Synthesis of the first heterometalic star-shaped oxido-bridged MnCu 3 complex and its conversion into trinuclear species modulated by pseudohalides (N3-, NCS- and NCO-): Structural analyses and magnet

Article abstract of DOI:10.1039/c1dt11333j

A tetra-nuclear, star-shaped hetero-metallic copper(ii)-manganese(ii) complex, [{CuL(H₂O)}₂(CuL)Mn](ClO₄)₂ (1) has been synthesized by reacting the "complex as ligand" [CuL] with Mn(ClO₄)₂

Full text of DOI:10.1039/c1dt11333j

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
Dalton
Transactions
Cite this: Dalton Trans., 2012, 41, 462
www.rsc.org/dalton
PAPER
Synthesis of the first heterometalic star-shaped oxido-bridged MnCu3
complex and its conversion into trinuclear species modulated by pseudohalides
-
(N3 , NCS- and NCO-): Structural analyses and magnetic properties†
Saptarshi Biswas,a Subrata Naiya,a,b Carlos J. Go´mez-Garc´ıa*c and Ashutosh Ghosh*a
Received 14th July 2011, Accepted 21st September 2011
DOI: 10.1039/c1dt11333j
A tetra-nuclear, star-shaped hetero-metallic copper(II)–manganese(II) complex, [{CuL(H2O)}2-
(CuL)Mn](ClO4)2 (1) has been synthesized by reacting the “complex as ligand” [CuL] with Mn(ClO4)2
where H2L is the tetradentate di-Schiff base derived from 1,3-propanediamine and
2-hydroxyacetophenone. Upon treatment with the polyatomic anions azide, cyanate, or thiocyanate in
methanol medium, complex 1 transforms into the corresponding trinuclear species [(CuL)2Mn(N3)2]
(2), [(CuL)2Mn(NCO)2] (3) and [(CuL)2Mn(NCS)2] (4). All four complexes have been structurally and
magnetically characterized. In complex 1 the central Mn(II) ion is encapsulated by three terminal [CuL]
units through the formation of double phenoxido bridges between Mn(II) and each Cu(II). In complexes
2–4 one of the CuL units is replaced by a couple of terminal azide, N-bonded cyanate or N-bonded
thiocyanate ions respectively and the central Mn(II) ion is connected to two terminal Cu(II) ions
through a double asymmetric phenoxido bridge. Variable temperature magnetic susceptibility
measurements show the presence of moderate ferrimagnetic exchange interactions in all the cases
mediated through the double phenoxido bridges with J values (H = -JSiSi + 1) of -41.2, -39.8 and
-12.6 cm-1 (or -40.5 and -12.7 cm-1 if we use a model with two different exchange coupling constants)
for the tetranuclear MnCu3 cluster in compound 1 and -20.0, -17.3 and -32.5 cm-1 for the symmetric
trinuclear MnCu2 compounds 2–4. These ferrimagnetic interactions lead to spin ground states of 1
(5/2 - 3*1/2) for compound 1 and 3/2 (5/2 - 2*1/2) for compounds 2–4.
3d, 4d, 5d, 4f and 5f metal ions.3–6 The building of hetero-metallic
Introduction
coordination complexes has generally been done with two main
The area of polynuclear metal complexes have attracted and
approaches. The first one is based on a very simple idea: metal
attracts considerable interest for chemists not only for their intrigu-
ions show different affinity for the different coordinating atoms
ing architectures and topologies, but also for their applications
and thus, the combination of ligands bearing different donor
in a wide range of fields such as catalysis,1 photoluminescence,2
atoms with a mixture of metal ions is expected to lead to the
magnetism3 and multi-functional molecular materials.4 Although
self-assembly of well-ordered hetero-metallic systems. The second
the most used metals to prepare these complexes are the 3d first
strategy consists of using previously formed metal complexes
row transition metals,5 there are also many examples with 4d,
having vacant coordination sites, potentially bridging groups or
5d as well as 4f and 5f rare earth metals.6 Furthermore, there
labile ligands. The complexes containing bridging groups can
are also many hetero-metallic complexes containing two or more
act as ligands and coordinate to additional metal centers. Such
different metal ions with all the possible combinations between
“complex as a ligand” approaches have been applied successfully
by several groups to construct many hetero-bimetallic complexes
with interesting magnetic properties.7 Since Cu(II) chelates are the
aDepartment of Chemistry, University College of Science, University of
most stable ones among the divalent first row transition metals,
they have been widely used for this purpose and the use of Cu(II)
chelates as ligands has led to several hundreds of polynuclear
clusters with different transition metal ions. Among these, the
tri-nuclear MCu2 ones are the most common,8 whereas the star-
shaped tetra-nuclear complexes MCu3 in which the hetero atom,
M, is surrounded by three “ligand Cu complexes” are less common
and are only known with polyatomic bridging ligands but not
with monoatomic bridges. Among the many different complexes
Calcutta, 92, A.P.C. Road, Kolkata, 700 009, India. E-mail: ghosh_59@
yahoo.com
bSusil Kar College, Ghoshpur, Champahati, Baruipur, 24 Parganas(S), West
Bengal, 743330, India
cInstituto de Ciencia Molecular (ICMol). Parque Cient´ıfico. Universidad de
Valencia, 46980, Paterna, Valencia, Spain. E-mail: carlos.gomez@uv.es
† Electronic supplementary information (ESI) available: UV-visible spectra
of the five complexes (including the [CuL] precursor), Fig. S1 and S2, and
crystallographic data for 1–4. CCDC reference numbers 833841–833844.
For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c1dt11333j
462 | Dalton Trans., 2012, 41, 462–473
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
that may be used as ligands, those formed with the di-Schiff
bases prepared by condensation of diamines with salicyaldehyde
derivatives constitute a very promising group since they present
two monoatomic phenoxido groups that can bridge another metal
ion.9 A search in the CCDC database (updated to May 2011)
for polynuclear complexes containing any central transition metal
atom (M) connected to peripheral copper atoms with double
monoatomic bridges shows several hundred of such complexes.
Among these, the most common ones are the trinuclear MCu2
complexes (with ca. 120 complexes) but there is no star-shaped
tetranuclear MCu3 complex. Therefore, complex 1 of this article is
the first known example of star-shaped MCu3 complex with double
monoatomic bridges (of any type). Among these ca. 120 trinuclear
MCu2 complexes, one half present bridging oxygen atoms (60
examples) and the other half contain other bridging atoms such
as sulfur (35 examples), halogen atoms (15 examples, most of
them with X = Cl), nitrogen (6 examples) and even selenium (1
example). Interestingly, most of the known examples of MCu2
complexes with double oxido bridges contain a central Cu ion (47
out of 60) and only three contain a Mn central ion, as observed in
complexes 2–4 of the present article. If we do not limit to copper
ions in the periphery of the polynuclear complexes but include any
transition metal, then the number of examples increases to several
hundreds of MM¢2 and MM¢3 complexes. The CCDC database
shows up to 51 examples of star-shaped MM¢3 complexes with
double oxido bridges (plus three very recent CrCr3 examples not
appearing in the database updated to May 2011). From the total of
54 examples, 42 are homometallic (M = M¢) and the remaining 12
heterometallic (M π M¢). Among the 42 homometallic complexes,
theFe complexes are, byfar, the mostabundant ones (with22“Fe4”
examples).10 The remaining 20 homometallic examples are “Co4”
(7 complexes),11 “Mn4”,12 “V4”13 and “Cr4”14 (four complexes
of each) and there is even one “Pt4” complex.15 Among the 12
heterometallic MM¢3 complexes there are four “LaZn3”,16 three
“CrFe3”10a,17 and one example for each composition: “CoCr3”,
“LaNb3”, “NiCo3”, “ZnCo3” and “MnCo3”.18 Only if we include
any metal (not only transition metals) in the search, we can find
four examples of tetranuclear star-shaped MCu3 complexes. These
examples include two19 with M = Na+, one20 with M = K+ and one
more with Cd2+.21
On the other hand, although the hetero-nuclear complexes
of Mn(II) containing another paramagnetic ion are well known
for their interesting magnetic properties,22 it has rarely been
incorporated into Cu(II) complexes of salen type Schiff bases. Only
two such examples of Cu(II)–Mn(II) species with double oxido
bridges were known previously23 and during the course of the
present work, one more compound (not found in the CCDC search
updated to May 2011) has been reported.24 If we include all kind of
ligands, then the number of double oxido-brigded Cu(II)–Mn(II)
systems increases to 22, although only 17 have been magnetically
characterized. Among these 22 Mn(II)–Cu(II) complexes with
double oxido bridges there are twelve dimers,25 three trimers,23,26
one tetramer,27 one hexamer formed by connecting three dimers28
and five chains.25i,29
In this context, with the help of our experience on the
Cu(II)–Cd(II) system,21 we have decided to design, prepare and
study new tri- and tetra-nuclear Cu(II)–Mn(II) complexes, by
carefully selecting the anionic co-ligands. Herein, we report the
synthesis, crystal structure and magnetic properties of a MnCu3
star-shaped complex [{CuL(H2O)}2(CuL)Mn](ClO4)2 (1) and
three MnCu2 species [(CuL)2Mn(N3)2] (2), [(CuL)2Mn(NCO)2]
(3) and [(CuL)2Mn(NCS)2] (4) prepared with the di-Schiff-base
ligand H2L (N,N¢-bis(a-methylsalicylidene)-1,3-propanediamine
Scheme 1). Furthermore, we also show here that the tetranuclear
MnCu3 complex 1 converts into the trinuclear MnCu2 ones (2–
4) when treated with sodium azide (NaN3), sodium cyanate
(NaOCN) and ammonium thiocyanate (NH4SCN), respectively,
in a methanolic solution. Complex 1 is the first example of oxido-
bridged star-shaped MnCu3 cluster whereas the three phenoxido
bridged trinuclear MnCu2 complexes (2–4) increase the number
Scheme 1 Synthetic route to 1–4.
The Royal Society of Chemistry 2012
This journal is
Dalton Trans., 2012, 41, 462–473 | 463
©

View Article Online
of this kind of complexes from three (with only one magnetically
characterized) to six.
C, 52.55; H, 4.41; N, 8.93. lmax (solid, reflectance): 353, 626 nm.
IR (KBr pellet, cm-1): u(C N), 1598 u(SCN), 2053.
All three compounds were also prepared directly, by addition,
with stirring, of a methanolic solution (20 mL) of the ligand
complex [CuL] (0.784 g, 2 mmol) to 5 mL of an aqueous solution
of Mn(ClO4)2·6H2O (0.362 g, 1 mmol) followed by 2 mL of an
aqueous solution of sodium azide (0.130 g, 2 mmol), sodium
cyanate (0.130 g, 2 mmol) or ammonium thiocyanate (0.159 g,
2 mmol) for complexes 2, 3 and 4, respectively. In all cases the
microcrystalline green solid started to separate immediately. The
stirring was continued for 30 min and the solid product was
isolated by filtration, washed with methanol and dried in a vacuum
desiccator containing anhydrous CaCl2. Yield = 0.664 g (75%),
0.654 g (74%) and 0.704 g (77%) for 2, 3 and 4, respectively.
Experimental
Starting materials
The o-hydroxyacetophenone and 1,3-propanediamine were pur-
chased from Lancaster and were of reagent grade. They were used
without further purification.
Caution! Azide salts and perchlorate salts of metal complexes
withorganicligands arepotentiallyexplosive. Onlyasmall amount
of material should be prepared and it should be handled with care.
Synthesis of the Schiff base ligand (H2L). The di-Schiff-
base ligand, H2L was prepared by usual methods: 5 mmol of
1,3-propanediamine (0.42 mL) were mixed with 10 mmol of
2-hydroxyacetophenone (1.20 mL) in methanol (10 mL). The
resulting solution was refluxed for ca. 2 h and allowed to cool. The
yellow colored methanolic solution was used directly for complex
formation.
Physical measurements
Elemental analyses (C, H and N) were performed using a Perkin-
Elmer 2400 series II CHN analyzer. IR spectra in KBr pellets
(4500–500 cm-1) were recorded using a Perkin-Elmer RXI FT-IR
spectrophotometer. Electronic spectra in the solid state (1800–
250 nm) were recorded with a Hitachi U-3501 spectrophotometer.
Variable temperature susceptibility measurements were carried out
in the temperature range 2–300 K with an applied magnetic field
of 0.1 T on polycrystalline samples of the four compounds (with
masses of 120.28, 12.88, 22.80 and 23.90 mg for compounds 1–
4, respectively) with a Quantum Design MPMS-XL-5 SQUID
magnetometer. The isothermal magnetizations were made at 2 K
with magnetic fields of up to 5 T. The susceptibility data were
corrected for the sample holder previously measured using the
same conditions and for the diamagnetic contributions of the salt
as deduced by using Pascal’s constant tables (cdia = -708.56 ¥ 10-6,
-444.44 ¥ 10-6, -463.04 ¥ 10-6 and -479.04 ¥ 10-6 emu mol-1 for
1–4, respectively).31
Synthesis of the complex [{CuL(H2O)}2(CuL)Mn](ClO4)2 (1).
To a methanolic solution (20 mL) of Cu(ClO4)2·6H2O (1.852 g, 5
mmol) was added a methanolic solution of H2L (5 mmol, 10 mL)
to prepare the “ligand complex” [CuL] as reported earlier.30 The
resulting complex (1.174 g, 3 mmol) was dissolved in methanol
(20 mL). 2 mL of an aqueous solution of Mn(ClO4)2·6H2O
(0.382 g, 1 mmol) was added to this solution, stirred for 10 min
and allowed to stand overnight to yield green colored X-ray
quality single crystals at the bottom of the vessel. The crystals
were isolated, washed with methanol and dried in a desiccator
containing anhydrous CaCl2. Complex 1: Yield: 1.041 g. (74%).
Anal. Calc. for C57H64Mn1Cl2Cu3N6O16 (1405.60): C, 48.71; H,
4.59; N, 5.97. Found: C, 48.87; H, 4.31; N, 5.88. lmax (solid,
reflectance): 357, 627 nm. IR (KBr pellet, cm-1): u(C N), 1597
Crystallographic data collection and refinement
-
u(ClO4 ), 1089.
Suitable single crystals of each complex were mounted on a
Bruker-AXS SMART APEX II diffractometer equipped with a
Synthesis of the complexes [(CuL)2Mn(N3)2] (2), [(CuL)2-
Mn(NCO)2] (3) and [(CuL)2Mn(NCS)2] (4). An aqueous solution
(5 mL) of sodium azide (0.260 g, 4.0 mmol), sodium cyanate
(0.260 g, 4.0 mmol) or ammonium thiocyanate (0.318 g, 4.0 mmol)
for complexes 2, 3 and 4, respectively, was added to a methanolic
solution (30 mL) of compound 1 (2.811 g, 2 mmol) with stirring.
In all cases a green colored microcrystalline product started to
separate immediately. The stirring was continued for 30 min and
then the solid compound was collected by filtration, washed with
methanol and dried in vacuum desiccator containing anhydrous
CaCl2. The filtrate was allowed to stand overnight to yield green
colored X-ray quality single crystals at the bottom of the vessel in
all the cases.
˚
graphite monochromator and Mo-Ka (l = 0.71073 A) radiation.
The crystals were positioned at 60 mm from the CCD. 360 frames
were measured with a counting time of 5 s. The structures were
solved using Patterson method by using the SHELXS 97. Sub-
sequent difference Fourier synthesis and least-square refinement
revealed the positions of the remaining non-hydrogen atoms that
were refined with independent anisotropic displacement parame-
ters. Hydrogen atoms were placed in idealized positions and their
displacement parameters were fixed to be 1.2 times larger than
those of the attached non-hydrogen atom. Absorption corrections
were carried out using the SADABS program.32 All calculations
were carried out using SHELXS 97,33 SHELXL 97,34 PLATON
99,35 ORTEP-3236 and WinGX system Ver-1.64.37 Data collection
and structure refinement parameters and crystallographic data for
the four complexes are given in Table 1.
Compound 2: Yield: 1.112 g. (63%). Anal. Calc. for
C38H40Mn1Cu2N10O4 (882.84): C, 51.70; H, 4.56; N, 15.86. Found:
C, 51.98; H, 4.57; N, 15.97. lmax (solid, reflectance): 382, 618 nm.
IR (KBr pellet, cm-1): u(C N), 1598 u(NNN), 2054.
Compound 3: Yield: 1.044 g. (59%). Anal. Calc. for
C40H40Mn1Cu2N6O6 (882.82): C, 54.42; H, 4.56; N, 9.52. Found:
C, 54.61; H, 4.79; N, 9.57. lmax (solid, reflectance): 383, 630 nm.
IR (KBr pellet, cm-1): u(C N), 1598 u(NCO), 2185.
Compound 4: Yield: 1.116 g. (61%). Anal. Calc. for
C40H40Mn1Cu2N6O4S2 (914.96): C, 52.39; H, 4.39; N, 9.17. Found:
Results and discussion
Syntheses, IR and UV-Vis spectra of the complexes
The Schiff-base ligand (H2L) and its Cu(II) complex,
[CuL] was synthesized using the reported procedure.30 The
464 | Dalton Trans., 2012, 41, 462–473
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
Table 1 Crystal data and structure refinement for complexes [{CuL(H2O)}2(CuL)Mn](ClO4)2 (1), [(CuL)2Mn(N3)2] (2), [(CuL)2Mn(NCO)2] (3) and
[(CuL)2Mn(NCS)2] (4)
1
2
3
4
Formula
C57H64Cu3MnN6O16Cl2
1405.60
P1
C38H40Cu2MnN10O4
882.84
C2/c
Monoclinic
22.7481(6)
10.0972(3)
17.6258(5)
90
97.242(1)
90
4016.2(2)
4
1.460
1. 411
0.0284
C40H40Cu2MnN6O6
882.82
C2/c
Monoclinic
21.1530(7)
9.9031(3)
18.0054(6)
90
91.833(1)
90
3769.8(2)
4
1.555
1.504
0.0725
6121
3256
C40H40Cu2MnN6O4S2
914.92
C2/c
Monoclinic
23.540(5)
10.194(5)
17.215(5)
90
95.494(5)
90
4112(3)
4
1.478
1.476
0.0292
4969
3617
Formula weight
Space group
Crystal system
¯
Triclinic
12.478(5)
15.326(5)
18.404(5)
68.759(5)
77.929(5)
69.453(5)
3058.2(18)
2
1.526
1.390
0.030
20 577
˚
a/A
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
V (A )
Z
dcal (g cm-3)
m/mm-1
Rint
No. of unique data
Data with I > 2s(I)
R1 on I > 2s(I)
wR2 on I > 2s(I)
Goof Value
9007
5696
0.0532
0.2098
13 908
0.0585
0.1995
1.018
0.0512
0.1578
0.899
0.0486
0.1904
1.090
1.053
Cu(II) complex when reacted with Mn(ClO4)2·6H2O in
methanol/water medium (10 : 1, v/v) resulted in the tetranuclear
[{CuL(H2O)}2(CuL)Mn](ClO4)2 (1) complex by self-assembly
(Scheme 1). When a polyatomic anion X- (X- = azide, cyanate or
thiocyanate) was added to a solution of 1, one of the CuL moieties
was replaced by two terminally coordinated anions resulting in
the formation of the tri-nuclear species: [(CuL)2Mn(N3)2] (2),
[(CuL)2Mn(NCO)2] (3) and [(CuL)2Mn(NCS)2] (4). Considering
the stronger coordinating ability of these anions compared to the
perchlorate anion, this conversion is not surprising. Albeit, it is
important to notice that only one of the three CuL complexes
has been displaced by the X- anions. Although in principle the
trinuclear and tetranuclear structures are closely related, there is a
slight difference in the coordination mode of one of the two oxygen
atoms in both double oxido bridges connecting the Mn and Cu
ions. In the MnCu2 species (2–4), two CuL units come closer to
each other and one oxygen atom of each double oxido bridge
coordinates additionally to the axial position of the other Cu(II)
ion to form a double m3-oxido bridge that connects the Mn(II) ion
and the two Cu(II) ions (see structural description). The formation
of the m3-oxido bridge becomes possible because the coordinated
water molecules in two of the three CuL units of 1 are lost and,
therefore, the phenoxido oxygen atoms coordinate to the vacant
axial sites left by the water molecules.
In all complexes, a strong and sharp band due to the azomethine
u(C N) group of the Schiff base appears at 1597, 1598, 1598
and 1598 cm-1 for complexes 1–4 respectively. In the IR spectra of
complex 1, the broad band near 3435 cm-1 is probably due to the
O–H stretching of the coordinated water molecules.
The solid-state reflectance spectra of all the complexes show
a broad single absorption band near 357, 382, 383, and 353 nm
for 1–4, respectively, attributed to ligand-to-metal charge transfer
transitions. Besides this band, a single absorption band is observed
in the visible region at 627, 618, 630, and 626 nm for 1–4,
respectively (Fig. S1, ESI†). This band is typical of d–d transitions
of Cu(II) ions with a square-planar environment and, as expected,
is also observed in the mononuclear CuL precursor complex. (Fig.
S2, ESI†).
Description of structures
[{CuL(H2O)}2(CuL)Mn](ClO4)2 (1). The structure of 1 con-
tains a discrete, independent [{CuL(H2O)}2(CuL)Mn]2+ cation
and two perchlorate anions. The structure of the cation is shown
in Fig. 1. The selected bond lengths and angles are summarized
in Table 2. The structure of the [{CuL(H2O)}2(CuL)Mn]2+ cation
involves one [CuL] and two [CuL(H2O)] moieties surrounding
a manganese(II) cation. The manganese ion is six-coordinate
being bonded to three pairs of oxygen atoms from three “ligand
complexes”. Thus, the manganese ion is connected to three copper
atoms each through two oxygen atoms. Since each [CuL] complex
acts as a chelating unit through its two phenoxido oxygen atoms,
complex 1 belongs to the general family of complexes M(AA)3,
where AA is a chelating symmetrical ligand. These complexes
belong to the D3 space group and therefore are chiral. In the unit
cell of 1 we find the two enantiomers (D and K) of the MnCu3
complex related through an inversion center and therefore 1 is
a racemic mixture of both enantiomers and shows no overall
chirality. The geometry of Cu(1) and Cu(2) in the two [CuL(H2O)]
moieties is best described as square pyramidal with the four
coordinating atoms from the di-anionic Schiff base ligand (L2-)
Besides elemental analysis, all the complexes were initially
characterized by IR spectra. The precursor “ligand complex”
[CuL] is neutral and obviously does not have any counter anion.
All four synthesized hetero-nuclear complexes contain anions (non
-
-
coordinated ClO4 in 1 and coordinated N3 , NCO- or SCN- in
2–4). These anions show their characteristic bands in their IR
spectra. Therefore, isolation of 1 can easily be detected by the
presence of the characteristic intense peaks for perchlorate (u3) at
1089 cm-1. Similarly, the appearance of a strong and sharp peak at
2054 cm-1 for azide in complex 2, at 2185 cm-1 for cyanate in 3 and
at 2053 cm-1 for thiocyanate in 4 clearly indicates the formation
of the respective adducts. The rest of the spectral patterns and
band positions of adduct and the precursor, [CuL], is very similar.
This journal is
The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 462–473 | 465
©

View Article Online
◦
˚
Table 2 Bond distances (A) and angles ( ) around the metal centers in
complex 1
˚
˚
Atoms
Distance (A)
Atoms
Distance (A)
Cu1–O1
Cu1–N1
Cu1–N2
Cu1–O2
Cu1–O16
Cu2–O3
Cu2–O4
Cu2–N3
Cu2–N4
Cu2–O15
1.959(2)
1.963(3)
1.994(3)
1.934(2)
2.442(5)
1.937(2)
1.927(2)
1.979(4)
1.965(3)
2.644(6)
Cu3–O5
Cu3–O6
Cu3–N5
Cu3–N6
Cu3–O4
Mn1–O1
Mn1–O2
Mn1–O3
Mn1–O4
Mn1–O5
Mn1–O6
1.908(2)
1.938(2)
1.955(3)
1.995(3)
2.881(3)
2.196(2)
2.161(3)
2.117(2)
2.292(2)
2.324(2)
2.119(2)
Atoms
Angle (◦)
Atoms
Angle (◦)
O1–Cu1–O2
O1–Cu1–N1
O1–Cu1–N2
O1–Cu1–O16
O2–Cu1–N1
O2–Cu1–N2
O2–Cu1–O16
N1–Cu1–N2
O16–Cu1–N1
O16–Cu1–N2
O3–Cu2–O4
O3–Cu2–N3
O3–Cu2–N4
O3–Cu2–O15
O4–Cu2–N3
O4–Cu2–N4
O4–Cu2–O15
N3–Cu2–N4
O15–Cu2–N3
O15–Cu2–N4
O4–Cu3–O5
O4–Cu3–O6
O4–Cu3–N5
82.97(9)
O4–Cu3–N6
O5–Cu3–O6
O5–Cu3–N5
O5–Cu3–N6
O6–Cu3–N5
O6–Cu3–N6
N5–Cu3–N6
O2–Mn1–O6
O3–Mn1–O4
O3–Mn1–O5
O3–Mn1–O6
O4–Mn1–O5
O4–Mn1–O6
O5–Mn1–O6
O1–Mn1–O2
O1–Mn1–O3
O1–Mn1–O4
O1–Mn1–O5
O1–Mn1–O6
O2–Mn1–O3
O2–Mn1–O4
O2–Mn1–O5
94.64(9)
81.85(9)
92.55(10)
164.27(10)
168.71(10)
89.08(10)
98.45(11)
102.33(9)
70.48(9)
84.98(9)
147.67(9)
77.09(8)
84.88(8)
68.93(8)
72.55(8)
107.74(9)
102.32(8)
166.44(9)
97.52(8)
104.25(9)
171.52(8)
109.53(8)
89.17(10)
159.88(13)
103.77(15)
170.88(11)
89.82(11)
91.51(15)
99.10(12)
85.87(15)
95.14(17)
82.49(10)
89.04(12)
170.55(11)
88.77(17)
163.81(11)
90.07(11)
104.95(16)
99.55(13)
88.56(17)
87.53(17)
70.51(8)
Fig. 1 The structure of the K-[{CuL(H2O)}2(CuL)Mn]2+ cation in 1 with
ellipsoids at 30% probability.
in the basal plane and a semi-coordinated water molecule in one
of the axial sites (Cu1–O16 = 2.442(5) and Cu2–O15 = 2.644(6)
˚
A). The metal atoms Cu(1) and Cu(2) deviate from the N2O2 basal
˚
plane by 0.131(1) and 0.072(1) A towards the coordinated water
molecule. The Addison parameters38 0.183 for Cu(1) and 0.074 for
Cu(2) indicate slight distortion towards the trigonal bipyramidal
geometry. In the remaining [CuL] unit, both axial positions of
the copper atom Cu(3) are vacant. Thus the geometry around
Cu(3) is square planar with a tetrahedral distortion in which the
r.m.s. deviation of the donor atoms from their mean coordination
˚
˚
73.46(8)
113.99(9)
plane is 0.179 A. The metal atom is 0.025(1) A from this plane.
The tetrahedral distortion is also evident from the dihedral angles
(15.02◦) between the planes N(5)–Cu(3)–O(5) and N(6)–Cu(3)–
O(6) (it should be 0◦ for a perfectly square-planar arrangement and
90◦ for a perfect tetrahedral arrangement). This geometry is also
confirmed by the so-called t4 index that measures the distortion
between a perfect tetrahedron (t4 = 1) and a perfect square planar
geometry (t4 = 0) with the formula: t4 = [360◦ - (a + b)]/141◦,
with a and b (in ◦) being the two largest angles around the central
metal in the complex.39 The t4 value for Cu(3) is 0.192, confirming
a slightly distorted square planar geometry for this metal center.
The environment of the Mn(II) ion can be described as
a considerably distorted octahedron where the Mn(II) ion is
surrounded by six phenoxido oxygen atoms from three different
[CuL] units. There are four short Mn–O bonds to O(1), O(2), O(3)
plexes with different (polyatomic) bridging ligands. A search in
the CCDC database shows eleven such MM¢3 complexes with
oxamide-containing ligands.40–42 In nine of these complexes, the
peripheral atom, M¢, is Cu(II) and in the two remaining cases
M¢ is Ni(II). The central M atom is Mn (in six cases),40 Cu (in
two cases),40d,41 or even Cd, Cr and Co (there is one example of
each).40c,41,42 Besides the oxamide-like bridge, there are also other
star-shaped MM¢3 complexes containing other (also polyatomic)
bridging ligands, although their numbers are very limited.43 Albeit,
as already mentioned in the introduction, if we consider the
complexes only with monoatomic bridges then, compound 1 is
the first known example with “MnCu3” composition.
There is an intra-molecular C–H/p interaction between H49B
and the phenyl ring with a distance of 2.710 A from the centroid
(Fig. 2a). Besides this intra-molecular interactions there is an
inter-molecular one between the square planar Cu(3) ion and the
phenylring of aneighbouring molecule withacentroidCg ◊ ◊ ◊ Cu(3)
˚
and O(6) with distances in the range 2.117(2)–2.196(2) A, and
two longer bonds Mn–O(4) = 2.292(2) and Mn–O(5) = 2.324(2)
˚
˚
A. The bond angles also show significant deviations from the
ideal octahedral geometry. Thus, the three trans angles are lower
than 180◦ (171.52(8)◦, 166.44(9)◦ and 147.67(9)◦, Table 2) and the
cis angles vary in a wide range (from 68.93(8)◦ to 109.53(8)◦,
Table 2). Although the three Mn ◊ ◊ ◊ Cu distances are similar
˚
distance of 3.726 A (Fig. 2b).
˚
˚
(Mn(1) ◊ ◊ ◊ Cu(1) = 3.162(1) A, Mn(1) ◊ ◊ ◊ Cu(2) = 3.160(1) A and
[(CuL)2Mn(N3)2] (2), [(CuL)2Mn(NCO)2] (3) and [(CuL)2-
Mn(NCS)2] (4). The structure determination reveals that the
structures of 2, 3 and 4 are very similar: they consist of discrete
˚
Mn(1) ◊ ◊ ◊ Cu(3) = 3.105(1) A), the Cu(II) ions form an scalene tri-
angle with Cu ◊ ◊ ◊ Cu distances of 3.914(2), 5.686(2) and 6.119(2) A.
˚
trinuclear units with formula [(CuL)2Mn(X)2] with X- = N3
-
The overall geometry of the complex is a star-shaped triangle
topologically similar to those observed in other metal com-
(2), NCO- (3) and NCS- (4). The discrete trinuclear entities
466 | Dalton Trans., 2012, 41, 462–473
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
˚
Fig. 2 (a) Intra-molecular C–H/p interaction (H49B–Cg = 2.710 A).
(b) Inter-molecular phenyl–Cu(3) interaction in complex 1 (Cu(3)–Cg
=
˚
3.726 A).
of the three complexes contain a crystallographic two-fold axis
and consist of two [CuL] units, one manganese ion and two
terminally coordinated X- anions (azide for 2, N-bonded cyanate
for 3 and N-bonded thiocyanate for 4). The ORTEP views of
the complexes are shown in Fig. 3–5 and the bond distances
and angles are given in Table 3. The three complexes contain a
central Mn(II) ion coordinated to two terminal X- ligands and
Fig. 5 ORTEP view of the trinuclear complex 4. Ellipsoids are drawn at
30% probability level. The dotted bonds show the weak Mn–O and Cu–O
interactions.
◦
˚
Table 3 Bond distances (A) and angles ( ) around the metal centers in
complexes 2, 3 and 4
Complex
Atoms
2
3
4
˚
˚
˚
Distance (A)
Distance (A)
Distance (A)
Cu1–O1
Cu1–O2
Cu1–N1
Cu1–N2
Cu1–O1a
Mn1–O1
Mn1–O2
Mn1–N3
1.903 (2)
1.937 (2)
1.954(2)
1.962(2)
2.615(2)
2.481(2)
2.103(2)
2.109(3)
1.907(2)
1.938(2)
1.958(3)
1.961(3)
2.491(2)
2.534(2)
2.147(2)
2.072(3)
1.905(3)
1.923(2)
1.974(4)
1.949(3)
2.685(3)
2.438(3)
2.100(3)
2.128(3)
Atoms
Angle (◦)
Angle (◦)
Angle (◦)
O1–Cu1–O2
O1–Cu1–N1
O1–Cu1–N2
O1–Cu1–O1a
O2–Cu1–N1
O2–Cu1–N2
O1a–Cu1–O2
N1–Cu1–N2
O1a–Cu1–N1
O1a–Cu1–N2
O1–Mn1–O2
O1–Mn1–N3
O1–Mn1–O1a
O1–Mn1–O2a
O1–Mn1–N3a
O2–Mn1–N3
O2–Mn1–O2a
O2–Mn1–N3a
N3–Mn1–N3a
85.80(8)
89.78(9)
168.75(9)
70.26(7)
164.85(9)
89.15(8)
75.42(7)
97.57(9)
116.60(8)
98.74(9)
69.00(7)
99.13(10)
64.96(6)
75.94(7)
162.80(10)
105.38(10)
138.23(7)
101.86(11)
97.37(12)
87.25(9)
84.18(12)
166.48(13)
90.79(15)
69.84(10)
90.33(12)
163.10(13)
75.64(10)
97.82(15)
96.85(11)
117.70(13)
68.38(9)
98.06(11)
67.36(9)
78.68(9)
160.10(11)
109.40(11)
140.34(9)
96.22(11)
99.04(12)
169.73(10)
88.89(10)
72.44(7)
91.30(11)
156.32(11)
76.24(8)
96.42(12)
97.33(9)
124.54(9)
68.47(7)
97.12(10)
62.81(6)
71.98(7)
159.77(10)
104.19(11)
133.32(8)
104.36(11)
103.04(13)
Fig. 3 ORTEP view of the trinuclear complex 2. Ellipsoids are drawn at
30% probability level. The dotted bonds show the weak Mn–O and Cu–O
interactions.
a symmetry operation = 2 -x, y, 3/2 - z; -x, y, 1/2 - z; 1 - x, y, 1/2 - z for
complexes 2–4, respectively.
to two [CuL] chelating units. Both Cu(II) ions present a penta-
coordinated square pyramidal geometry where the basal plane is
formed by the two imine N atoms N(1) and N(2), and the two
phenoxido O atoms, O(1) and O(2), of the Schiff base (Fig. 3–5).
The two CuL units in the molecule are held together through the
Fig. 4 ORTEP view of the trinuclear complex 3. Ellipsoids are drawn at
30% probability level. The dotted bonds show the weak Mn–O and Cu–O
interactions.
This journal is
The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 462–473 | 467
©

View Article Online
semi-coordination of one of the phenoxido groups of one unit,
O(1), to the axial position of the Cu(II) ion of the other [CuL] unit
a
˚
with Cu(1)–O(1) distances of 2.615(2), 2.491(2) and 2.685(3) A
(a = 2 - x, y, 3/2 - z, -x, y, 1/2 - z and 1 - x, y, 1/2 - z for
2–4, respectively), completing, in this way, the square pyramidal
geometry. This semi-coordination leads to much closer Cu ◊ ◊ ◊ Cu
˚
distances (3.559(1), 3.385(1) and 3.621(2) A in 2–4, respectively)
compared with those observed in the MnCu3 complex 1 (in the
˚
range 3.914–6.119 A). The r.m.s. deviations of the four basal atoms
from the mean plane passing through them are 0.197, 0.275 and
0.227 for 2–4, respectively. The metal atom is 0.040(1), 0.112(1) and
˚
0.034(1) A from this plane towards the axially coordinated oxygen
Fig. 6 Thermal variation of the cmT product for compound 1. Inset
shows the low temperature region. Solid and dashed lines represent the
best fit to the 3J and 1J models (see text).
atom for 2–4, respectively. The Addison parameter of the Cu
atom is 0.065, 0.226 and 0.056 for 2–4, respectively, indicating that
the distortion towards trigonal bipyramid geometry is higher in
complex 3 than in the other two.38 It is to be noted that the average
Cu–O bond distances in the [CuL] units of the three complexes
are slightly greater than that of the mono-nuclear complex30 and
this lengthening is slightly more pronounced in complex 1.
In the three complexes, the manganese atom lies on a two-fold
axis and is bonded to two N atoms from two terminal azide,
two N-bonded cyanate or two N-bonded thiocyanate ligands in
2–4, respectively, and to two oxygen atoms from two different
[CuL] units in a distorted tetrahedral arrangement. These four
bond distances around the Mn(II) ion are in the range 2.072–
three Cu(II) ions (S = 1/2) and one Mn(II) ion (S = 5/2) (the
expected value for gMn = gCu = 2.0 is 3*0.375 + 4.375 = 5.5 emu
K mol-1). When the temperature is lowered, the cmT product
shows a progressive decrease to reach a plateau of ca. 1.1 emu
K mol-1 at ca. 10 K. (Fig. 6) This decrease suggests the presence of
moderate antiferromagnetic interactions between the Mn(II) ion
and the three Cu(II) ions in the MnCu3 cluster. This ferrimagnetic
coupling leads to a S = 1 spin ground state (arising from the partial
cancellation of the S = 5/2 sate of the Mn(II) ion (5/2 - 3*(1/2)
= 1). This assumption is confirmed by the plateau observed at low
temperatures (ca. 1.1 emu K mol-1), close to the expected value
for a S = 1 spin ground state (the expected value for gMn = gCu = 2
is 1.0 emu K mol-1).
˚
2.147 A (Table 3). Besides these four short bonds, there are two
additional long bonds formed by the other oxygen atoms, O(1),
of the two terminal [CuL] units, with Mn–O bond distances of
˚
2.481(2), 2.534(2) and 2.438(3) A in 2–4, respectively. Note that
The structure of compound 1 shows a tetrameric MnCu3
cluster where the central Mn(II) ion is connected to the three
terminal Cu(II) ions through double oxido bridges. The Cu(II)
ions are not connected to each other and therefore the magnetic
exchange pathway expected in compound 1 is the one described
in the left part of Scheme 2. From the structural parameters and
symmetry, we can deduce that the three Mn–Cu connections are,
in principle, different and accordingly we have used a magnetic
model assuming three different magnetic pathways as described in
Scheme 2. In order to fit the data we have used the MAGPACK
this O(1) atom is the one which is semi-coordinated to the axial
position of the other copper atom Cu(1)a in the trinuclear unit
(see above). It is also of interest to note that the stronger the
interaction of O(1) with the Mn(II) is, the weaker the Cu(1)–O(1)
axial bond is and the larger the O(2)–Mn–O(2)a angle is. If these
weak interactions are not considered as bonds, then the geometry
around manganese can be considered as distorted tetrahedral. The
distortion arises due to the large O(2)–Mn–O(2)a angle [(138.23(7),
133.32(8) and 140.34(9) for 2–4, respectively] and to the small
N(3)–Mn–N(3)a angle [97.37(12), 103.04(13) and 99.04(12) for
2–4, respectively]. On the other hand, if these interactions are
considered as bonds, the environment of the manganese ion is
six-coordinate but the geometry is very distorted from the ideal
octahedron, more than that observed in complex 1. Thus the
three trans angles are significantly smaller than 180◦ in the three
complexes (in the range 133.32–162.80◦) and among the cis angles,
the one between the two weakly coordinated atoms, O1–Mn1–O1a,
is considerably smaller than 90◦ [64.96(6), 62.81(6) and 67.36(9)◦
for 2–4, respectively]. Considering all these aspects and the fact
program.44 The Hamiltonian is written as H = -[J11SMnSCu1
J12SMn Cu2 + J13SMn Cu3]. This simple tetrameric model reproduces
+
S
S
very satisfactorily the magnetic properties of compound 1 in the
whole temperature range (solid line in Fig. 6) with the following
parameters: g = 2.082, J11 = -41.2 cm-1, J12 = -39.8 cm-1 and
J13 = -12.6 cm-1 with a temperature independent term, Na
=
4.0 ¥ 10-4 emu mol-1 (Table 4, for a justification of the assignation
of the J constants see below). Given the similarity between the
J11 and J12 values, we decided to use a model with only two
different J values (i.e., we fixed J11 = J12). This 2J model produced,
as expected, almost the same result (in fact the two plots are
˚
that a Mn–O distance as long as ca. 2.5 A may be considered as a
weak bond25f ,29b the geometry around Mn(II) is best described as
a distorted octahedron and thus in the three structures the central
Mn(II) ion can be considered as connected to two terminal Cu(II)
ions through a double asymmetric phenoxido bridge.
Magnetic properties
The thermal variation of the cmT product for compound 1 per
MnCu3 unit is shown in Fig. 6. At room temperature the cmT
value is ca. 4.8 emu K mol-1, below the expected value for
Scheme 2 Magnetic exchange scheme in compounds 1 (left) and 2–4
(right).
468 | Dalton Trans., 2012, 41, 462–473
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
Table 4 Magnetic parameters for compounds 1–4
Compound
gav
J11 (cm-1)
J12 (cm-1)
J13 (cm-1)
Na (emu mol-1)
R
1 (3J model)
2.082
2.082
2.118
2.037
2.027
2.002
-41.2
-40.5
-27.3
-20.0
-17.3
-32.5
-39.8
-40.5
-27.3
-12.6
-12.7
-27.3
4.0 ¥ 10-4
4.0 ¥ 10-4
18.8 ¥ 10-4
5.0 ¥ 10-4
5.7 ¥ 10-4
7.2 ¥ 10-4
6.1 ¥ 10-5
6.1 ¥ 10-5
2.4 ¥ 10-3
4.7 ¥ 10-5
2.1 ¥ 10-4
2.3 ¥ 10-4
1 (2J model)
1 (1J model)
2
3
4
superimposable) with also very similar parameters: g = 2.082, J11
= J12 = -40.5 cm-1 and J13 = -12.7 cm-1 with a temperature indepen-
dent term, Na = 4.0 ¥ 10-4 emu mol-1 (Table 4). With this model the
resulting ground spin state is, as expected an S = 1 (resulting from
the ferrimagnetic coupling of the central S = 5/2 spin state with
the three S = 1/2 of the periphery centres. The first excited state is
an S = 2, lying 34.2 cm-1 above the ground state. Finally, we also
suggests the presence of a zero field splitting (ZFS) in the S =
3/2 spin ground state (although an additional antiferromagnetic
intercluster interaction cannot be excluded). Finally, besides the
presence of the plateau at ca. 1.9 emu K mol-1, the isothermal
magnetization data at low temperatures (see below) confirm the
presence of the ferrimagnetic interactions in compounds 2–4.
Since the structure of the three compounds shows the same kind
of symmetrical trinuclear Cu–Mn–Cu cluster with two identical
Mn–Cu interactions through a double asymmetric oxido bridge
and without any noticeable interaction between the two terminal
Cu(II) ions, we have assumed a simple symmetrical linear trimer
with a central Mn(II) ion (S = 5/2) and two terminal Cu(II) ions
(S = 1/2) connected to the central Mn(II) ion through the same
exchange coupling (J11, Scheme 2). In this model we assume that
the two Cu(II) ions are not interacting since a close inspection
of the structure shows that the Cu(II) ions are only connected
through a very long asymmetric Cu–O–Cu bridge through O(1).
In all cases one of the Cu–O bonds in these bridges is long enough
tried a simpler model with only one exchange coupling (i.e., J11
=
J12 = J13). As expected, this model leads to a significantly worse
fit (dashed line in Fig. 6) and yields an intermediate J value: g =
2.118, J11 = J12 = J13 = -27.3 cm-1 with a temperature independent
term, Na = 18.8 ¥ 10-4 emu mol-1 (Table 4).
The thermal variation of the product of the molar magnetic
susceptibility times the temperature (cmT) per MnCu2 cluster in
compounds 2–4 is very similar to that of compound 1 although
with different values. They show room temperature values in the
range 5.0–5.1 emu K mol-1 and a progressive decrease when the
temperature is lowered to reach a plateau of ca. 1.9 emu K mol-1
below ca. 10–20 K, depending on the compound (Fig. 7). At very
low temperatures (below ca. 5 K), the cmT product in compound
4 further decreases to reach a value of 1.55 emu K mol-1 at 2 K.
The room temperature value is close to the expected one for a
Mn(II) and two Cu(II) non-interacting ions (the expected value
for gMn = gCu = 2.0 is 4.375 + 2*0.375 = 5.125 emu K mol-1).
The decrease observed when lowering the temperature suggests
again the presence of moderate antiferromagnetic interactions
between the Mn(II) ion and the two Cu(II) ions in the MnCu2
clusters. The plateau at low temperatures suggests the presence
of a S = 3/2 spin ground state (the expected value is 1.875 emu
K mol-1) and confirms the presence of a ferrimagnetic coupling
between the Mn(II) ion and the two Cu(II) ions inside the cluster
(resulting in a spin ground state of 5/2 - 2*1/2 = 3/2). Finally, in
compound 4 the sharp decrease observed at very low temperatures
˚
to be considered as negligible (2.615, 2.491 and 2.685 A in 2–
4, respectively). Furthermore, the possible coupling through this
long bridge is not expected to provide an effective overlap of
the magnetic orbitals since O(1) connects an axial position of
one Cu(II) ion with a basal position on the other Cu(II) ion,
precluding any effective overlap of the magnetic orbitals. This
simple symmetric trimer model reproduces very satisfactorily the
magnetic properties of compounds 2–4 in the whole temperature
range (solid line in Fig. 7) with the parameters displayed in Table
4. As for compound 1, the data were fit with the MAGPACK
program.44 Note that the Hamiltonian is written as: H = -J
[S1S2 + S1S3], with S1 = SMn and S2 = S3 = SCu. In order to
reduce the number of adjustable parameters, we have assumed
that the g values for all the ions are equal. Finally, to be sure that
the Cu1–Cu1 interaction is negligible; we have initially included
this interaction in the model (as an additional J¢ constant). This
triangular model leads to an almost identical fit with a J¢ value
very close to 0 (J¢ = 0.01 cm-1), confirming the absence of any
Cu1–Cu1 interaction.
A further confirmation of the antiferromagnetic nature of the
interactions in compounds 1–4 and of the resulting S = 1 (for 1) and
S = 3/2 (for 2–4) spin ground states is provided by the isothermal
magnetizations at 2 K (Fig. 8). These measurements show
paramagnetic behaviours with saturation values of ca. 2 mB, which
is the expected value for a S = 1 spin ground state for compound
1. As expected, the magnetization of compound 1 can be very well
reproduced with a Brillouin function for a S = 1 spin ground state
(solid line in Fig. 8). As expected, compounds 2–4 show saturation
values of ca. 3 mB and the magnetization behaviours can be well
reproduced with the Brillouin function for a S = 3/2 spin ground
state with g values close to 2 (solid lines in Fig. 8).
Fig. 7 Thermal variation of the cmT product for compounds 2–4. Inset
shows the low temperature region. Solid lines represent the best fit to the
model (see text).
This journal is
The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 462–473 | 469
©

View Article Online
analysed are the Cu–O and Mn–O bond distances, the Cu–O–Mn
bond angle and the dihedral angle in the central CuO2Mn unit. As
can be seen in Table 5 and in Fig. 9, there is no clear relationship
between the J value and only one of these structural parameters.
Nevertheless, there are some trends in all the parameters and a
combination of all of them may allow us to assign the J values
to the different double oxido bridges. Thus, the J value shows a
trend to decrease (in absolute value) as the dihedral angle in the
MnO2Cu central unit becomes bigger (Fig. 9a) and also as the Cu–
O–Mn bond angle approaches 90◦ (Fig. 9d). These trends reflect
on one side the decrease in the overlap of the magnetic orbitals
as the dihedral angle increases and on the other hand the increase
of the ferromagnetic component and therefore a decrease of the
antiferromagnetic coupling, as the Cu–O–Mn angle approaches
90◦. With these two trends in mind, we can clearly assign the
lower J value (J13 = -12.6 cm-1) to the Mn(1)–Cu(3) bridge since
it presents by far the largest dihedral angle (28.0◦) and the lowest
average Cu–O–Mn bond angle (96.8◦) (Fig. 10a) (note that the
two other structural parameters also support this assignment, see
Table 5). The other two J values are not so easy to assign from these
relationships since their values are almost identical. Nevertheless,
if we look at the variation of J with the other structural parameters
we can see that J increases (in absolute value) as the Cu–O bond
distance increases (Fig. 9b) and as the Mn–O bond distance
decreases (Fig. 9c). The first of these trends is slightly counter-
intuitive since a decrease in the distance implies an increase in the
(antiferromagnetic) coupling. This trend may be due to a faster
decrease of the ferromagnetic term of the coupling as compared
with the antiferromagnetic one as the distance increases (i.e.,
both terms, the ferro- and antiferromagnetic ones decrease
Fig. 8 Isothermal magnetizations at 2 K for compounds 1–4. Solid lines
are the best fit to the Brillouin function for a S = 1 spin state (for 1) and
S = 3/2 spin states (for 2–4).
As mentioned earlier, compound 1 is a tetranuclear MnCu3
cluster where the central Mn(II) ion is connected to three terminal
Cu(II) ions through double oxido bridges. A search in the CCDC
database shows no other examples of tetrameric MnCu3 clusters
neither with double nor with single oxido bridges. Complex 1 is
therefore the first know example of this kind. Since the structure of
complex 1 shows three different Mn(II)–Cu(II) exchange pathways
corresponding to the three different double oxido bridges, it is not
straightforward (although not impossible) to assign each of the
three J values obtained in the fit to each of the three different oxido
bridges present in complex 1. Thus, in Table 5 we have assembled
the J values together with the main structural parameters in all
the structurally and magnetically characterized double or single
oxido bridged Mn(II)–Cu(II) complexes (most of them are Mn–Cu
dimers with a double oxido bridge). The structural parameters
Table 5 Magnetic and structural parameters of Mn(II)–Cu(II) complexes with oxido bridges
J (cm-1)
Cu–O (A)
Mn–O (A)
Cu–O–Mn (◦)
Dihedral Cu–O2–Mn (◦)
Reference
˚
˚
CCDC Code
BIXXEMa
QUKYAXb,c
CEPLIT
-28.5
-16.8
-41.6
1.918/1.924
2.281/2.317
1.933/1.886
1.941/1.891
1.894
2.225/2.175
2.159/2.121
2.173/2.138
2.234/2.157
2.199
101.7/03.3
121.3/118.7
99.8/102.6
97.5/101.8
103.7
96.9/94.4
98.6/99.9
12.9
—
9.8
23a
46
29a
11.4
0.01
26.1
15.6
16.1
11.7
0.42
1.4
10.8
3.4
9.7
8.5
2.1
3.2
8.9
3.0
8.2
24.4
15.5
20.7
28.0
22.1
21.9
24.5
DEXQUT
FAEPCU
HETZIQ
-28
-26.4
-39
25a
25b
26
1.897/1.889
1.918/1.900
1.902/1.908
1.898/1.907
1.910/1.929
1.938/1.944
1.894/1.879
1.878/1.897
1.917/1.887
1.958/1.960
1.945/1.960
1.955/1.951
1.950/1.936
1.938/1.943
1.940/1.951
1.925
2.154/2.235
2.250/2.228
2.240/2.255
2.247/2.150
2.203/2.213
2.248/2.259
2.188/2.167
2.169/2.249
2.301/2.285
2.126/2.130
2.198/2.176
2.201/2.210
2.167/2.135
2.178/2.191
2.204/2.184
2.218
100.1/99.4
100.0/103.2
107.8/106.7
100.3/99.8
99.6/100.8
105.2/101.6
100.1/101.7
100.6/100.4
106.2/106.5
106.1/105.9
104.4/106.1
107.1/106.4
106.3/106.7
96.8
98.94/100.93
102.36/96.64
93.91/99.78
91.8/103.5
91.3/103.2
103.3/92.5
ILAKOV
JAFLIM
KEYNEI
LEGJAI
MIXLEL
QEKFIW
UKIPEJ
VOBKUT
VOBLAA
-22
-56.6
-37
27
25c
25d
25e
25f
25g
25h
29b
29b
-22.4
-31.8
-36.8
-60
-48.9
-64.7
VOBLII
YADNIB
1d
-60.4
-16.7
-41.2
-39.8
-12.6
-20.0
-17.3
-32.5
29b
28
This work
1.958/1.934
1.937/1.927
1.908/1.938
1.903/1.937
1.907/1.938
1.923/1.905
2.196/2.161
2.116/2.292
2.324/2.119
2.103/2.481
2.147/2.534
2.100/2.438
2a
3a
4a
This work
This work
This work
a Trimeric MnCu2 complex; b Single Mn–Cu oxido bridge; c This complex presents a Cu–O–P–O–Mn additional bridge; d Tetrameric MnCu3 complex.
470 | Dalton Trans., 2012, 41, 462–473
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
Fig. 9 Variation of the magnetic coupling (J) in Mn(II)–Cu(II) double oxido bridged complexes with: (a) the dihedral MnO2Cu angle, (b) the average
Cu–O bond distance, (c) the average Mn–O bond distance and (d) the average Mn–O–Cu bond angle. White dots are the three exchange constants
obtained in compound 1.
model including only two coupling constants (i.e., assuming J11
=
J12) gives very similar results with almost superimposable plots
and an intermediate J value (J11 = J12 = -40.5 cm-1).
As already mentioned in the structural description, compounds
2–4 present very similar structures with a central Mn(II) ion con-
nected to two terminal Cu(II) ions through a double asymmetric
oxido bridge (Fig. 10b and Table 6). This asymmetric double oxido
bridge contains a short–short Cu–O(2)–Mn bridge and a short–
long Cu–O(1)–Mn one. Besides this Cu–Mn connection, there is
an almost negligible Cu–Cu one through a short–long Cu–O–Cu
bridge. If we consider that these long Cu–O and Mn–O bonds are
not contributing to the magnetic exchange, then compounds 2–4
can be considered as symmetric linear trimers with a single oxido
bridge. A search in the CCDC database (updated to May 2011)
shows that there are only two structurally characterized trimeric
MnCu2 clusters with double oxido bridges: BIXXEM23a and
PODGOE23b but none with single oxido bridges. In both MnCu2
trimers the Cu(II) ions are surrounded by a Schiff-base ligand and
the Mn(II) ion completes its coordination with additional donor
atoms from the Schiff-base ligand (2 O atoms in BIXXEM case
and 4 N atoms in PODGOE). The magnetic properties of the only
Fig. 10 Structure of (a) the MnCu3 (in 1) and (b) MnCu2 (in 2–4) clusters.
The bridging bond distances and angles for b are listed in Table 6.
but the ferromagnetic component decreases faster, resulting in an
increase of the overall antiferromagnetic coupling). In summary,
the J value increases in absolute value when the Cu–O distance and
the Mn–O–Cu bond angle increase and when the Mn–O distance
and the dihedral MnO2Cu angle decrease (Fig. 9).
If we now compare the Mn(1)–Cu(1) and Mn(1)–Cu(2) bridges
(Fig. 10a and Table 5) we can see that the Mn(1)–Cu(1) bridge has:
˚
(i) a larger average Cu–O bond distance (1.946 A compared with
˚
1.932 A for the Mn(1)–Cu(2) bridge), (ii) a larger Mn–O–Cu bond
angle (99.94◦ compared with 99.65◦ for the Mn(1)–Cu(2) bridge),
◦
˚
Table 6 Bridging bond distances (in A) and angles ( ) in the MnCu2
clusters (2–4) (Fig. 10b)
˚
(iii) a lower average Mn–O bond distance (2.178 A compared with
˚
2.204 A for the Mn(1)–Cu(2) bridge) and, finally, (iv) a lower
2
3
4
dihedral angle in the central MnO2Cu moiety (15.5◦, compared
with 20.7◦ for the Mn(1)–Cu(2) bridge).
Interestingly, the four parameters suggest that the Mn(1)–Cu(1)
bridge should present a larger (absolute) J value than the Mn(1)–
a
b
c
d
e
1.903
1.937
2.103
2.615
2.481
103.5
102.8
77.0
1.907
1.938
2.147
2.491
2.534
103.2
99.8
1.905
1.923
2.100
2.685
2.438
103.3
102.9
75.9
Cu(2) bridge and, accordingly, we assign the larger J value (J11
=
=
-41.2 cm-1) to the Mn(1)–Cu(1) bridge and the smaller one (J12
a
b
g
-39.8 cm-1) to the Mn(1)–Cu(2) bridge; although, of course, given
the small difference between both J values, we cannot have a total
certitude in this assignation. In fact, as mentioned above, a simpler
79.2
91.3
d
91.8
92.5
This journal is
The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 462–473 | 471
©

View Article Online
studied complex (BIXXEM) show a moderate antiferromagnetic
coupling with a J value of -28.5 cm-1,23a similar to those observed
in 2–4. If we search in the CCDC database for single oxido-
bridged Cu–Mn structures with any nuclearity, we find only three
examples: two nonanuclear complexes45 and a tetranuclear one.46
The three complexes show antiferromagnetic couplings although
the magnetic coupling has only been determined in two of them
(with values of -16.8 and -22.5 cm-1). These values are also similar
to those observed in complexes 2–4. Finally, if instead of single,
we search for double oxido bridged Mn–Cu complexes with any
nuclearity we find up to fifteen magnetically and characterized
complexes (most of them are dimers, Table 5). In these complexes
the magnetic coupling is moderate and antiferromagnetic with J
values similar to those found in compounds 1–4 and always in the
range -16 to -65 cm-1 (Table 5).
J. Barbour, Chem. Commun., 2006, 1163; (c) M. Dinca´ and J. R. Long,
J. Am. Chem. Soc., 2005, 127, 9376.
2 (a) J. R. Berenguer, E. M. Lalinde and T. Moreno, Coord. Chem. Rev.,
2010, 254, 832; (b) V. W. W. Yam and K. K. W. Lo, Chem. Soc. Rev.,
1999, 28, 323; (c) X.-X. Lu, C.-K. Li, E. C.-C. Cheng, N. Zhu and V.
W. - W. Ya m , Inorg. Chem., 2004, 43, 2225.
3 (a) O. Kahn, Molecular Magnetism, VCH, New York, 1993; (b) C.
Biswas, P. Mukherjee, M. G. B. Drew, C. J. Go´mez-Garc´ıa, J. M.
Clemente-Juan and A. Ghosh, Inorg. Chem., 2007, 46, 10771; (c) S.
Naiya, C. Biswas, M. G. B. Drew, C. J. Go´mez-Garc´ıa, J. M. Clemente-
Juan and A. Ghosh, Inorg. Chem., 2010, 49, 6616; (d) A. Palii, B.
Tsukerblat, S. Klokishner, K. R. Dunbar, J. M. Clemente-Juan and E.
Coronado, Chem. Soc. Rev., 2011, 40, 3130; (e) T. Glasera, I. Liratzis,
A. M. Ako and A. K. Powell, Coord. Chem. Rev., 2009, 253, 2296.
4 (a) E. Coronado, J. R. Gala´n-Mascaro´s, C. J. Go´mez-Garc´ıa and
V. Laukhin, Nature, 2000, 408, 447; (b) E. Coronado, J. R. Gala´n-
Mascaro´s and C. Mart´ı-Gastaldo, J. Am. Chem. Soc., 2008, 130, 14987.
5 See, for example: (a) M. Andruh, Chem. Commun., 2011, 47, 3025;
(b) S. Benmansour, C. Atmani, F. Setifi, S. Triki, M. Marchivie and
C. J. Go´mez-Garc´ıa, Coord. Chem. Rev., 2010, 254, 1468; (c) S. Naiya,
H.-S. Wang, M. G. B. Drew, Y. Song and A. Ghosh, Dalton Trans.,
2011, 40, 2744; (d) P. Kar, R. Biswas, M. G. B. Drew, Y. Ida, T. Ishida
and A. Ghosh, Dalton Trans., 2011, 40, 3295; (e) R. Biswas, P. Kar, Y.
Song and A. Ghosh, Dalton Trans., 2011, 40, 5324; (f) C. Biswas, M. G.
B. Drew, E. Ruiz, M. Estrader, C. Diaz and A. Ghosh, Dalton Trans.,
2010, 39, 7474.
Conclusions
The old “complex as ligand” strategy used in this work has
proven to be very useful in the synthesis of novel poly-nuclear
hetero-metallic magnetic complexes. Thus, the use of a [CuL]
complex as a ligand towards Mn(II) ions (H2L = tetradentate
di-Schiff base) has yielded the first star-shaped MnCu3 cluster
where the central Mn(II) ion is connected to three peripheral Cu(II)
ions through double oxido bridges. Reaction of this tetra-nuclear
MnCu3 complex with diverse linear triatomic anionc ligands as
6 See, for example: (a) M. Andruh, J. P. Costes, C. Diaz and S. Gao,
Inorg. Chem., 2009, 48, 3342; (b) R. Sessoli and A. K. Powell, Coord.
Chem. Rev., 2009, 253, 2328; (c) C. Benelli and D. Gatteschi, Chem.
Rev., 2002, 102, 2369.
7 (a) Y. Pei, M. Verdaguer, O. Kahn, J. Sletten and J. P. Renard,
Inorg. Chem., 1987, 26, 138; (b) V. Baron, B. Gillon, A. Cousson, C.
¨
Mathonie`re, O. Kahn, A. Grand, L. Ohrstro¨m, B. Delley, M. Bonnet
N3 , NCO- and NCS- has yielded three very similar trinuclear
-
and J. X. Boucherle, J. Am. Chem. Soc., 1997, 119, 3500; (c) C. L. M.
Pereira, E. Pedroso, H. O. Stumpf, M. A. Novak, L. Ricard, R. Ruiz-
Garc´ıa, E. Rivie`re and Y. Journaux, Angew. Chem., Int. Ed., 2004, 43,
956.
8 (a) E. Sinn and C. M. Harris, Coord. Chem. Rev., 1969, 4, 391; (b) A.
Bencini, C. Benelli, A. Caneschi, R. L. Carlin, A. Dei and D. Gatteschi,
J. Am. Chem. Soc., 1985, 107, 8128; (c) S. Chattopadhyay, G. Bocelli,
A. Musatti and A. Ghosh, Inorg. Chem. Commun., 2006, 9, 1053; (d) J.
M. Epstein, B. N. Figgis, A. H. White and A. C. Willis, J. Chem.
Soc., Dalton Trans., 1974, 1954; (e) P. Mukherjee, M. G. B. Drew, V.
Tangoulis, M. Estrader, C. Diaz and A. Ghosh, Inorg. Chem. Commun.,
2009, 12, 929.
complexes of formula [(CuL)2Mn(X)2], X = N3 (2), NCO- (3)
-
and NCS- (4), where one of the chelating [CuL] units has been
replaced by two terminal N-coordinated X- ligands. These three
compounds increase the number of this kind of complexes from
three to six.
The magnetic coupling through the double asymmetric oxido
bridges is in all cases moderate and antiferromagnetic leading
to spin ground states of S = 1 (in 1) and S = 3/2 (in 2–4).
These couplings have been rationalized from the previous existing
Mn–Cu complexes with oxido bridges. Furthermore, a tentative
magneto-structural correlation has been established between the J
values and four structural parameters in the double oxido bridged
Mn–Cu clusters: (1) the average Mn–O bond distance, (2) the
average Cu–O bond distance, (3) the average Mn–O–Cu bond
angle and (4) the dihedral angle in the central MnO2Cu unit. This
magneto-structural correlation has allowed us to assign the differ-
ent coupling constants found in the star-shaped MnCu3 complex 1.
9 (a) G. A. Brewer and E. Sinn, Inorg. Chim. Acta, 1987, 134, 13; (b) P.
Mukherjee, M. G. B. Drew, A. Figuerola and A. Ghosh, Polyhedron,
2008, 27, 3343; (c) Y. Xie, Q. Liu, H. Jiang and J. Ni, Eur. J. Inorg.
Chem., 2003, 4010.
10 (a) R. W. Saalfrank, I. Bernt, M. M. Chowdhry, F. Hampel and
G. B. M. Vaughan, Chem.–Eur. J., 2001, 7, 2765; (b) A. Cornia, L.
Gregoli, C. Danieli, A. Caneschi, R. Sessoli, L. Sorace, A. Barra and
W. Wernsdorfer, Inorg. Chim. Acta, 2008, 361, 3481; (c) R. Singh,
A. Banerjee, E. Colacio and K. K. Rajak, Inorg. Chem., 2009, 48,
4753; (d) A. L. Barra, A. Caneschi, A. Cornia, F. Fabrizi de Biani, D.
Gatteschi, C. Sangregorio, R. Sessoli and L. Sorace, J. Am. Chem. Soc.,
1999, 121, 5302; (e) L. Bogani, C. Danieli, E. Biavardi, N. Bendiab, A.
Barra, E. Dalcanale, W. Wernsdorfer and A. Cornia, Angew. Chem.,
Int. Ed., 2009, 48, 746; (f) C. Schlegel, J. v. Slageren, M. Manoli,
E. K. Brechin and M. Dressel, Polyhedron, 2009, 28, 1834; (g) M.
Acknowledgements
We thank CSIR, India for awarding a Senior Research Fellowship
[Sanction No. 09/028 (0732)/2008-EMR-I] to S. Biswas. Crystal-
lography was performed at the DST-FIST, India-funded Single
Crystal Diffractometer Facility at the Department of Chemistry,
University of Calcutta. We also thank to the Generalitat Valen-
ciana (Project PROMETEO 2009/095) and the Spanish Ministe-
rio de Ciencia e Innovacio´n (Project Consolider-Ingenio 2010 CSD
2007-00010 in Molecular Nanoscience and CTQ2011-26507).
´
Moragues-Ca´novas, E. Rivie`re, L. Ricard, C. Paulsen, W. Wernsdorfer,
G. Rajaraman, E. Brechin and T. Mallah, Adv. Mater., 2004, 16, 1101;
(h) S. Accorsi, A. Barra, A. Caneschi, G. Chastanet, A. Cornia, A. C.
Fabretti, D. Gatteschi, C. Mortalo`, E. Olivieri, F. Parenti, P. Rosa, R.
Sessoli, L. Sorace, W. Wernsdorfer and L. Zobbi, J. Am. Chem. Soc.,
2006, 128, 4742; (i) A. Cornia, A. C. Fabretti, P. Garrisi, C. Mortalo`, D.
Bonacchi, D. Gatteschi, R. Sessoli, L. Sorace, W. Wernsdorfer and A.
Barra, Angew. Chem., Int. Ed., 2004, 43, 1136; (j) N. T. Madhu, J. Tang,
I. J. Hewitt, R. Cle´rac, W. Wernsdorfer, J. v. Slageren, C. E. Anson
and A. K. Powell, Polyhedron, 2005, 24, 2864; (k) R. W. Saalfrank, A.
Scheurer, I. Bernt, F. W. Heinemann, A. V. Postnikov, V. Schunemann,
A. X. Trautwein, M. S. Alam, H. Rupp and P. Muller, Dalton Trans.,
2006, 2865; (l) G. G. Condorelli, A. Motta, G. Pellegrino, A. Cornia,
L. Gorini, I. L. Fragala, C. Sangregorio and L. Sorace, Chem. Mater.,
2008, 20, 2405; (m) L. Gregoli, C. Danieli, A. Barra, P. Neugebauer, G.
References
1 (a) H. K. Chae, D. Y. Siberio-Pe´rez, J. Kim, Y. Go, M. Eddaoudi, A. J.
Matzger, M. O’Keeffe and O. M. Yaghi, Nature, 2004, 427, 523; (b) L.
472 | Dalton Trans., 2012, 41, 462–473
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
Pellegrino, G. Poneti, R. Sessoli and A. Cornia, Chem.–Eur. J., 2009,
15, 6456; (n) M. J. Rodriguez-Douton, A. Cornia, R. Sessoli, L. Sorace
and A. Barra, Dalton Trans., 2010, 39, 5851.
Julve, J. Faus, M. C. Mun˜oz and X. Solans, Inorg. Chim. Acta, 1993, 213,
261; (f) M. Nayak, S. Hazra, P. Lemoine, R. Koner, C. R. Lucas and S.
Mohanta, Polyhedron, 2008, 27, 1201; (g) L. Bo, Z. Hong, P. Zhi-Quan,
S. You, W. Cheng-Gang, Z. Han-Ping, H. Jing-Dong and C. Ru-An, J.
Coord. Chem., 2006, 59, 1271; (h) A. Hori, Y. Mitsuka, M. Ohba and
H. Okawa, Inorg. Chim. Acta, 2002, 337, 113; (i) H. Okawa, J. Nishio,
M. Ohba, M. Tadokoro, N. Matsumoto, M. Koikawa, S. Kida and D.
E. Fenton, Inorg. Chem., 1993, 32, 2949; (j) C. Fraser, R. Ostrander,
A. L. Rheingold, C. White and B. Bosnich, Inorg. Chem., 1994, 33,
324; (k) D. G. Branzea, A. M. Madalan, S. Ciattini, N. Avarvari, A.
Caneschi and M. Andruh, New J. Chem., 2010, 34, 2479.
26 D. Visinescu, J. P. Sutter, C. Ruiz-Pe´rez and M. Andruh, Inorg. Chim.
Acta, 2006, 359, 433.
11 (a) C. P. Pradeep, P. S. Zacharias and S. K. Das, Eur. J. Inorg. Chem.,
2007, 5377; (b) U. Thewalt, Chem. Ber., 1971, 104, 2657; (c) U. Thewalt
and J. Z. Ernst, Naturforsch., B: Chem. Sci., 1975, 30, 818; (d) D. A.
Dixon, R. E. Marsh and W. P. Schaefer, Acta Crystallogr., Sect. B:
Struct. Crystallogr. Cryst. Chem., 1978, 34, 807; (e) M. Du, Y. Guo, X.
Bu and J. Ribas, Eur. J. Inorg. Chem., 2004, 3228; (f) S. W. Gordon-
Wylie, E. L. Bominaar, T. J. Collins, J. M. Workman, B. L. Claus, R. E.
Patterson, S. A. Williams, B. J. Conklin, G. T. Yee and S. T. Weintraub,
Chem.–Eur. J., 1995, 1, 528; (g) E. Porzsolt, T. Berg and J. Bjerrum,
Acta Chem. Scand., Ser. A, 1978, 32, 319.
12 (a) S. Khanra, K. Kuepper, T. Weyhermu¨ller, M. Prinz, M Raekers, S.
Voget, A. V. Postnikov, F. M. F. de Groot, S. J. George, M. Coldea, M
Neumann and P. Chaudhuri, Inorg. Chem., 2008, 47, 4605; (b) E. Gao,
S. Bai, Z. He and C. Yan, Inorg. Chem., 2005, 44, 677; (c) C. Liu, D.
Zhang and D. Zhu, Inorg. Chem., 2009, 48, 792; (d) N. Reddig, M. U.
Triller, D. Pursche, A. Rompel and B. A. Krebs, Z. Anorg. Allg. Chem.,
2002, 628, 2458.
13 I. S. Tidmarsh, L. J. Batchelor, E Scales, R. H. Laye, L. Sorace, A.
Caneschi, J. Schnack and E. J. L. McInnes, Dalton Trans., 2009, 9402.
14 (a) H. U. Gu¨del and U. Hauser, Inorg. Chem., 1980, 19, 1325; (b) L. J.
Batchelor, M. Sander, F. Tuna, M. Helliwell, F. Moro, J. van Slageren,
E. Burzuri, O. Montero, M. Evangelisti, F. Luis and E. J. L. McInnes,
Dalton Trans., 2011, 40, 5278.
27 S. Osa, Y. Sunatsuki, Y. Yamamoto, M. Nakamura, T. Shimamoto, N.
Matsumoto and N. Re, Inorg. Chem., 2003, 42, 5507.
28 M. Pascu, F. Lloret, N. Avarvari, M. Julve and M. Andruh, Inorg.
Chem., 2004, 43, 5189.
29 (a) R. Tao, F. Li, S. Zang, Y. Cheng, Q. Wang, J. Niu and D. Liao,
Polyhedron, 2006, 25, 2153; (b) D. G. Branzea, A. Guerri, O. Fabelo,
C. Ruiz-Pe´rez, L. Chamoreau, C. Sangregorio, A. Caneschi and M.
Andruh, Cryst. Growth Des., 2008, 8, 941.
30 K. Iida, I. Oonishi, A. Nakahara and Y. Komoyama, Bull. Chem. Soc.
Jpn., 1970, 43, 2347.
31 G. A. Bain and J. F. Berry, J. Chem. Educ., 2008, 85, 532.
32 SAINT, version 6.02; SADABS, version 2.03Bruker AXS, Inc., Madi-
son, WI, 2002.
15 K. Noro, Y. Ozawa, M. Taguchi and A. Yagasaki, Chem. Commun.,
2002, 1770.
33 G. M. Sheldrick, SHELXS-97, Program for solution of crystal struc-
tures, University of Go¨ttingen, Germany, 1997.
16 (a) S. Akine, S. Sunaga, T. Taniguchi, H. Miyazaki and T. Nabeshima,
Inorg. Chem., 2007, 46, 2959; (b) S. Daniele, L. G. Hubert-Pfalzgraf and
J. Vaissermann, Polyhedron, 1998, 17, 4249; (c) S. Akine, T. Matsumoto
and T. Nabeshima, Chem. Commun., 2008, 4604.
17 E. Tancini, M. J. Rodriguez-Douton, L. Sorace, A. Barra, R. Sessoli
and A. Cornia, Chem.–Eur. J., 2010, 16, 10482.
18 (a) D. J. Hodgson, K. Michelsen, E. Pedersen and D. K. Towle, J.
Chem. Soc., Chem. Commun., 1988, 426; (b) V. G. Kessler, L. G. Hubert-
Pfalzgraf, S. Halut and J. Daran, J. Chem. Soc., Chem. Commun., 1994,
705; (c) S. Muller and U. Thewalt, Z. Naturforsch. B: Chem. Sci.,
1989, 44, 257; (d) U. Thewalt and S. Mu¨ller, Chem. Ber., 1988, 121,
2111.
19 (a) F. Corazza, C. Floriani and M. Zehnderb, J. Chem. Soc., Chem.
Commun., 1986, 1270; (b) S. Biswas, S. Naiya, M. G. B. Drew, C.
Estarellas, A. Frontera and A. Ghosh, Inorg. Chim. Acta, 2011, 366,
219.
34 G. M. Sheldrick, SHELXL-97, Program for refinement of crystal
structures, University of Go¨ttingen, Germany, 1997.
35 A. L. Spek, Acta Crystallogr., Sect. A, 1990, 46, C34.
36 L. J. Farrugia, J. Appl. Crystallogr., 1997, 30, 565.
37 L. J. Farrugia, J. Appl. Crystallogr., 1999, 32, 837.
38 A. W. Addison, T. N. Rao, J. Reedjik, J. V. Rijn and C. G. Verschoor, J.
Chem. Soc., Dalton Trans., 1984, 1349.
39 L. Yang, D. R. Powell and R. P. Houser, Dalton Trans., 2007, 955.
40 (a) Z. Liu, D. Zhang, J. Luo, Z. Jiang, D. Liao and D. Zhu, J. Coord.
Chem., 2004, 57, 647; (b) Y. He, H. Z. Kou, M. Xiong and R. J. Wang,
Chin. J. Struct. Chem., 2004, 23, 574; (c) Y. Ouyang, W. Zhang, Y. Ma,
N. Xu, D. Z. Liao, K. Yoshimura and S. P. Yan, Struct. Chem., 2007,
18, 891; (d) S. Wang, G. Yang, R. Li, Y. Wang and D. Liao, Eur. J. Inorg.
Chem., 2004, 4907; (e) J. Tang, Q. Wang, E. Gao, J. Chen, D. Liao, Z.
Jiang, S. Yan and P. Cheng, Helv. Chim. Acta, 2002, 85, 175.
41 R. Zhang, Q. Wang, J. Huang, F. Yang and G. Yang, Z. Anorg. Allg.
Chem., 2010, 636, 242.
20 L. Shen, G. Sheng, J. Qiu and Y. Zhang, J. Coord. Chem., 2003, 56, 603.
21 S. Biswas and A. Ghosh, Polyhedron, 2011, 30, 676.
22 (a) T. M. Rajendiran, C. Mathonie`re, S. Golhen, L. Ouahab and O.
Kahn, Inorg. Chem., 1998, 37, 2651; (b) P. Ren, W. Shi and P. Cheng,
Cryst. Growth Des., 2008, 8, 1097.
42 L. Zhang, S. Wang, G. Yang, J. Tang, D. Liao, Z. Jiang, S. Yan and P.
Cheng, Inorg. Chem., 2003, 42, 1462.
43 (a) V. Pavlishchuk, F. Birkelbach, T. Weyermu¨ller, K. Wieghardt and
P. Chaudhuri, Inorg. Chem., 2002, 41, 4405; (b) S. Khanra, B. Biswas,
C. Golze, B. Buchner, V. Kataev, T. Weyhermu¨ller and P. Chaudhuri,
Dalton Trans., 2007, 481; (c) F. Corazza, E. Solari, C. Floriani, A.
Chiesi-Villa and C. A. Guastini, J. Chem. Soc., Chem. Commun., 1986,
1562.
44 (a) J. J. Borra´s-Almenar, J. M. Clemente-Juan, E. Coronado and B. S.
Tsukerblat, Inorg. Chem., 1999, 38, 6081; (b) J. J. Borra´s-Almenar, J. M.
Clemente-Juan, E. Coronado and B. S. Tsukerblat, J. Comput. Chem.,
2001, 22, 985.
23 (a) C.-Z. Mei, R.-J. Tao and Q.-L. Wang, Acta Chim. Sinica., 2007, 65,
1129; (b) K. Brychcy, K.-J. Jens, M. Tilset and U. Behrens, Chem. Ber.,
1994, 127, 991.
¨
¨
24 S. Oz, R. Kurtaran, C. Arıcı, U. Ergun, F. N. D. Kaya, K. C. Emregu¨l,
¨
O. Atakol and D. Ulku¨, J. Therm. Anal. Calorim., 2010, 99, 363.
25 (a) M. Nayak, R. Koner, H. Lin, U. Flo¨rke, H. Wei and S. Mohanta,
Inorg. Chem., 2006, 45, 10764; (b) C. J. O’Connor, D. P. Freyberg and
E. Sinn, Inorg. Chem., 1979, 18, 1077; (c) Y. Elerman, A Elmali, C. T.
Zeyrek, I. Svoboda and H. Z. Fuess, Naturforsch. B: Chem. Sci., 2003,
58, 271; (d) Visinescu, J. P. Sutter, H. W. Roesky, J. Magull and M.
Andruh, Rev. Roum. Chim., 2005, 50, 737; (e) R. Ruiz, F. Lloret, M.
45 L. N. Dawe, K. V. Shuvaev and L. K. Thompson, Inorg. Chem., 2009,
48, 3323.
46 Z. Gu and S. C. Sevov, J. Mater. Chem., 2009, 19, 8442.
This journal is
The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 462–473 | 473
©