Dinuclear lanthanoid(III) dithiocarbamato complexes bridged by (E)-N-benzylidenepicolinohydrazonate: Syntheses, crystal structures and spectroscopic properties

Article abstract of DOI:10.1016/j.ica.2019.119124

(E)-N-Benzylidenepicolinohydrazide (Hbphz) was used to synthesize a series of hydrazonato-bridged homodinuclear Ln^III₂ dithiocarbamato (RR′dtc^?) complexes of the form [{Ln(RR′ dtc)₂}₂(μ-bphz)₂

Full text of DOI:10.1016/j.ica.2019.119124

InorganicaChimicaActa498(2019)119124
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Inorganica Chimica Acta
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Dinuclear lanthanoid(III) dithiocarbamato complexes bridged by (E)-N-
benzylidenepicolinohydrazonate: Syntheses, crystal structures and
spectroscopic properties
⁎
Abdallah Yakubua, Takayoshi Suzukia,b, , Masakazu Kitac
a Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima-Naka, Kita-ku, Okayama 700-8530, Japan
b Research Institute for Interdisciplinary Science, Okayama University, 3-1-1 Tsushima-Naka, Kita-ku, Okayama 700-8530, Japan
c Faculty of Education, Okayama University, 3-1-1 Tsushima-Naka, Kita-ku, Okayama 700-8530, Japan
A R T I C L E I N F O
A B S T R A C T
Keywords:
Hydrazone
Dithiocarbamate
Crystal structures
Lanthanoid
(E)-N-Benzylidenepicolinohydrazide (Hbphz) was used to synthesize a series of hydrazonato-bridged homodi-
nuclear Ln2III dithiocarbamato (RR′dtc−) complexes of the form [{Ln(RR′ dtc)2}2(µ-bphz)2] {Ln = La, Pr, Nd, Sm
or Eu; RR′ = dimethyl-(Me2) or pyrrolidine-(pyr)}. X-ray crystallographic studies revealed that these complexes
possessed a common head-to-tail type dinuclear structural motif in which two hydrazonato ligands bridged two
LnIII centers in the μ − 1 κ2N(py),O:2 κ2O,N(imine) mode and two RR′dtc ligands coordinated to each LnIII
center. Interestingly, while the SmIII and EuIII complexes crystallized as simple 8:8-coordinate dinuclear mole-
cules, the lighter LnIII (i.e. LaIII, PrIII and NdIII) complexes afforded in some cases 9:9-coordinate molecules,
where the ninth coordination site was occupied by a solvent ethanol or methanol molecule. Even for the lighter
LnIII complexes, the complexes were solved in dichloromethane or chloroform as the 8:8-coordinate dimer, as
revealed by 1H NMR spectroscopy. In the UV–visible absorption and magnetic circular dichroism (MCD) spectra
of the complexes, similar spectral patterns for ligand-centered and Laporte forbidden f–f transitions were ob-
served. The MCD spectral studies demonstrated the characteristic magneto-optical behavior of the complexes.
Magnetic circular dichroism
1. Introduction
collaborators characterized dinuclear 2-acetylpyridine-substituted hy-
drazone complexes with four bridging acetate groups [8]. The struc-
The coordination chemistry of hydrazones is an active research area
in view of their general interests and application of hydrazone com-
plexes [1,2]. Hydrazones can coordinate to a metal center either as
neutral molecules or deprotonated anionic forms; therefore, the hy-
drazone complexes often exhibit interesting reversible properties de-
pendent on the solvent acidity [3,4]. In addition, the exploitation of
possible ligating substitutional groups affords a variety of coordination
modes of the hydrazones which would give the complexes with inter-
esting structural diversity, magnetic and spectroscopic properties [5].
Lanthanoid complexes of hydrazones are being investigated for
potential applications in various fields including supramolecular as-
semblies and magnetic materials. Chandrasekhar et al. have prepared a
series of hydrazone-based homodinuclear lanthanoid complexes and
revealed the presence of weak antiferromagnetic coupling between the
LnIII centers at low temperature [6]. Thompson and co-authors have
investigated the coordination chemistry of tritopic pyridinebis(hy-
drazone) with some LnIII ions [7]. Klouras, Perlepes and their
tural characterizations and magnetic properties of other hydrazone-
based dinuclear DyI2II [9] and tetranuclear LnI4II [10] complexes have
also been reported. In addition, several mixed-ligand lanthanoid com-
plexes bearing hydrazones (or the deprotonated hydrazonates) and β-
diketonates (or other oxygen-donor ligands) have been reported;
however, those of the analogous mixed-ligand complexes with dithio-
carbamates have not yet been investigated. Lanthanoid dithiocarba-
mato compounds have important practical applications in catalysis,
nanotechnology and microelectronics, and, therefore, their structural,
thermodynamical and spectroscopic properties have been studied in
detail [11,12]. So far, most of the mixed-ligand dithiocarbamato lan-
thanoid complexes studied involve 1,10-phenanthroline or 2,2′-bipyr-
idine as an ancillary ligand.
In this study, a hydrazone derived from picolinohydrazide and
benzaldehyde, (E)-N-benzylidenepicolinohydrazide (Hbphz) was syn-
thesized and used to prepare a series of lanthanoid dithiocarbamato
complexes (Scheme 1). The structural features and spectroscopic
⁎ Corresponding author.
E-mail address: suzuki@okayama-u.ac.jp (T. Suzuki).
https://doi.org/10.1016/j.ica.2019.119124
Received 31 July 2019; Received in revised form 27 August 2019; Accepted 2 September 2019
Availableonline04September2019
0020-1693/©2019ElsevierB.V.Allrightsreserved.

A. Yakubu, et al.
InorganicaChimicaActa498(2019)119124
(KBr disc)/cm−1: ν(C]N), 1540; ν(NeN), 1163; ν(CeN), 1430; ν(CeS)
1006.
2.2.5. [{Nd(Me2dtc)2}2(μ-bphz)2] (3a)
Scheme 1. (E)-N-benzylidenepicolinohydrazide (Hbphz).
Pale green crystals were obtained from CHCl3 and MeOH mixture in
42% yield. Anal. Found: C, 36.82; H, 3.70; N, 11.16; S, 18.87%. Calcd.
for C38H44N10O2Nd2S8·2CH3OH·0.5CHCl3: C, 36.26; H, 3.95; N, 10.44;
S, 19.12%. IR (KBr disc)/cm−1: ν(C]N), 1543; ν(NeN), 1159; ν(CeN),
1349; ν(CeS) 980.
properties of these hydrazonato-bridged homodinuclear lanthanoid
dithiocarbamato complexes were investigated.
2. Experimental section
2.2.6. [{Nd(pyrdtc)2}2(μ-bphz)2] (3b)
2.1. Synthesis of (E)-N-benzylidenepicolinohydrazide (Hbphz)
Pale green crystals were obtained from CH2Cl2 and EtOH mixture in
43% yield. Anal. Found: C, 41.56; H, 4.56; N, 9.78; S, 17.57%. Calcd.
for C46H52N10O2Nd2S8·2CH3CH2OH·CH2Cl2·H2O: C, 41.25; H, 4.62; N,
9.43; S, 17.27%. IR (KBr disc)/cm−1: ν(C]N), 1541; ν(NeN), 1163;
ν(CeN), 1431; ν(CeS) 1007. 1H NMR (300 MHz, Chloroform-d, 22 °C) δ
9.56 (dd, J = 14.6, 7.2 Hz, 1H), 8.94–8.23 (m, 2H), 7.99–7.70 (m, 1H),
7.69–7.37 (m, 1H), 7.26 (s, 1H), 4.39–3.40 (m, 8H), 1.67–1.04 (m, 8H).
2-Pyridinecarboxylic
acid
hydrazide
(=picolinohydrazide)
(343 mg, 2.5 mmol) was dissolved in ethanol (20 mL) and benzaldehyde
(265 mg, 2.5 mmol) was added. The mixture was stirred for 3 h at room
temperature and, then, allowed to stand overnight. A slight shaking of
the mixture triggered precipitation of the product. Analytically pure
white fluffy product was isolated in 73% yield. Slow evaporation of a
methanolic solution of the product yielded colorless needle-shaped
crystals suitable for X-ray diffraction analysis. Anal. Found: C, 69.23; H,
4.67; N, 18.55%. Calcd. for C13H11N3O: C, 69.32; H, 4.92; N, 18.66%.
IR (KBr disc)/cm−1: ν(NeH), 3212; ν(C]O), 1664; ν(C]N), 1522;
ν(NeN), 1141. 1H NMR (300 MHz, Chloroform-d, 22 °C): δ 10.99 (s,
1H), 8.58 (ddd, J = 4.8, 1.8, 0.9 Hz, 1H), 8.42–8.16 (m, 2H), 8.02–7.64
(m, 3H), 7.60–7.31 (m, 4H).
2.2.7. [{Nd(pyrdtc)2}2(μ-bphz)2] (3b′)
Pale green crystals were obtained from CH2Cl2 and Et2O. Anal.
Found: C, 41.58; H, 4.00; N, 10.56; S, 19.20%. Calcd. for
C
46H52N10O2Nd2S8: C, 41.79; H, 3.96; N, 10.60; S, 19.40%. IR (KBr
disc)/cm−1: ν(C]N), 1544; ν(NeN), 1163; ν(CeN), 1436; ν(CeS)
1004. 1H NMR (300 MHz, Chloroform-d, 22 °C) δ 9.56 (t, J = 10.2 Hz,
1H), 8.89–8.21 (m, 2H), 7.77 (t, J = 8.7 Hz, 1H), 7.69–7.37 (m, 1H),
7.26 (s, 2H), 4.27–3.47 (m, 6H), 1.61–1.03 (m, 6H).
2.2. Synthesis of complexes
2.2.8. [{Sm(Me2dtc)2}2(μ-bphz)2] (4a)
Pale yellow crystals were obtained from CHCl3 and EtOH in 18%
yield. Anal. Found: C, 35.97; H, 3.33; N, 10.93; S, 20.37%. Calcd. for
All complexes reported in this article were similarly prepared by a
method described below. To a mixture of Hbphz (1.00 mmol) and Et3N
(1.00 mmol) in MeOH (10 mL) was added a methanolic solution
C
38H44N10O2Sm2S8·0.5CHCl3: C, 35.85; H, 3.48; N, 10.86; S 19.89%. IR
(10 mL) of LnX3·6H2O (Ln = La, Pr, Nd, Sm or Eu; X− = Cl− or NO3
)
−
(KBr disc)/cm−1: ν(C]N), 1545; ν(NeN), 1129; ν(CeN), 1351; ν(CeS)
(1.00 mmol) with stirring. Na(Me2dtc) or NH4(pyrdtc) (2.00 mmol) in
MeOH (10 mL) was added. The mixture was stirred for 5 h at room
temperature and the resulting precipitate was collected by filtration,
washed with MeOH and dried in air. The crude product was purified by
recrystallization from a dichloromethane or chloroform solution by
layering of ethanol, methanol or diethyl ether. The analytical and FT-IR
spectral data are given below.
982.
2.2.9. [{Sm(pyrdtc)2}2(μ-bphz)2] (4b)
Pale yellow crystals were obtained from CH2Cl2 and EtOH in 22%
yield. Anal. Found: C, 40.69; H, 3.71; N, 10.36; S, 19.06%. Calcd. for
C
46H52N10O2Sm2S8·0.5CH2Cl2: C, 40.57; H, 3.88; N, 10.17; S, 18.63. IR
(KBr disc)/cm−1: ν(C]N), 1545; ν(NeN), 1164; ν(CeN), 1437; ν(CeS)
1005.
2.2.1. [{La(Me2dtc)2}2(μ-bphz)2] (1a)
Pale green crystals were obtained from a mixture of CH2Cl2 and
EtOH in 18% yield. Anal. Found: C, 36.29; H, 3.77; N, 11.21; S, 19.30%.
Calcd. for C38H44N10O2La2S8·2CH3OH·2H2O: C, 36.75; H, 4.32; N,
10.71; S, 19.62%. IR (KBr disc)/cm−1: ν(C]N), 1540; ν(NeN), 1161;
ν(CeN), 1349; ν(CeS) 982.
2.2.10. [{Eu(Me2dtc)2}2(μ-bphz)2] (5a)
Orange crystals were obtained from CHCl3 and MeOH in 37% yield.
Anal. Found: C, 35.12; H, 3.41; N, 10.55; S, 19.20%. Calcd. for
C
38H44N10O2Eu2S8·CHCl3: C, 35.04; H, 3.39; N, 10.48; S, 19.19%. IR
(KBr disc)/cm−1: ν(C]N), 1545; ν(NeN), 1131; ν(CeN), 1351; ν(CeS)
982.
2.2.2. [{La(pyrdtc)2}2(μ-bphz)2] (1b)
Pale green crystals were obtained from a mixture of CHCl3 and
EtOH in 21% yield. Anal. Found: C, 40.55; H, 3.99; N, 10.37; S, 18.65%.
Calcd for C46H52N10O2La2S8·CH3OH·2H2O: C, 40.92; H, 4.38; N, 10.15;
S, 18.60%. IR (KBr disc)/cm−1: ν(C]N), 1539; ν(NeN), 1163; ν(CeN),
1430; ν(CeS) 1005.
2.2.11. [{Eu(pyrdtc)2}2(μ-bphz)2] (5b)
Orange crystals were obtained from CHCl3 and EtOH in 40% yield.
Anal. Found: C, 38.03; H, 3.70; N, 9.41; S, 17.23%. Calcd. for
C46H52N10O2Eu2S8·CHCl3: C, 38.76; H, 3.67; N, 9.62; S, 17.61%. IR
(KBr disc)/cm−1: ν(C]N), 1545; ν(NeN), 1165; ν(CeN), 1436; ν(CeS)
1005.
2.2.3. [{Pr(Me2dtc)2}2(μ-bphz)2] (2a)
Green crystals were obtained from a mixture of CH2Cl2 and EtOH in
19% yield. Anal. Found: C, 37.23; H, 3.50; N, 11.41; S, 19.85%. Calcd.
for C38H44N10O2Pr2S8·0.5CH2Cl2: C, 36.89; H, 3.62; N, 11.17; S,
20.46%. IR (KBr disc)/cm−1: ν(C]N), 1540; ν(NeN), 1158; ν(CeN),
1347; ν(CeS) 979.
2.3. Physical measurements
C, H, N and S analysis were carried out on a Perkin Elmer Series II
CHNS/O Analyzer 2400 at Department of Instrumental Analyses,
Advanced Science Research Center, Okayama University. The FT-IR
spectra were recorded on a JASCO FT-001 FT-IR spectrophotometer by
a KBr disc method in the 400–4000 cm−1 range. The UV–visible ab-
sorption spectra of the complexes in dichloromethane were obtained on
a JASCO V-550 UV/VIS spectrophotometer at room temperature. Room
temperature magnetic circular dichroism (MCD) spectra were measured
2.2.4. [{Pr(pyrdtc)2}2(μ-bphz)2] (2b)
Green crystals were obtained from CH2Cl2 and EtOH in 21% yield.
Anal. Found: C, 41.49; H, 4.25; N, 9.86; S, 18.90%. Calcd. for
C
46H52N10O2Pr2S8·2H2O: C, 40.88; H, 4.18; N, 10.37; S, 18.98%. IR
2

A. Yakubu, et al.
InorganicaChimicaActa498(2019)119124
on a JASCO J-1500 CD spectropolarimeter equipped with a home-made
neodymium magnet apparatus (ca. 0.5 T magnetic field) [13].
2.4. X-ray crystallographic study
X-ray diffraction intensity data were collected on a Rigaku R-AXIS
Rapid diffractometer, except for those of compound 5b which were
obtained on a Rigaku VariMax diffractometer with a Saturn-70 CCD
detector, using graphite or multi-layered mirror monochromated Mo
Kα (λ = 0.71075 Å) radiation. The diffraction data were processed
using the PROCESS-AUTO or CrystalClear software package [14] and
the numerical absorption corrections were applied [15]. The structures
were solved by the direct method employing the SIR2008 [16] or
SHELXT [17] software package and expanded using Fourier techniques,
and refined on F2 (with all independent reflections) using SHELXL
Version 2014/7 software package [18]. All non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were introduced at the theo-
retical positions and refined using riding models. All calculations were
performed using the CrystalStructure software package [19].
3. Results and discussion
3.1. Synthesis and characterization of (E)-N-benzylidenepicolinohydrazide
(Hbphz)
Fig. 2. (a) An ORTEP drawing of Hbphz (at 50% probability level), and (b)
hydrogen-bonding interaction in the crystal of Hbphz.
The hydrazone, Hbphz, was synthesized by a one-pot condensation
reaction of equimolar amounts of 2-pyridinecarboxylic acid hydrazide
and benzaldehyde in ethanol in 73% yield [20,21]. The product was
characterized by elemental analysis, X-ray diffraction analysis, and IR
and 1H NMR spectroscopy. The 1H NMR spectrum (Fig. 1a) suggested
that the isolated hydrazone was a single product of possible E and Z
isomers. The X-ray crystallographic analysis (Table S1) revealed the
molecular structure of Hbphz as an E-isomer, which is depicted in
Fig. 2a. The molecule has an almost planar structure; the planes of the
pyridyl (N1, C1–C5) and phenyl (C8–C13) rings form a dihedral angle
of 10.4(1)°. The plane defined by the central hydrazone linkage, eC]
NeNeC(]O)e, is tilted by 8.0(1) and 16.4(1)°, respectively, to the
planes of the pyridyl and phenyl rings. The hydrazone C6]O1 bond
length, 1.226(3) Å, indicates a ketonic character [7], and the imine
N3]C7 bond length, 1.279(3) Å, shows its double bond character,
while the N2eN3 and N2eC6 bond lengths are 1.381(2) and
1.356(3) Å, respectively. Therefore, the N2 atom should have an amide-
H atom. Intermolecular NeH⋯O hydrogen bonds form a one-dimen-
sional chain structure (Fig. 2b), running along the b axis. The UV–vi-
sible absorption spectra of Hbphz (Fig. S1) showed a characteristic in-
tense band due to the π → π* transition centered at 306 nm.
Fig. 1. 1H NMR (300 MHz, Chloroform-d) spectra of (a) Hbphz, (b) [{Nd(pyrdtc)2}2(µ-bphz)2] and (c) [{Nd(pyrdtc)2(EtOH)}2(µ-bphz)2].
3

A. Yakubu, et al.
InorganicaChimicaActa498(2019)119124
Scheme 2. Synthetic route of the bphz-bridged complexes.
3.2. Synthesis and characterization of LnIII complexes with the
hydrazonate, bphz−
the crystallographic inversion center forms further coordination of the
neighboring bphz− anion via a bidentate O,N(imine) mode. Thus, the
molecule has a Ci symmetric (head-to-tail type) bphz-bridged dinuclear
structure, as similar to the above pyrdtc complex: [{Eu(Me2dtc)2}(μ-
bphz)2] (Fig. S3).
A reaction of Hbphz, LnX3·6H2O (Ln = La, Pr, Nd, Sm or Eu; X
= Cl− or NO3−), and sodium dimethyldithiocarbamate {Na(Me2dtc)}
or ammonium pyrrolidinedithiocarbamate {NH4(pyrdtc)} in a 1:1:2 M
ratio in the presence of Et3N in methanol at room temperature gave a
pale-yellow or green precipitate of the respective LnIII(bphz)(RR′dtc)2
complexes {Ln = La (1x), Pr (2x), Nd (3x), Sm (4x) or Eu (5x);
RR′ = Me2 (x = a) or pyr (x = b)} (Scheme 2). Recrystallization of
each product from dichloromethane (or chloroform) and ethanol (or
methanol) afforded single-crystals suitable for the X-ray diffraction
study. The elemental analysis of these products suggested the compo-
sition of Ln(bphz)(RR′dtc)2·n(solvent).
The SmIII–Me2dtc complex, 4a, is isomorphorous to that of 5a, and a
similar molecular structure is resulted: [{Sm(Me2dtc)2}(μ-bphz)2] (Fig.
S4). In the case of SmIII–pyrdtc complex of 4b, a similar dinuclear
molecular structure with two solvent CH2Cl2 molecules of crystal-
lization, [{Sm(pyrdtc)2}2(μ-bphz)2]·2CH2Cl2 (Fig. S5) was obtained in a
triclinic space group P–1 with Z = 1 (based on the dinuclear unit).
All four complexes of EuIII and SmIII, 4a, 4b, 5a and 5b, have similar
structural features with two LnIII ions having a N2O2S4 dodecahedral 8-
coordination and two bridging monodeprotonated hydrazonate anions
(bphz−). Compared to the metric parameters of the complexes with
those of free Hbphz, the C]O and CeN bonds become longer (by ca.
0.07 Å) and shorter (by ca. 0.05 Å), respectively, while the NeN and
N]C(imine) bond lengths are not different so much. This fact indicates
that delocalization of the anionic character of the hydrazonate is lim-
ited in the [O]CeN] moiety, although the whole hydrazonato moiety
[eC(]O)eNeN]Ce] has a planar structure. Two LnIII ions are placed
on the hydrazonato planes, and the pyridine ring is also coplanar, while
the phenyl ring of bphz− is slightly tilted from the planes (Table S2).
Two RR′dtc ligands at each LnIII ion are located above and below the
Ln2(μ-bphz)2 plane, i.e., at mutually pseudo trans-positions, and their
coordination planes are almost parallel to each other but perpendicular
to the Ln2(μ-bphz)2 plane. The coordination bond lengths around EuIII
or SmIII centers are: LneS, 2.85–2.93 Å; LneN, 2.50–2.62 Å; LneO,
2.75–2.41 Å, the bite angles of RR′dtc are 61.8–62.5°, and the bridging
angles of LneOeLn are 112.2–113.6°.
Fig. S2 showed the FT-IR spectra of Hbphz and its complexes 3b and
5b as representative examples; other pyrdtc complexes of 1b, 2b and 4b
gave a similar spectral pattern. Also, the Me2dtc complexes 1a–5a
showed similar IR spectra to one another. The ν(NeH) and ν(C]O)
stretching bands appeared at 3212 cm−1 and 1664 cm−1, respectively,
in the spectrum of free Hbphz were disappeared in the spectra of the
complexes, which indicated that the ligand has an anionic (i.e. bphz−
)
and enolate character [22]. The ν(C]N)imine and ν(NeN) bands ob-
served at 1522 and 1141 cm−1, respectively, in the free Hbphz were
shifted to higher wavenumber regions on complexation, suggesting the
coordination of the imine-N donor to a LnIII ion [1]. The ν(CeS) and
ν(CeN) bands associated with the pyrdtc− ligand in the complexes
appeared at 1007 and 1430 cm−1 in 3b and 1005 and 1436 cm−1 in 5b,
respectively.
In contrast to the above complexes, the LaIII complexes of 1a and 1b
were found to have a different molecular structure (Figs. 4 and S6,
respectively) in the crystals. The Me2dtc complex of 1a was crystallized
in a monoclinic space group P21/n with Z = 2 (based on the dinuclear
unit), and the pyrdtc complex of 1b was crystallized in a triclinic space
group P–1 with Z = 1 (based on the dinuclear unit). Both complexes
showed a dinuclear bphz-bridged LaI2II(μ-bphz)2 structure having a
crystallographic inversion center in the molecule. The bridging mode of
the hydrazonato is the same as those in the EuIII and SmIII complexes,
but the coordination bond lengths around the LaIII are longer by
0.15–0.20 Å, which is consistent with the longer ionic radius of LaIII
than EuIII and SmIII. Because of the larger ionic size, the LaIII center is
deviated from the plane defined by two bridging ligands (Fig. 4b). In
addition, the LaIII center is coordinated by an ethanol molecule as well
as two dithiocarbamato (RR′dtc−) ligands. The coordinated ethanol
molecule is hydrogen-bonded to one of the S atoms of RR′dtc− ligand
coordinated to the other LaIII center (O2eH⋯S4: Fig. 4a). Two dithio-
carbamato ligand planes are almost perpendicular to each other and to
the bridging bphz ligand plane, and, therefore, the coordination geo-
metry around each LaIII center is characterized as a 9-coordinate
3.3. Crystal structure of the complexes
Further characterization of the bphz complexes, 1a–5b, were per-
formed by the single-crystal X-ray analysis. The crystallographic data
are summarized in Table S1 in the Supporting Information. The selected
structural parameters are listed in Table 1.
The EuIII–pyrdtc complex, 5b, was crystallized in a monoclinic space
group Cc (with Z = 4), and the asymmetric unit contains two EuIII ions,
each of which attaches two bidentate S,S′-donating pyrdtc− ligands,
two bridging bphz− (deprotonated hydrazonate) anions and three
chloroform
molecules
of
crystallization:
[{Eu(pyrdtc)2}2(μ-
bphz)2]·3CHCl3 (Fig. 3). The bphz− anions are bridged two EuIII ions in
a μ −1 κ2N(py),O:2 κ2O,N(imine) mode and form a head-to-tail type
Eu2(μ-bphz)2 core. Each EuIII center accomplishes a distorted dodeca-
hedral 8-coordination geometry with N2O2S4 donor atoms, and two
pyrdtc ligands in the mutually pseudo-trans positions are almost co-
planar and perpendicular to the Eu2(bphz)2 plane (Fig. 3b). Analogous
EuIII–Me2dtc complex, 5a, was crystallized in a triclinic space group P–1
with Z = 1 (based on the dinuclear unit). The asymmetric unit consists
of an EuIII ion, two bidentate S,S′-donating Me2dtc− anions, and a bi-
dentate N(py), O-bonding bphz− anion, but the symmetry expansion by
4

A. Yakubu, et al.
InorganicaChimicaActa498(2019)119124
Table 1
Selected parameters of LnI2II complexes.a
Parameters
1a
1b
2a
2b
3a(mol1)b
3a(mol2)b,c
3b
3b′
4a
4b
5a
5b
Bond Lengths (Å)
Ln1eS1
Ln1eS2
Ln1eS3
Ln1eS4
Ln1eN1
Ln1eN3*
Ln1eO1
Ln1eO1*
Ln1eO2EtOH
C6eO1
3.002(3)
3.031(3)
3.032(3)
3.052(3)
2.695(8)
2.692(7)
2.506(5)
2.518(6)
2.583(7)
1.297(9)
1.332(10)
3.015(3)
3.000(3)
3.029(3)
3.032(3)
2.688(10)
2.702(10)
2.520(6)
2.543(8)
2.586(7)
1.310(14)
1.355(13)
2.906(4)
2.921(3)
2.919(3)
2.889(4)
2.658(9)
2.585(9)
2.451(8)
2.488(10)
–
2.968(2)
2.982(2)
3.006(2)
2.999(3)
2.627(8)
2.639(7)
2.480(4)
2.499(6)
2.549(6)
1.311(10)
1.332(9)
2.920(3)
2.895(3)
2.898(3)
2.889(2)
2.629(7)
2.573(6)
2.430(5)
2.432(5)
–
2.973(2)
2.941(3)
2.970(2)
2.986(3)
2.637(7)
2.624(7)
2.456(5)
2.484(5)
2.525(9)d
1.307(9)
1.281(10)
2.990(2)
2.992(2)
2.963(2)
2.952(2)
2.620(7)
2.632(6)
2.464(4)
2.483(5)
2.533(5)
1.286(9)
1.329(8)
2.899(2)
2.940(1)
2.903(2)
2.890(2)
2.627(5)
2.589(6)
2.409(5)
2.444(4)
–
2.856(5)
2.863(6)
2.893(6)
2.870(5)
2.620(13)
2.530(12)
2.405(10)
2.410(8)
–
2.876(1)
2.884(1)
2.932(1)
2.865(1)
2.586(4)
2.560(4)
2.375(3)
2.412(3)
–
2.853(3)
2.844(3)
2.857(3)
2.870(3)
2.589(7)
2.510(7)
2.380(5)
2.398(6)
–
2.867(3)
2.877(5)
2.921(5)
2.854(4)
2.577(11)
2.498(10)
2.390(7)
2.392(9)
–
1.294(13)
1.329(17)
1.312(9)
1.329(10)
1.309(7)
1.295(9)
1.301(17)
1.327(16)
1.303(5)
1.298(6)
1.297(10)
1.302(9)
1.332(15)
1.300(14)
C6eN2
Bond angles (°)
S1eLn1eS2
S3eLn1eS4
58.43(9)
57.63(8)
115.48(19)
58.57(8)
58.30(9)
114.7(3)
61.32(12)
61.38(11)
111.9(3)
59.30(6)
58.94(7)
115.7(2)
61.30(7)
61.56(8)
113.3(2)
59.44(9)
59.69(6)
116.11(19)
59.27(7)
59.74(6)
115.5(2)
61.58(5)
62.11(5)
113.1(2)
62.04(15)
61.79(14)
112.2(4)
62.12(3)
61.90(4)
113.6(1)
62.48(9)
62.15(8)
112.9(2)
62.35(11)
62.02(10)
113.5(3)
Ln1eO1eLn1*
Average
Bond length (Å)
LneS
LneN
LneO
3.029(4)
2.694(11)
2.512(8)
3.019(4)
2.695(14)
2.532(10)
2.909(7)
2.622(13)
2.470(13)
2.989(5)
2.633(11)
2.490(7)
2.900(4)
2.601(10)
2.431(7)
2.967(4)
2.631(11)
2.470(7)
2.974(4)
2.626(9)
2.474(6)
2.908(3)
2.608(8)
2.427(6)
2.871(1)
2.575(18)
2.408(13)
2.889(3)
2.573(6)
2.394(4)
2.856(6)
2.510(10)
2.389(8)
2.8798(9)
2.538(15)
2.391(21)
Bond angles (°)
SeLn1eS
58.03(12)
58.44(12)
61.35(16)
59.12(9)
61.43(10)
59.57(11)
59.51(9)
61.85(7)
61.9(2)
62.01(5)
62.3(12)
62.17(15)
a
The asterisk (*) indicates the symmetry-related atom.
Mol1 and mol2 have 8:8- and 9:9-coordinate structures, respectively.
Atom-numberings of mol2 should be modified appropriately: see Fig. 5 and Supplementary Information for details.
b
c
d
Ln2eO3MeOH
.
tricapped trigonal prism.
bridging bphz ligands (Figs. S7b and S8b).
Since the LaIII(RR′dtc)2 fragments form a 9-coordinate dinuclear
bphz-bridged complex with a coordinated EtOH ligand, while the cor-
responding SmIII and EuIII ones gave an 8-coordinate dinuclear com-
plexes where two dithiocarbamato ligand planes at each LnIII center are
co-planar, it is interesting to investigate the molecular structures of the
PrIII and NdIII analogues. The PrIII–pyrdtc complex of 2b and the
NdIII–pyrdtc complex of 3b were found to be isomorphous to the
LaIII–pyrdtc complex of 1b, and a similar molecular structure with 9-
coordinate PrIII ions (Fig. S7) or NdIII ions (Fig. S8) resulted in. The
structural characteristics of 2b and 3b are also the same as those of 1b.
The coordination bond lengths around PrIII center in 2b are slightly
shorter than the corresponding ones around LaIII in 1b by 0.02–0.06 Å
and those around NdIII in 3b are further shorter by ca. 0.01 Å, although
the PrIII and NdIII centers in 2b and 3b are still not on the plane of the
The crystal structure of PrIII–Me2dtc complex, 2a, was found to be
rather different from the above examples. It was crystallized in a tri-
clinic space group P–1 with Z = 4 (based on the dinuclear unit), and its
asymmetric unit contains a whole molecule of bphz-bridged dinuclear
PrIII complex, two fragments of ‘PrIII(Me2dtc)2(bphz)’ which gives a
dinuclear bphz-bridged complex by symmetry operation, and four
molecules of solvent CH2Cl2 molecules; thus, the crystals of 2a can be
assigned as [{Pr(Me2dtc)2}2(μ-bphz)2]·2CH2Cl2. There are three kinds
of crystallographically different dinuclear complexes, but all of them
are found to be 8-coordinate around the PrIII centers (Fig. S9). The
characteristics of the molecular structures are also similar to those of
the Sm2III and Eu2III complexes of 4a and 5a.
The NdIII–Me2dtc complex, 3a, showed a further characteristic
crystal structure (Fig. 5). It was crystalized in a triclinic space group P–1
Fig. 3. (a) A perspective view of dinuclear complex of [{Eu(pyrdtc)2}2(µ-bphz)2] in 5b·3CHCl3 and (b) its side view from the Eu2(bphz)2 plane. Hydrogen atoms and
lattice solvent molecules are omitted for clarity.
5

A. Yakubu, et al.
InorganicaChimicaActa498(2019)119124
Fig. 4. (a) A perspective view of dinuclear complex of [{La(Me2dtc)2(EtOH)}2(µ-bphz)2] in 1a and (b) its side view from the (μ-bphz)2 plane. Hydrogen atoms and
lattice solvent molecules are omitted for clarity.
with Z = 2 (based on the dinuclear unit), and the asymmetric unit
contains two halves of the dinuclear bphz-bridged NdIII molecules and
two solvent CHCl3 molecules. Interestingly, these two fragments have
different molecular structures; one of the molecules (with Nd1) has a
similar 8-coordinate structure (Fig. 5a and b) to those of the SmIII (4a)
and EuIII (5a) analogues (where two mutually trans-positioned Me2dtc
ligand planes are co-planar to each other), while the other molecule
(with Nd2) is coordinated by an additional MeOH molecule to complete
a 9-coordinate coordination geometry (Fig. 5c and d). Therefore, the
form a 9-coordinate complex by a coordination of solvent EtOH (or
MeOH) molecule used for recrystallization, when a larger LnIII ion (e.g.,
LaIII, PrIII or NdIII) was applied. Then, an interesting question arose;
would an 8:8- or 9:9-coordinate molecule be obtained by recrystallizing
these complexes from non-coordinating solvents? We have attempted
several crystallization and finally isolated pale green and block single-
crystals of the NdIII–pyrdtc complex, 3b′, from a mixture of di-
chloromethane and diethyl ether. Although the crystallinity was not
good enough to obtain a satisfactory R value, we have confirmed the
successful crystallization of the 8:8-coordinate [{Nd(pyrdtc)2}2(μ-
bphz)2] (3b′) complex (Table S1 and Fig. S10).
crystals
is
assigned
as
[{Nd(Me2dtc)2}2(μ-bphz)2]·[{Nd
(Me2dtc)2(MeOH)}2(μ-bphz)2]·4CHCl3.
The above-mentioned crystallographic analyses suggested that the
bphz-bridged dinuclear lanthanoid dithiocarbamato complexes tend to
Fig. 5. Perspective views of (a and b) a 8:8-coordinate dinuclear complex of [{Nd(Me2dtc)2}2(µ-bphz)2] and (c and d) a 9:9-coordinate dinuclear complex of [{Nd
(Me2dtc)2(MeOH)}2(µ-bphz)2] in 3a (b and d are their side views from the (μ-bphz)2 plane. Hydrogen atoms and lattice solvent molecules are omitted for clarity.
6

A. Yakubu, et al.
InorganicaChimicaActa498(2019)119124
3.4. Spectroscopic properties
3.4.1. 1H NMR study
The 1H NMR spectra of Hbphz and some LnIII complexes in
chloroform-d were measured. As representative examples, the spectra
of free Hbphz and the NdIII–pyrdtc complexes with 9:9- and 8:8-co-
ordinate structures, [{Nd(pyrdtc)2(EtOH)}2(µ-bphz)2] (3b) and [{Nd
(pyrdtc)2}2(µ-bphz)2] (3b′), which were obtained by recrystallization
from dichloromethane/ethanol and dichloromethane/diethyl ether,
respectively, are shown in Fig. 1. In the spectrum of free Hbphz
(bottom), the amide (NH) and imine (N]CH) proton resonances are
observed at δ 10.99 and 8.58, respectively. In addition, multiplet re-
sonances due to the aromatic (CH) protons are observed in the range of
δ 7.31–8.42. The NdI2II complexes gave relatively sharp resonances in
the typical range (δ 10–0) for diamagnetic compounds (middle and
top), although they contain NdIII ions. In these spectra, the dis-
appearance of the amide NH resonance indicates the deprotonation
from the hydrazone. The resonance for the imine (N]CH) proton is
observed at δ 9.56, while those for the aromatic (CH) protons occurred
in the range of δ 7.26–8.94. The methylene (CH2) protons of pyrdtc−
ligands gave two pseudo triplets around δ 3.8 and 1.3. In addition, in
the spectrum of 3b three sharp resonances due to free ethanol are ob-
served [23]. These spectral features of 3b and 3b′ suggest that the EtOH
(or MeOH) molecule in the 9:9-coordinate complex dissociates in a
chloroform solution to exist as an 8:8-coordinate dinuclear bphz-
bridged complex.
Fig. 7. Absorption (top) and MCD (bottom) spectra of [{Nd
(pyrdtc)2(EtOH)}2(µ-bphz)2] 3b.
3.4.2. UV–visible absorption and MCD spectra
UV–visible absorption and MCD spectra of the pyrdtc− complexes,
1b–5b, were measured in CH2Cl2 solutions. The complexes exhibited
similar absorption spectral pattern in the UV region as shown in Fig.
S11. The band at 340 nm was assigned to the intra-ligand charge
transfer transition [24,25]. In the visible region, sharp but weak ab-
sorption bands and MCD signals characteristic of f–f transitions were
observed in the complexes. The spectra are presented in Figs. 6–9 and
discussed below.
The absorption spectrum of 2b (Fig. 6, top) shows four sharp but
Fig. 8. Absorption (top) and MCD (bottom) spectra of [{Sm(pyrdtc)2}2(µ-
bphz)2] 4b.
weak bands at 16,580, 20,200, 20,830 and 22,050 cm−1. These bands
are due to the f–f transition from the ground state 3H4 to the 1D2, 3P0,
(3P1,1I6) and 3P2 excited states, respectively, which are based on the
reported signal assignments for an aqueous Pr(NO3)3 and Pr(ClO4)3
solutions [26]. In the MCD spectrum (bottom), the f–f transition bands
are observed as characteristic positive A-term MCD signals at 16,500
and 21,930 cm−1, while negative A- and C-term MCD signals at 20,240
and 20,830 cm−1, respectively.
The absorption spectrum (top) of complex 3b (Fig. 7) shows four
sharp but weak f–f bands with maximum peaks at 12,420, 13,320,
Fig. 6. Absorption (top) and MCD (bottom) spectra of [{Pr(pyrdtc)2(EtOH)}2(µ-
bphz)2] 2b.
7

A. Yakubu, et al.
InorganicaChimicaActa498(2019)119124
negative B-term observed in the previously reported mononuclear EuIII
dithiocarbamato complexes [29]. The MCD results show that the co-
ordination environment of the lanthanoid with a mixed N,O,S donor set
gives a significant difference in the electronic structure from that of an
N,S donor set. This finding shows that the sensitivity of the MCD
technique [34] can be used as an effective tool to probe the electronic
structure(s) and physical properties of LnIII complexes in solution.
4. Conclusion
A series of novel hydrazonato-bridged homodinuclear LnI2II dithio-
carbamato complexes were prepared and their crystal and molecular
structures and spectroscopic properties were investigated. The crystal
structures revealed that the early LnIII ions tend to crystallize as a 9:9-
coordinate complex with the ninth position occupied by a solvent al-
cohol molecule, while the middle LnIII ions deposit the crystals of only
8:8-coordinate complex. The coordination of a deprotonated mono-
anionic hydrazonato ligand was confirmed by the IR and 1H NMR
spectroscopy. Similar spectral patterns of ligand-centered and Laporte
forbidden f–f transitions were observed in the UV–visible spectral re-
gion. The MCD parameters exhibited by the complexes demonstrate
their potential in magneto-optical applications. In addition, these hy-
drazonato-bridged dinuclear lanthanoid(III) complexes with some sui-
table modification would be used as an effective building block for
supramolecular chemistry. In particular, the late (heavier) LnIII ions
would be interesting in their magnetic and catalytic properties. Such an
investigation of a series of complexes are now in progress in our la-
boratory.
Fig. 9. Absorption (top) and MCD (bottom) spectra of [{Eu(pyrdtc)2}2(µ-
bphz)2] 5b.
17,040 and 18,800 cm−1, which are assigned to the 4
I
9/2 → (4F5/2, 4H9/
4
2), (4S3/2
,
4F7/2), (2G7/2
,
4G5/2) and G7/2 transitions, respectively. The
Declaration of Competing Interest
4I9/2 → (4F5/2 4H9/2), (4S3/2 4F7/2) and (2G7/2 4G5/2) transitions oc-
, , ,
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
curred at slightly lower in energies than those of a similar hydrazone-
based NdIII complex reported by Singh et al. [27]. Compared to the
related NdIII complex with N-(furfuralidene)-N-isonicotinoylhydrazine
[28], only the 4 9/2 → (4F5/2 4H9/2) band was consistent, and the other
I ,
Acknowledgements
transitions occurred at lower energies. In the MCD spectrum (bottom),
the MCD signals were observed at 12,380, 13,290, 13,500, 16,910 and
17,040 cm−1. These signals are dominated by room temperature C-
terms, except for the signal at 12,380 cm−1 which appeared as a posi-
tive pseudo A-term [29].
The authors wish to thank Dr. Yukinari Sunatsuki of his assistance in
the crystallographic analysis. This work was supported by a Grant-in-
Aid for Scientific Research No. 18K05146 from the Ministry of
Education, Culture, Sports, Science, and Technology, Japan.
The characteristic 4I9/2 → (4G5/2 2G7/2) hypersensitive transition
,
exhibits splitting at 16,910 and 17,040 cm−1. These crystal-field split-
ting was also observed in the second derivative absorption spectra of Nd
(C2H3O2)3H2O [30] and neodymium complex with fleroxacin [31] at
Appendix A. Supplementary data
higher energies. The 4I9/2 → (4G5/2 2G7/2) hypersensitive transition C-
,
Details of the crystal structures and the infrared and UV-visible
absorption spectra of the complexes in PDF format. Crystallographic
data for compounds Hbphz and complexes 1a–5b have been deposited
with the Cambridge Crystallographic Data Centre, CCDC
1944410–1944421. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
term MCD signals are more clearly resolved in 3b than those in pre-
viously reported mononuclear NdIII analogues [29].
In Fig. 8 (top), no f–f bands were detected in the absorption spec-
trum for complex 4b probably because they were overlapped or buried
underneath the strong metal-ligand charge–transfer band around
24,000 cm−1 [28,32]. In the MCD spectrum (bottom), the structure of
the MCD bands is very complicated due to the Zeeman splitting of the
ground state and all the excited states [33]. Two characteristic MCD
signals showing a positive A-term and a negative C-term occurred at
23,510 and 21,260 cm−1, owing probably to the f–f transition from the
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.ica.2019.119124.
References
6
4
6H6/2 ground state to the P3/2 and I13/2 excited states, respectively.
In Fig. 9 (top), complex 5b exhibited two very weak bands at 21,450
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The positions of these bands are in good agreement, but the shapes are
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