Structure and Magnetic Behavior of a New 1-D Compound with Simultaneous End-On Azido and Carboxylato Bridges. Unexpected Strong Ferromagnetic Coupling for a Cu-N-Cu Bond Angle of 111.9° as a Consequence of Ligand HOMOs Countercomplementarity

Article abstract of DOI:10.1021/ic961107j

The X-ray structure of the μ-carboxylate-μ_1.1-azido-bridged compound {[Cu(Hpht)(N₃)]·H₂O}_n has been determined (Hpht = hydrogen phthalate). Crystal data: formula C₈H₇CuN₃O₅, monoclinic, P2₁/m (No. 11), a = 7.383(3) A?, b = 6.568(4) A?, c = 10.659(4) A?, β= 93.38(3)°, Z = 2. The compound is found to be a system formed by chains of copper atoms bridged simultaneously by syn-syn carboxylato and end-on azido bridges. The copper chains are linked by a second carboxylato bridge, giving a 2-D compound. Magnetic measurements indicate strong ferromagnetic coupling, which affords a good example of unexpected magnetic properties due to the countercomplementarity of the superexchange pathways of the two ligands.

Full text of DOI:10.1021/ic961107j

Inorg. Chem. 1997, 36, 1233-1236
1233
Structure and Magnetic Behavior of a New 1-D Compound with Simultaneous End-On
Azido and Carboxylato Bridges. Unexpected Strong Ferromagnetic Coupling for a
Cu-N-Cu Bond Angle of 111.9° as a Consequence of Ligand HOMOs
Countercomplementarity
Albert Escuer,*,†,‡ Ramon Vicente,† Franz A. Mautner,§ and Mohamed A. S. Goher*,|,
Departament de Qu´ımica Inorga`nica, Universitat de Barcelona, Diagonal 647, 08028 Barcelona, Spain,
Institut fu¨r Physikalische und Theorestische Chemie, Technische Universita¨t Graz,
A-8010 Graz, Austria, and Department of Chemistry, Faculty of Science, Alexandria University,
Alexandria 21321, Egypt
ReceiVed September 6, 1996X
The X-ray structure of the µ-carboxylate-µ1,1-azido-bridged compound {[Cu(Hpht)(N3)]‚H2O}n has been
determined (Hpht ) hydrogen phthalate). Crystal data: formula C8H7CuN3O5, monoclinic, P21/m (No. 11), a )
7.383(3) Å, b ) 6.568(4) Å, c ) 10.659(4) Å, â ) 93.38(3)°, Z ) 2. The compound is found to be a system
formed by chains of copper atoms bridged simultaneously by syn-syn carboxylato and end-on azido bridges.
The copper chains are linked by a second carboxylato bridge, giving a 2-D compound. Magnetic measurements
indicate strong ferromagnetic coupling, which affords a good example of unexpected magnetic properties due to
the countercomplementarity of the superexchange pathways of the two ligands.
Introduction
Polynuclear compounds bridged by the azido ligand show
different magnetic behaviors according to the coordination mode
of the bridge: generally, end-to-end (1,3-µ-N3) allows anti-
ferromagnetic interactions whereas the end-on (1,1-µ-N3) bridge
allows ferromagnetic interactions.1 In the past few years the
end-to-end coordination mode has been exhaustively studied
and the dependence of the antiferromagnetic component of J
on structural parameters has been established for Cu and Ni2
and even the predicted ferromagnetic behavior for large
M-N-N bond angles has been experimentally found.3 Cor-
relations of this kind have recently been extended to the
Mn(II)-1,3-azido system.4
For the end-on azido bridge, the most common kind of
compound shows two azido bridges with M-N-M bond angles
in the 100-106° range for M ) Cu, Ni and Mn(II).5 Recently,
some larger Cu-N-Cu angles have been reported by Thomp-
son, (up to 122.5°), in series of dinuclear compounds with two
simultaneous bridges, one end-on azido bridge and one py-
ridazine bridge.6
in the end-on azido bridge occurs at Cu-N-Cu bond angles
close to 108°, and so antiferromagnetic interaction should be
found for greater Cu-N-Cu bond angles. Following the
characterization of the magnetic properties of large M-N-M
end-on azido compounds, in this paper we present the synthesis
and structural characterization of the end-on azido-bridged
compound {[Cu(Hpht)(N3)]‚H2O}n which shows a Cu-N-Cu
bond angle of 111.9(1)°. The title compound was obtained
following the strategy of mixing different potential bridging
ligands with the copper salt. The most interesting property was
the very strong ferromagnetic coupling attributable to the
countercomplementarity of the ligands HOMO. The magnetic
properties of the title compound were compared with the
copper-µ-diazine-µ-azido system and the global magnetic
From magnetic measurements performed on compounds of
this kind it has been proposed that the accidental orthogonality
† Universitat de Barcelona.
‡ World Wide Web: www.ub.es/inorgani/molmag.htm.
§ Technische Universita¨t Graz.
| Alexandria University.
Present address: Chemistry Department, Faculty of Science, Kuwait
University, P. O. Box 5969 Safat, 13060 Kuwait.
X Abstract published in AdVance ACS Abstracts, February 1, 1997.
(1) Kahn, O. Molecular Magnetism; VCH Publishers Inc.: New York,
1993.
(2) Ribas, J.; Monfort, M.; Diaz, C.; Bastos, C.; Solans, X. Inorg. Chem.
1993, 32, 3557. Escuer, A.; Vicente, R.; El Fallah, M. S.; Solans, X.;
Font-Bardia, M. Inorg. Chem. 1994, 33, 1842. Vicente, R.; Escuer,
A. Polyhedron 1995, 14, 2133. Escuer, A.; Vicente, R.; El Fallah, M.
S.; Solans, X.; Font-Bardia, M. J. Chem. Soc., Dalton Trans. 1996,
1013.
(3) Harding, C. J.; Mabbs, F. E.; MacInnes, E. J.; McKee, V.; Nelson, J.
J. Chem. Soc., Dalton Trans., submitted for publication. Private
communication.
(4) Escuer, A.; Vicente, R.; Goher, M. A. S.; Mautner, F. A. Inorg. Chem.
1996, 35, 6386.
(5) Vicente, R.; Escuer, A.; Ribas, J.; El Fallah, M. S.; Solans, X.; Font-
Bardia, M. Inorg. Chem. 1993, 32, 1920. Ribas, J.; Monfort, M.; Diaz,
C.; Bastos, C.; Solans, X. Inorg. Chem. 1994, 33, 484. Ribas, J.;
Monfort, M.; Ghosh, B. K.; Solans, X. Angew. Chem. Int. Ed. Engl.
1994, 33, 2087. Escuer, A.; Vicente, R.; Ribas, J.; Solans, X. Inorg.
Chem. 1995, 34, 1793. Beer, P. D.; Drew, M. G. B.; Leeson, P. B.;
Lyssenko, K.; Ogden, M. I. J. Chem. Soc., Chem. Commun. 1995,
929. Corte´s, R.; Pizarro, L.; Arriortua, M. S.; Rojo, T. Inorg. Chem.
1994, 33, 2697.
(6) Tandon, S. S.; Thompson, L. K.; Manuel, M. E.; Bridson, J. N. Inorg.
Chem. 1994, 33, 5555. Thompson, L. K.; Tandon, S. S.; Manuel, M.
E. Inorg. Chem. 1995, 34, 2356.
S0020-1669(96)01107-X CCC: $14.00 © 1997 American Chemical Society

1234 Inorganic Chemistry, Vol. 36, No. 6, 1997
Escuer et al.
Table 1. Crystallographic Data and Processing Parameters for the
{[Cu(Hpht)(N3)]‚H2O}n Complex
formula
fw
C8H7CuN3O5
288.71
V, Å3
Z
516.0(4)
2
25
space group monoclinic P21/m T, °C
(No. 11)
7.383(3)
λ(Mo KR), Å
0.71069
a, Å
b, Å
µ(Mo KR), mm-1 2.13
6.568(4)
10.659(4)
93.38(3)
D
calc/Dobs (g/cm-3
)
1.858/1.85(3)
0.028
0.029
c, Å
â, deg
R(F)a
Rw(F)a
2
a R(F) ) ∑{|Fo| - |Fc|}/∑Fo. Rw(F) ) [w∑(|Fo| - |Fc|)2/∑wFo ]1/2
.
properties are explained in terms of complementary-counter-
complementary interactions.
Experimental Section
Synthesis. A 20 mL aliquot of an aqueous solution of copper nitrate,
(3 mmol, 0.72 g), was mixed with an ethanolic solution (20 mL) of
phthalic acid (4.3 mmol, 0.71 g) followed by the addition of a
concentrated solution of sodium azide (3 mmol, 0.39 g). The final
clear green mixture was left to stand at room temperature. Green
crystals were collected after several weeks. The IR spectrum shows
the characteristic bands attributable to the phthalate and strong bands
at 2085 cm-1 (υas N3) and 1307-1279 cm-1 (υs N3), which suggest an
asymmetric azido ligand. Anal. Calcd (Found) for C8H7CuN3O5: C,
33.28 (33.4); H, 2.44 (2.6); N 14.55 (14.2); Cu 22.00 (22.3).
X-ray Crystallography. A prismatic crystal (0.50 × 0.35 × 0.25
mm) was selected and mounted in a modified STOE four-circle
diffractometer. Orientation matrix and lattice parameters were obtained
by least-squares refinement of the diffraction data from 32 reflections
in the 2θ range 10-26°. The intensities collected were corrected for
Lorentz polarization and absorption7 effects. Selected crystallographic
data are given in Table 1. The structure was solved by Patterson
superposition methods and subsequent Fourier analyses. Anisotropic
displacement parameters were applied to the non-hydrogen atoms in
full-matrix least-squares refinements. Hydrogen positions were obtained
from ∆F maps and included in the final refinement cycles by
geometrical constraints. The programs DIFABS,7 SHELX-76,8 SHELX-
86,9 PLATON,10 and THE XRAY SYSTEM11 were used for computa-
tions. Analytical expressions of neutral-atom scattering factors were
used and anomalous dispersion corrections were incorporated.12 Atomic
coordinates are given in Table 2 and selected bond angles and distances
are given in Table 3.
Figure 1. ORTEP (50% probability) labeled plot of {[Cu(Hpht)-
(N3)]‚H2O}n and a view of a sheet of {[Cu(Hpht)(N3)]‚H2O}n showing
the three simultaneous bridges between the copper atoms and the general
structure of chains weakly linked by the phthalate anions.
Table 2. Atomic Coordinates (×104) and Ueq values (Å2 × 103) of
Non-Hydrogen Atoms of {[Cu(Hpht)(N3)]‚H2O}n
atom
x/a
y/b
z/c
Ueq
Cu(1)
N(11)
N(12)
N(13)
O(1)
O(2)
O(3)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
O(4)
0
5000
2500
2500
2500
4215(2)
2500
2500
2500
2500
2500
2500
2500
2500
2500
2500
2500
0
20(0)
22(1)
29(2)
60(2)
24(1)
45(2)
40(1)
22(1)
31(2)
39(2)
41(2)
34(2)
24(2)
20(1)
28(2)
32(1)
673(4)
709(4)
759(7)
-904(3)
-2049(3)
-3115(4)
1456(2)
975(3)
1629(2)
7804(3)
4865(3)
3778(4)
3325(5)
4673(6)
6473(6)
6939(5)
5615(4)
2242(4)
6192(4)
5963(3)
356(3)
2802(3)
4058(4)
5023(4)
4749(4)
3516(4)
2526(3)
1805(3)
1220(4)
-1880(3)
Results and Discussion
Description of the Structure of {[Cu(Hpht)(N3)]‚H2O}n.
An ORTEP plot of the basic unit of {[Cu(Hpht)(N3)]‚H2O}n is
shown in Figure 1. The structure consists of neutral two-
dimensional sheets of [Cu(Hpht)(N3)] complexes. Coordination
around the copper atoms is an elongated octahedron in which
the short distances correspond to two trans Cu(1)-O(1) bonds
at 1.975(2) Å and to two trans Cu(1)-N(11) bonds at 1.982(2)
Å, whereas the two large axial distances correspond to two
Cu(1)-O(2) bonds at 2.570(4) Å. The azido ligand acts as a
bridge between neighboring copper atoms in the µ2-1,1 coor-
dination mode. The deprotonated carboxylate group acts as a
syn-syn carboxylato bridge, whereas the protonated carboxylate
also acts as a bridge through the O(1) oxygen atom, the
protonated O(3) atom remaining uncoordinated. The hydro-
genphthalate anion shows the two carboxylate planes tilted 90°.
Table 3. Selected Bond Distances (Å) and Bond Angles (deg) for
{[Cu(Hpht)(N3)]‚H2O}n
Cu(1)‚‚‚Cu(1a)
Cu(1)-O(1)
Cu(1)-O(2)
Cu(1)-N(11)
O(1)-C(7)
3.284(2)
1.975(2)
2.570(4)
1.982(2)
1.262(2)
O(2)-C(8)
1.233(4)
1.304(5)
1.222(4)
1.139(5)
O(3)-C(8)
N(11)-N(12)
N(12--N(13)
O(1)-Cu(1)-N(11)
O(2)-Cu(1)-N(11)
O(1)-Cu(1)-O(2)
90.4(1) Cu(1)-N(11)-Cu(1a) 111.9(1)
81.4(1) N(11)-N(12)-N(13) 179.3(6)
83.4(1) O(1)-C(7)-O(1a)
126.5(3)
123.0(4)
Cu(1)-N(11)-N(12) 120.4(1) O(2)-C(8)-O(3)
(7) Walker, N.; Stuart, D. Acta Crystallogr. 1983, A39, 158.
(8) Sheldrick, SHELX-76, A Program for Crystal Structure Determination.
University Chemical Laboratory, Cambridge, U.K., 1976.
(9) Sheldrick, SHELX-86. Universita¨t Gottingen, Germany, Gottingen,
1986.
(10) Spek, A. L. Computational Crystallography; Clarendon Press: Oxford,
U.K., 1982; p 528.
Hydrogen Bond Distances
O(3)-H(5)
0.94(3)
1.63(3)
1.73(4)
2.563(4)
O(4)-H(6)
0.93(3)
1.94(3)
1.57(4)
2.815(3)
H(5)‚‚‚O(4)
H(6)‚‚‚O(1)
O(3)-H(5)‚‚‚O(4)
O(3)‚‚‚O(4)
O(4)-H(6)‚‚‚O(1)
O(4)‚‚‚O(1)
(11) Stewart, J. M. The X-RAY SYSTEM, Version 1976; Technical report
TR-466; University of Maryland: College Park, MD, 1976.
(12) International Tables for X-ray Crystallography; Kynoch Press: Bir-
mingham, U.K., 1974; Vol. IV, pp 99 and 149.
Then, three kinds of simultaneous bridge are present in the
compound, Figure 1. The C(8)-O(3) bond distance 1.304(5)

Azido- and Carboxylato-Bridged Compounds
Inorganic Chemistry, Vol. 36, No. 6, 1997 1235
Figure 3. Magnetization measurement for {[Cu(Hpht)(N3)]‚H2O}n
(magnetization, solid circles; first derivative, open circles), showing
the metamagnetic behavior at very low fields, pointing out the very
low interchain antiferromagnetic coupling.
assuming g ) 2.16, from experimental EPR data
øM ) NAg2â2/4kT[NM/DN]2/3
where
NM ) 1.0 + 5.79799x + 16.902653x2 + 29.376885x3 +
29.832959x4 + 14.036918x5
DN ) 1.0 + 2.79799x + 7.008678x2 + 8.6538644x3 +
4.5743114x4
and x ) J/2kT.
Figure 2. (a) øMT vs T plots between 25 and 2 K for {[Cu(Hpht)-
(N3)]‚H2O}n measured under different fields. (b) øMT vs T plot between
300 and 2 K measured at 0.05 T. Solid line shows the fit up to 10 K
for the measurement performed at 0.05 T.
The decay at low temperatures, due to antiferromagnetic
interactions in the 2-D sheets, was evaluated from a magnetiza-
tion experiment as J′ ) -0.07 cm-1 (Figure 3). EPR measure-
ments performed at variable temperature show well-defined
signals at g| ) 2.32 and g ) 2.09 between 300 and 15 K.
Below this temperature the intensity of the signal decreases
continuously due probably to a saturation effect due to an
increase in the relaxation time. Shift of the resonance field14
at low temperature found for strongly ferromagnetic coupled
copper(II) chains15 was not observed for the title compound.
According to the structural data, the strong ferromagnetic
interaction corresponds to the superexchange through the
carboxylato-azido-bridged chains, whereas the very weak
antiferromagnetic interaction may be propagated by the poorly
efficient phthalato ligand which links the chains at long distance.
Magnetostructural Correlations. The net superexchange
constant coupling found between the copper atoms in the title
compound corresponds to the combined interactions due to the
single syn-syn carboxylato and the end-on azido bridges.
Compounds derived from the copper acetate structure show
typical J values close to -300 cm-1 for four simultaneous
bridges,16 but less efficient superexchange was found in
compounds with one or two carboxylato bridges, as a function
of the structural parameters that may reduce the overlap between
Å, is greater than the C(8)-O(2), 1.233(4) Å, or C(7)-O(1),
1.262(2) Å, bond distances; the N(11)-N(12) bond distance,
1.222(4) Å, is also larger than the N(12)-N(13) distance,
1.139(5) Å, as is common for end-on azido bridges. The water
molecule forms a set of hydrogen bonds that involves the O(1)
and O(3) oxygen atoms: O(3)-H(5) ) 0.94(3) Å, H(5)-O(4)
) 1.63(3) Å, O(4)-H(6) ) 0.93(3) Å, and finally H(6)-O(1)
) 1.94(3) Å. O(3)-O(4) and O(4)-O(1) distances are
2.563(4) and 2.815(3) Å, respectively. From the magnetic point
of view, the most appropriate description of the structure is as
quasi-isolated chains of copper atoms bridged simultaneously
by one end-on azido and one syn-syn carboxylato bridge, with
a Cu-Cu distance of 3.282(2) Å. Superexchange through the
pathway provided by the large axial bonds to O(2) atoms can
be expected not relevant due to the low unpaired electronic
2
density along the dz atomic orbital in the octahedral coordination
around the copper atoms.
ø
Magnetic Behavior. The MT value increased when the
temperature decreased, indicating ferromagnetic behavior. The
high øMT value at low temperature indicates that the compound
acts as a ferromagnetic chain, consistent with the structural data.
(13) Baker, G. A.; Rushbrooke, G. S.; Gilbert, H. E. Phys. ReV. A 1964,
135, 1272.
(14) Bencini, A.; Gatteschi, D. EPR of Exchange Coupled Systems;
Springer-Verlag: Berlin, 1990.
(15) Poertadji, S.; Ablart, G.; Pescia, J.; Clement, S.; Cheikh-Rouhou, A.
J. J. Phys. Lett. 1983, 44, L561.; Hoogerbeets, R.; van Duyneveldt,
A. J. Physica 1983, 121B, 233.
(16) Kato, M.; Muto, Y. Coord. Chem. ReV. 1988, 92, 45. Neels, A.;
Stoeckli-Evans, H.; Escuer, A.; Vicente, R. Inorg. Chem. 1995, 34,
1946.
ø
The plots of MT vs T, measured at several fields between 1.5
and 0.05 T are given in Figure 2. The dependence of the plot
on the applied magnetic fields confirms the ferromagnetic
interaction. The superexchange parameter J ) 75 cm-1 was
obtained from the expansion series expression proposed by
Baker13 based on the Hamiltonian -1/2J∑Si‚Sj - (µH)∑Szi and

1236 Inorganic Chemistry, Vol. 36, No. 6, 1997
Escuer et al.
the atomic orbitals of the copper atoms and the appropiatete
MOs of the carboxylato bridge. A parametric approach to the
J values has been pointed out by Wieghardt17 by means of the
relationship between J/n and the Cu-O-C bond angle in which
n is the number of carboxylate bridges. Taking into account
the large Cu-O(1)-C(7) bond angle of the single carboxylato
bridge (131°) in the title compound, a moderately weak
antiferromagnetic behavior should be expected.
Thompson et al.6 have proposed that the accidental ortho-
gonality for the 1,1-azido bridge takes place at a Cu-N-Cu
bond angle close to 108°, on the basis of measurements
performed on series of diazine-azido bridged compounds. For
larger angles the antiferromagnetic behavior of the 1,1-azide
bridge increases to the maximum J ) -921 cm-1 value found
for the [Cu2(PPD35Me)(µ2-N3)Br3(CH3OH)] compound,
(Cu-N-Cu 122.5°).6 From these considerations, a moderately
antiferromagnetic behavior should also be expected for the azido
bridge of the title compound taking into account the Cu-N-
Cu bond angle of 111.9°.
Figure 4. Bridging HOMOs complementarity and noncomplementarity
for the pyridazine-azido and the carboxylato-azido systems. (a) Each
ligand interacts with one of the two A1 or B2 combinations of the atomic
dx -y orbitals, giving a low ∆ value. (b) The two HOMOs of the ligands
interact with the same combination B2, giving large ∆ and JAF values.
2
2
Table 4. Bond Magnetic Data for a Set of Mixed Bridged Copper
Compounds with Similar Cu-N-Cu Bond Anglesa
To explain the apparently anomalous net ferromagnetic
behavior of {[Cu(Hpht)(N3)]‚H2O}n we chose a dimeric frag-
ment under C2V symmetry which models the superexchange
pathway of the chain:
J
compound
Cu-N-Cu (cm-1
)
interaction
[Cu2(PAP)(µ1,1-N3)Br3]
108.7
110.9
111.7
-241
-234
-187
C
C
C
[Cu2(PAP6Me)(µ1,1-N3)(µ-Br)Br2]
[Cu2(PAP6Me)(µ1,1-N3)(µ-H2O)-
(NO3)2]+
[Cu2(PAN)(µ1,1-N3)(µ-NO3)(NO3)2]
{[Cu(Hpht)(N3)]‚H2O}n
111.1
111.9
-220
C
+75 counter-C
a Data for PAP and PAN phthalazines were taken from ref 6).
Notations C and counter-C refer to the complementary or counter-
complementary kind of interaction between the ligand HOMOs and
the active atomic orbitals of the copper atoms.
It is interesting to compare the magnetic properties of {[Cu-
(Hpht)(N3)]‚H2O}n with the pyridazine-1,1-azido system de-
scribed by Thompson: using the same C2V symmetry, the
HOMO of the pyridazine has B2 symmetry, as occurs with the
Πxy of the azido bridge: in this case φA MO results strongly
unstabilized due the complementary antibonding overlap,
allowing a high ∆ and consequently a high JAF, Figure 4b. The
magnetic data for a homogeneous group of copper compounds
with the Cu-N-Cu bond angle between 108.7 and 111.9° are
shown in Table 4.
In this model the coordination sites of the copper atoms not
involved in the bridging region have been replaced by NH3
molecules. The MO calculations were performed by means of
the CACAO program.18
In the above dimeric fragment, the magnetically active atomic
2
2
orbitals of the copper atoms are the dx -y orbitals, which allows
the symmetric φS and the antisymmetric φA combinations (A1
and B2 respectively under C2V). From the proposal of Hoff-
mann,19 the square of the gap between the two antibonding φS
and φA, named ∆2, is proportional to the antiferromagnetic
component of the J constant coupling. To transmit the
antiferromagnetic coupling, the most useful molecular orbitals
of the two bridges are the highest filled MOs, which have A1
symmetry for the acetate and B2 for the azido ligands. The
antibonding character of φS is then enhanced by the overlap
with the appropiate MO of the acetate bridge, whereas φA
overlaps with the Πxy MO of the azido group as is shown in
Figure 4a. The gap between the two MOs φS and φA should
be lower than the interaction with the two “antiferromagnetic”
ligands due to the countercomplementarity of the ligand
HOMOs. Incidentally, if this countercomplementary interaction
of the bridging ligands allows a very low ∆ value, it is possible
to find a net ferromagnetic interaction from two ligands which
commonly allow antiferromagnetic coupling. MO extended
Hu¨ckel calculations for the above model give ∆2 ) 0.005 eV2,
(E(φS) ) -11.544 eV and E(φA) ) -11.614 eV), e.g., quasi-
degenerate φS and φA levels.
The copper-azido vs. carboxylate or diazine bridges described
above is a new example of an unusual kind of complementary-
countercomplementary magnetic system, pointed out by Mc-
Kee20 for the [Cu2(L-Et)(µ-L)]2+ series of complexes, (HL-Et
) N,N,N′,N′-tetrakis(2-(1-ethylbenzimidazolyl)-2-hydroxy-1,3-
diaminopropane), in which countercomplementarity was found
for the acetate derivative, J ) + 24 cm-1, whereas the
complementary systems with µ-L ) µ1,3-N3 and µ-NO2 bridges
show values of J ) -1100 and -278 cm-1, respectively.
Acknowledgment. A.E. and R.V. acknowledge CICYT
Grant PB093/0772 for support this research. F.A.M. expresses
thanks to Prof. C. Kratky (University of Graz) for the use of
experimental equipment.
Supporting Information Available: Text giving details of the
structure determination and tables of crystallographic data, complete
bond lengths and angles, atom coordinates, thermal parameters, and
hydrogen atom coordinates (7 pages). Ordering information is given
on any current masthead page.
(17) Bu¨rger, K. S.; Chaudhuri, P.; Wieghardt, K. Inorg. Chem. 1996, 35,
2704.
(18) Mealli, C.; Proserpio, D. M. Computer Aided Composition of Atomic
Orbitals, CACAO program. J. Chem. Educ. 1990, 67, 3399.
(19) Hay, J. P.; Thibeault, J. C.; Hoffmann, R. J. Am. Chem. Soc. 1975,
97, 4884.
IC961107J
(20) McKee, V.; Zvagulis, M.; Reed, C. A. Inorg. Chem. 1985, 24, 2914.