[Fe(bipy)(CN)4]- as a versatile building block for the design of heterometallic systems

Article abstract of DOI:10.1021/ic0107882

The new cyano complexes of formulas PPh₄[Fe^III(bipy)(CN)₄]·H₂O (1), [{Fe^III(bipy) (CN)₄}₂M^II(H₂O)₄] ·4H₂O with M = Mn (2) and Zn (3), and [{Fe^III(bipy)(CN)₄}₂Zn^II] ·2H₂O (4) [bipy = 2,2′-bipyridine and PPh4 = tetraphenylphosphonium cation] have been synthesized and structurally characterized. The structure of complex 1 is made up of mononuclear [Fe(bipy)(CN)₄]^- anions, tetraphenyphosphonium cations, and water molecules of crystallization. The iron(III) is hexacoordinated with two nitrogen atoms of a chelating bipy and four carbon atoms of four terminal cyanide groups, building a distorted octahedron around the metal atom. The structure of complexes 2 and 3 consists of neutral centrosymmetric [{Fe^III(bipy)(CN)₄}₂M^II (H₂O)₄] heterotrinuclear units and crystallization water molecules. The [Fe(bipy)(CN)₄]^- entity of 1 is present in 2 and 3 acting as a monodentate ligand toward M(H₂O)₄ units [M = Mn(II) (2) and Zn(II) (3)] through one cyanide group, the other three cyanides remaining terminal. Four water molecules and two cyanide nitrogen atoms from two [Fe(bipy)(CN)₄]^- units in trans positions build a distorted octahedron surrounding Mn(II) (2) and Zn(II) (3). The structure of the [Fe(phen)(CN)₄]^- complex ligand in 2 and 3 is close to that of the one in 1. The intramolecular Fe-M distances are 5.126(1) and 5.018(1) A in 2 and 3, respectively. 4 exhibits a neutral one-dimensional polymeric structure containing two types of [Fe(bipy)(CN)₄]^- units acting as bismonodentate (Fe(1)) and trismonodentate (Fe(2)) ligands versus the divalent zinc cations through two cis-cyanide (Fe(1)) and three fac-cyanide (Fe(2)) groups. The environment of the iron atoms in 4 is distorted octahedral as in 1-3, whereas the zinc atom is pentacoordinated with five cyanide nitrogen atoms, describing a very distorted square pyramid. The iron-zinc separations across the single bridging cyanides are 5.013(1) and 5.142(1) A at Fe(1) and 5.028(1), 5.076(1), and 5.176(1) A at Fe(2). The magnetic properties of 1-3 have been investigated in the temperature range 2.0-300 K. 1 is a low-spin iron(III) complex with an important orbital contribution. The magnetic properties of 3 correspond to the sum of two magnetically isolated spin triplets, the antiferromagnetic coupling between the low-spin iron(III) centers through the -CN-Zn-NC- bridging skeleton (iron-iron separation larger than 10 A) being very weak. More interestingly, 2 exhibits a significant intramolecular antiferromagnetic interaction between the central spin sextet and peripheral spin doublets, leading to a low-lying spin quartet.

Full text of DOI:10.1021/ic0107882

Inorg. Chem. 2002, 41, 818−826
[Fe(bipy)(CN)4]- as a Versatile Building Block for the Design of
Heterometallic Systems: Synthesis, Crystal Structure, and Magnetic
III
Properties of PPh4[Fe (bipy)(CN)4]‚H O,
2
[{Fe (bipy)(CN)4}2M (H O)4]‚4H O, and [{Fe (bipy)(CN)4}2ZnII]‚2H O [bipy
III
II
III
2
2
2
) 2,2′-Bipyridine; M ) Mn and Zn]
Rodrigue Lescoue1zec,1a Francesc Lloret,1a Miguel Julve,*,1a Jacqueline Vaissermann,1b and
,1b
Michel Verdaguer*
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 Laboratoire de
Chimie Inorganique et Mate´riaux Mole´culaires, Unite´ CNRS 7071, UniVersite´ Pierre et
Marie Curie, 4 Place Jussieu, Case 42, 75252 Paris Cedex 05, France
Received July 24, 2001
III
III
II
The new cyano complexes of formulas PPh4[Fe (bipy)(CN)4]‚H O (1), [{Fe (bipy)(CN)4}2M (H O)4]‚4H O with
2
2
2
III
II
M ) Mn (2) and Zn (3), and [{Fe (bipy)(CN)4}2Zn ]‚2H O(4) [bipy ) 2,2′-bipyridine and PPh4 ) tetraphenylphos-
2
phonium cation] have been synthesized and structurally characterized. The structure of complex 1 is made up of
mononuclear [Fe(bipy)(CN)4]- anions, tetraphenyphosphonium cations, and water molecules of crystallization. The
iron(III) is hexacoordinated with two nitrogen atoms of a chelating bipy and four carbon atoms of four terminal
cyanide groups, building a distorted octahedron around the metal atom. The structure of complexes 2 and 3 consists
III
II
of neutral centrosymmetric [{Fe (bipy)(CN)4}2M (H O)4] heterotrinuclear units and crystallization water molecules.
2
The [Fe(bipy)(CN)4]- entity of 1 is present in 2 and 3 acting as a monodentate ligand toward M(H O)4 units [M )
2
Mn(II) (2) and Zn(II) (3)] through one cyanide group, the other three cyanides remaining terminal. Four water
molecules and two cyanide nitrogen atoms from two [Fe(bipy)(CN)4]- units in trans positions build a distorted
octahedron surrounding Mn(II) (2) and Zn(II) (3). The structure of the [Fe(phen)(CN)4]- complex ligand in 2 and 3
is close to that of the one in 1. The intramolecular Fe−M distances are 5.126(1) and 5.018(1) Å in 2 and 3,
respectively. 4 exhibits a neutral one-dimensional polymeric structure containing two types of [Fe(bipy)(CN)4]-
units acting as bismonodentate (Fe(1)) and trismonodentate (Fe(2)) ligands versus the divalent zinc cations through
two cis-cyanide (Fe(1)) and three fac-cyanide (Fe(2)) groups. The environment of the iron atoms in 4 is distorted
octahedral as in 1−3, whereas the zinc atom is pentacoordinated with five cyanide nitrogen atoms, describing a
very distorted square pyramid. The iron−zinc separations across the single bridging cyanides are 5.013(1) and
5.142(1) Å at Fe(1) and 5.028(1), 5.076(1), and 5.176(1) Å at Fe(2). The magnetic properties of 1−3 have been
investigated in the temperature range 2.0−300 K. 1 is a low-spin iron(III) complex with an important orbital contribution.
The magnetic properties of 3 correspond to the sum of two magnetically isolated spin triplets, the antiferromagnetic
coupling between the low-spin iron(III) centers through the −CN−Zn−NC− bridging skeleton (iron−iron separation
larger than 10 Å) being very weak. More interestingly, 2 exhibits a significant intramolecular antiferromagnetic
interaction between the central spin sextet and peripheral spin doublets, leading to a low-lying spin quartet.
Introduction
and B are transition-metal ions) has provided a large family
of three-dimensional compounds known as Prussian blue
analogues which exhibit very interesting spectroscopic,
magnetic, and magnetooptical properties.2-15 The two most
The use of the hexacyanometalate unit [B(CN)6]q- as a
complex toward totally hydrated metal ions [A(H2O)6]p+ (A
* To whom correspondence should be addressed. E-mail: miguel.julve@
uv.es.
(1) (a) Universitat de Vale`ncia. (b) Universite´ Pierre et Marie Curie.
818 Inorganic Chemistry, Vol. 41, No. 4, 2002
10.1021/ic0107882 CCC: $22.00 © 2002 American Chemical Society
Published on Web 01/25/2002

[Fe(bipy)(CN)4]- as a Versatile Building Block
exciting results of this research activity are (i) the preparation
of molecule-based magnets with critical temperatures (Tc)
as high as 3765 and 315 K15 and (ii) the achievement of
photoinduced magnetization upon light irradiation on Prus-
sian blue analogues9,10 and also on lower dimensional
cyanide-bridged bimetallic assemblies containing a light-
sensitive complex as the building block.11-14
If the Prussian blue analogues present exciting magnetic
properties, single crystals of these highly insoluble three-
dimensional complexes are hardly obtained. Furthermore,
vacancies and channels accommodate guest molecules,16,17
which makes difficult both the determination of the crystal-
lographic structure and the interpretation of the magnetic
behavior of these three-dimensional magnetic systems. To
overcome some of these problems, a highly rewarding
synthetic strategy has been widely used which consists of
reacting the hexacyanometalate unit with the coordinatively
unsaturated complex [A(L)x(H2O)y]p+, L being a neutral or
anionic polydentate ligand.18 Apart from a few examples of
high-spin penta- and heptanuclear complexes with ground
spin states up to 27/2,19,20 this strategy has provided one-,
two- and three-dimensional cyanide-bridged bimetallic net-
works as the main products, the dimensionality being strongly
dependent on the charges of the A- and B-containing units
and the number and relative positions of the coordinated
water molecules of A.18 These results show that the prepara-
tion of discrete cyano-bridged polynuclear species would
require a decrease of the number of cyano groups on the B
precursor. A few results have been reported in this respect
in bioinorganic,21 organometallic,22,23 and magnetostructural24-26
studies. So, the monocyano building block of formula [Fe-
(OEP)(py)(CN)] (OEP ) octaethylporphyrinate dianion and
py ) pyridine) was used to prepare heterobimetallic com-
plexes containing the FeIII-CN-CuII unit to mimic the iron-
copper binuclear site in cyanide-inhibited cytochrome c
oxidase and terminal quinol oxidases.21 A new class of or-
ganometallic solids with cyanide as a bridge (trinuclear spe-
cies, cages, and helical chains) have been reported recently,
the mononuclear cyano precursors being [Cp*(dppe)Fe-
(CN)],22 [Cp*(PPh3)2Ru(CN)],22 and [Cp*(M(CN)3]- (M )
Ir and Rh).23 Very recently, nice discrete cluster analogues
of the cubic cages existing in the Prussian blue type structure
such as the 14-metal, [(Me3tacn)8Cr8Ni6(CN)24]12+, and 19-
metal, [(Me3tacn)10Cr10Ni9(CN)42]6+, assemblies (Me3tacn )
N,N′,N′′-trimethyl-1,4,7-triazacyclononane) were prepared
when the neutral [(Me3tacn)Cr((CN)3] mononuclear complex
was allowed to react with hydrated metal ions.24b Finally,
the dicyano25 and tetracyano26 low-spin iron(III) complexes
of formulas [Fe(bipy)2(CN)2]+ (bipy ) 2,2′-bipyridine) and
[Fe(phen)(CN)4]- (phen ) 1,10-phenanthroline) allowed the
preparation of the cyanide-bridged cyclic tetranuclear com-
plex [Fe2(bipy)4(CN)4Cu2(bipy)2]6+ and the isostructural
double zigzag chains [{Fe(phen)(CN)4}2M(H2O)2]‚4H2O with
M ) Mn and Zn. A quintet spin ground state occurs in the
tetranuclear compound because of the intramolecular ferro-
magnetic interaction between the Fe(III) and Cu(II) local spin
doublets, whereas the intrachain antiferromagnetic coupling
between the Fe(III) (spin doublet) and Mn(II) (spin sextuplet)
leads to ferrimagnetic behavior.
(2) Fehlhammer, W. P.; Fritz, M. Chem. ReV. 1993, 93, 1243 and
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In an effort to continue this remarkably diverse chemistry
starting from a tailored cyanometalate molecular precursor,
we explored the use of the new low-spin iron(III) complex
[Fe(bipy)(CN)4]- as a ligand. Our first results presented here
concern the preparation and crystal structure of the precursor
(19) (a) Mallah, T.; Auberger, C.; Verdaguer, M.; Veillet, P. J. Chem. Soc.,
Chem. Commun. 1995, 61. (b) Scuiller, A.; Mallah, T.; Nivorozkhin,
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R.; Moubaraki, B.; Murray, K. S. Inorg. Chem. 1997, 36, 5006. (b)
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Inorganic Chemistry, Vol. 41, No. 4, 2002 819

Lescoue1zec et al.
Table 1. Crystallographic Data for PPh4[FeIII(bipy)(CN)4]‚H2O (1), [{FeIII(bipy)(CN)4}2MII(H2O)4]‚4H2O with M ) Mn (2) and Zn (3), and
[{FeIII(bipy)(CN)4}2ZnII]‚2H2O (4)
1
2
3
4
empirical formula
fw
C38H30FePN6O
673.5
C28H32Fe2MnN12O8
831.2
C28H32Fe2ZnN12O8
841.7
C28H20Fe2ZnN12O2
733.6
space group
a, Å
b, Å
P21/c
P21/n
P21/n
P21/n
12.013(4)
19.888(8)
14.486(6)
100.70(3)
3400(2)
4
6.620(7)
19.134(4)
14.319(4)
93.90(5)
1809(2)
2
6.499(6)
19.155(5)
14.338(4)
93.32(5)
1781(2)
2
19.872(4)
7.242(3)
20.776(4)
96.47(2)
2971(2)
4
c, Å
â, deg
V, Å3
Z
λ, Å
0.71069
1.31
22
5.26
0.0830
0.0926
0.71069
1.53
22
11.8
0.0591
0.0693
0.71069
1.57
22
15.5
0.0441
0.0512
0.71069
1.64
22
18.3
0.0460
0.0527
F
calcd, g cm-3
T, °C
µ(Mo KR), cm-1
Ra
Rw
b
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) [∑w(|Fo| - |Fc|)2/∑wFo ]1/2. w ) w′[1 - ((||Fo| - |Fc||)/6σ(Fo))2]2, where w′ ) 1/∑rArTr(X) with three coefficients
for a Chebyshev series (4.46, -1.37, and 2.91 for 1, 5.65, -0.712, and 4.28 for 2, 4.58, -1.61, and 3.47 for 3, and 4.39, -0.608, and 3.32 for 4) for which
X ) Fc/Fc(max).
2
complex PPh4[FeIII(bipy)(CN)4]‚H2O (1) and its derivatives
2. Zinc(II) nitrate hexahydrate (0.1 mmol, 30 mg) was used as the
[{FeIII(bipy)(CN)4}2MII(H2O)4]‚4H2O with M ) Mn (2) and
zinc source. Two types of crystals were obtained by slow evapora-
tion of the final solution containing a 1:1 Fe:Zn molar ratio: orange
needles of 3 as the main product (49 mg) and only a few red prisms
Zn (3) and [{FeIII(bipy)(CN)4}2ZnII]‚2H2O (4) [bipy ) 2,2′-
bipyridine and PPh4 ) tetraphenylphosphonium cation] and
of 4. The overall yield was about 60%. This relatively low yield
the investigation of the magnetic properties of 1-3.
compared to the parent manganese system is due to the formation
of an unidentified iron-zinc cyano polymer which is insoluble in
common solvents. The formula of complex 4 was determined by
X-ray diffraction on single crystals. Anal. Calcd for C28H32Fe2-
ZnN12O8 (3): C, 39.97; H,3.80; N, 19.97. Found: C, 39.85; H,
3.74; N, 19.83. IR stretching cyanide (KBr)/cm-1: 2167m and
2119m (3) and 2171m and 2157m (4).
Experimental Section
Materials. Chemicals were purchased from commercial sources
as reagents pure for analysis and used as received. K2[FeII(bipy)-
(CN)4]‚3H2O was prepared as described in the literature.27 Elemental
analysis (C, H, N) was performed by the Microanalitycal Service
of the Universidad Auto´noma de Madrid. The values of the Fe:P
(1), Fe:Mn (2), and Fe:Zn (3 and 4) molar ratios 1:1 (1), 2:1 (2),
and 2:1 (3 and 4) were determined by electron microscopy at the
Servei de Microscopia Electro`nica de la Universitat de Vale`ncia.
Syntheses. PPh4[FeIII(bipy)(CN)4]‚H2O (1). Chlorine gas was
bubbled through a warm dark red aqueous solution (200 mL) of
K2[FeII(bipy)(CN)4]‚3H2O (4 mmol, 1.80 g) for 1/2 h under
continuous stirring. A color change from red to orange was
observed. The addition of a concentrated warm aqueous solution
(20 mL) of tetraphenylphosphonium chloride (4 mmol, 1.50 g)
caused the precipitation of complex 1 as an orange solid. Recrys-
tallization in acetonitrile afforded X-ray-quality prismatic orange
crystals of 1. Yield: 2.15 g, 80%. Anal. Calcd for C38H30FeN6OP
(1): C, 67.80; H, 4.46; N, 12.45. Found: C, 67.63; H, 4.41; N,
12.50. IR stretching cyanide (KBr)/cm-1: 2118m.
[{FeIII(bipy)(CN)4}2MnII(H2O)4]‚4H2O (2). The slow addition
of solid lithium perchlorate (0.2 mmol, 22 mg) to an acetonitrile
solution (20 mL) of complex 1 (0.2 mmol, 135 mg) caused the
precipitation of Li[FeIII(bipy)(CN)4] as an orange crystalline solid.
The solid was dissolved in 20 mL of water, and the resulting orange
solution was mixed with an aqueous solution (20 mL) containing
manganese(II) nitrate tetrahydrate (0.1 mmol, 26 mg). Red platelike
crystals of 2 were separated from the resulting red solution by slow
evaporation at room temperature. The yield was practically
quantitative. Anal. Calcd for C28H32Fe2MnN12O8 (2): C, 40.47; H,
3.85; N, 20.22. Found: C, 40.21; H, 3.74; N, 20.3. IR stretching
cyanide (KBr)/cm-1: 2151m and 2117m.
Physical Measurements. The IR spectra of 1-4 (KBr pellets)
were recorded with a Bruker IF S55 spectrophotometer. Magnetic
susceptibility measurements on polycrystalline samples of 1-3 were
carried out with a Quantum Design SQUID magnetometer in the
temperature range 2.0-300 K and under an applied magnetic field
of 0.1 T. The magnetic study of complex 4 was not carried out
because of the very small amount of this complex that we obtained.
Diamagnetic corrections of the constituent atoms were estimated
from Pascal constants28 as -405 × 10-6 (1), -452 × 10-6 (2),
and -453 × 10-6 (3) cm3 mol-1
.
X-ray Data Collection and Structure Refinement. Crystals of
dimensions 0.04 × 0.20 × 0.32 (1), 0.20 × 0.32 × 0.65 (2),
0.10 × 0.20 × 0.80 (3), and 0.05 × 0.10 × 0.60 (4) mm were
mounted on an Enraf-Nonius CAD-4 diffractometer and used for
data collection. Diffraction data were collected at room temperature
by using graphite-monochromated Mo KR radiation (λ ) 0.71069
Å) with the ω-2θ method. Accurate cell dimensions and orientation
matrixes were obtained by least-squares refinements of 25 accurately
centered reflections with 8.0° < θ < 9.0° (1) and 12.0° < θ <
12.5° (2-4). No significant variations were observed in the
intensities of two checked reflections during data collections. The
data were corrected for Lorentz and polarization effects. An
empirical correction was performed by the use of DIFABS29
(1 and 2) or the ψ-scan curve (3 and 4). The maximum and
minimum transmission factors were 1 and 0.87 for 1, 1 and 0.95
for 2, 1 and 0.88 for 3, and 1 and 0.91 for 4. Information concerning
the crystallographic data collections and structure refinements is
summarized in Table 1. Of the 3511 (1), 3581 (2), 3923 (3), and
[{FeIII(bipy)(CN)4}2ZnII(H2O)4]‚4H2O (3) and [{FeIII(bipy)-
(CN)4}2ZnII]‚2H2O (4). The preparation of complexes 3 and 4 was
carried out using a procedure similar to that employed for complex
(28) Earnshaw, A. Introduction to Magnetochemistry; Academic Press:
London, 1968.
(27) Schilt, A. A. J. Am. Chem. Soc. 1960, 82, 3000.
820 Inorganic Chemistry, Vol. 41, No. 4, 2002
(29) Walker, N.; Stuart, D. Acta Crystallogr. 1983, A39, 156.

[Fe(bipy)(CN)4]- as a Versatile Building Block
Table 2. Selected Bond Lengths (Å) and Angles (deg)a,b for 1
Table 3. Selected Bond Lengths (Å) and Angles (deg)a,b for 2
Fe(1)-N(11)
Fe(1)-C(1)
Fe(1)-C(3)
C(1)-N(1)
C(3)-N(3)
1.98(2)
1.87(2)
1.90(2)
1.14(2)
1.17(2)
Fe(1)-N(12)
Fe(1)-C(2)
Fe(1)-C(4)
C(2)-N(2)
C(4)-N(4)
2.00(2)
1.89(3)
1.91(2)
1.16(3)
1.15(2)
Fe(1)-N(11)
Fe(1)-C(1)
Fe(1)-C(3)
Mn(1)-O(1)
Mn(1)-N(1)
C(2)-N(2)
C(4)-N(4)
1.971(5)
1.911(7)
1.960(7)
2.185(3)
2.183(6)
1.142(9)
1.124(9)
Fe(1)-N(12)
Fe(1)-C(2)
Fe(1)-C(4)
Mn(1)-O(2)
C(1)-N(1)
C(3)-N(3)
1.984(5)
1.911(7)
1.950(7)
2.212(7)
1.149(9)
1.126(8)
N(11)-Fe(1)-N(12)
N(12)-Fe(1)-C(1)
N(12)-Fe(1)-C(2)
N(11)-Fe(1)-C(3)
C(1)-Fe(1)-C(3)
N(11)-Fe(1)-C(4)
C(1)-Fe(1)-C(4)
C(3)-Fe(1)-C(4)
Fe(1)-C(2)-N(2)
Fe(1)-C(4)-N(4)
80.2(8)
N(11)-Fe(1)-C(1)
N(11)-Fe(1)-C(2)
C(1)-Fe(1)-C(2)
N(12)-Fe(1)-C(3)
C(1)-Fe(1)-C(2)
N(12)-Fe(1)-C(4)
C(2)-Fe(1)-C(4)
Fe(1)-C(1)-N(1)
Fe(1)-C(3)-N(3)
96.4(9)
176.3(9)
96.1(10)
90.8(8)
86.6(9)
89.8(8)
90.3(10)
176.9(10)
172.6(23)
177.2(20)
176.2(9)
87.3(10)
92.1(8)
88.8(9)
91.0(9)
90.8(10)
174.9(22)
174.4(20)
N(11)-Fe(1)-N(12)
N(12)-Fe(1)-C(1)
N(12)-Fe(1)-C(2)
N(11)-Fe(1)-C(3)
C(1)-Fe(1)-C(3)
N(11)-Fe(1)-C(4)
C(1)-Fe(1)-C(4)
C(3)-Fe(1)-C(4)
Fe(1)-C(2)-N(2)
Fe(1)-C(4)-N(4)
O(1)-Mn(1)-O(2a)
O(1)-Mn(1)-N(1a)
O(2)-Mn(1)-N(1a)
81.2(2)
178.6(2)
96.7(3)
90.2(2)
91.3(3)
90.7(2)
89.8(3)
178.5(3)
177.6(8)
177.8(6)
87.7(3)
92.0(2)
88.1(3)
N(11)-Fe(1)-C(1)
N(11)-Fe(1)-C(2)
C(1)-Fe(1)-C(2)
N(12)-Fe(1)-C(3)
C(2)-Fe(1)-C(3)
N(12)-Fe(1)-C(4)
C(2)-Fe(1)-C(4)
Fe(1)-C(1)-N(1)
Fe(1)-C(3)-N(3)
O(1)-Mn(1)-O(2)
O(1)-Mn(1)-N(1)
O(2)-Mn(1)-N(1)
Mn(1)-N(1)-C(1)
97.5(2)
177.6(3)
84.6(3)
88.4(2)
88.5(3)
90.6(2)
90.6(3)
174.2(6)
177.2(6)
92.3(3)
88.0(2)
91.9(3)
159.5(6)
Hydrogen Bonds
2.981(28)
O(1)‚‚‚N(1a)
O(1)‚‚‚N(2b)
2.835(27)
a Estimated standard deviations in the last significant digits are given
in parentheses. b Symmetry code: (a) 1 + x, 1/2 - y, 1/2 + z; (b) 1 +
x, y, 1 + z.
Hydrogen Bonds
O(1)‚‚‚O(11)
O(2)‚‚‚O(10)
O(10)‚‚‚N(4d)
2.415(23)
2.769(9)
2.795(9)
O(1)‚‚‚N(2b)
O(10)‚‚‚N(3c)
O(10)‚‚‚O(11)
2.779(9)
2.869(8)
2.921(20)
5851 (4) measured reflections in the θ ranges 1-20° (1) and
1-25° (2-4) with index ranges 0 e h e 11, 0 e k e 19, and
-13 e l e +13 (1), 0 e h e 7, 0 e k e 22, and -16 e l e +16
(2), 0 e h e 8, 0 e k e 23, and -17 e l e +17 (3), and
0 e h e 23, 0 e k e 8, and -24 e l e +24 (4), 3182 (1), 3167
(2), 3479 (3), and 5219 (4) were unique. From these, 955 (1), 1799
(2) 1635 (3), and 2825 (4) were observed [I > 2σ(I) (1) and
I > 3σ(I) (2-4)] and used for the refinement of the structures.
The structures were solved by direct methods through SHELX-
8630 and subsequently refined by Fourier recycling. For 1, all atoms
were isotropically refined and the phenyl rings were refined as rigid
bodies. All non-hydrogen atoms for 2-4 were refined anisotropi-
cally. All hydrogen atoms (except those of the water molecules)
were introduced in calculated positions and were allocated one
overall isotropic thermal parameter. The final full-matrix least-
squares refinement on F through the PC version of CRYSTALS31
reached convergence with values of the R and Rw indices listed in
Table 1, the number of variables being 142 (1), 233 (2 and 3), and
407 (4). The residual maxima and minima in the final Fourier
difference maps were 0.41 and 0.49 e Å-3 for 1, 0.94 and -0.63
e Å-3 for 2, 0.62 and -0.36 e Å-3 for 3, and 0.99 and -0.73 e
Å-3 for 4. The values of the goodness-of-fit were 1.11 (1), 1.13
(2 and 4), and 1.14 (3). Selected interatomic bond distances and
angles are given in Tables 2 (1), 3 (2), 4 (3), and 5 (4).
a Estimated standard deviations in the last significant digits are given
in parentheses. b Symmetry code: (a) -x, -y, -z; (b) 1 - x, -y, -z;
(c) -1/2 + x, -1/2 - y, -1/2 + z; (d) -1 + x, y, z.
Table 4. Selected Bond Lengths (Å) and Angles (deg)a,b for 3
Fe(1)-N(11)
Fe(1)-C(1)
Fe(1)-C(3)
Zn(1)-O(1)
Zn(1)-N(1)
C(2)-N(2)
C(4)-N(4)
1.976(5)
1.913(7)
1.948(7)
2.097(5)
2.082(5)
1.145(8)
1.131(8)
Fe(1)-N(12)
Fe(1)-C(2)
Fe(1)-C(4)
Zn(1)-O(2)
C(1)-N(1)
C(3)-N(3)
1.980(5)
1.909(6)
1.929(7)
2.169(5)
1.132(9)
1.124(8)
N(11)-Fe(1)-N(12)
N(12)-Fe(1)-C(1)
N(12)-Fe(1)-C(2)
N(11)-Fe(1)-C(3)
C(1)-Fe(1)-C(3)
N(11)-Fe(1)-C(4)
C(1)-Fe(1)-C(4)
C(3)-Fe(1)-C(4)
Fe(1)-C(2)-N(2)
Fe(1)-C(4)-N(4)
O(1)-Zn(1)-O(2a)
O(1)-Zn(1)-N(1a)
O(2)-Zn(1)-N(1a)
81.2(2)
179.6(2)
95.9(2)
90.8(2)
91.4(3)
89.9(2)
90.0(3)
178.3(3)
178.2(6)
178.6(6)
86.3(2)
92.4(2)
87.7(2)
N(11)-Fe(1)-C(1)
N(11)-Fe(1)-C(2)
C(1)-Fe(1)-C(2)
N(12)-Fe(1)-C(3)
C(2)-Fe(1)-C(3)
N(12)-Fe(1)-C(4)
C(2)-Fe(1)-C(4)
Fe(1)-C(1)-N(1)
Fe(1)-C(3)-N(3)
O(1)-Zn(1)-O(2)
O(1)-Zn(1)-N(1)
O(2)-Zn(1)-N(1)
Zn(1)-N(1)-C(1)
98.6(2)
177.1(2)
84.3(3)
88.2(2)
88.7(3)
90.4(2)
90.4(3)
175.5(6)
176.6(5)
93.7(2)
87.6(2)
92.3(2)
159.0(6)
Hydrogen Bonds
O(1)‚‚‚O(11)
O(2)‚‚‚O(10)
O(10)‚‚‚N(4d)
2.682(8)
2.846(7)
2.779(8)
O(1)‚‚‚N(2)
2.811(8)
2.875(8)
2.785(8)
Results and Discussion
O(10)‚‚‚N(3c)
O(10)‚‚‚O(11)
Description of the Structures. PPh4[FeIII(bipy)(CN)4]‚
H2O (1). The structure of compound 1 consists of mono-
nuclear [Fe(bipy)(CN)4]- anions (Figure 1), tetraphenylphos-
phonium cations, and water molecules of crystallization
which are linked by electrostatic forces, hydrogen bonds,
and van der Waals interactions.
Each iron(III) cation is coordinated by two bipy nitrogen
atoms and four cyanide carbon atoms, taking a distorted
octahedral geometry. The short bite of chelating bipy [80.2-
a Estimated standard deviations in the last significant digits are given
in parentheses. b Symmetry code: (a) -x, -y, -z; (b) 1 - x, -y, -z;
(c) -1/2 + x, -1/2 - y, -1/2 + z; (d) -1 + x, y, z.
(8)° for N(11)-Fe(1)-N(12)] is one of the main factors
accounting for this distortion. The values of the Fe(1)-
N(bipy) bonds in 1 [1.98(2) and 2.00(2) Å] are the same as
those found in the low-spin iron(II) K2[FeII(bipy)(CN)4]‚
2.5H2O [1.987(4)-2.003(4) Å]32 and iron(III) [FeIII(bipy)2-
(CN)2]ClO4 [1.954(4)-1.993(5) Å]33 complexes. Good agree-
ment is observed between the Fe(1)-C(cyano) bond distances
(30) (a) Sheldrick, G. M. SHELX-86: Program for Crystal Structure
Solution; University of Go¨ttingen: Go¨ttingen, Germany, 1986. (b)
Watkin, D. J.; Prout, C. K.; Pearce, L. J. C. Crystallography
Laboratory, University of Oxford, Oxford, U.K., 1996.
(31) Watkin, D. J.; Prout, C. K.; Carruthers, J. R.; Betteidge, P. W.
CRYSTALS; Chemical Crystallography Laboratory, University of
Oxford: Oxford, U.K., 1996; Issue 10.
(32) Nieuwenhuyzen, M.; Bertram, B.; Gallagher, J. F.; Vos, J. G. Acta
Crystallogr. 1998, C54, 603.
(33) Lu, T.-H.; Kao, H.-Y.; Wu, D. I.; Kong, K. C.; Cheng, C. H. Acta
Crystallogr. 1988, C44, 1184.
Inorganic Chemistry, Vol. 41, No. 4, 2002 821

Lescoue1zec et al.
Table 5. Selected Bond Lengths (Å) and Angles (deg)a,b for 4
cation in the structure and the magnetic moment of 1 (see
below) unambiguously reveal a low-spin iron(III) species.
The cyanide stretching frequency in the infrared spectrum
of 1, which appears as a medium-intensity peak at 2118 cm-1
(single peak at 2120 cm-1 for PPh4[FeIII(phen)(CN)4]‚2H2O
and [Fe(bipy)2(CN)2]ClO4) provides additional evidence of
this low-spin iron(III) character.
Fe(1)-N(11)
Fe(1)-C(1)
Fe(1)-C(4)
Fe(2)-N(21)
Fe(2)-C(2)
Fe(2)-C(7)
Zn(1)-N(1)
Zn(1)-N(3b)
Zn(1)-N(8d)
C(2)-N(2)
C(4)-N(4)
C(6)-N(6)
C(8)-N(8)
1.974(5)
1.882(7)
1.896(7)
1.974(5)
1.908(6)
1.930(6)
2.121(6)
2.074(6)
2.048(6)
1.135(8)
1.152(8)
1.130(8)
1.133(8)
Fe(1)-N(12)
Fe(1)-C(3)
Fe(1)-C(5)
Fe(2)-N(22)
Fe(2)-C(6)
Fe(2)-C(8)
Zn(1)-N(2)
Zn(1)-N(6c)
C(1)-N(1)
C(3)-N(3)
C(5)-N(5)
C(7)-N(7)
1.976(5)
1.950(7)
1.932(7)
1.977(5)
1.950(6)
1.911(7)
1.997(5)
2.113(5)
1.150(8)
1.135(8)
1.134(8)
1.141(8)
The bipy ligand as a whole is close to planarity, the
dihedral angle between the two planar pyridyl rings being
ca. 5°. Bond lengths and angles within the bipy ligand are
in agreement with those reported for the free bipy molecule.35
The C(1)C(2)N(11)N(12)Fe(1) set of atoms defining a five-
membered chelate at the metal atom is coplanar, the largest
deviation from their mean plane being 0.0016 Å at the iron
atom. Although the separation between the mean planes of
two bipy ligands from adjacent [Fe(bipy)(CN)4]- units is ca.
3.5 Å, they are so slipped that no graphitic-like interaction
may be considered. The bond lengths and angles involving
the cyanide ligands compare well with those found in other
cyano-containing low-spin mononuclear iron(III) com-
plexes.26,33,36 The iron atom and each cyanide are almost in
a line [values for Fe-C-N ranging from 172.6(23)° to
177.2(20)°]. The bulky tetraphenylphosphonium cation ex-
hibits the expected tetrahedral shape, and its bond lengths
and angles are as expected. Interestingly, the PPh4+ cations
are grouped by pairs exhibiting the sextuple phenyl embrace
type interaction37 with an intrapair P‚‚‚P distance of ca. 6.20
Å. Regular alternating layers of PPh4+ cations and [Fe(bipy)-
(CN)4]- anions occur in the unit cell (Figure S1 in the
Supporting Information). In addition, two of the four cyanide
groups and the water molecule are involved in hydrogen-
bonding interactions with donor-acceptor distances of less
than 3.0 Å (see the end of Table 2), leading to a chain of
water-linked [Fe(bipy)(CN)4]- units along the z axis (Figure
S2). The shortest intermolecular iron-iron separation is
7.840(6) Å [Fe(1)‚‚‚Fe(1c); (c) 1 - x, -y, -z].
N(11)-Fe(1)-N(12)
N(12)-Fe(1)-C(1)
N(12)-Fe(1)-C(3)
N(11)-Fe(1)-C(4)
C(1)-Fe(1)-C(4)
N(11)-Fe(1)-C(5)
C(1)-Fe(1)-C(5)
C(4)-Fe(1)-C(5)
N(21)-Fe(2)-C(2)
N(21)-Fe(2)-C(6)
C(2)-Fe(2)-C(6)
N(22)-Fe(2)-C(7)
C(6)-Fe(2)-C(7)
N(22)-Fe(2)-C(8)
C(6)-Fe(2)-C(8)
Fe(1)-N(11)-C(11)
Fe(1)-N(12)-C(16)
Fe(2)-N(21)-C(21)
Fe(2)-N(22)-C(26)
Fe(1)-C(1)-N(1)
Fe(1)-C(3)-N(3)
Fe(1)-C(5)-N(5)
Fe(2)-C(7)-N(7)
N(1)-Zn(1)-N(2)
N(2)-Zn(1)-N(3b)
N(2)-Zn(1)-N(6c)
N(1)-Zn(1)-N(8d)
N(3b)-Zn(1)-N(8d)
Zn(1)-N(1)-C(1)
Zn(1e)-N(3)-C(3)
Zn(1b)-N(8)-C(8)
80.8(2)
172.0(2)
96.6(2)
176.6(3)
86.5(3)
90.4(2)
85.2(3)
89.4(3)
177.3(2)
90.1(2)
89.4(3)
86.9(2)
175.7(3)
171.2(2)
90.7(2)
124.5(5)
114.2(5)
126.2(4)
113.8(4)
175.4(6)
174.7(6)
178.4(6)
179.2(6)
99.9(2)
107.3(2)
98.9(2)
84.2(2)
147.2(2)
154.3(6)
173.9(5)
173.2(6)
N(11)-Fe(1)-C(1)
N(11)-Fe(1)-C(3)
C(1)-Fe(1)-C(3)
N(12)-Fe(1)-C(4)
C(3)-Fe(1)-C(4)
N(12)-Fe(1)-C(5)
C(3)-Fe(1)-C(5)
N(21)-Fe(2)-N(22)
N(22)-Fe(2)-C(2)
N(22)-Fe(2)-C(6)
N(21)-Fe(2)-C(7)
C(2)-Fe(2)-C(7)
N(21)-Fe(2)-C(8)
C(2)-Fe(2)-C(8)
C(7)-Fe(2)-C(8)
Fe(1)-N(11)-C(15)
Fe(1)-N(12)-C(20)
Fe(2)-N(21)-C(25)
Fe(2)-N(22)-C(30)
Fe(2)-C(2)-N(2)
Fe(1)-C(4)-N(4)
Fe(2)-C(6)-N(6)
Fe(2)-C(8)-N(8)
N(1)-Zn(1)-N(3b)
N(1)-Zn(1)-N(6c)
N(3b)-Zn(1)-N(6c)
N(2)-Zn(1)-N(8d)
N(6c)-Zn(1)-N(8d)
Zn(1)-N(2)-C(2)
Zn(1d)-N(6)-C(6)
96.9(3)
91.9(2)
91.2(3)
95.9(3)
88.5(3)
87.2(2)
175.9(3)
81.0(2)
96.4(2)
97.4(2)
90.7(2)
90.0(3)
95.6(2)
87.0(3)
85.0(3)
114.8(4)
126.8(5)
114.4(4)
125.5(4)
178.8(5)
178.6(7)
175.1(6)
175.0(6)
89.3(2)
161.0(2)
87.6(2)
105.5(2)
88.3(2)
172.7(5)
173.0(5)
a Estimated standard deviations in the last significant digits are given
in parentheses. b Symmetry code: (b) x, -1 + y, z; (c) 1/2 - x,
-1/2 + y, 1/2 - z; (d) 1/2 - x, 1/2 + y, 1/2 - z; (e) x, 1 + y, z.
[{FeIII(bipy)(CN)4}2MII(H2O)4]‚4H2O (M ) Mn (2) and
Zn (3)). 2 and 3 are isostructural compounds whose structure
is made up of centrosymmetric neutral trinuclear entities of
formula [{FeIII(bipy)(CN)4}2MII(H2O)4] where the [Fe-
(phen)(CN)4]- unit acts as a monodentate ligand through one
of its four cyanide groups toward a central [M(H2O)4]2+ motif
with M ) Mn (1) and Zn (3) (Figure 2). Four water
molecules of crystallization contribute to the stabilization of
the lattice by hydrogen-bonding interactions which involve
the coordinated water molecules and three of the four cyanide
groups (see the end of Tables 3 and 4).
As in 1, each iron atom in 2 and 3 is coordinated by two
bipy nitrogen atoms and four cyanide carbon atoms, in a
distorted octahedral geometry. The values of the Fe-N(bipy)
bonds and that of the angle subtended at the iron atom by
the chelating bipy are very close to those found in 1. The
Fe(1)-C bond lengths in 2 and 3 are equal within error to
those found in 1. The values of the two Fe-C(cyano) bonds
Figure 1. Perspective drawing of the mononuclear [Fe(bipy)(CN)4]- unit
of complex 1 showing the atom numbering. Thermal ellipsoids are drawn
at the 30% probability level.
of 1 [1.87(2)-1.91(2) Å] and those reported for other cyano-
containing mononuclear low-spin iron(III) [1.906(8)-1.95-
(1) Å]26,33 and iron(II) [1.891(5)-1.936(5) Å]32,34 complexes.
Nevertheless, the occurrence of the tetraphenylphosphonium
(35) Merrit, L. L.; Schroeder, E. D. Acta Crystallogr. 1956, 9, 801.
(36) Vannerberg, N. G. Acta Chem. Scand. 1972, 26, 2863.
(37) Dance, I.; Scudder, M. Chem.sEur. J. 1996, 2, 481 and references
therein.
(34) Zhan, S.; Meng, Q.; You, X.; Wang, G.; Zheng, P. J. Polyhedron 1996,
15, 2665.
822 Inorganic Chemistry, Vol. 41, No. 4, 2002

[Fe(bipy)(CN)4]- as a Versatile Building Block
Figure 2. Perspective drawing of the structure of the trinuclear species
[{FeIII(bipy)(CN)4}2MII(H2O)4]‚4H2O (M ) Mn (2) and Zn (3)) along with
the atom numbering. Thermal ellipsoids are drawn at the 30% probability
level. Hydrogen bonds between the water molecules are illustrated by broken
lines.
Figure 3. Perspective drawing of the crystallographically independent unit
of 4 showing the cyanide bridges and the atom numbering. Thermal
ellipsoids are drawn at the 30% probability level.
The values of the intramolecular Fe(1)‚‚‚M separation
through bridging cyanide are 5.126(1) Å [Fe(1)‚‚‚Mn(1)] and
5.018(1) Å [Fe(1)‚‚‚Zn(1)], whereas the shortest intermo-
lecular metal-metal distances are 6.620(1) Å (2) and 6.499-
(1) Å (3) [Fe(1)‚‚‚Fe(1d) and Fe(1)‚‚‚Fe(1e); (e) -1 + x, y,
z], 8.601(2) Å (2) and 8.697(2) Å (3) [Fe(1)‚‚‚Fe(1f);
(f) -x, -y, 1 - z], and 8.654(2) Å (2) and 8.756(2) Å (3)]
[Fe(1)‚‚‚Fe(1g); (g) 1 - x, -y, -1 - z].
corresponding to the cyano groups coordinated in trans
positions to each other are slightly longer than those in the
cis-coordinated ones. The Fe-C-N angles for both terminal
(177.2(6)-177.8(6)° in 2 and 176.6(5)-178.6(6)° in 3) and
bridging (174.2(6)° in 1 and 175.5(6)° in 3) cyanide groups
are somewhat bent, their deviations from strict linearity
comparing well with those observed in the parent bimetallic
double chains [{FeIII(phen)(CN)4}2MII(H2O)2]‚4H2O (M )
Mn and Zn).26 The manganese (2) and zinc (3) atoms are
hexacoordinated with two cyanide nitrogen atoms in trans
positions and four water molecules, building a distorted
MN2O4 octahedral surrounding. The values of the angle
M-N(1)-C(1) [159.5(6)° (M ) Mn) and 150.0(6)° (M )
Zn)] depart significantlty from 180°. The occurrence of two
peaks of medium intensity in the CN stretching region of
the IR spectra of 2 and 3 is consistent with the presence of
bridging and terminal cyanide ligands.
The chelating bipy ligand is quasi-planar, the dihedral
angle between the planes of its two pyridyl rings being ca.
4° (2) and 5° (3). The five-membered chelate Fe(1)N(11)C-
(15)C(16)N(12) is practically planar [the largest deviation
from the mean plane is 0.014 Å (2) and 0.007 Å (3) for
Fe(1)]. The trinuclear units of 2 and 3 in the unit cell are
well isolated from each other (Figure S3). Although the
shortest intermolecular bipy-bipy contact is ca. 3.52 Å (2)
and 3.51 Å (3) along the x axis (Figure S4), a weak overlap
between the bipy mean planes occurs because of their large
slipping.
[{FeIII(bipy)(CN)4}2ZnII]‚2H2O (4). The structure of
complex 4 is made up of neutral one-dimensional [{FeIII-
(bipy)(CN)4}2ZnII] units running parallel to the b axis and
crystallization water molecules which are held together by
van der Waals interactions. The crystallographically inde-
pendent unit contains two types of iron atoms (Fe(1) and
Fe(2)) and one zinc atom (Zn(1)) (see Figure 3), the latter
being connected to five iron atoms through cyanide bridges.
The [{FeIII(bipy)(CN)4}2ZnII] motif (see Figure 4) builds a
corrugated ladder-like chain with regular alternating Fe(2)
and Zn(1) atoms along the edges, each rung being defined
by an iron-zinc pair. In addition, each pair of adjacent zinc
atoms are connected through another iron atom (Fe(1)). A
single cyano group bridges each iron-zinc pair.
The two crystallographically independent iron atoms (Fe(1)
and Fe(2)) exhibit the same distorted octahedral FeN2C4
surrounding observed in 1-3. The difference between
[Fe(1)(bipy)(CN)4]- and [Fe(2)(bipy)(CN)4]- is that the
former acts as a bismonodentate ligand toward the zinc atoms
through two (cis positions) of its four cyanide groups,
whereas the latter adopts a trismonodentate coordination
Inorganic Chemistry, Vol. 41, No. 4, 2002 823

Lescoue1zec et al.
Chart 1
Figure 4. A view of a fragment of the structure of 4 along the b axis.
The metal atoms are represented as orange (Fe) and blue (Zn) circles, and
the crystallization water molecules have been omitted for clarity.
mode (three cyanides in fac positions), only one of its four
cyanide groups being terminal. As in 1-3, the values of the
two Fe-C(cyano) bonds corresponding to the two trans-
coordinated cyano groups at the Fe(1) and Fe(2) atoms are
significantly longer than those in the cis-coordinated ones.
The Fe-C-N angles for both terminal [178.4(6)° and 178.6-
(7)° (Fe(1)) and 179.2(6)° (Fe(2))] and bridging [174.7(6)°
and 175.4(6)° (Fe(1)) and 175.0(6)°, 175.1(6)°, and 178.8-
(5)° (Fe(2))] cyanide groups are bent. The zinc atom is
pentacoordinated with five cyanide nitrogen atoms, forming
a severely distorted ZnN5 square pyramid. The deviations
from the mean basal plane are (0.12 Å, the zinc atom being
shifted by 0.46 Å from this mean plane toward the apical
N(2) atom. All the values of the Zn-N-C bond depart from
linearity, but whereas four of them vary in a narrow range
somewhat below 180° [172.7(5)-173.9(5) Å], the remaining
one is highly bent [154.3(6)° for Zn(1)-N(1)-C(1)]. The
C-N bond lengths for terminal and bridging C-N ligands
are in agreement with those observed in 3. The IR spectrum
of 4 provides spectral evidence of the occurrence of bridging
(doublet at 2171 and 2157 cm-1) and terminal (single peak
at 2124 cm-1) cyanide ligands.
The dihedral angle between the planes of the two pyridyl
rings of the bipy group coordinated to Fe(1) is ca. 2° (7° in
that bound to Fe(2)). The five-membered chelates Fe(1)N-
(11)C(15)C(16)N(12) and Fe(2)N(21)C(25)C(26)N(22) are
quasi-planar, the largest deviation from the mean planes
being 0.07 Å at Fe(1). The large separation (7.24 Å) between
the parallel quasi-eclipsed bipy ligands along the b axis
precludes any significant intrachain π-π interaction (Figure
4). Weak interchain bipy-bipy contacts are observed, the
separation between the significantly slipped bipy ligands of
neighboring [Fe(bipy)(CN)4]- units being 3.8 Å (Figure S5).
The value of the dihedral angle between adjacent mean
planes of the corrugated ladder-like motif is 90° (angle at
the Fe(2)‚‚‚Zn(1) hinge in Chart 1), whereas those between
the Fe(1)Zn(1e)Zn(1)Fe(2d) mean plane and Fe(2d)Zn(1d)-
Fe(2)Zn(1) and Fe(2e)Zn(1e)Fe(2d)Zn(1d) mean planes are
99° and 80°. The values of the iron-zinc distances though
bridging cyanide are 5.013(1) [Fe(1)‚‚‚Zn(1)], 5.142(1)
[Fe(1)‚‚‚Zn(1e)], 5.028(1) [Fe(2)‚‚‚Zn(1)], 5.076(1) [Fe(2)‚‚‚
Zn(1c)], and 5.176(1) Å [Fe(2)‚‚‚Zn(1d)]. The remaining
intrachain iron-iron and zinc-zinc separations are 7.242-
(1) [Fe(1)‚‚‚Fe(1b), Fe(2)‚‚‚Fe(2b) and Zn(1)‚‚‚Zn(1e)],
6.662(1) [Fe(1)‚‚‚Fe(2d)], 8.468(1) [Fe(1)‚‚‚Fe(2)], 8.485-
(1) [Fe(1)‚‚‚Fe(2e)], 7.546(1) [Fe(2)‚‚‚Fe(2d)], and 6.795-
(1) Å [Zn(1)‚‚‚Zn(1d)].
Magnetic Properties of 1-3. The temperature depen-
dence of the øMT product for complexes 1 and 3 (øM being
the magnetic susceptibility per mole of Fe(III)) is shown in
Figure 5. øMT for 1 monotonically decreases from 0.71 cm3
mol-1 K at room temperature to 0.53 cm3 mol-1 K at 1.9 K.
The value of µeff (ca. 2.38 µB) at room temperature for 1
agrees with those previously reported for other low-spin iron-
(III) complexes.38 It is clearly above the spin-only value for
an isolated low-spin iron(III) center (0.375 cm3 mol-1 K for
S ) 1/2 assuming gFe ) 2.0) because of the presence of a
significant orbital contribution. The variation of øMT versus
T for 1 is characteristic of a low-spin octahedral iron(III)
system with spin-orbit coupling of the 2T2g ground term.39-41
The significant distortion of the iron(III) environment in 1
(roughly C2V symmetry around the metal atom) caused by
the presence of one bidentate bipy ligand and four terminal
cyanide ligands is not enough to totally quench the orbital
contribution of the ground state. The øMT versus T plot for
3 matches that of 1 from room temperature to 25 K, as
expected due to the fact that the same low-spin iron(III)
complex occurs in 1 and 3. Then, in the low-temperature
range, øMT for 3 slightly decreases and attains a value of
0.42 cm3 mol-1 K at 1.9 K. Weak intra- and/or intermolecular
antiferromagnetic interactions between the low-spin iron-
(38) Casey, A. T.; Mitra, S. In Theory and Applications of Molecular
Paramagnetism; Boudreaux, E. A., Mulay, L. N., Eds.; John Wiley
and Sons: New York, 1976; Chapter 3, p 191.
(39) Pavlishchuk, V. V.; Koval, I. A.; Goreshnik, E.; Addison, A. W.; van
Albada, G. A.; Reedijk, J. Eur. J. Inorg. Chem. 2001, 297.
(40) Patra, A. K.; Ray, M.; Mukherjee, R. Inorg. Chem. 2000, 39, 652.
(41) Ray, M.; Mukherjee, R.; Richardson, J. F.; Buchanan, R. M. J. Chem.
Soc., Dalton Trans. 1993, 2451.
824 Inorganic Chemistry, Vol. 41, No. 4, 2002

[Fe(bipy)(CN)4]- as a Versatile Building Block
with the presence of a high-spin Mn(II) atom and two low-
spin Fe(III) atoms magnetically isolated. As the temperature
is lowered, the øMT product continuously decreases at it
reaches a value of 3.20 cm3 mol-1 K at 1.9 K. This value is
clearly below that of a magnetically isolated spin sextet
(4.375 cm3 mol-1 K for S ) 5/2 with g ) 2.0), indicating
that a significant antiferromagnetic interaction between the
Mn(II) and Fe(III) occurs. This is well visualized in the inset
of Figure 6, where we have plotted the difference between
the øMT data of 2 and twice those of 1 plus a Curie law
term per two noninteracting spin doublets with g ) 2.0. As
done for complex 3 and for lack of a better approach, we
analyzed the magnetic data of the inset of Figure 6 through
the isotropic Hamiltonian (eq 1),
Figure 5. Thermal dependence of the øMT product for complexes 1 (O)
and 3 (4). The inset shows the corrected øMT versus T plot for 3 in the
low-temperature region (see the text).
Hˆ ) -J[SˆFe1‚SˆMn + SˆFe2‚SˆMn] - jSˆFe1‚SˆFe2
(1)
where J and j are the intramolecular exchange coupling
parameters between adjacent and peripheral spin carriers,
respectively. A common value of 2.0 was fixed for gMn, gFe1
,
and gFe2. Least-squares fit (solid line in the inset of Figure
6) leads to the following set of parameters: J ) -0.87 cm-1,
j ) -1.3 cm-1, and R ) 4.9 × 10-5. The fitted values of J
and j are correlated. Variations in j slightly affect the J values.
A fit obtained with a fixed j value at 0 cm-1 results in J )
-0.9 cm-1 with a similar quality of fit.
Several points concerning the nature and magnitude of the
computed exchange couplings in 2 and 3 deserve to be
commented on. First, the values must be considered with
caution because of the crude approach used to estimate them.
As they are the first ones to be reported, any comparison is
precluded. More experimental data are needed to substantiate
them and to establish their dependence on relevant structural
parameters such as the bond lengths and the bending at the
bridging cyanide. Second, the antiferromagnetic coupling
between high-spin Mn(II) and low-spin Fe(III) through
bridging cyanide in 2 results from a net overlap of the
Figure 6. Thermal dependence of the øMT product for complex 2 (O).
The inset shows the corrected øMT versus T plot for 2 (see the text).
(III) centers in 3 would account for this decrease. Given that
the trimeric units of 3 are well isolated from each other (the
shortest intermolecular iron-iron separation is ca. 6.5 Å),
the small antiferromagnetic coupling observed would most
likely involve the intramolecular Fe(1)-CN-Zn(1)-NC-
Fe(1a) exchange pathway. To get a rough estimate of this
antiferromagnetic coupling, we have subtracted first the øMT
data from 1 from those of 3 (for two iron atoms). Then, 0.75
cm3 mol-1 K (Curie law term per two noninteracting spin
doublets with g ) 2.0) was added to the difference data.
The corrected øMT data for T < 100 K are shown in the
inset of Figure 5. The procedure is expected to rule out the
orbital contribution to the magnetic behavior of 3, and to
allow the analysis through a spin-only formalism. The
corrected øMT data of 3 were treated by the isotropic
Hamiltonian Hˆ ) -JSˆFe1‚SˆFe2, which corresponds to a low-
spin iron(III) dimer (two interacting local spin doublets with
gFe1 ) gFe2 ) 2.0) with J as the exchange coupling parameter.
Least-squares fit (solid line in the inset of Figure 5) leads
to J ) -1.3 cm-1 with R ) 1.4 × 10-4 (R is the agree-
ment factor defined as ∑i[(øMT)obsd(i) - (øMT)calcd(i)]2/
[(øMT)obsd(i)]2). This small exchange coupling is obtained
through a crude approximation and can be considered as an
upper limit of the intramolecular antiferromagnetic coupling.
The temperature dependence of the øMT product for
complex 2 (øM being the magnetic susceptibility per Fe2Mn
unit) is shown in Figure 6. The value of øMT at room
temperature is 5.70 cm3 mol-1 K. This value is consistent
2
magnetic orbitals through the π t2g-t2g pathway (t2g3eg and
0
t2g5eg configurations for Mn(II) and Fe(III), respectively).
Two exchange pathways are particularly efficient, the xz and
yz ones, if one defines the z axis along Fe-Mn. The same π
t
2g-t2g exchange pathway is operative in 3 with only one
magnetic orbital per center and leads to an antiferromagnetic
coupling (ca. -1.3 cm-1) through the diamagnetic -CN-
Zn-CN- bridging skeleton. In both cases, the weak π
overlap leads to a small interaction. Third, it is satisfying to
find good agreement between the exchange couplings
between the peripheral low-spin iron(III) centers in the
isostructural trinuclear units of 2 and 3. Fourth, at first sight
it seems surprising that j is larger than J in 3, the separation
between the interacting spins in the former being double that
in the latter. This can be understood when taking into account
the different numbers of unpaired electrons (nM) of the
interacting centers (five versus one in J and one versus one
in j). In fact, the coupling energies to be compared43 are
nMnnFeJ () 5J ) -4.5 cm-1) versus nFenFej () j ) -1.3
cm-1).
(42) Martin, L. L.; Martin, R. L.; Murray, K. S.; Sargeson, A. M. Inorg.
Chem. 1990, 29, 1387.
Inorganic Chemistry, Vol. 41, No. 4, 2002 825

Lescoue1zec et al.
Let us finish with a brief comment on different products
obtained when using [FeL(CN)4]- (L ) bipy and phen) as a
complex toward Mn(II) and Zn(II) (M) ions. In a previous
work with the phen-containing precursor, we obtained neutral
bimetallic Fe2M double chains,26 whereas here, using the bipy
derivative, we only obtained the neutral heterotrinuclear
Fe2M compounds and also an unprecedented Fe2Zn ladder-
like compound. Most likely, the insolubility of the neutral
trinuclear complexes 2 and 3 would preclude the formation
of the double chains observed in the phen case, which require
the assembling of the trinuclear units through additional
cyano bridges.
In summary, the main results of the present work are the
following: (i) a new anionic building block containing
cyanide and bipy as ligands has been characterized (complex
1); (ii) its use as a ligand toward first-row transition-metal
ions has been explored, allowing the preparation of the first
cyano-bridged trinuclear FeIII2MII species (M ) Mn (2) and
Zn (3)) and an unprecedented corrugated ladder-like FeIII2ZnII
compound (4); (iii) weak but significant antiferromagnetic
interactions between Fe(III) and Mn(II) through bridging
cyanide (2) and between terminal Fe(III) ions through the
-CN-M(II)-NC- pathway [M ) Mn (2) and Zn (3)] are
observed and evaluated.
Safety Note. Perchlorate complexes are potentially ex-
plosive, and every attempt should be made to substitute
anions such as the fluorosulfonates for the perchlorates. We
used in our syntheses only small amounts of material, and
the perchlorate-containing solids were never heated. The
dilute solutions were handled with care and evaporated
slowly in an open hood (cf. ref 44).
Acknowledgment. This work was supported by the TMR
Program from the European Union (Contract ERBFM-
RXCT98-0181), the Spanish Direccio´n General de Investi-
gacio´n Cient´ıfica y Te´cnica (DGICYT) (Project PB97-1397),
and the European Science Foundation through the Molecular
Magnets Programme.
Supporting Information Available: Figures S1-S5 (crystal
packing of 1, hydrogen-bonding pattern in 1, crystal packing of 2,
bipy-bipy overlap in 2, and projection of the neutral chains of 4
down the b axis) and X-ray crystallographic files in CIF format
for complexes 1-4. This material is available free of charge via
the Internet at http://pubs.acs.org.
IC0107882
(44) J. Chem. Educ. 1973, 50, A335; 1985, 62, 1001. Chem. Eng. News
1983, 61 (Dec 5), 4; 1963, 41 (July 8), 47.
(43) Kahn, O. Struct. Bonding (Berlin) 1987, 68, 89.
826 Inorganic Chemistry, Vol. 41, No. 4, 2002