Toward Rational Control of Metal Stoichiometry in Heterobimetallic Coordination Complexes: Synthesis and Characterization of Pb(Hsal) 2(Cu(salen*))2, [Pb(NO3)(Cu(salen* ))2](NO3), Pb(OAc)2(Cu(salen*)), and [Pb(OAc)(Ni(salen*))2](OAc)

Article abstract of DOI:10.1021/ic035427w

The ability of the transition metal complex M(salen)* (M = Ni, Cu) to form Lewis acid-base adducts with lead(II) salts has been explored. The new complexes Pb(Hsal)₂(Cu(salen*))₂ (1), {Pb(NO ₃)(Cu(salen*))₂}(NO₃) (2), Pb-(OAc) ₂(Cu(salen*)) (3), and {Pb(OAc)(Ni(salen*) ₂}(OAc) (4) (Hsal = O₂CC₆H₄-2-OH, salen* = bis(3-methoxy)-salicylideneimine) have been synthesized and characterized spectroscopically and by single-crystal X-ray diffraction. The coordination environment of the lead in the heterobimetallic complex is sensitive both to the initial lead salt and to the transition metal salen complex that is employed in the synthesis. As a result, we have been able to access both 2:1 and 1:1 adducts by varying either the lead salt or the transition metal in the heterobimetallic coordination complex. In all cases, the salen* complex is associated with the lead center via dative interactions of the phenolic oxygen atoms. The relationship between the coordination requirements of the lead and the chemical nature of the anion is examined. In compound 1, the Pb²⁺ ion is chelated by two Cu(salen*) moieties, and both salicylate ligands remain attached to the lead center and bridge to the Cu²⁺ ions. The two Cu(salen*) groups are roughly parallel and opposed to each other as required by crystallographic inversion symmetry at lead. In contrast, the two Cu(salen*) groups present in 2 and 4 attached to the lead ion show considerable overlap. Furthermore, only one nitrate ion in 2 and one acetate ion in 4 remain bonded to the lead center. Compound 3 is unique in that only one Cu(salen*) group can bind to lead. Here, both acetate ligands remain attached, although one is chelating bidentate and the other is monodentate.

Full text of DOI:10.1021/ic035427w

Inorg. Chem. 2004, 43, 2708−2713
Toward Rational Control of Metal Stoichiometry in Heterobimetallic
Coordination Complexes: Synthesis and Characterization of
Pb(Hsal)2(Cu(salen*))2, [Pb(NO )(Cu(salen*))2](NO ), Pb(OAc)2(Cu(salen*)),
3
3
and [Pb(OAc)(Ni(salen*))2](OAc)
John H. Thurston, Christopher G.-Z. Tang, Daniel W. Trahan, and Kenton H. Whitmire*
Department of Chemistry, Rice UniVersity, 6100 Main Street, Houston, Texas 77005
Received December 12, 2003
The ability of the transition metal complex M(salen)* (M ) Ni, Cu) to form Lewis acid−base adducts with lead(II)
salts has been explored. The new complexes Pb(Hsal)2(Cu(salen*))2 (1), {Pb(NO )(Cu(salen*))2}(NO ) (2), Pb-
3
3
(OAc)2(Cu(salen*)) (3), and {Pb(OAc)(Ni(salen*)2}(OAc) (4) (Hsal ) O CC H -2-OH, salen* ) bis(3-methoxy)-
2
6 4
salicylideneimine) have been synthesized and characterized spectroscopically and by single-crystal X-ray diffraction.
The coordination environment of the lead in the heterobimetallic complex is sensitive both to the initial lead salt
and to the transition metal salen complex that is employed in the synthesis. As a result, we have been able to
access both 2:1 and 1:1 adducts by varying either the lead salt or the transition metal in the heterobimetallic
coordination complex. In all cases, the salen* complex is associated with the lead center via dative interactions of
the phenolic oxygen atoms. The relationship between the coordination requirements of the lead and the chemical
nature of the anion is examined. In compound 1, the Pb2+ ion is chelated by two Cu(salen*) moieties, and both
salicylate ligands remain attached to the lead center and bridge to the Cu2+ ions. The two Cu(salen*) groups are
roughly parallel and opposed to each other as required by crystallographic inversion symmetry at lead. In contrast,
the two Cu(salen*) groups present in 2 and 4 attached to the lead ion show considerable overlap. Furthermore,
only one nitrate ion in 2 and one acetate ion in 4 remain bonded to the lead center. Compound 3 is unique in that
only one Cu(salen*) group can bind to lead. Here, both acetate ligands remain attached, although one is chelating
bidentate and the other is monodentate.
Introduction
different metal species in the complex generally prevents
the formation of unwanted phases, allowing for the formation
and isolation of the desired materials in much higher purity
than what is generally accessible via traditional routes.11
One of the most significant challenges in developing the
chemistry of heterobimetallic coordination complexes to act
as potential precursors for the formation of oxide materials
is the development of accessible synthetic approaches to these
complexes that allow for control over the stoichiometry of
the individual metal species with relationship to one another
Many bimetallic or multimetallic oxide systems containing
heavy main group metal and transition metals are being
explored for the unique physical or chemical properties that
these materials may possess. For example, BiAlO3 is an
extremely efficient oxide ion conducting ceramic,1 while
BaTiO3 and PbTixZr1-xO3 are highly promising ferroelectric
materials.2,3 It has been shown by our group and others that
discrete bimetallic coordination complexes can offer access
to oxide materials at significantly reduced temperatures
compared to what are required for traditional solid-state
syntheses.4-10 Additionally, the intimate mixing of the
(4) Kessler, V. G. Chem. Commun. 2003, 11, 1213-1222.
(5) Hubert-Pfaltzgraf, L. G. Inorg. Chem. Commun. 2003, 6, 102-120.
(6) Hubert-Pfaltzgraf, L. G. New J. Chem. 1995, 19, 727-750.
(7) Hubert-Pfalzgraf, L. G. Crit. ReV. Opt. Sci. Technol. 1997, CR68,
3-24.
(8) Hubert-Pfalzgraf, L. G.; Daniele, S.; Boulmaaz, S.; Papiernik, R. Mater.
Res. Soc. Symp. Proc. 1994, 346, 21-27.
(9) Thurston, J. H.; Whitmire, K. H. Inorg. Chem. 2002, 41, 4194-4205.
(10) Thurston, J. H.; Whitmire, K. H. Inorg. Chem. 2003, 42, 2014-2023.
(11) Veith, M. J. Chem. Soc., Dalton Trans. 2002, 12, 2405-2412.
* Author to be contacted for correspondence. E-mail: whitmir@rice.edu.
Phone: 713-348-5650. Fax: 713-348-5155.
(1) Bloom, I.; Hash, M. C.; Zebrowski, J. P.; Myles, K. M.; Krumpelt,
M. Solid State Ionics 1992, 53-56, 739-747.
(2) Jones, A. C.; Chalker, P. R. J. Physics D: Appl. Phys. 2003, 36, R80-
R95.
(3) Schneller, T.; Waser, R. Ferroelectrics 2002, 267, 293-301.
2708 Inorganic Chemistry, Vol. 43, No. 8, 2004
10.1021/ic035427w CCC: $27.50 © 2004 American Chemical Society
Published on Web 03/16/2004

Heterobimetallic Coordination Complexes
in the final product.4 In this regard, the formation of Lewis
acid-base adducts is a particularly promising synthetic
approach due to the generally high yields, relatively rapid
reaction times, and absence of complicating side reactions.
This approach has been successfully employed to produce
heterobimetallic and heterotrimetallic coordination com-
pounds.12-21 As part of our ongoing studies into the develop-
ment of the coordination chemistry of the heavy main group
elements, we have investigated the reaction of a series of
Pb(II) salts with M(salen)* (M ) Ni, Cu), and wish to report
here the synthesis and characterization of the bimetallic
coordination complexes Pb(Hsal)2‚(Cu(salen*))2 (1), {Pb-
(NO3)‚(Cu(salen*))2}(NO3) (2), Pb(OAc)2‚(Cu(salen*)) (3),
and {Pb(OAc)‚(Ni(salen*))2}(OAc) (Hsal ) O2CC6H4-2-OH,
salen* ) bis(3-methoxy)salicylideneimine). The new com-
pounds have been characterized spectroscopically and by
single-crystal X-ray diffraction experiments. Differences in
the ligands attached to lead in the starting Pb2+ salts as well
as the nature of the metal in the M(salen*) complexes
influence the final stoichiometry and geometry of the
products. The source of these differences will be discussed.
assisted laser desorptive ionization-time-of-flight (MALDI-TOF)
techniques on a Bruker Biflex III instrument, with a matrix of
dithranol.
Syntheses. Preparation of Lead(II) Salicylate. A mixture of
yellow lead(II) oxide (10.0 g, 45 mmol) and salicylic acid (13.8 g,
100 mmol) was placed in 200 mL of toluene. The suspension was
heated to reflux for 24 h. During this time, the color of the
suspension changed from yellow to white. The water that forms in
the reaction was removed by azeotropic distillation using a Dean-
Stark apparatus. After the reaction period, the solid was collected
by filtration, washed repeatedly with diethyl ether (5 × 50 mL),
and dried well under vacuum to give [Pb(Hsal)2]n as a white free
flowing solid. Yield: 20 g (93%). FT-IR: 1620, 1587, 1543, 1518,
1481, 1457, 1398, 1387, 1359, 1301, 1249, 1224, 1153, 1145, 1030,
984, 952, 872, 819, 761, 754, 703. Elemental analysis: % obsd
(% calcd for PbC14H10O6) C, 34.90 (35.01); H, 2.17 (2.09).
Pb(Hsal)2‚[Cu(salen*)]2 (1). Compound 1 was synthesized by
the addition of Cu(salen*) (0.8 g, 2.0 mmol) to a suspension of
[Pb(Hsal)2]n (0.47 g, 0.98 mmol), in dichloromethane (20 mL). The
resulting burgundy solution was stirred until complete dissolution
of the lead salt occurred, and then, the reaction mixture was allowed
to stand undisturbed at room temperature for 24 h. The large
burgundy crystals that deposited in the flask were collected by
filtration, washed with dichloromethane and diethyl ether, and dried
briefly under reduced pressure. Compound 1 yield: 0.92 g (0.73
mmol, 74%). Elemental analysis % obsd (% calcd for C46H46-
Cu2N4O14Pb): C 45.12 (45.54), H 3.76 (3.82), N 4.45 (4.62). IR:
1635, 1622, 1602, 1590, 1562, 1484, 1471, 1456, 1447, 1400, 1381,
1353, 1320, 1303, 1290, 1246, 1223, 1170, 1140, 1082, 1028, 982,
961, 897, 863, 816, 806, 776, 756, 750, 734. This complex was
essentially insoluble in organic solvents, precluding the measure-
ment of solution spectroscopic data.
{Pb(NO3)‚(Cu(salen*))2}NO3 (2). Compound 2 was synthesized
in a manner analogous to 1 with the substitution of Pb(NO3)2 for
[Pb(Hsal)2]n. Large burgundy crystals of 2 were grown by slow
evaporation of a dichloromethane solution of the compound. The
solid was collected by filtration, washed with dichloromethane and
diethyl ether, and dried briefly under reduced pressure. Compound
2 yield: 1.01 g (0.90 mmol, 92%). Elemental analysis: % obsd
(% calcd for PbCu2C36H32N6O14‚2H2O): C 37.22 (37.24); H 3.64
(3.13); N 7.21 (7.24). IR: 1618, 1601, 1554, 1480, 1467, 1446,
1395, 1368, 1309, 1280, 1242, 1221, 1163, 1140, 1078, 972, 869,
819, 771, 757, 737, 705, 667. MALDI-TOF MS: 985 (10%, 2 -
NO3 + Cu(salen*)), 821 (100%, 2 - NO3 + dithranol), 658 (90%,
2 - Cu(salen*)), 390 (70%, Cu(salen*)). ꢀ0 ) 11 382 L‚mol-1‚cm-1
at 362 nm in CH2Cl2.
Experimental Section
Solvents were purified over an appropriate reagent under argon
and were distilled immediately prior to use.22 The ligand bis(3-
methoxy)salicylideneimine (H2salen*) and the transition metal
complexes copper(II)(salen*) and nickel(II)(salen*) were prepared
as previously reported.23 The starting materials lead(II) oxide, lead-
(II) acetate, lead(II) nitrate, copper(II) acetate, and nickel(II) acetate
were purchased (Aldrich Chemical Co. or Strem Chemical Co.)
and were used as received. Galbraith Laboratories performed all
elemental analyses. NMR spectra were collected on a Bruker 400
Avance instrument and are referenced to tetramethylsilane (TMS)
as an internal standard. Infrared spectra of the complexes were
collected on a Thermo-Nicolet 630 FT-IR using ATR methodology.
UV-vis data were collected on a GBC Spectral 918 instrument as
dichloromethane solutions. Mass spectra were collected using matrix
(12) Ryazanov, M. V.; Troyanov, S. I.; Malkerova, I. P.; Alikhanyan, A.
S.; Kuz’mina, N. P. Zh. Neorg. Khim. 2001, 46, 256-265.
(13) Ryazanov, M.; Nikiforov, V.; Lloret, F.; Julve, M.; Kuzmina, N.;
Gleizes, A. Inorg. Chem. 2002, 41, 1816-1823.
(14) Kuz’mina, N. P.; Rogachev, A. Y.; Spiridonov, F. M.; Dedlovskaya,
E. M.; Ketsko, V. A.; Gleizes, A.; Battiston, J. Zh. Neorg. Khim. 2000,
45, 1468-1475.
(15) Gleizes, A. N.; Senocq, F.; Julve, M.; Sanz, J. L.; Kuzmina, N.;
Troyanov, S.; Malkerova, I.; Alikhanyan, A.; Ryazanov, M.; Rogachev,
A.; Dedlovskaya, E. J. Phys. IV 1999, 9, 943-951.
Pb(OAc)2‚(Cu(salen*)) (3). Compound 3 was synthesized in a
manner analogous to 1 with the substitution of Pb(OAc)2 for [Pb-
(Hsal)2]n. Burgundy crystals of 3 were grown by slow evaporation
of a dichloromethane solution of the compound in air. The solid
was collected by filtration, washed with dichloromethane and diethyl
ether, and dried briefly under reduced pressure. Compound 3
yield: 0.85 g (0.85 mmol, 83% based on Pb). Elemental analysis:
% obsd (% calcd for PbCuC22H22O8N2‚2H2O): C 35.18 (35.27),
H 3.56 (3.23), N 3.70 (3.74). FT-IR (ATR): 1637, 1602, 1569,
1541, 1508, 1471, 1493, 1395, 1338, 1293, 1243, 1223, 1167, 1083,
1051, 1011, 984, 968, 923, 851, 781, 736. MALDI-TOF MS: 821
(100%, 3 - 2OAc + dithranol), 655 (50%, 3 - OAc), 596 (35%,
3 - 2OAc), 390 (20%, Cu(salen*)). ꢀ0 ) 17 567 L‚mol-1‚cm-1 at
376 nm in CH2Cl2.
(16) Gleizes, A.; Julve, M.; Kuzmina, N.; Alikhanyan, A.; Lloret, F.;
Malkerova, I.; Sanz, J. L.; Senocq, F. Eur. J. Inorg. Chem. 1998,
1169-1174.
(17) Siddiqi, K. S.; Aqra, F. M. A. M.; Shah, S. A.; Zaidi, S. A. A.; Khan,
N. H.; Kureshy, R. I. Synth. React. Inorg. Met.-Org. Chem. 1993, 23,
1645-1654.
(18) Kondoh, N.; Shimizu, Y.; Kurihara, M.; Sakiyama, H.; Sakamoto, M.;
Nishida, Y.; Sadaoka, Y.; Ohba, M.; Okawa, H. Bull. Chem. Soc. Jpn.
2003, 76, 1007-1008.
(19) Sakamoto, M.; Manseki, K.; Okawa, H. Coord. Chem. ReV. 2001,
219-221, 379-414.
(20) Kuzmina, N.; Ryazanov, M.; Malkerova, I.; Alikhanyan, A.; Gleizes,
A. N. Eur. J. Inorg. Chem. 2001, 701-706.
(21) Sasaki, M.; Manseki, K.; Horiuchi, H.; Kumagai, M.; Sakamoto, M.;
Sakiyama, H.; Nishida, Y.; Sakai, M.; Sadaoka, Y.; Ohba, M.; Okawa,
H. Dalton 2000, 259-263.
{Pb(OAc)‚(Ni(salen*))2}(OAc) (4). Compound 4 was synthe-
sized in a manner analogous to 3 with the substitution of Ni(salen*)
for Cu(salen*). Orange-red crystals of 4 were grown by slow
(22) Armarego, W. L. F.; Perry, D. D. Purification of Laboratory
Chemicals, 4th ed.; Butterworth-Heinemann: Boston, 1996.
(23) Thurston, J. H.; Whitmire, K. H. Chem. Mater., in press.
Inorganic Chemistry, Vol. 43, No. 8, 2004 2709

Thurston et al.
evaporation of a dichloromethane solution of the compound in air.
The solid was collected by filtration, washed with dichloromethane
and diethyl ether, and dried briefly under reduced pressure. Yield:
1
0.97 g (0.97 mmol, 76%). H NMR (CDCl3, 400 MHz, 25 °C):
1.87 (s, O2CCH3, 6H), 2.00 (br, s, H2O, 15H), 3.49 (s, -CH2, 8H),
3.77 (s, -OCH3, 12H), 6.48 (t, ArH, 4H, J ) 7.85 Hz), 6.66 (d,
ArH, 4H, J ) 7.41 Hz), 6.71 (d, ArH, 4H, J ) 7.88 Hz). 13C{1H}
NMR (CDCl3, 100 MHz, 25 °C): 55.56, 58.13, 113.19, 115.07,
120.29, 123.93, 151.76, 154.20, 159.85, 162.49, 179.87. Elemental
analysis: % obsd (% calcd for PbNi2C40H38O12N4‚7.5H2O) C, 38.80
(39.17); H, 4.57 (4.36); N, 4.64 (4.57). FT-IR (ATR): 1637, 1602,
1569, 1541, 1508, 1471, 1493, 1395, 1338, 1293, 1243, 1223, 1167,
1083, 1051, 1011, 984, 968, 923, 851, 781, 736. MALDI-TOF
MS: 1040 (10%, 4 - OAc), 816 (100%, 4 - 2OAc + dithranol),
650 (35%, 4 - OAc - Ni(salen*)), 591 (25%, PbNi(salen*)), 385
(Ni(salen*)). ꢀo ) 8641 L‚mol-1‚cm-1 at 353 nm in CH2Cl2.
Solid-State Structures. Compounds 1-4 were studied on a
Bruker Smart 1000 diffractometer equipped with a CCD area
detector. The data were corrected for Lorentz and polarization
effects. An absorption correction was applied using the program
SADABS.24 No appreciable decay of the crystals was detected
during data collection. Heavy atoms in the compounds were located
using Patterson methods with the SHELXTL software package.25
All other atoms were located by successive Fourier difference maps
and were refined using the full-matrix least-squares technique on
F2. All non-hydrogen atoms were refined anisotropically. Hydrogen
atoms in all of the complexes were placed in calculated positions
and allowed to ride on the adjacent atom. Hydrogen atoms
associated with phenolic oxygen atoms were placed in calculated
positions and refined geometrically using a riding model. The
hydrogen atom was oriented so that the most likely hydrogen bond,
in this case to a carboxylate oxygen of the same molecule, was
realized. The presence of intermolecular hydrogen bonding in the
complexes was explored using the program PLATON.26
Figure 1. ORTEP representation of the solid-state structure of 1. Thermal
ellipsoids are drawn at the 30% probability level. Hydrogen atoms have
been omitted for clarity. Broken lines represent dative interactions between
salicylate ligands and copper(II) centers.
In the course of structure solution and refinement of complexes
2 and 4, only one of the two anions (those coordinated to the lead
center) could be located from the Fourier map of the residual
electron density. Analysis of the packing behavior of these two
compounds reveals that, in the solid state, they form weak pseudo-
one-dimensional polymeric assemblies. In the case of 2, the
intermolecular interactions are π stacking forces between salen*
ligands, while in 4, there are apparent weak Ni‚‚‚Ni interactions.
The displaced anions, in addition to any lattice water that might be
present (presence of small amounts of lattice water were confirmed
by NMR and were included in calculating the elemental analyses),
are presumably located in the interstitial spaces of the crystal lattice,
as suggested by the high residual electron density that is found in
these areas. However, the displaced anions are subject to disorder
and could not be located. Consequently, the electron density
associated with this fragment was artificially subtracted from the
data set using the program SQUEEZE.26 The composition of the
compounds was confirmed through both elemental analysis and
spectroscopic techniques. The complete elucidation of these two
compounds is discussed in more depth in the Results section.
Figure 2. ORTEP representation of the cation of complex 2. Thermal
ellipsoids are drawn at the 30% probability level, and hydrogen atoms have
been omitted for clarity.
dination compounds. The structure and composition of these
compounds, as determined spectroscopically and by single-
crystal X-ray diffraction experiments, vary dramatically both
with changes in the lead salt and with changes in the
transition metal salen* compounds. The structures of the
compounds, as determined by single-crystal X-ray diffraction
experiments, are provided in Figures 1-6, while pertinent
details relating to the data collection and refinement are
provided in Tables 1-5.
The lead center in all of the compounds developed in this
study interacts with the transition metal salen* complexes
through the phenoxy groups of the salen* ligand. The Pb-
Osalen bond lengths in compounds 1-4 range from 2.479(3)
to 2.971(5) Å and are similar to the bond distances observed
for other main group metal-transition metal salen* com-
plexes that have been produced by our group and by
others;14,16,23 however, the interaction of the lead with the
two oxygen atoms is asymmetric, and in the case of 3, the
second interaction is so much weaker than the first (dPb-O
) 2.479(3) and 2.971(5) Å) (Figure 3) that the Cu(salen*)
might be more appropriately considered as essentially a
monodentate ligand. In compounds 1-4, the angle between
the Osalen*-Pb-Osalen* plane and the plane defined by the
Results
Divalent lead salts react smoothly with transition metal
salen* complexes to produce stable heterobimetallic coor-
(24) SADABS; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(25) SHELXTL; University of Go¨ttingen: Go¨ttingen, Germany, 2001.
(26) Spek, A. Platon, A Multipurpose Crystallographic Tool; Utrecht: The
Netherlands, 2001.
2710 Inorganic Chemistry, Vol. 43, No. 8, 2004

Heterobimetallic Coordination Complexes
Figure 3. ORTEP representation of complex 3. Thermal ellipsoids are
drawn at the 50% probability level. A broken line represents weak
interactions between Pb(1) and O(1). Lattice solvent has been omitted for
clarity.
Figure 6. Ball-and-stick representation of the packing orientation of 4.
Short Ni-Ni contacts in the crystal lattice are illustrated by broken lines.
Hydrogen atoms have been omitted for clarity.
Table 1. Crystallographic Data for New Compounds
1
2
3
4
formula
C50H46Cu2- C36H36Cu2-
N4O14Pb N6O10Pb
1261.18 1126.98
C22H26Cu- C38H39N4-
N2O9Pb Ni2O10Pb
733.16 1064.86
fw
space group
Z
P1h
1
Pbca
8
P1h
2
C2/c
4
cryst syst
a (Å)
b (Å)
triclinic
10.480(2)
10.515(2)
11.988(2)
71.50(3)
64.50(3)
79.52(3)
1129.1(4)
orthorhombic triclinic
monoclinic
18.688(4)
22.868(5)
15.543(3)
23.434(5)
9.990(2)
10.759(2) 26.355(5)
12.756(3) 13.377(3)
110.96(3)
c (Å)
R (deg)
â (deg)
γ (deg)
V, Å3
D(calcd), g/mm 1.855
temp (°C)
103.97(3) 133.01(3)
97.73(3)
8329(3)
1.698
28
1188.0(4) 4818.0(17)
2.044
28
Figure 4. ORTEP representation of the cation of complex 4. Thermal
ellipsoids have been drawn at the 30% probability level, and hydrogen atoms
have been omitted for clarity.
1.468
28
28
λ, Mo KR (Å)
0.71073
47.29
0.0352
0.0728
0.71073
51.08
0.0582
0.2004
0.71073
80.27
0.0196
0.0509
0.71073
43.14
0.0533
0.1626
µ (cm-1
R1a
)
wR2b
2
a Conventional R on Fhkl: ∑|Fo| - |Fc|/∑|Fo|. b Weighted R on |Fhkl| :
2
2
2
{∑[w(Fo - Fc )2]/∑[w(Fo )2]}1/2
.
Table 2. Selected Bond Lengths [Å] and Angles [deg] for 1a
Pb(1)-O(1)
Pb(1)-O(2)
Pb(1)-O(22)
Cu(1)-O(1)
2.690(4)
2.579(4)
2.545(5)
1.910(4)
Cu(1)-O(2)
Cu(1)-N(1)
Cu(1)-N(2)
1.906(4)
1.905(5)
1.938(5)
O(1)#1-Pb(1)-O(1)
O(2)-Pb(1)-O(1)#1
O(2)#1-Pb(1)-O(1)
O(2)-Pb(1)-O(1)
O(2)#1-Pb(1)-O(2)
O(2)#1-Pb(1)-O(1)#1
O(22)-Pb(1)-O(1)
O(22)#1-Pb(1)-O(1)
O(22)-Pb(1)-O(1)#1
180.00(16) O(22)#1-Pb(1)-O(2)#1 99.73(15)
120.46(11) O(22)-Pb(1)-O(2)
120.46(11) O(22)#1-Pb(1)-O(2)
59.54(11) O(1)-Cu(1)-N(2)
180.00(12) O(2)-Cu(1)-O(1)
59.54(11) O(2)-Cu(1)-N(2)
92.51(14) N(1)-Cu(1)-O(2)
87.49(14) N(1)-Cu(1)-O(1)
87.49(14) N(1)-Cu(1)-N(2)
99.73(15)
80.27(15)
172.45(19)
86.65(15)
93.35(18)
173.5(2)
94.45(19)
84.7(2)
Figure 5. Ball-and-stick representation of the packing orientation of 3.
Hydrogen atoms have been omitted for clarity. Broken lines represent short
contacts between copper atoms and phenolic oxygen atoms.
O(22)#1-Pb(1)-O(1)#1 92.51(14) Cu(1)-O(1)-Pb(1)
O(22)-Pb(1)-O(22)#1 180.000(1) Cu(1)-O(2)-Pb(1)
97.31(14)
101.19(15)
O(22)-Pb(1)-O(2)#1
80.27(15)
a Symmetry transformations used to generate equivalent atoms: #1 -x
+ 1, -y + 1, -z + 1.
salen* ligand ranges from ca. 143.6° to 154.8°, indicating
that the lead center sits well out of the plane of the salen*
ligand. This orientation of the lead presumably maximizes
the interaction of the main group metal with the phenolic
oxygen lone pair electrons and is similar to what has been
observed in other complexes.23 The stability of the Pb-
M(salen*) interactions is strong enough that the parent ion,
plus several daughter fragments of each of these compounds,
is observed in the MALDI-TOF mass spectra.
As noted above, the geometry at the lead center varies
dramatically both under the influence of the lead salt and
under the influence of the transition metal salen* compound.
Inorganic Chemistry, Vol. 43, No. 8, 2004 2711

Thurston et al.
Table 3. Selected Bond Lengths [Å] and Angles [deg] for 2
Compounds 2 and 4 resemble 1 in that they are also 2:1
adducts; however, in these compounds the interaction of the
M(salen*) complex (M ) Cu, Ni) with the lead salt results
in displacement of one of the anions. Additionally, there is
a significant difference in the orientations of the two salen*
ligands in 1, 2, and 4. In the solid-state structure of 1, the
salen* ligands are directly opposed to one another as imposed
by crystallographic inversion symmetry, and consequently,
the Cu‚‚‚Pb‚‚‚Cu angle is exactly 180.0°. In contrast to this
orientation, the Cu‚‚‚Pb‚‚‚Cu angles in 2 and 4 are ca. 71.8°
and 63.4°, respectively, reflecting that the M(salen*) ligands
overlap to a significant extent that does not occur for 1.
A subtle difference between compounds 2 and 4 lies in
the nature of the interaction of the coordinated anion with
the lead center. In the case of 2, the nitrate ion adopts a
monodetate interaction with the lead, whereas in the case of
4, the acetate adopts a bidentate chelating coordination mode.
As a result of the different coordination modes of the anions
in these complexes, the lead center in compound 2 can be
most effectively described as adopting a distorted square
pyramidal geometry whereas the lead center in compound 4
is a distorted trigonal pyramid.
It is important to note that the solid-state structures of
compounds 2 and 4 indicate that the association of the
M(salen*) complex with the lead center results in the
displacement of one of the anions from the lead center, and
consequent formation of an ionic complex. As noted above,
we were not able to locate the anions directly from the
residual electron density due to disordering of the remaining
counterion. Both structures show large vacant channels, and
presumably, the counterions are dispersed throughout these
spaces in a highly disordered fashion. Confirmation of the
identity of the displaced anions has been achieved by
elemental analysis, in which the observed composition shows
excellent agreement with the values predicted from the
proposed formulas. Additionally, spectroscopic interrogation
of 4 by multinuclear NMR studies reveals a 1:1 ratio of
acetate to salen*, consistent with our formulation for this
compound. Similar analysis was not possible for 2 owing to
the presence of the paramagnetic Cu2+ ion.
Pb(1)-O(11)
Pb(1)-O(12)
Pb(1)-O(21)
Pb(1)-O(22)
Pb(1)-O(101)
Cu(1)-O(21)
Cu(1)-O(22)
2.481(8)
2.604(7)
2.637(8)
2.648(8)
2.651(11)
1.889(8)
1.911(8)
Cu(1)-N(21)
Cu(1)-N(22)
Cu(2)-O(11)
Cu(2)-N(12)
Cu(2)-O(12)
Cu(2)-N(11)
1.913(11)
1.914(11)
1.891(8)
1.908(11)
1.910(8)
1.913(12)
O(11)-Pb(1)-O(12)
O(11)-Pb(1)-O(21)
O(12)-Pb(1)-O(21)
O(11)-Pb(1)-O(22)
O(12)-Pb(1)-O(22)
O(21)-Pb(1)-O(22)
O(11)-Pb(1)-O(101)
O(12)-Pb(1)-O(101)
61.1(2) O(22)-Cu(1)-N(22)
82.2(3) N(21)-Cu(1)-N(22)
130.5(3) O(11)-Cu(2)-N(12)
71.8(3) O(11)-Cu(2)-O(12)
78.4(3) N(12)-Cu(2)-O(12)
58.3(3) O(11)-Cu(2)-N(11)
84.4(3) N(12)-Cu(2)-N(11)
85.2(3) O(12)-Cu(2)-N(11)
94.4(4)
84.3(5)
176.2(4)
85.7(3)
94.5(4)
94.9(4)
85.2(5)
175.8(4)
105.6(3)
100.5(3)
101.7(3)
100.7(3)
O(21)-Pb(1)-O(101) 125.2(3) Cu(2)-O(11)-Pb(1)
O(22)-Pb(1)-O(101) 155.6(3) Cu(2)-O(12)-Pb(1)
O(21)-Cu(1)-O(22)
O(21)-Cu(1)-N(21)
O(22)-Cu(1)-N(21)
O(21)-Cu(1)-N(22)
85.2(3) Cu(1)-O(21)-Pb(1)
96.3(4) Cu(1)-O(22)-Pb(1)
177.1(4) N(100)-O(101)-Pb(1) 108.1(9)
175.4(4)
Table 4. Selected Bond Lengths [Å] and Angles [deg] for 3
Pb(1)-O(2)
Pb(1)-O(11)
Pb(1)-O(12)
Pb(1)-O(21)
2.479(3)
2.433(3)
2.584(3)
2.356(3)
Cu(1)-O(1)
Cu(1)-O(2)
Cu(1)-N(1)
Cu(1)-N(2)
1.928(3)
1.923(3)
1.929(3)
1.940(3)
O(21)-Pb(1)-O(11)
O(21)-Pb(1)-O(2)
O(11)-Pb(1)-O(2)
O(21)-Pb(1)-O(12)
O(11)-Pb(1)-O(12)
O(2)-Pb(1)-O(12)
O(2)-Cu(1)-O(1)
77.48(12) O(2)-Cu(1)-N(1)
86.87(11) O(1)-Cu(1)-N(1)
74.23(10) O(2)-Cu(1)-N(2)
88.27(12) O(1)-Cu(1)-N(2)
51.62(12) N(1)-Cu(1)-N(2)
175.87(13)
92.84(13)
93.18(13)
176.92(12)
84.08(14)
125.32(11) Cu(1)-O(2)-Pb(1) 106.69(11)
89.90(11)
Table 5. Selected Bond Lengths [Å] and Angles [deg] for 4a
Pb(1)-O(1)
Pb(1)-O(2)
Pb(1)-O(21)
Ni(1)-N(2)
2.613(7)
2.633(7)
2.663(10)
1.826(11)
Ni(1)-O(2)
Ni(1)-O(1)
Ni(1)-N(1)
1.841(7)
1.844(8)
1.854(11)
O(1)#1-Pb(1)-O(1)
O(1)#1-Pb(1)-O(2)
O(1)-Pb(1)-O(2)
O(1)#1-Pb(1)-O(2)#1
O(1)-Pb(1)-O(2)#1
O(2)-Pb(1)-O(2)#1
113.9(3) O(2)-Pb(1)-O(21)
76.7(2) O(2)#1-Pb(1)-O(21)
55.6(2) O(21)#1-Pb(1)-O(21)
55.6(2) N(2)-Ni(1)-O(2)
76.7(2) N(2)-Ni(1)-O(1)
86.5(3) O(2)-Ni(1)-O(1)
112.8(3)
160.6(3)
47.8(5)
95.7(5)
178.1(4)
83.2(3)
86.6(6)
176.8(4)
94.5(5)
103.7(3)
103.0(3)
O(1)#1-Pb(1)-O(21)#1 113.4(3) N(2)-Ni(1)-N(1)
O(1)-Pb(1)-O(21)#1
O(2)-Pb(1)-O(21)#1
126.9(3) O(2)-Ni(1)-N(1)
160.6(3) O(1)-Ni(1)-N(1)
Complex 3 is unique in this study as it is the only 1:1
adduct that was produced under the conditions explored. As
noted above, the interaction of the salen* compound with
the lead center is highly asymmetric resulting in the geometry
at the lead center being intermediate to that of a distorted
tetrahedron and a distorted trigonal bipyramid. In addition
to the transition metal compound, the coordination environ-
ment of the lead is completed by interactions with the two
acetate ions, one of which is monodentate, while the other
is bidentate and chelating. The general structural and
geometric parameters of the four complexes developed in
this study, including Pb-O bond lengths and angles, all agree
well with what was anticipated from the reports of other
similar complexes.14,16,17,23
O(2)#1-Pb(1)-O(21)#1 112.8(3) Ni(1)-O(1)-Pb(1)
O(1)#1-Pb(1)-O(21)
O(1)-Pb(1)-O(21)
126.9(3) Ni(1)-O(2)-Pb(1)
113.4(3)
a Symmetry transformations used to generate equivalent atoms: #1 -x,
1
y, -z + /2.
The influence of the anion on the coordination environment
of the lead center in the heterobimetallic complexes is
succinctly illustrated in the solid-state structures of com-
pounds 1-3. Interaction of lead(II) salicylate with Cu(salen*)
results in the formation of the neutral 2:1 adduct 1. In this
case, the lead is six-coordinate and adopts a distorted
octahedral coordination environment in which four of these
sites are occupied by the two Cu(salen*) ligands and two
by the monodentate salicylate ligands that are oriented trans
to one another. These salicylate ligands also bridge to the
Cu2+ ions.
An additional consideration in this regard is that the
identity and consequent electronic structure of the transition
metal appears to assert some influence on the overall packing
structure of the complexes. The Cu(salen*) complexes in
2712 Inorganic Chemistry, Vol. 43, No. 8, 2004

Heterobimetallic Coordination Complexes
compounds 1 and 3 contain five-coordinate copper atoms.
In the case of compound 1, the coordination sphere of the
copper is completed intramolecularly by the bridging sali-
cylate ligands. Complex 3, on the other hand, is observed to
pack so that the apical coordination site of the five-coordinate
copper center is occupied by a phenolic oxygen in an adjacent
salen* ligand (Figure 5). Some additional stabilization of this
packing mode may arise from π stacking interactions
between adjacent salen* ligands (dcentroid-centroid ) 3.827(4)
Å). Unlike compounds 1 and 3, the copper centers in
complex 2 adopt strictly four-coordinate, square planar
geometries. The reasons for the different coordination
requirments of the copper in these compounds are not clear
at this point.
the only heterobimetallic complex produced from the reac-
tion, even if only 1 equiv of Cu(salen*) is employed in the
synthesis.
In addition to the effects of the anions, the electronic
environment of the salen* ligand also appears to have a
profound impact on the composition and resulting structure
of these coordination compounds. This is most clearly
illustrated in the case of complexes 3 and 4, in which the
only chemical difference between the starting reagents is the
electronic environment of the two transition metals. As noted
above, complex 3 consists of a neutral 1:1 adduct in which
both acetate anions are bound to the lead center. In contrast,
compound 4 consists of an ionic 2:1 adduct in which one of
the acetate anions has been displaced from the lead coordina-
tion sphere, while the remaining anion adopts a bidentate
chelating coordination mode. The compositional differences
between these two molecules likely arise from the differences
In contrast to the packing behavior of the Cu(salen*)
compounds, complex 4 is observed to adopt an orientation
in the crystal lattice that affords short intermolecular Ni-
Ni contacts (dNi-Ni ) 3.497(3) Å) (Figure 6). It is important
to note that the packing behavior of all four complexes,
particularly with regard to the formation of close intermo-
lecular ring contacts in the copper systems or metal-metal
contacts in the nickel systems, is in accord with similar
compounds that have been prepared by our group and
others.14,16,23
in the relative acidities of the two different transition metal
2+
centers (cf., pKa Cu(H2O)62+(aq) ) 7.49, pKa Ni(H2O)6
-
(aq) ) 9.03).27 The less acidic Ni2+ ion would be expected
to produce greater electron density at the phenolic oxygen
atoms, allowing it to bind more effectively to the lead center
than the Cu(salen*) complex, resulting in displacement of
an acetate ion. The shorter Pb-Osalen bond distances that are
observed in 3 as opposed to 4 (3: dPb-O ) 2.479(3) Å, 4:
dPb-O ) 2.613(7) and 2.633(7) Å) are believed to stem from
steric interactions relating to the orientation of the relatively
bulky salen* complex in the lead coordination sphere when
two such ligands are present. Additionally, it is possible that
the presence of two transition metal salen* complexes
attenuates that Lewis acidity of the lead center, resulting in
weaker binding of the transition metal complex.
Discussion
The composition and geometry of the complexes produced
in this study can be most directly viewed as arising from a
competition between the anion and the salen* complexes for
coordination with the lead center. The influence of this
competition can be seen in the solid-state structures of
complexes 1-3. The anions employed in this study range
from the nonbasic NO3- ion to the somewhat more strongly
basic salicylate ligand (pKa1, salicylic acid ) 2.75) to the
acetate ion (pKa, acetic acid ) 4.74). The acetate ion, which
is the most strongly coordinating, is able to compete
efficiently with the salen* ligands for interaction with the
lead center, resulting in the formation of the 1:1 adduct 3. It
is important to note that complex 3 is the only heterobime-
tallic compound that is produced in this reaction, even if an
excess of Cu(salen*) is employed. In contrast, the weakly
coordinating nitrate ligand is readily displaced from the lead
coordination sphere in the case of complex 2, and the 2:1
adduct 2 is obtained as the sole product. As expected from
the relative pKa of the salicylate ligand, complex 1 is
structurally intermediate between compounds 2 and 3. The
salicylate ligands are basic enough that they are not displaced
completely, similar to 3, but the coordination mode of the
carboxylate anions is now monodentate, as opposed to the
bidentate chelating interaction that is more commonly
encountered in main group carboxylate coordination chem-
istry. As was observed for complex 3, the 2:1 adduct 1 is
Conclusions
The results of this study indicate that the formation of
heterobimetallic coordination complexes via Lewis acid-
base interactions can be accurately viewed as arising from a
direct competition between an M(salen*) complex and
acetate, salicylate, or nitrate for binding to a lead center.
Clearly, precisely tuning the composition of heterobimetallic
coordination complexes through careful selection of both the
metal species and the respective ligands is possible. Ad-
ditionally, the apparent generality of this chemistry suggests
that it may be possible to apply these techniques to a wide
variety of metal species. Similar results have been obtained
for coordination of M(acac)3 (acac ) 2,4-pentanedionate-1)
complexes bound to bismuth salicylate.28 In this manner, it
may be possible to move beyond “fortuitous self-assembly”
in the design of molecular precursors for the formation of
advanced materials.
Acknowledgment. We would like to thank the Robert
A. Welch Foundation and the National Science Foundation
CHE-9983352 for support of this work.
Supporting Information Available: Crystallographic data in
CIF format. This material is available free of charge via the Internet
at http://pubs.acs.org.
(27) Lange’s Handbook of Chemistry, 15th ed.; McGraw-Hill: New York,
1999.
(28) Thurston, J. H.; Trahan, D. W.; Ould Ely, T.; Whitmire, K. H. Inorg.
Chem., submitted for publication.
IC035427W
Inorganic Chemistry, Vol. 43, No. 8, 2004 2713