Synthesis, spectroscopic and X-ray crystallographic properties of manganese compounds of keto- and enol-coordinated di-2-pyridyl ketone benzoyl hydrazone (dpkbh). Reactions of [Mn(CO)5Br] with dpkbh

Article abstract of DOI:10.1080/00958972.2016.1162789

Reactions between [Mn(CO)₅Br] and dpkbh in low boiling solvents in air gave fac-[Mn^I(CO)₃(Κ²-N_py,N_im-dpkbh)Br]·H₂O, [Mn^IIBr₂(Κ³-N_py,N<

Full text of DOI:10.1080/00958972.2016.1162789

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Synthesis, spectroscopic and X-ray crystallographic
properties of manganese compounds of keto-
and enol-coordinated di-2-pyridyl ketone benzoyl
hydrazone (dpkbh). Reactions of [Mn(CO) Br] with
5
dpkbh
Mohammed Bakir & Rebecca Conry
To cite this article: Mohammed Bakir & Rebecca Conry (2016): Synthesis, spectroscopic and X-
ray crystallographic properties of manganese compounds of keto- and enol-coordinated di-2-
pyridyl ketone benzoyl hydrazone (dpkbh). Reactions of [Mn(CO) Br] with dpkbh, Journal of
5
Coordination Chemistry, DOI: 10.1080/00958972.2016.1162789
To link to this article: http://dx.doi.org/10.1080/00958972.2016.1162789
Accepted author version posted online: 08
Mar 2016.
Published online: 23 Mar 2016.
View supplementary material
Submit your article to this journal
View related articles
Article views: 5
View Crossmark data
Full Terms & Conditions of access and use can be found at
http://www.tandfonline.com/action/journalInformation?journalCode=gcoo20
Download by: [Gazi University]
Date: 27 March 2016, At: 19:57

JOURNAL OF COORDINATION CHEMISTRY, 2016
http://dx.doi.org/10.1080/00958972.2016.1162789
Synthesis, spectroscopic and X-ray crystallographic properties
of manganese compounds of keto- and enol-coordinated di-
2
-pyridyl ketone benzoyl hydrazone (dpkbh). Reactions of
[
Mn(CO) Br] with dpkbh
5
Mohammed Bakir and Rebecca Conryb
a
a
b
Department of Chemistry, The University of the West Indies-Mona Campus, Kingston, Jamaica; Department of
Chemistry, Colby College, Waterville, ME, USA
ABSTRACT
ARTICLE HISTORY
Received 31 July 2015
Accepted 18 February 2016
Reactions between [Mn(CO) Br] and dpkbh in low boiling solvents in air
5
I
2
II
3
gave fac-[Mn (CO) (κ -N ,N -dpkbh)Br]·H O, [Mn Br (κ -N ,N ,O-dpkbh)],
3
py im
2
2
py im
II
3
and [Mn (κ -N ,N ,O-dpkbh-H) ]·0.5H O (N = imine nitrogen and
py im
2
2
im
KEYWORDS
I
2
Npy = pyridyl nitrogen). Crystallization of fac-[Mn (CO) (κ -N ,N -dpkbh)
3
py im
Synthesis; manganese;
di-2-pyridyl ketone
benzoyl hydrazone; X-ray;
spectroscopy
II
3
Br]·H O from dmso or CH CN produced dark red crystals of [Mn (κ -N ,N ,O-
2
3
py im
dpkbh-H) ]·nX (X = dmso, n = 1 and X = H O, n = 0.22). This is in contrast
2
2
to the reaction of [Re(CO) Cl] with dpkbh in refluxing toluene to form fac-
5
I
2
[
Re (CO) (κ -,N ,N -dpkbh)Cl] which can be crystallized from CH CN, dmso
3
p
y
p
y
3
I
2
or dmf to form fac-[Re (CO) (κ -,N ,N -dpkbh)Cl]·nX (X = CH CN, n = 0 and
3
py py
3
solvate = dmso or dmf, n = 1). Infrared spectral measurements are consistent
I
2
with keto coordination of dpkbh to Mn(I) in fac-[Mn (CO) (κ -N ,N -dpkbh)
3
py im
II
3
Br]·H O and Mn(II) in [Mn Br (κ -N ,N ,O-dpkbh)] plus enol coordination of
2
2
py im
II
3
the amide-deprotonated dpkbh, to the Mn(II) center in [Mn (κ -N ,N ,O-
py im
dpkbh-H) ]·0.5H O. Electronic absorption spectral measurements in non-
2
2
I
2
aqueous solvents indicate sensitivity of fac-[Mn (CO) (κ -N ,N -dpkbh)
3
py im
II
3
Br]·H O and [Mn (κ -N ,N ,O-dpkbh-H) ]·0.5H O to changes in their outer-
2
py im
2
2
shell environments. X-ray crystallographic analyses elucidated the identities
II
3
II
3
of [Mn Br (κ -N ,N ,O-dpkbh)] and [Mn (κ -N ,N ,O-dpkbh-H) ]·nX and
2
py im
py im
2
II
3
divulged weaker coordination of [dpkbh] to Mn(II) in [Mn Br (κ -N ,N ,O-
2
py im
II
−
3
dpkbh)] and stronger coordination of [dpkbh-H] to Mn(II) in [Mn (κ -
N ,N ,O-dpkbh-H) ]·0.22H O. Low-temperature X-ray structural analyses
py im
2
2
II
3
were employed to account for the disorder in the structure of [Mn (κ -
N ,N ,O-dpkbh-H) ] and the short NH bond distance observed in the
py im
2
II
3
structure of [Mn Br (κ -N ,N ,O-dpkbh)]. A PLATON SQUEEZE treatment
2
py im
was invoked to account for the fractional occupancy of lattice water in the
II
3
structure of [Mn (κ -N ,N ,O-dpkbh-H) ].
py im
2
CONTACT Mohammed Bakir
mohammed.bakir@uwimona.edu.jm
Supplemental data for this article can be accessed http://dx.doi.org/10.1080/00958972.2016.1162789.
©
2016 Informa UK Limited, trading as Taylor & Francis Group

2
M. BAꢀIR ANꢁ R. CONRꢂ
1. Introduction
ꢁi-2-pyridyl ketone (dpk) and a variety of its hydrazonic derivatives (dpk-h) such as hydrazones, sem-
icarbazones, and thiosemicarbazones (see scheme 1) continue to attract research interest because
of their physicochemical properties and applications in many areas including medicine [3–5, 8, 9, 12,
1
9], sensors [17, 18], supramolecular networks [1], catalysis [2], etc. [1–21]. ꢁi-2-pyridyl ketone and its
derivatives possess a flexible backbone, a variety of donor-acceptor sites, and have the ability to bind
to metal moieties in mono- or polydentate fashion to form a broad range of complexes. The excellent
chelating properties of dpk-h account in part for their biological and molecular sensing behavior. The
biological activities of dpk-h are due to several factors: extraction of metal ions from cells, depriving
cells from essential nutrients leading to cell death, intercalation to ꢁNA, or inhibition of certain enzymes.
We are interested in the chemistry of di-2-pyridyl ketone derivatives (dpk-h) and have reported the
synthesis, solution chemistry, and solid state structures of several dpk-h derivatives as well as their metal
compounds [22–30]. Spectroscopic and electrochemical measurements on non-aqueous solutions of
dpk-h and their metal compounds indicate sensitivity to changes in their surroundings to make them
potentially useful as sensors for the detection of trace amounts of substrates including acids, bases, or
group 12 metal chlorides [22–25, 28]. In this report, reactions of dpkbh with [Mn(CO) Br] that formed
5
I
2
II
3
II
3
fac-[Mn (CO) (κ -N ,N -dpkbh)Br]·H O, [Mn Br (κ -N ,N ,O-dpkbh)], and [Mn (κ -N ,N ,O-dpkbh-
3
py im
2
2
py im
py im
H) ]·0.5H O are described. In previous reports, we described the synthesis, characterization, solution
2
2
I
2
I
2
chemistry, and solid state structures of dpkbh, fac-[Re (CO) (κ -N ,N -dpkbh)Cl], fac-[Re (CO) (κ -N ,
3
py py
3
py
II
3
N -dpkbh)Cl]·solvent (solvent = dmso or dmf), and [Zn Cl (κ -N ,N ,O-dpkbh] [22–25].
py
2
py im
R
N
N
R = alkyl or arylhydrazone
R= COR acetylhydrazone
N
NH
N
O
R = CONH semicarbazone
2
N
R= CSNH thiosemicarbazone
2
dpk
dpk-h
Scheme 1. Representation of dpk and dpk-h.

3
2. Experimental
2
.1. Reagents and reaction procedures
The dpkbh, melting point 141–142 °C, was prepared by refluxing a mixture of di-2-pyridyl ketone,
benzhydrazide, EtOH, and two drops of HCl using a standard procedure as described previously for
the synthesis of several di-2-pyridyl ketone hydrazones, including dpkbh [22]. All reactions were done
in open air.
2
.2. Reactions of [Mn(CO) Br] with dpkbh
5
(
1) In diethyl ether at 0 °C. Equi-volume (15 mL) diethyl ether solutions of Mn(CO) Br (0.20 g,
5
0.72 mmol) and dpkbh (0.27 g, 0.84 mmol) were prepared separately. The solutions were com-
bined and allowed to react at ~0 °C for 15 min. The resulting yellow solid was filtered off, washed
with diethyl ether, and dried in air at room temperature, yield 0.08 g (0.15 mmol) (21%). Found:
I
2
C, 47.3; H, 3.4; N, 9.8. C H BrMnN O {fac-[Mn (CO) (κ -N ,N -dpkbh)Br]·H O} requires: C, 46.8;
21
19
5
5
3
py im
2
−1
H, 3.0 and N, 10.4. Infrared (IR) data (cm ): ν(N–H) and ν(O–H) 3420 (broad), ν(C–H) 3150 and
035, ν(C≡O) 2026, 1941, and 1896, ν(C=O) 1656, ν(C=N) and ν(C=N) of pyridine and phenyl
rings 1615–1550, and ν(N–N) 1142. UV-vis {λ nm , (ε ± 500 cm M )}: dmso: 395 (22,300), 322
17,500); dmf: 393 (17,000), 322 (13,900).
3
−1
−1
−1
(
(
(
2) In diethyl ether at room temperature. When (i) was carried out at room temperature for 1 h a red-
brown precipitate was isolated from the reaction mixture. Infrared spectra of the red-brown
precipitate showed a significant decrease in the intensity of ν(C≡O) of the carbonyl groups of
2
2
fac-[Mn(CO) (κ -N ,N -dpkbh)Br] pointing to thermal instability of fac-[Mn(CO) (κ -N ,N -
3
py im
3
py im
dpkbh)Br]. No attempt was made to separate the mixture.
3) In CH CN at 0 °C with [Mn(CO) Br]:dpkbh mole ratio of 1.00:1.20. A mixture of [Mn(CO) Br] (0.20 g,
3
5
5
0
.75 mmol), dpkbh (0.28 g, 0.87 mmol), and CH CN (30 mL) was allowed to react (stirred) in
3
an ice bath for 1.0 h. Over this time the reaction mixture changed color from orange to deep
red. The resulting reaction mixture was warmed to room temperature and left to crystallize
II
3
for several days, giving orange crystals of [Mn Br (κ -N ,N ,O-dpkbh)] and red crystals of
2
py im
II
3
[
Mn (κ -N ,N ,O-dpkbh-H) ]·0.22H O which were separated by hand and identified using X-ray
crystallography (see Table 1). Infrared data for [MnBr (κ -N,N,O-dpkbh)] (cm ): ν(N–H) and
py im 2 2
3
−1
2
ν(O–H) 3370 broad, ν(C–H) 3223 and 3062, δ(O–H) 1707, ν(C=O) 1640, ν(C=N), and ν(C=N) of
3
pyridine and phenyl rings 1606–1550, and 1146 ν(N-N). Infrared data for [Mn(κ -N,N,O-dpkbh-
−1
H) ]·0.5H O (cm ): ν(O–H) 3420 broad, ν(C–H) 3062, δ(O–H) 1657, ν(C=N), and ν(C=N) of pyridine
2
2
and phenyl rings 1610–1540, ν(N–N) 1136, and ν(C–O) 1077.
(
4) In CH CN under reflux with [Mn(CO) Br]:dpkbh mole ratio of 1.00:2.20. A mixture of [Mn(CO) Br]
3
5
5
(
0.10 g, 0.36 mmol), dpkbh (0.23 g, 0.76 mmol) and CH CN (50 mL) was refluxed for 3 h. The
3
volume of the reaction mixture was reduced to ~15 mL under reduced pressure and the result-
ing dark red solid was filtered off, washed with hexanes, diethyl ether and dried in air at room
II
3
temperature, yield 0.16 g (0.25 mmol, 67%). Found: C, 64.8; H, 4.5. C H MnN O {[Mn (κ -
3
6
25
8
2.5
−1
N ,N ,O-dpkbh-H) ]·0.5H O} requires: C, 65.3; H, 4.0. Infrared (cm ): ν(O–H) 3420 broad, ν(C–H)
py im
2
2
3
062, δ(O–H) 1657, ν(C=N), and ν(C=N) of pyridine and phenyl rings 1610–1540, ν(N–N) 1136
−1
−1 −1
and ν(C–O) 1077. UV-vis {λ ± 2 nm , (ε ± 500 cm M )} CH CN: 390 (45,800); dmso: 398 (46,900);
dmf: 398 (42,550).
3
2
.3. Physical measurements
An HP 8452A spectrophotometer was used to measure the electronic absorption spectra. Infrared
spectra were recorded as ꢀBr disks on a Perkin-Elmer Spectrum 1000 FT-IR spectrometer.

4
M. BAꢀIR ANꢁ R. CONRꢂ
II
3
II
3
Table 1. Crystal data and structure refinement for [Mn Br (κ -N ,N ,O-dpkbh)] (1), [Mn (κ -N ,N ,O-dpkbh-H) ]·0.22H O (2), and
2
py im
py im
2
2
II
3
[
Mn Br (κ -N ,N ,O-dpkbh)]·dmso (3).
2 py im
Identification code
(1)
C H Br MnN O
(2)
(3)
Empirical formula
C H MnN O
C H MnN O S
1
8
14
2
4
36 26
8
2.22
38 34 8 3
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
517.09
296(2)
0.71073
Monoclinic
Cc
661.59
295(2)
0.71073
737.73
298(2)
0.71073
Triclinic
P-1
Monoclinic
1
Space group
P2 /c
Unit cell dimensions (Å, °)
a
b
c
12.2389(9)
19.5907(14)
8.2865(6)
90
103.8560(10)
90
1929.0(2)
4
1.780
11.168(2)
11.057(2)
26.581(5)
90
98.58(3)
90
3245.4(11)
4
1.353
11.6291(9)
11.6476(11)
15.1523(11)
75.617(7)
86.759(5)
64.899(7)
1797.5(3)
2
α
β
γ
3
Volume (Å )
Z
−
3
Calculated density (Mg m )
1.363
0.474
−1
Absorption coefficient (mm )
4.841
0.453
F(0 0 0)
1012
2.00→28.27
1363
1.55→28.29
766
1.94→25.00
Theta range for data collection (°)
Limiting indices
h
−16→16
−14→14
−14→14
−35→34
29,712/7902
0.0276
98.1% [28.29]
Multi-scan
−13→1
k
−26→25
−13→12
−18→18
7123/6103
0.0213
l
−10→10
8640/4209
0.0330
97.9% [28.27]
Multi-scan
1.0000 and 0.671906
Full-matrix least-squares on F
4209/3/239
Reflections collected/unique
[
R(int)]
Completeness to [θ]
96.6% [25.00]
Empirical
0.5127 and 0.4965
Absorption correction
Max. and min. transmission
Refinement method
1.0000 and 0.883082
2
Data/restraints/parameters
Goodness-of-fit on F
Final R indices [I>2σ (I)]
7902/0/434
1.024
R1 = 0.0405;
wR2 = 0.1035
R1 = 0.0535;
wR2 = 0.1134
6103/0/465
1.013
R1 = 0.0565;
wR2 = 0.1210
R1 = 0.0932;
wR2 = 0.1424
2
1.010
R1 = 0.0327;
wR2 = 0.0652
R1 = 0.0420;
wR2 = 0.0672
0.023(8)
R indices (all data)
Absolute structure parameter
Extinction coefficient
Largest diff. peak and hole e A
–
–
0.0029(6)
0.821 and −0.61
−
−3
0.512 and −0.285
0.385 and −0.175
2
.4. X-ray crystallography
II
3
3
Crystals of [Mn Br (κ -N ,N ,O-dpkbh)] and [Mn(κ -N ,N ,O-dpkbh) ]·0.22H O were isolated from
2
py im
py im
2
2
3
reaction (ii) and crystals of [Mn(κ -N ,N -dpkbh) ]·dmso were obtained from a dmso solution of fac-
py im
2
I
2
[
Mn (CO) (κ -N ,N -dpkbh)Br]·H O. A single crystal of each complex was selected and mounted on a
3 py im 2
glass fiber using epoxy cement prior to data collection. Bruker AXS or a Bruker SMART CCꢁ area-detector
diffractometers with Mo-ꢀ radiation and a graphite monochromator were used for data collection of
α
II
3
II
3
II
3
[
Mn (κ -N ,N ,O-dpkbh-H) ]·dmso, [Mn Br (κ -N ,N ,O-dpkbh)], and [Mn (κ -N ,N ,O-dpkbh-H) ].
py im 2 2 py im py im 2
The SHELXTL software version 5.1, SHELXTL software version 2014/7 and PLATON software version
40,413 were used for structure analysis [31–34]. Cell parameters and other crystallographic information
are given inTable 1. The atomic coordinates and equivalent isotropic displacement parameters are given
2
II
3
II
3
in the Supplementary Material. All hydrogens for [Mn Br (κ -N ,N ,O-dpkbh)] and [Mn (κ -N ,N ,O-
2
py im
py im
II
3
dpkbh-H) ]·nX except H4 of the amide nitrogen in [Mn Br (κ -N ,N ,O-dpkbh)] were assigned by assum-
2
2
py im
ing idealized geometries with d =0.93 and d
0.86 Å with Uiso (H)=1.2 U (N) and Uiso(H)=1.5
C–H)
(N–H)
eq
II
3
Ueq(C). The amide hydrogen of [Mn Br (κ -N ,N ,O-dpkbh)] was located in a difference Fourier map and
2
py im
II
3
refined with restrained distance of ~0.86 Å. All non-hydrogen atoms of [Mn Br (κ -N ,N ,O-dpkbh)] and
2
py im
II
3
[
Mn (κ -N ,N ,O-dpkbh-H) ]·nX were refined anisotropically. ꢁuring the course of structure refinement
py im 2

5
II
3
− 3
of [Mn (κ -N ,N ,O-dpkbh-H) ] a region of electron density (1.18 e Å ) at a non-bonding distance to
py im
2
the manganese complex was assumed to be a lattice H O incorporated into the crystal from dissolved
2
H O in CH CN. The occupancy of the oxygen of lattice H O was allowed to refine freely in the absence
2
3
2
of hydrogens of H O because difference Fourier maps did not show electron density assignable to dis-
2
II
3
crete hydrogens. In the final refinement of [Mn (κ -N ,N ,O-dpkbh-H) ]·0.22H O, the highest peak and
py im
2
2
deepest hole were 0.03 and 0.72 Å from the Mn. The anisotropic displacement parameters of N2, C21,
II
3
C22, and C23 [Mn (κ -N ,N ,O-dpkbh-H) ] are higher than those of other carbons and nitrogens in the
py im
2
molecule. This may represent the effects of static (i.e. caused by positional disorder) as well as dynamic
i.e. thermal) displacements. In order for the refinement to represent the disorder as authentically as
possible, we did not apply any restraints or constraints at the anisotropic displacement parameters
(
II
3
of any atom. PLATON SQUEEZE was invoked to support the assigned lattice H O in [Mn (κ -N ,N ,O-
2
py im
dpkbh-H) ]·0.22H O [34]. The least-squares refinement against the intensities corrected by Squeeze
2
2
-
−3
converges to R[F > 2σ(F)] and wR(F) values of 0.041 and 0.116, respectively, with Δρ and Δρ (e Å ) of
.40 and −0.17 at 0.03 and 1.01 Å from Mn and N2, respectively. At 173 ꢀ, the least-squares refinement
against the intensities converges to R[F > 2σ(F)] and wR(F) values of 0.044 and 0.117, respectively, with
Δρ and Δρ (e Å ) of 0.62 and −0.18 at 0.02 and 1.31 Å from Mn and C21, respectively. These results
support the proposed partial occupancy of the voids by H O as R[F > 2σ(F )], wR(F ), Δρmax, and Δρmin
0
−
−3
2
2
2
values of the SQUEEZE model are similar. Low temperature measurements conducted at 173 ꢀ yielded
II
3
II
3
essentially the same structural solutions for [Mn Br (κ -N ,N ,O-dpkbh)] and [Mn (κ -N ,N ,O-dpkbh-
2
py im
py im
H) ]·0.22H O with the expected smaller AꢁP’s for the constituent atoms compared to room temperature
2
2
(
296 ± 2) ꢀ measurements and 0.25 fractional occupancy of lattice H O. The decrease in the AꢁP’s of
2
II
3
the constituent atoms of [Mn (κ -N ,N ,O-dpkbh-H) ]·0.25H O at low temperature may account for
py im
2
2
the 0.25 versus 0.22 fractional occupancy of lattice H O determined at 173 and 295 ꢀ, respectively.
2
II
3
II
3
Refinements for [Mn Br (κ -N ,N ,O-dpkbh)] and [Mn (κ -N ,N ,O-dpkbh-H) ]·0.22H O data collected
2
py im
py im
2
2
at 173 ꢀ contained smaller AꢁP’s of the constituent atoms but otherwise essentially identical structural
features as refinements for data were collected at room temperature (296 ± 2 ꢀ) as expected. CCꢁC
reference number 1,416,398–1,416,400.
2
.5. Analytical procedures
Elemental microanalyses were performed by MEꢁAC Ltd., ꢁepartment of Chemistry, Brunel University,
Uxbridge, United ꢀingdom.
3. Results and discussion
When [Mn(CO) Br] was allowed to react with dpkbh in a mole ratio of ~1 : 1 in diethyl ether at ~0 °C
5
I
2
for ~15 min, a yellow precipitate of fac-[Mn (CO) (κ -N ,N -dpkbh)Br]·H O was isolated. When the
3
py im
2
reaction was carried out at room temperature for ~1 h, a red-brown precipitate was isolated. Infrared
I
2
spectra of the isolated red-brown precipitate showed a trace of fac-[Mn (CO) (κ -N ,N -dpkbh)Br]·H O
3
py im
2
I
2
as evident from the significant decrease in the intensity of ν(C≡O) associated with fac-[Mn (CO) (κ -
N ,N -dpkbh)Br]·H O. This suggests that fac-[Mn (CO) (κ -N ,N -dpkbh)Br]·H O is thermally unsta-
3
I
2
py im
2
3
py im
2
ble. No attempt was made to further identify and or purify the isolated precipitate as the goal was to
I
2
find suitable procedure(s) for the synthesis of fac-[Mn (CO) (κ -N ,N -dpkbh)Br]. When CH CN was
3
py py
3
used as a solvent instead of diethyl ether and the reaction mixture was left to stand at room tem-
II
3
II
3
perature for several days, orange crystals of [Mn Br (κ -N ,N ,O-dpkbh)] and red crystals of [Mn (κ -
2
py im
N,N,O-dpkbh-H) ]·0.22H O were formed and mechanically separated from the reaction mixture. When
2
2
[
[
Mn(CO) Br] was allowed to react with dpkbh in a mole ratio of ~1 : 2 in refluxing CH CN for 3 h, red
5
3
II
3
Mn (κ -N ,N ,O-dpkbh-H) ]·0.5H O was isolated from the reaction mixture after it was allowed to
py im
2
2
I
2
cool at room temperature. The crystallization of fac-[Mn (CO) (κ -N ,N -dpkbh)Br]·H O from dmso or
CH CN produced dark red crystals of [Mn (κ -N ,N ,O-dpkbh-H) ]·nX (X = dmso, n = 1 and X = H O,
n = 0.22). These reactions suggest that fac-[Mn (CO) (κ -N ,N -dpkbh)Br]·H O is an intermediate in
3
py im
2
II
3
3
py im
I
2
2
2
3
py im
2

6
M. BAꢀIR ANꢁ R. CONRꢂ
II
3
II
3
the formation of [Mn Br (κ -N ,N ,O-dpkbh)] and [Mn (κ -N ,N ,O-dpkbh-H) ]·nX and demonstrate
2
py im
py im
2
-
keto- and enol-coordination behavior of dpkbh and its amide-deprotonated conjugate base (dpkbh-H) .
Plausible pathways for reactions between [Mn(CO) Br] and dpkbh in low boiling solvents (diethyl ether
5
or CH CN) in air are shown in scheme 2. The proposed pathways account for the isolated complexes
3
I
2
and the crystallization of fac-[Mn (CO) (κ -N ,N -dpkbh)Br]·H O from dmso and CH CN that gave
Mn (κ -N ,N ,O-dpkbh-H) ]·nX. These reactions are in contrast to those reported for the synthesis of
a variety of rhenium carbonyl compounds of the type fac-[Re(CO) (κ -N,N-L-L)Cl] (L-L = dpk-h or N,N-
3
py im
2
3
II
3
[
py im 2
2
3
bidentate ligands) from reactions between [Re(CO) Cl] and L-L in refluxing non-aqueous solvents [22–24,
5
2
8]. These reactions differ from those reported for the reaction between [Mn(CO) Br] and di-2-pyridyl
5
4
ketone thiosemicarbazone (dpktsc) in CH CN under ultrasonic radiation that gave [MnBr(κ -N,N,S,N-
3
dpktsc] and are similar to those reported for the reactions between [Mn(CO) Br] and excess dpktsc
2
5
in refluxing CH CN that gave [Mn(dpktsc-H) ]·2H O [26]. Under the current reaction conditions, there
3
2
2
2
4
is no evidence for κ -N ,N -bidentate or κ -N ,N ,O,N -tetradentate coordination of dpkbh to form
py py
py py
py
I
2
4
fac-[Mn (CO) (κ -N ,N -dpkbh)Br] or [Mn(κ -N ,N ,O,N -dpkbh)Br] . The facile reactions between
3
py py
py py
py
2
dpkbh and [Mn(CO) Br] in non-aqueous solvents under mild conditions are due to enhanced keto–
5
enol tautomerization due to the delocalization of electron density over the benzoyl group, facilitating
3
κ -N,N,O-coordination of dpkbh to [Mn(CO) Br].
5
OC
OC
Br
N
O
Mn(I)
OC
O
N
N
N
H
[Mn(CO) Br]
5
N
N
H
(
C H ) O or CH CN
N
2
5
2
3
N
-
3CO3
Br
Br
N
Br
N
Mn(II)
N
(I)Mn
[
O ], -e-
2
O
O
Br-
N
+
N
H
N
H
N
N
+
[dpkbh]
N
N
N
H
N
N
O
N
[
O ], -e_
2
N
O
Br
N
Mn(II)
Br-, -2H+
-
N
O
Mn(I)
N
O
N
N
N
N
H
N
N
Scheme 2. Representation of plausible pathways for the reactions between [Mn(CO) Br] and dpkbh in CH CN and diethyl ether.
5
3

7
I
2
II
3
II
3
Figure 1. Infrared spectra of dpkbh, fac-[Mn (CO) (κ -N ,N -dpkbh)Br]·H O, [Mn Br (κ -N ,N ,O-dpkbh) ], and [Mn (κ -N ,N ,O-
3
py im
2
2
py im
2
py im
dpkbh-H) ]·H O.
2
2
The identities of the isolated compounds were established from the results of their elemental analy-
I
2
ses, and spectroscopic properties or X-ray structural analyses. Infrared spectra of dpkbh, fac-[Mn (CO) (κ -
3
II
3
II
3
N ,N -dpkbh)Br]·H O, [Mn Br (κ -N ,N ,O-dpkbh)] and [Mn (κ -N ,N ,O-dpkbh-H) ]·0.5H O are
shown in figure 1. In the spectrum of fac-[Mn (CO) (κ -N ,N -dpkbh)Br]·H O, peaks assignable to ν(N–H),
py im
2
2
py im
py im
2
2
I
2
3
py im
2
ν(C≡O), ν(C=O), combined ν(C=N and C=C) of the pyridyl group, and ν(N–N) appeared, consistent with
the coordination of dpkbh to fac-[Mn(CO) Br]. The ν(C≡O) peaks appeared in the same region observed
3
for other metal complexes of the type fac-[M(CO) (L-L)ꢂ] (M = Re or Mn, L-L = bidentate ligand and
3
I
2
ꢂ = halide) [28]. The ν(C=O) of coordinated dpkbh in fac-[Mn (CO) (κ -N ,N -dpkbh)Br]·H O observed
3
py im
2
at 1652 cm− shifts to lower wavenumbers compared to ν(C=O) of free dpkbh observed at 1683 cm ,
1
−1
pointing to a decrease in electron density about the carbonyl group due to the coordination of dpkbh to
II
3
[
Mn(CO) Br]. In the infrared spectrum of [Mn Br (κ -N ,N ,O-dpkbh)], peaks due to ν(N–H), ν(C=O), and
3 2 py im
combined ν(C=N and C=C) indicate coordination of dpkbh to [MnBr ]. The ν(C=O) of coordinated dpkbh
2
at 1640 cm− shifts to lower wavenumbers compared to fac-[Mn (CO) (κ -N ,N -dpkbh)Br]·H O, sug-
1
I
2
3
py im
2
II
3
gesting a stronger interaction between the carbonyl group and the metal center. For [Mn (κ -N ,N ,O-
py im
dpkbh-H) ]·0.5H O, the ν(C=O) for uncoordinated dpkbh disappeared and a strong peak appeared in the
2
2
−
ν(C–O) region pointing to enol coordination of (dpkbh-H) to Mn. Peaks in the ν(O–H) and δ(O–H) regions
are consistent with the incorporation of water in fac-[Mn (CO) (κ -N ,N -dpkbh)Br]·H O and [Mn (κ -
I
2
II
3
3
py im
2
N ,N ,O-dpkbh-H) ]·0.5H O. This may account for the slightly lower elemental analysis values observed
py im
2
2
I
2
II
3
compared to that predicted for fac-[Mn (CO) (κ -N ,N -dpkbh)Br] and [Mn (κ -N ,N ,O-dpkbh-H) ]
3
py im
py im
2

8
M. BAꢀIR ANꢁ R. CONRꢂ
I
2
−5
Figure 2. Electronic absorption spectra of fac-[Mn (CO) (κ -N ,N -dpkbh)Br]·H O measured in CH CN 7.82 × 10 M (1), dmf
3
py im
2
3
5
−5
−5
4
.06 × 10− M (2), CH Cl 5.34 × 10 M (3) and dmso 1.7 × 10 M (4).
2 2
and are close to those predicted for hydrated molecules (see Experimental section). This is due in part
to the availability of a variety of donor–acceptor sites in the coordinated ligand, residual water in the
solvent, or incomplete drying of the isolated products. Previous studies have shown high tendency of
dpk-h’s and their metal complexes to undergo solvolysis [22–24, 26, 29]. For example, when [Mn(CO) Br]
5
reacted with dtktsc in refluxing CH CN, [Mn(dpktsc-H) ]·2H O was isolated.
3
2
2
II
3
I
2
The electronic absorption spectra of [Mn (κ -N ,N ,O-dpkbh-H) ]·0.5H O and fac-[Mn (CO) (κ -
py im
2
2
3
N ,N -dpkbh)Br]·H O are sensitive to changes in their surroundings. The electronic absorption spectra
py im
II
2
3
of [Mn (κ -N ,N ,O-dpkbh-H) ]·0.5H O measured in different solvents (see Experimental section) show
py im
2
2
I
2
a single electronic transition at 395 ± 3 nm. In the case of fac-[Mn (CO) (κ -N ,N -dpkbh)Br]·H O, two
3
py im
2
electronic transitions appeared at 395 ± 3 and 330 ± 10 nm (see figure 2 and Experimental section).
The low energy electronic transition at 395 ± 3 is likely an intra-ligand charge-transfer transition (ILCT)
−
from the deprotonated amide (dpkbh-H) , mixed with a metal→ligand charge-transfer (MLCT) band.
The high energy electronic transition observed at 330 ± 10 nm is due to an ILCT for dpkbh. When stoi-
chiometric amounts of dmso or dmf solutions of an acid (HCl or benzoic acid) were added to protophilic
II
3
solutions of [Mn (κ -N ,N ,O-dpkbh-H) ]·0.5H O, the intensity of the electronic transition at ~395 nm
py im
2
2
gradually decreased and a new electronic transition appeared at 324 nm (see figure 3). The addition of
I
2
protophilic solution of an acid to a protophilic solution of fac-[Mn (CO) (κ -N ,N -dpkbh)Br]·H O shows
3
py im
2
a decrease in the intensity of the low energy electronic transition and an increase in the intensity of the
high energy electronic transition. The reverse was observed when a protophilic solution of a base was
I
2
added to a protophilic solution of fac-[Mn (CO) (κ -N ,N -dpkbh)Br]·H O. These spectral results point
3
py im
2
to deprotonation of coordinated dpkbh in fac-[Mn(CO) (dpkbh)Br]·H O under basic conditions. In the
3
2

9
II
3
−6
Figure 3. The electronic absorption spectra of [Mn (κ -N ,N ,O-dpkbh-H) ]·H O 9.35 × 10 M in dmf in the presence of 0.00 (1),
py im
−5
2
2
5
−5
−5
0
.50 × 10− (2), 1.00 × 10 (3), 1.50 × 10 (4), 2.00 × 10 (5), M benzoic acid in dmf.
II
3
Figure 4. A view of the molecular structure of [Mn Br (κ -N ,N ,O-dpkbh)] measured at 296 K. All hydrogen atoms except that of
2
py im
the amide nitrogen atom were removed for clarity. The thermal ellipsoids are drawn at the 30% probability level.
I
2
absence of an acid or a base, an equilibrium between fac-[Mn (CO) (κ -N ,N -dpkbh)Br]·H O and its
3
py im
2
I
2
conjugate base fac-[Mn (CO) (κ -N ,N -dpkbh-H)Br]·H O is present in protophilic solvents (dmso and
3
py im
2
dmf) (see equation 1).

10
M. BAꢀIR ANꢁ R. CONRꢂ
II
3
Figure 5. Views of the molecular structures of [Mn (κ -N ,N ,O-dpkbh-H) ]·X (X = H O or dmso) measured at room temperature
py im
2
2
(
296 ± 2 K). All hydrogen atoms were removed for clarity. The thermal ellipsoids are drawn at the 30% probability level.
I
fac − [Mn (CO) (ꢀ − N , N − dpkbh)Br] H O + S ↔ fac−
2
3
py
im
2
I
2
−
+
(1)
{
[Mn (CO) (ꢀ − N , N − dpkbh − H)Br] H O} + SH
3 py im 2
II
3
I
2
The assigned electronic transitions for [Mn (κ -N ,N ,O-dpkbh-H) ]·0.5H O and fac-[Mn (CO) (κ -
py im
2
2
3
N ,N -dpkbh)Br]·H O are consistent with the spectral results reported for spectrophotometric titrations
py im
2
of protophilic solutions of dpkbh and other related compounds with protophilic solutions of acids or
bases [22]. In the case of dpkbh, an equilibrium between dpkbh and its amide-deprotonated conju-
−
gate base (dpkbh-H) was established from a series of spectrophotometric titrations [22]. The addition
of stoichiometric amounts of protophilic solutions of a base to protophilic solution of dpkbh causes
an increase in the intensity of the low energy electronic transition at ~400 nm and a decrease in the
intensity of the electronic transition at 330 nm. A reverse effect was observed when stoichiometric
amounts of an acid were added to protophilic solutions of dpkbh.
II
3
The molecular structure of [Mn Br (κ -N ,N ,O-dpkbh)] is shown in figure 4 and views of the molec-
2
py im
II
3
II
3
ular structures of [Mn (κ -N ,N ,O-dpkbh-H) ]·0.22H O and [Mn (κ -N ,N ,O-dpkbh-H) ]·dmso meas-
py im
2
2
py im
2
ured at room temperature (296 ± 2 ꢀ) are shown in Figure 5. The ligand (dpkbh) and its conjugate base
−
3
(
dpkbh-H) coordinate to Mn(II) in these compounds in a κ -N,N,O-binding mode through nitrogen of a

1
1
II
3
II
3
Table 2. Bond lengths [Å] and angles [°] for [Mn Br (κ -N ,N ,O-dpkbh) ] and [Mn Br (κ -N ,N ,O-dpkbh) ]·X (X = 0.22H O or
2
py im
2
2
py im
2
2
dmso) measured at room temperature.
II
3
3
3
[
Mn Br (κ -N ,N ,O-dpkbh) ] [Mn(κ -N ,N ,O-dpkbh-H) ]·0.22H O [Mn(κ -N ,N ,O-dpkbh-H) ]·dmso
2 py im 2 py im 2 2 py im 2
Mn1–O1
Mn1–O1’
Mn1–N1
Mn1–N1’
Mn1–N3
2.213(3)
2.1232(12)
2.115(2)
2.1429(13)
2.2903(14)
2.3319(15)
2.2066(13)
2.2118(14)
2.138(3)
2.284(3)
2.293(3)
2.195(3)
2.210(3)
2.226(3)
2.228(3)
Mn1–N3’
Mn1–Br1
Mn1–Br2
O1–C2
O1’–C2’
N3–C1
N3’C1’
N3–N4
N3’–N4’
N4–C2
2.4836(7)
2.4809(7)
1.240(5)
1.2747(18)
1.2700(19)
1.289(2)
1.2981(19)
1.3815(18)
1.3753(17)
1.3341(19)
1.335(2)
1.270(4)
1.272(4)
1.303(4)
1.291(4)
1.373(4)
1.378(4)
1.333(4)
1.337(4)
1.290(5)
1.362(4)
1.354(5)
N4’–C2’
O1–Mn1–N1
O1’–Mn1–N1
O1–Mn1–N(3)
O1’–Mn1–N(3)
N1–Mn1–N3
N1–Mn1–N3’
N1–Mn1–N1’
O1–Mn–O1’
N3–Mn1–Br1
Br2–Mn1–Br1
139.48(11)
71.00(10)
70.29(11)
142.97(5)
97.84(5)
71.89(4)
126.65(5)
71.24(5)
92.32(5)
142.91(10)
95.56(11)
72.36(10)
119.05(10)
70.69(10)
94.50(11)
89.03(11)
99.41(10)
90.30(5)
101.29(5)
103.21(8)
119.58(2)
pyridyl ring and the oxygen and imine of the hydrazone backbone. This coordination leaves a nitrogen
of one pyridyl ring for potential binding to other moieties.
II
3
Coordination about Mn(II) in [Mn Br (κ -N ,N ,O-dpkbh)] is quasi-tetragonal pyramidal with dpkbh
2
py im
and two bromides occupying the coordination sites. The equatorial sites are occupied by a pyridyl
nitrogen, the imine nitrogen, and an oxygen of the hydrazone backbone and a bromide. The other
bromide occupies the apical site. The trigonality index τ of 0.04 (τ =(φ -φ )/60 where φ and φ are
1
2
1
2
the two largest angles of the coordination sphere, with φ = 0 for a perfect square pyramidal and φ = 1
for a perfect trigonal bipyramidal) was calculated and is consistent with the tetragonal character of
the coordinated site [35]. The fused metallocycles [Mn1-N3–C1–C15–N1] and [Mn1–N3–N4–C2–O1]
are coplanar with a dihedral angle [N4–N3–C1–C15] of 179.64(13). The uncoordinated pyridyl and
II
3
phenyl rings are not coplanar with the metallocyclic rings. For [Mn (κ -N ,N ,O-dpkbh-H) ]·nX, the
py im
2
II
3
asymmetric units show well-separated solvent molecules (X) and [Mn (κ -N ,N ,O-dpkbh-H) ]. Two
py im
2
−
amide-deprotonated dpkbh anions, (dpkbh-H) , occupy the coordination sites of Mn(II) in a distorted
octahedral geometry. The distortions from idealized octahedral geometry are severe as apparent from
the [O1-Mn1–N1], [O1’–Mn1–N1’], and [N3–Mn1–N3’] trans angles of 142.97(5), 141.01(5), and 156.09(5)°,
respectively. The fused metallocyclic rings of each [dpkbh-H] are coplanar with [N4-N3–C1–C15] and
[
N4’–N3’–C1’–C15’] dihedral angles of 179.64(13) and −178.83(13)°, respectively.
II
3
Structural comparisons of bond distances and angles between dpkbh, [Mn Br (κ -N ,N ,O-dpkbh)]
2
py im
II
3
II
3
and [Mn (κ -N ,N ,O-dpkbh-H) ]·nX show [dpkbh] is more weakly coordinated to MnBr in [Mn Br (κ -
N ,N ,O-dpkbh)] than [dpkbh-H] is to Mn(II) in [Mn (κ -N ,N ,O-dpkbh-H) ]·nX. The d(C=N), d(N–N)
py im
2
2
2
−
II
3
,
py im
py im
2
d(N–C) and d(C=O) of 1.30(2), 1.36(2), 1.36(2), and 1.22(2) Å of dpkbh are essentially identical as those
II
3
II
3
observed in [Mn Br (κ -N ,N ,O-dpkbh)] (see Table 2) [22]. The average d and d(Mn–N3) of [Mn (κ -
2
py im
(Mn1–O)
II
3
N ,N ,O-dpkbh-H) ] are shorter than those observed in [Mn Br (κ -N ,N ,O-dpkbh)], while the aver-
py im
age d(Mn1–N1), d(
2
2
py im
II
3
and d(N3–N4) are longer than those observed in [Mn Br (κ -N ,N ,O-dpkbh)]. The
C–O1)
2 py im
II
3
II
3
d(Mn1–O) in [Mn Br (κ -N ,N ,O-dpkbh)]and [Mn (κ -N ,N ,O-dpkbh-H) ]·0.22H O are longer than the
2
py im
py im
2
2

12
M. BAꢀIR ANꢁ R. CONRꢂ
II
3
Figure 6. A view of the hydrogen bonds in the structure of [Mn Br (κ -N ,N ,O-dpkbh)] measured at 296 K.
2
py im
3
d(Mn–O) of 2.00Å observed in fac-[Mn(CO) (κ -N,O,N-dpkO,OH)] and other related compounds [27, 30]. The
3
average [O1–Mn1–N3] and [O1’–Mn1–N3’] bond angles of 71.67(4) and [N1-Mn1-N3] and [N1’–Mn1–
3
N3’] bond angles of 70.70(4)° in Mn(κ -N,N,O-dpkbh-H) ]·0.22H O are larger than the corresponding
2
2
II
3
[
O1–Mn1–N3] and [N1–Mn1–N3] bond angles [70.99(14) and 70.29(15)°, respectively] in [Mn Br (κ -
2
N ,N ,O-dpkbh)]. These results confirm the keto [(py) C═N–NH–(C═O)–C H ] coordination of dpkbh
py im
II
6
5
3
−
in [Mn Br (κ -N ,N ,O-dpkbh)] and the enol [(py) C≐N≐N≐(C≐O)-C H ] coordination of (dpkbh-H) in
2
py im
6
5
II
3
[
Mn (κ -N ,N ,O-dpkbh-H) ]·nX. ꢁeprotonation of the hydrazone backbone enhances delocalization
py im 2
II
3
of electron density on the chelating metallocyclic rings of [Mn (κ -N ,N ,O-dpkbh-H) ]·nX compared
py im
2
II
3
to [Mn Br (κ -N ,N ,O-dpkbh)] and may account in part for the variation in their bond distances and
2
py im
angles. The weak coordination of MnBr to dpkbh may have significant implications in C–C cross cou-
2
pling catalytic reactions. In previous reports, MnBr was utilized as an efficient catalyst in the Stille
2
reaction of aryl halides [36].
II
3
Views depicting selected hydrogen bonds within the solid state structures of [Mn Br (κ -N ,N ,O-
2
py im
II
3
II
3
dpkbh)], [Mn (κ -N ,N ,O-dpkbh-H) ]·0.22H O, and [Mn (κ -N ,N ,O-dpkbh-H) ]·dmso are shown
py im
2
2
py im
2
in figures 6 and 7. These views show stacks of molecules locked via a web of hydrogen bonds. The
II
3
II
3
neighboring molecules in the stacks of [Mn Br (κ -N ,N ,O-dpkbh)] and [Mn (κ -N ,N ,O-dpkbh-
2
py im
py im
II
3
H) ]·0.22H O are related by the c, 2 glide plane, and screw axis, respectively. In the case of [Mn (κ -
2
2
1/c
N ,N ,O-dpkbh-H) ]·dmso, neighboring molecules are related by the ī inversion operation. Bond
py im
2
distances and angles of the hydrogen bonds are similar to those observed in a variety of compounds
II
3
containing such bonds [27]. Analysis of solvent accessible voids in the structure of [Mn Br (κ -N ,N ,O-
2
py im
II
3
dpkbh)] and [Mn (κ -N ,N ,O-dpkbh-H) ]·dmso revealed zero void grid points in both and 67.6% and
py im
2
II
3
6
6.1% of filled space (packing index), respectively. In the case of [Mn (κ -N ,N ,O-dpkbh-H) ]·0.22H O,
py im 2 2
analysis of solvent accessible areas revealed that the unit cell contains no residual solvent accessible
II
3
voids. In the absence of lattice H O from [Mn (κ -N ,N ,O-dpkbh-H) ]·0.22H O, PLATON SQUEEZE rou-
2
py im
2
2
3
tine revealed that the volume of total potential solvent accessible voids is 76.8 Å per unit cell volume
3
3
of 3245.4 Å and the voids are distributed over four regions of 18 Å per void, each occupied by two
II
3
electrons. Solvent and cavity plots of [Mn (κ -N ,N ,O-dpkbh-H) ] show the voids are interconnected,
py im
2
hence they may accommodate a small molecule such as H O scattered between the voids. The residual
2
−
−3
electron density of 1.18 e Å at a non-bonding distance from the manganese complex disappeared
II
3
after implementation of PLATON SQUEEZE on [Mn (κ -N ,N ,O-dpkbh-H) ].
py im
2

1
3
II
3
II
3
Figure 7. Views of the hydrogen bonds in the structures of [Mn (κ -N ,N ,O-dpkbh-H) ]·0.22H O and [Mn (κ -N ,N ,O-dpkbh-
py im
2
2
py im
H) ]·dmso measured at 295.2 K.
2
4. Conclusion
Facile reactions occur between [Mn(CO) Br] and dpkbh in diethyl ether or CH CN in air to form fac-
5
3
I
2
II
3
II
3
[
Mn (CO) (κ -N ,N -dpkbh)Br]·H O, [Mn Br (κ -N ,N ,O-dpkbh)], and [Mn (κ -N ,N ,O-dpkbh-
3 py im 2 2 py im
py im
2
I
H) ]·0.5H O. The crystallization of fac-[Mn (CO) (κ -N ,N -dpkbh)Br]·H O from dmso and CH CN
to form [Mn (κ -N ,N ,O-dpkbh-H) ]·nX marks the first instance a κ -N,N-coordinated dpk-h rear-
ranges to κ -N,N,O-coordination. Spectroscopic and X-ray crystallographic results indicate weaker
coordination of neutral dpkbh and a stronger coordination of ionic (dpkbh-H) to Mn(II). Electronic
2
2
3
py im
2
3
II
3
2
py im
2
3
−
absorption spectral measurements in non-aqueous solvents point to enol coordination of dpkbh to
II
3
Mn(II) in [Mn (κ -N ,N ,O-dpkbh-H) ]·0.5H O and an equilibrium between the keto and enol forms
py im
2
2
I
2
of coordinated dpkbh in fac-[Mn (CO) (κ -N ,N -dpkbh)Br]·H O. X-ray crystallographic analyses of
3
py im
2

1
4
M. BAꢀIR ANꢁ R. CONRꢂ
3
II
II
3
[
Mn Br (κ -N ,N ,O-dpkbh)] and [Mn (κ -N ,N ,O-dpkbh-H) ]·nX confirmed the weak coordination
2 py im py im 2
−
of dpkbh and strong coordination of ionic (dpkbh-H) to Mn(II) in these complexes.
ue to their rich physicochemical properties and potential applications in several areas, further
ꢁ
studies are in progress in our laboratory to explore the coordination chemistry of a variety of di-2-
pyridyl ketone derivatives.
Acknowledgements
The authors acknowledge the University of the West Indies for financial support, ꢁr. Ishmael Hassan, Mr. Orain Brown,
ꢁr. Mark Lawrence and Mr. Orville Green for technical assistance, and the United States National Science Foundation for
support of the X-ray diffraction facility at Colby College.
Disclosure statement
No potential conflict of interest was reported by the authors.
References
[
[
[
1] L. Bravo-García, G. Barandika, B. Bazán, M.ꢀ. Urtiaga, M.I. Arriortua. Polyhedron, 92, 117 (2015).
2] H. Zhu, P. Chen, G. Liu. Org. Lett., 17, 1485 (2015).
3] V.M. Leovac, M.V. Rodić, L.S. Jovanović, M.ꢁ. Joksović, T. Stanojković, M. Vujčić, ꢁ. Sladić, V. Marković, L.S. Vojinović-
Ješić. Eur. J. Inorg. Chem., 2015, 882 (2015).
[
[
4] P.C. Souza, P.I.S. Maia, H.B. Barros, C.Q.F. Leite, V.M. ꢁeflon, F.R. Pavan. Curr. Clin. Pharmacol., 10, 66 (2015).
5] G. Marandi, L. Saghatforoush, V. Golsanamlou, E. Tofighjoo, F.A. Hassanabad, S. Hajari, R. Ghadimkhani. Res. Chem.
Intermediat., 41, 631 (2015).
[
[
[
[
6] ꢀ. Matelková, R. Boča, Ľ. ꢁlháň, R. Herchel, J. Moncol, I. Svoboda, A. Mašlejová. Polyhedron, 95, 45 (2015).
7] S. ꢁhers, H.L.C. Feltham, S. Brooker. Coord. Chem. Rev., 296, 24 (2015).
8] F. Trudu, F. Amato, P. Vaňhara, T. Pivetta, E.M. Peña-Méndez, J. Havel. J. Appl. Biomed., 13, 79 (2015).
9] A.ꢂ. Lukmantara, ꢁ.S. ꢀalinowski, N. ꢀumar, ꢁ.R. Richardson. J. Inorg. Biochem., 141, 43 (2014).
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
10] X.-ꢂ. Qiu, C. Zhang, S.-Z. Li, G.-X. Cao, P. Qu, F.-Q. Zhang, J.-G. Ma, B. Zhai. Inorg. Chem. Commun., 46, 202 (2014).
11] B. An, R.-M. Zhou, L. Sun, ꢂ. Bai, ꢁ.-B. ꢁang. Spectrochim. Acta, Part A, 128, 319 (2014).
12] A. Gaál, G. Orgován, Z. Polgári, A. Réti, V.G. Mihucz, S. Bősze, N. Szoboszlai, C. Streli. J. Inorg. Biochem., 130, 52 (2014).
13] J. Xiang, L.-L. Zhao, ꢂ. Luo, Z.-H. ꢂan, C.-H. Wang, J. Zhang, F. Zhou, P. Mei. Inorg. Chem. Commun., 30, 29 (2013).
14] M.N. Patel, B.S. Bhatt, P.A. ꢁosi. Inorg. Chem. Commun., 29, 190 (2013).
15] N.A. Mangalam, S.R. Sheeja, M.R.P. ꢀurup. Polyhedron, 29, 3318 (2010).
16] ꢀ. Latham, ꢀ.F. White, ꢀ.B. Szpakolski, C.J. Rix, J.M. White. Inorg. Chim. Acta, 362, 1872 (2009).
17] L.E.M. Vieira, F.P. Vieira, L.H.S. Ávila-Terra, I. Gaubeur, M. Guekezian, M.E.V. Suárez-Iha. Anal. Lett., 41, 779 (2008).
18] J.J. Pinto, M. García-Vargas, C. Moreno. Talanta, 103, 161 (2013).
19] P.V. Bernhardt, P.C. Sharpe, M. Islam, ꢁ.B. Lovejoy, ꢁ.S. ꢀalinowski, ꢁ.R. Richardson. J. Med. Chem., 52, 407 (2009).
20] A. Sreekanth, S. Sivakumar, M.R. Prathapachandra ꢀurup. J. Mol. Struct., 655, 47 (2003).
21] C.ꢂ. ꢁuan, B.M. Wu, T.C.W. Mak. J. Chem. Soc., Dalton Trans., 3485 (1996).
22] M. Bakir, O. Brown. J. Mol. Struct., 609, 129 (2002).
23] M. Bakir, O. Brown. Inorg. Chim. Acta, 353, 89 (2003).
24] M. Bakir, O. Brown, T. Johnson. J. Mol. Struct., 691, 265 (2004).
25] M. Bakir, O. Green, W.H. Mulder. J. Mol. Struct., 873, 17 (2008).
26] M. Bakir, R.R. Conry, ꢁ. Thomas. J. Coord. Chem., 67, 249 (2014).
27] M. Bakir, O. Green, M. Wilmot-Singh. J. Mol. Struct., 967, 174 (2010).
28] M. Bakir, J.A.M. A. M. Mcꢀenzie. J. Chem. Soc., Dalton Trans., 3571 (1997).
29] M. Bakir, M.A.W. Lawrence, S. McBean. Spectrochim. Acta, Part A, 146, 323 (2015).
30] M. Bakir, I. Hassan, O. Green. J. Mol. Struct., 657, 57 (2003).
31] Bruker-SHELXTL. Software Version 5.1., Bruker AXS, Inc., Madison, Wisconsin, USA (1997).
32] G.M. Sheldrick. SHELX97 and SHELXL97, University of Göttingen, Göttingen, Germany (1997).
33] G.M. Sheldrick, Shelx version 2014/7. http://shelx.uni-ac.gwdg.de/SHELX/index.php.
34] A.L. Spek. J. Appl. Cryst., 36, 7 (2003).
35] A.W. Addison, T.N. Rao, J. Reedijk, J.V. van Rijn, G.C. Verschoor. J. Chem. Soc., Dalton Trans., 1349 (1984).
36] T. ꢀluge, E. Bette, M. Bette, J. Schmidt, ꢁ. Steinborn. J. Organomet. Chem., 762, 48 (2014).