Syntheses and Structures of Nickel(II) and Copper(II) Complexes of 2,6-Bis[(2-acetylphenyl)carbamoyl]pyridine: Effects of Molecular Structure on Crystal Lattice Architecture

Full text of DOI:10.1021/ic9713184

3424
Inorg. Chem. 1998, 37, 3424-3427
having additional donors that can weakly interact with coordi-
nated metal ions. The molecular structures of the complexes
are determined by the orientations of the appended groups which
in turn can direct the assembly process during crystallization
to produce varied lattice architectures. This concept is illustrated
herein by the syntheses and structural analyses of the Cu(II)
and Ni(II) complexes of 2,6-bis[(2-acetylphenyl)carbamoyl]-
pyridine, H21, a ligand which contains appended acetophenone
groups.
Syntheses and Structures of Nickel(II) and
Copper(II) Complexes of
2,6-Bis[(2-acetylphenyl)carbamoyl]pyridine:
Effects of Molecular Structure on Crystal Lattice
Architecture
T. Kawamoto,† B. S. Hammes,† R. Ostrander,‡
A. L. Rheingold,‡ and A. S. Borovik*,†,§
Experimental Section
Departments of Chemistry, Kansas State University,
Manhattan, Kansas 66506, and University of Delaware,
Newark, Delaware 19716
All reagents and solvents were purchased from commercial sources
and used as received, unless noted otherwise. Elemental analysis of
all compounds was performed by Desert Analytics, Inc., Tucson, AZ.
All samples were dried in vacuo prior to analysis.
ReceiVed October 16, 1997
2,6-Bis[(2-acetylphenyl)carbamoyl]pyridine (H21). A solution of
2,6-pyridinedicarbonyl dichloride (1.0 g, 4.9 mmol) in 30 mL of THF
was added dropwise to a solution of 2′-aminoacetophenone (1.5 g, 11
mmol) and triethylamine (2.0 g, 20 mmol) under a nitrogen atmosphere
at 0 °C. When the addition was completed, the mixture was allowed
to warm to room temperature and stirred an additional 1.5 h and
volatiles were removed under reduced pressure. The residue was
dissolved in 150 mL of ethyl acetate and extracted with two 150 mL
portions of water and 100 mL of brine and dried over Na2SO4. The
solvent was evaporated under reduced pressure to give a light yellow
solid. Purification was accomplished by layering a concentrated CH2Cl2
solution of H21 with cyclohexane to yield 1.4 g (69%) of H21 as white
crystals. 1H NMR (400 MHz, CDCl3, 303 K, TMS): δ 13.13 (s, 2 H,
OC-NH), 8.78 (d, 2 H, Ha), 8.46 (d, 2 H, He), 8.12 (t, 1 H, Hf), 7.91
(d, 2 H, Hd), 7.64 (t, 2 H, Hb), 7.23 (t, 2 H, Hc), 2.58 (s, 6 H, OC-
CH3). 13C NMR (100.4 MHz, CDCl3, 303 K): δ 200.7, 162.6, 149.4,
139.0, 139.1, 134.1, 131.0, 125.2, 125.0, 123.3, 122.0, 28.3. FTIR
(CH2Cl2, cm-1): νNH(amide) ) 3350 (w), 3209 (w, br); νCO(amide) )
1690 (s), νCO(ketone) ) 1660 (s). FTIR (KBr, cm-1): νNH(amide) )
3330 (s), 3189 (w, br); νCO(amide) ) 1689 (s); νCO(ketone) ) 1658
(m), 1653 (m). Mp (uncorrected): 177-178 °C. MH+ m/e: 402
(positive FAB).
[2,6-Bis[(2-acetylphenyl)carbamoyl]pyridine]nickel(II) (Ni1). The
ligand H21 (0.21 g, 0.53 mmol) was dissolved in 80 mL of hot methanol.
KOH (0.092 g, 1.6 mmol) and NiCl2‚6H2O (0.19 g, 0.80 mmol) were
successively added to the reaction mixture. The solution was refluxed
for 24 h and then allowed to cool to room temperature. A red
precipitate formed and was collected by filtration. The precipitate was
redissolved in CH2Cl2, and excess NiCl2‚6H2O was removed by
filtration. The resulting red solution was evaporated to dryness to afford
a red solid, which was crystallized from hot toluene or methanol to
give 0.14 g (55%) of Ni1 as red crystals. Anal. Calcd for Ni1‚H2O,
C23H19N3NiO5: C, 58.02; H, 4.02; N, 8.83. Found: C, 58.14; H, 3.55;
N, 8.90. 1H NMR (400 MHz, CDCl3, 303 K, TMS): δ 8.33 (d, 2 H,
Ha), 8.04 (t, 1 H, Hf), 7.75 (d, 2 H, He), 7.68 (d, 2 H, Hd), 7.49 (t, 2 H,
Hb), 7.11 (t, 2 H, Hc), 2.63 (s, 6 H, OC-CH3). 13C NMR (100.4 MHz,
CDCl3, 303 K): δ 202.4, 168.4, 151.2, 144.9, 141.1, 134.5, 130.9,
130.5, 126.6, 124.3, 123.18, 28.97. FTIR (CH2Cl2, cm-1): νCO(ketone)
) 1680 (m), 1653(m); νCO(amide) ) 1635 (s). FTIR (KBr, cm-1):
Metal complexes that assemble into specific supramolecular
structures in crystal lattices have generated considerable interest
because of their potential use in developing new materials.1 A
variety of different synthetic methods have been recently
reported2 that produce intricate lattice architectures: these
include coordination networks formed by polyfunctional organic
ligands and transition metal salts3 and supramolecular assemblies
derived from helicates.4 However, it is still difficult to reliably
predict lattice structure because several factors, such as solvent,
counterion(s), and the geometry of the ligands bonded to the
metal ion(s), influence the assembly process. We have been
investigating the effects of ligand geometry and solvent on the
lattice structure for neutral transition metal complexes derived
from the chelating ligands 2,6-bis[(2-R-phenyl)carbamoyl)]-
pyridine (R ) acetyl or carbamoyl).5 These ligands contain a
tridentate pyridyl diamidate chelate with appended groups
* To whom correspondence should be addressed.
† Kansas State University.
‡ University of Delaware.
§ Current address: Department of Chemistry, University of Kansas,
Lawrence, KS 66045.
(1) (a) Lehn, J.-M. Angew. Chem., Int. Ed. Engl. 1990, 29, 1304. (b)
Robson, R.; Abrahams, B. F.; Batten, S. R.; Gable, R. W.; Hoskins,
B. F. In Supramolecular Architecture; Bein, T., Ed.; American
Chemical Society: Washington, DC, 1992; p 256. (c) Transition
Metals in Supramolecular Chemistry; Fabbrizzi, L., Poggi, A., Eds.;
Kluwer Academic: Dordrecht, The Netherlands, 1994.
(2) Selected examples: (a) Mu¨ller, A.; Reuter, H.; Dillinger, S. Angew.
Chem., Int. Ed. Engl. 1995, 34, 2328. (b) Eichen, Y.; Lehn, J.-M.;
Scherl, M.; Haarer, D.; Fischer, J.; DeCian, A.; Corval, A.; Tromms-
dorff, H. P. Angew. Chem., Int. Ed. Engl. 1995, 34, 2530. (c) Frey,
W.; Schief, W. R., Jr.; Pack, D. W.; Chen, C.-T.; Chilkoti, A.; Stayton,
P.; Vogel, V.; Arnold, F. Proc. Natl. Acad. Sci. U.S.A. 1996, 93, 4937.
(d) Medina, J. C.; Gay, I.; Chen, Z.; Eschegoyen, L.; Gokel, G. W. J.
Am. Chem. Soc. 1991, 113, 365. (e) Saalfrank, R. W.; Stark, A.;
Bremer, M.; Hummel, H.-U. Angew. Chem., Int. Ed. Engl. 1990, 29,
311. (f) Copp, S. B.; Subramanian, S.; Zaworotko, M. J. Chem. Soc.,
Chem. Commun. 1993, 1078.
(3) Recent reports: (a) Fujita, M.; Kwon, Y. J.; Washizu, S.; Ogura, K.
J. Am. Chem. Soc. 1994, 116, 1151. (b) Gardner, G. B.; Venkataraman,
D.; Moore, J. S.; Lee, S. Nature 1995, 374, 792. (c) Yaghi, O. M.; Li,
G.; Li, H. Nature 1995, 374, 792. (d) Robson, R. In ComprehensiVe
Supramolecular Chemistry; Atwood, J., Davies, J. E. D., MacNicol,
D. D., Vo¨gtle, F., Eds.; Elsevier Science: Oxford, England, 1996; p
773. (e) Hirsch, K. A.; Wilson, S. R.; Moore, J. S. Inorg. Chem. 1997,
36, 2960.
(4) (a) Lehn, J.-M.; Rigault, A.; Siegel, J.; Harrowfield, J.; Chevier, B.;
Moras, D. Proc. Natl. Acad. Sci. U.S.A. 1987, 84, 2565. (b) Dietrich-
Buchecker, C. O.; Sauvage, J.-M. Angew. Chem., Int. Ed. Engl. 1989,
28, 189. (c) Constable, E. D.; Elder, S. M.; Healy, J.; Ward, M. D.;
Tocher, D. A. J. Am. Chem. Soc. 1990, 112, 4590. (d) Piguet, C.;
Bernardinelli, G.; Bocquet, B.; Quattropani, A.; Williams, A. F. J.
Am. Chem. Soc. 1992, 114, 7440.
ν
CO(ketone) ) 1676 (m), 1649 (s); νCO(amide) ) 1634 (s). λmax (CHCl3;
ꢀ, M-1 cm-1): 326 (sh), 357 (10 200), 406 (sh), 423 (sh), 482 (2120),
528 (1320).
[2,6-Bis[(2-acetylphenyl)carbamoyl]pyridine]copper(II) (Cu1). A
0.10 g (0.25 mmol) sample of H21 was dissolved in 40 mL of refluxing
methanol. KOH (0.042 g, 0.76 mmol) and Cu(CH3COO)2‚H2O (0.075
g, 0.38 mmol) were successively added to the reaction mixture. The
(5) (a) Kawamoto, T.; Prakash, O.; Ostrander, R.; Rheingold, A. L.;
Borovik, A. S. Inorg. Chem. 1995, 34, 4294. (b) Kawamoto, T.;
Hammes, B. S.; Haggerty, B.; Yap, G. P. A.; Rheingold, A. L.;
Borovik, A. S. J. Am. Chem. Soc. 1995, 118, 285.
S0020-1669(97)01318-9 CCC: $15.00 © 1998 American Chemical Society
Published on Web 05/30/1998

Notes
Inorganic Chemistry, Vol. 37, No. 13, 1998 3425
Table 1. Crystallographic Data for Ni1‚2H2O, Cu1‚0.5C7H8
Ni1‚2H2O
Cu1‚0.5C7H8
empirical formula
fw
T (°C)
C23H21N3NiO6
494.1
25
C26.5H21CuN3O4
509.0
20
space group
a (Å)
b (Å)
P21/c
P1h
11.655(4)
7.449(3)
24.432(8)
90
101.580(3)
90
8.173(1)
11.095(2)
12.833(2)
93.72(3)
103.18(1)
98.91(1)
2
c (Å)
R (deg)
â (deg)
γ (deg)
Z
4
Figure 1. Schematic of the design concepts used in this study.
V (Å3)
2077.9(12)
1.580
9.82
0.71073
0.0351
0.0427
1113.2(3)
1.518
10.22
0.71073
0.0497
0.0723
F
calc (g/cm3)
µ
calc (cm-1
)
related ligands. Deprotonation of the pyridyl diamide center
affords a mer chelate that becomes planar after coordination to
a metal ion. This planar structure is caused by the rigidity of
the pyridyl diamidate chelate and is independent of the
coordinated metal ion. The molecular structure of the com-
plexes is determined by the relative orientation of the groups
appended from each amide nitrogen. The orientations of the
appended groups are directed, to a large extent, by their
interactions with the bonded metal. Each appended group is
designed to contain additional donor atoms capable of binding
to the metal ion. These donors are relatively weak Lewis bases
whose interactions depend on the stereochemical preference of
the coordinated metal ion, and not on the geometric requirements
of the ligand.6 For H21, acyl oxygen donors from the appended
acetophenone groups are predisposed to furnish additional
electron density to the coordinatively unsaturated metal center.
A variety of molecular structures can therefore be obtained by
binding metal ions with different coordination requirements.
Moreover, these differences in molecular structure between
complexes should result in varied lattice architectures. This is
particularly true for complexes containing divalent metal ions
of [1]2- which are neutral. The assembly of these complexes
will be governed by intermolecular hydrogen bonds and
π-stacking interactions.
Molecular Structures. The structures of Ni1 and Cu1 were
examined by single-crystal X-ray diffraction methods. Views
of the molecular structures of Ni1 and Cu2 are found in Figures
2 and 3, and selected bond distances and angles are listed in
Table 2. Both complexes have three of their coordination sites
occupied by nitrogen donors from the diamidate-pyridyl
chelate. In Ni1 the geometry around the Ni(II) is approximately
square planar, with the fourth donor provided by a carbonyl
oxygen, O(4), from one of the appended acetophenone groups.
The acyl oxygen coordination orients this group nearly coplanar
with the rigid, tridentate chelate. The remaining acetophenone
oxygen O(3) is pointed away from the Ni(II) center at a distance
of ∼5.5 Å (vide infra).
λ (Å)
R(Fo)a
Rw(Fo)b
2
a R ) ∑|∆F|/∑|Fo|]. b Rw ) ∑w(∆F)2/∑wFo .
solution was refluxed for 24 h. After cooling, the methanol was
removed under vacuum to give a green solid. The residue was dissolved
in CH2Cl2, and the solution was filtered to remove any excess Cu(CH3-
COO)2‚H2O. The CH2Cl2 was removed under reduced pressure to
afford a green solid, which was crystallized from hot toluene to yield
0.055 g (43%) of Cu1 as green crystals. Anal. Calcd for Cu1‚0.5C7H8,
26.5H21CuN3O4: C, 62.53; H, 4.16; N, 8.26. Found: C, 62.79; H,
4.03; N, 8.33. FTIR (CH2Cl2, cm-1):
CO(ketone) ) 1627 (s);
CO(amide) ) 1617 (s). FTIR (KBr, cm-1): νCO(ketone) ) 1676 (m),
1649 (s); νCO(amide) ) 1617 (s). λmax (CHCl3; ꢀ, M-1 cm-1): 356
C
ν
ν
(10 100). X-band EPR (1:1 toluene/CH2Cl2, 77 K): g| ) 2.21, g
2.08, A| ) 158 G. X-band EPR (powder, 77 K): g ) 2.06.
)
Physical Methods. 1H and 13C NMR spectra and NOE measure-
ments were collected on a Bruker 400 MHz NMR spectrometer.
Chemical shifts are reported in ppm relative to an internal standard of
TMS. FTIR spectra were recorded on a Bio-Rad FTS-20 FTIR
spectrometer interfaced to a PC computer and are reported in wave-
numbers. UV-vis spectra were collected on an SLM-Aminco diode
array spectrophotometer using a 1.0 cm Suprasil quartz cell. EPR
spectra were collected using a Bruker TE102 cavity and a Bruker 200D-
SRC control console (which housed a Bruker ER022 signal channel, a
Bruker ER031 field controller, and a Bruker ER001 time base
oscilloscope). The console was interfaced to a Bruker ER040 XR
microwave bridge and a Varian V3603 magnet (powered by Varian
model 907015-03 power supply and a Varian V-FR2503 fieldial
magnetic field regulator). Spectra were collected at 77 K, and all g
values reported are referenced to DPPH.
Crystallographic Structural Determinations. Single crystals of
Ni1‚2H2O and Cu1‚0.5C7H8 were obtained under similar conditions
using hot toluene as the solvent. Crystal data collection and refinement
parameters for Ni1‚2H2O and Cu1‚0.5C7H8 are given in Table 1. The
systematic absences in the diffraction data are uniquely consistent with
the space group, P21/c for Ni1‚2H2O and P1h for Cu1‚0.5C7H8. For
Cu1‚0.5C7H8, P1h was initially chosen, and this assignment was
supported by the stable and chemically reasonable results of refinement.
The structures were solved using direct methods, completed by
subsequent difference Fourier syntheses and refined by full-matrix least-
squares procedures. The asymmetric unit of Ni1‚2H2O contains two
molecules of H2O while that of Cu1 has half a molecule of toluene.
All non-hydrogen atoms were refined with anisotropic displacement
coefficients, and hydrogen atoms were treated as idealized contributions.
All software and sources of the scattering factors are contained in the
SHELXTL PLUS (5.3) program library (G. Sheldrick, Siemens XRD,
Madison, WI).
In contrast to those in Ni1, both acetophenone oxygens in
Cu1 interact with the copper(II) center, producing a square
pyramidal five-coordinate species with O(3) occupying the axial
position. These oxygen donors are coordinated unsymmetrically
to Cu(II), with distances of 2.357(3) and 1.933(3) Å for the
Cu-O(3) and Cu-O(4) bonds, respectively. Dual coordination
of carbonyl oxygens causes the appended acetophenone groups
to orient on opposite faces of the plane formed by the Cu(II)-
[pyridyl diamidate] chelate. The structural consequence of this
displacement gives Cu1 an overall helical morphology.5,7
Results and Discussion
(6) Representative papers: (a) Wentworth, R. A. D. Coord. Chem. ReV.
1972, 9, 172. (b) Wester, D.; Palenik, G. J. J. Am. Chem. Soc. 1974,
96, 7565.
Design Considerations and Syntheses. Figure 1 shows the
design factors used in developing metal complexes of [1]2- and

3426 Inorganic Chemistry, Vol. 37, No. 13, 1998
Notes
Figure 2. Thermal ellipsoid diagram of Cu1 (left) and a portion of the crystal lattice for Cu1 (view of the b,c plane) showing the open-framework
structure. Solvent molecules have been omitted for clarity, and the ellipsoids are drawn at the 40% probability level.
Figure 3. Thermal ellipsoid diagram of Ni1 (left) and a portion of the crystal lattice for Ni1 illustrating the hydrogen-bonding network used to
stabilized the column motifs. Intraccolumnar Ni-Ni distances: a, 4.42 Å; b, 6.21 Å.
Table 2. Selected Bond Distances (Å) and Angles (deg) for Ni1
acyl oxygen to the M(II)-[pyridyl diamidate] chelate, the
and Cu1
oxygen donor must reside ca. 1.9 Å from the bound metal center.
This inflexibility in the ligand system restricts all near-planar
metal-carbonyl oxygen interactions; thus we propose that these
short bond lengths in Cu1 and Ni1 are actually caused by the
structural constraints imposed by [1]2-. This hypothesis is
supported by two lines of structural evidence in Ni1 which show
that the Ni-O(4) interaction is indeed weak. First, the Ni-
N(2) bond distance of 1.805 (2) Å is exceptionally short
compared to those of known pyridine nitrogen-nickel bonds
incorporated into two five-membered metallocycles (>1.95 Å).10
Ni1
Cu1
M-N(1)
M-N(2)
M-N(3)
M-O(3)
M-O(4)
1.918(3)
1.805(2)
1.885(3)
1.981(3)
1.887(3)
1.980(3)
2.355(3)
1.932(3)
1.828(2)
N(1)-M-N(2)
N(1)-M-N(3)
N(1)-M-O(3)
N(1)-M-O(4)
N(2)-M-N(3)
N(2)-M-O(3)
N(2)-M-O(4)
N(3)-M-O(3)
N(3)-M-O(4)
O(3)-M-O(4)
82.7(1)
167.7(1)
80.9(1)
163.8(1)
78.0(1)
102.8(1)
83.0(1)
117.4(1)
161.4(1)
109.6(1)
92.6(1)
81.2(1)
95.2(1)
85.1(1)
(8) (a) Tandon, S. S.; Larkworthy, L. F. J. Chem. Soc., Dalton Trans.
1984, 2389. (b) Foxman, B. M.; Mazurek, H. Inorg. Chem. 1979, 18,
113. (c) Sheldrick, G. M.; Stotter, D. A. J. Chem. Soc., Dalton Trans.
1975, 666. (d) Wiesemann, F.; Krebs, B. Z. Anorg. Allg. Chem. 1995,
621, 1883. (e) Kastner, M. E.; Tang, K.; Birdsall, W. J. Inorg. Chim.
Acta 1995, 227, 159. (f) Birdsall, W. J.; Long, D. P.; Smith, S. P. E.;
Kastner, M. E.; Tang, K.; Kirk, C. Polyhedron 1994, 13, 2055. (g)
Matt, D.; Huhn, M.; Fischer, J.; De Cian, A.; Kla¨ui, W.; Tkatchenko,
I.; Bonnet, M. C. J. Chem. Soc., Dalton Trans. 1993, 1173. (h)
Kwiatkowski, M.; Kwiatkowski, E.; Olechnowicz, A.; Ho, D. M.;
Deutsch, E. J. Chem. Soc., Dalton Trans. 1990, 2497.
(9) (a) Costes, J.-P.; Dahan, F.; Laurent, J.-P Inorg. Chem. 1985, 24, 1018.
(b) Keturah, C.; Tasker, P. A.; Trotter, J. J. Chem. Soc., Dalton Trans.
1978, 1057. (c) Scott, M. J.; Holm, R. H. J. Am. Chem. Soc. 1994,
116, 11357. (d) Munakata, M.; Kuroda-Sowa, T.; Maekawa, M.;
Nakamura, M.; Akiyama, S.; Kitagawa, S. Inorg. Chem. 1994, 33,
1284. (e) Costes, J.-P.; Serra, J.-F.; Kahan, F.; Laurent, J.-P. Inorg.
Chem. 1986, 25, 2790. (f) Solans, X.; Aguilo´, M.; Gleizes, A.; Faus,
J.; Julve, M.; Verdaguer, M. Inorg. Chem. 1990, 29, 775. (g) Scott,
M. J.; Goddard, C. A.; Holm, R. H. Inorg. Chem. 1996, 35, 2558. (h)
Vezzosi, I. M.; Zanoli, F. A.; Battaglia, L. P.; Corradi, A. B. Inorg.
Chim. Acta 1985, 105, 13. (i) Goher, M. A. S.; Mak, T. C. W. Inorg.
Chim. Acta 1985, 99, 223. (j) Mak, T. C. W.; Goher, M. A. S. Inorg.
Chim. Acta 1986, 115, 17. Vezzoli, I. M.; Antolini, L. Inorg. Chim.
Acta 1984, 85, 155.
177.5(1)
97.1(1)
The equatorial Ni-O(4) and Cu-O(4) bond distances are
1.828(3) and 1.932(3) Å, which are shorter than the apical Cu-
O(3) bond length of 2.355(3) Å.8,9 Comparison of these
distances to those reported for other complexes with Ni(II)-
and Cu(II)-ketonyl oxygen bonds (average M-O distance of
∼1.93 Å) suggests relatively strong equatorial M-O interactions
are present in Ni1 and Cu1. However, molecular modeling
studies (CAChe) show that, for equatorial coordination of an
(7) Examples of metal complexes with mulitdentate ligands that form
helical structures: (a) Lindoy, L. F.; Busch, D. H. J. Chem. Soc., Chem.
Commun. 1972, 683. (b) Wester, D.; Palenik, G. J. J. Chem. Soc.,
Chem. Commun. 1975, 74. (c) Lehn, J.-M.; Rigault, A. Angew. Chem.,
Int. Ed. Engl. 1988, 27, 1095. (d) Williams, A. F.; Piquet, C.;
Bernardinelli, G. Angew. Chem., Int. Ed. Engl. 1991, 30, 1490.

Notes
Inorganic Chemistry, Vol. 37, No. 13, 1998 3427
This short bond length is consistent with a weak trans influence
of O(4) on the Ni center. Moreover, short trans bond lengths
have been documented in acyl Pd(II) and Pt(II) complexes.11
Second, the C(22)-O(4) bond length of 1.260(4) Å is only
slightly longer than that normally observed for a CdO bond
(1.23 Å) but is still much shorter than the distance for a C-O
single bond (1.43 Å).12 This minor elongation of the CdO bond
reflects the small decrease in the carbonyl bond order that occurs
from the PhCdO- - -Ni interaction, which agrees with our FTIR
measurements (see Experimental Section).
The major difference between the molecular structures of Ni1
and Cu1 is the orientation of the acetophenone groups containing
O(3). In Ni1, this group is oriented such that the aryl ring is
rotated 118.5° out of the coordination square plane. The acetyl
oxygen O(3) is pointed away from the Ni(II) center and is
hydrogen-bonded to one solvated water molecule (vide infra).
However, in Cu1, where O(3) is coordinated to the Cu(II) center,
this appended group is displaced only 48° from the plane of
the pyridyl-diamide chelate. This structural difference has a
significant influence on the assembly of the complexes in their
respective crystal lattices.
Lattice Structures for Cu1 and Ni1. The Cu1 complexes
are arranged in coils that are aligned along the crystallographic
b axis. These coils are stabilized by two π-stacking interactions
with centroid-centroid distances of 3.92 and 4.45 Å. Adjacent
coils interact via π-stacking interactions between the aryl rings
of the apically coordinated acetophenone groups (i.e., the
appended group containing O(3)) with a centroid-centroid
distance of 3.74 Å. An open-framework lattice structure results
(Figure 2 (right)) where the distance between adjacent set of
stack rings is 7.74 Å. This space in the present structure of
Cu1 is filled with toluene molecules which come from the
solvent used in crystallization.13
The Ni1 complexes assemble into supramolecular columns
that are positioned along the crystallographic b axis (Figure 3
(right)). The columns are stabilized by two hydrogen-bond
networks that are on opposite sides of each column. The
hydrogen-bond networks connect every other complex through
repeated units consisting of two hydrogen-bonded water mol-
ecules. These pairs of water molecules in turn hydrogen-bond
to O(3) of an appended acetophenone group from one complex
and O(1) of a pyridyl diamidate chelate of an alternating
complex. Additional columnar stabilization comes from stack-
ing interactions between the coordination square planes of
adjacent molecules where the average interplane distance is 3.75
Å. This arrangement of Ni1 complexes results in two unique
intraccolumnar Ni-Ni distances of 4.42 and 6.21 Å.
Summary. In this work, we have demonstrated that neutral
transition metal complexes of 2,6-bis[(2-acetylphenyl)carbam-
oyl]pyridine can be used as building blocks to assemble varied
supramolecular species in the solid state. The structures of
complexes with this ligand are affected by the orientation of
the acetophenone groups appended from the pyridyl diamidate
chelates, which are controlled by their interactions with the metal
centers. The modular design of 2,6-bis[(2-R-phenyl)carbamoyl]-
pyridine (R ) acetyl or carbamoyl) ligands allows for additional
ligands to be generated having different appended groups. For
example, we recently showed that appended groups containing
hydrogen-bonded arrays can form complexes with helical
structures.5 These complexes also assemble into diverse lattice
structures. Extension of this design concept to include appended
redox-active groups and peptides will be reported in due course.
Acknowledgment. We thank NSF (Grant OSR-9255223),
the NIH (Grant GM50781), and Kansas State University for
financial support of this research.
(10) (a) Alyea, E. C.; Ferguson, G.; Restivo, R. J. Inorg. Chem. 1975, 14,
2491. (b) Wester, D.; Palenik, G. J. J. Am. Chem. Soc. 1975, 96, 7565.
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Supporting Information Available: Tables of X-ray structural data
for Ni1 and Cu1 (12 pages). Ordering information is given on any
current masthead page.
IC9713184
(13) For examples of π-stacking interactions in supramolecular chemistry
see: (a) Desiraju, G. D. Crystal Engineering: The Design of Organic
Solids; Elsevier: New York, 1989. (b) Hunter, C. A. Chem. Soc. ReV.
1994, 101 and references therein.
(12) CRC Handbook of Chemistry and Physics, 53rd ed.; Weast, R. C.,
Ed.; CRC Press: Boca Raton, FL, 1972; p F180.