[Cr(phen)(ox)2]-: A versatile bis-oxalato building block for the design of heteropolymetallic systems

Article abstract of DOI:10.1039/b002246m

The new complexes of formula AsPh₄[Cr(phen)(ox)₂] · H₂O (1), [NaCr(phen)(ox)₂(H₂O)] · 2H₂O (2) and {[Cr(phen)(ox)₂]₂[Mn₂(bpy)₂(H₂O)₂(ox)]} · 6H₂O (3) (AsPh₄ = tetraphenylarsonium cation; phen = 1,10- phenanthroline; ox = oxalate dianion; bpy = 2,2'-bipyridine) have been prepared and characterized by single-crystal X-ray diffraction. The structure of 1 consists of discrete [Cr(phen)(ox)₂]^- anions, tetraphenylarsonium cations and uncoordinated water molecules. The chromium environment in 1 is distorted octahedral with Cr-O bond distances between 1.959(3) and 1.947(3) A? and Cr-N bonds of 2.083(4) and 2.072(4) A?. The angles subtended at the chromium atom by the two oxalates are 83.6(2) and 83.3(1)°whereas the N-Cr-N angle is 79.9(2)°. The [Cr(phen)(ox)₂]- unit of 1 is also present in 2 and 3 but it accomplishes different coordination functions, acting as a bridging (2) or terminal (3) ligand. 2 has a layered structure made up of oxalato-bridged bimetallic Cr(III)Na(I) helical chains that are interconnected through centrosymmetric Na₂O₂ units. The two oxalates of [Cr(phen)(ox)₂]^- in 2 are bis-chelating within the bimetallic chain but one of them is in addition monodentate towards a sodium atom of a neighbouring chain, yielding a sheetlike structure. The sodium atom in 2 has a distorted octahedral geometry with five Na-O(ox) bonds ranging from 2.453(5) to 2.319(4) A? and the sixth position being occupied by an aqua ligand with Na-O(w) = 2.384(6) A?. The intralayer chromium-sodium and sodium-sodium separations through bridging oxalate in 2 are 5.560(4) and 3.643(8) A?, respectively. The structure of 3 consists of neutral tetranuclear Cr₂(III)Mn₂(II) units in which two terminal [Cr(phen)(ox)₂]- entities act as monodentate ligands towards a central oxalato-bridged manganese(II) dimer. Each manganese atom is six- coordinated as MnN₂O₄: two nitrogen atoms of a chelating bpy, one aqua ligand and three oxalate oxygens build a distorted octahedron around the manganese atom. The Mn-O(ox) and Mn-N(bpy) bond lengths vary in the ranges 2.219(12)-2.160(13) and 2.33(2)-2.14(2) A?, respectively. The intramolecular chromium-manganese separation [5.507(5) and 5.502(5) A? for Cr(2)···Mn(2) and Cr(1)···Mn(1)] is somewhat shorter that the manganese-manganese one [5.703(2)A?]. The magnetic properties of 1-3 have been investigated in the temperature range 1.9-300 K. Very weak antiferromagnetic interactions between the chromium centers are observed in 1 and 2 in agreement with their crystal structures. In the case of 3, significant intramolecular antiferromagnetic interactions between the adjacent chromium(m) and manganese(n) ions (j = -1.1 cm^-1, through the chelating/monodentate oxalato) and between the two manganese(II)ions (J = -2.2 cm^-1, through the bis-chelating oxalato) occur, the Hamiltonian being defined as H = -JS(Mn1) · (Mn2) -j[S(Cr1) · S(Mn1) + S(Cr2) · S(Mn2)].

Full text of DOI:10.1039/b002246m

View Article Online / Journal Homepage / Table of Contents for this issue
[Cr(phen)(ox) ]—: a versatile bis-oxalato building block for the
2
design of heteropolymetallic systems. Crystal structures and
magnetic properties of AsPh [Cr(phen)(ox) ] Æ H O,
4
2
2
[NaCr(phen)(ox) (H O)] Æ 2H O and
2 2
2
2 2 2
{ [Cr(phen)(ox) ] [Mn (bpy) (H O) (ox)]} Æ 6H O¤
2 2
2
2
Gabriela Marinescu,a Marius Andruh,*a Rodrigue Lescouezec,b Mari Carmen Munoz,c
Juan Cano,bd Francesc Lloretb and Miguel Julve*b
a Inorganic Chemistry L aboratory, Faculty of Chemistry, University of Bucharest, Str. Drumbrava
Rosie nr. 23, 70254 Bucharest, Romania. E-mail: Marius.Andruh=dnt.ro
b Departament de Qu•mica Inorganica, Facultat de Qu•mica de la Universitat de V alencia,
Dr. Moliner 50, 46100 Burjassot (V alencia), Spain. E-mail: Miguel.Julve=uv.es
c Departamento de F•sica Aplicada, Universidad Politecnica de V alencia, Camino de V era s/n,
46071 V alencia, Spain
d L aboratoire de Chimie Inorganique (CNRS UMR 8653), Universite de Paris-Sud, 91405 Orsay,
France
Received (in Montpellier, France) 16th March 2000, Accepted 26th April 2000
Published on the Web 21st June 2000
The new complexes of formula AsPh [Cr(phen)(ox) ] É H O (1), [NaCr(phen)(ox) (H O)] É 2H O (2) and
4
2
2
2
2
2
M[Cr(phen)(ox) ] [Mn (bpy) (H O) (ox)]N É 6H O (3) (AsPh \ tetraphenylarsonium cation; phen \ 1,10-
2 2
2
2
2
2
2
4
phenanthroline; ox \ oxalate dianion; bpy \ 2,2@-bipyridine) have been prepared and characterized by
single-crystal X-ray di†raction. The structure of 1 consists of discrete [Cr(phen)(ox) ]~ anions, tetraphenylarsonium
2
cations and uncoordinated water molecules. The chromium environment in 1 is distorted octahedral with CrÈO
bond distances between 1.959(3) and 1.947(3) A and CrÈN bonds of 2.083(4) and 2.072(4) A. The angles subtended
at the chromium atom by the two oxalates are 83.6(2) and 83.3(1)¡ whereas the NÈCrÈN angle is 79.9(2)¡. The
[Cr(phen)(ox) ]~ unit of 1 is also present in 2 and 3 but it accomplishes di†erent coordination functions, acting as a
2
bridging (2) or terminal (3) ligand. 2 has a layered structure made up of oxalato-bridged bimetallic CrIIIÈNaI helical
chains that are interconnected through centrosymmetric Na O units. The two oxalates of [Cr(phen)(ox) ]~ in 2
2
2
2
are bis-chelating within the bimetallic chain but one of them is in addition monodentate towards a sodium atom of
a neighbouring chain, yielding a sheetlike structure. The sodium atom in 2 has a distorted octahedral geometry
with Ðve NaÈO(ox) bonds ranging from 2.453(5) to 2.319(4) A and the sixth position being occupied by an aqua
ligand with NaÈO(w) \ 2.384(6) A. The intralayer chromiumÈsodium and sodiumÈsodium separations through
bridging oxalate in 2 are 5.560(4) and 3.643(8) A, respectively. The structure of 3 consists of neutral tetranuclear
CrIIIMnII units in which two terminal [Cr(phen)(ox) ]~ entities act as monodentate ligands towards a central
2
2
2
oxalato-bridged manganese(II) dimer. Each manganese atom is six-coordinated as MnN O : two nitrogen atoms
2
4
of a chelating bpy, one aqua ligand and three oxalate oxygens build a distorted octahedron around the manganese
atom. The MnÈO(ox) and MnÈN(bpy) bond lengths vary in the ranges 2.219(12)È2.160(13) and 2.33(2)È2.14(2) A,
respectively. The intramolecular chromiumÈmanganese separation [5.507(5) and 5.502(5) A for Cr(2)É É ÉMn(2) and
Cr(1)É É ÉMn(1)] is somewhat shorter that the manganeseÈmanganese one [5.703(2) A]. The magnetic properties of
1È3 have been investigated in the temperature range 1.9È300 K. Very weak antiferromagnetic interactions between
the chromium centers are observed in 1 and 2 in agreement with their crystal structures. In the case of 3, signiÐcant
intramolecular antiferromagnetic interactions between the adjacent chromium(III) and manganese(II) ions ( j \ [1.1
cm~1, through the chelating/monodentate oxalato) and between the two manganese(II) ions (J \ [2.2 cm~1,
through the bis-chelating oxalato) occur, the Hamiltonian being deÐned as H \ [JS
] S É S ].
É S
[ j[S É S
Mn1 Mn2
Cr1 Mn1
Cr2 Mn2
The use of the tris-chelated species [M(ox) ]3~ (M \ trivalent
trolled nuclearity and dimensionality.5h19 A very interesting
observation concerning this type of compound is the forma-
tion of two- (2D) and three-dimensional (3D) structures
depending on the templating counterion. For instance,
3
metal ion; ox \ oxalate dianion) as ligands towards transition
metal ions is well documented in chemistry.1h4 Its negative
charge and the ability of the oxalato to adopt a bis-chelating
coordination mode make it a suitable starting material to
prepare oxalato-bridged heterometallic compounds with con-
honeycomb-layered structures of formula [MIIMIII(ox) ]~ are
3
obtained when the cation is [XR ]` (X \ N, P; R \ phenyl,
4
¤ Three of the authors of the present work (M. Andruh, F. Lloret and M. Julve) were postdoctoral students in Prof. KahnÏs laboratory. We are
deeply indebted to him because he was not only our scientiÐc father in molecular magnetism but he transmitted his enthusiasm, savoir faire and
creativity to us. Unfortunately he passed away recently, and the present work is just one of our modest contributions to his living memory.
DOI: 10.1039/b002246m
New J. Chem., 2000, 24, 527È536
527
This journal is ( The Royal Society of Chemistry and the Centre National de la Recherche ScientiÐque 2000

View Article Online
n-propyl, n-butyl, n-pentyl) or ferrocenium. However, chiral
3D networks of formula [MII(ox) ]2~, [MIMIII(ox) ]2~ and
oxalate and tetraphenylarsonium chloride monohydrate were
purchased from commercial sources and used as received. Ele-
mental analysis (C, H, N) were carried out by the Microana-
lytical Service of the Universidad Autonoma de Madrid. The
Na : Cr (2) and Mn : Cr (3) ratios were determined by elec-
tron microscopy at the Servicio Interdepartamental de
Investigacion of the University of Valencia.
2
3
3
[MIIMIII(ox) ]~ result when the cation is the tris-chelated
3
[M(bpy) ]m` (bpy \ 2,2@-bipyridine; m \ 2, 3). These supra-
3
molecular systems are very interesting not only from a struc-
tural point of view, but because of the photochemical,
photophysical and magnetic properties that they exhibit,
arising from the interaction among their constituents.1h4,20,21
In the case of M \ CrIII, the inert character of the
tris(oxalato)chromate(III) species makes the preparation of the
desired polymetallic compounds easier.5,6h8,15h17,19,20
Preparation of AsPh [Cr(phen)(ox) ] Æ H O (1). An aqueous
4
2
2
solution (20 cm3) containing chromium(III) chloride (1 mmol)
and phen (1 mmol) was reÑuxed under continuous stirring for
half an hour. Sodium oxalate (2 mmol), dissolved in a
minimum amount of hot water (10 cm3), was added to the
resulting deep green solution and the color turned deep violet
under gentle warming and stirring for 20 min. A small amount
of a deep violet solid that appeared was removed and dis-
carded. The addition of a concentrated aqueous solution of
tetraphenylarsonium chloride (1 mmol, 10 cm3) caused the
crystallization of a Ðrst crop of crystals of 1 as violet parallel-
epipeds on standing at room temperature. Yield ca. 35%.
Apart from the homoleptic [Cr(ox) ]3~ species, three het-
3
eroleptic and mononuclear oxalato-containing chromium(III)
complexes of formula [Cr(salen)(ox)]~22,23 (salen2~ \ N,N@-
ethylenebis(salicylideneiminate), [Cr(bpy)(ox) ]~24h27 and
2
[Cr(bpm)(ox) ]~28,29 (bpm \ 2,2@-bipyrimidine) have been
2
used so far to prepare heterometallic compounds. Oxalato-
bridged heterobinuclear complexes of the type CrIIIÈoxÈMII
(M \ Cu, Ni, Co, Fe, Mn) were prepared by reaction of the
[Cr(salen)(ox)]~ with the divalent cation previously bound to
a tri- or terdentate blocking ligand.23 As far as the second
Anal. calcd for C
3.46. Found: C, 59.42; H, 3.45; N, 3.56%.
H
AsCrN O (1): C, 59.36; H, 3.71; N,
40 30
2 9
brick is concerned, [Cr(bpy)(ox) ]~, we have recently illus-
2
trated its exceptional versatility in designing heterometallic
complexes.24h27 The self-assembly of this mononuclear
unit with mono- or dipositive cations led to two series of
heteropolynuclear complexes with di†erent stoichio-
metries: [MICr(bpy)(ox) (H O) ] (M \ Na, Ag)24,25 and
Preparation of [NaCr(phen)(ox) (H O)] Æ 2H O (2). Sodium
2
2
2
perchlorate (0.1 mmol), dissolved in a minimum amount of
water, was added to an aqueous solution of 1 (0.1 mmol, 20
cm3). The white precipitate of tetraphenylarsonium perchlor-
ate was Ðltered o† and a saturated aqueous solution of NaCl
was added to the violet mother liquor. Red prisms of 2 were
grown on standing at room temperature. Yield ca. 65%. Anal.
2
2
x
[MIICr (bpy) (ox) (H O) ] (M \ Ba, Mn, Co, Ni, Cu,
2
2
4
2
y
Zn).25h27 Within each series, completely di†erent structures
are obtained according to the coordination algorithm of the
assembling cation. The sodium derivative exhibits a two-
dimensional framework with hexa-coordinated sodium
atoms,24 while in the case of silver(I) the structure consists of
discrete tetranuclear cycles formed by two chromium and two
penta-coordinated silver atoms bridged by the oxalato
groups.25 Within the second series, the barium derivative is a
calcd for C
Found: C, 39.53; H, 2.80; N, 5.72%.
H
CrN NaO (2): C, 39.61; H, 2.89; N, 5.77.
16 14
2
11
Preparation of { [Cr(phen)(ox) ] [Mn (bpy) (H O) (ox)]} Æ
2 2
2
2
2
2
6H O (3). To an aqueous solution of 2 (1 mmol, 20 cm3) were
2
successively added an aqueous solution of manganese(II) chlo-
sca†olding-like material with
a 3D structure and ten-
ride (1 mmol, 10 cm3), an ethanolic solution of 2,2@-bipyridine
(1 mmol, 10 cm3) and an aqueous solution of sodium oxalate
(0.5 mmol, 10 cm3). The resulting mixture was Ðltered and left
undisturbed. Slow evaporation at room temperature after two
weeks a†orded a Ðrst crop of chunky red purple crystals of 3.
coordinated barium atoms,26 the manganese derivative
exhibits a new type of heterobimetallic chain with octa-
coordinated manganese atoms,26 whereas the structures of the
MCoCr N26 and MCuCr N25 complexes consist of discrete,
2
2
linear MCrIIIMIICrIIIN trinuclear species with hexa-coordinated
Yield ca. 30%. Anal. calcd for C
44.11; H, 3.26; N, 7.62. Found: C, 44.03; H, 3.10; N, 7.53.%
H
CrMnN O (3): C,
27 24
4 14
MII ions. Finally, the hybrid building block [Cr(bpm)(ox) ]~,
which can coordinate to the metal ions through both bpm and
2
oxalate, was prepared and structurally characterized.28 The
crystallographic investigation of its sodium28 and potassium29
derivatives revealed the occurrence of two di†erent sheetlike
IR characterisation
The out-of-plane bending vibrations of the phenyl rings of the
tetraphenylarsonium cation appear as two sharp and medium
intensity peaks at 760 and 750 cm~1 in the IR spectrum of 1.
In the 3500 cm~1 region, sharp and medium intensity peaks
occur in 1 (ca. 3495 cm~1 with a shoulder at 3550 cm~1),
whereas strong and broad absorptions centered at 3440 and
3450 cm~1 are observed for 2 and 3, respectively. These high
frequency features are in agreement with the presence of water
molecules of crystallization in the former complex and both
coordinated and uncoordinated water molecules linked by
hydrogen bonds in the two latter ones.30 Finally, slight but
signiÐcant di†erences are observed in the l (CO) stretching
region of the IR spectra of 1È3: three strong intensity peaks at
1715, 1700 and 1679 cm~1 (1), two strong intensity doublets at
1710 and 1675 cm~1 (2) and three strong peaks at 1710, 1680
and 1639 cm~1 (3). The di†erent coordination modes of
oxalate that occur in 1È3 (see structural discussion) account
for these spectral di†erences in the carbonyl vibrations.
polymers of formula [NaCr(bpm)(ox) ] É 5H O
and
2
2
[K(H O)Cr(bpm)(ox) ].
2
2
The richness and variety of the structures reported so far
induced us to carry out a systematic study of the complexing
ability of the bis-oxalato-chromium(III) building block. In this
context, we have investigated the coordinating properties of
the mononuclear [Cr(phen)(ox) ]~ (phen \ 1,10-phenanthrol-
2
ine) species. Our Ðrst results concerning the preparation, the
structural and magnetic characterization of the complexes
of formula AsPh [Cr(phen)(ox) ] É H O (1) (AsPh \
4
2
2
4
tetraphenylarsonium cation), [NaCr(phen)(ox) (H O)] É 2H O
2
2
2
as
(2) and M[Cr(phen)(ox) ] [Mn (bpy) (H O) (ox)]N É 6H O (3)
are presented here. The structures of the heterobimetallic com-
2 2
2
2
2
2
2
pounds 2 (a sheetlike polymer) and 3 (a tetranuclear complex)
illustrate the versatility as a ligand of the [Cr(phen)(ox) ]~
2
mononuclear complex, which is present in 1.
Experimental
Physical techniques
Materials
IR spectra (4000È400 cm~1) were recorded on a Bruker IF
S55 spectrophotometer with samples prepared as KBr pellets.
Variable-temperature (1.9È290 K) magnetic susceptibilty mea-
1,10-Phenanthroline, 2,2@-bipyridine, chromium(III) chloride
hexahydrate, manganese(II) chloride tetrahydrate, sodium
528
New J. Chem., 2000, 24, 527È536

View Article Online
surements on polycrystalline samples were carried out with a
Quantum Design SQUID operating at 0.5 T in the high
temperature range (20È290 K) and at 250 G at T \ 20 K in
order to avoid saturation phenomena. Diamagnetic correc-
tions of the constituent atoms were estimated from PascalÏs
constants31 as [388 ] 10~6 (1), [235 ] 10~6 (2) and
[745 ] 10~6 (3) cm3 mol~1.
Selected bond lengths and angles are gathered in Tables 2È4
for 1È3, respectively.
CCDC reference number 440/186.
Results and discussion
Description of the structures
X-Ray data collection and structure reÐnement
Crystals of dimensions 0.15 ] 0.10 ] 0.10 (1), 0.10 ] 0.15
] 0.10 (2) and 0.15 ] 0.20 ] 0.10 mm (3) were mounted on an
Enraf-Nonius CAD-4 di†ractometer and used for data collec-
tion. The unit cell parameters were determined from least-
squares reÐnement on the setting angles from 25 centered
reÑections in the range 12 \ h \ 20¡. A summary of the crys-
tallographic data and structure reÐnement is given in Table 1.
No signiÐcant Ñuctuations were observed in the intensities of
three standard reÑections monitored periodically thoughout
data collection. Intensity data were corrected for Lorentz
polarization and absorption corrections.
The structures of 1È3 were solved by standard Patterson
methods and reÐned by the full-matrix least-squares method
on F2. All our attempts to solve the structure of 3 in the P1
space group were unsuccessful. The computations were per-
formed with SHELX 86 and SHELXL 93.32 All non-hydrogen
atoms were reÐned anisotropically. The hydrogen atoms of
the water molecules of 1È3 were neither found nor calculated.
The hydrogen atoms of the phen (1È3) and bpy (3) ligands
were set in calculated positions and reÐned as riding atoms
with a common Ðxed isotropic thermal parameter.
AsPh [Cr(phen)(ox) ] Æ H O (1). The structure of complex 1
4
2
2
consists of tris-chelated [Cr(phen)(ox) ]~ anions, AsPh `
2
4
cations and water molecules of crystallization (Fig. 1), which
are linked by electrostatic forces and van der Waals inter-
actions.
Each chromium atom is coordinated by two phen nitrogen
and four oxalate oxygen atoms, adopting a distorted octa-
hedral geometry. The short bites of bidentate phen and ox
ligands [79.90(14), 85.58(13) and 83.38(13)¡ for N(1)ÈCr(1)È
N(2), O(1)ÈCr(1)ÈO(2) and O(3)ÈCr(1)ÈO(4), respectively] are
the main factors accounting for the distortion of the metal
environment from the ideal octahedron. The four CrÈO(ox)
bond lengths are very similar [values vary in the range
1.947(3)È1.949(3) A] and they compare well with the average
value reported in the parent mononuclear [Cr(bpm)(ox) ]~
2
[1.945(6) A],28 [Cr(bpy)(ox) ]~ [1.953(2) A]24 and
2
[Cr(hm)(ox) ]~ [1.974(2) A]35 (hm \ histamine) units. The
2
CrÈN(phen) bond distances [2.082(3) and 2.073(4) A] are
somewhat longer than the CrÈO(ox) ones but they agree with
those reported for other phen-containing chromium(III) com-
plexes.36,37 The phen and ox ligands do not exhibit signiÐcant
deviations from planarity. The dihedral angle between the two
oxalate planes is 89.57(9)¡ whereas those of phen with the two
oxalate planes are 89.67(9) and 88.36(9)¡. Bond lengths and
angles within the phen ligand are in agreement with those
reported for the free phen molecule.38 The carbonÈcarbon
bond distances in the ox ligand are as expected for single CÈC
bonds [1.578(7) and 1.559(7) A for C(13)ÈC(14) and C(15)È
The Ðnal full-matrix least-squares reÐnement on F2, mini-
mizing the function &w[( o F o )2 [ ( o F o )2)]2 with w \
o
c
1/[r2(F2) ] (mP)2 ] nP] and P \ (F2 ] 2F2)/3 [m \ 0.0567
o
o
c
(1), 0.1075 (2) and 0.1006 (3); n \ 0.3034 (1), 3.4949 (2) and
1.9006 (3)], converged at the values of R and R listed in
w
Table 1. The values of f, f @ and f A were taken from ref. 33. The
molecular plots were drawn with the ORTEP program.34
Fig. 1 Perspective view of compound 1 along with the atom numbering. The thermal ellipsoids are drawn at the 30% probability level and the
hydrogen atoms have been omitted for clarity.
New J. Chem., 2000, 24, 527È536
529

View Article Online
Table
1
Crystallographic
data
for
AsPh [Cr(phen)(ox) ] É H O
(1),
[NaCr(phen)(ox) (H O)] É 2H O
(2)
and
4
2
2
2
2
2
M[Cr(phen)(ox) ] [Mn (bpy) (H O) (ox)]N É 6H O (3)
2 2
2
2
2
2
2
1
2
3
Formula
FW
Crystal system
C
807.56
H
AsCrN O
C
970.56
Monoclinic
P2 /n(no. 14)
9.092(2)
13.828(2)
15.882(2)
90.0
92.977(14)
90.0
1994.0(5)
4
293(2)
6.59
H
CrN NaO
C
744.45
H
CrMnN O
40 30
2
9
16 14
2
11
27 24
4
14
Triclinic
P1(no. 2)
9.503(2)
14.264(4)
14.642(3)
103.34(2)
99.51(2)
106.43(2)
1794.9(7)
2
Triclinic
P1(no. 1)
9.014(2)
10.0404(11)
18.445(2)
79.343(10)
77.989(13)
86.773(13)
1604.4(4)
2
Space group
1
a/A
b/A
c/A
a/¡
b/¡
c/¡
U/A
Ž
3
Z
T /K
293(2)
12.94
4649
293(2)
8.07
4498
k(Mo-Ka)/cm~1
No. measd. ind. reÑ.
3504
No. obsd. reÑ. [I P 2p(I)]
4627
0.0419
0.0941
3437
0.0638
0.1728
4455
0.0506
0.1301
Ra
R b
w
a R \ &(pF o [ o F p)/& o F o. b R \ [&w(o F o2 [ o F o2)2]/&w o F o2]1@2.
o
c
o
w
o
c
c
Table 2 Selected bond lengths (A) and angles (deg)a for compound 1
Table 4 Selected bond lengths (A) and angles (deg)a for compound 3
Cr(1)ÈN(1)
Cr(1)ÈO(1)
Cr(1)ÈO(3)
2.073(4)
1.956(3)
1.959(3)
Cr(1)ÈN(2)
Cr(1)ÈO(2)
Cr(1)ÈO(4)
2.082(3)
1.956(3)
1.947(3)
Chromium environment
Cr(1)ÈN(7)
Cr(1)ÈN(8)
Cr(1)ÈO(16)
Cr(1)ÈO(17)
Cr(1)ÈO(19)
Cr(1)ÈO(21)
2.05(2)
2.07(2)
1.969(12) Cr(2)ÈO(8)
2.029(13)
1.92(2)
1.97(2)
Cr(2)ÈN(5)
Cr(2)ÈN(6)
2.06(2)
2.10(2)
1.957(13)
1.923(14)
1.939(14)
1.97(2)
N(1)ÈCr(1)ÈO(1)
N(1)ÈCr(1)ÈO(3)
N(1)ÈCr(1)ÈO(4)
N(2)ÈCr(1)ÈO(2)
N(2)ÈCr(1)ÈO(4)
O(1)ÈCr(1)ÈO(3)
O(2)ÈCr(1)ÈO(3)
O(3)ÈCr(1)ÈO(4)
91.13(13)
89.34(13)
169.86(13)
170.44(14)
93.22(13)
178.38(13)
94.84(13)
83.38(13)
N(1)ÈCr(1)ÈO(2)
N(1)ÈCr(1)ÈN(2)
N(2)ÈCr(1)ÈO(1)
N(2)ÈCr(1)ÈO(3)
O(1)ÈCr(1)ÈO(2)
O(1)ÈCr(1)ÈO(4)
O(2)ÈCr(1)ÈO(4)
93.22(13)
79.90(14)
89.89(13)
91.73(13)
83.58(13)
96.34(13)
94.42(13)
Cr(2)ÈO(9)
Cr(2)ÈO(11)
Cr(2)ÈO(13)
N(7)ÈCr(1)ÈO(17)
N(7)ÈCr(1)ÈN(8)
N(7)ÈCr(1)ÈO(19)
N(7)ÈCr(1)ÈO(16)
N(7)ÈCr(1)ÈO(21)
N(8)ÈCr(1)ÈO(17)
N(8)ÈCr(1)ÈO(16)
N(8)ÈCr(1)ÈO(21)
N(8)ÈCr(1)ÈO(19)
O(16)ÈCr(1)ÈO(19)
O(16)ÈCr(1)ÈO(17)
O(16)ÈCr(1)ÈO(21)
O(19)ÈCr(1)ÈO(17)
O(19)ÈCr(1)ÈO(21)
85.9(6)
80.7(7)
173.2(7)
92.8(6)
95.1(6)
92.4(6)
171.4(6)
92.4(6)
92.9(6)
93.8(6)
81.9(6)
93.8(6)
93.0(6)
82.9(6)
N(5)ÈCr(2)ÈO(11)
N(5)ÈCr(2)ÈN(6)
N(5)ÈCr(2)ÈO(8)
N(5)ÈCr(2)ÈO(13)
N(5)ÈCr(2)ÈO(9)
N(6)ÈCr(2)ÈO(11)
N(6)ÈCr(2)ÈO(13)
N(6)ÈCr(2)ÈO(9)
N(6)ÈCr(2)ÈO(8)
O(8)ÈCr(2)ÈO(13)
O(8)ÈCr(2)ÈO(11)
O(8)ÈCr(2)ÈO(9)
O(13)ÈCr(2)ÈO(11)
O(13)ÈCr(2)ÈO(9)
O(9)ÈCr(2)ÈO(11)
90.7(6)
80.0(7)
175.5(7)
93.2(6)
94.7(6)
89.9(7)
171.3(13)
94.5(6)
96.3(6)
90.7(7)
91.7(6)
83.1(6)
84.7(7)
91.5(6)
173.6(6)
a Estimated standard deviations in the last signiÐcant digits are given
in parentheses.
Table 3 Selected bond lengths (A) and angles (deg)a,b for compound
2
Chromium environment
Cr(1)ÈN(1)
Cr(1)ÈO(1)
Cr(1)ÈO(3)
2.077(4) Cr(1)ÈN(2)
1.954(3) Cr(1)ÈO(2)
1.955(3) Cr(1)ÈO(4)
2.068(4)
1.956(3)
1.949(3)
O(17)ÈCr(1)ÈO(21) 173.8(6)
Manganese environment
N(1)ÈCr(1)ÈO(1)
N(1)ÈCr(1)ÈO(4)
N(1)ÈCr(1)ÈO(2)
N(2)ÈCr(1)ÈO(3)
N(2)ÈCr(1)ÈO(2)
O(1)ÈCr(1)ÈO(4)
O(3)ÈCr(1)ÈO(4)
O(4)ÈCr(1)ÈO(2)
92.90(14) N(1)ÈCr(1)ÈO(3)
91.7(2)
79.88(14)
91.8(2)
93.60(14)
92.21(14)
82.81(13)
94.9(2)
91.9(2)
N(1)ÈCr(1)ÈN(2)
Mn(1)ÈN(1)
Mn(1)ÈN(2)
Mn(1)ÈO(1)
Mn(1)ÈO(2)
Mn(1)ÈO(5)
Mn(1)ÈO(15)
2.14(2)
2.20(2)
Mn(2)ÈN(3)
Mn(2)ÈN(4)
2.238(14)
2.33(2)
2.19(2)
2.210(14)
2.17(2)
2.211(13)
172.26(14) N(2)ÈCr(1)ÈO(1)
170.9(2)
93.8(2)
173.4(2)
83.06(14) O(3)ÈCr(1)ÈO(2)
92.9(2)
N(2)ÈCr(1)ÈO(4)
O(1)ÈCr(1)ÈO(3)
O(1)ÈCr(1)ÈO(2)
2.169(14) Mn(2)ÈO(3)
2.219(12) Mn(2)ÈO(4)
2.21(2)
Mn(2)ÈO(6)
2.160(13) Mn(2)ÈO(7)
N(1)ÈMn(1)ÈN(2)
N(1)ÈMn(1)ÈO(5)
N(1)ÈMn(1)ÈO(1)
N(1)ÈMn(1)ÈO(2)
N(1)ÈMn(1)ÈO(15)
N(2)ÈMn(1)ÈO(5)
N(2)ÈMn(1)ÈO(1)
N(2)ÈMn(1)ÈO(2)
N(2)ÈMn(1)ÈO(15)
O(5)ÈMn(1)ÈO(1)
O(5)ÈMn(1)ÈO(2)
O(5)ÈMn(1)ÈO(15)
O(1)ÈMn(1)ÈO(2)
O(1)ÈMn(1)ÈO(15)
73.6(6)
168.4(7)
95.1(7)
94.8(6)
97.0(6)
95.2(6)
165.8(6)
97.9(5)
98.0(5)
96.5(7)
89.9(6)
81.1(6)
74.0(5)
91.9(5)
N(3)ÈMn(1)ÈN(4)
73.8(6)
165.0(6)
96.3(6)
94.5(5)
100.1(5)
93.8(6)
169.6(6)
94.2(5)
95.5(5)
96.4(6)
77.6(5)
89.4(5)
89.9(5)
82.7(5)
164.2(5)
Sodium environment
N(3)ÈMn(2)ÈO(4)
N(3)ÈMn(2)ÈO(6)
N(3)ÈMn(2)ÈO(3)
N(3)ÈMn(2)ÈO(7)
N(4)ÈMn(2)ÈO(4)
N(4)ÈMn(2)ÈO(6)
N(4)ÈMn(2)ÈO(3)
N(4)ÈMn(2)ÈO(7)
O(4)ÈMn(2)ÈO(6)
O(4)ÈMn(2)ÈO(3)
O(4)ÈMn(2)ÈO(7)
O(6)ÈMn(2)ÈO(3)
O(6)ÈMn(2)ÈO(7)
O(3)ÈMn(2)ÈO(7)
Na(1)ÈO(5a)
Na(1)ÈO(6a)
Na(1)ÈO(8)
2.319(4) Na(1)ÈO(5b)
2.418(5) Na(1)ÈO(7)
2.453(5) Na(1)ÈO(9)
2.445(4)
2.403(4)
2.384(6)
O(5a)ÈNa(1)ÈO(5b)
O(5a)ÈNa(1)ÈO(8)
O(5a)ÈNa(1)ÈO(7)
O(6a)ÈNa(1)ÈO(8)
80.22(14) O(5a)ÈNa(1)ÈO(6a)
68.94(13)
117.2(3)
81.9(2)
84.4(2)
139.6(2)
91.2(2)
O(5a)ÈNa(1)ÈO(9)
O(6a)ÈNa(1)ÈO(7)
O(6a)ÈNa(1)ÈO(9)
O(7)ÈNa(1)ÈO(8)
O(7)ÈNa(1)ÈO(5b)
O(8)ÈNa(1)ÈO(9)
Na(1)ÈO(5b)ÈNa(1b)
96.0(3)
O(6a)ÈNa(1)ÈO(5b) 149.1(2)
68.36(14)
126.0(2)
158.3(3)
99.78(14)
O(7)ÈNa(1)ÈO(9)
O(8)ÈNa(1)ÈO(5b)
O(9)ÈNa(1)ÈO(5b)
92.4(2)
88.2(2)
95.9(2)
O(2)ÈMn(1)ÈO(15) 162.4(5)
a Estimated standard deviations in the last signiÐcant digits are given
in parentheses. b Symmetry code: (a) x ] 1/2, y [ 1/2, [z ] 1/2; (b)
x [ 1/2, [y ] 1/2, z ] 1/2.
a Estimated standard deviations in the last signiÐcant digits are given
in parentheses.
530
New J. Chem., 2000, 24, 527È536

View Article Online
C(16), respectively]. The average values for the peripheral and
inner CÈO bonds are 1.213(5) and 1.295(3) A, respectively, the
shorter values being due to the greater double bond character
of the free CÈO bonds. The uncoordinated water molecule
[O(9)] interacts only very weakly with the oxalate oxygens
O(1) and O(4): the O(9)É É ÉO(1) and O(9)É É ÉO(4) distances are
3.120(2) and 3.405(2) A, values that are somewhat greater than
the sum of the van der Waals radii. The bulky tetra-
phenylarsonium cation exhibits the expected tetrahedral shape
and its bond distances and angles are in agreement with those
observed in previous AsPh `-containing compounds.24,28,39
4
Interestingly, alternating sextuple and double phenyl
embraces40,41 between the AsPh ` cations occur along the z
4
axis (see Fig. 2), the arsoniumÈarsonium distances involved
being 6.209(2) [As(1)É É ÉAs(1a); (a) \ [x, 1 [ y, 1 [ z] and
8.736(4) A [As(1)É É ÉAs(1b); (b) \ [x, 1 [ y, 2 [ z], respec-
tively. In this latter case, where the o†set face-to-face inter-
action occurs between two phenyl rings of two adjacent
cations, the interplanar distance is 3.85(9) A. In addition, the
Scheme 1
Cr Na unit (see Fig. 5), with a four-fold axis passing through
two phen ligands of two adjacent [Cr(phen)(ox) ]~ units
2
4
4
exhibit a signiÐcant graphite-like interaction (see Scheme 1),
the middle point between two opposite chromium atoms. This
topology was also observed in the complex of formula
[NaCr(bpy)(ox) (H O)] É 2H O24 where the phen ligand of 2
the separation between the two somewhat slipped phen planes
being 3.53(9) A. The separation between the chromium atoms
within this couple is 8.721(6) A [Cr(1)É É ÉCr(1c); (c) \ [x, [y,
[z]. The shortest intermolecular chromiumÈchromium and
chromiumÈarsonium distances are 7.052(2) [Cr(1)É É ÉCr(1d);
(d) \ 1 [ x, [y, [z] and 7.587(2) A [Cr(1)É É ÉAs(1a)].
2
2
2
is replaced by bpy. The main di†erence between these two
compounds is the presence in the bpy derivative of two crys-
tallographically independent tris-chelated chromium atoms,
which alternate regularly in each CrIIIÈNaI bimetallic chain.
The octanuclear holes are Ðlled by two phen ligands, which do
not exhibit any pÈp interaction, the separation between the
two phen planes being ca. 5 A.
[NaCr(phen)(ox) (H O)] Æ 2H O (2). Complex 2 has an
Each chromium atom in 2 exhibits a distorted octahedral
environment, the bond lengths and angles around the metal
atom being very close to those observed in 1 (see Table 3). The
sodium atom is also six-coordinated with a water oxygen
[2.384(6) A for Cr(1)ÈO(9)] and Ðve oxalate oxygen atoms
2
2
2
extended two-dimensional structure made up by bimetallic
oxalato-bridged CrIIIÈNaI helical chains (Fig. 3), which are
linked through centrosymmetric Na O units (see Fig. 4). The
2
2
resulting sheetlike polymer grows in the yz plane. Because of
the inversion center, the chromium complexes of neighbouring
chains have opposite chirality. The sheets are eclipsed to each
other and the intersheet separation is 9.092(2) A. Hydrogen
bonds involving one of the oxalate oxygens [O(8)] and both
the coordinated [O(9)] and uncoordinated [O(10) and O(11)]
water molecules [values of 2.785(11) and 2.82(3) A for the
O(8)É É ÉO(11) and O(9)É É ÉO(10) distances, respectively] play an
important stabilizing role in the crystal packing energy.
Within a sheet, four octanuclear Cr Na rings and four tetra-
4
4
nuclear Cr Na rhombuses alternate regularly around each
2
2
Fig. 3 Perspective view of two symmetry-related units of complex 2
with the atom numbering. The thermal ellipsoids are drawn at the
30% probability level and the hydrogen atoms as well as the hydra-
tion water molecules have been omitted for clarity.
Fig. 2 A projection of the crystal packing of 1 down the x axis. The
water molecules have been omitted for clarity.
New J. Chem., 2000, 24, 527È536
531

View Article Online
in the three-dimensional [Fe(bpy) ][NaFe(ox) ]9 and
3
3
[MIII(bpy) ][NaCr(ox) ]X with M \ Cr (X \ ClO ~) or Co
3
(X \ PF ~).15
6
3
4
As in 1, neither phen nor ox ligands exhibit signiÐcant devi-
ations from planarity. The dihedral angle between the two ox
ligands is 85.3(3)¡ and those of phen with the two oxalate
groups are 88.9(2) and 89.7(2)¡. The oxalate groups in 2 are
bisbidentate but one of them also acts as a monodentate
ligand through one of its oxygen atoms [O(5)]. Consequently,
each sodium atom is surrounded by two Ðve- [from two
oxalate ligands] and one four-membered chelate rings [Na(1)È
O(5a)ÈNa(1c)ÈO(5b); (c) \ [x, [y, [z ] 1]. The Na O
units are planar and the Na(1)É É ÉNa(1c) separation is 3.643(8)
A. The chromiumÈsodium separation through bridging
oxalate is 5.560(4) A. The shortest intra- and intersheet
chromiumÈchromium separations are 7.658(9) [Cr(1)É É ÉCr(1d);
2
2
(d) \ 1/2 [ x,
1/2 ] y,
1/2 [ z]
and
8.141(9)
A
[Cr(1)É É ÉCr(1e); (e) \ 1 [ x, 1/2 [ y, 1/2 ] z].
{ [Cr(phen)(ox) ] [Mn (bpy) (H O) (ox)]} Æ 6H O (3). The
2 2
complex
2
2
2
2
2
Fig. 4 Perspective drawing of a fragment of a sheet of compound 2
showing the CrIIINaI cavities partially Ðlled with two phen ligands.
structure
of
2 2
3
consists
of
neutral
[Cr(phen)(ox) ] [Mn (bpy) (H O) (ox)] tetranuclear units
4
4
2
2
2
2
(Fig. 6) and water molecules of crystallization linked by van
der Waals interactions and an extensive network of hydrogen
[CrÈO(ox) bond lengths varying in the range 2.453(5)È2.319(4)
A] building very distorted octahedron. These values
bonds. Two [Cr(phen)(ox) ]~ entities act as monodentate
a
2
ligands through an oxalate oxygen atom, O(15) [at Cr(1)] and
compare well with those observed for the sodium
O(7) [at Cr(2)], towards a central l-oxalatobis[(aqua)(2,2@-
bipyridyl)manganese(II)] unit. The peripheral chromium com-
plexes are trans with respect to the central dinuclear
manganese(II) moiety. The most striking feature of the present
structure is the occurrence of three di†erent coordination
modes of oxalate in the same complex: the usual bisbidentate
(between the two manganese atoms) and bidentate (peripheral
chromium atoms) coordination modes together with the
unprecedented simultaneously bidentate (towards chromium)
and monodenate (towards manganese) bridging mode.
atom in the layered [NaCr(bpy)(ox) (H O)] É 2H O24 and
2
2
2
[N(CH ) Ph][NaCr(ox) ] Cl É 5H O11 compounds as well as
3 3
3 2
2
The two crystallographically independent chromium atoms
exhibit a distorted octahedral environment with bond lengths
and angles very similar to each other, the main di†erences
being the lengthening of one of the CrÈO(ox) bonds whose
value [2.029(13) A for Cr(1)ÈO(17)] is signiÐcantly above the
remaining ones at either Cr(1) [1.97(2)È1.92(2) A] or Cr(2)
[1.97(2)È1.923(14) A]. Apart from this detail, the bond lengths
and angles around the chromium atoms in 3 agree well with
those observed in the structures of 1 and 2. The phen and ox
ligands around Cr(1) and Cr(2) are planar as expected. The
dihedral angle between the oxalate planes is 79.8(6)¡ [at Cr(1)]
Fig. 5 A topological drawing of one layer of compound 2 showing
the alternating arrangement of the Cr Na octogons and Na O
4
4
2 2
rhombuses. Only the chromium (black circles) and sodium (open
circles) atoms are shown for simplicity.
Fig. 6 Perspective drawing of the neutral CrIIIÈMnIIÈMnIIÈCrIII tetranuclear unit of complex 3 with the atom numbering. The thermal ellipsoids
are drawn at the 30% probability level and the hydrogen atoms have been omitted for clarity.
532
New J. Chem., 2000, 24, 527È536

View Article Online
and 79.4(7)¡ [at Cr(2)], whereas those between phen and
oxalate are 80.9(4) and 79.8(6)¡ [at Cr(1)] and 87.0(6) and
82.9(4)¡ [at Cr(2)]. The average carbonÈcarbon bond lengths
of the oxalate ligands bound to the chromium atoms is 1.55(5)
A, a value that is as expected for a single CÈC bond. The
values of the free CÈO oxalate bonds are shorter [values
varying in the ranges 1.23(3)È1.20(2) for Cr(1) and 1.25(3)È
1.18(3) A for Cr(2)] than those coordinated to the chromium
[the average values for CrÈO are 1.27 A at Cr(1) and 1.32 A at
Cr(2)].
perature range 1.9È100 K is shown in Fig. 8. Both curves are
quite similar. s T at 290 K is equal to 1.85 cm3 mol~1 K (1
M
and 2), a value which is as expected for a magnetically isolated
spin quartet (the calculated value of s T for S \ 3/2 with
M
g \ 2.0 is 1.88 cm3 mol~1 K). This value remains practically
unchanged when cooling and it decreases smoothly in the
lower temperature region, the curve of 1 being slightly below
that of 2 (the s T values for 1 and 2 at 2.0 K are 1.43 and 1.74
M
cm3 mol~1 K, respectively). No susceptibility maximum was
observed for 1 or 2 in the temperature range explored. The
The two crystallographically independent manganese atoms
are also six coordinated: two nitrogen atoms from a bidentate
bpy, a water oxygen and three oxalate oxygen atoms (two of a
decrease of s T in the lower temperature range for both com-
M
plexes can be due to the zero Ðeld splitting (D) of the
chromium(III) ion, to weak antiferromagnetic interactions
between the local spin quartets or both of these. Keeping in
mind the mononuclear nature of 1, we have analyzed its mag-
bis-chelating oxalate and one of the terminal [Cr(phen)(ox) ]~
2
unit) form a distorted octahedron around each manganese
atom. The short bites of the bpy [73.6(6)¡ at Mn(1) and
73.8(6)¡ at Mn(2)] and ox [74.0(5) at Mn(1)¡ and 77.6(5)¡ at
Mn(2)] ligands are the main factors for the distortion of the
MnN O chromophores. The values of the MnÈN(bpy) bond
2
4
lengths are somewhat shorter for Mn(1) [2.14(2) and 2.20(2)
A] than for Mn(2) [2.238(14) and 2.33(2) A] but they compare
well with the values reported for other bpy- and carboxylato-
containing manganese(II) complexes.42 The bis-chelating
oxalato ligand is asymmetrically coordinated to the man-
ganese atoms [2.169(14) and 2.219(12) A at Mn(1) and 1.19(2)
and 2.210(14) A at Mn(2)]. This structural fact is in agreement
with the results of the X-ray data of other oxalato-bridged
manganese(II)
complexes
such
as
[Mn(bpy)(ox)],42b
[Mn(ox)(H O) ]43 and [Mn (ox) (H O) ]2~.44 The value of
2
2
3
4
2
2
the remaining MnÈO(ox) bond involving the oxalato oxygen
of the terminal chromium complex [2.160(13) and 2.211(13) A
for Mn(1)ÈO(15) and Mn(2)ÈO(7), respectively] compares well
with previous structures. The MnÈO(w) bond distances
[2.21(2) and 2.17(2) A for Mn(1)ÈO(5) and Mn(2)ÈO(6)] lie
within the range of the MnÈO(ox) distances. The bond lengths
and angles within the two bidentate bpy ligands are as
observed in the free molecule.45 The two bpy ligands are
approximately planar, the dihedral angles between the two
pyridyl rings being equal to 3(1)¡ [(N(1)/N(2) and (N(3)/N(4)].
There are no unusual bond lengths or angles in the planar
bis-chelating oxalate. It forms dihedral angles of 86.8(4) and
85.9(3)¡ with the mean planes of the two bpy ligands and
of 87.7(4) and 85.1(4)¡ with those of the two chelating/
monodentate oxalates [O(3)/O(7) and O(3)/O(15)]. Finally,
the dihedral angle between mean planes of the N(1)/N(2) bpy
and O(15)-containing oxalate is 85.1(6)¡, a value very close to
that of N(3)/N(4) bpy and the O(7)-containing oxalate
[85.8(5)¡].
Fig. 7 Projection of the packing of complex 3 along the y axis. Black
circles represent the metal ions.
The intramolecular metalÈmetal separations are 5.703(2)
[Mn(1)É É ÉMn(2)],
[Mn(2)É É ÉCr(2)],
5.502(5)
9.957(5)
[Mn(1)É É ÉCr(1)],
[Mn(1)É É ÉCr(2)],
5.507(5)
9.952(5)
[Mn(2)É É ÉCr(1)] and 15.042(3) A [Cr(1)É É ÉCr(2)], whereas
the shortest intermolecular separations are 5.927(2)
[Mn(1)É É ÉMn(2a); (a) \ 1 ] x, y, z] and 9.014(2)
A
[Mn(1)É É ÉMn(1a), Mn(2)É É ÉMn(2a), Cr(1)É É ÉCr(1a) and
Cr(2)É É ÉCr(2a)]. SigniÐcant pÈp interactions between bpy
ligands [interplanar distance of 3.7(2) A] of neighbouring
tetranuclear units are observed whereas much weaker pÈp
interactions occur between the phen groups [the shortest
interplanar phenÈphen separation is 4.7(2) A] (see Fig. 7). An
extensive network of hydrogen bonds involving the six
uncoordinated water molecules and some of the oxalato
oxygens are also present [2.61(2), 2.65(4), 2.74(4), 2.78(2),
2.82(3) and 2.93(2)
A for O(20)É É ÉO(27), O(23)É É ÉO(28),
O(12)É É ÉO(24), O(4)É É ÉO(25), O(22)É É ÉO(23) and O(18)É É ÉO(26),
respectively].
Fig. 8 s T vs. T plot for 1 (L) and 2 (|). The solid lines correspond
M
to the best Ðt through the corresponding expressions (see text). The
inset shows the magnetization vs. the applied magnetic Ðeld at 2.0 K
for 1: (L) experimental data; (ÈÈ), (É É É É É) and (È È È) calculated
curves for a magnetically isolated spin of S \ 3/2 with D values of 0.0,
1.0 and 2.0 cm~1, respectively.
Magnetic properties of 1–3
The temperature dependence of s T for 1 and 2 [s being the
magnetic susceptibility per mole of chromium(III)] in the tem-
M
M
New J. Chem., 2000, 24, 527È536
533

View Article Online
netic data through eqn. (1),46 which is derived from the
Nb2g2
s \
(s ] 2 s )
(1)
(2)
M
A
M
3kT
1 ] 9 exp([2 D/kT )
4(1 ] exp([2 D/kT )
s \
A
4 ] (3kT /D)[1 [ exp([2 D/kT )]
4[1 ] 2 exp([2 D/kT )]
s \
(3)
(4)
M
H \ D[S2 [ 1S(S ] 1)]
Z
3
Hamiltonian given by eqn. (4), where we have considered an
axial zero Ðeld splitting and S \ 3/2. Least-squares Ðt of the
susceptibility data of 1 through eqn. (1) leads to D \ 2.7 cm~1
and g \ 1.98, the agreement with the calculated and theoreti-
cal data being quite good. Assuming that the decrease of the
susceptibility data of 1 is only due to intermolecular inter-
actions (h), D is made equal to zero in eqns. (1)È(3) and T is
replaced by T [ h in eqn. (1). Least-squares Ðt through the
modiÐed expression of eqn. (1), where the variable parameters
are h and g, leads to h \ [0.5 K and g \ 1.98, the quality of
the Ðt being as good as the preceding one. To evaluate the
magnitude of D, we have measured the magnetization curve of
1 as a function of the Ðeld at 2.0 K which is shown in the inset
of Fig. 8. An inspection of this curve shows that the magne-
tization data are well reproduced by a curve with D \ 0 cm~1
and g \ 1.97 (the curves for D values of 1 and 2 cm~1 are
clearly below the experimental data). The slightly smaller
value of g (\1.98È1.99, expected for CrIII) may be due to the
occurrence of weak intermolecular magnetic interactions. In
summary, the Ðt with D ca. zero and h \ [0.5 K is the best
for the magnetization curve of 1. Given that h \ zJS(S ] 1)/3k
and that S \ 3/2 in the present case, zJ \ [0.9 cm~1. As the
packing of 1 shows that pairs of tris-chelated chromium(III)
units are present (through a weak pÈp phenÈphen overlap), z
is equal to 1 and consequently, J \ [0.9 cm~1. In accord
with this reasoning, a weak magnetic interaction through p
stacking was reported previously.47 This value of J is the
upper limit for the magnetic coupling in 1 given that a very
small but non-zero value of the zero-Ðeld splitting may be
involved. In the case of the magnetic properties of 2, we
analyzed them through eqn. (1) with D and g as the variable
parameters and further, setting D equal to zero and replacing
T by T [ h in eqn. (1). Least-squares Ðts led to g \ 1.98 in
both cases, the values of D and h being 0.1 cm~1 and [0.1 K,
respectively. Taking into account that within a sheet in 2, the
chromium atoms describe a square lattice (z \ 4), a value of
J \ [0.02 cm~1 (this value being the upper value of the mag-
netic interaction in 2 as mentioned above for 1) is easily
obtained from that of h. Finally, the treatment of the suscepti-
bility data of 2 through the Lines model for an isotropic
square lattice with local spins S \ 3/2,48 leads to J \ [0.014
cm~1 and g \ 1.98. The quality of the three Ðts is very similar
and the computed g value is the same in the three models.
However, the fact that the D value is practically zero in 1 and
the occurrence of the same environment for the chromium
atom in 1 and 2, induce us to attribute the slight decrease of
Fig. 9 s T vs. T plot for 3: (L) experimental data; (ÈÈ) best Ðt
M
through eqn. (5). The inset shows the susceptibility curve in the low
temperature region.
decreases sharply when cooling and attains a value of 1.50
cm3 mol~1 K at 2.0 K. The susceptibility curve exhibits an
incipient maximum at 2.5 K (see inset of Fig. 9). These features
are indicative of the occurrence of an overall anti-
ferromagnetic behaviour of complex 3. Keeping in mind its
crystal structure (tetranuclear unit with two types of bridging
oxalate), we analyzed the susceptibility data through the sim-
pliÐed isotropic Hamiltonian of eqn. (5)
H \ [JS
É S
[ j[S É S
Cr1 Mn1
] S É S
]
(5)
Mn1 Mn2
Cr2 Mn2
where J is the magnetic interaction through bis-chelating
oxalato (inner manganese pair) and j represents the magnetic
coupling through chelating/monodentate oxalato (each per-
ipheral chromium atom with its adjacent manganese atom).
The interactions between peripheral chromium atoms and
those of each chromium atom with its non-adjacent man-
ganese atom are neglected and the two peripheral chromium
atoms are assumed to be identical. The best agreement
between the experimental and calculated data is obtained for
J \ [2.2 cm~1, j \ [1.1 cm~1, g \ 1.99 and g \ 1.98
Mn
Cr
with R \ 1.0 ] 10~5 where R is the agreement factor deÐned
as & [(s T ) (i) [ (s T ) (i)]2/&[(s T ) (i)]2N. The theoreti-
i
M
obs
M
calc
M
obs
cal curve (solid line in Fig. 9) matches very well the experi-
mental data.
The value of the antiferromagnetic coupling between the
two manganese(II) ions through the bischelating oxalato
ligand in 3 (J \ [2.2 cm~1) is in agreement with those
reported for other oxalato-bridged manganese(II) compounds
(values of the magnetic coupling range from [1.8 to [2.5
cm~1).42c,49,50 The exchange pathway for this signiÐcant anti-
ferromagnetic interaction between paramagnetic centres
through bis-chelating oxalato is well known51 and several
theoretical papers have been devoted to its analysis.52h54 In
fact, the good overlap between the two d
type metal-
x2~y2
centred magnetic orbitals [the x and y axes being roughly
deÐned by the Mn(1)ÈO(1) and Mn(1)ÈO(2) bonds] accounts
for the antiferromagnetic interaction observed. As far as the
exchange coupling between the CrIII and MnII through the
chelating/monodentate bridging oxalate ( j \ [1.1 cm~1) is
concerned, no previous magneto-structural data are available
to our knowledge. Preceding studies on oxalato-bridged CrIIIÈ
MII compounds (M \ Cu, Ni, Co, Fe, Mn) in which the
oxalato adopts a bisbidentate coordination mode and the two
metal atoms are six-coordinated, reveal the occurrence of
weak intramolecular ferromagnetic coupling.5,23,55 This ferro-
magnetic coupling through bisbidentate oxalate can be
s T in 2 to weak intrasheet antiferromagnetic interactions
M
between chromium(III) ions separated by more than 7.6 A.
The temperature dependence of s T for 3 (s is the mag-
M
M
netic susceptibility per CrIIIMnII unit) in the temperature range
2
2
2.0È300 K is shown in Fig. 9. At room temperature, s T is
M
equal to 11.8 cm3 mol~1 K, a value which is somewhat
smaller than the expected one for two chromium(III) and two
manganese(II) ions without any magnetic interaction [s T \
M
12.4 cm3 mol~1
K
with
g
\ g \ 2.00]. This value
Cr
Mn
534
New J. Chem., 2000, 24, 527È536

View Article Online
10 W. M. Rei†, J. Kreisz, L. Meda and R. U. Kirss, Mol. Cryst. L iq.
Cryst., 1995, 273, 181.
explained on simple orbital symmetry considerations. The
chromium(III) ion in O symmetry has three unpaired electrons
h
11 R. P. Farrell, T. W. Hambley and P. A. Lay, Inorg. Chem., 1995,
34, 757.
on the t orbitals whereas the CuII and NiII have unpaired
2g
electrons only on the e orbitals (e1 and e2 for CuII and NiII,
12 P. Roman, C. GuzmanÈMiralles and A. Luque, J. Chem. Soc.,
Dalton T rans., 1996, 3985.
13 C. Mathoniere, C. J. Nuttall, S. G. Carling and P. Day, Inorg.
Chem., 1996, 35, 1201.
14 S. G. Carling, C. Mathoniere, P. Day, K. M. Abdul Malik, S. J.
Coles and M. B. Hursthouse, J. Chem. Soc., Dalton T rans., 1996,
1839.
15 S. Decurtins, H. W. Schmalle, R. Pellaux, P. Schneuwly and A.
Hauser, Inorg. Chem., 1996, 35, 1451.
16 M. ClementeÈLeon, E. Coronado, J. R. GalanÈMascaros and C.
GomezÈGarc•a, Chem. Commun., 1997, 1727.
g
g
g
respectively). Consequently, the overlap for the t3 Èe1 CrIIIÈ
2g
g
oxÈCuII and t3 Èe2 CrIIIÈoxÈNiII cases is zero (classical exam-
2g
g
ples of strict orthogonality between the magnetic orbitals
involved in the bimetallic unit) and ferromagnetic coupling
arises, as observed. For the three other cases [t3 Èt5 e2 (CrIIIÈ
2g 2g g
oxÈCoII), t3 Èt4 e2 (CrIIIÈoxÈFeII) and t3 Èt3 e2 (CrIIIÈoxÈ
2g 2g g
2g 2g g
MnII)], net overlapping between the t Èt orbitals (and thus
2g 2g
an antiferromagnetic contribution) is also involved, in addi-
tion to the above speciÐed ferromagnetic one. As both contri-
butions have opposite signs, the overall coupling will depend
on their relative magnitudes. In light of the reported results
through bisbidentate oxalato, the ferromagnetic contribution
is somewhat stronger and a weak ferromagnetic coupling is
observed for this family of bimetallic complexes. In the case of
3, the lower symmetry of the oxalato bridge (bidentate
towards CrIII and monodentate towards MnII) should decrease
the efficiency of the ferromagnetic pathway and the anti-
ferromagnetic one becomes dominant.
17 S. Decurtins, M. Gross, H. W. Schmalle and S. Ferlay, Inorg.
Chem., 1998, 37, 2443.
18 M. HernandezÈMolina, F. Lloret, C. RuizÈPerez and M. Julve,
Inorg. Chem., 1998, 37, 4131.
19 T. Sanada, S. Suzuki, T. Yoshida and S. Kaizaki, Inorg. Chem.,
1998, 37, 4712.
20 R. Pellaux, H. W. Schmalle, R. Huber, P. Fischer, T. Hauss, B.
Ouladdiaf and S. Decurtins, Inorg. Chem., 1997, 36, 2301.
21 S. Decurtins, H. W. Schmalle, R. Pellaux, R. Huber, P. Fischer
and B. Ouladdiaf, Adv. Mater., 1996, 8, 647.
22 F. Lloret, M. Julve, M. Mollar, I. Castro, J. Latorre and J. Faus,
J. Chem. Soc., Dalton T rans., 1989, 729.
23 M. Ohba, H. Tamaki, N. Matsumoto and H. Okawa, Inorg.
Chem., 1993, 32, 5385.
24 M. C. Munoz, M. Julve, F. Lloret, J. Faus and M. Andruh, J.
Chem. Soc., Dalton T rans., 1998, 3125.
In
summary,
the
building
block
of
formula
[Cr(phen)(ox) ]~ has been prepared and structurally charac-
2
terized (complex 1) and its complexing ability towards
sodium(I) (complex 2) and manganese(II) (complex 3) metal
ions tested. The sheetlike polymer 2 and the tetranuclear
complex 3 with two bridging modes of oxalate (bisbidentate
oxalate and bisbidentate/monodentate) (2) and three coordi-
nation modes of oxalate (terminal bidentate and bridging bis-
bidentate and bidentate/monodentate) (3) are obtained.
Antiferromagnetic coupling between CrIII and MnII through
the unprecedented chelating/monodentate bridging oxalato is
reported.
25 M. Andruh, R. Melanson, C. V. Stager and F. D. Rochon, Inorg.
Chim. Acta, 1996, 251, 309.
26 F. D. Rochon, R. Melanson and M. Andruh, Inorg. Chem., 1996,
35, 6086.
27 N. Stanica, C. V. Stager, M. Cimpoesu and M. Andruh, Poly-
hedron, 1998, 17, 1787.
28 G. De Munno, D. Armentano, M. Julve, F. Lloret, R. Lescouezec
and J. Faus, Inorg. Chem., 1999, 38, 2234.
29 F. Berezovsky, A. A. Hajem, S. Triki, J. Sala Pala and P. Molinie,
Inorg. Chim. Acta, 1999, 284, 8.
30 K. Nakamoto, Infrared and Raman Spectra of Inorganic and
Coordination Compound, Wiley, New York, 4th edn., 1986, p. 228.
31 A. Earshaw, Introduction to Magnetochemistry, Academic Press,
London, 1968.
32 (a) G. M. Sheldrick, SHEL X 86, A Program for Crystal Structure
Determination, University of Gottingen, Gottingen, Germany,
1986; (b) G. M. Sheldrick, SHEL X 93, A Program for the ReÐne-
ment of Crystal Structures, University of Gottingen, Gottingen,
Germany, 1993.
Acknowledgements
Financial support from the Spanish Direccion General de
Investigacion Cient•Ðca y Tecnica (DGICYT) through Project
PB97-1397, the Romanian Ministry of Education (Grants
30C/CNCSIS and 1D/CMCSIS), the TMR Program from the
European Union (Contract ERBFMRXCT98-0181) and the
COST Program (Action 518) is gratefully acknowledged.
Thanks are also extended to the Centre dÏInformatica de la
Universitat de Valencia for computer resource support.
33 International T ables for X-ray Crystallography, Kynoch Press,
Birmingham, 1974, vol. 4, p. 99.
34 C. K. Jonhson, ORT EP, Report ORNL-3794, Oak Ridge
National Laboratory, Oak Ridge, TN, 1971.
35 N. Sakagami, E. Kita, P. Kita, J. W•sniewska and S. Kaizaki,
Polyhedron, 1999, 18, 2001.
36 R. P. Scaringe, P. Singh, R. P. Eckberg, W. E. HatÐeld and D. J.
Hodgson, Inorg Chem., 1975, 14, 1127.
References
37 J. T. Veal, W. E. HatÐeld and D. J. Hodgson, Acta Crystallogr.,
Sect. B, 1973, 29, 12.
1
2
O. Kahn, Adv. Inorg. Chem., 1995, 43, 179.
S. Decurtins, R. Pellaux, A. Hauser and M. E. von Arx, in Mag-
netism: A Supramolecular Function, ed. O. Kahn, NATO ASI
Series C484, Kluwer, Dordrecht, 1996, pp. 487È508.
S. Decurtins, H. W. Schmalle, R. Pellaux, P. Fischer and A.
Hauser, Mol. Cryst. L iq. Cryst., 1997, 305, 227 and references
therein.
38 S. Nishigaki, H. Yoshioka and K. Nakatsu, Acta Crystallogr.,
Sect. B, 1978, 34, 875.
39 (a) J. Baldas, S. F. Colmanet and M. F. MacKay, J. Chem. Soc.,
Dalton T rans., 1988, 1725; (b) R. Vicente, J. Ribas, S. Alvarez, A.
Segu•, X. Solans and M. Verdaguer, Inorg. Chem., 1987, 26, 4004;
(c) R. Grenz, F. Gotzfried, U. Nagel and W. Beck, Chem. Ber.,
1986, 119, 1217.
3
4
S. Decurtins, S. Ferlay, R. Pellaux, M. Gross and H. Schmalle, in
Supramolecular Engineering of Synthetic Magnetic Materials, eds.
J. Veciana, C. Rovira and D. B. Amabilino, NATO ASI Series
C518, Kluwer, Dordrecht, 1999, pp. 175È196.
40 I. Dance and M. Scudder, Chem. Eur. J., 1996, 2, 481.
41 I. Dance and M. Scudder, J. Chem. Soc., Dalton T rans., 1998,
1341.
5
6
Y. Pei, Y. Journaux and O. Kahn, Inorg. Chem., 1989, 28, 100.
H. Tamaki, Z. J. Zhong, N. Matsumoto, S. Kida, M. Koikawa,
N. Achiwa, Y. Hashimoto and H. Okawa, J. Am. Chem. Soc.,
1992, 114, 6974.
42 (a) J. Cano, G. DeMunno, J. Sanz, R. Ruiz, F. Lloret, J. Faus and
M. Julve, J. Chem. Soc., Dalton T rans., 1994, 3465; (b) D. Degue-
non, G. Bernardelli, J. P. Tuchagues and P. Castan, Inorg. Chem.,
1990, 29, 3031; (c) S. Menage, S. E. Vitols, P. Bergerat, E.
Codjovi, O. Kahn, J. J. Girerd, M. Guillot, X. Xolans and T.
Calvet, Inorg. Chem., 1991, 30, 2666; (d) J. H. Jiang, S. L. Ma, D.
Z. Liao, S. P. Yan, G. L. Wang, X. K. Yao and R. J. Wang, J.
Chem. Soc., Chem. Commun., 1993, 745; (e) M. Andruh, H. W.
Roesky, M. Noltemeyer and H. G. Schmidt, Polyhedron, 1993, 12,
2901; ( f ) H. Oshio, E. Ino, I. Mogi and T. Ito, Inorg. Chem.,
1993, 32, 5697.
7
8
9
L. O. Atovmyan, G. V. Shilov, R. N. Lyubovskaya, E. I. Zhilaeva,
N. S. Ovanesyan, S. I. Pirumova and I. G. Gusakovskaya, JET P
L ett. Engl. T ransl., 1993, 58, 766.
S. Decurtins, H. W. Schmalle, H. R. Oswald, A. Linden, J.
Ensling, P. Gutlich and A. Hauser, Inorg. Chim. Acta, 1994, 216,
65.
S. Decurtins, H. W. Schmalle, P. Schneuwly, J. Ensling and P.
Gutlich, J. Am. Chem. Soc., 1994, 116, 9521.
New J. Chem., 2000, 24, 527È536
535

View Article Online
43 R. Deyrieux, C. Berro and A. Peneloux, Bull. Soc. Chim. Fr., 1973,
1, 25.
44 K. Wieghardt, U. Bossek, B. Nuber, J. Weiss, J. Bonvoisin, M.
Corbella, S. E. Vitols and J. J. Girerd, J. Am. Chem. Soc., 1998,
110, 7398.
45 L. L. Merrit and E. D. Schroeder, Acta Crystallogr., 1956, 9, 801.
46 C. J. OÏConnors, Prog. Inorg. Chem., 1986, 29, 203.
47 A. J. Amoroso, J. C. Je†ery, P. L. Jones, J. A. McCleverty, P.
Thornton and M. D. Ward, Angew. Chem., Int. Ed. Engl., 1995,
34, 1443.
51 (a) T. R. Felthouse, E. J. Laskowski and D. N. Hendrickson,
Inorg. Chem., 1977, 16, 1077; (b) M. Julve, M. Verdaguer, A.
Gleizes, M. PhilocheÈLevisalles and O. Kahn, Inorg. Chem., 1984,
23, 3808; (c) P. Roman, C. GuzmanÈMiralles, A. Luque, J. I.
Beitia, J. Cano, F. Lloret, M. Julve and S. Alvarez, Inorg. Chem.,
1996, 35, 3741 and references therein.
52 M. F. Charlot, M. Verdaguer, Y. Journaux, P. de Loth and J. P.
Daidey, Inorg. Chem., 1984, 23, 3802.
53 S. Alvarez, M. Julve and M. Verdaguer, Inorg. Chem., 1990, 29,
4500.
48 M. E. Lines, J. Phys. Chem. Solids, 1970, 31, 101.
49 M. Verdaguer, Ph. D. T hesis, University of Orsay, France, 1984.
50 J. Glerup, P. A. Goodson, D. J. Hodgson and K. Michelsen,
Inorg. Chem., 1995, 34, 6255.
54 J. Cano, P. Alemany, S. Alvarez, M. Verdaguer and E. Ruiz,
Chem. Eur. J., 1998, 4, 476.
55 M. Ohba, H. Tamaki, N. Matsumoto, H. Okawa and S. Kida,
Chem. L ett., 1991, 1157.
536
New J. Chem., 2000, 24, 527È536