1,10-Phenanthroline-dithiolate mixed ligand transition metal complexes. Synthesis, characterization and EPR spectroscopy

Article abstract of DOI:10.1016/j.ica.2010.01.021

A series of new N₂S₂ mixed ligand transition metal complexes, where N₂ is phenanthroline and S₂ is 1,2-dithiooxalate (dto) or 1,2-dithiosquarate (dtsq), has been synthesized and characterized. IR spectra reveal that the 1,2-dithiolate ligands are coordinated via the sulfur atoms forming a N₂S₂ coordination sphere. The copper(II) complex [Cu(phen)(dto)] was studied by EPR spectroscopy as a diamagnetically diluted powder. The diamagnetic dilution resulted from doping of the copper complex into the isostructural host lattice of the nickel complex [Ni(phen)(dto)]. The electronic situation in the frontier orbitals of the copper complex calculated from the experimental data is compared to the results of EHT and DFT calculations. Furthermore, one side product, chlorobis(1,10-phenanthroline)copper(I) ethanol solvate hydrate [(phen)₂CuCl]·C₂H₅OH·H₂O, was formed by a reduction process and characterized by X-ray diffraction. In the crystal packing one-dimensional columns of dimers are formed, stabilized by significant π-π interactions.

Full text of DOI:10.1016/j.ica.2010.01.021

Inorganica Chimica Acta 363 (2010) 1488–1494
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1,10-Phenanthroline-dithiolate mixed ligand transition metal complexes.
Synthesis, characterization and EPR spectroscopy
Duha Jawad Awad a, Franziska Conrad b, Andreas Koch a, Uwe Schilde a, Andreas Pöppl c, Peter Strauch a,
*
a University of Potsdam, Institute of Chemistry, Karl-Liebknecht-Str. 24-25, D-14476 Golm, Germany
b University of Zurich, Institute of Inorganic Chemistry, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
c University of Leipzig, Institute of Experimental Physics, Linnéstr. 5, D-04103 Leipzig, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of new N2S2 mixed ligand transition metal complexes, where N2 is phenanthroline and S2 is 1,2-
dithiooxalate (dto) or 1,2-dithiosquarate (dtsq), has been synthesized and characterized. IR spectra reveal
that the 1,2-dithiolate ligands are coordinated via the sulfur atoms forming a N2S2 coordination sphere.
The copper(II) complex [Cu(phen)(dto)] was studied by EPR spectroscopy as a diamagnetically diluted
powder. The diamagnetic dilution resulted from doping of the copper complex into the isostructural host
lattice of the nickel complex [Ni(phen)(dto)]. The electronic situation in the frontier orbitals of the copper
complex calculated from the experimental data is compared to the results of EHT and DFT calculations.
Furthermore, one side product, chlorobis(1,10-phenanthroline)copper(I) ethanol solvate hydrate
[(phen)2CuCl]ꢀC2H5OHꢀH2O, was formed by a reduction process and characterized by X-ray diffraction.
Received 7 September 2009
Accepted 19 January 2010
Available online 25 January 2010
Keywords:
1,2-Dithiosquarate
1,2-Dithiooxalate
1,10-Phenanthroline
X-ray crystal structure
EPR
In the crystal packing one-dimensional columns of dimers are formed, stabilized by significant
interactions.
p–p
Copper(II)
Transition metals
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
the experimental spin density distribution is compared with the
results of quantum chemical calculations on different levels (EHT
and DFT). A chlorobis(phenanthroline)copper(I) complex as a re-
duced by-product was isolated and structurally characterized.
Mixed ligand complexes with a diimine/dithiolate ligand com-
bination have attracted an increasing interest over the last decades
because of their properties [1], e.g. as conducting and supercon-
ducting materials [2–4], optical materials [5,6] and solar cell dyes
[7–9]. Some of these complexes have also shown very promising
anti-tumor activities (in vitro and in vivo) in cis-platin-resistant
model systems [10].
2. Experimental
2.1. Synthesis
Copper as an essential element is always interesting to study in
nature related compounds. With its d9 electron configuration and
the well separated ground state (S = 1/2) and a nuclear spin of
I = 3/2, Cu2+ is also very well suited to be studied by EPR spectros-
copy. The blue copper enzymes of type 1 are an interesting group
of transition metal centered enzymes with a N2S2 coordination
sphere. The distorted coordination geometry between the typical
square planar coordination of copper(II) and the tetrahedral of
copper(I) is known as an entatic state, ready to switch easily be-
tween both oxidation states. In the present paper we have synthe-
sized and studied a series of phenanthroline N2S2 coordinated
mixed ligand complexes. To get more insight into the electronic
situation, EPR spectroscopic measurements were performed, and
1,10-Phenanthroline and the transition metal chlorides were
used as purchased without any further purification. For the palla-
dium complexes, Pd(CH3–CN)2Cl2 was used as starting material,
prepared by dissolving PdCl2 in acetonitrile and evaporation of
the excess solvent [11], whereas K2PtCl4 was used for the platinum
complexes.
The dithiolate ligands dipotassium-1,2-dithiooxalate (K2dto)
[12] and dipotassium-1,2-dithiosquarate [13] were synthesized
as described in the literature.
Dipotassium-1,2-dithiooxalate (K2dto): decomposes > 200 °C;
IR [KBr, cmꢁ1]:
m
(C–O) = 1514,
m(C–C–O) = 1371, m(C–C–S) = 1113,
m(C–S) = 875; Elemental Anal. Calc.: C, 12.11; O, 16.13; S, 32.33.
Found: C, 11.67, 12.33; O, 13.78, 13.92; S, 32.14%, 32.26%.
Dipotassium-1,2-dithiosquarate (K2dtsq): decomposes > 200 °C;
IR [KBr, cmꢁ1]:
m
m
(C–O) = 1707, 1623,
(C–S) = 923; Elemental Anal. Calc.: C, 21.61; O, 14.39; S, 28.84.
Found: C, 21.83, 21.33; O, 16.60, 18.49; S, 26.98%, 26.84%.
m(C–C–O) = 1343, m(C–C–S) = 1209,
* Corresponding author. Tel.: +49 331 977 5190; fax: +49 331 977 5054.
E-mail address: pstrauch@uni-potsdam.de (P. Strauch).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.01.021

D.J. Awad et al. / Inorganica Chimica Acta 363 (2010) 1488–1494
1489
2.2. Preparation of the dichlorophenanthroline complexes of
2.4. Methods
[M(phen)Cl2] type (general procedure)
EPR spectra were recorded at 9.4 GHz (X-band) with a Bruker
CW Elexsys E500 spectrometer as powders. The Q-band spectra
were recorded at ꢂ36 GHz with a Bruker EMX spectrometer at
295 K. The spectra were simulated with the experimental parame-
ters using the program WIN-Simfonia [16].
The program CACAO (Computer Aided Composition of Atomic
Orbitals) by Mealli and Proserpio [17] has been used for the EHT
calculations (Extented Hückel Theory). For the DFT-Calculations
the program package GAUSSIAN 03 and the basis set B3LYP/6-31G*
was applied [18].
IR-Spectra were recorded on a Perkin–Elmer type 16 PC FT-IR
spectrophotometer in the region between 4000 and 400 cmꢁ1 as
KBr-pellets (reference KBr).
The magnetic susceptibilities of the synthesized complexes
were measured with Gouy method using a magnetic balance type
MSB-Auto (Sherwood Scientific Ltd.).
Metal-1,10-phenanthroline-dichloro complexes were synthe-
sized according to the method described by Jäger and van Dijk
[14]. An ethanolic solution of 1,10-phenanthroline was added
slowly to a well stirred warm ethanolic solution of the appropriate
metal chloride (MCl2 Å nH2O) (M = Ni, Cu, Zn) or the appropriate
bis(acetonitrile)dichloro complex [(AN)2PdCl2] or tetrachloroplati-
nate(II) complex [PtCl4]2ꢁ. After 1 h the reaction mixture was al-
lowed to cool to room temperature. The micro crystalline
products were filtered off, washed with ethanol and dried in vac-
uum. For the platinum complex the method was slightly modified:
water with some drops of HCl was used as solvent and the mixture
was refluxed for 1 day [15]. These 1,10-dichlorophenanthroline
metal(II) complexes were directly used for the synthesis of the
dithiolate complexes without further purification.
2.3. Preparation of the phenanthroline-dithiolate complexes
[M(phen)(dto)] and [M(phen)(dtsq)] (general procedure)
Diffraction data were collected at 210 K on a STOE Imaging Plate
Diffraction System IPDS-II using graphite monochromatized Mo K
a
radiation (k = 0.71 073 Å). The data were corrected by a spherical
absorption correction using the program X-Area (STOE, 2004) as
well as for Lorentz, polarization and extinction effects. The solution
of the crystal structure was performed using the program SHELXS-97
by direct methods (Sheldrick, 1997) [19], and refined using the
program SHELXL-97 (Sheldrick, 1997) [20]. All non-hydrogen atoms
were refined anisotropically. The hydrogen atoms were located
from the difference Fourier map and allowed to ride on their parent
atoms with Uiso(H) = 1.2 Ueq(C). The crystal structure contains dis-
ordered water and ethanol as solvate molecules. In spite of several
attempts, the electronic density in this area could not be resolved
satisfactory. Therefore the contribution of the disordered solvent
species was subtracted from the structure factor calculations by
the SQUEEZE instruction of the program PLATON [21].
To a well stirred solution of the appropriate dichloro-1,10-phe-
nanthroline metal(II) complex in an ethanol/water mixture (3:1)
was added an aqueous solution of the equimolar amount of the
potassium dithiolate, K2dto or K2dtsq. After 1 h (for the Pt-complex
one day) the colored micro crystalline products were filtered off,
washed with ethanol and dried in vacuo. The yield is practically
quantitative.
[Cu(phen)(dto)]; dark green, decomposes at 160 °C; elemental
Anal. Calc. for C14H8N2S2O2Cu: C, 46.21; H, 2.22; N, 7.70; S,
17.62; O, 8.79. Found: C, 44.21; H, 1.77; N, 7.52; S, 16.72; O,
9.00%. Susceptibility: leff = (1.8 0.5) B.M.
[Cu(phen)(dtsq)]: brown, decomposes at 230 °C; elemental
Anal. Calc. for C16H8N2S2O2Cu: C, 49.54; H, 2.08; N, 7.22; S,
16.53; O, 8.25. Found: C, 46.29; H, 1.88; N, 7.17; S, 14.73; O,
8.15%. Susceptibility: leff = (2.0 0.5) B.M.
3. Results and discussion
[Ni(phen)(dto)]; brown, decomposes at 242 °C; elemental Anal.
Calc. for C14H8N2S2O2Ni: C, 46.83; H, 2.25; N, 7.80; S, 17.86; O, 8.91.
Found: C, 45.19; H, 2.14; N, 7.53; S, 17.73; O, 8.75% (9.25). Suscep-
The series of complexes was synthesized by a straight forward
synthesis (see Scheme 1) via the dichloro-1,10-phenanthroline me-
tal(II) species followed by an exchange of the chloro ligands by the
dithiolates 1,2-dithiooxalate (dto: K2C2O2S2) and 1,2-dithiosqua-
rate (dtsq: K2C4O2S2). The problem of the synthesis is the poor sol-
ubility of the final complexes, reducing the chance of purification
by recrystallization. Also all attempts to grow single crystals of dif-
fractometer quality for the M(II) complexes failed.
tibility: leff = (1.3 0.5) B.M.
[Ni(phen)(dtsq)]:dark green, decomposes at 245 °C; elemental
Anal. Calc. for C16H8N2S2O2Ni: C, 50.17; H, 2.11; N, 7.31; S, 16.74;
O, 8.35. Found: C, 51.36; H, 2.17; N, 7.77; S, 14.29; O, 8.05%. Sus-
ceptibility: (2.7 0.5) B.M.
[Zn(phen)(dto)]; yellow, decomposes at 202 °C; elemental Anal.
Calc. for C14H8N2S2O2Zn: C, 45.98; H, 2.20; N, 7.66; S, 17.53; O,
8.75. Found: C, 45.07; H, 2.17; N, 7.59; S, 16.90; O, 8.62%.
[Zn(phen)(dtsq)]: yellow, decomposes at 309 °C; elemental
Anal. Calc. for C16H8N2S2O2Zn: C, 49.31; H, 2.07; N, 7.19; S, 16.45.
Found: C, 46.10; H, 2.04; N, 6.79; S, 16.35%.
[Pd(phen)(dto)]; light yellow, decomposes at 274 °C; elemental
Anal. Calc. for C14H8N2S2O2Pd: C, 41.34; H, 1.98; N, 6.89; S,
15.76; O, 7.87. Found: C, 39.53; H, 1.97; N, 6.49; S, 15.41; O,
8.79%.
[Pd(phen)(dtsq)]:dark orange, decomposes at 300 °C; elemental
Anal. Calc. for C16H8N2S2O2Pd: C, 44.61; H, 1.87; N, 6.50; S,
14.88; O, 7.43. Found: C, 40.58; H, 2.23; N, 6.36; S, 8.93/8.56 ; O,
7.45%.
[Pt(phen)(dto)]; light orange, decomposes > 300 °C; elemental
Anal. Calc. for C14H8N2S2O2Pt: C, 33.94; H, 1.63; N, 5.65; S, 12.94;
O, 6.46. Found: C, 33.19; H, 1.58; N, 5.62; S, 9.61 ; O, 6.12%.
[Pt(phen)(dtsq)]: orange, decomposes at 310 °C; elemental Anal.
Calc. for C16H8N2S2O2Pt: C, 37.00; H, 1.55; N, 5.39; S, 12.34; O, 6.16.
Found: C, 33.79; H, 1.78; N, 5.51; S, 6.14/5.97 ; O, 6.13%. We
have often observed that especially Pd- and Pt-dithiolate com-
plexes gave abnormal results for the determination of sulfur.
3.1. IR spectroscopy
A comparison of the IR spectra of the series of diimine/dithiolate
complexes (Tables 3 and 4) as well as the dichlorophenanthroline
intermediates (Table 2) show that all these complexes have the
same structure with only some slight differences in the absorption
energies due to the different metal centers. The IR-results give also
a clear evidence of the coordination of the two dithiolate ligands
(1,2-dithiooxalate and 1,2-dithiosquarate) via their sulfur atoms
being reflected by a shift of the carbonyl absorptions (dto:
)
*
m
(C–O) = 1514 cmꢁ1, dtsq: (C–O) = 1707 cmꢁ1) towards higher wave
m
numbers in the complexes.
)
*
3.2. EPR spectroscopy
Copper(II) with a d9 electron configuration is well suited to be
studied by EPR spectroscopy. Fig. 1 shows the EPR-spectrum of a
pure powdered sample of dichloro-1,10-phenanthrolinecopper(II)
at 150 K as a glass (frozen solution). The spectrum is of axial
)
*
)
*

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D.J. Awad et al. / Inorganica Chimica Acta 363 (2010) 1488–1494
N
N
N
N
Cl
Cl
S
S
O
O
N
N
K2C2O2S2
EtOH
MCl2 . xH2O
M
M
+
EtOH
S
O
N
N
K2C4O2S2
EtOH
M
S
O
Scheme 1. Synthesis of the 1,10-phenanthroline-dithiolate mixed ligand complexes [M(phen)(dto)] and [M(phen)(dtsq)].
Table 1
Table 3
Crystal data and details of structure determination of [Cu(phen)2Cl]ꢀC2H5OHꢀH2O.
Characteristic IR absorptions of 1,10-phenanthroline-1,2-dithiooxalato(S,S0) metal(II)
complexes of type [M(phen)(dto)].
Formulaa
Formula weighta
Crystal size (mm)
Temperature (K)
Crystal system
Space group
a (Å)
C24H16ClCuN4
459.41
Assignment
IR-frequency (cmꢁ1
)
0.15 ꢃ 0.22 ꢃ 1.00
M
Cu
Ni
Zn
Pd
Pt
210(2)
Monoclinic
C2/c
mC–H
3052
3058
3055
3061
3083ꢁ3058
1632 s
1516 m
1428 s
1152 m
1112 m
880 w
mC
mring
@
1620 s
1517 m
1426 s
1146 m
1106 w
870 w
723 m
644 w
428 w
1629 s
1515 s
1426 s
1142 w
1105 w
870 w
724 m
646 w
426 w
1621 m
1517 s
1426 s
1143 m
1103 m
868 s
1623 s
1515 m
1426 s
1150 m
1110 m
876 w
716 s
O
16.5080(13)
15.8475(15)
17.6002(12)
95.379(6)
4584.1(6)
8
1.331
1.086
1872
b (Å)
c (Å)
mring + dH
dH
(in plane)
b (°)
mC–C–S
mC–S
dH
dring
Ring torsion
V (Å3)
Z
726 s
710 s
(out of plane)
Dcalc (g cmꢁ3
)
642 w
422 w
650 w
421 w
655 w
417 w
l
(mm)
F(0 0 0)
m: medium, s: sharp, w: weak.
h (°)
1.8–25.0
Collected reflections (Rint
Unique reflections (Rint
Observed data [I > 2 (I)]
)
14 490
4016 [0.061]
2884
4016/0/320
0.0683, 0.1068
0.0480, 0.1014
1.014
)
r
centers are not sufficiently separated by the solvent and the com-
plex is only suspended and not dissolved.
Data/restraints/parameters
b
R1, wR2 (all data)
b
R1, wR2 [I > 2
r(I)]
Fig. 2 shows the room temperature EPR-spectrum of a pow-
dered sample of 1,10-phenanthroline-1,2-dithiooxalatocopper(II),
[Cu(phen)(dto)], diamagnetically diluted in the isostructural [Ni(-
phen)(dto)] host lattice measured at 295 K in X-band (9.4 GHz).
The spectrum reflects the axial symmetry of the g-tensor and the
Cu hyperfine interaction tensor ACu. The hyperfine structure quar-
tet due to the coupling with the nuclear spin of the copper (I = 3/2)
is well resolved in the parallel part (lower field) as well as the
super hyperfine structure due to the coupling with the two nitro-
gen atoms (14N: I = 1, natural abundance 99.6%). The perpendicular
part is only poorly resolved because of some overlap. Overall 80
lines could be expected in the axial symmetric spectrum. The
Goodness of fit (GOF) on F2
Minimum/maximum resd. dens. (eÅꢁ3
)
ꢁ0.479/0.351
a
Data only reflect known cell content.
w = 1/[ns2(Fo2) + (0.0571P)2], where P = (Fo2 + 2Fc2)/3.
b
symmetry with the parameters g|| = 2.284 0.002 and g\
=
2.067 0.002. The hyperfine structure due to the coupling of the
electron spin (S = 1/2) with the nuclear spin of the two copper iso-
topes (63Cu: I = 3/2 natural abundance 69.2% and 65Cu: I = 3/2 nat-
ural abundance 30.8%) is not resolved. This indicates that the metal
Table 2
Characteristic IR absorptions of dichloro-1,10-phenanthroline metal(II) complexes of type [M(phen)Cl2].
Assignment
IR-frequency (cmꢁ1
Cu
)
M
Nia
Zn
Pd
Pt
mC–H
mring
mring
mring
3079–3010
1606 m
1584 s
1516 s
1423 s
1145 m
1107 m
856 s
3050–3006
1605 m
1583 s
1516 s
1425 s
1144 m
1106 m
849 s
3054
3077–3058
1602 m
1581 s
1515 s
1425 s
1151 m
1109 m
842 s
3082–3059
1604 m
1578 s
1515 s
1427 s
1153 m
1112 m
841 s
1602 m
1583 s
1519 s
1427 s
1145 m
1105 m
853 s
(C@C, C@N)
mring + dH
dH
dH
dH
dH
(in plane)
(in plane)
(out of plane)
(out of plane)
722 s
725 s
726 s
724 s
725 s
dring
Ring torsion
644 m
429 m
644 m
427 m
647 m
427 m
651 m
434 m
656 w
419 w
m: medium, s: sharp, w: weak.
a
As [Ni(phen)(H2O)2Cl2]; m .
(O–H) = 3357 cmꢁ1

D.J. Awad et al. / Inorganica Chimica Acta 363 (2010) 1488–1494
1491
Table 4
Characteristic IR absorptions of 1,10-phenanthroline-1,2-dithiosquarato(S,S0)
metal(II) complexes of [M(phen)(dtsq)] type.
Assignment
IR-frequency (cmꢁ1
)
M
Cu
Ni
Zn
Pd
Pt
mC–H
3061
3058
1817 w
1723 s
1681 m
1658 m
1583 m
1514 m
1423 s
3057
3058
3082ꢁ3058
1820 w
1748 s
mC
@
1822 w
1743 s
1706 s
1726 s
1687 w
1663 m
1816 w
1744 s
1710 s
O
1708 s
mring
mring
1601 m
1518 m
1425 s
1317 w
1224 w
1584 w
1518 m
1427 m
1317 w
1360 s
1191 s
1142 w
898 w
725 s
1600 m
1515 m
1426 s
1311 w
1220 m
1603 w
1516 m
1428 s
1309 w
1220 m
mring + dH
mring + dH
mC–C–S
1368 s
1182 s
1143 w
897 w
725 s
dH
1158 s
909 w
720 s
1152 m
913 m
713 s
1154 w
910 w
709 s
(in plane)
mC–S
dH
(out of plane)
Fig. 3. EPR-spectrum of the same powdered sample of [(phen)Cu(dto)] diamag-
netically diluted in the isostructural [(phen)Ni(dto)] host lattice at 295 K (Q-band).
dring
Ring torsion
644 w
428 w
641 w
423 w
642 w
424 w
651 w
433 w
654 w
418 w
m: medium, s: sharp, w: weak.
hyperfine coupling to the two other magnetic nuclei, 33S and 15N,
that are present in the complex structure, cannot be observed be-
cause of their low natural abundance of 0.75 and 0.367%, respec-
tively. Not all of the 80 lines are resolved due to the partial
overlapping of the two line quintets for the two copper isotopes,
resulting in a seven line pattern in the parallel part and a not fully
resolved perpendicular part. For a better resolution namely of this
perpendicular part we have also measured the same sample at
higher frequency in Q-band (32 GHz). The Q-band-spectrum is de-
picted in Fig. 3. The parallel part and the perpendicular part are
well separated but likewise the perpendicular part is not better re-
solved as at X-band frequencies. Obviously a slightly rhombic dis-
tortion of the g-tensor is observed at higher frequency preventing a
better resolution of this spectral part in the Q-band spectrum. The
spectra can be explained with the following effective spin
Hamiltonian:
X
Hsp ¼ gleSB0 þ SACuICu
þ
SANi IN
ð1Þ
i
All symbols have their usual meaning. The quadrupole and the
nuclear Zeeman terms have been neglected because they only
influence the EPR-spectrum in higher order perturbation theory.
The resulting EPR parameters for [(phen)Cu(dto)] in the
[(phen)Ni(dto)] host lattice are gll = 2.116 0.002, g\ = 2.026
Fig. 1. EPR-spectrum of [Cu(phen)Cl2] in water at 150 K.
0.002, ACu|| = 174.6 0.5 ꢃ 10ꢁ4 cmꢁ1 ACu\ = 40 1.0 ꢃ 10ꢁ4 cmꢁ1
,
AN|| = 11 1.0 ꢃ 10ꢁ4 cmꢁ1 and AN\ = 11 1.0 ꢃ 10ꢁ4 cmꢁ1
. The
Q-band spectrum of the same powder indicates a slightly rhombic
g-tensor with gxx = 2.0275, gyy = 2.0310, gzz = 2.1170 derived from
Q-band. From these parameters we can calculate the experimental
spin density of the unpaired electron in the SOMO at the copper
center. This MO is of in-plane-p type and has the following compo-
sition (Eq. (2)):
wðb1ÞÞ ¼
a
j3dxyðCuÞi ꢁ a0j2px;yðSÞi ꢁ a00j2px;yðNÞi
ð2Þ
a
2, ( )2 and (a00 2 are expressions for the covalency of the Cu–S and
a )
the Cu–N bonds and can be determined from the Cu-tensor param-
2
eters. These are also in correlation with the spin densities cs2, cp
2
and cd in the involved s-, p- and d-orbitals (n2 is the degree of
hybridization between the Cu 4s- and the Cu 3d-orbitals (Eq. (3)).
Cu : c2s ¼ a2ð1 ꢁ n2Þ; cd2 ¼
a
2n2
ð3Þ
Applying the generally accepted formalism of Morton and Pres-
ton [22] the individual spin densities can be calculated by the fol-
lowing simple equations (Eqs. (4a), (4b), (4c)):
Fig. 2. EPR-spectrum of a powdered sample of [(phen)Cu(dto)] diamagnetically
diluted in the isostructural [(phen)Ni(dto)] host lattice at 295 K (X-band).

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D.J. Awad et al. / Inorganica Chimica Acta 363 (2010) 1488–1494
2
the graphical result of the SOMO with a square planar coordination
ðcsÞ ¼ ðAiso:;exp:Þ=ðAiso:;th:
Þ
ð4aÞ
ð4bÞ
ð4cÞ
sphere (left) and the energy minimum at a twist of 30° (right).
A comparison of the Figs. 4 and 5 (middle) shows, that the
molecular orbital with the unpaired electron (SOMO) is qualita-
tively represented in a similar manner by both methods (EHT
and DFT). A structure optimization during the DFT calculations
points out, that the energetic ground state is not the square planar
arrangement as expected but a slightly twisted configuration with
a dihedral angle between the two ligand planes of about 30°. This
twist might be the reason for the paramagnetic behavior of the two
nickel complexes [(phen)Ni(dto)] and [(phen)Ni(dtsq)] (see Sec-
tion 2) As it can be seen from Fig. 5 the composition of the molec-
ular orbital does not change significantly.
2
ðcp;dÞ ¼ ðAdip:;exp:Þ=ðAdip:;th:
ðAdip:exp: ¼ ðA ꢁ A Þ=3
Þ
k
?
Cu
iso:th:
the theoretical values are for A
= 1999.7 ꢃ 10ꢁ4 cmꢁ1 and for
Cu
A
= 114.1 ꢃ 10ꢁ4 cmꢁ1. The experimental parameters of the
dip:th:
Cu-hfs tensor allow a determination of the spin density at the cop-
per center atom by using the Eqs. (4a), (4b), (4c). With the values of
Morton and Preston we get c2s ¼ 0:04, cp2;d ¼ 0:40 and
a
2 = 0.44.
Therefore, 44% of the spin density is located at the copper center
(calculated values EHT: 37 (42%); DFT 50%). There are two values
from the EHT results given where the 37% is the result for the
MO-contributions normalized to 100% and the value in brackets
(42%) is the result from the MO-coefficients of the direct EHT
output.
3.3. X-ray structure analysis
The calculated energies as well as the relative atomic contribu-
tions to the molecular orbitals of the square planar complex 1,2-
dithiooxalato-1,10-phenanthrolinecopper(II) with the point group
C2v are summarized in Table 5. The molecular orbital with the un-
paired electron (SOMO) is a combination of d (Cu) and p (N, S)
atomic orbitals and both the HOMO and the LUMO are mainly lo-
cated at the diimine and dithiolate ligands, respectively. Fig. 4 pre-
sents the drawings of the HOMO, SOMO and LUMO for
[Cu(phen)(dto)] as result of the EHT calculation and Fig. 5 shows
Attempts to crystallize the synthesized [(phen)Cu(dtsq)] com-
plex resulted in light blue prism-shaped crystals of the reduced
copper(I) complex chlorobis(1,10-phenanthroline-N,N0)copper(I)
ethanol solvate hydrate, [(phen)2CuCl]ꢀC2H5OHꢀH2O. Due to the
high degree of disorder the atomic positions of the solvent mole-
cules could not be determined. However, a total potential solvent
area of 889.5 Å (19.4% of the cell volume) was calculated by the
program PLATON [21]. Fig. 6 shows the ORTEP plot and the atom num-
bering scheme of this complex. The crystallographic and structure
refinement data are summarized in Table 1. Selected bond lengths
and angles are collected in Table 6. The reduction of Cu(II) to Cu(I)
in the presence of the 1,2-dithiosquarato ligand as reducing agent
is not surprising and this redox sensibility of Cu(II) with the 1,2-
dithiosquarato ligand was already observed earlier [23] and is con-
sistent with our laboratory experience over years. The primer oxi-
dation step of the ligand is possibly the formation of a disulfide
often followed by desulfurization and decomposition steps. The
resulting complex was completely EPR silent due to the reduction
of the Cu(II) to Cu(I) (d10). The chloro and the two phenanthroline
ligands are coordinated to the Cu(I) in a distorted trigonal-bipyra-
Table 5
Symmetry, relative energies and MO-coefficients of the frontier orbitals in
[(phen)Cu(dto)] (direct from EHT output).
Orbital
Symmetry
eꢁ
E (eV)
MO-coefficients
Cu
N
S
LUMO (42)
SOMO (43)
HOMO (44)
b2
b1
a1
0
1
2
ꢁ10.29
ꢁ10.79
ꢁ12.20
0.104 pz
0.049 dxz
0.015 py
0.650 dxy
0.128 px
0.069 dz2
0.017 pz
0.388 pz
0.227 py
0.382 px
0.212 py
0.052 px
0.261 py
0.317 px
0.077 py
0.070 px
Fig. 4. Frontier orbitals of [Cu(phen)(dto)], HOMO (left), SOMO (middle) and LUMO (right) from EHT calculations.
Fig. 5. Shape of the SOMO in a square planar coordination sphere (left) and in the energetic minimum with a twist angle of ꢂ30° (right) from DFT calculations.

D.J. Awad et al. / Inorganica Chimica Acta 363 (2010) 1488–1494
1493
Fig. 7. Stereo view on the crystal packing of [Cu(phen)2Cl], the intermolecular
hydrogen bonds from chlorine to hydrogen atoms of the phenanthroline ligands are
also depicted.
Fig. 6. ORTEP plot of the molecular structure and atom labeling scheme of
[Cu(phen)2Cl].
Table 6
Selected bond lengths (Å) and bond angles (°) for [Cu(phen)2Cl]ꢀC2H5OHꢀH2O.
Cu1–Cl1
Cu1–N2
Cu1–N4
N1–C5
N2–C10
N3–C17
C5–C6
Cl1–Cu1–N1
Cl1–Cu1–N2
Cl1–Cu1–N4
Cl1–Cu1–N3
N1–Cu1–N2
Hydrogen bonds
2.2811(9)
1.995(3)
1.993(3)
1.362(5)
1.325(5)
1.360(4)
1.426(6)
119.02(8)
93.08(9)
91.08(9)
134.18(8)
80.76(13)
Cu1–N1
Cu1–N3
N1–C1
N2–C6
N3–C13
N4–C18
C17–C18
N1–Cu1–N3
N1–Cu1–N4
N2–Cu1–N3
N2–Cu1–N4
N1–Cu1–N2
2.146(3)
2.096(3)
1.314(5)
1.352(5)
1.329(5)
1.352(5)
1.419(5)
106.80(10)
99.82(13)
94.58(12)
174.86(13)
80.36(12)
C–H
Clꢀ ꢀ ꢀH
C(H)ꢀ ꢀ ꢀCl
3.660(4)
3.486(4)
3.710(5)
C–Hꢀ ꢀ ꢀCl
146(3)°
143(4)°
165(4)°
Symm.
3_575
7_565
4_574
C10–H10ꢀ ꢀ ꢀCl1
C11–H11ꢀ ꢀ ꢀCl1
C14–H14ꢀ ꢀ ꢀCl1
1.07(4)
0.94(5)
1.00(5)
2.73(4)
2.69(5)
2.74(5)
Translation of symmetry code to equivalent positions: 3_575 = ꢁx, 2 ꢁ y, ꢁz;
7_565 = 1/2 ꢁ x, 3/2 ꢁ y, ꢁz; 4_574 = x, 2 ꢁ y, ꢁ1/2 + z.
midal arrangement (see Fig. 6). The dihedral angle between the
planar phenanthroline ligands is 68.65(9)°. As it can be seen from
the packing diagram (Fig. 7) intermolecular hydrogen bonds be-
tween the chlorine and the hydrogen atoms of the phenanthroline
ligands are present stabilizing the molecular packing motif. The
complex molecules are arranged in dimers and stabilized by signif-
icant p–p stacking between two nearly coplanar phenanthroline li-
gands. The averaged interplanar distance between the two ligand
planes is 3.369(5) Å. These dimers are stacked along the crystallo-
Fig. 8. Unit cell packing of [Cu(phen)2Cl]. View along the crystallographic b-axis
which coincides with the main axis of the stacked columns.
graphic b-axis (see Fig. 8) by slightly weaker intermolecular
p–p
interactions (averaged interplanar distance of 3.478(5) Å) and the
formed one-dimensional columns are interconnected by weak
to the structures reported for chlorobis(1,10-phenanthroline-
N,N0)copper(II) hydroxide hexahydrate reported by Ma et al. [27]
and recently chlorobis(1,10-phenanthroline-N,N0)copper(I) hexa-
hydrate reported by Zhong et al. [28]. The first complex is reported
as a copper(II) complex and the second as copper(I) but both hav-
ing very related unit cell parameters and the structural details
hydrogen bonds (see Table 6). The
p–p interactions reflected by
the interplanar distances are slightly weaker as reported for a poly-
meric complex [Cu2(phen)2Cl2(C6H8O4)]ꢀ4H2O (3.30 Å) [24] but sig-
nificant stronger as reported for some other phenanthroline
complexes (3.52–3.79) Å [24–26]. The structure is comparable

1494
D.J. Awad et al. / Inorganica Chimica Acta 363 (2010) 1488–1494
(interatomic distances and angles) slightly differ from herein re-
ported complexes. Therefore, the real oxidation state of the copper
in at least one of these complexes might still be questionable.
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Two series of diimine/dithiolate mixed ligand complexes, 1,2-
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5. Supplementary material
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Acknowledgment
The financial support by a DAAD Ph.D. scholarship A/05/06200
(D. Jawad Awad) is gratefully acknowledged.