-picoline
1570 (34), 855 (18), 800 (16, sh), 585 (52), 360 (9820)
575 (156), 352 (16 200)
590 (370), 358 (13 300), 305 (4,100)
625 (116), 350 (15 200)
625 (500), 360 (9000), 305 (7200)
580 (265), 360 (11 000)
[Cu2(Dampn)](NO3)2‚4H2O (9)
[Cu2(Dampn)](NO3)2‚4H2O
[Cu2(Dambn)](NO3)2‚2H2O (11)
[Cu2(Dambn)](NO3)2‚2H2O
[Cu(Apmpn)] (14)
MeOH
pyridine
MeOH
pyridine
CH3CN
a Solid-state data from diffuse reflectance in MgCO3 matrix.
Table 5. Selected Interatomic Distances (Å) and Angles (deg) for
[Ni2(Damox)2(Py)4]‚2Py (3a)
Ni‚‚‚Ni′
Ni-N(1)
Ni-N(3)
3.058(2)
2.154(5)
2.038(6)
Ni-O(1)
Ni-N(2)
Ni-N(4)
2.042(4)
2.017(5)
2.265(5)
O(1)-Ni-O(1)
O(1)-Ni-N(2)
O(1)-Ni-N(4)
O(1)-Ni-N(2)
O(1)-Ni-N(4)
N(1)-Ni-N(3)
N(2)-Ni-N(3)
Ni-O(1)-Ni
83.1(2)
171.2(2)
92.2(2)
88.5(2)
93.9(2)
91.7(2)
101.4(2)
96.9(2)
O(1)-Ni-N(1)
O(1)-Ni-N(3)
O(1)-Ni-N(1)
O(1)-Ni-N(3)
N(1)-Ni-N(2)
N(1)-Ni-N(4)
N(2)-Ni-N(4)
N(3)-Ni-N(4)
92.3(2)
87.0(2)
91.5(2)
169.7(2)
90.3(2)
173.4(2)
85.9(2)
83.7(2)
pyridine nitrogens. The two nickel atoms are separated by 3.058
Å with a Ni-O-Ni bridge angle of 96.9°. On each nickel, the
two Ni-N(pyridine) bonds are, however, not equal (Ni-N(1)
) 2.154 and Ni-N(4) ) 2.265 Å). The pyridine rings on the
same side of the metals’ equatorial plane are almost parallel
(the rings are inclined at 12.5° to each other) and are separated
by approximately 3.5 Å. This π-interaction is probably
responsible for the stability of the octahedral tetrapyridine adduct
in pyridine solution and in the solid state under a sensible
pyridine vapor pressure. The apparent equivalence of the two
nickels in Ni2(Damox)2(Py)3 indicates that the hexapyridine
adduct loses two coordinated pyridine molecules and a pyridine
of solvation in the absence of pyridine vapor and forms square-
pyramidal [Ni2(Damox)2(Py)2]‚Py (3). Strong H-bonding be-
tween oxime-H’s and oximato-O’s renders the structure
pseudomacrocyclic.
Description of the Structure of [Ni2(Dabfb)] (8). The
molecule consists of a neutral binuclear nickel(II) complex with
no close intermolecular contacts. The asymmetric unit consists
of half the molecule, the other half being mirrored in a plane
that bisects the O(1)-O(2) line of the bridging phenoxide
oxygen atoms. The ORTEP representation of 8 with the atom-
numbering scheme is given in Figure 2a, and interatomic
distances and angles relevant to the nickel coordination sphere
are in Table 6. The molecular diagram in Figure 2b shows the
marked saddle-shaped bending of the macrocyclic ligand. This
dramatic curvature puts the boron atoms a full 1.45 Å above
the NiN2O2 center. Molecular models indicate that diimine end
caps on the dimetallic bis(diimino-phenolate) moiety would
be essentially planar if these diimine ends were closed off as
Figure 2. (a) Top: ORTEP diagram and atom-labeling scheme of [Ni2-
(Dabfb)] (8) (H’s omitted for clarity). (b) Bottom: Perspective view
showing the saddle shape of the molecule.
five-membered rings. However, construction of the six-
membered ring (NiBN2O2) forces out of the plane the only ring

CuII and NiII Complexes of Dinucleating Macrocycles
Inorganic Chemistry, Vol. 37, No. 5, 1998 1033
Table 6. Selected Interatomic Distances (Å) and Angles (deg) for
[Ni2(Dabfb)] (8)
Ni‚‚‚Ni′
2.831(2)
1.36(1)
1.396(7)
1.869(6)
1.48(1)
1.35(1)
Ni-O(1)
Ni-O(2)
Ni-N(1)
O(4)-N(2)
O(4)-B
1.865(5)
1.854(5)
1.863(7)
1.364(7)
1.46(1)
O(2)-C(11)
O(3)-N(1)
Ni-N(2)
O(3)-B
F(1)-B
F(2)-B
1.38(1)
O(1)-Ni-O(2)
O(1)-Ni-N(1)
O(1)-Ni-N(2)
O(2)-Ni-N(1)
O(2)-Ni-N(2)
F(1)-B-F(2)
F(1)-B-O(3)
F(1)-B-O(4)
F(2)-B-O(4)
O(3)-B-O(4)
80.9(2)
90.7(3)
172.9(3)
171.6(3)
92.1(3)
N(2)-O(4)-B
Ni-N(1)-O(3)
O(3)-N(1)-C(5)
Ni-N(2)-O(4)
N(1)-Ni-N(2)
Ni-O(1)-Ni′
Ni-O(2)-Ni′
F(2)-B-O(3)
N(1)-O(3)-B
115.2(7)
119.5(5)
113.5(6)
118.7(5)
96.4(3)
98.7(3)
99.5(3)
114(1)
Figure 3. Cyclic voltammogram of [Ni2(Dabfb)] in CH3CN with Pt
106.0(8)
108.4(9)
110.1(9)
108.2(9)
working and auxiliary electrodes and Ag+ (0.01 M, 0.1 M NEt4ClO4,
109.6(9)
113.9(7)
CH3CN)/Ag reference electrode at a scan rate of 100 mV s-1
.
previously,2,28-30 and the normally substantial separation (E1
- E2) had generally been considered to be dominated by
Coulombic effects,28,29 though later work31 has called this
proposition into doubt. Nonetheless, simple extrapolation of
the E1 - E2 values for dinuclear ruthenium(III/II) systems32,33
with 5-11 Å Ru-Ru separations to the 2.85 Å Cu-Cu
distances in the present compounds34 leads to an E1 - E2 of
220-320 mV. In addition, a naive estimate for the change in
Coulombic work for electron addition to a binuclear center:35
Table 7. Electrochemicala Data for the Complexes
b
E1/2
MIIMII/
MIIMI
MIIMI/
MIMI
complex
medium
DMF
108Dηc
[Cu2(Damox)2] (1)
[Cu2(Damox)2] (1)
[Cu2(Damox)2] (1)
[Cu2(Damfb)] (4)
[Cu2(Dabox)2] (5)
[Cu2(Dabfb)]‚H2O (7)
[Ni2(Dabfb)] (8)
[Cu2(Dampn)](ClO4)2 (10)
[Cu2(Dampn)](ClO4)2 (10)
[Cu2(Dampn)](ClO4)2 (10)
[Cu2(Dambn)](ClO4)2 (12)
[Cu2(Dambn)](CF3SO3)2 (13) DMF
[Cu2(Dambn)](CF3SO3)2 (13) DMF/CO -0.72 (r) -1.07 (q)
[Cu(Apmpn)] (14)
-1.22 (q) -1.58 (i)d
1.1
1.1
2.4
1.5
1.8
1.8
1.8
1.0
1.0
3.3
1.3
1.6
1.6
1.1
DMF/CO -1.16 (q)e -1.71 (i)f
Pyridine -1.17 (q) -1.72 (i)
DMF
DMF
DMF
-0.94 (q) -1.45 (q)
-1.24 (q) -1.68 (q)
-0.93 (q) -1.45 (q)
CH3CN -1.15 (q) -1.54 (q)
DMF
-0.96 (q)
g,h
g
DMF/CO -0.88 (i)f
MeNO2 -0.80f
-1.13f
DMF
-0.80 (q) -1.17 (i)
-0.78 (r) -1.17 (q)
CH3CN -1.43 (i)
a E1/2 in V vs Ag+ (0.01 M, 0.1 M NEt4ClO4, CH3CN)/Ag with Pt
electrode, scan rate 0.1 V s-1. This electrode is at ca. +0.545 V vs the
yields a value of 340 mV for the change in E1/2 of CuA due to
the change in Coulombic potential associated with CuB.
Electrostatic effects are also consistent with the lowered E1/2
seen for [Cu(Apmpn)], the uncharged mononuclear analogue
of [Cu2(Dampn)]2+. These approaches support the contention
that the electrostatic factor is a major if not the dominant
component of E1 - E2.
SHE. b Key: i, irreversible (Ep,c); q, quasireversible (mean of Ep,c, Ep,a);
d
r, reversible. c Dη in g cm s-2, not adjusted for R, Ψ.36
E1/2 values
are -1.23 and -1.59 V in rde polarogram. H2Damox itself has an
e
irreversible reduction with E1/2 ) -2.22 V in MeCN. Epc ) -1.175
V. E1/2 values in rde polarogram. g Poorly defined wave at E1/2
)
f
-1.35 V in rde polarogram. h -1.66 V in MeCN.
Analysis of the appropriate current functions36-38 for the
compounds indeed yielded Dη values ((1-3) × 10-8, Table 7)
consistent with n ) 1 processes,39 and this was confirmed in
the case of [Cu2(Dambn)](ClO4)2 by its n ) 2 coulometry in
DMF/NEt4ClO4 at - 1.5 V at a Pt-mesh cathode, the i:Q plot40
for 100 µmol of which extrapolated to 210 µF at t ) ∞. The
reduced nickel chelates do not all possess long-term stability,
atom (B) not attached to the obligatorily trigonal nitrogens. The
Schiff base ligand planes O(1)-C(1)-C(2)-C(5)-N(1) and
O(2)-C(11)-C(12)-C(15)-N(2) make angles of 32.4 and
27.7°, respectively, with the Ni2O2 plane and 59.4° with each
other. The phenyl rings C(1)-C(12)-C(13)-C(14)-C(13)′-
C(14)′ are at 36.1 and 32.3°, respectively with the NiN2O2 center
and 68.4° with each other. On the other hand, the first
coordination sphere about the nickel atoms is planar within 1°,
and the 1H-NMR confirms the S ) 0 nature of the nickel ions.
Redox Properties. The compounds are readily reducible
from the MIIMII to the MIMII level (Table 7), as exemplified in
Figure 3, and in all but a few cases this process is at least
quasireversible on the voltammetry time scale, the ∆Ep values
being 15-90 mV greater than those for a Nernstian standard
under the same conditions. (The following discussion assumes
that kr = kf (≡ko) for the quasireversible processes.) The
sequential nature of the reductions
(28) Gagne´, R. R.; Koval, C. A.; Smith, T. J.; Cimolino, M. C. J. Am.
Chem. Soc. 1979, 101, 4571.
(29) Long, R. C.; Hendrickson, D. N. J. Am. Chem. Soc. 1983, 105, 1513.
(30) Mandal, S. K.; Nag, K. J. Chem. Soc., Dalton Trans. 1983, 2429.
(31) Mandal, S. K.; Adhikary, B.; Nag, K. J. Chem. Soc., Dalton Trans.
1986, 1175.
(32) Goldsby, K. A.; Meyer, T. J. Inorg. Chem. 1984, 23, 3002.
(33) Sutton, J. E.; Sutton, P. M.; Taube, H. Inorg. Chem. 1979, 18, 1017.
(34) Carlisle, W. D.; Fenton, D. E.; Roberts, P. B.; Casellato, U.; Vigato,
P. A.; Graziani, R. Trans. Met. Chem. (Weinheim) 1986, 11, 292.
(35) Using E ) (Nqe/4πꢀ)((qA/x) + (qB/d)), adopting a value of 35ꢀo for
the dielectric (typical of DMF, MeCN, and MeNO2) and a value of
+4.35 V for the absolute potential of the SHE, and thus setting d )
2.85 Å and x ) 0.23 Å to match an E1 of -0.45 V vs SHE.
(36) Nicholson, R. S.; Shain, I. Anal. Chem. 1964, 36, 706.
(37) Piekarski, S.; Adams, R. N. in Techniques of Chemistry, Weissberger,
A., Rossiter, B. W., Eds.; Wiley-Interscience: New York, 1971; Vol.
1, Part IIA, p 541.
MIIMII + e- f MIIMI
MIIMI + e- f MIMI
E1
E2
(38) (a) Stephens, M. M.; Moorhead, E. D. J. Electroanal. Chem. 1984,
164, 17. (b) Varadharajan, U.; Butcher, R. J.; Kanters, R. F. P.;
Addison, A. W.; Jasinski, J. P. Submitted for publication.
in such bis(µ-phenoxo) systems has been explored

1034 Inorganic Chemistry, Vol. 37, No. 5, 1998
Nanda et al.
as evidenced by significantly less than unity values for ipa,ipc,
for example for [Ni2(Dabfb)]. Indeed, a butyronitrile/NEt4ClO4
solution in which [Ni2(Dabfb)]- had been cathodically electro-
generated yielded no EPR signal at 77 K. Similarly, the fully
reduced [CuI2(Dabox)2]2- is not stable in DMF while
[CuI2(Damox)2]2- and [CuI2(Dambn)]0 are unstable in pyridine,
as revealed by the irreversible voltammograms (∆Ep,corr > 70
mV, ipa,ipc , 1) for their generation (Table 7). The oxidative
electrochemistry is also generally irreversible, as typically
represented by an n ) 1 wave at +0.65 V in the rde polarogram
of Cu2(Damox) and an oxidation at ca. +1.5 V for [Ni2(Dabfb)].
However, some interactions of the reduced species with carbon
monoxide were observable in DMF solution; the carbonyl
formed by the 2,6-diformyl-4-methylphenol-derived analogue
of [Cu2(Dampn)]+/0 has been examined previously in MeCN
by Gagne´ et al.28,41 We were initially surprised to see that in
DMF under 1 atm of CO the reversible E1 process for the copper
complex of the quite basic ligand Damox becomes completely
irreversible (ipa,ipc , 1). The same is true for [Cu2(Damfb)]
and [Cu2(Dampn)]2+. On the other hand, for [Cu2(Dambn)]2+
both voltammetric waves move to more anodic potential under
CO and their reversibility is not significantly affected (Table
7). The concomitant shifts enable estimation22 of these rather
weak copper(I)-CO binding constants as KIA1 ) 12 ( 2 atm-1
and KIB1 ) 50 ( 9 atm-1. We conclude that ligand structural
flexibility (for stabilization of a Cu(I)-CO center with nonplanar
geometry) is a more effective influence on CO-adduct formation
than the increased donor basicity in the more rigid Damox2-
complex. One might also note that the decrease in E1 - E2
under CO is in itself indicative of positive cooperativity (ca. 4
kJ mol-1) between the two copper centers in [Cu(Dambn)], for
CO binding. The structural and spectroscopic details germane
to the cooperativity will be addressed elsewhere.
Figure 4. First-derivative EPR spectra of mixed-valence CuICuII
complexes in MeCN: (a) [Cu2(Dampn)]+ at ambient temperature, with
go ) 2.113, Ao(Cu) ) 81 × 10-4 cm-1, and Ao(N) ) 14 × 10-4 cm-1
.
The shf-structure from the two imine N’s on the CuII are most evident
in the highest-field resonance line. (b) [Cu2(Dambn)]+ at 77 K.
Overlapping Cu hf and imine-N shf contribute to the ∼8-line fine
structure typical of a CuNN center, around 3150 G with aN and a
≈
Cu
13 G.
dependence of E1 - E2 itself is apparent, others workers having
commented on the consequences for the resulting compropor-
tionation constant.31 The full range of variation in this quantity
(from 360 to 560 mV) across the complexes is expressed by
just Cu2(Damox)2 between DMF and pyridine as solvents, while
the effects of CO on the voltammograms are qualitatively quite
solvent dependent as well.
A few other features also emerge from the redox results.
Replacing -OHO- by -OB(F2)O- raises the E1/2 values by a
few hundred mV,22,42 while the more flexible butylene linkages
raises the E1/2 vs the propylene ones.43,44 Similarly, the chelates
analogous to [Cu2(Dampn)]2+ and [Cu2(Dambn)]2+ but prepared
from 2,6-diformyl-4-tert-butylphenol show elevations in DMF
of 133 and 2 mV for the two waves,29 while those from 2,6-
diformyl-4-methylphenol show elevations of 90 and 130 mV
for the two waves in dimethyl sulfoxide.45 In connection with
these results, axial interaction with solvent molecules renders
the redox potentials quite solvent-sensitive, as is seen from the
progression of the CuIICuII/CuICuII E1/2’s for [Cu2(Dampn)]2+
and [Cu2(Dambn)]2+ in DMF (-0.96, -0.80 V, respectively)
vs CH3CN (-0.74 and - 0.63 V, respectively2) and Cu2-
(Damox)2 in pyridine (-1.65 V) vs DMF (-1.22 V): the greater
axial donicity stabilizes Cu(II) relative to Cu(I). Solvent
Cathodic n ) 1 electrolyses of the EPR-silent CH3CN
solutions of [Cu2(Dampn)]2+ and [Cu2(Dambn)]2+ (the latter
with NBu4PF6) at the appropriate potentials yielded the mixed-
valence species [Cu2(Dampn)]+ and [Cu2(Dampbn)]+. The S
1
3
) /2, I ) /2 EPR spectra (Figure 4) obtained for these, each
including shf-lines from two unsaturated nitrogen donor atoms
in the g region, characterize both complexes as being valence-
localized at both ambient temperature and 77 K. These
resonances for [Cu2(Dampn)]+ (g ) 2.222, A ) 207 × 10-4
||
||
||
cm-1, g ) 2.05) and [Cu2(Dambn)]+ (77 K, g ) 2.239, A )
||
177, g ) 2.05; 295 K, go ) 2.117, Ao ) 63 × 10-4 cm-1
)
may be compared with those43 for planar cis-CuN2O2 chelates
such as [Cu(Apmpn)] (g ) 2.243, A ) 186, g ) 2.10 in
||
||
(39) (a) Addison, A. W.; Rao, T. N.; Sinn, E. Inorg. Chem. 1984, 23, 1957.
(b) McDevitt, M. R.; A. W. Addison, A. W. Inorg. Chim. Acta 1993,
204, 141. This product of the diffusion coefficient and the medium’s
viscosity, Dη, corresponds to RT/6πNr, where r is the effective Stokes-
Einstein radius (Semenikhin, O. A. Personal communication, 1996),
CH3CN) which indicate that the nonreduced Cu2+ centers retain
their tetragonal stereochemistry. It is interesting to note that
replacement of the acyl methyl groups by protons in [Cu2-
(Dambn)]+ is a major contributory factor for transformation of
the system from a valence-localized to a valence-delocalized
one at ambient temperature in CH3CN,45 acting as a reminder
of the dramatic sensitivity of the delocalization rate to substit-
uents (and solvent).29
whence ip,rev (µA) ) 0.0125 AC*V1/2n3/2r-1/2η-1/2 (mM, cgsu, r in Å).
o
(40) Addison, A. W.; Dalal, N. S.; Hoyano, Y.; Huizinga, S.; Weiler, L.
Can. J. Chem. 1977, 55, 4191.
(41) Gagne´, R. R.; Allison, J. L.; Ingle, D. M. Inorg. Chem., 1979, 18,
2767.
(42) Addison, A. W.; Watts, B.; Wicholas, M. Inorg. Chem. 1984, 23, 813.
(43) (a) Yokoi, H.; Addison, A. W. Inorg. Chem. 1977, 16, 1341. (b)
Sakaguchi, U.; Addison, A. W. J. Chem. Soc., Dalton Trans. 1979,
600.
(44) Nanda, K. K.; Addison, A. W.; Butcher, R. J.; McDevitt, M. R.; Rao,
T. N.; Sinn, E. Inorg. Chem. 1997, 36, 134.
Magnetochemistry. Variable-temperature magnetic suscep-
tometry was performed for [Cu2(Damox)2] (1), [Ni2(Damox)2-
(MeOH)2]‚MeOH (2), [Ni2(Damox)2(Py)2]‚Py (3), [Cu2(Damfb)]
(4), [Cu2(Dabox)2] (5), [Ni2(Dabox)2(H2O)2] (6), [Cu2(Dampn)]-
(NO3)2‚4H2O (9), and [Cu2(Dambn)](NO3)2‚2H2O (11). The
(45) Mandal, S. K.; Thompson, L. K.; Newlands, M. J.; Gabe, E. J. Inorg.
Chem. 1989, 28, 3707.

CuII and NiII Complexes of Dinucleating Macrocycles
Inorganic Chemistry, Vol. 37, No. 5, 1998 1035
Table 8. Magnetic Data for the Complexes
complex
-2J, cm-1
g
zJ′, cm-1
-0.69
D, cm-1
Fa,b
[Cu2(Damox)2] (1)
[Ni2(Damox)2(MeOH)2]‚
MeOH (2)
554
3.2
2.15
2.08
<10-6
4.66
2 × 10-4
[Ni2(Damox)2(Py)2]‚Py (3)
[Cu2(Damfb)] (4)
[Cu2(Dabox)2] (5)
[Ni2(Dabox)2(H2O)2] (6)
[Cu2(Dampn)](NO3)2‚
4H2O (9)
19.5
778
738
-5.1
656
2.16
2.2
2.11
2.17
2.13
-2.33
15.82
1 × 10-3
1.4 × 10-2
1.4 × 10-2
7 × 10-5
<10-6
-9.4 × 10-5
9.55
[Cu2(Dambn)](NO3)2‚
2H2O (11)
594
2.13
8 × 10-3
1
a Fraction of paramagnetic impurity. b EPR data for S ) /2 copper(II) impurity centers: [Cu2(Damox)2] g| ) 2.317, A| ) 162 × 10-4 cm-1, g
) 2.061; [Cu2(Dabox)2], g| ) 2.205, g ) 2.060; [Cu2(Dabfb)]‚H2O, g| ) 2.206, g ) 2.060; [Cu2(Dampn)](NO3)2‚4H2O, g| ) 2.251, g ) 2.072;
[Cu2(Dambn)](NO3)2‚2H2O, g| ) 2.251, g ) 2.075. When appropriate, these values were used for gj.
same order of magnitude as the electron spin-exchange integral
(J).50 Accordingly, a magnetic model (eq 2)
2Ng2â2
3k
kF1(J,D,T)
øm(J,g,D,zJ′,F) )
+
[
kT - 4 zJ′F1(J,D,T)
4FNg2â2
2kF′(J,D,T)
(1 - F) +
+ 2tip (2)
F4(J,D,T)
]
3kT
1 - 4zJ′F′(J,D,T)
2
3C2
1
D
F′(J,D,T) ) F2(J,D,T) +
F3(J,D,T) +
3J - δ
2
3C1
3J + δ
F1(J,D,T) )
1 + e4J/kT + 4e4J/kTeD/kT
-δ/kT + eJ/kT δ/kT + 2e4J/kT + 2e4JkTeD/kT
Figure 5. Variable-temperature magnetic data for [Cu2(Damfb)] (4).
The points [ represent the experimental data, and the solid line
represents the fit to eq 1.
2 + eD/kT + eJ/kT
F2(J,D,T) )
e
e
results are summarized in Table 8, and some data are depicted
as øT vs T plots in Figures 5-7.
2e4J/kTeD/kT + eD/kT - 1 - 2e4J/kT
2 + eD/kT + eJ/kT
F3(J,D,T) )
e
e
e
-δ/kT + eJ/kT δ/kT + 2e4J/kT + 2e4JkTeD/kT
e
For the dicopper(II) complexes [Cu2(Damox)2] (1), [Cu2-
(Damfb)] (4), and [Cu2(Dabox)2] (5) the ømT values increase
with rising temperature, which indicates antiferromagnetic
exchange interactions between the copper(II) centers. The
variable-temperature magnetic susceptibility data for these
complexes were fitted to the modified Bleaney-Bowers equa-
tion46 (eq 2) using the isotropic exchange Hamiltonian (H )
e
4J/kT - eJ/kTeδ/kT
-δ/kT + eJ/kT δ/kT + 2e4J/kT + 2e4JkTeD/kT
2 + eD/kT + eJ/kT
F4(J,D,T) )
e
1
-2JS1‚S2) for the two interacting S ) /2 centers:
e
4J/kT - eJ/kTe-δ/kT
-δ/kT + eJ/kT δ/kT + 2e4J/kT + 2e4JkTeD/kT
2 + eD/kT + eJ/kT
e
2Ng2â2
kT(3 + e-J/kT
2Ng2â2F
4kT
øm(J,g,F) )
(1 - F) +
+ 2tip (1)
δ ) [(3J + D)2 - 8JD]1/2
)
F and tip are the fraction of metal possibly present as a
paramagnetic impurity and the temperature-independent para-
magnetism per metal ion, respectively, the tip for Cu2+ being
2.828D
C1 )
[(9J - D + 3δ)2 + 8D2]1/2
taken to be 6 × 10-5 cm3 g atom-1 47
.
In all of the above
9J - D + 3δ
[(9J - D + 3δ)2 + 8D2]1/2
C2 )
copper(II) complexes, the metal ions are very strongly antiferro-
magnetically coupled, which is commonly observed in phenoxo-
bridged dicopper(II) complexes of this type.48,49 Figure 5 shows
the temperature dependence of ømT for [Cu2(Damfb)] (4).
For dinuclear nickel(II) complexes, the zero-field splitting
is used which includes zero-field splitting (D), the usual
intradimer exchange (J), and also an interdimer exchange
parameter (zJ′). The resulting magnetic susceptibility equation,
ø(g,J,D,zJ′,F), derived by Ginsberg et al.50 and corrected by
Wen51 has been used to fit the magnetic data for the dinickel-
(II) complexes, 2, 3, and 6. Equation 2 yields the susceptibility
ø/mole of dinuclear complex, the term zJ′ representing any
3
3
of the S ) 1 ground state (3T1, A2g, or B1g) is often of the
(46) Bleaney, B.; Bowers, K. D. Proc. R. Soc. (London) 1952, A214, 451.
(47) Earnshaw, A. Introduction to Magnetochemistry; Academic Press:
New York, 1968.
(48) Lambert, S. L.; Hendrickson, D. N. Inorg. Chem. 1979, 18, 2638.
(49) Mandal, S. K.; Thompson, L. K.; Nag, K.; Charland, J.-P.; Gabe, E.
J. Can. J. Chem. 1987, 65, 2815.
(50) Ginsberg, A. P.; Martin, R. L.; Brookes, R. W.; Sherwood, R. C. Inorg.
Chem. 1972, 11, 2884.

1036 Inorganic Chemistry, Vol. 37, No. 5, 1998
Nanda et al.
Figure 7. Variable-temperature magnetic data for [Ni2(Dabox)2(H2O)2]
(6). The points [ represent the experimental data, and the solid line
represents the fit to eq 2.
Figure 6. Variable-temperature magnetic data for [Ni2(Damox)2(Py)2]‚
Py (3). The points [ represent the experimental data, and the solid
line represents the fit to eq 2.
for the crossover from antiferromagnetic to ferromagnetic
exchange interaction is 97°. The crystal structure of [Ni2-
(Damox)2(Py)4]‚2Py (3a), the precursor of [Ni2(Damox)2(Py)2]‚
Py (3), has a Ni-O-Ni angle of 96.9°. If the basic structure
of 3a is preserved in 3, we should expect a weak ferromagnetic
exchange interaction. Instead, we observe a moderate antifer-
romagnetic exchange interaction in 3 (-2J ) 19.5 cm-1) which
suggests a Ni-O-Ni bridge angle of 99.6°. This kind of
increase in bridge angle has been seen for phenoxo-bridged
dinickel(II) macrocyclic complexes when the stereochemistry
of the nickel(II) centers changes from octahedral to square-
pyramidal.53 The small values of |2J| for 2 and 6 indicate that
the Ni-O-Ni bridge angle in both the complexes is probably
near 97°. Such an angle increase would be inevitable if one
associates the axial ligands in the square-pyramidal complexes
with a trans-relationship, as a result of the normal out-of-plane
excursion of the metal ions.54 This indeed appears to have been
observed in the dicopper(II) systems.55
interdimer interaction. The compositions and spectroscopic data
evidence the nickel(II) geometry in [Ni2(Damox)2(MeOH)2]‚
MeOH (2), [Ni2(Damox)2(Py)2]‚Py (3), and [Ni2(Dabox)2-
(H2O)2] (6) to be square-pyramidal. The ground term for
3
square-pyramidal nickel(II) is B1g, for which no temperature-
independent paramagnetism is expected,47 so we have taken their
tip values as zero. The g-values resulting from the least-squares
fits are also in accord with expectation for nickel(II).52 The
complexes [Ni2(Damox)2(MeOH)2]‚MeOH (2) and [Ni2(Damox)2-
(Py)2]‚Py (3) exhibit antiferromagnetism, with -2J values of
3.2 and 19.5 cm-1, respectively. However, in [Ni2(Dabox)2-
(H2O)2] (6) the two nickel(II) centers are coupled ferromag-
netically (-2J ) -5.1 cm-1). The very evident decrease in
µeff below 20 K (Figure 7) is due to population of the Ms ) 0
state associated with the zero field splitting. In each case, the
interdimer interaction term is, as expected, considerably smaller
than the intramolecular coupling or the zero field splitting.
Nag and co-workers have proposed53 a correlation between
the Ni-Ophenoxo-Ni bridge angle and the extent of exchange
coupling between nickel(II) centers in diphenoxo-bridged di-
nickel(II) complexes. According to their proposal, the angle
Acknowledgment. A.W.A. and K.K.N. thank Drexel Uni-
versity for support and Ms. S. Ghosh for assistance in growing
crystals for diffractometry.
Supporting Information Available: Tables of crystal data, posi-
tional parameters, U-values, interatomic distances and angles, and least-
squares planes for 3a and 8 (22 pages). Ordering information is given
on any current masthead page.
(51) Wen, T. Ph.D. Thesis, Memorial University of Newfoundland, Canada,
1988; p 53. N, â, g, and k have their usual meanings, so that when
Nâ2/3k is taken as 0.125 erg K G-2 mol-1, then, within the brackets,
the values of k, Fi, and zJ′ are self-consistently expressible in cm-1
-
based units.
IC9712434
(52) Wertz, J. E.; Bolton, J. R. Electron Spin Resonance: Elementary
Theory and Practical Applications; McGraw-Hill Book Co.: New
York, 1972.
(53) Nanda, K. K.; Thompson, L. K.; Bridson, J. N.; Nag, K. J. Chem.
Soc., Chem. Commun. 1994, 1337.
(54) Hoskins, B. F.; Whillans, F. D. Coord. Chem. ReV. 1972, 9, 365.
(55) Mandal, S. K.; Thompson, L. K.; Newlands, M. J.; Gabe, E. J.; Nag,
K. Inorg. Chem. 1990, 29, 1324.