Malonate-containing manganese(III) complexes: Synthesis, crystal structure, and magnetic properties of AsPh4[Mn(mal)2(H 2O)2]

Article abstract of DOI:10.1021/ic0508526

The novel manganese(III) complexes PPh₄[Mn(mal) ₂(H₂O)₂] (1) and AsPh₄[Mn(mal) ₂(H₂O)₂] (2) (PPh₄⁺ = tetraphenylphosphonium cation, AsPh₄⁺ = tetraphenylarsonium cation, and H₂mal = malonic acid) have been prepared, and the structure of 2 was determined by X-ray diffraction analysis. 2 is a mononuclear complex whose structure is made up of trans- diaquabis(malonato)manganate(III) units and tetraphenylarsonium cations. Two crystallographically independent manganese(III) ions (Mn(1) and Mn(2)) occur in 2 that exhibit elongated octahedral surroundings with four oxygen atoms from two bidentate malonate groups in equatorial positions (Mn(1)-O = 1.923(6) and 1.9328(6) A and Mn(2)-O = 1.894(6) and 1.925(6) A) and two trans-coordinated water molecules in the axial sites (Mn(1)-Ow = 2.245(6) A and Mn(2)-Ow = 2.268(6) A). The [Mn(mal)₂(H ₂O)₂]- units are linked through hydrogen bonds involving the free malonate-oxygen atoms and the coordinated water molecules to yield a quasi-square-type anionic layer growing in the ab plane. The shortest intralayer metal-metal separations are 7.1557(7) and 7.1526(7) A (through the edges of the square). The anionic sheets are separated from each other by layers of AsPh₄⁺ where sextuple- and double-phenyl embraces occur. The magnetic behavior of 1 and 2 in the temperature range 1.9-290 K reveals the occurrence of weak intralayer ferromagnetic interactions (J = +0.081 (1) (1) and +0.072(2) cm^-1 (2)). These values are compared to those of the weak antiferromagnetic coupling [J = -0.19(1) cm^-1], which is observed in the chain compound K₂[Mn(mal)₂(MeOH)₂][Mn(mal) ₂] (3), where the exchange pathway involves the carboxyate-malonate bridge in the anti-syn conformation. The structure of 3 was reported elsewhere. Theoretical calculations on fragment models of 2 and 3 were performed to analyze and substantiate both the nature and magnitude of the magnetic couplings observed.

Full text of DOI:10.1021/ic0508526

Inorg. Chem. 2006, 45, 1012
−1020
Malonate-Containing Manganese(III) Complexes: Synthesis, Crystal
Structure, and Magnetic Properties of AsPh4[Mn(mal)2(H2O)2]
Fernando S. Delgado,† Nicolas Kerbellec,‡ Catalina Ruiz-Pe´rez,*,† Joan Cano,§ Francesc Lloret,‡ and
Miguel Julve‡
Laboratorio de Rayos X y Materiales Moleculares, Departamento de F´ısica Fundamental II,
Facultad de F´ısica, UniVersidad de La Laguna, AVda, Astrof´ısico Francisco Sa´nchez s/n,
38204 La Laguna, Tenerife, Spain, Departament de Qu´ımica Inorga`nica/Instituto de Ciencia
Molecular, Facultat de Qu´ımica de la UniVersitat de Vale`ncia, Dr. Moliner 50, 46100-Burjassot,
Vale`ncia, Spain, and Institucio´ Catalana de Recerca i Estudis AVanc¸ats (ICREA)/Departament de
Qu´ımica Inorga`nica i Centre de Recerca en Qu´ımica Teo´rica, UniVersitat de Barcelona,
Diagonal 647, 08028 Barcelona, Spain
Received May 26, 2005
+
The novel manganese(III) complexes PPh4[Mn(mal)2(H2O)2] (1) and AsPh4[Mn(mal)2(H2O)2] (2) (PPh4
tetraphenylphosphonium cation, AsPh4
)
+
) tetraphenylarsonium cation, and H2mal ) malonic acid) have been
prepared, and the structure of 2 was determined by X-ray diffraction analysis. 2 is a mononuclear complex whose
structure is made up of trans-diaquabis(malonato)manganate(III) units and tetraphenylarsonium cations. Two
crystallographically independent manganese(III) ions (Mn(1) and Mn(2)) occur in 2 that exhibit elongated octahedral
surroundings with four oxygen atoms from two bidentate malonate groups in equatorial positions (Mn(1)
1.923(6) and 1.9328(6) Å and Mn(2) 1.894(6) and 1.925(6) Å) and two trans-coordinated water molecules in
the axial sites (Mn(1) Ow 2.245(6) Å and Mn(2) Ow
2.268(6) Å). The [Mn(mal)2(H2O)2]- units are linked
through hydrogen bonds involving the free malonate oxygen atoms and the coordinated water molecules to yield
a quasi-square-type anionic layer growing in the ab plane. The shortest intralayer metal metal separations are
−O )
−O )
−
)
−
)
−
−
7.1557(7) and 7.1526(7) Å (through the edges of the square). The anionic sheets are separated from each other
+
by layers of AsPh4 where sextuple- and double-phenyl embraces occur. The magnetic behavior of 1 and 2 in the
temperature range 1.9−290 K reveals the occurrence of weak intralayer ferromagnetic interactions (J ) +0.081(1)
1
(1) and
0.19(1) cm-1], which is observed in the chain compound K2[Mn(mal)2(MeOH)2][Mn(mal)2] (3), where the exchange
pathway involves the carboxyate malonate bridge in the anti syn conformation. The structure of 3 was reported
+ )
0.072(2) cm- (2)). These values are compared to those of the weak antiferromagnetic coupling [J
−
−
−
elsewhere. Theoretical calculations on fragment models of 2 and 3 were performed to analyze and substantiate
both the nature and magnitude of the magnetic couplings observed.
Introduction
row transition-metal ions, the case of carboxylato-bridged
manganese(II) complexes is specially relevant because such
systems are known to exist at the active centers of some
manganese-containing enzymes.3 Focusing on the magnetic
studies and without being exhaustive, examples are known
of structurally characterized oxalate-,4 terephthalate-,5 adi-
pate-,6 and malonate-bridged7 manganese(II) compounds with
antiferromagnetic interactions ranging from maximum values
of -2.5 (through oxalato) to -0.70 cm-1 (through carboxy-
The use of deprotonated dicarboxylic acids as bridging
ligands between paramagnetic transition-metal ions to afford
polynuclear compounds is an area of continuous interest both
in molecular magnetism1 and in biology.2 Among the first-
* To whom correspondence should be addressed. E-mail: caruiz@ull.es.
† Universidad de La Laguna.
‡ Universitat de Vale`ncia.
§ Universitat de Barcelona.
(1) (a) Oldham, C. In ComprehensiVe Coordination Chemistry; Wilkinson,
G., Gillard, R. D., McCleverty, J. A., Eds.; Pergamon Press: Oxford,
U.K., 1987; Vol. 2, p 435. (b) Kahn, O. Molecular Magnetism; VCH:
New York, 1993.
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Chem., Int. Ed. Engl. 1989, 28, 1153.
1012 Inorganic Chemistry, Vol. 45, No. 3, 2006
10.1021/ic0508526 CCC: $33.50
© 2006 American Chemical Society
Published on Web 01/11/2006

Malonate-Containing Manganese(III) Complexes
late-malonate). The case of the malonate dianion (hereafter
noted as mal) is very appealing mainly due to two features
which are well illustrated by its copper(II) complexes: (i)
the great versatility as a ligand given that it can adopt not
only the chelating bidentate coordination mode but also the
syn-syn, syn-anti, and anti-anti carboxylate-bridging
modes; (ii) the ability to mediate ferromagnetic interactions
between the metal ions that it bridges.8-11 Interestingly, this
ferromagnetic interaction between the copper(II) ions through
the carboxylate-malonate bridge is kept when one of the
hydrogen atoms of the methylene group is replaced by a
phenyl group (that is, phenylmalonate as the ligand instead
of malonate).12
because of its fairly oxidizing power and easy disproportion.
However, its presence in discrete polynuclear transition-metal
complexes, which exhibit a slow relaxation of the magnetiza-
tion,17 have caught the eyes of magnetochemists interested
in the design of molecular magnets. This property is strongly
related to the occurrence of a large spin in the ground state
and a strong axial anisotropy in the cluster. This last
requirement can be fulfilled by the presence of Mn(III),
known to possess a pronounced magnetic anisotropy. In the
search for stable manganese(III) building blocks to be used
as precursors of these so-called single-molecule magnets, we
have prepared the new manganese(III) complexes PPh4[Mn-
+
(mal)2(H2O)2] (1) and AsPh4[Mn(mal)2(H2O)2] (2) (PPh4
+
) tetraphenylphosphonium cation, AsPh4 ) tetraphenyl-
The extensive magneto-structural work that has been
carried out with the malonate complexes with divalent first-
row transition-metal ions7-11,13 contrasts with the paucity of
investigations concerning the manganese(III) ion.14-16 The
coordination chemistry of this cation is not an easy task
arsonium cation, and H2mal ) malonic acid). Their prepara-
tion, structural characterization, magnetic study, and a
theoretical analysis of the exchange pathway are presented
here. The magnetic properties of the previously reported
chain compound K2[Mn(mal)2(MeOH)2][Mn(mal)2]14b (3)
were investigated for comparison.
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Experimental Section
Materials. Malonic acid, potassium permanganate, tetraphen-
ylphosphonium chloride, and tetraphenylarsonium chloride mono-
hydrate were purchased from commercial sources and used as
received. Polycrystalline samples of K2[Mn(mal)2(MeOH)2][Mn-
(mal)2] (3) were prepared by the method of Cartledge and Nichols,18
and well-formed green crystals of this compound were grown by
the receipt of Lis and Matuszewski.14a These crystals, once crushed,
were used for the magnetic measurements. Elemental analyses
(C, H) were carried out by the Microanalytical Service of the
Universidad Auto´noma de Madrid. The X-Mn (X ) P (1), As
(2), and K (3)) molar ratio was determined by electron probe X-ray
microanalysis at the Servicio Interdepartamental de Investigacio´n
de la Universidad de Valencia.
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M. J. Chem. Soc., Dalton Trans. 1994, 3465.
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35, 2212. (b) Sain, S.; Maji, T. K.; Mostafa, G.; Lu, T. H.; Chaudhuri,
N. R. Inorg. Chim. Acta 2003, 351, 12. (c) Rodr´ıguez-Mart´ın, Y.;
Herna´ndez-Molina, M.; Sanchiz, J.; Ruiz-Pe´rez, C.; Lloret, F.; Julve,
M. Dalton Trans. 2003, 2359. (d) Maji, T. K.; Sain, S.; Mostafa, G.;
Lu, T. H.; Ribas, J.; Monfort, M.; Chaudhuri, N. R. Inorg. Chem.
2003, 42, 709.
Preparation of PPh4[Mn(mal)2(H2O)2] (1) and AsPh4[Mn-
(mal)2(H2O)2] (2). 1 and 2 were obtained as polycrystalline, olive-
green powders by adding solid PPh4Cl (1 mmol, 1) and AsPh4Cl‚
H2O (1 mmol, 2) to an aqueous solution (30 mL, 0.05 M H2mal)
of K2[Mn(mal)2(MeOH)2][Mn(mal)2] (1 mmol, 1 and 2). The yield
(8) Sain, S.; Maji, T. K.; Mostafa, G.; Lu, T. H.; Chaudhuri, N. R. New
J. Chem. 2003, 27, 185.
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M. I.; Rojo, T. Inorg. Chem. 1998, 37, 3243. (b) Ruiz-Pe´rez, C.;
Sanchiz, J.; Herna´ndez-Molina, M.; Lloret, F.; Julve, M. Inorg. Chim.
Acta 2000, 298, 202. (c) Ruiz-Pe´rez, C.; Herna´ndez-Molina, M.;
Sanchiz, J.; Lo´pez, T.; Lloret, F.; Julve, M. Inorg. Chim. Acta 2000,
298, 245. (d) Rodr´ıguez-Mart´ın, Y.; Sanchiz, J:; Ruiz-Pe´rez, C.; Lloret,
F.; Julve, M. CrystEngComm 2002, 4, 631. (e) Delgado, F. S.; Sanchiz,
J.; Ruiz-Pe´rez, C.; Lloret, F.; Julve, M. CrystEngComm 2003, 5, 280.
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Crystallogr. 1977, B33, 1943. (b) Lis, T.; Matuszewski, Polish J.
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W. E.; Brunel, L. C.; Ishimoto, H.; Christou, G.; Hendrickson, D. N.
Inorg. Chem. 2001, 40, 4604. (c) Gatteschi, D. Sessoli, R. Angew.
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M. Inorg. Chem. 2000, 39, 1363 (b) Ruiz-Pe´rez, C.; Herna´ndez-Molina,
M.; Lorenzo-Luis, P.; Lloret, F.; Cano, J.; Juve, M. Inorg. Chem. 2000,
39, 3845. (c) Sanchiz, J.; Rodr´ıguez-Mart´ın, Y.; Ruiz-Pe´rez, C.;
Mederos, A.; Lloret, F.; Julve, M. New J. Chem. 2002, 26, 1624. (d)
Rodr´ıguez-Mart´ın, Y.; Ruiz-Pe´rez, C.; Sanchiz, J.; Lloret, F.; Julve,
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Sanchiz, J.; Lloret, F.; Julve, M. CrystEngComm 2002, 4, 440. (f)
Rodr´ıguez-Mart´ın, Y.; Herna´ndez-Molina, M.; Delgado, F. S.; Pasa´n,
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Inorganic Chemistry, Vol. 45, No. 3, 2006 1013

Delgado et al.
Table 1. Crystal Data and Details of Structure Determination
was ∼70%. The recrystallization of these powder samples in a 1:2
H2O-MeOH (v/v) mixture in a hood afforded platelike crystals of
1 and rods of 2. The rods were suitable for X-ray diffraction,
whereas the plates poorly diffract. Anal. Calcd for C30H28MnO10P
(1): C, 56.81; H, 4.42. Found: C, 56.45; H, 4.36. Anal. Calcd for
C30H28AsMnO10 (2): C, 53.13; H, 4.12. Found: C, 52.93; H, 4.06.
Selected IR peaks (KBr disk, cm-1): 3500-3200 s,br (1 and 2)
[ν(O-H)], 2904 w (1) and 2908 w (2) [ν(C-H)], 1636 s,sh (1 and
2) [νa(COO-)], 1368 s,sh (1) and 1363 s,sh (2) [νs(COO-)], 789,
759, 722, and 691 m,sh (1) and 795, 750, and 690 m,sh (2)
[δ(C-H)].
Physical Techniques. IR spectra (4000-400 cm-1) were
recorded on a Bruker IF S55 spectrophotometer with samples
prepared as KBr pellets. Variable-temperature (1.9-295 K) magnetic-
susceptibility measurements on polycrystalline samples of 1-3 were
carried out with a Quantum Design SQUID operating at 5000 Oe
in the high-temperature range (30-295 K) and at 250 Oe at T <
30 K to avoid saturation phenomena. Diamagnetic corrections for
the molar units were estimated from Pascal constants19 as -365 ×
10-6 (1), -370 × 10-6 (2), and -141 × 10-6 cm3 mol-1 (3) (per
mol of manganese(III)).
cpmpd
formula
M
2
C30H24AsMnO10
674.35
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
triclinic
P1h
9.8888(8)
10.3411(13)
14.136(2)
85.499(4)
84.737(6)
89.975(7)
1435.0(3)
2
T, K
F
293(2)
1.561
0.71073
1.662
0.090 (0.150)
0.205 (0.255)
11083 (0.074)
5426 (3526)
calc, Mg m-3
λ, Mo-KR, Å
µ, Mo-KR, mm-1
R1, I > 2σ(I) (all)
wR2, I > 2σ(I) (all)
measured reflns (Rint
)
independent reflns [I > 2σ(Ι)]
Crystal Data Collection and Refinement. A single crystal of
2 was mounted on a Bruker-Nonius KappaCCD diffractometer.
Orientation matrix and lattice parameters were obtained by least-
squares refinement of the reflections obtained by a θ-ø scan (Dirax/
lsq method). Diffraction data of 2 were collected at 293(2) K using
graphite-monochromated Mo KR radiation (λ ) 0.71073 Å). A
summary of the crystallographic data and structure refinement is
given in Table 1. The indexes of data collection were -11 e h e
11, -12 e k e 12, and -11 e l e 17. Of the 5426 measured
independent reflections in the θ range 1.98-26° (2), 3526 have I
g 2σ(I). The sample diffracts weakly over 26°. All of the measured
independent reflections were used in the analysis. All calculations
for data reduction, structure solution, and refinement were done
by standard procedures (WINGX).34 The structure was solved by
direct methods and refined with the full-matrix least-squares
technique on F2 using the SHELXS-9735 and SHELXL-9735
programs. The hydrogen atoms of the malonate and tetraphenyl-
arsonium groups were set in calculated positions and isotropically
refined as riding atoms. The hydrogen atoms of the water molecules
were not found. The final Fourier-difference map showed maxi-
Computational Strategy. All theoretical calculations were
carried out with the hybrid B3LYP method,20-22 as is implemented
in Gaussian03 program.23 Double- and triple-ú quality basis sets
proposed by Ahlrichs and co-workers have been used for all
atoms.24,25 The broken-symmetry approach has been employed to
describe the unrestricted solutions of the antiferromagnetic spin
states.26-29 Two models have been built from the experimental
crystal structure to analyze the magnetic interactions between the
manganese(III) ions in 2 and 3 (see Figure 9). A quadratic
convergence method was used to determine the more-stable wave
functions in the SCF process.30 The atomic spin densities were
obtained from natural bond orbital (NBO) analysis.31-33
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M. A.; Cheeseman, J. R.; Montgomery, J. A.; Vreven, Jr., T.; Kudin,
K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone,
V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G.
A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.;
Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R.
E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J.
W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.;
Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.;
Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari,
K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.;
Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.;
Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.;
Johnson, B.; Chen, W.; Wong, M. W.; Gonza´lez, C.; Pople, J. A.
Gaussian 03, Revision C.02.; Gaussian, Inc.: Wallingford, CT, 2004.
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mum- and minimum-height peaks of 0.843 and -0.806 e Å-3
,
respectively. The final geometrical calculations and the graphical
manipulations were carried out with PARST97,36 CRYSTAL
MAKER,37 and DIAMOND38 programs. Selected bond distances
and angles for 2 are listed in Table 2. The CCDC reference number
for 2 is 271896.
Results and Discussion
Description of the Structure of 2. The solid-state
structure of 2 comprises trans-diaquabis(malonato)manga-
nate(III) anions and tetraphenylarsonium cations, which are
linked through electrostatic forces, hydrogen bonds, and van
der Waals interactions. Two crystallographically independent
(33) Weinhold, F.; Carpenter, J. E. The Structure of Small Molecules and
Ions; Plenum: New York, 1988; p 227.
(34) Farrugia, L. J. WINGX, J. Appl. Cryst, 1999, 32, 837.
(35) Sheldrick, G. M. SHELX97, Programs for Crystal Structure Anlysis
(Release 97-2), Institu¨t fu¨r Anorganische Chemie der Universita¨t:
Go¨ttingen, Germany, 1998.
(36) Nardelli, M. J. Appl. Crystallogr. 1995, 28, 659.
(37) CRYSTAL MAKER 4.2.1. Crystalmaker Sofware: Oxfordside, UK,
2001.
(38) DIAMOND 2.1d, Crystal Impact GbR, CRYSTAL IMPACT, K;
Brandenburg & H. Putz GbR: Bonn, Germany, 2000.
1014 Inorganic Chemistry, Vol. 45, No. 3, 2006

Malonate-Containing Manganese(III) Complexes
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 2
Table 3. Relevant H-bond Distances (Å) for 2
D‚‚‚A
Mn(1)-O(1)
Mn(1)-O(2)
Mn(1)-O(1w)
1.923(6)
1.932(6)
2.245(6)
Mn(2)-O(11)
Mn(2)-O(12)
Mn(2)-O(2w)
1.894(6)
1.925(6)
2.268(6)
O(1w)‚‚‚O(13)
O(1w)‚‚‚O(14c)a
O(2w)‚‚‚O(3d)a
O(2w)‚‚‚O(4)
2.634(10)
2.753(9)
2.672(9)
2.760(9)
O(1)-Mn(1)-O(2)
91.7(3)
88.3(3)
90.9(2)
89.1(2)
93.1(2)
86.9(2)
O(11)-Mn(2)-O(12)
O(11)-Mn(2)-O(12b)a
O(11)-Mn(2)-O(2w)
O(11)-Mn(2)-O(2wb)a
O(12)-Mn(2)-O(2w)
O(12)-Mn(2)-O(2wb)a
91.5(3)
88.5(3)
89.5(2)
90.5(2)
88.7(2)
91.3(2)
O(1)-Mn(1)-O(2a)a
O(1)-Mn(1)-O(1w)
O(1)-Mn(1)-O(1wa)a
O(2)-Mn(1)-O(1w)
O(2)-Mn(1)-O(1wa)a
a Symmetry code: (c) -x + 1, -y, -z; (d) -x, -y + 1, -z.
a Symmetry codes: (a) -x, -y, -z; (b) -x + 1, -y + 1, -z.
Figure 2. Perspective view of the manganese(III) malonato-bridged layer
of 2 growing in the ab plane. Hydrogens bonds are drawn as blue broken
lines.
Figure 1. Perspective view showing the two crystallographically inde-
+
pendent metal ions (Mn(1), Mn(2)) and the AsPh4 cation in 2. Thermal
ellipsoids are drawn at the 50% probability level.
91.5(3)° (O(11)-Mn(2)-O(12)). Each malonate ligand
exhibits a twist-boat conformation.40 The values of the C-C
(1.488(13)-1.518(13) Å) and C-O (1.219(10)-1.289(10)
Å) malonate bond distances and O-C-O (118.3(8)-
121.2(9)°) bond angles agree well with those previously
reported for malonic acid41 and other malonate-containing
metal complexes.11,13,14a-16 The [MnIII(mal)2(H2O)2]- units
are linked through hydrogen-bonds involving the free mal-
onate-oxygen atoms and the coordinated water molecules
(see Table 3), leading to a quasi square, two-dimensional
anionic network in the ab plane (see Figure 2). The shortest
manganese‚‚‚manganese intralayer distances are 7.1557(7)
(Mn(1)‚‚‚Mn(2)), 7.1526(7) (Mn(1)‚‚‚Mn(2e); (e) x - 1, y,
z), 9.8890(8) (Mn(1)‚‚‚Mn(1f); (f) x, y + 1, z), and
10.3410(13) Å (Mn(2)‚‚‚Mn(2e)).
manganese(III) units (Mn(1) and Mn(2)) occur in 2 (see
Figure 1), the manganese atoms being located on crystal-
lographic inversion centers. The manganese atoms are six-
coordinated with four coplanar oxygen atoms from two
bidentate malonate ligands in the equatorial plane (the mean
Mn-O(mal) bond distances being 1.928(6) and 1.910(6) Å
for Mn(1) and Mn(2), respectively), whereas the axial
positions are filled by two water molecules (2.245(6) and
2.268(6) Å for Mn(1)-O(1w) and Mn(2)-O(2w), respec-
tively). The resulting MnO6 elongated octahedron has
geometric values φ ) 55.88 and s/h ) 1.341 at Mn(1) and
φ ) 55.57 and s/h ) 1.361 at Mn(2), with φ and s/h being
the twist angle and the compression ratio, respectively.39 The
values of the average Mn-O(malonate) bonds of 2 agree
with those observed in the related mononuclear compound
K[Mn(mal)2(H2O)2]‚2H2O (1.90 Å).16a As far as for the
values of 2.245(6) and 2.268(6) Å for the Mn-Ow bond
distance in 2, they are rather long for coordinated water,
indicating that this bond is quite weak. However, they
compare well with the value of 2.30 Å reported for this bond
in the compound K[Mn(mal)2(H2O)2]‚2H2O.16a Such marked
axial elongations are typical of high-spin d4 systems.
The AsPh4+ cations exhibit the expected tetrahedral shape,
and its bond distances are in agreement with those observed
in previous AsPh4+-containing compounds.42 Multiple phenyl
+
embraces involving AsPh4 lead to a two-dimensional
(40) Cremer, D.; Pople, J. A. J. Am. Chem. Soc. 1975, 97, 1354.
(41) Goedkoop, J. A.; MacGillavry, C. H. Acta Crystallogr. 1957, 10, 125.
(42) (a) Baldas, J.; Colmanet, S. F.; Mackay, M. F. J. Chem. Soc., Dalton
Trans. 1988, 1725. (b) Vicente, R.; Ribas, J.; Alvarez, S.; Segu´ı, A.;
Solans, X.; Verdaguer, M Inorg. Chem. 1987, 26, 4004. (c) Grenz,
R.; Go¨tzfried, F.; Nagel, U.; Beck, W. Chem. Ber. 1986, 119, 1217.;
(d) Mun˜oz, M. C.; Julve, M.; Lloret, F.; Faus, J.; Andruh, M. J. Chem.
Soc., Dalton Trans. 1998, 3125. (e) De Munno, G.; Armentano, D.;
Julve, M.; Lloret, F.; Lescoue¨zec, R.; Faus, J. Inorg. Chem. 1999, 38,
2234. (f) Marinescu, G.; Andruh, M.; Lescoue¨zec, R.; Mun˜oz, M. C.;
Cano, J. Cano; Lloret, F.; Julve, M. New J. Chem. 2000, 24, 527. (g)
Lescoue¨zec, R.; Marinescu, G.; Mun˜oz, M. C.; Luneau, D.; Andruh,
M.; Lloret, F.; Faus, J.; Julve, M.; Mata, J. A.; Llusar, R.; Cano, J.
New. J. Chem. 2001, 25, 1224.
Two crystallographycally independent malonate ions are
present in 2. They act as bidentate ligands toward the
manganese(III) ions, the values of the angles subtended at
the metal atom being 91.7(3)° (O(1)-Mn(1)-O(2)) and
(39) Stiefel, E. I.; Brown, G. F. Inorg. Chem. 1972, 2, 434.
Inorganic Chemistry, Vol. 45, No. 3, 2006 1015

Delgado et al.
Figure 3. (a) Perpective view of the sextuple-phenyl embrace between
AsPh4+ groups. (b) Perspective view of a AsPh4+ layer of 2 growing in the
ab plane, showing the multiple phenyl embrace. Double-phenyl embraces
(DPE) along the a (green rings) and b axes (yellow rings) between AsPh4
cations are shown.
Figure 4. (a) Perspective view of the stacking of the manganese(III)
malonato-bridged anionic (yellow) and AsPh4+ cationic (green) layers of 1
along the a axis. (b) Perspective view of the stacking of the anionic (yellow)
and cationic (green) layers of 1 along the b axis. Hydrogen bonds are drawn
as yellow broken lines.
+
cationic network (see Figure 3). Interestingly, alternating
sextuple (SPE)- and double-phenyl embraces (DPE)43 be-
tween AsPh4 cations occur along the a and b axis, the
onate groups that are connected together by potassium atoms
(see Figure 5). Two crystallographically independent man-
ganese(III) atoms are present in 3, the manganese atoms
being located on a crystallographic inversion center. Both
metal atoms are six-coordinated, and they exhibit a slightly
distorted 4 + 2 elongated octahedron. Four oxygen atoms
from two bidentate malonate ions (the bite angle at the metal
atom is 91.5(2)°) conform the equatorial plane around
Mn(1) (the Mn(1)-O(equatorial) bond distances are
1.901(5) and 1.913(5) Å), the apical positions being occupied
by two malonate oxygen atoms (the Mn(1)-O(apical) bond
distance being 2.262(5) Å). Mn(2) is bound to four oxygen
atoms from two bidentate malonate groups (bite angle )
92.1(2)°) in the equatorial plane (the Mn(2)-O(equatorial)
bond distances are 1.901(4) and 1.918(5) Å) and to two
oxygen atoms from two methanol molecules (2.203(7) Å for
Mn(2)-O(MeOH)) in the axial positions.
+
arsonium-arsonium distances involved being 6.4369(15)
[(SPE):As(1)‚‚‚As(1g); (g) -x + 1, -y, -z + 1],
8.6321(15) [(DPE) along the a axis: As(1)‚‚‚As(1h); (h) -x,
-y, -z + 1], and 7.5371(15) Å [(DPE) along the b axis:
As(1)‚‚‚As(1i); (i) -x + 1, -y + 1, -z + 1]. In the case of
a DPE where the offset face-to-face interaction occurs
between two phenyl rings of two adjacent cations, the
interplanar distances are 3.961(13) (along the a axis) and
4.95(2) Å (along the b axis). Regular alternating anionic and
cationic layers occur along the c axis, as shown in Figure 4.
We finish this structural discussion by recalling the
structure of K2[Mn(mal)2(MeOH)2][Mn(mal)2]14b (3) and
comparing it with that of 2. The structure of 3 is made up of
chains of regular alternating [Mn(mal)2(MeOH)2]- and
[Mn(mal)2]- units, bridged by anti-syn carboxylate-mal-
The [Mn(mal)2(MeOH)2]- and [Mn(mal)2]- units are
bridged by anti-syn carboxylate groups (Figure 5a), which
involve an apical oxygen atom at Mn(1) and an equatorial
(43) (a) Dance, I.; Scudder, M. Chem. Eur. J. 1996, 2, 481. (b) Dance, I.;
Scudder, M. J. Chem. Soc. Dalton Trans. 1998, 1341.
1016 Inorganic Chemistry, Vol. 45, No. 3, 2006

Malonate-Containing Manganese(III) Complexes
Figure 6. Thermal dependence of the øMT product for 1: (O) experimental
data; (s) best-fit curve (see text). (Inset) Low-temperature region in detail.
Figure 5. (a) Perspective view of a fragment of the alternating carboxylate-
(malonate)-bridged manganese(III) chain of 3 growing along the [110]
direction. (b) Perspective view of the arrangement of the manganese(III)
chains and the potassium cations. Bronze and purple broken lines represent
the intra- and interchain O-K-O-bridging units.
one at Mn(2), affording an alternating manganese(III) chain
which grows along the [110] direction. These units are further
connected through O-K-O bridges (see bronze broken lines
in Figure 5) and hydrogen bonds involving the hydroxyl
group of the methanol molecule and the malonate oxygen
atoms. The intrachain Mn(1)‚‚‚Mn(2) separation through the
carboxylate-malonate group is 5.501 Å, and the dihedral
angle between the adjacent mean equatorial planes is 49.4°.
The manganese(III) chains are held together by potassium
cations. Each chain is connected to nine adjacent ones
through O-K-O bridges (see purple broken lines in Figure
5b) leading to a three-dimensional network. The shortest
interchain Mn‚‚‚Mn separations are 6.552 and 8.562 Å for
Mn(1)‚‚‚Mn(2a) and Mn(1)‚‚‚Mn(2b), respectively ((a) x +
1, y, z; (b) x, y, z + 1).
Figure 7. Thermal dependence of the øMT product for 2: (O) experimental
data; (s) best-fit curve (see text). (Inset) Low-temperature region in detail.
In contrast with 2, where the [Mn(III)(mal)2](H2O)2]- units
are connected by hydrogen bonds involving the water
molecules and the uncoordinated malonate-oxygens to
create a quasi-square layer of manganese(III) ions, the
[Mn(III)(mal)2](CH3OH)2]- entities in 3 are linked to the
[Mn(III)(mal)2]- units through anti-syn carboxylate bridges
affording chains. The main difference between 2 and 3 is
the character and size of the counterion present in both
compounds. In 2, the hydrophobic and aromatic character
of the AsPh4+ cation are at the origin of the two-dimensional
structure with alternating hydrophobic and hydrophilic units.
Figure 8. Thermal dependence of the øMT product for 3: (O) experimental
data; (s) best-fit curve (see text). (Inset) Magnetization versus H plot at
2.0 K for 3 (O) and 2 (∆). The solid line is an eye-guide line.
Magnetic Properties of 1-3. The magnetic properties of
1-3 are shown in Figures 6-8 under the form of øMT versus
T plot (øM is the magnetic susceptibility per Mn(III) ion).
The values øMT at 300 K are 2.93 (1), 2.95 (2), and 3.0 cm3
mol-1 K (3). They are in agreement for the spin-only value
of a magnetically isolated high-spin d4 ion (øMT ) 3.0 cm3
mol-1 K with g ) 2.0). Upon cooling, øMT for 1 smoothly
Inorganic Chemistry, Vol. 45, No. 3, 2006 1017

Delgado et al.
increases to reach a maximum value of ca. 2.97 cm3 mol-1
K at 17 K, then it decreases to a minimum of 2.85 cm3 mol-1
K at 4.5 K, and it increases further to 3.12 cm3 mol-1 K at
1.9 K. In the case of 2, the value of øMT remains practically
constant from room temperature to 30 K, then it decreases
to reach a minimum of ca. 2.76 cm3 mol-1 K at 4.0 K, and
it increases further to 2.95 cm3 mol-1 K at 1.9 K. Finally, in
the case of 3, a Curie law behavior is observed from room
temperature to 90 K followed by a sharp decrease of øMT at
lower temperatures to reach 1.4 cm3 mol-1 K at 1.9 K. The
magnetic plots of 1 and 2 are as expected for the coexistence
of large single-ion zero-field splitting (ZFS) effects (D) and
ferromagnetic coupling, whereas in the case of 3, the
significant reduction of øMT at T < 90 K is attributed to the
simultaneous occurrence of D and antiferromagnetic interac-
tions. An inspection of the M versus H plot at 2.0 K for 2
and 3 (see inset of Figure 8) supports the occurrence of a
weak ferromagnetic interaction in 2, given that its magne-
tization data are well above those of 3. No susceptibility
maximum is observed in the magnetic plots of 1-3 in the
temperature range explored. Finally, the lack of ac signals
for 1-3 down to 1.9 K reveals the absence of magnetic
ordering in the temperature range explored in this series.
The appropriate Hamiltonian to account for all of these
factors is given by eq 1
where
and
2
2
W1 ) (1 + u1 )(1 + u2 ) + 4u1u2
2
2
W2 ) 2u1(1 + u2 ) + 2u2(1 + u1 )
JiS(S + 1)
kT
ui ) coth
-
[
]
kT
JiS(S + 1)
The influence of the ZFS on the powder susceptibility
measurements is expressed by eqs 4-6
2Nâ2g|2
exp(-D/kT) + 4 exp(-4D/kT)
1 + 2 exp(-D/kT) + 2 exp(-4D/kT)
2 9 - 7 exp(-D/kT) - 2 exp(-4D/kT)
1 + 2 exp(-D/kT) + 2 exp(-4D/kT)
ø| )
ø )
(4)
kT
2Nâ2g
3D
(5)
(6)
ø| + 2ø
øZFS
)
3
Keeping in mind that the magnetic plots in 1-3 are
dominated by D (the ferro (1 and 2)- and antiferromagnetic
(3) interactions are predicted to be very weak in light of their
structures and shape of their magnetic plots), a perturbational
approach11d,46 would be a suitable model to analyze their
magnetic data (eqs 7 and 8).
N
N
Hˆ ) D [Sˆ 2 - 1/3S(S + 1)] + E [Sˆ 2 - Sˆiy2] -
∑
∑
i)1
iz
ix
i)1
N
1 + u
N
N
øcomp(3) ) ø
(7)
(8)
ZFS1 - u
J
[Sˆ Sˆ ] + g â Sˆ H + g â (Sˆ H + Sˆ H ) (1)
i i+1 z z x x y y
∑
∑
∑
|
(g12 + g2 )W1 + 2g1g2W2
2
i)1
i)1
i)1
øcomp(1,2) ) øZFS
2
2
2(1 - u1 )(1 - u2 )
where the two first terms take into account the axial and
rhombic ZFS of the single-ion spin state S ) 2, the third
one takes into account states for the magnetic-exchange
interaction, and the two last ones correspond to the Zeeman
effect. D, E, g|, and g apply for each ion. The application
of this Hamiltonian becomes very complicated because of
the large number of parameters involved. As the dependence
of the magnetic susceptibility on the rhombic splitting
parameter (E) is negligible, this term was discarded. In
addition, we considered that D, g|, and g are the same for
the two manganese sites in 2 and 3 and g| ) g (and also in
1, whose structure is most likely like that of 2). Under these
assumptions, the number of parameters is reduced to a
reasonable size, namely D, J, and g.
Taking into account that the size of local interacting spins
in 1-3 (S ) 2) is large enough to be considered as a classical
spin and that we are dealing with a uniform chain (3) and
quasi-quadratic layers (1 and 2), eqs 2 and 3, which were
derived by Fisher44 and Cure´ly45 for isotropic Heisenberg
systems, can be used to analyze their magnetic properties.
with
and
g1 ) g2
u1 ) u2
Thus, the magnetic behavior of 1-3, which is dictated by
the dominant D factor, is slightly perturbed by the weak
magnetic interactions observed in the very-low-temperature
region. Best-fit parameters through eqs 8 (1 and 2) and 7
(3) are: D ) -3.91(2) cm-1, J ) +0.081(1) cm-1, and g )
1.98(1) for 1, D ) -3.96(2) cm-1, J ) +0.072(1) cm-1,
and g ) 1.99(1) for 2 and D ) -3.95(2) cm-1, J )
-0.19(1) cm-1, and g ) 1.99(1) for 3. As seen in Figures
6-8, a satisfactory match is obtained between the magnetic
data and the theoretical curve in the whole temperature range
explored. We have used a negative D value in the fits because
it is more usual, but a similar fit is obtained when considering
a positive value for D.
Analysis of the Exchange Pathways in 2 and 3. To
substantiate the magnetic interactions between manganese-
Nâ2g2
3kT
1 + u
1 - u
øchain
)
S(S + 1)
(2)
(3)
(44) Fisher, M. E. Am. J. Phys. 1964, 32, 343.
(45) (a) Cure´ly, J. Europhys. Lett. 1995, 32, 529. (b) Cure´ly, J. Physica B
1998, 245, 263.
(46) Lloret, F.; Ruiz, R.; Julve, M.; Faus, J.; Journaux, Y.; Castro, I.;
Verdaguer, M. Chem. Mater. 1992, 4, 1150.
(g12 + g2 )W1 + 2g1g2W2
2
Nâ2
ø2Dsquare
)
S(S + 1)
2
2
3kT
2(1 - u1 )(1 - u2 )
1018 Inorganic Chemistry, Vol. 45, No. 3, 2006

Malonate-Containing Manganese(III) Complexes
2
Figure 10. Schematic drawing showing the orientation of the dz -type
magnetic orbitals in the dinuclear fragment of 3 (model Figure 5a).
fact, the manganese(III) ions in 3 (also in 2) exhibits
elongated octahedral environments with an idealized D4h
symmetry. Consequently, if one takes the elongation axis as
2
the z direction, one unpaired electron is placed in the dz
2
2
orbital and the dx -y orbital is non magnetic, given that this
last orbital has the highest energy. The relative orientation
of the two dz magnetic orbitals is represented in Figure 10.
2
Although an anti-syn coordination topology occurs in 3 with
the two metal ions and the carboxylate group being practi-
cally coplanar, the strict orthogonality is avoided because
of the values of the Mn-O-C angles (127.3(5) and
Figure 9. Structural models used in the DFT calculations concerning 3
(a) and 2 (b). Bond lengths and angles of the models are those of the
corresponding crystal structures.
137.8(5)°).14a One can see that the equatorial ring dz electron
2
(III) ions in 2 and 3 and to get an orbital picture of the
exchange pathways involved in them, we have performed
density functional theory-type (DFT) calculations on two
model fragments whose structural parameters were taken
from the respective crystal structures: a dinuclear unit of
the chain structure of 3 (Figure 9a) and a trinuclear
manganese(III) entity corresponding to the two edges of the
quasi-square units of the anionic layers of 2 (Figure 9b).
Let us start the analysis with 3 for the sake of simplicity.
This compound can be considered as a one-dimensional
system where two crystallographically independent manga-
nese(III) ions are connected in a regular way by a carboxylate
group of a malonate ligand that exhibits the anti-syn
bridging mode. A nonet A (2,2) and a broken-symmetry
singlet B (2,-2) spin configurations were calculated (A and
B being defined as (MS Mn1, MS Mn2)). From the energies of
these configurations and eq 9
2
density in a manganese atom and the axial dz in the other
manganese center are involved in the exchange pathway;
thus, a small overlap between the two magnetic orbitals
through the carboxylate-malonate bridge is predicted, and
a weak antiferromagnetic interaction is expected, as observed.
Indeed, the small magnitude of the magnetic interaction is
also related to the weak spin delocalization observed in the
atomic spin densities (3.98 electron units for the manganese-
(III) ion).
The hydrogen bonds between the mononuclear [MnIII(mal)2-
(H2O)2]- units in 2 have to be responsible for the ferromag-
netic coupling observed for this compound. Recently,
Desplanches et al. have shown that hydrogen bonds can
mediate weak magnetic interactions in metal complexes.47
As described in the structural part, the [MnIII(mal)2(H2O)2]-
units in 2 are linked by hydrogen bonds to form an anionic
quasi-quadratic layer of manganese(III) ions (Figure 2) with
two intralayer magnetic interactions noted J1 (between
Mn(1) and Mn(2)) and J2 (between Mn(1) and Mn(2e)).
These layers are well separated from each other by the bulky
tetraphenylarsonium cations (Figure 4). The only intralayer
exchange pathway occurring in 2 involves the axially
coordinated water molecule of one manganese unit and a
carboxylate-malonate from the neighboring unit. Two of
these pathways connect each pair of manganese(III) ions.
Small structural differences in them lead to an alternating
character of the network. Thus, in the model used for 2, three
EB - EA ) -10J
(9)
we have evaluated the exchange coupling constant between
the manganese(III) ions in 3, which is J ) -4.7 cm-1. This
value has the same sign and it is not far from that obtained
for 3 by fit (J ) -0.19 cm-1) and also for the family of the
chain compounds of formula (cat)2[MnIII(sal)2(CH3OH)2]-
MnIII(sal)2] with sal ) salicylate and cat ) Na+ (J ) -0.46
cm-1), K+ (J ) -0.46 cm-1), and NH4+ (J ) -1.40 cm-1),14b
where the same type of carboxylate-malonate bridge occurs.
An inspection of the magnetic orbitals involved accounts for
the antiferromagnetic nature of the magnetic coupling. In
(47) Desplanches, E.; Ruiz, E.; Rodr´ıguez-Fortea, A.; Alvarez, S. J. Am.
Chem. Soc. 2002, 124, 5197.
Inorganic Chemistry, Vol. 45, No. 3, 2006 1019

Delgado et al.
Figure 11. One can see there that the spin density in the
2
ring of the dz orbital leads to a delocalization via a
σ-exchange pathway of carboxylate (blue), whereas the axial
spin density in the same orbital involves a delocalization via
a π-exchange pathway (red). This situation corresponds to
a case of orthogonality between the interacting magnetic
orbitals, and consequently, a ferromagnetic coupling is
predicted, as observed.
Conclusions
A new malonate-containing manganse(III) building block
of formula AsPh4[Mn(mal)2(H2O)2] (2) has been prepared
and magneto-structurally characterized. Hydrogen bonds
appear as effective mediators of weak but significant
ferromagnetic interactions between the manganese(III) ions,
which were substantiated by DFT-type calculations. A weak
intrachain antiferromagnetic coupling through the carboxy-
late-malonate bridge occurs in the related compound of
formula K2[Mn(mal)2(MeOH)2][Mn(mal)2] (3), whose struc-
ture was the subject of a previous report. The hydrophobic
Figure 11. (Top) Schematic drawing of a Mn(OCO‚‚‚Ow)2Mn couple in
2. (Bottom) Orbital picture of the exchange pathway in 2.
metal ions and two exchange coupling constants have been
considered (Figure 9b). Using eqs 10 and 11
ED - EC ) -10J1
EF - EC ) -10J2
(10)
(11)
+
and hydrophilic characters of the AsPh4 and K+ cations
seem to be at the origin of the layered and one-dimensional
structures of 2 and 3, respectively.
applied to the energy obtained for the configurations C
(2,2,2), D (-2,2,2), and F (2,2,-2) (C, D, and F being
defined as (MS Mn1, MS Mn2, MS Mn3, respectively)), we have
obtained the values +0.04 and +0.02 cm-1 for J1 and J2,
respectively. Thus, weak ferromagnetic interactions between
the metal ions are obtained by DFT calculations whose values
are close to the mean value obtained by fit. A close inspection
of the dinuclear fragment Mn-(OCO‚‚‚Ow)2-Mn of 2,
depicted on the top of Figure 11, shows that the two Mn-
OCO‚‚‚Ow units are in parallel planes, and the axial Mn-
Ow bonds are quasi-perpendicular to these planes. The
corresponding orbital picture is shown in the bottom of
Acknowledgment. This work was supported by the
Ministerio Espan˜ol de Educacio´n y Ciencia, (Projects
CTQ2004-03633 and MAT2004-03112). F.S.D. acknowl-
edges the Gobierno Auto´nomo de Canarias for a predoctoral
fellowship.
Supporting Information Available: Table S1. Weak hydrogen
bonds (Å) involving C-aromatic and oxygen atoms for 1.
This material is available free of charge via the Internet at
http://pubs.acs.org.
IC0508526
1020 Inorganic Chemistry, Vol. 45, No. 3, 2006