Rhenium(IV)-copper(II) heterobimetallic complexes with a bridge malonato ligand. Synthesis, crystal structure, and magnetic properties

Article abstract of DOI:10.1021/ic0493853

The Re(IV) complex [ReCl₄(mal)]^2-, in the form of two slightly different salts, (AsPh₄)_1.5(HNEt ₃)_0.5[ReCl₄(mal)] (1a) and (AsPh ₄)(HNEt₃)[ReCl₄(mal)] (1b), and the Re(IV)-Cu(II) bimetallic complexes [ReCl₄(μ-mal)Cu(phen) ₂]·CH₃CN (2), [ReCl₄(μ-mal)Cu(bpy) ₂] (3), and [ReCl₄(μ-mal)Cu(terpy)] (4) (mal = malonate dianion, AsPh₄ = tetraphenylarsonium cation, HNEt₃ = triethylammonium cation, phen = 1,10-phenanthroline, bpy = 2,2′-bipyridine and terpy = 2,2′:6′,2″-terpyridine) have been synthesized and the structures of 1a, 1b, 2, and 3 determined by single-crystal X-ray diffraction. The structures of 1a and 1b are made up of discrete [ReCl ₄(mal)]^2- anions and AsPh₄⁺ and HNEt₃⁺ cations, held together by electrostatic forces and hydrogen bonds. The Re(IV) atom is surrounded by four chloride anions and a bidentate malonate group, in a distorted octahedral environment. The structure of 2 consist of neutral dinuclear units [ReCl₄(μ-mal)Cu(phen) ₂], with the metal ions united through a bridge carboxilato. The environment of Re(IV) is nearly identical to that in the mononuclear complex, and Cu(II) is five coordinate, being surrounded by four nitrogen atoms of two bidentate phen ligands and one oxygen atom of the malonato ligand. In 3, there are also dinuclear units, [ReCl₄(μ-mal)Cu(bpy)₂], but the Cu(II) ions complete a distorted octahedral coordination by binding with the free malonato oxygen atom of a neighbor unit, resulting in an infinite chain. The magnetic properties of 1-4 were also investigated in the temperature range 2.0-300 K. The magnetic behavior of 1a and 1b is as expected for a Re(IV) complex with a large value of the zero-field splitting (2D ca. 110 cm ^-1). For the bimetallic complexes, the magnetic coupling between Re(IV) and Cu(II) is antiferromagnetic in 2 (J = -0.39 cm^-1), ferromagnetic in 4 (J = +1.51 cm^-1), and nearly negligible in 3 (J = -0.09 cm^-1).

Full text of DOI:10.1021/ic0493853

Inorg. Chem. 2004, 43, 7823−7831
Rhenium(IV)−Copper(II) Heterobimetallic Complexes with a Bridge
Malonato Ligand. Synthesis, Crystal Structure, and Magnetic Properties
Alicia Cuevas,† Rau´l Chiozzone,† Carlos Kremer,*,† Leopoldo Suescun,‡ Alvaro Mombru´,‡
Donatella Armentano,§ Giovanni De Munno,§ Francesc Lloret,| Juan Cano,| and Juan Faus*,|
Ca´tedra de Qu´ımica Inorga´nica y Laboratorio de Cristalograf´ıa, Facultad de Qu´ımica de la
UniVersidad de la Repu´blica, AVenida General Flores 2124, CC 1157 MonteVideo,
Uruguay, Dipartimento di Chimica, UniVersita` degli Studi della Calabria, 87030 ArcaVacata di
Rende, Cosenza, Italy, and Departamento de Qu´ımica Inorga´nica/Instituto de Ciencia Molecular,
Facultad de Qu´ımica de la UniVersidad de Valencia, Dr. Moliner 50,
46100 Burjassot, Valencia, Spain
Received May 11, 2004
The Re(IV) complex [ReCl4(mal)]2-, in the form of two slightly different salts, (AsPh4)1.5(HNEt3)0.5[ReCl4(mal)] (1a)
and (AsPh4)(HNEt3)[ReCl4(mal)] (1b), and the Re(IV) Cu(II) bimetallic complexes [ReCl4( -mal)Cu(phen)2] CH3CN
(2), [ReCl4( -mal)Cu(bpy)2] (3), and [ReCl4( -mal)Cu(terpy)] (4) (mal malonate dianion, AsPh4 tetrapheny-
larsonium cation, HNEt3 triethylammonium cation, phen 1,10-phenanthroline, bpy 2,2 -bipyridine and terpy
2,2 :6
−
µ
‚
µ
µ
)
)
)
)
)
′
)
′ ′,2′′-terpyridine) have been synthesized and the structures of 1a, 1b, 2, and 3 determined by single-crystal
-
+
X-ray diffraction. The structures of 1a and 1b are made up of discrete [ReCl4(mal)]2 anions and AsPh4 and
+
HNEt3 cations, held together by electrostatic forces and hydrogen bonds. The Re(IV) atom is surrounded by four
chloride anions and a bidentate malonate group, in a distorted octahedral environment. The structure of 2 consist
of neutral dinuclear units [ReCl4(µ-mal)Cu(phen)2], with the metal ions united through a bridge carboxilato. The
environment of Re(IV) is nearly identical to that in the mononuclear complex, and Cu(II) is five coordinate, being
surrounded by four nitrogen atoms of two bidentate phen ligands and one oxygen atom of the malonato ligand. In
3, there are also dinuclear units, [ReCl4(
coordination by binding with the free malonato oxygen atom of a neighbor unit, resulting in an infinite chain. The
magnetic properties of 1 4 were also investigated in the temperature range 2.0 300 K. The magnetic behavior of
µ-mal)Cu(bpy)2], but the Cu(II) ions complete a distorted octahedral
−
−
1a and 1b is as expected for a Re(IV) complex with a large value of the zero-field splitting (2D ca. 110 cm-1). For
the bimetallic complexes, the magnetic coupling between Re(IV) and Cu(II) is antiferromagnetic in 2 (J ) −0.39
cm-1), ferromagnetic in 4 (J ) +1.51 cm-1), and nearly negligible in 3 (J ) −0.09 cm-1).
Introduction
containing Re(IV) and an M(II) 3d metal ion (M ) Cu, Ni,
Mn, Fe) bridged by an oxalato ligand.3 These compounds
contain [ReCl4(ox)]2- (ox ) oxalate dianion) as building
bloc, which exhibits different coordination modes depending
on M and the auxiliary ligand used to complete its coordina-
tion sphere. Very different architectures can be found,
ranging from isolated dinuclear units, for example, [ReCl4-
(µ-ox)Mn (dmphen)2]‚CH3CN (dmphen ) 2,9-dimethyl-1,-
10-phenanthroline),3b,3c to infinite chains with helicoidal
conformation, as in the case of [ReCl4(µ-ox)Cu(bpy)2] (bpy
) 2,2′- bipyridine).3a The formation of such structures
together with the particular characteristics of Re(IV) (5d3
During the past 20 years, magneto-structural studies on
polynuclear complexes have comprised a very active research
field.2 One of the crucial points in this area is the under-
standing of the structural and chemical factors that determine
the exchange coupling between paramagnetic centers, either
through space or through chemical bridges.
Along these lines, we have reported a detailed description
of the magnetic behavior of heteropolynuclear complexes
* To whom correspondence should be addressed. E-mail: juan.faus@uv.es
(J.F.), ckremer@fq.edu.uy (C.K.).
† Ca´tedra de Qu´ımica Inorga´nica, Universidad de la Repu´blica.
‡ Laboratorio de Cristalograf´ıa, Universidad de la Repu´blica.
§ Universita` degli Studi della Calabria.
4
ion with a A2 ground term and a significant zero-field
splitting) result in interesting magnetic properties. Hence,
we can find either ferromagnetic or antiferromagnetic
| Universidad de Valencia.
(1) Deleted in proof.
10.1021/ic0493853 CCC: $27.50
Published on Web 10/23/2004
© 2004 American Chemical Society
Inorganic Chemistry, Vol. 43, No. 24, 2004 7823

Cuevas et al.
coupling between Re(IV) and M(II) depending on the relative
positions of the magnetic orbitals involved. This last fact is
a consequence of the coordination mode of the oxalate ligand
and the overall structure of the polynuclear complex.
dimium(III)13 homometallic and copper(II)-manganese(II)
heterometallic polynuclear species.
14
With this in mind, this work reports the synthesis, crystal
structure, and magnetic properties of two salts of [ReCl4-
(mal)]2-. This novel Re(IV) complex is used as a ligand to
form new bimetallic Re(IV)-Cu(II) species: [ReCl4(µ-mal)-
Cu(phen)2], [ReCl4(µ-mal)Cu(bpy)2], and [ReCl4(µ-mal)-
Cu(terpy)] (phen ) 1,10-phenanthroline, terpy ) 2,2′:6′,2′′-
terpyridine). Their syntheses, crystal structures, and magnetic
behavior over the temperature range 2-300 K are also
reported herein.
Following with this idea, the malonate ion (dianion of the
propanedioic acid, H2mal) seems to be a good candidate for
the preparation of Re(IV) complexes that can act as ligands
toward M(II) 3d ions. As recently reviewed,4 malonato ligand
can adopt different bridging modes, with the carboxylate
group in a syn-syn, anti-syn, or anti-anti conformation.
These different spatial arrangements affect the magnitude
of the magnetic interaction between spin centers (governed
by the overlap density), resulting in ferro- or antiferromag-
netic couplings. Even though this ligand has not been as
extensively assayed as a bridging ligand as oxalate, several
reports account for the versatility of malonate to build
copper(II),5,6 nickel(II),7 cobalt(II),6a,8 manganese(II),6b,6c,6d,9
manganese(III),10 molybdenum(II),11 gadollinium(III),12 praseo-
Experimental Section
Materials. Copper(II) trifluoromethanesulfonate; copper(II) per-
chlorate hexahydrate; 1,10-phenanthroline monohydrate; 2,2′-
bipyridine; 2,2′:6′,2′′-terpyridine; malonic acid; tetraphenylarsonium
chloride monohydrate (AsPh4Cl‚H2O); and the organic solvents
acetonitrile, N,N-dimethylformamide, and 2-propanol were pur-
chased from commercial sources and used as received. Triethy-
lamine was distilled from CaH2 before use.15 The complex
(NBu4)2[ReCl6] was prepared as previously reported.3a,16
(2) (a) Kahn, O. Molecular Magnetism; VCH: New York, 1993. (b)
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J.; Lloret, F.; Julve, M.; Faus, J. Inorg. Chem. 1999, 38, 4745. (b)
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gado, F. S.; Pasa´n, J.; Sanchiz, J.; Lloret, F.; Julve, M. Polyhedron
2003, 22, 2111.
(5) (a) Chattopadhyay, D.; Chattopadhyay, S. K.; Lowe, P. R.; Schwalke,
C. H.; Mazumder, S. K.; Rana, A.; Ghosh, S. J. Chem. Soc., Dalton
Trans. 1993, 913. (b) Li, J.; Zeng, H.; Chen, J.; Wang, Q.; Wu, X.
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Synthesis of the Complexes. (AsPh4)1.5(HNEt3)0.5[ReCl4(mal)]
(1a). A mixture of 352 mg of (NBu4)2[ReCl6] (0.40 mmol), 250
mg of malonic acid (2.40 mmol), and 350 µL of triethylamine (2.50
mmol) in 20 mL of 2-propanol was refluxed under nitrogen
atmosphere for 10 min. The light brown solution was filtered
through paper, and a solution of 384 mg of AsPh4Cl‚H2O (0.92
mmol) in 10 mL of 2-propanol was added. After 10-12 h, a green
crystalline solid of the final product was obtained. The solid was
filtered off and washed with 2-propanol (3 × 3 mL). Yield: 50-
60%. Suitable crystals for X-ray diffraction studies were obtained
by slow evaporation of a solution in acetonitrile at room temper-
ature. Anal. Calcd for C41H40As1.5Cl4O4N0.5Re: C, 47.2; H, 3.9;
N, 0.7; O, 6.1%. Found: C, 48.1; H, 4.3; N, 0.7; O, 6.3%. IR:
bands associated to the malonate ligand appear at (cm-1) 1649 (vs,
broad), 1345 (vs), 958 (m), and 935 (m).
(AsPh4)(HNEt3)[ReCl4(mal)] (1b). This compound was prepared
similarly to 1a but with different amounts of malonic acid (500
mg, 4.80 mmol), triethylamine (700 µL, 5.0 mmol), and 2-propanol
(30 mL) and a different refluxing time (30 min). The resulting
solution was treated as above. Yield: 35-40%. Suitable crystals
for X-ray diffraction studies were obtained directly from the mother
liquor by slow evaporation at room temperature. Anal. Calcd for
C32H38AsCl4O4NRe: C, 42.5; H, 4.2; N, 1.6%. Found: C, 43.7;
H, 4.2; N, 1.6%. IR: bands associated to the malonate ligand appear
at (cm-1) 1665 (vs), 1613 (vs), 1355 (vs), 970 (m), and 936 (m).
[ReCl4(µ-mal)Cu(phen)2]‚CH3CN (2). A solution of 53 mg of
1a (0.05 mmol) in 10 mL of acetonitrile was added to a solution
of 18.1 mg of copper(II) trifluoromethanesulfonate (0.05 mmol)
and 15.6 mg of phen‚H2O (0.10 mmol) in 15 mL of acetonitrile.
(10) Saadeh, S. M.; Trojan, K. L.; Kampf, J. W.; Hatfield, W. E.; Pecoraro,
V. L. Inorg. Chem. 1993, 32, 3034.
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Mautner, F. A.; Insausti, M.; Lezama, L.; Arriourtua, M. I.; Rojo, T.
Inorg. Chem. 1998, 37, 3243. (c) Gil de Muro, I.; Insausti, M.; Lezama,
L.; Urtiaga, M. K.; Arriourtua, M. I.; Rojo, T. J. Chem. Soc., Dalton
Trans. 2000, 3360. (d) Sain, S.; Maji, T. K.; Mostafa, G.; Lu, T. H.;
Chaudhuri, N. R. Inorg. Chim. Acta 2003, 351, 12.
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F.; Julve, M. Inorg. Chim. Acta 2000, 298, 245.
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Chaudhuri, R. Inorg. Chem. 2003, 42, 709.
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J.; Varughese, P. A.; Saban, K. V.; Varghese, G. J. Mol. Struct. 2003,
659, 81.
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M. Inorg. Chim. Acta 2000, 298, 202.
(15) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals; Pergamon Press: Oxford, U.K., 1988.
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1963; Vol. VII, p 189.
7824 Inorganic Chemistry, Vol. 43, No. 24, 2004

Re(IV)-Cu(II) Complexes with a Bridge Malonato Ligand
Table 1. Summary of Crystal Dataa for (AsPh4)1.5(HNEt3)0.5[ReCl4(mal)] (1a), (AsPh4)(HNEt3)[ReCl4(mal)] (1b), [ReCl4(µ-mal)Cu(phen)2]‚CH3CN (2),
and [ReCl4(µ-mal)Cu(bpy)2] (3)
1a
1b
2
3
chem formula
M
cryst syst
space group
a, Å
C42H40As1.50Cl4N0.50O4Re
1056.13
triclinic
P1h
10.703(1)
11.629(1)
38.132(5)
88.44(1)
84.25(1)
63.19(1)
4213.76(80)
4
1665
2080
4.347
14918/9084
0.057
C33H38AsCl4NO4Re
915.56
monoclinic
P21/n
9.737(5)
20.344(2)
18.954(3)
90.00
96.71(2)
90.00
3728.6(19)
4
1631
1804
4.461
C29H21Cl4CuN5O4Re
895.05
triclinic
P1h
10.120(1)
17.864(1)
9.558(1)
98.56(1)
115.97(1)
96.18(1)
1506.72(30)
2
1973
868
5.119
6900/5114
0.042
C23H18Cl4CuN4O4Re
805.95
monoclinic
P21/n
10.866(3)
15.559(5)
15.995(2)
90.00
97.30(2)
90.00
2682.3(12)
4
1996
1552
5.738
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
Dc/kg m-3
F(000)
µ(Mo K), cm-1
refln unique/obs
Rb
6925/3206
0.057
0.151
4708/2890
0.063
0.163
c
Rw
0.137
0.954
0.108
1.039
Sd
0.979
1.105
2
a Details in common: T ) 20 °C, I > 2σ(I). b R ) ∑(|Fo| - |Fc|)/∑|Fo|. c Rw ) [∑w(|Fo| - |Fc|)2/∑w|Fo| ]1/2
.
d Goodness of fit ) [∑w(|Fo| - |Fc|)2/(No
- Np)]1/2
.
After 2 days, emerald green crystals were separated and washed
with acetonitrile (3 × 2 mL). Yield: 70-80%. Anal. Calcd for
C29H21Cl4O4N5CuRe: C, 38.9; H, 2.4; N, 7.8%. Found: C, 38.5;
H, 1.9; N, 7.1%. IR: bands associated to the malonate ligand appear
at (cm-1) 1662 (vs), 1384 (s), 970 (m), and 940 (m).
AFC-7S (1b, 2, and 3) automatic four-circle diffractometer and used
for data collection. Diffraction data were collected at room
temperature by using graphite-monochromated Mo KR radiation (λ
) 0.71069 Å) with the ω-2θ scan method. The unit cell param-
eters were determined from least-squares refinement of the setting
angles of 25 (1a, 1b, 2) and 13 (3) reflections in the 2θ ranges
of 15-30° (1a) and 10-20° (1b, 2, and 3). Information con-
cerning crystallographic data collection and structure refinements
is summarized in Table 1. Examination of two (1a) or three (1b,
2, and 3) standard reflections, monitored after every 50 (1a) or
150 (1b, 2, and 3) reflections, showed no sign of crystal deteriora-
tion. Lorentz-polarization and Ψ-scan absorption corrections18,19a
were applied to the intensity data. The structures were solved
by standard Patterson methods and subsequently completed by
Fourier recycling. All non-hydrogen atoms were refined anisotro-
pically. The C2 atom in 3 show positional disorder and was re-
fined split into two nonequivalent positions. The occupation of
both positions was refined (constraining the sum of occupancies
to 1) and converged to 0.5 within experimental uncertainty;
thus the occupancy was fixed at 0.5 in the last refinement cycle.
The hydrogen atoms were placed in geometrically suitable posi-
tions and were refined as riding atoms with Uiso ) 1.2Ueq of the
parent atom except when the parent atom was a methyl group,
where Uiso ) 1.2Ueq of the C atom. The refinement was per-
formed on F2 against 14918 (1a), 6925 (1b), 6900 (2), and 4708
(3) using 920 (1a), 96 (1b), and 82 (3) geometrical or thermal
parameter constraints. The maximum and minimum found in the
final Fourier difference maps were 0.90 and -0.67 for 1a, 1.27
and -2.33 eA-3 for 1b, 1.88 and -1.38 eA-3 for 2, and 3.19 and
-1.72 eA-3 for 3. Maximum peaks were found, in the four cases,
less than 1 Å from the Re atom. Solution and refinements were
performed with the SHELXTL NT20 (1a) and SHELX-97 (1b, 2,
and 3) packages.19b,c The final geometrical calculations were
performed using the PARST21 and PLATON19d programs. The main
interatomic bond distances and angles for 1a, 1b, 2, and 3 are listed
in Tables 2-4.
[ReCl4(µ-mal)Cu(bpy)2] (3). A solution of 53 mg of 1a (0.05
mmol) in 50 mL of acetonitrile was added to a solution of 18.1 mg
of copper(II) trifluoromethanesulfonate (0.05 mmol) and 15.6 mg
of bpy (0.10 mmol) in 50 mL of acetonitrile. After 3-4 days,
laminar blue-green crystals were separated and washed with
acetonitrile (3 × 2 mL). Yield: 60-80%. Anal. Calcd for C23H18-
Cl4O4N4CuRe: C, 34.3; H, 2.3; N, 7.0; O, 7.9%. Found: C, 34.3;
H, 2.0; N, 7.0; O, 8.2%. IR: bands associated to the malonate ligand
appear at (cm-1) 1605 (vs), 1359 (s), 976 (m), and 930 (m).
[ReCl4(µ-mal)Cu(terpy)] (4). A solution of 53 mg of 1a (0.05
mmol) in 10 mL of acetonitrile/dimethylformamide (10:3) was
added to a solution of 18.5 mg of copper(II) perchlorate hexahydrate
(0.05 mmol) and 12 mg of terpy (0.05 mmol) in 10 mL of
acetonitrile/dimethylformamide (10:3). After 1-2 days, blue-green
crystals were separated and washed with acetonitrile (3 × 2 mL).
Yield: 50-60%. Anal. Calcd for C20H18Cl4O5N4CuRe: C, 30.6;
H, 2.3; N, 7.1%. Found: C, 30.6; H, 2.3; N, 6.7%. IR: bands
associated to the malonate appear at (cm-1) 1666 (vs), 1365 (vs),
and 937 (w).
Physical Techniques. The IR spectra (KBr pellets) were recorded
on a Bomen MB FT-IR spectrophotometer. Elemental analysis was
accomplished on a Carlo Erba model 1108 elemental analyzer.
Magnetic susceptibility measurements (2-300 K) were carried out
with a Quantum Design SQUID magnetometer under an applied
magnetic field of 1 T in the high-temperature range (T > 50 K)
and only 50 G at low temperatures to avoid any problem of
magnetic saturation. The device was calibrated with (NH4)2Mn-
(SO4)2‚6H2O. The corrections for the diamagnetism were estimated
from Pascal’s constants.17
X-ray Data Collection and Structure Refinement. Crystals of
dimensions 0.41 × 0.32 × 0.23 mm3 (1a), 0.45 × 0.12 × 0.10
mm3 (1b), 0.15 × 0.10 × 0.02 mm3 (2), and 0.17 × 0.09 × 0.03
mm3 (3) were mounted on a Bruker R3m/V (1a) and a Rigaku
(18) North, A. C. T.; Philips, D. C.; Mathews, F. S. Acta Crystallogr. A
1968, 24, 351.
(19) SHELX NT, version 5.10; Bruker Analytical X-ray Instruments Inc.:
Madison, WI, 1998.
(20) Nardelli, M. Comput. Chem. 1983, 7, 95.
(17) Earnshaw, A. Introduction to Magnetochemistry; Academic Press:
London, 1968.
Inorganic Chemistry, Vol. 43, No. 24, 2004 7825

Cuevas et al.
Table 2. Selected Bond Distances (Å) and Bond Angles (deg) for the
[ReCl4(mal)]2- Anion in Compounds 1a and 1b
Table 4. Selected Bond Distances (Å) and Bond Angles (deg) for
[ReCl4(µ-mal)Cu(bpy)2] (3)
1a (R unit)
Distances
1a (â unit)a
1b
Distances
Re(1)-O(1)
Re(1)-O(2)
Re(1)-Cl(1)
Re(1)-Cl(2)
Re(1)-Cl(3)
Re(1)-Cl(4)
2.020(9)
2.027(9)
2.331(3)
2.318(4)
2.380(4)
2.337(4)
Cu(1)-N(11)
Cu(1)-N(12)
Cu(1)-N(21)
Cu(1)-N(22)
Cu(1)-O(3)
Cu(1)-O(4*)
1.987(10)
1.991(10)
2.005(11)
1.991(11)
2.546(9)
Re(1)-O(1)
Re(1)-O(2)
Re(1)-Cl(1)
Re(1)-Cl(2)
Re(1)-Cl(3)
Re(1)-Cl(4)
2.017(7)
2.015(8)
2.328(3)
2.341(3)
2.357(3)
2.366(3)
2.014(7)
1.963(8)
2.336(3)
2.306(4)
2.302(4)
2.320(4)
2.004(8)
2.011(8)
2.337(3)
2.333(3)
2.345(3)
2.366(3)
2.851(14)
Angles
N(11)-Cu(1)-N(12)
Angles
O(1)-Re(1)-O(2)
O(1)-Re(1)-Cl(1)
O(2)-Re(1)-Cl(1)
O(1)-Re(1)-Cl(2)
O(2)-Re(1)-Cl(2)
O(1)-Re(1)-Cl(3)
O(2)-Re(1)-Cl(3)
O(1)-Re(1)-Cl(4)
O(2)-Re(1)-Cl(4)
Cl(1)-Re(1)-Cl(2)
Cl(1)-Re(1)-Cl(3)
Cl(1)-Re(1)-Cl(4)
Cl(2)-Re(1)-Cl(3)
Cl(2)-Re(1)-Cl(4)
88.2(4)
82.4(4)
O(1)-Re(1)-O(2)
O(1)-Re(1)-Cl(1)
O(2)-Re(1)-Cl(1)
O(1)-Re(1)-Cl(2)
O(2)-Re(1)-Cl(2)
O(1)-Re(1)-Cl(3)
O(2)-Re(1)-Cl(3)
O(1)-Re(1)-Cl(4)
O(2)-Re(1)-Cl(4)
Cl(1)-Re(1)-Cl(2)
Cl(1)-Re(1)-Cl(3)
Cl(1)-Re(1)-Cl(4)
Cl(2)-Re(1)-Cl(3)
Cl(2)-Re(1)-Cl(4)
Cl(3)-Re(1)-Cl(4)
86.8(3)
175.4(2)
88.6(2)
91.6(2)
178.2(3)
87.2(3)
88.2(3)
88.6(3)
90.1(3)
93.1(1)
92.9(1)
91.2(1)
90.9(1)
90.6(1)
175.6(1)
86.6(3)
177.6(2)
91.0(2)
89.8(3)
176.3(3)
88.8(2)
89.0(4)
89.8(2)
90.3(4)
92.6(2)
91.6(1)
89.9(1)
90.3(3)
90.3(3)
178.4(2)
87.1(3)
178.2(2)
91.1(2)
87.7(2)
174.8(2)
89.9(2)
88.6(3)
90.7(2)
88.0(2)
94.0(1)
89.6(1)
89.6(1)
91.2(1)
92.3(1)
176.4(1)
179.2(3)
91.1(3)
89.1(3)
176.6(3)
87.7(3)
87.1(3)
88.8(3)
90.3(3)
91.6(1)
91.9(1)
91.6(1)
90.7(2)
91.8(2)
N(11)-Cu(1)-N(21) 149.4(4)
N(11)-Cu(1)-N(22) 100.6(5)
N(11)-Cu(1)-O(3)
N(11)-Cu(1)-O(4*)
N(12)-Cu(1)-N(21) 105.1(4)
N(12)-Cu(1)-N(22) 160.7(4)
119.8(4)
78.1(4)
N(12)-Cu(1)-O(3)
N(12)-Cu(1)-O(4*)
N(21)-Cu(1)-N(22)
N(21)-Cu(1)-O(3)
N(21)-Cu(1)-O(4*)
N(22)-Cu(1)-O(3)
75.9(4)
81.4(4)
82.1(5)
90.8(4)
73.9(4)
86.3(4)
N(22)-Cu(1)-O(4*) 117.9(4)
O(3)-Cu(1)-O(4*) 148.2(3)
Cl(3)-Re(1)-Cl(4) 175.7(2)
*-0.5 + x, 0.5 - y, -0.5 + z.
a The numbering scheme for the [ReCl4(mal)]2- â unit differs from that
for the R unit and of 1b. The chemically equivalent distances and angles
are compared in this table.
Table 3. Selected Bond Distances (Å) and Bond Angles (deg) for
[ReCl4(µ-mal)Cu(phen)2]‚CH3CN (2)
Distances
Re(1)-O(1)
Re(1)-O(2)
Re(1)-Cl(1)
Re(1)-Cl(2)
Re(1)-Cl(3)
Re(1)-Cl(4)
2.045(5)
2.000(4)
2.346(2)
2.347(2)
2.352(2)
2.363(2)
Cu(1)-N(11)
Cu(1)-N(12)
Cu(1)-N(21)
Cu(1)-N(22)
Cu(1)-O(3)
2.029(5)
1.999(5)
2.072(5)
2.000(6)
2.273(5)
Figure 1. View of the [ReCl4(mal)]2- anion in 1b showing the atom
numbering. Thermal ellipsoids are plotted at the 30% probability level, and
hydrogen atoms were omitted for clarity.
Angles
O(1)-Re(1)-O(2)
O(1)-Re(1)-Cl(1)
O(2)-Re(1)-Cl(1)
O(1)-Re(1)-Cl(2)
O(2)-Re(1)-Cl(2)
O(1)-Re(1)-Cl(3)
O(2)-Re(1)-Cl(3)
O(1)-Re(1)-Cl(4)
O(2)-Re(1)-Cl(4)
Cl(1)-Re(1)-Cl(2)
Cl(1)-Re(1)-Cl(3)
Cl(1)-Re(1)-Cl(4)
Cl(2)-Re(1)-Cl(3)
87.8(2)
Cl(2)-Re(1)-Cl(4)
Cl(3)-Re(1)-Cl(4)
N(11)-Cu(1)-N(12)
91.2(1)
175.3(1)
82.6(2)
178.0(1)
90.4(1)
88.7(1)
176.1(1)
87.6(2)
87.0(1)
88.4(2)
90.5(1)
93.1(1)
93.4(1)
90.6(1)
91.2(1)
generalized gradient approximation functionals.25 Atomic spin
densities were calculated through the natural bond orbital analysis.26
N(11)-Cu(1)-N(21) 142.1(2)
N(11)-Cu(1)-N(22)
N(11)-Cu(1)-O(3)
99.4(2)
134.8(2)
N(12)-Cu(1)-N(21) 101.4(2)
N(12)-Cu(1)-N(22) 171.9(2)
Results and Discussion
N(12)-Cu(1)-O(3)
N(21)-Cu(1)-N(22)
N(21)-Cu(1)-O(3)
N(22)-Cu(1)-O(3)
85.2(2)
82.0(2)
82.9(2)
87.9(2)
Crystal Structures of (AsPh4)1.5(HNEt3)0.5[ReCl4(mal)]
(1a) and (AsPh4)(HNEt3) [ReCl4(mal)] (1b). Compounds
1a and 1b contain the [ReCl4(mal)]2- dianionic unit, packed
with tetraphenylarsonium and triethylammonium cations in
2:3:1 and 1:1:1 ratios, respectively. This leads to different
crystal structures for the two salts. However and despite the
presence of two crystallographically nonequivalent [ReCl4-
(mal)]2- units in 1a, the anions are structurally quite similar
in the two salts, as is shown in Table 2. With this in mind,
only the anion complex in 1b will be fully described, a
drawing of which showing the atom numbering is provided
in Figure 1. The Re(IV) atom is in a distorted octahedral
environment, surrounded by four chloride anions and a
Density Functional Theory (DFT) Calculations. All calcula-
tions were performed with the Gaussian 94 program22 and using
the double-ú pseudopotential basis set (LanL2DZ).23 The adiabatic
connection method with three parameters (B3LYP)24 was used,
mixing the Hartree-Fock contribution for the exchange with
(21) (a) MSC/AFC Diffractometer Software, 1993. (b) Sheldrick, G. M.
Acta Crystallogr. 1990, A46, 467. (c) Sheldrick, G. M. SHELXL97.
Program for Structure Refinement; University of Go¨ttingen: Go¨ttingen,
Germany, 1997. (d) Spek, A. L. PLATON. A Multiporpose Crystal-
lographic Tool; Utrecht University: Utrecht, The Netherlands, 2003.
(22) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Gill, P. M. W.; Johnson,
B. G.; Robb, M. A.; Cheeseman, J. R.; Keith, T.; Petersson, G. A.;
Montgomery, J. A.; Raghavachari, K.; Al-Laham, M. A.; Zakrzewski,
V. G.; Ortiz, J. V.; Foresman, J. B.; Cioslowski, J.; Stefanov, B. B.;
Nanayakkara, A.; Challacombe, M.; Peng, C. Y.; Ayala, P. Y.; Chen,
W.; Wong, M. W.; Andres, J. L.; Replogle, E. S.; Gomperts, R.;
Martin, R. L.; Fox, D. J.; Binkley, J. S.; Defrees, D. J.; Baker, J.;
Stewart, J. P.; Head-Gordon, M.; Gonzalez, C.; Pople, J. A. Gaussian
98; Gaussian Inc.: Pittsburgh, PA, 1998.
(23) (a) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270. (b) Wadt,
W. R.; Hay, P. J. J. Chem. Phys. 1985, 82, 284. (c) Hay, P. J.; Wadt,
W. R. J. Chem. Phys. 1985, 82, 299.
(24) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(25) (a) Becke, A. D. Phys. ReV. A 1988, 38, 3098. (b) Lee, C.; Yang, W.;
Parr, R. G. Phys. ReV. A 1988, 37, 785.
(26) Weinhold, F.; Carpenter, J. E. In The Structure of Small Molecules
and Ions; Plenum Press: New York, 1988; p 227.
7826 Inorganic Chemistry, Vol. 43, No. 24, 2004

Re(IV)-Cu(II) Complexes with a Bridge Malonato Ligand
bidentate malonate group. The Re-O bond distances are
2.005(9) and 2.011(12) Å, and the Re-Cl bond distances
fall within the range 2.333(13)-2.366(21) Å. These values
agree well with those found in the literature for other
rhenium(IV) compounds27 and especially for the analogous
oxalato complexes with the [ReCl4(ox)]2- unit.3,28 Bonding
angles are close to the ideal values, even the O(1)-Re-
O(2) angle of 87.1(3)°, which corresponds to the bite angle
of the malonato ligand. This point and the fact that little
distortion is introduced in the dicarboxylate by the coordina-
tion represent a remarkable difference from the [ReCl4(ox)]2-
analogue.3a Cl(1), Cl(2), O(1), and O(2) atoms constitute an
almost perfect equatorial plane around Re, the largest
deviation from planarity being 0.003(3) Å for O(1). The Re
atom is only 0.006(3) Å out of this plane toward Cl(4). Also
O(3), O(4), and the malonate carbon atoms are clearly shifted
from this plane toward Cl(4). The six-membered chelate ring
exhibits a boat conformation in which C(1), O(1), O(2), and
C(3) are nearly planar, and this ring planar section forms a
dihedral angle of 16.1(5)° with the mean equatorial plane.
C(1)O(1)O(3) and C(3)O(2)O(4) carboxylate groups form
dihedral angles of 23.5(2) and 19.8(1)°, respectively,
with the mean equatorial plane. Hydrogen bonding
[O(3)‚‚‚H(1A)-N(1) in 1a and O(4)‚‚‚H(1)-N(1) in 1b] and
short contacts between hydrogen atoms from the organic
substituents in cations and several chloro atoms in anions
contribute to stabilize of the tridimensional ionic lattices of
both compounds. The anions are well separated from each
other. The shortest rhenium-rhenium distances are 10.204-
(44) Å [Re(1)‚‚‚Re(1′)] and 9.737(5) Å [Re(1)‚‚‚Re(1a), a
) 1 + x, y, z] in 1a and 1b, respectively. These distances
are shorter than those reported for (AsPh4)2[ReCl4(ox)].3a
Both the partial substitution of (AsPh4)+ by the smaller
(HNEt3)+ and the presence of hydrogen bonding contribute
to this result. Nevertheless, the large separation precludes
any significant contact between ligand atoms of different
anions. The closest atoms, O(3) and Cl(3′) in 1a and O(4)
and O(3b) (b ) -x, -y, 1 - z) in 1b are at 5.404(25) and
4.291(33) Å, respectively. The shortest Cl‚‚‚Cl distances are
6.891(30) Å for Cl(2)‚‚‚Cl(2′a) in 1a and 5.514(47) Å for
Cl(4)‚‚‚Cl(3c) in 1b (c ) -0.5 + x, 0.5 - y, -0.5 + z).
[As(C6H5)4]+ and [HN(C2H5)3]+ cations show the expected
geometry, and we do not discuss them further.
Figure 2. (a) View of dinuclear complex 2. Thermal ellipsoids are plotted
at the 30% probability level. Noncoordinated acetonitrile molecule and
hydrogen atoms were omitted for clarity. (b) View of adjacent dinuclear
units of 2 down z axis. Thermal ellipsoids are plotted at the 30% probability
level.
compound and the next is the same as in 1b. The malonato
ligand is bidentate toward rhenium and monodentate toward
copper. In this way, each unit contains Re(IV) and Cu(II)
centers bridged by one carboxylate group exhibiting the
anti-syn conformation. The [ReCl4(mal)] fragment is almost
undistorted compared to the mononuclear anion in 1b. As
an example, the Re-Cl distances range from 2.345(10) to
2.363(10) Å, whereas the Re-O bond distances are 2.000-
(6) and 2.045(10) Å. The Re atom is 0.006(2) Å out of the
Cl(1)Cl(2)O(1)O(2) mean equatorial plane toward Cl(4). The
chelate ring adopts a boat conformation. The C(1)O(1)O(3)
and C(3)O(2)O(4) carboxylate groups form dihedral angles
with the equatorial plane of 25.3(3) and 31.8(8)°, respec-
tively.
The copper atom is bound to one malonate oxygen atom
and four nitrogen atoms from two phen ligands (Figure S1).
The coordination around the metal is intermediate between
square pyramidal and trigonal bipyramidal, the geometric τ
factor being 0.50 (the τ values for square pyramidal and
trigonal bipyramidal metal environments are 0 and 1,
respectively).29 The almost linear N(12)-Cu-N(22) moiety
[171.9(2)°] appears as the axis in a rough trigonal bipyramid,
with equatorial positions occupied by N(11), N(21), and O(3),
the metal atom being 0.037(3) Å out of this plane toward
N(22). In this case, Cu-N(eq) distances [average 2.050(16)
Å] are longer than Cu-N(axial) ones [average 2.000(8) Å],
and the Cu-O(3) distance is 2.273(10) Å. Distortion of the
geometry also becomes evident in other bonding angles, such
as N(11)-Cu-N(21) [142.2(2)°] or O(3)-Cu-N(21)
Crystal Structure of [ReCl4(µ-mal)Cu(phen)2]‚CH3CN
(2). The structure of 2 is made up of neutral dinuclear units
of [ReCl4(µ-mal)Cu(phen)2] and one acetonitrile molecule
of crystallization. A perspective drawing of the heterodi-
nuclear unit in 2 is provided in Figure 2a. The atom
numbering scheme for the [ReCl4(mal)] fragment in this
(27) (a) Linke, H.; Preetz, W. Z. Anorg. Allg. Chem. 1998, 624, 595. (b)
Maslen, E. N.; Dewan, J. C.; Kepert, D. L.; Trigwell, K. R.; White,
A. H. J. Chem. Soc., Dalton Trans. 1974, 2128. (c) von Gudenberg,
D. W.; Sens, I.; Mu¨ller, U.; Neumu¨ller, B.; Dehnicke, K. Z. Anorg.
Allg. Chem. 1992, 613, 49. (d) Engelhardt, L. M.; Figgis, B. N.;
Sobolev, A. N.; Reynolds, P. A. Aust. J. Chem. 1996, 49, 489. (e)
Herrmann, W. A.; Thiel, W. R.; Herdtweck, E. Chem. Ber. 1990, 123,
271. (f) Swidersky, H.-W.; Pebler, J.; Dehnicke, K.; Fenske, D. Z.
Naturforsch. 1990, 45b, 1227. (g) von Gudenberg, D. W.; Frenzen,
G.; Massa, W.; Dehnicke, K. Z. Anorg. Allg. Chem. 1995, 621, 525.
(28) Tomkiewicz, A.; Bartczak, T. J.; Kruszynski, R.; Mrozinski, J. J. Mol.
Struct. 2001, 595, 225.
(29) Addison, A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J.; Verschoor, G.
C. J. Chem. Soc., Dalton Trans. 1984, 1349.
Inorganic Chemistry, Vol. 43, No. 24, 2004 7827

Cuevas et al.
[82.9(2)°] in the basal plane. The phen ligands as a whole
are quite planar, the dihedral angle between them being
36.6(1)°. The values of the angle subtended at the metal atom
by the chelating phen [average 82.3(2)°] are reduced with
respect to the ideal value but in agreement with those
reported in similar copper complexes.3b The bond angle at
the bridging O(3) atom is 110.1(5)°. The dihedral angle
between the O(3)N(11)N(21) plane and the C(1)O(1)O(3)
carboxylate group is 33.7(3)°.
The Re‚‚‚Cu distance in the [ReCl4(µ-mal)Cu(phen)2] unit
is 4.800(8) Å. These units are arranged along the a direction,
giving an intermolecular Re(1)‚‚‚Cu(1d) distance of
5.475(7) Å, (d ) -1 + x, y, z). Figure 2b shows a drawing
of two adjacent units viewed down the z axis. In this
representation, one can see that the Cl(1) atom of the unit at
the right is 3.714(11) Å from the Cu(1d) atom in the unit at
the left. The shortest Cl‚‚‚Cl and Cl‚‚‚O contacts between
units are 4.357(15) Å for Cl(3)‚‚‚Cl(3e) (e ) -x, 1 - y, 2
- z) and 3.745(12) Å for Cl(2)‚‚‚O(4f) (f ) x, y, -1 + z).
A comparison with the structure of the analogous [ReCl4-
(µ-ox)Cu(phen)2]‚CH3CN3b allows the influence of the bridge
on the overall structure to be studied. In this latter compound,
Re(IV) and Cu(II) are bridged by an asymmetric bis-
(bidentate) oxalate ligand, resulting in a six-coordinated
copper ion. The Cu-O distances are 2.32 and 2.41 Å, larger
than the 2.273 Å in 2. As a consequence and even when
malonate is monodentate toward Cu(II), the resulting
Re‚‚‚Cu intramolecular distance is shorter (4.800 Å in 2
compared to 5.649 Å in the analogous oxalate). Inter-
molecular Re‚‚‚Cu and Cl‚‚‚Cl distances are also shorter in
compound 2, at 5.475 and 4.357 Å, respectively, compared
to 6.57 and 5.84 Å in [ReCl4(µ-ox)Cu(phen)2]‚CH3CN. The
structure is more compact in the case of [ReCl4(µ-mal)Cu-
(phen)2]‚CH3CN.
Crystal Structure of [ReCl4(µ-mal)Cu(bpy)2] (3). Com-
pound 3 can be described as being built of [ReCl4(mal)]2-
anions acting as bis(monodentate) ligands toward two
adjacent [Cu(bpy)2]2+ cations, with the OCO carboxylate
bridges exhibiting the anti-syn conformation. Despite the
thermal disorder of the C(2) atom in the malonate ligand,
bond distances and angles within the [ReCl4(mal)]2- anion
are comparable to those previously mentioned for 1b and 2.
Re-Cl distances range from 2.317(12) to 2.381(4) Å, and
the Re-O bond distances are 2.021(10) and 2.027(12) Å.
The Re atom is 0.024(4) Å out of the Cl(1)Cl(2)O(1)O(2)
mean equatorial plane. This equatorial plane forms dihedral
angles of 16.2(10) and 20.5(9)° with the C(1)O(1)O(3) and
C(3)O(2)O(4) carboxylate groups, respectively.
Figure 3. Perspective drawing of the local coordination environment of
Cu(II) in compound 3. Thermal ellipsoids are plotted at the 30% probability
level, and hydrogen atoms were omitted for clarity.
82.3(5)°. Oxygen atoms are at axial positions, Cu-O
distances being 2.546(9) Å [Cu(1)‚‚‚O(3)] and 2.851(14) Å
[Cu(1)‚‚‚O(4g), g ) -0.5 + x, 0.5 - y, -0.5 + z], as
expected for axial Cu(II)-O bonds.30 However, the O(3)-
Cu(1)-O(4 g) angle is only 148.2(3)°, significantly far from
the ideal. The bond angles at the bridging O(3) and O(4)
atoms are 112.5(9) and 109.1(8)°, respectively. Finally, the
N(11)N(12)N(21)N(22) mean plane forms dihedral angles
of 71.8(7) and 69.6(12)° with the C(1)O(1)O(3) and C(3g)O-
(2g)O(4g) carboxylate groups, respectively.
As in the case of the analogous [ReCl4(µ-ox)Cu(bpy)2],
well-defined chains are formed in the structure. Dinuclear
units are connected by means of the sixth coordination
position of the Cu(II) ion, now occupied by the oxygen atom
O(4g) belonging to the malonate of an adjacent unit.
Replacing oxalate by malonate in the polymeric structure
results in the formation of Re-mal-Cu-mal-Re- chains
instead of Re-ox-Cu-Cl-Re- ones. The chains run along
the [101] direction, separated a b/2 distance in the (10-1)
planes (Figure 4). Additional π-π stacking interactions
contribute to the stabilization of the crystal structure. The
intrachain Re‚‚‚Cu distances are 5.032(14) and 5.115(42) Å
through O(3) and O(4), respectively, larger than those
reported for [ReCl4(µ-ox)Cu(bpy)2], which are near 4.8 Å.
Intrachain Cu‚‚‚Cu separations through malonate are 9.083-
(76) Å. The shortest chloro-chloro contacts among chains,
Cl(1)‚‚‚Cl(3h) and Cl(3)‚‚‚Cl(1h) (with h ) 1 - x, - y, 2
- z), are at 5.592(12) Å.
Magnetic Properties. Compounds 1a and 1b have nearly
identical magnetic behaviors (Figure 5), as can be expected
given that they both contain the same paramagnetic complex,
[ReCl4(mal)]2-. The variation of øMT with the temperature
can be attributed exclusively to the zero-field splitting, which
is very large for Re(IV), a 5d3 ion, in a distorted octahedral
environment, because of the high value of its spin-orbit
coupling constant (λ ca. 1000 cm-1 in the free ion). The
separation between the anions in the lattice precludes any
magnetic interaction. When smaller countercations are used,
The copper atom is bonded to four nitrogen atoms from
twobpyligandsandtwooxygenatomsfromtwo[ReCl4(mal)]2-
anions, showing a distorted six-coordinated geometry (Figure
3). Nitrogen atoms can be considered to occupy equatorial
positions, defining a flattened tetrahedron. The Cu-N
distances average 1.994(12) Å, and the dihedral angle
between the N(11)N(12)Cu(1) and N(21)N(22)Cu(1) planes
is 38.8(6)°, practically the same values as found in [ReCl4-
(µ-ox)Cu(bpy)2].3a That is also the case for the angle
subtended at the copper atom by the bpy, which average
(30) Hathaway, B. J. In ComprehensiVe Coordination Chemistry; Wilkinson,
G., Gillard, R. D., McCleverty, J. A., Eds.; Pergamon Press: New
York, 1987; Vol. 5, p 603.
7828 Inorganic Chemistry, Vol. 43, No. 24, 2004

Re(IV)-Cu(II) Complexes with a Bridge Malonato Ligand
Figure 4. Ball-and-stick diagram of compound 3 showing the chain structure. Perspective view toward plane (10-1). Re and Cu atoms are represented as
black balls, O and N atoms as gray balls, and Cl atoms as white balls.
Figure 5. Thermal variation of the product øMT for compounds 1a and
Figure 6. Thermal variation of the product øMT for compounds 2-4. A
detail of the low-temperature range is shown in the inset. Continuous lines
represent the best theoretical fit (see text).
1b. Continuous lines represent the best theoretical fit (see text).
Table 5. Best-Fit Magnetic Parameters for Complexes 1-4
a
|2D|
Jb
Rc
compound
gRe gCu cm-1 cm-1 × 10-5
we have measured the magnetic susceptibility of microcrys-
talline powder samples, and from these measurements, it is
not possible to define reliable and unique values for g| and
(AsPh4)1.5(HNEt3)0.5[ReCl4(mal)] (1a) 1.79
(AsPh4)(HNEt3)[ReCl4(mal)] (1b) 1.82
[ReCl4(µ-mal)Cu(phen)2]‚CH3CN (2) 1.78 2.12
-
114
107
88 -0.39
-
5.4
6.3
1.6
1.8
1.0
-
-
[ReCl4(µ-mal)Cu(bipy)2] (3)
[ReCl4(µ-mal)Cu(terpy)] (4)
1.79 2.13 119 -0.09
1.7 2.08 114 +1.51
g
or the sign of D. The fit of the experimental data
considering all of these parameters results in several (math-
ematically) possible solutions. However, in all of them the
absolute value of D and the mean value of g remain
practically constants. These are the values reported in Table
5.
The magnetic properties of 2-4 in the form of øMT versus
T plots (where øM is the magnetic susceptibility per
ReIVCuII heterodinuclear unit) are shown in Figure 6. øMT
values at room temperature for the three compounds are in
the range of 1.90-1.95 cm3 mol-1 K, within the expected
range for an uncoupled ReIVCuII pair. These values decrease
upon cooling, reaching a value of 1.17 (2) and 1.35 (3) cm3
mol-1 K at 2 K. The behavior of 4 is different: øMT reaches
a minimum at ca. 10 K, with a øMT value of 1.54 cm3 mol-1
K, and then increases sharply at lower temperatures.
a 2D is the energy gap between the (3/2 and (1/2 Kramers doublets [the
zero-field splitting of Re(IV)]. b J is the exchange magnetic coupling
parameter between Re(IV) and Cu(II) local spins. c R is the agreement factor,
defined as ∑i[(øMT)obsd - (øMT)calc]2/∑i[(øMT)obsd]2.
the direct anion-anion (Cl‚‚‚Cl) contacts are not avoided,
and significant magnetic interactions occur.3a,31
Least-squares fitting of the experimental data through the
theoretical expression for the magnetic susceptibility3a de-
rived from the Hamiltonian (eq 1) leads to the parameters
reported in Table 5. These results are very similar to those
obtained for the analogous oxalato complex, [ReCl4(ox)]2-,
(g ) 1.85, 2D ) 120 cm-1).3a
H ) D[Sz2 - S(S + 1)/3] + g|âHzSz + g â(HxSx + HySy)
(1)
(31) Gonza´lez, R.; Chiozzone, R.; Kremer, C.; De Munno, G.; Nicolo´, F.;
Lloret, F.; Julve, M.; Faus, J. Inorg. Chem. 2003, 42, 2512 and
references therein.
Obviously, this large D value causes a significant axial
anisotropy and, thus, different values for g| and g . However,
Inorganic Chemistry, Vol. 43, No. 24, 2004 7829

Cuevas et al.
Table 6. DFT-Calculated Atomic Spin Densities on the ReCl4(mal)
To analyze the magnetic interaction between Re(IV) an
Cu(II) in 2-4, it is interesting to compare the øMT values at
2 K of 1a and 1b with those of 2-4. As shown in Figure 5,
the lowest øMT value for the mononuclear Re(IV) complexes
(1a and 1b) varies between 0.9 and 1.0 cm3 mol-1 K,
depending on the values of g and D. This limit is well-known
for others mononuclear magnetically isolated Re(IV) com-
plexes.3 Given that one copper(II) is present in each 2-4,
in the absence of magnetic interactions, the value of this limit
Moiety for 2a
atom
spin density
atom
spin density
Re(1)
O(1)
O(2)
O(3)
O(4)
2.4985 (2.25)b
0.0327
Cl(1)
Cl(2)
Cl(3)
Cl(4)
C(1)
C(2)
C(3)
0.0981
0.0727
0.0727
0.0727
0.0006
0.0064
0.0025
0.0553
0.0227 (0.027)b
0.0228 (0.027)b
a Very similar spin densities were obtained for 3. b The corresponding
spin density for [ReCl4(µ-ox)Cu(bpy)2]3a are given in parentheses.
1
would increase by 0.4 (S ) /2 and g ) 2.08), that is, the
limit of øMT would be in the range 1.3-1.4 cm3 mol-1 K.
Inspection of Figure 6 shows that the lowest value of øMT
for 2 is 1.17 cm3 mol-1 K, a value clearly below the above
limit (1.3-1.4). This fact suggests the occurrence of an
antiferromagnetic interaction between the metal ions. For 3,
the øMT value at 2 K is 1.35 cm3 mol-1 K, a value that lies
within the above range (1.3-1.4), suggesting the lack of any,
or an extremely weak, magnetic interaction. Finally, in the
case of 4, the value of øMT at its minimum at 10 K is 1.54
cm3 mol-1 K. This value is significantly greater than the
calculated limit (1.3-1.4), indicating that a ferromagnetic
coupling occurs between Re(IV) and Cu(II) in this com-
pound.
Taking into account the discrete dinuclear structure of 2,
the decrease of øMT upon cooling could be attributed only
to zero-field splitting of Re(IV) and intramolecular Re(IV)-
Cu(II) magnetic interactions. Consequently, we analyzed the
magnetic behavior of 2 through the Hamiltonian of eq 2. A
least-squares fit leads to the parameters reported in Table 5.
The calculated curve matches very well the magnetic data.
O(4)] has to be negligible, and thus, the chain 3 would
behave magnetically as a Cu(II)-Re(IV) dinuclear complex
through the Cu(1)-O(3) exchange pathway.
It is interesting to note that the analogous oxalato-bridged
Re(IV)-Cu(II) complex of formula [ReCl4(µ-ox)Cu(bipy)2]
with Cu-O distances similar to those of 3 behaves as a
ferrimagnetic chain, that is, the exchange pathways involved
is more effective than those of 3. The reason for this different
magnetic behavior could be a decreased orbital overlapping
associated with the large deviation of the O(3)CuO(4) angle
from the ideal value as well as the different spin density
values on the oxygen atoms: 0.023 in 3 versus 0.027 in
[ReCl4(µ-ox)Cu(bipy)2]; see Table 6.
Discussion of the magnetic properties of 4 requires some
considerations of its structure, which is unknown because it
was not possible to obtain sutable crystals for the X-ray
diffraction study. Taking into account the coordination modes
of the malonato bridge, i.e., bidentate/monodentate as in 2
or bidentate/bis(monodentate) as in 3, we can imagine the
structure of 4 as a dinuclear complex (only one magnetic
coupling parameter) or as an alternating chain (two magnetic
coupling parameters). The magnetic properties of 4 can be
reproduced satisfactorily with a simple dinuclear model (eq
2) with a ferromagnetic coupling of J ) +1.51 cm-1 (see
Table 5). This high-quality fit means that, if an alternating
chain is involved, the additional coupling must be negligible.
Thus, 4 behaves as a dinuclear species (as do 2 and 3),
but in this case, a weak but significant ferromagnetic coupling
occurs. In this bimetallic species, because the terpy ligand
fills only three equatorial positions around the Cu(II), the O
atom of malonate could occupy an axial position or the
remaining equatorial one. The ferromagnetic nature of the
coupling strongly suggests that the O atom fills the axial
position given that, in the related oxalato complexes, only
this coordination mode, observed in the structure of [ReCl4(µ-
ox)Cu(terpy)(CH3CN)],3b leads to a ferromagnetic coupling.
The strict coplanarity of the three N equatorial atoms in 4,
in contrast to the flattened tetrahedron in 3, produces the
orthogonality between the magnetic orbitals of rhenium and
copper. Then, the fourth equatorial position in 4 should be
occupied by a solvent molecule. However, the presence of
CH3CN (the solvent used in the synthesis) can be ruled out
by the IR spectrum and the elemental analysis, and thus, a
water molecule is probably the lacking ligand, as occurs in
[ReCl4(µ-ox)Cu(terpy)(H2O)],3b although in this case, it is
located in an axial position. The proposed structure of 4 is
shown in Chart 1. The dinuclear molecules can be united
H ) -JSReSCu + D[SzRe2 - S(S+1)/3] + gâSReH +
gâSCuH (2)
The value of J ) -0.39 cm-1 reveals a weak antiferromag-
netic coupling between Re(IV) and Cu(II), a value somewhat
lower than that of the analogous oxalato complex [ReCl4-
(µ-ox)Cu(phen)2] (J ) -0.90 cm-1),3b although the two
complexes are not strictly comparable because of the different
coordination modes of the bridge ligand, bidentate/mono-
dentate in the malonato and bis(bidentate) in the oxalato. It
is important to note that, although the shape of the magnetic
plot for 2 is monitored basically by the zero-field splitting,
the experimental data at low temperature cannot be repro-
duced theoretically without the presence of magnetic cou-
pling.
As mentioned above, the magnetic properties of 3 sug-
gested the lack of any, or an extremely weak, magnetic
interaction between the metal ions. In fact, its magnetic
properties can be reproduced theoretically using only the
zero-field splitting (eq 1), that is, Cu(II) and Re(IV)
magnetically isolated. However, a better fit is obtained when
a magnetic interaction between these two ions through the
Hamiltonian of eq 2 is considered. One can see in 3 that a
regular alternation of two exchange pathway occurs: one
through the Cu(1)-O(3) bond (2.54 Å) and the other through
the Cu(1)-O(4) bond (2.84 Å). Given that the magnetic
coupling so weak, the longer exchange pathway [Cu(1)-
7830 Inorganic Chemistry, Vol. 43, No. 24, 2004

Re(IV)-Cu(II) Complexes with a Bridge Malonato Ligand
Chart 1
included in Table 6. The spin density of the rhenium atom
is somewhat delocalized onto the atoms of the ligands. The
values are always positive in these atoms and vary in the
order Cl > O > C, being higher in the atoms nearest to the
metal ion. The calculation also reveals that the delocalization
is less extensive in the malonato species than in the oxalato,
although the differences are small. Thus, in the ReCl4(ox)
fragment, the spin densities on the metal ion and the O(3)
and O(4) atoms are 2.248, 0.027, and 0.027, respectively.3a
forming chains similar to the observed ones in 3, with
relatively long Cu-O intermolecular distances.
Acknowledgment. Financial support from the Training
and Mobility Research Program from the European Union
(TMR Contract ERBFMRXCT-980181), the Ministerio
Espan˜ol de Ciencia y Tecnolog´ıa (Project BQU2001-2928),
CSIC (Uruguay), and the Italian Ministero dell’Universita` e
della Ricerca Scientifica e Tecnologica is gratefully ac-
knowledged.
DFT Calculations. Magnetic interactions between Re(IV)
and Cu(II) through a malonato bridge can vary from weak
antiferromagnetic to weak ferromagnetic depending on the
molecular structure of the bimetallic species. These results
are qualitatively similar to those observed in the analogous
oxalato complexes, but quantitatively, the magnetic exchange
is quite a bit smaller. With the aim of clarifying whether
there are intrinsic differences between the two ligands as
magnetic couplers, we performed DFT calculations on the
ReCl4(mal) fragment in 2 and 3 and compared the results
with identical calculations performed previously on the
ReCl4(ox) fragment.3a The computed spin densities for the
two compounds were basically the same, and they are
Supporting Information Available: Perspective drawing of the
Cu(II) polyhedron in compound 2 (Figure S1). X-ray crystal-
lographic files of compounds 1a, 1b, 2, and 3 in CIF format.
This material is available free of charge via the Internet at
htpp://pubs.acs.org.
IC0493853
Inorganic Chemistry, Vol. 43, No. 24, 2004 7831