Alcoholysis of 2,2'-pyridil, (2-C5H4N)C(O)C(O)(2-C5H4N), iin the presence of copper(II): A family of planar pentanuclear copper(II) complexes stabilized by [(2-C5H4N)C(O)(OR)C(O)(OR)(2-C5H4N)]2- and carboxylate ligands

Article abstract of DOI:10.1021/ic991169k

'Blends' of 2,2'-pyridil, (2-C₅>H₄>N)C(O)C(O)(2-C₅>H₄>N), and carboxylate ligands, R'CO₂^-, in alcohols (ROH) at room temperature are used to produce three clusters of the general formula [Cu₅(OH)₂{[(2-C₅H₄N)C(O)-(OR)C(O)(OR)(2-C₅H₄N)}₂>(O₂>CR')₄>(ROH)₂ >]. The five Cu(II) atoms are coplanar, exhibiting a rectangular arrangement of four metal ions with the fifth at the center of the rectangle. The representative complex with R = Et and R' = Me exhibits antiferromagnetic behavior.

Full text of DOI:10.1021/ic991169k

4
658
Inorg. Chem. 2000, 39, 4658-4662
Alcoholysis of 2,2′-Pyridil,
2-C5H4N)C(O)C(O)(2-C5H4N), in the Presence of
carboxylate ligands and the formation of large polynuclear arrays
of metal ions. The structural diversity of the resultant species
stems from the ability of the singly and doubly deprotonated
anions of the gem-diol form of (2-C5H4N)C(O)(2-C5H4N) to
adopt a variety of coordination modes, sometimes two different
modes in the same complex. Restricting further discussion to
copper(II) chemistry, we note that the synthetic investigation
(
Copper(II): A Family of Planar Pentanuclear
Copper(II) Complexes Stabilized by
[
(2-C5H4N)C(O)(OR)C(O)(OR)(2-C5H4N)]2- and
Carboxylate Ligands
-
of the [Cu2(O2CMe)4(H2O)2]/(2-C5H4N)C(O)(2-C5H4N)/ClO4
Giannis S. Papaefstathiou,†
reaction mixture in H O has led to the isolation of the
2
‡
‡
2a
Catherine P. Raptopoulou, Alexandros Tsohos,
remarkable octanuclear complex [Cu {(2-C H N)C(O)(OH)-
8
5
4
,‡
,§
Aris Terzis,* Evangelos G. Bakalbassis,* and
5 4 8 2 4 4 4 2 2
(2-C H N)} (O CMe) ](ClO ) , whereas the reaction of [Cu (O -
,
†
Spyros P. Perlepes*
4 2 2 5 4 5 4
CMe) (H O) ] with (2-C H N)C(O)(2-C H N) in MeCN, in the
2b
absence of counterions, gave the novel molecules [Cu7(OH)2-
(2-C5H4N)CO2(2-C5H4N)}3(O2CMe)6] and [Cu12{(2-C5H4N)-
Department of Chemistry, University of Patras,
65 00 Patras, Greece, Institute of Materials Science, NCSR
{
2
CO2(2-C5H4N)}6(O2CMe)12].
“
Demokritos”, 153 10 Aghia Paraskevi Attikis, Greece, and
Laboratory of Applied Quantum Chemistry, Department of
Chemistry, Aristotle University of Thessaloniki,
More recently, our efforts have turned toward the use of 2,2′-
pyridil [(2-C5H4N)C(O)C(O)(2-C5H4N); Chart 1], which pre-
sents chemical similarities to (2-C5H4N)C(O)(2-C5H4N) but
contains an extra donor group, to see how incorporation of this
ligand type might affect the structures and physical properties
of the products. Here we report a study of a simple reaction
involving a “blend” of (2-C5H4N)C(O)C(O)(2-C5H4N) and
carboxylate ligands in alcohols, which produces a series of
planar pentanuclear copper(II) complexes. The structures of three
members of this family and the magnetic properties of one
representative complex are described. This work can also be
regarded as a contribution to the almost unexplored coordination
5
40 06 Thessaloniki, Greece
ReceiVed October 4, 1999
Introduction
1
The development of routes and strategies for the synthesis
of high-nuclearity complexes of 3d metals in moderate oxidation
states is of great importance because these species have provided
substantial impetus for developments in several different fields,
including bioinorganic chemistry, magnetochemistry, material
chemistry, and solid-state physics.
4
chemistry of 2,2′-pyridil.
We have been pursuing studies2 of polynuclear complexes
,3
Experimental Section
of the later 3d metals because such clusters may display unusual
structures and interesting magnetic properties. One of our routes
takes advantage of the observation that the reactions between
metal carboxylates and di-2-pyridyl ketone [(2-C5H4N)C(O)-
2
Syntheses. All manipulations were performed under aerobic
conditions using materials and solvents as received (Aldrich
Co.). The compound Cu(O2CPh)2‚EtOH was prepared as
5
described elsewhere.
(2-C5H4N); see Chart 1] lead to incomplete replacement of the
[
Cu5(OH)2{(2-C5H4N)C(O)(OEt)C(O)(OEt)(2-C5H4N)}2-
(O2CMe)4(EtOH)2]‚2EtOH (1). To a solution of (2-C5H4N)C-
O)C(O)(2-C5H4N) (0.12 g, 0.56 mmol) in EtOH (10 mL) was
†
University of Patras.
NCSR “Demokritos”.
Aristotle University of Thessaloniki.
‡
(
§
added a solution of [Cu2(O2CMe)4(H2O)2] (0.28 g, 0.70 mmol)
in the same solvent (30 mL). The blue solution obtained was
stirred at ambient temperature for 30 min and allowed to stand
undisturbed for 3 d. Well-formed, X-ray-quality crystals of 1
slowly appeared. The blue prismatic crystals were collected by
filtration, washed with EtOH, and dried in air. The yield was
(
1) (a) Libby, E.; Folting, K.; Huffman, C. J.; Huffman, J. C.; Christou,
G. Inorg. Chem. 1993, 32, 2549. (b) Winpenny, R. E. P. Comments
Inorg. Chem. 1999, 20, 233. (c) Burger, J.; Kl u¨ fers, P. Angew. Chem.,
Int. Ed. Engl. 1997, 36, 776. (d) Watton, S. P.; Fuhrmann, P.; Pence,
L. E.; Caneschi, A.; Cornia, A.; Abbati, G.-L.; Lippard, S. J. Angew.
Chem., Int. Ed. Engl. 1997, 36, 2774. (e) Powell, A. K.; Heath, S. L.;
Gatteschi, D.; Pardi, L.; Sessoli, R.; Spina, G.; Del Giallo, F.; Pieralli,
F. J. Am. Chem. Soc. 1995, 117, 2491. (f) Tandon, S. K.; Thompson,
L. K.; Bridson, J. N.; Benelli, C. Inorg. Chem. 1995, 34, 5507. (g)
Real, J. A.; De Munno, G.; Chiappetta, R.; Julve, M.; Lloret, F.;
Journaux, Y.; Colin, J.-C.; Blondin, G. Angew. Chem., Int. Ed. Engl.
∼
45% based on copper. Anal. Calcd for C48H74Cu5N4O22: C,
4
1.87; H, 5.41; N, 4.07; Cu, 23.07. Found: C, 41.70; H, 5.36;
-1
N, 4.22; Cu, 22.47. Selected IR data (cm ) (KBr pellet): 3444
1
994, 33, 1184. (h) Murray, K. S. AdV. Inorg. Chem. 1995, 43, 261.
(
(
m, br), 1590 (s), 1474 (m), 1408 (s), 1124 (m), 1092 (s), 1022
m), 772 (m), 656 (m).
(i) Escuer, A.; Font-Bardia, M.; Kumar, S. B.; Solans, X.; Vicente,
R. Polyhedron 1999, 18, 909.
n
n
(
2) (a) Tangoulis, V.; Raptopoulou, C. P.; Terzis, A.; Paschalidou, S.;
Perlepes, S. P.; Bakalbassis, E. G. Inorg. Chem. 1997, 36, 3996. (b)
Tangoulis, V.; Raptopoulou, C. P.; Paschalidou, S.; Bakalbassis, E.
G.; Perlepes, S. P.; Terzis, A. Angew. Chem., Int. Ed. Engl. 1997, 36,
[Cu5(OH)2{(2-C5H4N)C(O)(OPr )C(O)(OPr )(2-C5H4N)}2-
n
n
(
[
O2CMe)4(Pr OH)2]‚0.8Pr OH (2). To a stirred solution of
n
Cu2(O2CMe)4(H2O)2] (0.14 g, 0.35 mmol) in Pr OH (20 mL)
1
083. (c) Tangoulis, V.; Raptopoulou, C. P.; Paschalidou, S.; Tsohos,
A. E.; Bakalbassis, E. G.; Terzis, A.; Perlepes, S. P. Inorg. Chem.
997, 36, 5270. (d) Tsohos, A.; Dionyssopoulou, S.; Raptopoulou,
was added a solution of (2-C5H4N)C(O)C(O)(2-C5H4N) (0.06
g, 0.28 mmol) in the same solvent (10 mL). Layering of Et2O
1
C.; Terzis, A.; Bakalbassis, E. G.; Perlepes, S. P. Angew. Chem., Int.
Ed. Engl. 1999, 38, 983.
(4) (a) Black, D. S. C. Chem. Commun. 1967, 311. (b) Black, D. S. C.;
Srivastava, R. C. Aust. J. Chem. 1969, 22, 1439. (c) Black, D. S. C.;
Srivastava, R. C. Aust. J. Chem. 1970, 23, 2067. (d) Barandika, M.
G.; Serna, Z. E.; Urtiaga, M. K.; De Larramendi, J. I. R.; Arriortua,
M. I.; Cortes, R. Polyhedron 1999, 18, 1311. (e) Abrahams, B. F.;
Hoskins, B. F.; Hudson, T. A.; Robson, R. Acta Crystallogr., Sect. C
2000, 56, e126.
(
3) (a) Bakalbassis, E. G.; Diamantopoulou, E.; Perlepes, S. P.; Rapto-
poulou, C. P.; Tangoulis, V.; Terzis, A.; Zafiropoulos, Th. F. J. Chem.
Soc., Chem. Commun. 1995, 1347. (b) Tangoulis, V.; Raptopoulou,
C. P.; Terzis, A.; Bakalbassis, E. G.; Diamantopoulou, E.; Perlepes,
S. P. Inorg. Chem. 1998, 37, 3142. (c) Tangoulis, V.; Diamantopoulou,
E.; Bakalbassis, E. G.; Raptopoulou, C. P.; Terzis, A.; Perlepes, S. P.
Mol. Cryst. Liq. Cryst. 1999, 335, 463.
(5) Inoue, M.; Kishita, M.; Kubo, M. Inorg. Chem. 1964, 3, 239.
1
0.1021/ic991169k CCC: $19.00 © 2000 American Chemical Society
Published on Web 09/09/2000

Notes
Inorganic Chemistry, Vol. 39, No. 20, 2000 4659
Chart 1. Ligands Discussed in the Texta
a
5 4 5 4 5 4 2 5 4
Note that [(2-C H N)C(O)(OH)(2-C H H N)CO (2-C H
N)]- and [(2-C N)]2- do not exist as free species but exist only in their complexes.
Table 1. Crystallographic Data for Complexes 1-3
parameter
1
2
3
formula
fw
space group
a, Å
b, Å
c, Å
C
48
H
74Cu
5
N O
4 22
C
52.4
H
80.4Cu
5 4
N
O
20.8
C
72
H
5 4 22
90Cu N O
1376.81
P1h
1416.91
I2/a
25.12(1)
16.450(7)
17.254(7)
1681.24
P1h
12.522(1)
11.117(1)
12.643(1)
65.43(1)
81.49(1)
74.34(1)
1539.9(3)
1
12.488(5)
12.200(5)
15.373(6)
111.29(1)
92.93(1)
114.33(1)
1932.1(1)
1
R, deg
â, deg
γ, deg
92.32(1)
3
V, Å
7123(5)
4
Z
T, °C
λ, Å
25
1.541 80
1.485
2.539
0.0381
0.1011
25
25
0.710 73
1.444
1.427
0.0458
0.0966
0.710 73
1.321
1.533
0.0683
0.1736
-
3
F
calc, g cm
-
1
µ, mm
a
R1
a
wR2
a
2
2
2, 0) + 2F 2
)/3; R ) 0.0504, b ) 1.1669 for 1, a ) 0.0843, b ) 70.5315 for 2, and a ) 0.0000,
2 2 2 2 2 1/2
w ) 1/[σ (F
o
2) + (aP) + bP] and P ) (max(F
| - |F |)/∑(|F |) and wR2 ) [∑w(F
o
c
b ) 2.4010 for 3. R1 ) ∑(|F
o
c
o
o
c o
- F ) /∑w(F ) ] for 4350 (1), 3065 (2), and 5258 (3) reflections with I >
2
σ(I).
(
45 mL) over the dark blue solution gave a mixture of mauve
Found: C, 49.87; H, 4.70; N, 3.59; Cu, 20.96. Selected IR data
-
1
needles and blue prismatic crystals. These were carefully
collected by filtration. The two products were readily separated
manually, and the mauve and blue crystals were determined by
single-crystal X-ray crystallography to be trans-[Cu(pic)2] (pic-
)
2
in the 10-15% range (based on Cu). Anal. Calcd for C52.4H80.4-
Cu5N4O20.8: C, 44.41; H, 5.71; N, 3.95; Cu, 22.42. Found: C,
4
(cm ) (KBr pellet): 3446 (m, br), 1606 (s), 1568 (s), 1382
(s), 1366 (s), 1116 (m), 1084 (s), 960 (m), 768 (w), 656 (w).
Physical Techniques. C, H, and N microanalyses were
conducted by the microanalytical service of the University of
Ioannina, Greece, and copper analysis was carried out by EDTA
picolinate ion) and complex 2, respectively. The crystals of
were washed with Et2O and dried in air; typical yields were
-
1
titration. IR spectra (4000-500 cm ) were recorded on a
Perkin-Elmer 16 PC spectrometer. Magnetic susceptibility
measurements were carried out on a polycrystalline sample of
1 in the 3-300 K range under a magnetic field of 6 kG by
using a Quantum Design SQUID susceptometer. The suscep-
tibility of the sample was found to be field independent. The
experimental magnetic susceptibilities were corrected for the
diamagnetic response using Pascal’s constants. Solid-state EPR
spectra in the 5-300 K temperature range were recorded on a
Bruker ER 200D-SRC X-band spectrometer, equipped with an
Oxford ESR 9 helium continuous-flow cryostat, a Hall probe,
and a Hewlett-Packard frequency meter.
-
1
4.19; H, 5.55; N, 3.98; Cu, 23.00. Selected IR data (cm )
(
(
KBr pellet): 3470 (m), 3444 (m, br), 1588 (s), 1570 (m), 1396
s), 1120 (m), 1092 (s), 1034 (m), 770 (m), 656 (m).
[
Cu5(OH)2{(2-C5H4N)C(O)(OEt)C(O)(OEt)(2-C5H4N)}2-
(
O2CPh)4(EtOH)2]‚2Et2O (3). Solid Cu(O2CPh)2‚EtOH (0.13
g, 0.37 mmol) was dissolved with stirring in a solution of (2-
C5H4N)C(O)C(O)(2-C5H4N) (0.04 g, 0.19 mmol) in EtOH (30
mL) at room temperature. The blue solution obtained was
filtered and layered with Et2O (40 mL). Slow mixing yielded
mauve needles of trans-[Cu(pic)2] and blue prismatic crystals
of 3. The X-ray-quality blue crystals were separated manually
from the mixture, washed with copious amounts of Et2O, and
dried in air. The yield was ∼10% (based on Cu). An analysis
sample gave results consistent with [Cu5(OH)2{(2-C5H4N)C-
X-ray Crystallography. Blue prismatic crystals of 1-3 were
mounted in capillaries filled with drops of the mother liquors.
Complete crystal data and parameters for data collection for
the three complexes are reported in Table 1. Intensity data were
recorded using a θ-2θ scan. Three standard reflections
monitored every 97 reflections showed less than 3% variation
and no decay. Lorentz, polarization, and ψ-scan absorption (only
(O)(OEt)C(O)(OEt)(2-C5H4N)}2(O2CPh)4(EtOH)2]. Anal. Calcd
for C64H70Cu5N4O20: C, 50.14; H, 4.60; N, 3.65; Cu, 20.72.

4660 Inorganic Chemistry, Vol. 39, No. 20, 2000
Notes
for 1) corrections were applied using Crystal Logic software.
The structures were solved by direct methods using SHELXS-
6
a
2
8
6 and refined by full-matrix least-squares techniques on F
6
b
with SHELXL-93. Further crystallographic details are briefly
as follows. Complex 1: 2θ(max) ) 130° (Cu KR radiation),
scan speed 3.0°/min, scan range 2.4° + R1R2 separation,
reflections collected/unique/used ) 5464/5207 (Rint ) 0.0180)/
5
207, 432 parameters refined, (∆F)max/(∆F)min ) 0.444/-0.548
3
e/Å , (∆/σ) ) 1.295. Complex 2: 2θ(max) ) 45° (Mo KR
radiation), scan speed 1.5°/min, scan range 2.1° + R1R2
separation, reflections collected/unique/used ) 4290/4635 (Rint
)
0
5
+
6
(
0.0360)/4635, 377 parameters refined, (∆F)max/(∆F)min )
3
.623/-0.487 e/Å , (∆/σ) ) 0.124. Complex 3: 2θ(max) )
0° (Mo KR radiation), scan speed 2.5°/min, scan range 2.2°
R1R2 separation, reflections collected/unique/used ) 7161/
807 (Rint ) 0.0322)/6651, 615 parameters refined, (∆F)max/
3
∆F)min ) 0.458/-0.338 e/Å , (∆/σ) ) 0.738. For 1, all
hydrogen atoms of the methyl groups of the ligand and the
acetates, as well as hydrogens of the coordinated and solvated
EtOH molecules, were introduced at calculated positions as
riding on bonded atoms; the same was true for the hydrogen
atoms on C(36), C(37), and C(38) in 3. The remainder of the
hydrogen atoms in 1 and 3 were located by difference maps
and refined isotropically. All hydrogens of 2 were introduced
at calculated positions. All non-hydrogen atoms of 1 and 3 were
refined anisotropically. For 2, the methylene carbon C(26) of
n
the coordinated Pr OH molecule was found to be disordered
and was refined isotropically in two orientations with occupancy
fixed at 50%; the methyl group of the coordinated solvent
Figure 1. ORTEP view of the representative complex [Cu (OH) {(2-
C H N)C(O)(OEt)C(O)(OEt)(2-C H N)} (O CMe) (EtOH) ]‚2EtOH (1),
5 4 5 4 2 2 4 2
5
2
n
[C(27)] was refined isotropically, as was that of the solvate Pr -
with 50% thermal ellipsoids, showing the atom-labeling scheme. The
lattice EtOH molecules are not shown. Primes are used for symmetry-
related atoms. For clarity, all carbon atoms of the -OEt groups of the
OH, which diffused during data collection and refined with
occupation factors fixed at 10.4. The remainder of the non-
hydrogen atoms were refined anisotropically.
organic ligand and most aromatic carbon atoms have been omitted.
-
The µ
3
-OH oxygen atoms are O(5) and O(5′), and the -OEt oxygen
Results and Discussion
atoms are O(2), O(4), O(2′), and O(4′), while carbon atoms C(5), C(7),
C(5′), and C(7′) belong to the pyridyl rings; see also Chart 2.
Syntheses. The preparations of compounds 1-3 can be
achieved via the reactions of [Cu2(O2CMe)4(H2O)2] or Cu(O2-
n
(O)C(O)(2-C5H4N) in MeOH leads to a mixture of mauve
CPh)2‚EtOH with 2,2′-pyridil in EtOH (1, 3) or Pr OH (2) at
crystals of trans-[Cu(pic)2] and blue crystals of trans-[Cu(pic)2]‚
room temperature. The preparation of the representative complex
9
2
H2O. This observation was also made by Black and Srivastava,
1
is summarized in eq 1. The copper(II)-mediated alcoholysis
4
c
who proposed a mechanism for the reaction. (ii) The planar
pentanuclear complexes can be isolated either as a pure product
(
1) or in a mixture with trans-[Cu(pic)2] (2, 3) only in higher
n
alcohols (EtOH, Pr OH). (iii) The temperature is a particularly
important synthetic parameter. If the reaction mixtures in EtOH
or Pr OH are heated or refluxed, they yield exclusively trans-
n
[Cu(pic)2] or/and trans-[Cu(pic)2]‚2H2O.
Description of the Structures. Although complexes 1-3 are
not isostructural (see Table 1), their molecular structures are
similar. A labeled ORTEP plot of the representative complex
, whose structure will be discussed in detail, is shown in Figure
, and selected interatomic distances and angles for this
of (2-C5H4N)C(O)C(O)(2-C5H4N) to give the dianions of bis-
hemiacetals) (2-C5H4N)C(OH)(OR)C(OH)(OR)(2-C5H4N) in-
(
volves a nucleophilic attack of ROH molecules on the carbonyl
groups. In such reactions, it might not be necessary for the
carbonyl groups to be coordinated to the metal center; the
induced polarization from more remote coordination sites, i.e.,
1
1
compound are listed in Table 2.
7
the pyridyl nitrogen atoms, might be sufficient. There are few
(
8) (a) Deveson, A. C.; Heath, S. L.; Harding, C. J.; Powell, A. K. J.
Chem. Soc., Dalton Trans. 1996, 3173. (b) Papadopoulos, A.;
Tangoulis, V.; Raptopoulou, C. P.; Terzis, A.; Kessissoglou, D. P.
Inorg. Chem. 1996, 35, 559. (c) Kavounis, C. A.; Tsiamis, C.; Cardin,
C. J.; Zubavichus, Y. Polyhedron 1996, 15, 385. (d) Manzur, J.; Garcia,
A. M.; Garland, M. T.; Acuna, V.; Gonz a´ les, O.; Pena, O.; Atria, A.
M.; Spodine, E. Polyhedron 1996, 15, 821. (e) Alonzo, G.; Bertazzi,
N.; Maggio, F.; Benetollo, F.; Bombieri, G. Polyhedron 1996, 15,
4269. (f) Baggio, R.; Gonz a´ les, O.; Garland, M. T.; Manzur, J.; Acuna,
V.; Atria, A. M.; Spodine, E.; Pena, O. J. Cryst. Spectrosc. Res. 1993,
23, 749. (g) Alonzo, G.; Bertazzi, N.; Bombieri, G.; Bruno, G. J. Chem.
Soc., Dalton Trans. 1987, 2337.
examples in which a ketone group in a polydentate ligand is
attacked by alcohols in the presence of metal ions, the well
studied example being that of di-2-pyridyl ketone.2
c,7,8
The following points are of synthetic interest: (i) The reaction
of [Cu2(O2CMe)4(H2O)2] or Cu(O2CPh)2‚EtOH with (2-C5H4N)C-
(
6) (a) Sheldrick, G. M. SHELXS-86: Structure SolVing Program;
University of G o¨ ttingen: G o¨ ttingen, Germany, 1986. (b) Sheldrick,
G. M. SHELXL-93: Crystal Structure Refinement Program; University
of G o¨ ttingen: G o¨ ttingen, Germany, 1993.
(
7) Constable, E. W. Metals and Ligand ReactiVity, 2nd ed.; VCH:
(9) Segl’a, P.; Jamnicky, M.; Koman, M.; Sima, J.; Glowiak, T.
Weinheim, Germany, 1996: pp 46-48, 57-59.
Polyhedron 1998, 17, 4525.

Notes
Inorganic Chemistry, Vol. 39, No. 20, 2000 4661
Table 2. Selected Interatomic Distances (Å) and Angles (deg)
Relevant to the Copper Coordination Spheres in the Representative
Pentanuclear Complex 1
Cu(1)‚‚‚Cu(2)
Cu(1)‚‚‚Cu(3)
Cu(2)‚‚‚Cu(3)
Cu(2)‚‚‚Cu(3′)
Cu(1)-O(1)
Cu(1)-O(3)
Cu(1)‚‚‚O(5)
Cu(2)-O(5)
Cu(2)-O(6)
Cu(2)-O(10)
3.263(1)
3.222(1)
5.533(1)
3.382(1)
1.948(2)
1.941(2)
2.764(2)
1.909(2)
1.951(2)
2.417(3)
Cu(2)-N(1)
Cu(2)-O(1)
Cu(2)‚‚‚O(4)
Cu(3)-O(8)
Cu(3)‚‚‚O(9)
Cu(3)-O(5′)
Cu(3)-N(2)
Cu(3)-O(3)
Cu(3)‚‚‚O(2)
1.993(3)
1.999(2)
2.777(2)
1.940(2)
2.869(2)
1.890(2)
1.981(3)
1.993(2)
2.582(2)
Cu(1)-O(1)-Cu(2)
Cu(1)-O(3)-Cu(3)
Cu(1)-O(5)-Cu(2)
Cu(1)-O(5)-Cu(3)
111.5(1) O(1)-Cu(2)-O(6)
109.9(1) O(4)‚‚‚Cu(2)-N(1)
170.6(1)
75.8(1)
86.6(1) O(4)‚‚‚Cu(2)-O(10) 159.6(1)
85.4(1) O(2)‚‚‚Cu(3)-O(3)
Cu(2)-O(5)-Cu(3′) 125.8(1) O(2)‚‚‚Cu(3)-O(5′)
72.3(1)
95.9(1)
155.3(1)
90.8(1)
175.2(1)
171.2(1)
93.7(1)
50.3(1)
T/CuII
5
vs T for a polycrystalline sample of 1.
The solid line represents the fit to the theoretical model; see the text
for the fitting parameters.
Figure 2. Plot of ø
M
O(1)-Cu(1)-O(3)
O(1)-Cu(1)‚‚‚O(5)
O(3)-Cu(1)‚‚‚O(5′)
O(5)-Cu(2)-O(6)
O(5)-Cu(2)-N(1)
O(1)-Cu(2)-O(10)
85.0(1) O(2)‚‚‚Cu(3)‚‚‚O(9)
69.9(1) O(3)-Cu(3)-O(5′)
69.5(1) O(3)-Cu(3)-O(8)
98.6(1) O(5′)-Cu(3)-N(2)
163.0(1) O(5′)-Cu(3)-O(9)
91.8(1) O(8)‚‚‚Cu(3)-O(9)
Assuming that the Cu(1)-O(5), Cu(2)-O(4), Cu(3)-O(2),
and Cu(3)-O(9) distances represent weak bonding interactions,
the copper(II) centers have distorted octahedral coordination
geometries with Cu(1)O6, Cu(2)NO5, and Cu(3)NO5 chro-
mophores. Alternatively, Cu(1), Cu(2), and Cu(3) are four-,
five-, and four-coordinate, respectively; the four-coordination
sites have a perfect [Cu(1)] or a distorted [Cu(3)] square planar
geometry, while the five-coordinate site can be described as
distorted square pyramidal with the apical site occupied by
O(10). The Cu-OH-Cu angle involving the outer metal ions
of the pentanuclear core is in the range 121.1(3)-125.8(1)°, while
those around the central copper are in the range 85.4(1)-87.5-
Chart 2. Coordination of [(2-C5H4N)C(O)(OR)C(O)(OR)-
2-
(
2-C5H4N)] in Complexes 1-3a
(
1)°.
Compounds 1-3 are the first structurally characterized
complexes of any metal containing the dianions [(2-C5H4N)C-
a
The atomic labeling scheme corresponds to that used in Figure 1.
2
-
(
O)(OR)C(O)(OR)(2-C5H4N)] as ligands. They join a very
II
10
small class of discrete Cu clusters of nuclearity 5; two
members of this class have planar arrangements for the five
The pentanuclear assembly [Cu5(OH)2{(2-C5H4N)C(O)(OR)C-
n
(
)
O)(OR)(2-C5H4N)}2(O2CR′)4(ROH)2] of 1-3 (R ) Et, Pr ; R′
1
0e
8+
metal ions. The [Cu5(OH)2] core found in 1-3 is also
Me, Ph) is composed of a rectangular arrangement of four
present in the complexes Cu5(OH)2L2(NO3)4‚2.5H2O [L2
-
)
II
Cu atoms [Cu(2), Cu(3), Cu(2′), Cu(3′)] centered on the fifth
Cu(1)]. The central metal site lies on a crystallographic
1
0a
the dianion of 3,6-bis((4-methylpiperazino)methyl)pyrocatechol],
[
0e
[
Cu5(OH)2(O2CMe)6(Him)4(H2O)4](ClO4)2 (Him ) imidazole),1
inversion center, and thus, all the copper atoms are coplanar.
The distances from the central Cu atom to the peripheral ions
average to 3.24 Å in 1, 3.27 Å in 2, and 3.23 Å in 3. The lengths
of the short Cu‚‚‚Cu edges of the rectangle are 3.382(1), 3.318-
2), and 3.372(1) Å for 1-3, respectively; the lengths of the
long ones are 5.533(1), 5.632(2), and 5.523(1) Å, respectively.
The Cu atoms at each short edge of the rectangle are bridged
by an OH ion, which also interacts weakly [Cu(1)‚‚‚O(5) )
.764(2) Å in 1, 2.802(6) Å in 2, and 2.709(3) Å in 3] with the
central metal. The [(2-C5H4N)C(O)(OR)C(O)(OR)(2-C5H4N)]
ions behave as η :η :η :η :η :η µ3 ligands (Chart 2). Each
ligand spans a long edge of the Cu4 rectangle and is ligated to
the central metal, Cu(1), through both of its deprotonated
hydroxy oxygen atoms. The Cu-OR distances are long,
suggesting weak interactions, with the Cu(2)‚‚‚O(4) distances
2.770(3)-2.939(6) Å] being longer than the Cu(3)‚‚‚O(2)
distances [2.582(2)-2.693(6) Å]. A terminal ROH molecule and
a monodentate RCO2 ligand complete coordination at Cu(2)
and its symmetry-related partner [Cu(2′)]. The remaining
terminal coordination sites on Cu(3) and Cu(3′) are occupied
by chelating RCO2 groups; these groups are asymmetrically
ligated [Cu(3)-O(8) ) 1.932(3)-1.954(7), Cu(3)‚‚‚O(9) )
.868(9)-2.981(3) Å]. The crystal structures are stabilized by
intra- and intermolecular hydrogen bonds.
and [Cu5(OH)2(O2CMe)6(1-Meim)4](ClO4)2 (1-Meim ) 1-methyl-
imidazole).
II
1
0e
Magnetic Properties of 1. The magnetic behavior (3-300
K) of a powder sample of the representative complex 1 in the
form of a øM T versus T plot is shown in Figure 2 (øM is the
corrected molar magnetic susceptibility per pentamer). The
(
II
-
1
room-temperature value of øM T (1.94 emu mol K) is smaller
-
1
-1
than expected for five uncoupled S ) /2 spins (2.1 emu mol
2
K for g ) 2.1), indicative of antiferromagnetic coupling, even
at 300 K. The product decreases rapidly with decreasing
temperature down to 45 K, where it displays a minimum; the
2-
1
2
1
2
1
1
-1
value at 45 K (1.2 emu mol K) is what is expected for three
1
uncoupled S ) /2 spins. Below 45 K, the product increases
-1
and exhibits a maximum (1.3 emu mol K) at ca. 7 K.
[
(
10) (a) Gojon, E.; Gaillard, J.; Latour, J.-M.; Laugier, J. Inorg. Chem.
1987, 26, 2046. (b) Kurzak, B.; Farkas, E.; Glowiak, T.; Kozlowski,
-
H. J. Chem. Soc., Dalton Trans. 1991, 163. (c) Handley, J.; Collison,
D.; Garner, C. D.; Helliwell, M.; Docherty, R.; Lawson, J. R.; Tasker,
P. A. Angew. Chem., Int. Ed. Engl. 1993, 32, 1036. (d) Gibney, B.
R.; Kessissoglou, D. P.; Kampf, J. W.; Pecoraro, V. L. Inorg. Chem.
1994, 33, 4840. (e) Meenakumari, S.; Lakshminarayanan, M.; Tiwary,
S. K.; Chakravarty, A. R. Inorg. Chem. 1995, 34, 5091. (f) Doyle, A.
A.; Parsons, S.; Solan, G. A.; Winpenny, R. E. P. J. Chem. Soc., Dalton
Trans. 1997, 2131. (g) Murrie, M.; Collison, D.; Garner, C. D.;
Helliwell, M.; Tasker, P. A.; Turner, S. S. Polyhedron 1998, 17, 3031.
-
2

4662 Inorganic Chemistry, Vol. 39, No. 20, 2000
Notes
3
Chart 3. Exchange Pathways in 1
at g ) ∼4.3. The latter is characteristic of an effective S ) /2
ground state. The hyperfine-splitting-tensor components deduced
-
4
-1
from this spectrum are A| ) 190 × 10 cm and A⊥ < 10 ×
cm .
In an attempt to probe more deeply into the exchange
-
4
-1
1
0
interactions of 1, its magnetic behavior is closely correlated with
its molecular structure. The structure of 1 is built from four
II
coplanar Cu ions forming two triangles with a common vertex
II
which is the position of the central metal ion. All five Cu ions
in the rectangle exhibit distorted six-coordinate geometries.
Therefore, the unpaired electron around each of the magnetic
2
2
centers is described by a (x - y )-type magnetic orbital pointing
from the metal toward its corresponding four nearest-neighbor-
ing atoms. Consequently, the spin densities on O(1) and O(1′),
belonging to two neighboring magnetic orbitals, should be
different from zero, and this should also be the case with the
O(3) and O(3′) bridging atoms. However, no definite magne-
tostructural correlations has been established for the hydroxo-
or alkoxo- monobridged dicopper(II) complexes; this is also the
case for the mixed hydroxo- and alkoxo-dibridged complexes.
As far as the Cu(1)‚‚‚Cu(2) and Cu(1)‚‚‚Cu(3) exchange
interactions J1 are concerned, due to the nature of the Cu(1)-
centered magnetic orbital, involving the four nearest neighboring
atoms [O(1), O(1′), O(3), O(3′)], there is no spin density on
the second bridging atom [O(5), O(5′)] coming from the Cu-
(1)-centered magnetic orbital. Therefore, in contrast to the
molecular structure of 1 (see Figure 1), of the two bridging
pathways between Cu(1) and Cu(2), only the alkoxo group can
propagate the magnetic exchange interactions between them.
Moreover, there is also only one bridge, this being the hydroxo
group involving O(5), that propagates the magnetic exchange
interactions between Cu(2) and Cu(3′). However, the triply
bridging function of this single bridge, as compared to the
doubly bridging function of the alkoxo bridge mentioned above,
could account well for the weaker interaction calculated for J2
as compared to J1. Finally, the long Cu(2)‚‚‚Cu(3) distance of
A careful inspection of the crystal structure of 1 clearly
demonstrates that three exchange integrals, J1, J2, and J3 (see
Chart 3), are required to model the data properly. If we assume
that S1, S2, S3, S2′, and S3′ correspond to the spin operators of
Cu(1), Cu(2), Cu(3), Cu(2′), and Cu(3′) magnetic centers,
respectively, then the isotropic HDvV Hamiltonian for the
system of five spins under study should be as follows:
H ) -2J S (S + S + S + S ) - 2J (S ‚S + S ‚S ) -
1
1
2
3
2′
3′
2
2
3′
2′
3
2
J (S ‚S + S ‚S ) (2)
3 2 3 2′ 3′
The theoretical expression for the magnetic susceptibility used
to fit the data is
2
2
∑
2
n
Nâ g m exp(-E /kT)
n
n
ø )
(3)
M
5
.533(1) Å, along with the noncoplanarity of the intervening
exp(-E /kT)
∑
n
multiatomic bridge, could account well for the weak antiferro-
magnetic interaction (J3) derived from the fitting procedure.
n
where mn ) m1 + m2 + m3 + m4 + m5 for the nth level. Since
J3 is expected to be smallsdue to the very long Cu(2)‚‚‚Cu(3)
distance of 5.533(1) Åsa first fit of the 3-300 K data to the
above equation was performed by using a two-J model.
Although the model represented the experimental data of the
high-temperature range well, it failed to give a low-temperature
fit. However, a three-J model for the whole temperature range
Conclusions
The copper(II) carboxylate/(2-C5H4N)C(O)C(O)(2-C5H4N)
chemistry described here has fulfilled its promise as a source
of polynuclear complexes with interesting structures and proper-
ties. Although the outcome of this reaction system was
unpredictable, it is clear that the bis(hemiacetal) nature of the
2-
[(2-C5H4N)C(O)(OR)C(O)(OR)(2-C5H4N)] ions makes them
-
1
-1
-1
yielded J1 ) -37.9 cm , J2 ) -16.8 cm , J3 ) -2.7 cm ,
versatile ligands for use with a variety of metals.
2
2
and g ) 2.09 (R ) ∑n[(øMT)exptl - (øMT)calcd] /∑n(øMT)exptl )
Acknowledgment. This work was supported by the Research
Committee of the University of Patras (K. Caratheodory
Program No. 1941; S.P.P.), the Greek General Secretariat of
Research and Technology (Platon Program 1583; E.G.B.), and
the Greek Secretariat of Athletics, OPAP (A.T.).
-5
1
.0 × 10 ). This excellent fit is shown in Figure 2. The ground
3
state (mS ) ( /2), predicted by this model, has the central spin
up and the four others down, or vice versa, in close agreement
with the øMT value at 45 K. Although all J’s are negative, the
1
ground state does not correspond to an mS ) /2 value because
Supporting Information Available: A table of magnetic vs
temperature data for 1, an EPR spectrum at 4.5 K for 1, and X-ray
crystallographic files, in CIF format, for 1-3. This material is available
free of charge via the Internet at http://pubs.acs.org.
of spin frustration, as one would expect from the geometry of
the molecule.
The powder EPR spectrum of 1 at 4.5 K shows a multiple
line centered at g ) 2.05, displaying hyperfine interactions and
assigned to residual monomeric species, and a less intense line
IC991169K