Correlation between crystal symmetry and the splitting of d orbital in the thiocyanate nickel(II) complexes

Article abstract of DOI:10.1016/j.poly.2010.08.030

New [Ni(SCN)₂(L)_4/2] complexes, where L = py (1), γ-pic (2), pyCH₂OH (3), py(CH₂)₃OH (4) were synthesized in simple reactions of NiCl₂·6H₂O with ammonia thiocyanate and pyridine type ligands in methanol solutions. Blue crystals of [Ni(SCN)₂(py)₄] (1), [Ni(SCN) ₂(pyCH₂OH)₂] (3) and [Ni(SCN) ₂(py(CH₂)₃OH)₂] (4) crystallize in the monoclinic system, blue crystal of [Ni(SCN)₂(γ-pic) ₄] (2) - in the tetragonal one, and red crystal of [Ni(SCN) ₂(PPh₃)₂] (5) - in the triclinic one. The ligands of complexes (1) and (3) were indicated as rather strong π-acceptors while that of complex (4) one has some π-donor properties. When the aliphatic chain (CH₂) elongates in the sequence: (1), (3) and (4), an increase in the orbital contribution to the magnetic moment and a decrease in the 10Dq value of the d orbital splitting are related to the change of the point group symmetry from D_2h, via D_2v to C_2h.

Full text of DOI:10.1016/j.poly.2010.08.030

Polyhedron 29 (2010) 3198–3206
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Correlation between crystal symmetry and the splitting of d orbital
in the thiocyanate nickel(II) complexes
a
a
b,
c
⇑
´
´
J.G. Małecki , A. Switlicka , T. Gron , M. Bałanda
a Department of Crystallography, Institute of Chemistry, University of Silesia, ul. Szkolna 9, 40-006 Katowice, Poland
b Institute of Physics, University of Silesia, ul. Uniwersytecka 4, 40-007 Katowice, Poland
c
´
The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, ul. Radzikowskiego 152, 31-342 Kraków, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
New [Ni(SCN)2(L)4/2] complexes, where L = py (1), c-pic (2), pyCH2OH (3), py(CH2)3OH (4) were synthe-
Received 30 June 2010
Accepted 25 August 2010
Available online 7 September 2010
sized in simple reactions of NiCl2ꢀ6H2O with ammonia thiocyanate and pyridine type ligands in methanol
solutions. Blue crystals of [Ni(SCN)2(py)4] (1), [Ni(SCN)2(pyCH2OH)2] (3) and [Ni(SCN)2(py(CH2)3OH)2] (4)
crystallize in the monoclinic system, blue crystal of [Ni(SCN)2(
crystal of [Ni(SCN)2(PPh3)2] (5) – in the triclinic one. The ligands of complexes (1) and (3) were indicated
as rather strong -acceptors while that of complex (4) one has some -donor properties. When the ali-
c-pic)4] (2) – in the tetragonal one, and red
Keywords:
Inorganic chemistry
Paramagnetism
p
p
phatic chain (CH2) elongates in the sequence: (1), (3) and (4), an increase in the orbital contribution to the
magnetic moment and a decrease in the 10Dq value of the d orbital splitting are related to the change of
the point group symmetry from D2h, via D2v to C2h
.
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
mined [5–9]. Their interesting structural properties and potential
application are attractive in studies of magnetism or magnetic ex-
change ions.
Investigations on the syntheses, crystal, molecular, and elec-
tronic structures of metal complexes containing ambidentate li-
gands are of great interest in connection with the accumulation
of metal complexes having ambidentate ligands and with regula-
tion the reactivities of active sites in metal complexes. Many tran-
sition metal complexes containing ambidentate ligands have been
synthesized, and their structures, physical properties, and linkage
isomerisation reactions of the ambidentate units have been inves-
tigated. Thiocyanate complexes with the formula of [M(NCS)2L4],
where L is a N-donor ligand such as pyridine, are called Werner-
type complexes and they are well known. Nickel(II) thiocyanate
complexes with N-donor ligands are investigated due to their
structural properties (ability to occur in cis and trans isomers)
[1], formation of coordination polymers in which thiocyanate li-
gands are bridging ligands as linear anions [2], and examination
of solvatochromic behavior of metal complexes [3]. The complexes
of Ni(II) with thiocyanate ligands are interesting because of their
architectures organized by non-covalent contacts as hydrogen
2. Experimental
2.1. Synthesis
All reagents used for the synthesis of the complex are commer-
cially available and were used without further purification. The
[Ni(SCN)2(L)4/2] complexes, where L = py (1),
c-pic (2), pyCH2OH
(3), py(CH2)3OH (4) were synthesized in the reaction between
NiCl2ꢀ6H2O (0.24 g; 1 ꢁ 10ꢂ4 mol), NH4SCN (0.15 g; 2 ꢁ 10ꢂ4 mol)
and stoichiometric volumes of pyridine,
c-picoline, 2-(hydroxy-
methyl)pyridine and 2-(hydroxypropyl)pyridine in methanolic
solution (50 cm3). The mixtures of the compounds were refluxed
for 1 h. After this time, the volume of the solvent was reduced to
about 20 cm3, the solution was cooled and precipitated light blue
crystals suitable to X-ray analysis were filtered off. Additionally,
the reaction between pyridine, NH4SCN and triphenylphosphine
has been carried out, and finally the complex with coordination
number 4 – [Ni(SCN)2(PPh3)2] (5) – has been obtained.
bonds or
p
–
p
stacking interaction [4]. The crystal structures of iso-
-picoline and tri-
thiocyanate nickel(II) complexes with pyridine,
c
phenylphosphine ligands are known but their electronic structure
and/or spectroscopic and magnetic properties were not deter-
(1) [Ni(SCN)2(py)4]: Yield 74%. IR (KBr): 3059
SCN); 1600 mCN C@C; 1486, 1356 d(C–CH in the plane); 1442
d(C–CH in the plane); 1008 d(C–H
m
CH; 2079 m(CN from
,
m
m
Ph; 1069
plane); 800 m(SC from SCN), 768
out of the
d(C–C
plane); 713, 700 d(C–C
plane); 482 d(NCS), 429
out of the
in the
⇑
m
(Ni–Npy). UV–Vis (methanol; log
e) [calculated]: 953.1 (1.21), 746.4
Corresponding author. Tel.: +48 32 3591492.
E-mail address: Tadeusz.Gron@us.edu.pl (T. Gron´ ).
(1.13), 581.2 (1.75), 380.5 (3.14), 214.2 (4.97).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.08.030

J.G. Małecki et al. / Polyhedron 29 (2010) 3198–3206
3199
(2) [Ni(SCN)2(
c
-pic)4]: Yield 70%. IR (KBr): 3087
m
ArH; 2865 mCH
;
magnetometer in the external magnetic field of 1 kOe and in the
temperature range of 4.2–250 K as well as in the external magnetic
field up to 60 kOe and at 4.6 K, respectively. Both the magnetic sus-
ceptibility and magnetization were measured in the zero-field-
cooled mode. The magnetic susceptibility has been corrected by
2064 m(CN SCN); 1618 mCN
,
mC@C; 1503, 1211 d(C–CH
;
from
in the plane)
1421
from SCN), 725 d(C–C in the plane); 496 d(NCS). UV–Vis (methanol; log
1039.2 (1.19), 751.4 (1.09), 617.7 (1.61), 375.4 (3.05), 214.7 (4.84).
(3) [Ni(SCN)2(pyCH2OH)2]: Yield 68%. IR (KBr): 3182 OH; 2937
CH; 2114 (CN from SCN); 1610 mCN C@C; 1489, 1274 d(C–CH in the plane)
1449 ; 1032 d(C–CH in the plane); 966 d(C–H out of the plane); 818 m(SC from
SCN), 765 d(C–C
m
Ph; 1020 d(C–CH in the plane); 963 d(C–H out of the plane); 810 m(SC
e
):
m
the temperature independent contribution,
Weiss law fitting procedure [10]. The Landé factor has been esti-
mated from the magnetization isotherm (H) at 4.6 K using the
Brillouin fitting procedure (g ) and from the Curie constant C fitted
v0, using a Curie–
m
m
,
m
;
m
r
Ph
plane); 727 d(C–C
plane); 470 d(NCS), 422
out of the
in the
r
m
(Ni–Npy). UV–Vis (methanol; log
e
): 994.5 (1.19), 750.4 (1.11),
from the temperature dependence of magnetic susceptibility v(T)
599.2 (2.01), 399.6 (3.05), 217.9 (4.84).
and denoted as g . Because any of the (1), (3) and (4) complexes
v
(4) [Ni(SCN)2(py(CH2)3OH))2]: Yield 64%. IR (KBr): 3296 mOH
;
did not reach the saturation in the magnetic field up to 60 kOe,
2992, 2961
1270 d(C–CH in the plane); 1454
out of the plane); 822 (SC from SCN), 777 d(C–C out of the plane); 755 d(C–C
plane); 498 d(NCS), 437 (Ni–Npy). UV–Vis (methanol; log ):
1067.0 (1.19), 763.2 (1.12), 655.1 (1.99), 399.1 (3.05), 213.9 (4.84).
m
CH; 2106, 2062 m(CN
SCN); 1605 mCN
,
m
C@C; 1483,
the g values have only an estimated meaning.
from
r
mPh; 1038 d(C–CH in the plane); 929 d(C–H
m
2.3. Calculations
m
e
in the
The density functional theory (DFT) calculations were carried
out using GAUSSIAN 09 program [11]. The DFT/B3LYP [12,13] method
was used for the geometry optimization and electronic structure
determination. The calculations were performed using the polari-
zation functions for all atoms: 6-311(d,p) – nickel, 6-31g(2d,p) –
sulfur, 6-31(d,p) – carbon, nitrogen and 6-31g(d,p) – hydrogen.
The contribution of a group to a molecular orbital was calculated
using Mulliken population analysis. The GaussSum 2.2 [14] 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 FWHM of 0.3 eV.
(5) [Ni(SCN)2(PPh3)2]: IR (KBr): 3060
1479, 1308 d(C–CH in the plane); 1433 Ph(P–Ph); 1096 d(C–CH in the plane)
998 d(C–H out of the plane); 867
m
ArH; 2088 m(CN
;
;
from SCN)
m
m
(SC from SCN), 750 d(C–C out of the plane); 692
d(C–C in the plane); 523, 512, 497 d(NCS). UV–Vis (methanol; loge): 963.5
(1.17), 629.4 (1.30), 402.2 (1.86), 215.3 (5.12). 1H NMR (d, CDCl3):
7.284–7.692 (m, PPh3). 31P NMR (d, CDCl3): 30.213 (s, PPh3).
2.2. Measurements
Infrared spectra were recorded on a Nicolet Magna 560 spectro-
photometer in the spectral range of 4000–400 cmꢂ1 with the sam-
ple in the form of KBr pellet. Electronic spectra were measured on a
Lab Alliance UV–Vis 8500 spectrophotometer in the range of
1100–180 nm in methanol solution. The 1H and 31P NMR spectra
of complex [10] were obtained at room temperature in CDCl3 using
a Bruker 400 spectrometer.
2.4. Crystal structures determination and refinement
Crystals of [Ni(SCN)2(py)4] (1), [Ni(SCN)2(c-pic)4] (2), [Ni(SCN)2
The static (dc) susceptibility and magnetization measurements
were performed using a Lake Shore 7225 ac susceptometer/dc
(pyCH2OH)2] (3), [Ni(SCN)2(py(CH2)3OH)2] (4) and red crystal of
[Ni(SCN)2(PPh3)2] (5) were mounted in turn on a Xcalibur, Atlas,
Table 1
Crystal data and structure refinement details of [Ni(SCN)2(py)4] (1), [Ni(SCN)2(
c
-pic)4] (2), [Ni(SCN)2(pyCH2OH)2] (3), [Ni(SCN)2(py(CH2)3OH)2] (4) and [Ni(SCN)2(PPh3)2] (5)
complexes.
Complex
1
2
3
4
5
Empirical formula
Formula weight
C
22H20N6NiS2
C26H28N6NiS2
547.37
C14H14N4NiO2S2
393.12
C18H22N4NiO2S2
449.23
C38H30N2NiP2S2
699.45
491.27
T (K)
Crystal system
Space group
298.0(2)
monoclinic
C2/c
298.0(2)
tetragonal
I41/a
298.0(2)
monoclinic
C2/c
298.0(2)
monoclinic
P21/c
298.0(2)
triclinic
ꢀ
P1
Unit cell dimensions
a (Å)
b (Å)
c (Å)
a
12.4046(5)
12.9341(4)
15.1196(7)
90
107.241(5)
90
2316.83(16)
4
1.408
16.681(2)
16.681(2)
22.632(5)
90
90
90
6297.2(18)
8
1.155
0.771
2288
14.8446(4)
8.3106(2)
14.1261(4)
90
103.403(3)
90
1695.24(8)
4
1.540
9.5985(3)
10.1797(4)
10.9082(3)
90
107.451(3)
90
1016.78(5)
2
1.467
7.9451(4)
10.4777(5)
11.4926(5)
68.924(4)
74.572(2)
87.769(3)
858.84(7)
1
b
c
V (Å3)
Z
Dcalc (Mg/m3)
1.352
0.809
362
Absorption coefficient (mmꢂ1
F(0 0 0)
)
1.039
1016
1.415
808
1.180
468
Crystal dimensions (mm)
h Range for data collection (°)
Index ranges
0.42 ꢁ 0.10 ꢁ 0.07
3.43–25.05
ꢂ14 6 h 6 14
ꢂ15 6 k 6 15
ꢂ18 6 l 6 18
10 853
0.24 ꢁ 0.23 ꢁ 0.19
3.45–25.05
ꢂ19 6 h 6 19
ꢂ19 6 k 6 16
ꢂ26 6 l 6 26
14 915
0.22 ꢁ 0.10 ꢁ 0.07
3.59–25.05
ꢂ17 6 h 6 17
ꢂ9 6 k 6 9
ꢂ16 6 l 6 16
8153
0.39 ꢁ 0.21 ꢁ 0.14
3.88–25.05
ꢂ11 6 h 6 11
ꢂ12 6 k 6 12
ꢂ12 6 l 6 12
9448
0.44 ꢁ 0.09 ꢁ 0.07
3.48–25.05
ꢂ9 6 h 6 9
ꢂ12 6 k 6 12
ꢂ13 6 l 6 13
15 751
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
2025 [R(int) = 0.0273]
2025/0/142
1.053
2787 [R(int) = 0.0271]
2787/0/161
1.041
1497 [R(int) = 0.0216]
1497/0/105
1.102
1799 [R(int) = 0.0247]
1799/0/128
1.085
3371 [R(int) = 0.0288]
3371/0/205
0.912
Final R indices [I > 2
r
(I)]
R1 = 0.0232
wR2 = 0.0582
R1 = 0.0314
wR2 = 0.0592
0.189 and ꢂ0.244
R1 = 0.0308
wR2 = 0.0900
R1 = 0.0467
wR2 = 0.0936
0.238 and ꢂ0.211
R1 = 0.0474
wR2 = 0.1047
R1 = 0.0509
wR2 = 0.1064
1.108 and ꢂ1.132
R1 = 0.0218
wR2 = 0.0574
R1 = 0.0267
wR2 = 0.0585
0.248 and ꢂ0.282
R1 = 0.0324
wR2 = 0.0557
R1 = 0.0614
wR2 = 0.0649
0.277 and ꢂ0.171
R indices (all data)
Largest difference in peak and hole

3200
J.G. Małecki et al. / Polyhedron 29 (2010) 3198–3206
CH3
NCS
H3C
N
N
N
NCS
Ni
Ni
N
CH3
N
N
N
NCS
N
H3C
NCS
(2)
(1)
CH2
HO
N
HO
CH2
Ni
NCS
N
NCS
(3)
Fig. 1. The ORTEP drawing of [Ni(SCN)2(py)4] (1), [Ni(SCN)2(c-pic)4] (2), [Ni(SCN)2(pyCH2OH)2] (3), [Ni(SCN)2(py(CH2)3OH)2] (4) and [Ni(SCN)2(PPh3)2] (5) with 50%
probability displacement ellipsoids. Hydrogen atoms are omitted for clarity.

J.G. Małecki et al. / Polyhedron 29 (2010) 3198–3206
3201
CH2
CH2
CH2
N
SCN
N
OH
Ni
NCS
CH2
PPh3
NCS
SCN
Ph3P
Ni
HO
CH2
CH2
(5)
(4)
Fig. 1 (continued)
Table 2
Selected bond lengths (Å) and angles (°) for [Ni(SCN)2(py)4] (1), [Ni(SCN)2(c-pic)4] (2), [Ni(SCN)2(pyCH2OH)2] (3), [Ni(SCN)2(py(CH2)3OH)2] (4) and [Ni(SCN)2(PPh3)2] (5)
complexes with optimized geometries in gas phases.
Complex
1
2
3
4
5
Bond lengths (Å)
exp
calc
exp
calc
exp
calc
exp
calc
exp
calc
Ni(1)–N(1)
Ni(1)–N(2)
Ni(1)–N(3)
Ni(1)–O(1)
Ni(1)–P(1)
N(1)–C(1)
S(1)–C(1)
2.053(14)
2.157(12)
2.169(13)
2.041
2.234
2.243
2.072(2)
2.127(17)
2.131(16)
2.029
2.169
2.171
2.034(14)
2.058(12)
1.993
2.121
2.038(13)
2.167(12)
1.982
2.274
1.826(16)
1.835
2.125(12)
2.172
2.115(11)
2.127
2.247(4)
1.157(3)
1.612(2)
2.308
1.186
1.616
1.154(2)
1.624(18)
1.186
1.626
1.155(3)
1.617(3)
1.186
1.631
1.148(2)
1.631(18)
1.191
1.626
1.156(2)
1.636(16)
1.189
1.623
Angles (°)
N(1)–Ni(1)–N(2)
N(1)–Ni(1)–N(3)
N(2)–Ni(1)–N(3)
N(1)–Ni(1)–O(1)
N(2)–Ni(1)–O(1)
N(1)–Ni(1)–P(1)
Ni(1)–N(1)–C(1)
N(1)–C(1)–S(1)
90.97(5)
90.55(5)
92.77(5)
90.10
89.98
91.12
90.28(7)
90.33(7)
90.70(6)
90.06
90.12
90.15
95.46(5)
94.87
86.30(5)
86.58
172.01(5)
77.43(5)
163.87
75.68
85.81(5)
90.36(5)
86.27
90.38
92.13(5)
173.27(15)
179.46(18)
92.25
174.87
179.44
156.58(13)
178.80(15)
159.47
179.91
152.91(16)
179.80(2)
159.93
179.94
174.91(13)
178.29(15)
164.55
177.05
163.41(12)
179.31(15)
163.58
178.89
Table 3
Hydrogen bonds for (1–4) complexes (Å and °).
Gemini ultra Oxford Diffraction automatic diffractometer equipped
with a CCD detector, and used for data collection. X-ray intensity
D–Hꢀ ꢀ ꢀA
d(D–H)
d(Hꢀ ꢀ ꢀA)
d(Dꢀ ꢀ ꢀA)
<(DHA)
data were collected with graphite monochromated Mo K
tion (k = 0.71073 Å) at temperature of 298.0(2) K, with
a
radia-
x scan
[Ni(SCN)2(py)4] (1)
C(11)–H(11)ꢀ ꢀ ꢀN(1)
mode. 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 6500, 7620, 9298, 6738 and
7167 strongest reflections for complexes (1–5), respectively.
During the data reduction, the decay correction coefficient was
taken into account. Lorentz, polarization, and numerical absorption
corrections were applied. The structures were solved by direct
method. All the non-hydrogen atoms were refined anisotropically
using full-matrix, least-squares technique on F2. All the hydrogen
atoms were found from difference Fourier synthesis after four
0.93
0.93
2.59
2.61
3.119(2)
3.112(3)
116.7
114.1
[Ni(SCN)2(c-pic)4] (2)
C(2)–H(2)ꢀ ꢀ ꢀN(1)
[Ni(SCN)2(pyCH2OH)2] (3)
O(1)–H(1)ꢀ ꢀ ꢀS(2) #1
O(2)–H(2)ꢀ ꢀ ꢀS(1) #2
0.74(2)
0.75(2)
2.43(2)
2.49(2)
3.1579(14)
3.2088(14)
167(2)
164(2)
[Ni(SCN)2(py(CH2)3OH)2] (4)
O(1)–H(1)ꢀ ꢀ ꢀS(1) #3
0.78(2)
0.97
2.51(2)
2.45
3.2640(14)
3.304(2)
163(2)
146.1
C(7)–H(7A)ꢀ ꢀ ꢀN(1) #4
Symmetry transformations used to generate equivalent atoms: #1 1/2 + x, ꢂy, ꢂ1/
2 + z; #2 ꢂx, 1 ꢂ y, 2 ꢂ z; #3 1 ꢂ x, 1/2 + y, ꢂ1/2 ꢂ z; #4 1 ꢂ x, ꢂy, ꢂz.

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J.G. Małecki et al. / Polyhedron 29 (2010) 3198–3206
cycles of anisotropic refinement, and refined as ‘‘riding” on the
adjacent atom with individual isotropic temperature factor equal
to 1.2 times the value of equivalent temperature factor of the
The complexes (1–4) crystallise in the monoclinic space group
C2/c and P21/c respectively and the plane square complex (5) in tri-
clinic P1 space group. Details concerning crystal data and refine-
ꢀ
parent atom, with geometry idealization after each cycle. The OLEX
program [15] was used for all calculations. Atomic scattering
factors were those incorporated in the computer programs.
2
ment are gathered in Table 1. The molecular structures with the
structural drawings of the compounds are shown in Fig. 1. The se-
lected bond lengths and angles (experimental and calculated) are
listed in Table 2. In the complexes (1–4), nickel atoms have octahe-
dral environment with the thiocyanate ligands bonded to metal
center through nitrogen atom. In the complexes under study, the
nickel(II) ion is located in the crystallographic center of inversion
(1, 4, and 5) or on two-fold axis (2 and 3) and its coordination envi-
ronment consists of two thiocyanato ligands and four pyridine,
3. Results and discussion
Infrared spectra of the complexes present characteristic bands
due to ligands vibrations. The stretching modes of the aryl C–H bond
display maxima at 3059, 3061, 2937, 2992, and 3060 cmꢂ1 for com-
plexes (1–5), respectively. In the spectra of complexes (3) and (4),
bands with maxima at 3182 and 3296 cmꢂ1, characteristic to OH
c
-picoline ligands (1 and 2) or two 2-(hydroxymethyl/hydroxypro-
pyl)pyridine (3 and 4) molecules. In the case of complexes with
pyridine and -picoline ligands, the coordination polyhedron is
c
groups, are visible. The mC@N band of pyridine ring appears at about
an almost perfect octahedron with angular deviations smaller than
3°. In the case of complexes (3) and (4), the distortions from
1600 cmꢂ1. In the case of complex (5), the stretching modes of the
phosphine phenyl C–H have maximum at 1433 cmꢂ1, which is
characteristic for triphenylphosphine complexes. The mCN, mCS and
dNCS frequencies of isothiocyanato ligands present maxima at
2079 cmꢂ1 (1), 2064 (2), 2114 (3), 2114 cmꢂ1 (4), 2088 cmꢂ1 (5),
800, 810, 818, 822, 867 cmꢂ1, and 482, 496, 470, 498, 497 cmꢂ1
,
respectively, and it is in good agreement with the end-on NCS coor-
dination. In complex (3), two NCS ligands are in cis position and in
the IR spectrum two
mCN stretches are expected, but only one broad-
ening band has been recorded. The singlet at 30.213 ppm in the 31
P
NMR spectrum of complex (5) indicated that both triphenylphos-
phine ligands in the complex are equivalent and they are mutually
trans disposed. The 1H NMR spectrum of the complex displayed sets
of signals in the range of 7.284–7.692 ppm, characteristic to tri-
phenylphosphine ligands.
Fig. 3. The experimental (black) and calculated (red) IR transitions of
[Ni(SCN)2(py)4] (1) and [Ni(SCN)2(py(CH2)3OH)2] (4). (For interpretation of the
references to colour in this figure legend, the reader is referred to the web version of
this article.)
Fig. 2. The crystal packing of complexes (3) and (4) viewing down the c axis with
hydrogen bonds indicated by dotted lines.

J.G. Małecki et al. / Polyhedron 29 (2010) 3198–3206
3203
octahedron are visible in the angles N(1)–Ni(1)–O(1) with value
ꢃ8° for complex (3) and 4.2° for (4). The C–N and C–S bond length
values fall in the 1.148(2)–1.157(3) Å and 1.612(2) Å, 1.636(16) Å
ranges for the studied complexes, similar to those observed for
hydrogen bonds are observed and collected in Table 3. In Fig. 2,
the two dimensional networks formed by the hydrogen bonds in
the complexes (3) and (4) are shown.
thiocyanate complexes. The Ni–N(heterocyclic
and Ni–O dis-
ligand)
tances are normal and comparable with distances in other nicke-
l(II) complexes containing the heterocyclic ligands. The distances
between Ni-
observed for Ni-pyridine in complexes (2) and (1) respectively;
indicating -picoline is a stronger -acceptor than pyridine, which
c-picoline are shorter about 0.03 Å that those
c
p
was confirmed by the calculations described below. Ni–N–C angles
range from 152.91(16)° (2) to 174.91(13)° (3) in the studied com-
plexes. In all complexes, the values of Ni–N–C angles are in a good
agreement with those found for Ni2+ having bent terminally
bonded NCS ligand (141–174°) [16]. The conformations of mole-
cules (1 and 2) are stabilized by intramolecular hydrogen bonds,
and in crystal packing of complexes (3 and 4) intermolecular
Fig. 5. The overlap partial density-of-states (OPDOS) diagrams for interactions
between nickel and A – isothiocyanate ligands, and B – pyridine type ligands.
Fig. 4. The electrostatic potential (ESP) surfaces of [Ni(SCN)2(py)4] (1) and
[Ni(SCN)2(py(CH2)3OH)2] (4) complexes. The ESP surface is shown both in space
(with positive and negative regions shown in blue and red, respectively) and
mapped on electron densities (in the range of 0.05 a.u.
– deepest red – to
ꢂ0.005 a.u. – deepest blue) of the molecule (ESP colour scale is such that d+ ? dꢂ in
the direction red ? blue). (For interpretation of the references to colour in this
figure legend, the reader is referred to the web version of this article.)
Fig. 6. The UV–Vis spectrum of complex (1).

3204
J.G. Małecki et al. / Polyhedron 29 (2010) 3198–3206
Table 4
Calculated UV–Vis transitions for the [Ni(SCN)2(py)4] (1) and [Ni(SCN)2(pyCH2OH)2]
(3) complexes. The experimental values are given for comparison.
Wavelength Contributions
(nm)
Exp.
(nm)
(1)
881.1
795.8
785.5
H-8(b) ? LUMO(b) (97%)
953.1
746.4
581.2
H-12(b) ? L+2(b) (55%), H-1(b) ? LUMO(b) (11%)
H-13(b) ? LUMO(b) (12%), H-13(b) ? L+2(b) (30%),
H-10(b) ? L+2(b) (20%)
HOMO(b) ? LUMO(b) (20%)
H-12(b) ? LUMO(b) (35%), H-12(b) ? L+2(b) (25%)
H-17(b) ? L+2(b) (15%), H-8(b) ? L+2(b) (77%)
528.5
522.1
490.5
(3)
1052.4
H-8(b) ? LUMO(b) (87%), HOMO(b) ? LUMO(b)
994.5
(22%)
854.8
H-13(b) ? L+1(b) (11%), H-7(b) ? LUMO(b) (21%), H- 750.4
6(b) ? L+1(b) (48%)
829.9
540.6
518.4
H-7(b) ? L+1(b) (27%), H-6(b) ? LUMO(b) (39%)
H-7(b) ? LUMO(b) (25%), H-1(b) ? LUMO(b) (11%)
H-8(b) ? L+1(b) (49%), HOMO(b) ? L+1(b) (24%)
599.2
Fig. 7. The E/B vs. Dq/B dependence of Tanabe–Sugano diagram for octahedrally
coordinated Ni+2 ion. The vertical lines represent the case of [Ni(SCN)2(py)4] (1) and
[Ni(SCN)2(py(CH2)3OH)2] (4) chromophore.
to thiocyanate ligands are equal to 20.54, 31.16, 33.53 and
25.00 kcal/mol for (1–4), respectively. The atomic charge calcula-
tions may describe the relocation of electron density of the com-
pounds. The plots of the electrostatic potentials for the studied
compounds (1) and (4) are shown in Fig. 4. The isoelectronic con-
tours are plotted at 0.005 a.u. (3.1 kcal/mol). The color code of
these maps is in the range of 0.05 a.u. (deepest red) to
ꢂ0.005 a.u. (deepest blue), where blue indicates the strongest
attraction and red indicates the strongest repulsion. Regions of
negative V(r) are usually associated with the lone pair of electro-
negative atoms. The negative potential in the studied compounds
wrap thiocyanate ligands and oxygen atoms in the compounds
with 2-(hydroxymethyl) or 2-(hydroxypropyl)pyridine ligands. As
one can see in the Fig. 4, negative potentials on sulfur atoms in
the studied compounds are smaller than the ones on nitrogen
atoms (not to mention oxygen donor atoms). The natural charges
obtained from NBO analysis are close to each other: N(NCS) ꢂ0.8,
N(py) ꢂ0.6 and S(NCS) about ꢂ0.2. That is why, and additionally be-
cause of steric hindrance exerted by pyridine rings in compounds
(1) and (2), the studied complexes do not form polymeric systems
with NCSꢂ connector.
In the frontier region, neighboring orbitals may show quasi-
degeneracy of the energetic levels. In such cases, consideration of
only the HOMO and LUMO may not yield a realistic description
of the frontier orbitals. For this reason, the overlap population den-
sity-of-states (OPDOS) in terms of Mulliken population analysis
was calculated using the GaussSum program. The results provide
a pictorial representation of MOs compositions and their contribu-
tions to chemical bonding. The OPDOS diagrams are shown in
Fig. 5, and they may enable us to ascertain the bonding, non-bond-
ing and antibonding characteristics with respect to the particular
fragments. A positive value in OPDOS plots means a bonding inter-
action, while a negative value represents antibonding interaction,
3.1. Electronic structure
To form an insight in the electronic structures and bonding
properties of the studied complexes, calculations using the density
functional theory (DFT) method were carried out. Before the calcu-
lations their geometries were optimized in singlet states using the
DFT method with the B3LYP functional. In general, the predicted
bond lengths and angles are in a good agreement with the values
based on the X-ray crystal structure data, and the general trends
observed in the experimental data are well reproduced in the cal-
culations. As an example, the IR experimental and calculated spec-
tra of [Ni(SCN)2(py)4] (1) and [Ni(SCN)2(py(CH2)3OH))2] (4) are
presented in Fig. 3. Maximum differences between the optimized
and experimental geometries of the studied compounds are visible
in Ni(1)–N(2) distance (ꢃ0.100 Å) for complex (3) and in N(2)–
Ni(1)–N(3) angle (2.9°) for (1). Additionally from Fig. 3 is visible
that the hydrogen bonds are poorly interpreted by the calculations
in GAUSSIAN. The stabilization energies calculated in NBO [17] analy-
ses have shown that the lone pairs localized on the N atom of NCSꢂ
ligands in complex (1) donate the charge to nickel, and the stabil-
ization energy is 127.95 kcal/mol, and 68.69, 151.87 and
72.18 kcal/mol in the complexes (2–4), respectively. The stabiliza-
tion energies connected to interaction between N-heteroaromatic
ligands and nickel central ion are 170.53, 65.11, 157.74 and
59.17 kcal/mol in compounds (1–4), respectively. The back dona-
tions from nickel to N-heteroaromatic ligands have values
31.17 kcal/mol to pyridine ligand, 62.59 kcal/mol to
c-picoline
and 21.39, 25.42 kcal/mol to 2-(hydroxymethyl)pyridine and 2-
(hydroxypropyl)pyridine ligands, respectively. The back donations
Table 5
Magnetic parameters of the [Ni(SCN)2(py)4] (1), [Ni(SCN)2(pyCH2OH)2] (3) and [Ni(SCN)2(py(CH2)3OH)2] (4) complexes.
Complex
M (g/mol)
C (emu K/mol)
hCW (K)
leff
(lB
)
g
g
v
r
(1) [Ni(SCN)2(py)4]
(3) [Ni(SCN)2(pyCH2OH)2]
(4) [Ni(SCN)2(py(CH2)3OH)2]
491.27
393.12
449.23
1.04
1.23
1.38
0.3
ꢂ0.4
ꢂ1.6
2.88
3.14
3.32
2
2.07
2.03
2.04
2.22
2.30
M is the molar mass, C is the Curie constant, hCW is the paramagnetic Curie–Weiss temperature, leff is the effective magnetic moment, and g and g are the Landé factors
r
v
estimated from the magnetization isotherm
r(H) at 4.6 K using the Brillouin fitting procedure and from the Curie constant C fitted from the temperature dependence of
magnetic susceptibility (T), respectively.
v

J.G. Małecki et al. / Polyhedron 29 (2010) 3198–3206
3205
and a near zero value indicates a non-bonding interaction. As one
can see from the OPDOS plots, the interaction between thiocyanate
ligands and nickel ion in the complex with pyridine ligand is very
small in HOMO and LUMO molecular orbitals. Similar interactions
in the complexes (2) and (4) have antibonding character and the
one in complex (3) – non-bonding character. In the lower HOMO
orbitals (H-1, H-2), the interactions of N-donor ligands with nickel
d-orbitals have negative values likewise in lowest virtual molecu-
lar orbitals in complexes (1) and (2). In the case of complex (3),
LUMO has non-bonding character of Ni–L interaction, and in com-
plex (4) a significant bonding effect is observed which is connected
with the oxygen donor atoms in 2-(hydroxymethyl) – and 2-
(hydroxypropyl)pyridine ligands. In the frontier occupied and vir-
tual molecular orbitals, values of the interaction between nickel
ions and pyridine type ligands indicate the ligands as rather strong
field parameter 10Dq, calculated on the basis of electronic bands
positions for the investigated complexes (given in experimental
part), are equal to 10Dq = 10 492 (1), 9623 (2), 10 055 (3), 9372
(4), and 10 379 cmꢂ1 (5). Racah parameter B is equal to 896, 822,
891, 882 and 886 cmꢂ1 for complexes (1–5), respectively. The Ra-
cah 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
the d-orbitals overlap with the ligand orbitals. As a result, the
interelectronic repulsion within the d-orbitals decreases and B
value is lowered. The ratio B/B0 = b gives a measure of covalency
in the metal–ligand bond. The nepheloauxetic parameters calcu-
lated for the studied complexes are b = 0.86 for complexes (1)
and (3), 0.79 for compound (2) and 0.85 for (4) and (5). It is note-
worthy that the 10Dq value decreases in the sequence (1), (3) and
(4) for that the point group symmetry lowers. The bands recorded
in the electronic spectra of complexes (1–4) have small molar
extinction coefficients, and maxima about 750 nm. They are as-
cribed to 1Eg(1D) term in Oh symmetry, which separates in the D2
symmetry into 1A1 and 1B1 levels. This indicates that these bands
correspond to spin-forbidden 1A1/1B1(1D) ? 3A2(3F) transitions. In
Fig. 7, the Tanabe–Sugano diagram for d8 ions in octahedral coor-
dination is shown with the crystal field strength of the Ni2+ ions
in complexes (1) and (4) indicated by vertical lines. For the calcu-
lated Dq/B ratios (1.06–1.17) in the Tanabe–Sugano diagram for d8
ions in octahedral coordination one can see that the 1Eg(1D) singlet
p
p
-acceptors, and in the case of 2-(hydroxypropyl)pyridine ligand,
-donor properties are pointed out. This conclusion is confirmed
additionally by stabilization energy mentioned earlier.
3.2. Electronic spectra
The lowest state of the nickel(II) ion is 3F term, which splits into
3A2g, 3T2g and 3T1g terms in the field with Oh symmetry. The studied
complexes have D2/C2 (D2h/C2h) point group symmetry, and in this
symmetry 3T2 and 3T1 terms split into singlet 3A2 and 3B2 and dou-
blet 3E levels each. As a consequence, the first and second spin-al-
lowed transition bands observed on the UV–Vis spectra of the
complexes are assigned to 3T2(3F) ? 3A2(3F) and 3T1(3F) ? 3A2(3F),
respectively. The third absorption band results from a spin-allowed
transition 3T1(3P) ? 3A2(3F). In Fig. 6, the absorption spectrum of
complex (1) is presented with three spin-allowed crystal field
bands and one spin-forbidden transition. The values of the ligand
3
state is lower than the T1g(3F) term which confirms the bands
positions in the spectra.
Additionally the electronic spectra of these complexes were cal-
culated in the GAUSSIAN program with PCM model (Table 4). Because
Fig. 8. Magnetic susceptibility
vdc vs. temperature T recorded at H = 1 kOe. Inset: magnetization r vs. H/T at 4.6 K. The solid (red) line is for an estimation of the Landé factor.
(For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

3206
J.G. Małecki et al. / Polyhedron 29 (2010) 3198–3206
the d ? d transitions are forbidden their oscillator strange are very
small (close to 0.0) and the experimental spectra in the energy re-
gion of 1100–700 nm are widening that the calculated transitions
are adequate to theses ones. The calculated UV–Vis spectra of these
complexes (1) and (3) are collected in the Table 5. On the other
hand these complexes are Werner-type except the complex (3) in
which the donor properties of 2-(hydroxmethyl)pyridine pyridine
ligand play role (on the UV–Vis spectrum the calculated d ? d
transitions have values below 0.0009).
pointed out. The differences in acceptor properties of the ligands
were shown in the values of ligand field parameters determined
from electronic spectra of the complexes. Additionally, in the series
of complexes (1), (3), and (4) in which the N-donor ligands differ
from each other by CH2 group, point group symmetry lowering
(D2h ? D2v ? C2h) had an impact on the 10Dq value. Similar behav-
ior from the Landé factor calculations was also observed. It means
that the increase of the orbital contribution to the total magnetic
moment strongly influences the electronic structure and the chem-
ical bonds.
3.3. Magnetic properties
5. Supplementary data
The magnetic properties for blue crystals of [Ni(SCN)2(py)4] (1),
[Ni(SCN)2(pyCH2OH)2] (3), [Ni(SCN)2(py(CH2)3OH)2] (4) were stud-
CCDC 763538, 767567, 763407, 765806, and 763986 contains
the supplementary crystallographic data for [Ni(SCN)2(py)4],
[Ni(SCN)2(-pic)4], [Ni(SCN)2(pyCH2OH)2], [Ni(SCN)2(py(CH2)3OH)2]
and [Ni(SCN)2(PPh3)2]. These data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, UK; fax: (+44) 1223 336 033; or e-mail:
deposit@ccdc.cam.ac.uk.
ied. The
vdc(T) curves in Fig. 8a–c show paramagnetic behavior.
The insets of Fig. 8a–c reveal a lack of saturation of magnetization
up to 60 kOe. For the Ni2+ ion (S = 1) with 3d8 electronic configura-
tion, the Landé factor g = 2, theoretical Curie constant C = 1 emu
K/mol and the effective magneton spin-only value of peff
¼
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2
SðS þ 1Þ = 2.83. The effective magnetic moment
leff = 2.88 lB
for complex (1) is close to peff indicating the spin-only contribution
to the total magnetic moment. When the aliphatic chain (CH2)
elongates in the sequence: (1), (3) and (4), the Curie constant,
effective magnetic moment and Landé factor increase while the
paramagnetic Curie–Weiss temperature decreases (Table 5), sug-
gesting an increase of the orbital contribution to the magnetic mo-
ment. The small values of the paramagnetic Curie–Weiss
temperature, hCW, also confirm the paramagnetic behavior for the
(1), (3) and (4) complexes. A slight decrease of hCW from 0.3 K for
(1) via ꢂ0.4 for (2) to ꢂ1.6 K for (3) and a change of its sign with
elongating of the aliphatic chain show that the orbital contribution
favors a weak antiferromagnetic superexchange interaction. The
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4. Conclusions
In the simple one-pot syntheses isothiocyanate complexes of
nickel(II) with pyridine,
c-picoline, 2-(hydroxymethyl)pyridine
and 2-(hydroxypropyl)pyridine ligands were obtained. Addition-
ally, an attempt to synthesize nickel(II) thiocyanate complex with
pyridine and triphenylphosphine in coordination sphere was
undertaken and square planar [Ni(SCN)2(PPh3)2] complex was ob-
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(complex 5) spectroscopy, and their crystal structures were deter-
mined by X-ray diffraction. Electronic structures of the studied
complexes were calculated using DFT method, and apart from
the descriptions of frontier molecular orbitals and the relocation
of the electron density of the compounds, the bonding properties
in the complexes were determined. Based on calculated stabiliza-
tions energies, the values of the interaction between nickel ions
and pyridine type ligands and the energy decomposition analysis
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indicated the ligands were rather strong
of 2-(hydroxypropyl)pyridine ligand,
p
-acceptors. In the case
p
-donor properties were