X-ray studies, spectroscopic characterization and DFT calculations for Mn(II), Ni(II) and Cu(II) complexes with 2-benzoylpyridine

Article abstract of DOI:10.1016/j.poly.2010.11.013

[M(SCN)₂(bopy)₂], where M = Mn(II), Ni(II), Cu(II), and [CuCl₂(bopy)₂] complexes have been prepared and studied using IR, UV-Vis and EPR spectroscopy, and X-ray crystallography. Electronic structures of the comp

Full text of DOI:10.1016/j.poly.2010.11.013

Polyhedron 30 (2011) 410–418
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
X-ray studies, spectroscopic characterization and DFT calculations for Mn(II),
Ni(II) and Cu(II) complexes with 2-benzoylpyridine
a
a
b
J.G. Małecki a, , B. Machura , A. Switlicka , J. Kusz
⇑
´
a Department of Crystallography, Institute of Chemistry, University of Silesia, 9th Szkolna St., 40-006 Katowice, Poland
b Institute of Physics, University of Silesia, 4th Uniwersytecka St., 40-006 Katowice, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
[M(SCN)2(bopy)2], where M = Mn(II), Ni(II), Cu(II), and [CuCl2(bopy)2] complexes have been prepared and
studied using IR, UV–Vis and EPR spectroscopy, and X-ray crystallography. Electronic structures of the
complexes were calculated using the DFT method, and the descriptions of frontier molecular orbitals
and the relocation of the electron density of the compounds were determined.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 8 October 2010
Accepted 4 November 2010
Available online 24 November 2010
Keywords:
Manganese(II)
Nickel(II)
Copper(II)
2-Benzoylpyridine
Complexes
X-ray structure
DFT calculations
EPR
1. Introduction
established that in azido-bridging complexes, the exchange is gen-
erally anti-ferromagnetic in nature for the end-to-end mode, and
The pseudohalide ions (N3ꢀ, NCSꢀ, NCOꢀ and N(NC)2ꢀ) are ver-
satile ligands that can bind transition metal ions in a variety of
ways. These anions can act as both monodentate and bridging li-
gands, leading to the formation of mononuclear and polynuclear
species. The bridging azide and thiocyanate ions bind metals via
EO (end-on) and EE (end-to-end) modes. It generates various types
of supramolecular structures with particular properties. Addition-
ally, the SCNꢀ ion, having two different donor atoms, can coordi-
nate to metals through either the nitrogen or the sulfur atom, or
both. According to HSAB (hard soft acid base) theory, the SCNꢀ an-
ion coordinates to hard acids (Mn2+, Co2+ and Ni2+) through the
nitrogen atom, and the uncoordinated sulfur atom can be involved
in hydrogen bonds or SꢁꢁꢁS interactions. If the transition metal cen-
ter is a soft acid (Cd2+ and Hg2+), the SCNꢀ ligand binds to the cen-
tral ion through the sulfur atom. This feature not only generates
new types of network structures but it also offers an opportunity
for the formation of heterometallic complexes involving various
combinations of metal ion node points. Such combinations could
lead to the formation of materials with useful properties resulting
from the presence of the heterometallic arrays.
ferromagnetic for the end-on mode. Magnetic structural studies
performed on divalent metal(II) complexes with bridging thiocya-
nate groups is scarce [1–6].
Recent research on derivatives obtained by the reaction of 2-
benzoylpyridine with manganese(II), copper(II) and sodium azide
has provided an exceptional number of materials with new struc-
tural and magnetic features [7–10]. It prompted us to explore the
reactivity of 2-benzoylpyridine with manganese(II), nickel(II), cop-
per(II) and NH4SCN.
Here we present the synthesis, crystal, molecular and electronic
structures, and spectroscopy characterization of manganese(II),
nickel(II) and copper(II) thiocyanate complexes and a copper(II)
chloride complex with the 2-benzoylpyridine ligand. Similar to
the previously reported Mn(II) and Cu(II) azido coordination com-
pounds, 2-benzoylpyridine binds to central ions through the N–O
chelating site. This coordination mode produces a five-membered
ring containing an unsaturated
a
-iminoketo function which can
electron-rich metal center.
act as a acceptor towards a bound
p
p
However, in contrast to the previous studies, only formation of
mononuclear species has been observed in the case of thiocyanate
ions. Attempts to prepare a Cu/Co heterometallic complex by the
reaction of [Cu(bopy)2Cl2] with (NH4)2[Co(SCN)4] resulted in the
isolation of cis and trans isomers of [Cu(bopy)2(SCN)2]. The study
of geometric isomerism and the reactivity of specific isomers is a
topic of major importance in coordination chemistry.
The magnetic exchange interaction in these systems results
from the electronic interaction between the paramagnetic metal
centers via the bridging N3 or NCSꢀ ligands. Nowadays, it is well
ꢀ
⇑
Corresponding author.
E-mail address: gmalecki@us.edu.pl (J.G. Małecki).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.11.013

J.G. Małecki et al. / Polyhedron 30 (2011) 410–418
411
The experimental studies on the manganese(II), nickel(II) and
copper(II) thiocyanate complexes and the chloride copper(II) com-
plex with the 2-benzoylpyridine ligand have been accompanied by
density functional theory (DFT) calculations. Currently, density
functional theory (DFT) is commonly used to examine the elec-
tronic structures of transition metal complexes. It meets with the
requirements of being accurate, easy to use and fast enough to al-
low the study of the relatively large molecules of transition metal
complexes.
UV–Vis (methanol, nm (log
(1.12), 375.6 (1.19), 339.8 (1.56), 263.2 (4.17), 211.2 (4.95).
e
): 1061.0 (0.92), 745.2 (0.89), 673.4
2.4.3. [Cu(SCN)2(bopy)2] (3a)
IR (KBr, cmꢀ1): 3053
mArH; 2098 m(CN
SCN); 1640 mC@O;
from
1623
m
CN; 1592
mC@C; 1445
mPh; 1331 d(C–CH
plane);1107
in the
d(C–CH in the plane); 946 d(C–H out of the plane); 822 d(C–C out of the plane)
;
779, 757 m(SC SCN); 731 d(C–C plane); 457 d(NCS); 428
from
in the
m(Mn–Npy). UV–Vis (methanol, nm (log e): 790.0 (0.89), 440.0
(1.09), 373.0 (1.14), 262.1 (4.23), 210.5 (4.58).
2. Experimental
2.4.4. [Cu(SCN)2(bopy)2] (3b)
IR (KBr, cmꢀ1): 3053
mArH; 2082
m
(CN from SCN); 1650
m
C@O; 1594
All reagents used for the synthesis of the complexes are com-
mercially available. They were used without further purification.
mCN
;
1571 mC@C
;
1444 mPh
;
1322 d(C–CH
;
1028
;
in the plane)
d(C–CH
plane); 948 d(C–H
plane); 769, 757 m(SC
in the
out of the
from SCN)
650 d(NCS); 430
(1.10), 320.5 (2.21), 261.5 (2.69), 234.5 (4.29), 209.5 (4.84).
m(Mn–Npy). UV–Vis (methanol, nm (log e): 480.0
2.1. Synthesis of cis-[Mn(SCN)2(bopy)2], cis-[Ni(SCN)2(bopy)2] and
trans-[Cu(SCN)2(bopy)2]
2.4.5. [CuCl2(bopy)2] (4)
These complexes were synthesized by the reactions between
IR (KBr, cmꢀ1): 3060, 2986
m
ArH; 1647
mC@O; 1593 mCN; 1570
MnCl2ꢁ4H2O, NiCl2ꢁH2O and CuCl2ꢁ2H2O with NH4SCN and
a
mC@C; 1478, 1246 d(C–CH in the plane); 1446 Ph; 1001 d(C–CH in the plane)
m
;
stoichiometric amount of 2-benzoylpyridine in methanolic solu-
tions (50 cm3). The mixtures of the compounds were refluxed for
0.5 h. After this time, the volume of the solvent was reduced to
about 20 cm3; the solution was cooled and left out for slow evap-
oration. Cis-[Mn(SCN)2(bopy)2], cis-[Ni(SCN)2(bopy)2] and trans-
[Cu(SCN)2(bopy)2] complexes were isolated in 64, 68 and 80%
yields, respectively.
947 d
; 437
m(Mn–Npy). UV–Vis (methanol, nm (log
e):
out of the plane)
419.5(C(–1H.14), 320.0 (2.10), 263.0 (4.29), 208.0 (4.84).
2.5. Physical measurements
Infrared spectra were recorded on a Nicolet Magna 560 spectro-
photometer in the spectral range 4000–400 cmꢀ1 with the sample
in the form of a KBr pellet. Electronic spectra were measured on a
Lab Alliance UV–VIS 8500 spectrophotometer in the range 1100–
180 nm in methanol solution. EPR spectra were recorded for pow-
der samples at 298 K on a Bruker EMX-10 spectrometer using
100 kHz field modulation.
2.2. Synthesis of trans-[Cu(SCN)2(bopy)2] and cis-[Cu(SCN)2(bopy)2]
A methanolic solution of CuCl2ꢁ2H2O (0.1 g; 0.59 mmol) and 2-
benzoylpyridine (0.22 g; 1.20 mmol) was slowly added to an aque-
ous solution (20 ml) of NH4SCN (0.1 g; 1.31 mmol) and CoCl2ꢁ6H2O
(0.14 g; 0.59 mmol), and stirred at room temperature for 2 h. The
resulting solution was kept for evaporation at room temperature,
and after a few days green crystals of trans-[Cu(SCN)2(bopy)2]
and red crystals of cis-[Cu(SCN)2(bopy)2] were obtained, filtered
off, dried and separated using microscope. Green crystals of
trans-[Cu(SCN)2(bopy)2] and red crystals of cis-[Cu(SCN)2(bopy)2]
were collected in 40% and 30% yields, respectively.
2.6. DFT calculations
The calculations were carried out using the GAUSSIAN09 [11] pro-
gram. The DFT/B3LYP [12,13] method was used for the geometry
optimization and electronic structure determination. The calcula-
tions were performed using the polarization functions for all
atoms: 6–311 g – manganese, nickel and copper, 6–31 g** – sulfur,
carbon and nitrogen, and 6–31 g – hydrogen. Natural bond orbital
(NBO) calculations were performed with the NBO code [14] in-
cluded in GAUSSIAN09. The contribution of a group to a molecular
orbital was calculated using Mulliken population analysis. GAUSSSUM
2.2 [15] was used to calculate group contributions to the molecular
orbitals and to prepare the overlap population density of states
(OPDOS) spectra. The OPDOS spectra were created by convoluting
the molecular orbital information with Gaussian curves of unit
height and a FWHM (Full Width at Half Maximum) of 0.3 eV.
Mayer bond orders were calculated with use of the QMForge pro-
gram [16].
2.3. Synthesis of trans-[CuCl2(bopy)2]
A methanolic solution (10 ml) of 2-benzoylpyridine (0.22 g;
1.20 mmol) was added to
a methanolic solution (10 ml) of
CuCl2ꢁ2H2O (0.1 g; 0.59 mmol) and stirred for 1 h. After this time,
the volume of the solvent was reduced to about 10 cm3; the solu-
tion was cooled and left out for slow evaporation. Yield 90%. Crys-
tals suitable for X-ray investigation were obtained by
recrystallization from methanol.
2.4.1. [Mn(SCN)2(bopy)2] (1)
IR (KBr, cmꢀ1): 3065, 3002
m
ArH; 2078 m(CN
SCN); 1627
from
2.7. Crystal structure determination and refinement
m
C@O; 1590
m
C@N; 1566
mC@C; 1445
mArH; 1359 d(C–CH
;
in the plane)
1051 d(C–CH in the plane); 1009 d(C–H out of the plane); 825 d(C–C out of the
plane); 778, 754 m(SC from SCN); 693 d(C–C in the plane); 476 d(NCS); 405
m(Mn–Npy). UV–Vis (methanol, nm (log e): 648.0 (0.30), 426.0
(1.03), 361.5 (1.23), 339.5 (1.31), 262.5 (3.23), 242.5 (4.97), 210.0
Crystals of [Mn(SCN)2(bopy)2] (1), [Ni(SCN)2(bopy)2] (2),
cis-[Cu(SCN)2(bopy)2] (3a), trans–[Cu(SCN)2(bopy)2] (3b) and
[CuCl2(bopy)2] (4) were mounted in turn on a Xcalibur, Atlas, Gem-
ini ultra Oxford Diffraction automatic diffractometer equipped
with a CCD detector, and were used for data collection. X-ray
intensity data were collected with graphite monochromated Mo
(4.97).
2.4.2. [Ni(SCN)2(bopy)2]ꢁH2O (2)
K
a
radiation (k = 0.71073 Å) at ambient temperature, except for
IR (KBr, cm1): 3450
m
OH; 3092, 3057
m
ArH; 2091 m(CN
;
;
3b which was measured at 150.0(2) K, with the scan mode.
x
from SCN)
1623
1445
m
m
C@O; 1588
Ph; 1055 d(C–CH
m
C@N; 1568
m
C@C; 1491, 1177 d(C–CH
Ewald sphere reflections were collected up to 2h = 50.10°. The unit
cell parameters were determined from least-squares refinement of
the setting angles of 8027, 4878, 2327, 6001 and 3317 strongest
in the plane)
plane); 958 d(C–H
plane); 770,
in the
out of the
753 m(SC
SCN); 697 d(C–C
plane); 474 d(NCS); 406 m(Mn–Npy).
from
in the

412
J.G. Małecki et al. / Polyhedron 30 (2011) 410–418
Table 1
Crystal data and structure refinement details of the complexes [Mn(SCN)2(bopy)2] (1), [Ni(SCN)2(bopy)2] (2), cis-[Cu(SCN)2(bopy)2] (3a), trans-[Cu(SCN)2(bopy)2] (3a),
[CuCl2(bopy)2] (4).
1
2
3a
3b
4
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
Unit cell dimensions
a (Å)
C
42H28MnN10S2
C26H18N4NiO2S2
541.27
298.0(2)
C26H18Cu N4O2S2
546.13
150.0(2)
monoclinic
C2/c
C26H18CuN4O2S2
546.13
150.0(2)
monoclinic
P21/n
C24H18Cl2CuN2O2
500.84
150.0(2)
monoclinic
C2/c
791.80
298.0(2)
monoclinic
C2/c
triclinic
ꢀ
P1
15.7209(5)
9.3014(3)
26.3303(8)
90
96.214(3)
90
3827.6(2)
4
1.374
8.1272(9)
13.987(3)
10.452(4)
17.954(6)
90
109.32(3)
90
2476.9(14)
4
1.465
8.8927(4)
10.7625(5)
13.0583(6)
90
91.346(4)
90
1249.43(10)
2
1.452
15.0183(10)
7.3695(4)
21.1886(2)
90
110.171(5)
90
2201.27(19)
4
1.511
b (Å)
c (Å)
13.3208(17)
13.7299(18)
62.250(13)
87.336(10)
83.139(10)
1306.0(3)
a
(°)
b (°)
c
(°)
Volume (Å3)
Z
2
Dcalc (mg/m3)
1.376
0.932
556
Absorption coefficient (mmꢀ1
F(0 0 0)
)
0.500
1628
1.082
1116
1.072
558
1.259
1020
Crystal dimensions (mm)
h Range for data collection (°)
Index ranges
0 ꢃ 0 ꢃ 0
3.55–25.00
ꢀ18 6 h 6 18
ꢀ11 6 k 6 11
ꢀ31 6 l 6 31
18481
0.23 ꢃ 0.16 ꢃ 0.11
3.48–25.05
ꢀ9 6 h 6 9
ꢀ15 6 k 6 15
ꢀ16 6 l 6 16
12095
0.26 ꢃ 0.20 ꢃ 0.08
2.92–25.05
ꢀ16 6 h 6 11
ꢀ12 6 k 6 10
ꢀ21 6 l 6 21
7255
0.36 ꢃ 0.24 ꢃ 0.08
2.97–25.05
ꢀ9 6 h 6 10
ꢀ12 6 k 6 12
ꢀ15 6 l 6 14
7685
0.22 ꢃ 0.22 ꢃ 0.16
2.89–25.05
ꢀ17 6 h 6 8
ꢀ8 6 k 6 8
ꢀ23 6 l 6 25
6517
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
3347 [R(int) = 0.0372]
3347/0/250
1.043
4588 [R(int) = 0.0373]
4588/0/316
1.011
2184 [R(int) = 0.0360]
2184/0/159
1.075
2201 [R(int) = 0.0178]
2201/0/160
1.160
1907 [R(int) = 0.0180]
1907/0/142
1.083
Final R indices [I > 2
r
(I)]
R1 = 0.0295
wR2 = 0.0742
R1 = 0.0429
wR2 = 0.0766
0.249 and ꢀ0.240
R1 = 0.0496
wR2 = 0.1284
R1 = 0.0732
wR2 = 0.1356
0.616 and ꢀ0.552
R1 = 0.0388
wR2 = 0.1150
R1 = 0.0577
wR2 = 0.1308
0.362 and ꢀ0.624
R1 = 0.0219
wR2 = 0.0700
R1 = 0.0253
wR2 = 0.0712
0.316 and ꢀ0.489
R1 = 0.0246
wR2 = 0.0637
R1 = 0.0339
wR2 = 0.0679
0.376 and ꢀ0.311
R indices (all data)
Largest difference in peak and hole (e Åꢀ3
)
reflections for complexes 1, 2, 3a, 3b and 4, respectively. Details
concerning crystal data and refinement are gathered in Table 1.
During the data reduction, the decay correction coefficient was ta-
ken into account. Lorentz, polarization and numerical absorption
corrections were applied. The structures were solved by the direct
method. All non-hydrogen atoms were refined anisotropically
using the full-matrix, least-squares technique on F2. All hydrogen
atoms were found from difference Fourier synthesis after four cy-
cles of anisotropic refinement, and refined as ‘‘riding’’ on the adja-
cent atom with individual isotropic temperature factors equal to
1.2 times the value of the equivalent temperature factor of the par-
ent atom, with geometry idealisation after each cycle. OLEX2 [17]
with SHELXS97 [18] and SHELXL97 [19] programs were used for all
the calculations. Atomic scattering factors were those incorporated
in the computer programs.
weakness of the C@O bond in 2-benzoylpyridine is visible in the
complexes of manganese (1) and nickel (2) compared with the
complexes 3a, 3b, and 4 which suggests that the copper(II) com-
plexes have a coordination number of 4. The stretching modes of
the aryl C–H bond display maxima for the complexes at 3065
and 3002 (1), 3092 and 3057 (2), 3053 (3a and 3b), 3060 and
2986 (4) cmꢀ1. In the spectrum of complex 2, the band with a max-
imum at 3450 cmꢀ1 is assigned to the hydroxyl group of the water
molecule. The mC@N band of the pyridine ring appears at about
1600 cmꢀ1. The mCN
, mCS and dNCS frequencies of the isothiocyanato
ligands present maxima at 2078, 778, 754 and 476 (1), 2091, 770,
753 and 474 (2), 2098, 779, 757 and 457 (3a), 2082, 769, 757 and
650 cmꢀ1 (3b), and this is in good agreement with the end-on NCS
coordination. In complexes 1–3a, two NCS ligands are in cis posi-
tions and in the IR spectra two mCN stretches are expected, but only
broadening of the bands is visible. The coordination modes of the
thiocyanate ligands in the studied complexes are indeterminable
from the IR spectral data of these compounds. For N-bonded com-
plexes, generally the C–N stretching band is in a lower region,
around 2050 cmꢀ1, compared to a value of 2100 cmꢀ1 for S-bonded
complexes. However, the frequencies of the bands are sensitive to
other factors, like coexisting ligands, and the structures of the
examined compounds were determined using X-ray analysis.
While the M–S–C angles of S-bonded thiocyanato ligands in com-
plexes are bent to around 110°, the M–N–C angles of N-bonded
isothiocyanato ligands are close to linear. The complexes 1, 4, 3a
and 3b crystallize in the monoclinic space groups C2/c and P21/n.
3. Results and discussion
The cis-[Mn(SCN)2(bopy)2], cis-[Ni(SCN)2(bopy)2] and trans-
[Cu(SCN)2(bopy)2] complexes have been obtained from the
reactions of manganese(II), nickel(II) and copper(II) chloride with
2-benzoylpyridine and ammonium thiocyanate. The cis isomer of
[Cu(SCN)2(bopy)2] has been isolated together with trans-[Cu(SCN)2-
(bopy)2] in the reaction of [Cu(bopy)2Cl2] with (NH4)2[Co(SCN)4],
whereas the reaction of copper(II) chloride with 2-benzoylpyridine
lead to trans-[CuCl2(bopy)2].
ꢀ
The infrared spectra of the complexes present characteristic
bands due to the 2-benzoylpyridine and isothiocyanate ligand
vibrations. Coordination of the oxygen atom of 2-benzoylpyridine
to the metal center causes a weakening of the C@O bond and a de-
Complex 2 crystallizes in the triclinic P1 space group. Details con-
cerning crystal data and refinement are gathered in Table 1. The
molecular structures of the complexes are shown in Fig. 1. Selected
bond lengths and angles are listed in Table 2. In the complexes of
manganese(II) and nickel(II), and the copper(II) complex 3a, the
central ions have an octahedral environment, and the copper(II)
crease in
m
(C@O) from ꢂ1670 cmꢀ1 in the free ligand to about
1627 (1), 1623 (2), 1640 (3a), 1650 (3b) and 1647 (4) cmꢀ1. The

J.G. Małecki et al. / Polyhedron 30 (2011) 410–418
413
Fig. 1. ORTEP drawing of [Mn(SCN)2(bopy)2] (1), [NiCl2(bopy)2] (2), cis-[Cu(SCN)2(bopy)2] (3a), trans-[Cu(SCN)2(bopy)2] (3b), [CuCl2(bopy)2] (4) with 50% probability
displacement ellipsoids. Hydrogen atoms are omitted for clarity.
complexes 3b and 4 have coordination number 4, with the isothi-
ocyanate ligands bonded to the metal centre through the nitrogen
atom. In the complexes, the coordination environment of the me-
tal(II) ion consists of two thiocyanato ligands and two 2-benzoyl-
pyridine molecules. The C–N and C–S bond length values fall in
the 1.128(5)–1.159(2) and 1.616(4)–1.631(4) Å ranges for the com-
plexes, similar to those observed for isothiocyanate complexes. The
M–N and Mn–O distances are normal and are comparable with dis-
tances in other 3d metal complexes containing 2-benzoylpyridine
ligands. The M–N–C angles, 172.89(14)° in 1, 168.1(4)° in 2,
175.0(3)° in 3a and 161.57(14)° in 3b, are in good agreement with
those found for M2+ complexes having bent terminally bonded NCS

414
J.G. Małecki et al. / Polyhedron 30 (2011) 410–418
Table 2
Selected bond lengths [Å] and angles [°] for the complexes [Mn(SCN)2(bopy)2] (1), [Ni(SCN)2(bopy)2] (2), cis-[Cu(SCN)2(bopy)2] (3a), trans-[Cu(SCN)2(bopy)2] (3b) and
[CuCl2(bopy)2] (4).
1
2
3a
3b
4
Exp
Calc
Exp
Calc
Exp
Calc
Exp
Calc
Exp
Calc
Bond lengths (Å)
M(1)–N(1)
M(1)–N(2)
M(1)–N(3)
M(1)–N(4)
M(1)–O(1)
M(1)–O(2)
M(1)–Cl(1)
N(1)–C(1)
N(2)–C(2)
C(1)–S(1)
2.114(15)
2.315(13)
2.030
2.377
2.016(3)
2.002(4)
2.064(3)
2.064(3)
2.150(2)
2.145(2)
2.002
2.002
2.073
2.073
2.172
2.171
2.009(4)
2.131(3)
1.939
2.101
1.965(14)
2.011(13)
1.946
2.075
2.006(17)
2.281(6)
2.039
2.221(14)
2.287
2.193(3)
2.143
2.316
1.140(2)
1.187
1.624
1.128(5)
1.140(5)
1.616(4)
1.620(4)
1.186
1.187
1.631
1.633
1.139(4)
1.633(4)
1.189
1.621
1.159(2)
1.187
1.625
1.626(16)
1.627(17)
C(2)–S(2)
Angles (°)
N(1)–M(1)–N(2)
N(1)–M(1)–N(3)
N(1)–M(1)–N(4)
N(2)–M(1)–N(3)
N(3)–M(1)–N(4)
N(2)–M(1)–N(4)
N(1)–M(1)–O(1)
N(2)–M(1)–O(1)
N(3)–M(1)–O(1)
N(4)–M(1)–O(1)
N(1)–M(1)–O(2)
N(2)–M(1)–O(2)
N(3)–M(1)–O(2)
N(4)–M(1)–O(2)
O(1)–M(1)–O(2)
N(1)–M(1)–Cl(1)
C(1)–N(1)–M(1)
C(2)–N(2)–M(1)
N(1)–C(1)–S(1)
N(2)–C(2)–S(2)
92.93(5)
91.86
98.85(15)
94.24(13)
92.08(13)
96.24(12)
165.15(11)
96.04(12)
85.28(13)
172.65(11)
89.48(10)
77.66(10)
169.32(12)
88.03(13)
76.81(10)
95.33(9)
102.56
95.52
90.98
91.00
169.62
95.48
86.93
167.81
86.92
76.50
167.84
86.93
76.50
95.74
84.80
91.84(12)
96.90
92.06(6)
90.63
89.68(5)
107.76(4)
88.66
100.21
90.03(12)
74.63(9)
86.40
75.82
95.09(5)
74.33(5)
95.50
71.16
88.80(10)
90.34(5)
90.17
172.89(14)
179.26(16)
177.50
178.87
168.1(4)
171.1(4)
179.8(5)
178.5(4)
163.72
173.73
178.80
178.79
175.0(3)
179.1(3)
169.13
176.42
161.57(14)
178.43(15)
153.32
178.71
M denotes Mn in 1, Ni in 2 and Cu in 3a, 3b, 4.
ligands (141–174°). The isothiocyanate ligands are almost linear.
The Cu–Cl distance in complex 4 is normal. The conformation of
molecule 2 is stabilized by an intramolecular hydrogen bond, and
in the crystal packing of complexes 3a, 3b and 4, intermolecular
hydrogen bonds are observed. Details of these hydrogen bonds
are collected in Table 3. In Fig. 2, the crystal packing of complexes
1–3 along the a axis, with hydrogen bonds indicated by dotted
lines, are shown. In the figure, two-dimensional networks (brick
functional. From the data collected in Table 2, one m0ay see that
the bond lengths are elongated by a maximum of 0.07 ÅA in the cal-
culated structures of the gas phase DFT study, and the bond angles
are changed by about 8° in complex 3a. From Fig. 3, showing the
calculated and experimental IR spectra of complex 3b, one can
see that the optimized geometries of the complexes are in good
agreement with experimental data.
The interaction between the ligands and the central ions mani-
fests itself in charges on the complex metal ions. The metal ions in
all the studied complexes are formally in the +2 oxidation state,
but the calculated natural charges are lower than +2, and are as fol-
lows: Mn: 1.60; Ni: 1.73; Cu: 1.37 (3a), 1.41 (3b), 1.28 (4). The nat-
ural charges indicate that the donations from the ligands to the
central ions have the advantage over the back donations from
the metal to ligands. The stabilization energies calculated in the
NBO analyses have shown that the lone pairs localized on the iso-
thiocyanate ligands in complexes 1 and 2 donate the charge to
wall topology) formed by hydrogen bonds and p-stacking interac-
tions in the structures of complexes 3 and 4 are visible.
To obtain insight into the electronic structures and bonding
properties of the complexes, calculations using the density func-
tional theory method were carried out. Before calculation of the
electronic structures of the complexes, their geometries were opti-
mized in the triplet state using the DFT method with the B3LYP
manganese and nickel, and the stabilization energies (DEij) are
Table 3
Hydrogen bonds for [Ni(SCN)2(bopy)2] (2), cis-[Cu(SCN)2(bopy)2] (3a), trans-
[Cu(SCN)2(bopy)2] (3b) and [CuCl2(bopy)2] (4) (Å and °).
55.78 and 72.30 kcal/mol. The same interactions in complexes 3a
and 3b have stabilization energies equal to 44.81 and 69.70 kcal/
mol. The back donations to the isothiocyanate ligands are equal
to 43.55, 48.51, 16.30 and 20.76 kcal/mol for 1, 2, 3a, and 3b,
respectively. The charge flows between the chloride anions and
central Cu(II) ion in complex 4 were calculated as 56.78 kcal/mol
for donation from the chloride ligands to the central copper ion
and 7.34 kcal/mol for Cu ? Cl back donation. The values are lower
than the one obtained for the isothiocyanate complex 3b, which is
not surprising because of the more sophisticated NCS ligand. The
stabilization energy connected to the interaction between 2-ben-
zoylpyridine and the manganese, nickel, copper central ions are
55.94, 109.14, 33.64, 39.20 and 42.81 kcal/mol in compounds 1,
D–Hꢁ ꢁ ꢁA
2
d(D–H)
d(Hꢁ ꢁ ꢁA)
d(Dꢁ ꢁ ꢁA)
<(DHA)
C(3)–H(3)ꢁ ꢁ ꢁN(1)
0.93
0.93
2.58
2.59
3.124(6)
3.413(5)
117.80
147.80
C(4)–H(4) ꢁ ꢁ ꢁO(1)#1
3b
C(4)–H(4)ꢁꢁꢁS(1)#3
0.93
0.93
2.85
2.58
3.7742(19)
3.380(2)
171.00
145.00
C(13)–H(13)ꢁ ꢁ ꢁO(1)#4
4
C(2)–H(2)ꢁ ꢁ ꢁCl(1)#5
0.93
2.82
3.722(2)
163.00
Symmetry transformations used to generate equivalent atoms: #1 2 ꢀ x, 1 ꢀ y,
2 ꢀ z; #2 x, 1 + y, z; #3 x, ꢀ1 + y, z; #4 3 ꢀ x, 1 ꢀ y, ꢀz; #5 ꢀx, ꢀy, 1 ꢀ z.

J.G. Małecki et al. / Polyhedron 30 (2011) 410–418
415
Fig. 3. Experimental and calculated IR spectra of trans-[Cu(SCN)2(bopy)2] (3b).
The Mayer bond orders, calculated using the QMForge program,
of M–N(CS) are the same in complexes 1 and 2, and are equal to
0.28. The bond orders of M–N(py) are equal to 0.16 and 0.25 in
complexes 1 and 2, respectively. The bonds between the carbonyl
group of 2-benzoylpyridine and manganese and nickel(II) have
stronger ionic character than the M–N bonds, indicated by small
values of the Mayer bond orders (0.14). The bonds in the copper(II)
complexes have slightly more covalent character that the corre-
sponding bonds in complexes 1 and 2. The calculated bond orders
are close to each other and have values of 0.30 for Cu–N(py) and
0.36 for Cu–N(CS)/Cl. In accordance with the IR spectra of 3b and
4 complexes, the bond orders of Cu–O are very small (0.06), con-
firming the coordination number 4 for the complexes.
The HOMO and LUMO orbitals of the complexes 1–3b are local-
ized on thiocyanate ligands, and in complex 4 the HOMO orbital is
localized on the chloride ion with a notable contribution of the dCu
orbitals (20%). The d orbitals of the central ions play a significant
role (26–70%) in the lower HOMO-4/5 MOs in the complexes.
The LUMO orbitals are localized on the bopy ligands in the com-
plexes of manganese(II) and nickel(II), and in the case of the cop-
per(II) complexes 3a, 3b and 4, the dCu orbitals (47–66%)
participate in the b spin LUMO. In the virtual molecular orbitals,
the d orbitals of the central ions are visible in (b spin) LUMO+8
to LUMO+14 (29–74%) in complex 1, LUMO+6/7 (75% and 77%) in
2 and in the LUMO+10/11 (ꢂ5%) in the complexes of copper(II). Be-
cause in the frontier region, neighboring orbitals may have a quasi-
degeneracy of the energy levels, considering only the HOMO and
LUMO may not yield a realistic description of the frontier orbitals.
For this reason, the density of states (DOS) in terms of Mulliken
population analysis was calculated using the GaussSum program.
The results provide a pictorial representation of the MOs composi-
tions. The DOS diagrams for complexes 3a and 4 are shown in
Fig. 4, and they may enable us to ascertain the orbital composition
characteristics with respect to the particular fragments. As one
may see from the DOS diagrams, the bopy ligands play a significant
role in the virtual frontier orbitals and in the lower occupied
molecular orbitals. The chloride ion contributes in a wider range
of HOMO orbitals than the pseudohalide NCSꢀ ligands. Further-
more, the complexes with isothiocyanate ligands have a smaller
HOMO–LUMO gap than those with chloride ligands (1: 1.12 eV;
2: 2.1 eV; 3a: 2.66 eV; 3b: 2.61 eV; 4: 3.40 eV). The HOMO term
is shifted to higher energy by the pseudohalide ligands, which have
an impact on the contribution of the d orbitals of the central ions in
the HOMO orbitals.
Fig. 2. Crystal packing of complexes 1–3 along the a-axis with hydrogen bonds
indicated by dotted lines.
2, 3a, 3b, and 4, respectively. The back donations from the central
metal ions to the N,O-ligand have values of 46.04 kcal/mol in 1,
94.19 kcal/mol in 2, 18.52 kcal/mol in 3a, 18.82 in 3b, and
14.61 kcal/mol in complex 4.

416
J.G. Małecki et al. / Polyhedron 30 (2011) 410–418
Fig. 5. (a) Fragment of the UV–Vis spectrum of complex 2 with the E/B vs. Dq/B
dependence of the Tanabe–Sugano diagram for an octahedrally coordinated Ni+2
ion. (b) Experimental UV–Vis spectra and calculated transitions for complexes 3b
and 4.
Fig. 4. Partial density of states (DOS) diagrams for cis-[Cu(SCN)2(bopy)2] (3a) and
[CuCl2(bopy)2] (4).
The electronic spectra of the complexes exhibit, except for the
intense bands connected with the 2-benzoylpyridine ligands, weak
intensity absorption bands originating from d–d transitions. The
UV–VIS spectrum of complex 1 has maxima at 15 432, 23 474,
27 663 and 29 445 cmꢀ1, and these bands may be assigned to
the transitions: m1: :
6A1 ? 4T1(4G), m2 6A1 ? 4E/4A1(4G)(10B + 5C),

J.G. Małecki et al. / Polyhedron 30 (2011) 410–418
417
the d-orbitals overlap with the ligand orbitals. As a result, the
interelectronic repulsion within the d-orbitals decreases and the
B value is lowered. The ratio of B/Bo = b gives a measure of covalen-
cy in the metal–ligand bond. Considering that Bo for the Mn(II) free
ion is 786 cmꢀ1, the nephelauxetic parameter calculated for the
complex is b = 0.76. Based on the maximum of the first transition,
the crystal field splitting parameter 10 Dq has been calculated as
15 147 cmꢀ1 for complex 1.
The lowest state of the nickel(II) ion is the 3F term, which splits
into 3A2g, 3T2g and 3T1g terms in a field with Oh symmetry. Complex
2 has a lower symmetry than the octahedral point group symme-
try, and the 3T2 and 3T1 terms split into singlet 3A2 and 3B2 and dou-
blet 3E levels. As a consequence, the first and second spin allowed
transition bands observed in the UV–Vis spectra of the complexes
are assigned to 3T2(3F) ? 3A2(3F) (9425 cmꢀ1) and 3T1(3F) ?
3A2(3F) (14 850 cmꢀ1), respectively. The third absorption band
results from a spin allowed transition 3T1(3P) ? 3A2(3F), and it
has a maximum at 26 624 cmꢀ1. The value of the ligand field
parameter 10 Dq, calculated on the basis of the electronic band
positions for the complex, is equal to 9425 cmꢀ1, the Racah
parameter B is equal to 831 cmꢀ1 and the nephelauxetic parameter
b is 0.80. In the UV spectrum of complex 2, a band with a small mo-
lar extinction coefficient and a maximum at 745.2 nm was re-
corded. It is attributed to the 1Eg(1D) term in Oh symmetry,
which divides itself in the C2 symmetry into 1A1 and 1B1 levels. This
indicates that the band corresponds to spin forbidden
1A1/1B1(1D) ? 3A2(3F) transitions. From the calculated Dq/B ratio
(1.13) in the Tanabe–Sugano diagram for d8 ions in an octahedral
coordination, one can see, in Fig. 5a, that the 1Eg(1D) singlet state
3
is lower than the T1g(3F) term, which confirms the band position
in the spectra.
The electronic spectra of the copper(II) complexes 3a, 3b, and 4
show three absorption bands in the ranges m :
1: 12 658 cmꢀ1(3a), m2
22 727–23 895 cmꢀ1 and
m
3: 26 810–31 427 cmꢀ1, which may be
2
attributed to the following spin allowed transitions: B1g
?
?
2A1g(dx 2 ? dz2), 2B1g ? 2B2g(dx 2 ? dzy) and 2B ? 2Eg(dx
2
2
2
2
ꢀy
ꢀy
ꢀy
dzy, dyz). These bands suggest C2/D2 symmetry. For these com-
plexes, the nature of the transitions observed in the UV–Vis spectra
have been studied by the time-dependent density functional
(TDDFT) method, based on the optimized geometries, in the gas
phase without any symmetry restrictions, in the doublet states.
The PCM (Polarizable Continuum Model) solvent model was used
in the Gaussian calculations with methanol as the solvent. The
experimental spectra of complexes 3a and 3b, along with the cal-
culated transitions, are presented in Fig. 5b. The UV–Vis spectrum
of complex 4 is very similar to that of 3b. In the spectrum of com-
plex 3a, in the visible region, a broad poorly resolved absorption
band with a maximum at 790.0 nm is present. In this region, tran-
sitions between b-spin HOMOꢀ1/HOMOꢀ2 and LUMO orbitals
were calculated. As can be seen from the DOS plots, the LUMO orbi-
2
2
tal with b spin is composed of the Cu dx
orbital with contribu-
ꢀy
tions from bopy
p-bonding orbitals, and the Homoꢀ1/2 orbitals are
mainly localized on the chloride or isothiocyanate ligands with
some dCu orbital contribution. Accordingly, the transitions assigned
to the longest wavelength experimental bands can be seen as
mixed Cl/SCN ? Cu (LMCT) and d ? d (LF). The bands in the range
500–400 nm in the UV–VIS spectra of complexes 3b and 4 have
some LLCT character due to fact that the HOMOꢀ2 and LUMO orbi-
Fig. 6. EPR spectra of polycrystalline samples of complexes 3a, 3b and 4.
m
3: 6A1 ? 4 E(4D)(17B + 5C) and 4: 6A1 ? 4T1(4P)(7B + 7C), respec-
m
tively. The parameters B and C were calculated from the second
and third transitions because these transitions are free from crystal
field splitting and depend only on B and C parameters. The values
of the Racah parameters are: B = 598 cmꢀ1 and C = 3498 cmꢀ1. The
Racah parameter B for a metal ion varies as a function of the ligand
bound to the ion. The value of this parameter will be always lower
for the complexed ion than that for the free ion. The reduction of
the value of B is related to the extent of metal–ligand bond cova-
lency. The metal–ligand bond becomes partially covalent when
tals with
a spin have SCN/Cl and bopy character. In the energy
range attributed to the above mentioned m3 bands, LMCT transi-
tions between bopy and dCu orbtals were calculated. In the highest
energy part of the UV spectra, intraligand (IL) (
p
(bopy) ?
p*(bopy))
and ligand–ligand charge transfer (
p
(Cl/SCN) ? *(bopy)) transi-
p
tions are expected.
The X-band EPR spectra of the complexes were recorded at
room temperature at a frequency of 9.8 GHz, in the polycrystalline

418
J.G. Małecki et al. / Polyhedron 30 (2011) 410–418
form (Fig. 6). In the spectrum of the manganese(II) complex 1, one
broad signal with a g value of 2.036 is visible. The EPR spectrum of
the nickel(II) complex was not observable at the room temperature
conditions. The EPR spectrum of the polycrystalline sample of com-
plex 3a exhibit a single anisotropic broad signal with g = 2.0604. In
the spectrum of the trans isomer (3b), apart from the signal with
the same g value, a very poorly resolved line appears with
g = 2.3340. In the case of the chloride complex 4, two signals with
g|| = 2.0745 and g\ = 2.0283 are visible in the EPR spectrum. The
ordering of g values g|| > g\ > 2.0023 observed for the copper(II)
Appendix A. Supplementary data
CCDC 777120, 777593, 796024, 796025 and 796026 contains
the supplementary crystallographic data for [Mn(SCN)2(bopy)2]
(1), [Ni(SCN)2(bopy)2] (2), cis–[Cu(SCN)2(bopy)2] (3a), trans–
[Cu(SCN)2(bopy)2] (3b) and [CuCl2(bopy)2] (4). These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-
033; or e-mail: deposit@ccdc.cam.ac.uk.
complexes indicates that the unpaired electron most likely resides
in the dx 2 orbital, which is consistent with a planar stereochem-
istry and B1g ground state. The fact that g|| is less than 2.3 is an
2
ꢀy
2
References
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(g\ ꢀ 2.0023), amounts to about 2.8 and this suggests an exchange
interaction in the solid complex.
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manganese(II), nickel(II) and copper(II) with the 2-benzoylpyridine
ligand were obtained. The complexes of Mn(II) and Ni(II) are cis
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