Super-exchange interaction in a chair-piperazine bridged dicopper(II/II) complex: Synthesis, crystal structure, magnetic properties and molecular orbital calculations

Article abstract of DOI:10.1515/znb-2006-0302

Reaction of the μ-bis(tridentate) ligand H₃L′ (L′ = 1,3-bis[N-(5-chloro-2-hydroxybenzylidene)-2-aminoethylene]-2-(5-chloro-2- hydroxyphenyl)imidazolidine) with copper(II) chloride dihydrate gives the chair-piperazine bridged complex [Cu₂

Full text of DOI:10.1515/znb-2006-0302

Super-Exchange Interaction in a Chair-Piperazine Bridged
Dicopper(II/II) Complex: Synthesis, Crystal Structure, Magnetic
Properties and Molecular Orbital Calculations
C. T. Zeyreka, A. Elmalib, and Y. Elermanb
a Turkish Atomic Energy Authority, 06690 Lodumlu-Ankara, Turkey
b Department of Engineering Physics, Faculty of Engineering, Ankara University,
06100 Besevler-Ankara, Turkey
Reprint requests to Dr. C. Zeyrek. E-mail: zeyrek@taek.gov.tr
Z. Naturforsch. 61b, 237 – 242 (2006); received October 13, 2005
Reaction of the µ-bis(tridentate) ligand H3Lꢀ (Lꢀ = 1,3-bis[N-(5-chloro-2-hydroxybenzylidene)-
2-aminoethylene]-2-(5-chloro-2-hydroxyphenyl)imidazolidine) with copper(II) chloride dihydrate
gives the chair-piperazine bridged complex [Cu2(µ-L)Cl2]. The halves of the binuclear com-
plex are related by crystallographic inversion symmetry. The intramolecular Cu···Cu separation
˚
is 6.954(3) A. Temperature-dependent magnetic susceptibility measurements of the complex show
a weak intramolecular antiferromagnetic coupling. The super-exchange coupling constant (J) is
−10.5 cm−1. Semi-empirical extended Hu¨ckel molecular orbital (EHMO) calculations have been
performed in order to gain insight into the molecular orbitals that participate in the super-exchange
pathway.
Key words: Dinuclear Copper(II) Complex, Super-Exchange Interactions, Antiferromagnetic
Coupling, Schiff Base, Imidazolidine
Introduction
in both the boat and chair conformations of which
the later is thermodynamically more favorable [9].
The boat form gives mononuclear complexes [10],
whereas the chair form can give dinuclear complexes
with no exogenous bridging for trans-N,N’-coordina-
tion.
Series of binuclear transition-metal complexes
which display interesting physical properties have been
intensively investigated during the last two decades.
This is partly due to their relevance as active site struc-
tures of metal-proteins and enzymes [1, 2], and partly
because of attempts to understand the relationship be-
tween the structure and the magnetic properties [3 – 7].
Many of the studies have been concerned with ex-
change interactions in binuclear copper(II) complexes
and the results have indicated that the strength of the
exchange interaction depends primarily upon the sym-
metry and energy of the copper(II) ion ground state
relative to the highest occupied molecular orbitals of
the bridging moiety. The complexes exhibit ferromag-
netic or antiferromagnetic character depending on their
geometry.
Very recently, we reported the syntheses, structural
characterization and conformational analysis of the lig-
and H3Lꢀ (Fig. 1) and its mononuclear iron(III) com-
plex [11]. We also reported the magnetic properties of
its dinuclear iron(III) complex [12]. Herein we report
the complexation behavior of copper(II) towards the
µ-bis(tridentate) ligand (H3Lꢀ). The ligand reacts with
copper(II) chloride dihydrate in methanol to form the
dinuclear [Cu2(µ-L)Cl2] complex with the imidazoli-
dine ring transformed into chair-piperazine by hydrol-
ysis (Fig. 1). We present the synthesis, crystal struc-
ture and magnetic properties of the chair-piperazine
bridged dicopper(II/II) complex [Cu2(µ-L)Cl2] of the
new piperazino µ-bis(tridentate) ligand {N,N’-bis[2-
(5-chlorosalicylaldimino)ethyl]piperazine} (H2L). We
also performed extended Hu¨ckel molecular orbital
(EHMO) calculations to determine the nature of the
frontier orbitals.
The nature and number of metal ion coordination
of linear hexadentate ligand can be altered [8] with
the insertion of a spacer group such as imidazolid-
ine, forcing the parent hexadentate ligand to act as
a bis(tridentate) and/or bis(tetradentate) one. Chelat-
ing arm-substituted 1,4-piperazine can bind metal ions
c
0932–0776 / 06 / 0300–0237 $ 06.00 ꢀ 2006 Verlag der Zeitschrift fu¨r Naturforschung, Tu¨bingen · http://znaturforsch.com
- 10.1515/znb-2006-0302
Downloaded from De Gruyter Online at 09/12/2016 12:14:19AM
via free access

238
C. T. Zeyrek et al. · Super-Exchange Interaction in a Chair-Piperazine Bridged Dicopper(II/II) Complex
Table 1. Crystallographic data for the investigated complex.
Formula
C22H24Cl4Cu2N4O2
645.33
monoclinic
P21/c
11.6060(10)
6.9310(10)
15.4790(10)
102.881(8)
1213.8(2)
Formula weight (g·mol−1
Crystal system
Space group
)
˚
a [A]
˚
b [A]
˚
c [A]
β [◦]
3
˚
Vol [A ]
Z
2
Dcalcd. [g·cm−3
]
1.766
2.222
µ [cm−1
F(000)
θ Range for data collection
Index ranges
]
652 ◦
4.12 < θ < 26.36◦
−14 ≤ h ≤ 14
−8 ≤ k ≤ 8
−14 ≤ l ≤ 19
7312
Reflections collected
Independent reflections
Data / parameters
Goodness-of-fit on F2
Final R indices [I > 2σ(I)]
Final R indices (all data)
2457
2457 / 166
1.080
R = 0.0428, wR = 0.1004
R = 0.0608, wR = 0.1087
0.538 and −0.480
−3
˚
Largest diff. peak and hole [e·A
]
Fig. 1. Schemes of [Cu2(µ-L)Cl2] and H3Lꢀ.
Experimental Section
Preparation of [Cu2(µ-L)Cl2]
The dinuclear copper(II/II) complex was prepared in two
steps. A solution of triethylenetetramine (2.2 g, 15 mmol) in
methanol (20 ml) was added dropwise to a methanolic solu-
tion (40 ml) of 5-chlorosalicylaldehyde (6.32 g, 45 mmol)
with stirring at room temperature. The Schiff base ligand
was obtained in the form of yellow crystals (H3Lꢀ) (Fig. 1).
For the preparation of the copper(II/II) complex, the Schiff
base ligand H3Lꢀ (1.15 g, 2 mmol) was dissolved in hot
methanol (70 ml) and a solution of copper(II)chloride dihy-
drate (0.54 g, 4 mmol) in 50 ml of methanol was added with
stirring for 5 min. The blue solution was allowed to evaporate
at room temperature over one day to give prismatic blue crys-
tals, which were collected, washed with cold absolute ethanol
and finally dried in air. C22H24Cl4Cu2N4O2 (645.33): calcd.
C 40.95, H 3.71, N 8.66, Cu 9.85; found C 41.05, H 3.59,
N 8.76, Cu 9.91.
Fig. 2. View of the molecule. Displacement ellipsoids are
plotted at the 50% probability level.
rized in Table 1. Precise unit cell dimensions were deter-
mined by least-squares refinement on the setting angles of
25 reflections (4.12◦ ≤ θ ≤ 26.36◦) carefully centered on the
¯
diffractometer. The standard reflections (1 1 1, 2 1 2, 2 1 2)
were measured every 7200 s and the orientation of the crys-
tal was checked after every 600 reflections. A total of 7312
reflections were recorded, with Miller indices hmin = −14,
hmax = 14, kmin = −8, kmax = 8, lmin = −14, lmax = 19. Data
X-ray structure determination
A crystal of dimension 0.40 × 0.30 × 0.04 mm3 was reduction and corrections for absorption and decomposition
mounted on an Enraf-Nonius CAD 4 diffractometer [13] and were achieved using the Nonius Diffractometer Control Soft-
investigated with graphite monochromatized Mo-Kα radia- ware [13]. The structure was solved by SHELXS-97 [14] and
˚
tion (λ = 0.71073 A). Experimental conditions are summa- refined with SHELXL-97 [15]. The positions of the H atoms
- 10.1515/znb-2006-0302
Downloaded from De Gruyter Online at 09/12/2016 12:14:19AM
via free access

C. T. Zeyrek et al. · Super-Exchange Interaction in a Chair-Piperazine Bridged Dicopper(II/II) Complex
239
◦
˚
Table 2. Atomic coordinates and equivalent isotropic dis- Table 3. Selected bond lenghts (.A) and bond angles ( ) char-
placement parameters (A ) of the non-hydrogen atoms.
2
˚
acterizing the inner coordination sphere of the copper(II)
centers (see Fig. 2 for labeling scheme adopted).
Atom
C1
C2
C3
C4
C5
C6
C7
C8
x
y
z
∗U(eq)
Cu···Cua
N1–Cu1
O1–Cu1
Cu1–Cl1
C7–N1
6.954(3)
1.950(3)
1.913(3)
2.755(1)
1.281(5)
1.484(4)
0.2144(3)
0.1592(4)
0.0741(4)
0.0413(4)
0.0902(4)
0.1760(3)
0.2131(3)
0.2990(3)
0.4231(3)
0.5747(3)
0.3802(3)
0.2801(3)
0.4458(3)
0.2948(2)
0.4884(5)
0.5743(7)
0.4797(6)
0.2941(7)
0.2051(6)
0.3001(6)
0.2086(6)
0.1837(5)
0.2284(5)
0.4786(6)
0.5540(6)
0.2837(4)
0.4387(4)
0.5859(4)
0.3024(2)
0.3653(2)
0.3984(3)
0.3705(3)
0.3089(3)
0.2725(2)
0.1998(2)
0.0746(2)
0.0642(2)
0.0868(2)
0.0399(9)
0.0470(10)
0.0496(11)
0.0518(11)
0.0507(11)
0.0396(9)
0.0412(9)
0.0402(9)
0.0361(8)
0.0337(8)
0.0340(8)
N2–Cu1
Cl1–Cu1
C1–O1
C8–N1
C10–N2
2.101(3)
2.268(1)
1.299(4)
1.461(4)
1.492(5)
C9–N2
C7–N1–C8
119.9(3)
114.4(2)
112.4(3)
104.5(2)
107.2(2)
136.8(1)
173.5(1)
88.7(2)
C7–N1–Cu1
C9–N2–C10
C10–N2–C11
C10–N2–Cu1
C1–O1–Cu1
O1–Cu1–N1
N1–Cu1–N2
N1–Cu1–Cl1
O1–Cu1–Cl1
N2–Cu1–Cl1
125.4(2)
110.1(3)
108.1(3)
114.6(2)
127.8(2)
92.6(1)
83.9(1)
167.0(2)
91.3(2)
C8–N1–Cu1
C9–N2–C11
C9–N2–Cu1
C11–N2–Cu1
Cu1–Cl1–Cu1
O1–Cu1–N2
O1–Cu1–Cl1
N2–Cu1–Cl1
N1–Cu1–Cl1
Cl1–Cu1–Cl1
C9
C10
C11
N1
N2
O1
Cl1
Cl2
Cu1
−0.0030(2)
0.15340(18) 0.0348(7)
0.07532(17) 0.0309(6)
0.27484(17) 0.0469(7)
0.19495(5) 0.0400(3)
0.41335(9) 0.0868(5)
0.18452(3) 0.03285(17)
0.45653(9) 0.81472(12)
93.5(2)
91.7(2)
101.2(1)
−0.06756(13) 0.1765(2)
94.3(2)
0.37567(4) 0.51537(6)
∗ U(eq) = (1/3) ΣiΣjUija∗i a∗j aiaj.
a
(−x, 1−y, −z).
magnetic corrections of the molar magnetic susceptibility
were applied using Pascal’s constant [18]. The effective
magnetic moments were calculated by the equation µeff
=
2.828(χT)1/2, where χ is the magnetic susceptibility per
Cu(II) ion.
Molecular orbital calculations
Extended Hu¨ckel molecular orbital (EHMO) calculations
have been performed in order to gain insight into the molecu-
lar orbitals that participate in the super-exchange pathway by
using the Computer Aided Composition of Atomic Orbitals
(CACAO) package programs [19]. The interatomic distances
were taken from the X-ray results. Molecular orbital repre-
sentations were plotted using the CACAO software [19].
Fig. 3. Unit cell packing diagram of [Cu2(µ-L)Cl2].
˚
bonded to C atoms were calculated (C-H distance 0.96 A),
and refined using a riding model. H atom displacement para-
meters were restricted to be 1.2Ueq of the parent atom. The
final positional parameters are presented in Table 2. A per-
spective drawing of the molecule is shown in Fig. 2 [16]. The
packing diagram for [Cu2(µ-L)Cl2] is shown in Fig. 3. Se-
lected bond lengths and angles are summarized in Table 3.
Crystallographic data (excluding structure factors) for the
structure reported in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supplementary
publication no. CCDC-283155 [17].
Results and Discussion
X-ray crystal structures
The halves of the chair-bridged [Cu2(µ-L)Cl2] bin-
uclear complex are related by crystallographic inver-
sion symmetry. The structure of the dicopper com-
plex has singly bridged near square-planar coordina-
tion geometry of the metal atoms with no short inter-
molecular contacts between the dinuclear units. The
N1, N2, O1, Cl1, and Cu atoms lie approximately in
a plane. The atom with the greatest deviation from
Susceptibility measurements
˚
the [CuN2OCl] plane is the Cu atom at 0.135(1) A.
The two copper atoms are bridged by a chair-shaped
Variable-temperature magnetic susceptibility measure-
ments of a powdered sample were performed with a
QUANTUM Design SQUID magnetometer in the temper-
piperazine fragment of L2−. The distance between the
Cu1 and Cu1i [symmetry transformation used to gen-
i
ature range 4.6 – 301 K. The applied field was 1 T. Dia- erate equivalent atoms: (1 − x, 1 − y, −z)] centers in
- 10.1515/znb-2006-0302
Downloaded from De Gruyter Online at 09/12/2016 12:14:19AM
via free access

240
C. T. Zeyrek et al. · Super-Exchange Interaction in a Chair-Piperazine Bridged Dicopper(II/II) Complex
is the molar fraction of a monomeric impurity. Least
squares fitting of the data leads to J = −10.5 cm−1
,
g = 2.06, xp = 1.6%. The title compound shows a
maximum in magnetic susceptibility at ca. 12.1 K
(0.032 cm3 mol−1 K) which is typical of antiferromag-
netic behavior. The rapid increase in magnetic suscep-
tibility at low temperatures is due to the presence of a
small amount of monomeric impurity (1.6%) as com-
monly encountered is such systems [23]. The calcu-
lated magnetic moments values [µeff = 2.828(χT)1/2
]
decrease from a value of 0.82 µB at 301 K to 0.025 µB
at 4.6 K, indicating a moderate intramolecular antifer-
romagnetic interaction.
Fig. 4. The molar magnetic susceptibilities χ per copper(II)
vs. temperature T curves.
In general, several structural features of binuclear
copper(II) complexes are thought to regulate the
strength of exchange coupling interactions: (i) the
dihedral angle between the two coordination planes,
(ii) planarity of the bonds around the bridging
atom, and (iii) the bridging atom(s) and bridging
angles [24, 25]. However, the number of polynuclear
copper(II) complexes with piperazine-derivative
is very limited to draw magneto-structural corre-
lations. The observed antiferromagnetic coupling
between the copper(II) ions is propagated by the
piperazine bridge through a σ type of exchange
pathway. This through-bond coupling (via the two
intervening C–C bonds) has been already reported
for very few complexes [20, 26]. A simple compar-
ison between structural and magnetic parameters of
the title compound and related complexes [Cu2(µ-
L)(DMF)2](ClO4)2 (DMF = N,N-dimethylformamide)
of the new piperazino µ-bis(tridentate) ligand, {N,N’-
bis[2-((salicylaldimine)amino)ethyl]piperazine} and
[Cu(fum)(ppz)(H2O)2] (fum = fumarate dianion and
ppz = piperazine) reported recently [21, 26] confirms
this similarity: The Cu···Cu bond distances are 6.908
˚
the dimer is 6.954(3) A. The Npip – Npip distance is
˚
3.007(2) A.
The coordination sphere of each copper atom con-
˚
tains two cis nitrogen atoms (Cu–N(1)= 1.950(3) A,
2
˚
Cu–N(2)=2.101(3) A) (coordination to imine sp and
piperazine sp3 nitrogen atoms is clearly reflected
in the bond distance difference), one phenolic oxy-
˚
gen (Cu–O(1)=1.913(3) A) of the µ-bis(tridentate)
ligand and one chlorine atom. The N,N-bridging
mode of piperazine in the dicopper(II/II) complex is
similar to that characterized earlier for acetate and
dimethylformamide (DMF) coordinated neutral com-
plexes [20, 21].
Magnetic properties
Magnetic susceptibilities for a powdered sample of
the complex were measured with a SQUID magne-
tometer over the temperature range 4.6–301 K. The
magnetic susceptibilities of the complex are shown as
a function of temperature in Fig. 4. The data were fitted
using the Bleaney-Bowers equation [22]
˚
and 6.947 A; the Npip– Npip distances are 3.038
˚
and 2.963 A; the Cu–Npip distances are 2.058 and
ꢀ
ꢁ−1
NLg2µB
3kT
1
2
˚
2.047 A. In the investigated complex, the Cu···Cu
χ =
1+ exp(−2J/kT)
(1−xp)
3
˚
bond distance is 6.954(3) A; the Npip–Npip distance
˚
˚
is 3.007 A; the Cu–Npip distances is 2.101(3) A. The
J values reported from these studies are very close to
that obtained in the present work: J = −13.9 cm−1
and −14.7 cm−1 and g = 2.07 and 2.04, respectively.
NLg2µB
4kT
2
+
xp +Nα
(1)
and the isotropic (Heisenberg) exchange Hamiltonian
H = −2J S1.S2, where −2J corresponds to the
energy separation between spin-singlet and -triplet
states, for two interacting S = 1/2 centers. Nα is
the temperature-independent paramagnetism and its
Extended Hu¨ckel molecular orbital calculations
(EHMO)
We have carried out extended Hu¨ckel molecular
value is 6.10−5 cm3/mol for each copper atom. xp orbital calculations (EHMO) in order to gain in-
- 10.1515/znb-2006-0302
Downloaded from De Gruyter Online at 09/12/2016 12:14:19AM
via free access

C. T. Zeyrek et al. · Super-Exchange Interaction in a Chair-Piperazine Bridged Dicopper(II/II) Complex
241
bitals of the piperazine (bonding and antibonding) in
the HOMO and LUMO. The importance of this bond-
ing and antibonding contributions to the orbitals of the
piperazine is the main origin of the energy gap and
thus, of the antiferromagnetic coupling. As the anti-
ferromagnetic interaction increases, the two molecu-
lar orbitals ϕ1 and ϕ2 will separate in energy. The en-
ergy separation between these two new molecular or-
bitals is expected to determine the super-exchange cou-
pling constant. According to the theoretical analysis by
Hoffmann and co-workers [27, 28], the coupling con-
stant is expressed as
(ε1 −ε2)2
2J = 2Kab
−
(2)
Jaa −Jab
where Kab, Jaa and Jab are the exchange integral and
one-centre and two-centre Coulomb repulsion inte-
grals, respectively, and ε1 and ε2 are the energies of
the two orbitals ϕ1 (HOMO) and ϕ2 (LUMO), respec-
tively. The value of Kab is always positive, so the first
term in (2) contributes to the ferromagnetic interac-
tion, while the second term, which is always positive,
contributes to the antiferromagnetic interaction. The
energy difference between the two molecular orbitals
(ε1 − ε2) which corresponds to the HOMO – LUMO
energy gap, determines the magnitude of the antifer-
romagnetic interaction. From the above expression (2)
for the exchange parameter, it is seen that the binuclear
complex with the greater antiferromagnetic interaction
has the larger (ε1 − ε2) energy difference. The ex-
tended Hu¨ckel molecular orbital (EHMO) calculations
have shown that the ϕ1 and ϕ2 orbitals are separated by
0.011 eV, respectively. Very recently, we have studied
the crystal structures and magnetic properties of (µ-
hydroxo)(µ-acetato) and (µ-hydroxo)(µ-pyrazolate)
bridged dicopper(II) complexes [29, 30]. For these bin-
uclear copper complexes (ε1 − ε2) energy differences
are found to be 0.605, 0.645 [29] and 0.648 [30] with
the −J values 81.8, 89.6 and 92.7 cm−1, respectively.
These results indicate a stronger antiferromagnetic in-
teraction than in the investigated compound, suggest-
ing that a large energy separation of ϕ1 (HOMO) and
ϕ2 (LUMO) leads to a strong antiferromagnetic inter-
action.
Fig. 5. Schematic representation of the LUMO and HOMO
frontier orbitals for the investigated compound, obtained us-
ing the CACAO programme (for orbitals contributing more
than 1%). (ε1 −ε2) = 0.011 eV.
sight into the molecular orbitals that participate in
the super-exchange pathway. EHMO calculations we
reperformed from the crystallographic coordinates of
the Cu1, Cu1i, N1, N1i, O1, O1i, Cl1, Cl1i, C10, C10i,
C11, C11i, N2, and N2i atoms in the super-exchange
pathway. An energy difference of 0.011 eV is ob-
tained between the highest occupied molecular orbital
(HOMO) and the lowest unoccupied molecular orbital
(LUMO). A graph of HOMO and LUMO orbitals for
the investigated complex is depicted in Fig. 5. In both
MOs the magnetic orbitals are mainly centered in the
dx − y2 copper orbitals, in agreement with the geom-
2
etry of the metal ions. The LUMO is delocalized on
the atomic orbitals of the piperazine bridging ligand
and shows bonding character (ϕ1) for the N–N over-
lap. On the other hand, in the HOMO, the delocaliza-
tion on the piperazine ligand is less extended and the
main feature is the antibonding (ϕ1) character of the
N–N overlap in the piperazine bridge. From Fig. 4 it is
obvious that there is a good overlap between the N or-
[1] K. D. Karlin, Z. Tyeklar (eds): Bioinorganic Chemistry
of Copper, Chapman and Hall, New York (1993).
[2] L. Q. Jun, A. E. True, Prog. Inorg. Chem. 38, 97 (1990).
[3] D. Gatteschi, O. Kahn, R. D. Willet, Magnetostructural
Correlations in Exchange Coupled Systems, Reidel,
Dordrecht (1984).
- 10.1515/znb-2006-0302
Downloaded from De Gruyter Online at 09/12/2016 12:14:19AM
via free access

242
C. T. Zeyrek et al. · Super-Exchange Interaction in a Chair-Piperazine Bridged Dicopper(II/II) Complex
[4] O. Kahn, Angew. Chem. Int. Ed. Engl. 24, 834 (1985).
[5] O. Kahn, Struct. Bonding (Berlin) 68, 89 (1987).
[18] A. Weiss, H. Witte, Magnetochemie, Verlag Chemie,
Weinheim (1973).
[6] T. N. Doman, D. E. Williams, J. F. Banks, R. M.
Buchanan, H. R. Chang, R. J. Webb, D. N. Hendrick-
son, Inorg. Chem. 29, 1058 (1990).
[7] T. Kawato, M. Yamanaka, S. Ohba, Y. Nishida,
M. Nagamatsu, T. Tokii, M. Kato, O. W. Steward, Bull.
Chem. Soc. Japan 65, 2739 (1992).
[8] U. Mukhopadhyay, L. R. Falvallo, D. Ray, Eur. J. Inorg.
Chem. 2823 (2001).
[9] M. Boiocchi, M. Bonizzoni, L. Fabbrizzi, F. Foti,
M. Licchelli, A. Taglietti, M. Zema, J. Chem. Soc.,
Dalton Trans. 653 (2004).
[10] Z. Smekal, Z. Travny’cek, J. Mrozinski, J. Marek, In-
org. Chem. Commun. 6, 1395 (2003).
[11] C. T. Zeyrek, A. Elmali, Y. Elerman, Z. Naturforsch.
60b, 520 (2005).
[12] C. T. Zeyrek, A. Elmali, Y. Elerman, Z. Naturforsch.
60b, 940 (2005).
[13] Enraf-Nonius diffractometer control software, Release
5.1, Enraf-Nonius, Delft, Netherlands (1993).
[14] G. M. Sheldrick, SHELXS-97, Program for the solu-
tion of crystal structures, Univ. of Go¨ttingen, Germany
(1997).
[15] G. M. Sheldrick, SHELXL-97, Program for the refine-
ment crystal structures, Univ. of Go¨ttingen, Germany
(1997).
[19] C. Mealli, D. M. Proserpio, CACAO, Computer Aided
Compositon of Atomic Orbitals, a Package of Pro-
grams for Molecular Orbital Analysis, PC Version 4.0,
July (1994). Original Reference: J. Chem. Educ. 67,
399 (1990).
[20] B. Chiari, O. Piovesana, T. Tarantelli, P. F. Zanazzi, In-
org. Chem. 23, 2542 (1984).
[21] M. Bera, J. Ribas, W. T. Wong, D. Ray, Inorg. Chem.
Commun. 7, 1262 (2004).
[22] C. J. O’Connor, Prog. Inorg. Chem. 29, 203 (1982).
[23] W. Mazurek, B. J. Kennedy, K. S. Murray, M. J.
O’Connor, J. R. Rodgers, M. R. Snow, A. G. Wedd,
P. R. Zwack, Inorg. Chem. 24, 3258 (1985).
[24] T. Kawata, H. Uekusa, S. Ohba, T. Furukawa, T. Tokii,
Y. Muto, M. Kato, Acta Crystallogr. B48, 253 (1992).
[25] V. H. Crawford, H. W. Richardson, J. R. Wasson, D. J.
Hodgson, W. E. Hatfield, Inorg. Chem. 15, 2107
(1976).
[26] P. S. Mukherjee, S. Dalai, G. Mostafa, E. Zangrando,
T. Lu, G. Rogez, T.-H. Mallah, N. R. Chaudhuri, Chem.
Commun. 1346 (2001).
[27] P. J. Hay, J. C. Thibeault, R. Hoffman, J. Am. Chem.
Soc. 97, 4884 (1975).
[28] R. W. Jotham, S. F. A. Kettle, Inorg. Chem. 9, 1390
(1970).
[16] L. J. Farrugia, ORTEPIII. J. Appl. Crystallogr. 30, 565
(1997).
[29] E. Kavlakoglu, A. Elmali, Y. Elerman, Z. Naturforsch.
57b, 323 (2002).
[17] Further information may be obtained from: Cam- [30] A. Elmali, C. T. Zeyrek, Y. Elerman, J. Mol. Struct.
bridge Crystallographic Data Center (CCDC), 12
Union Road, Cambridge CB21EZ, UK, by quoting the
depository number CCDC-283155, E-mail: deposit@
ccdc.cam.
693, 225 (2004).
- 10.1515/znb-2006-0302
Downloaded from De Gruyter Online at 09/12/2016 12:14:19AM
via free access