Iron and cobalt complexes of 2,6-diacetylpyridine-bis(R-thiosemicarbazone) (R = H, phenyl) showing unprecedented ligand deviation from planarity

Article abstract of DOI:10.1016/j.ica.2008.06.031

The syntheses, characterization, and single-crystal X-ray crystal structures are reported for four complexes of iron and cobalt with the pentadentate ligands, 2,6-diacetylpyridinebis(thiosemicarbazone) (H₂L¹) and 2,6-diacetylpyridine

Full text of DOI:10.1016/j.ica.2008.06.031

Inorganica Chimica Acta 362 (2009) 1348–1354
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Inorganica Chimica Acta
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Iron and cobalt complexes of 2,6-diacetylpyridine-bis(R-thiosemicarbazone)
(R = H, phenyl) showing unprecedented ligand deviation from planarity
Anangamohan Panja a, Charles Campana b, Christopher Leavitt a, Michael J. Van Stipdonk a,
David M. Eichhorn a,
*
a Department of Chemistry, Wichita State University, Wichita, KS 67260, USA
b Bruker-AXS, Madison, WI, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The syntheses, characterization, and single-crystal X-ray crystal structures are reported for four com-
plexes of iron and cobalt with the pentadentate ligands, 2,6-diacetylpyridinebis(thiosemicarbazone)
(H2L1) and 2,6-diacetylpyridinebis(phenylthiosemicarbazone) (H2L2), including a cobalt dimer displaying
a deviation from planarity which is unprecedented for this class of ligands and allows the ligand to
occupy five positions of a pseudo-octahedral coordination sphere. This dimer reacts with KCN to produce
a mononuclear complex of relevance to the active site of cobalt nitrile hydratase.
Received 1 February 2008
Received in revised form 23 June 2008
Accepted 24 June 2008
Available online 3 July 2008
Keywords:
Ó 2008 Elsevier B.V. All rights reserved.
Iron complexes
Cobalt complexes
X-ray crystal structures
Nitrile hydratase
1. Introduction
With an eye on synthesizing model complexes for the active site
of the nitrile hydratase enzymes, which have a N2S3 donor set [9],
Thiosemicarbazone ligands, derived from the combination of a
thiosemicarbazide and an aldehyde or ketone, are a useful ligand
type for obtaining coordination spheres with mixed N/S donors.
Interest in these ligands has been driven, in part, by p’otentially
beneficial biological activity of the ligands and their metal com-
plexes, including antitumor [1], fungicidal [2], bactericidal [3],
and antiviral [4] activity. Our continued interest in synthesizing
model complexes for the active sites of metalloenzymes with
mixed N/S coordination spheres [5], such as nitrile hydratase [6]
and the A-cluster of carbon monoxide dehydrogenase/acetyl coen-
zyme A synthase [7], has led us to investigate metal complexes of
this class of ligands.
we have focused on Fe and Co complexes of pentadentate bis(thi-
osemicarbazone) ligands synthesized by the condensation of two
equivalents of a thiosemicarbazide with a dialdehyde or diketone
bearing a potential coordinating atom. In particular, we have em-
ployed thiofuran-2,5-dicarboxaldehyde and 2,6-diacetylpyridine –
complexes of ligands derived from the latter are described herein.
Although not as intensely studied as the monothiosemicarbazones,
the bis(thiosemicarbazones) have been the subject of a number of
investigations, with some indication of biological activity on the
part of these ligands and their metal complexes [10]. A search of
the Cambridge Crystallographic Database [8] for transition metal
complexes of bis(thiosemicarbazone) ligands derived from 2,6-
diacetylpyridine yields 13 structures including mononuclear
[3a,11], dinuclear [11a,11d,12], and tetranuclear [12c] species
and a total of seven different structural types (Fig. 2), indicating
the coordinative flexibility of this class of ligands. We have found
that the isolated crystalline material is highly dependent on the
semicarbazide substituent and the metal salt used to synthesize
the complex.
Coordination of the thiosemicarbazone ligand is generally
through the azomethine N atom and the S atom. The ligand can
bind either as the neutral species or monodeprotonated (Fig. 1).
Crystallographically, this difference can generally be monitored
by the length of the C–S bond; the neutral ligand contains a formal
0
C–S double bond with bond lengths on the order of 1.67–1.72 ÅA
while the deprotonated ligand undergoes tautomerization to pro-
duce a formal C–S single bond with bond lengths on the order of
0
1.71–1.80 ÅA [8].
2. Experimental
2.1. General
Unless otherwise stated, all solvents and reagents were used as
received from Aldrich, Acros, and Fisher Scientific without further
* Corresponding author. Tel.: +1 316 978 7367; fax: +1 316 978 3431.
E-mail address: david.eichhorn@wichita.edu (D.M. Eichhorn).
0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2008.06.031

A. Panja et al. / Inorganica Chimica Acta 362 (2009) 1348–1354
1349
2.3. 2,6-Diacetylpyridinebis(phenylthiosemicarbazone)(chloro)-
(methanol)iron(II) chloride [H2L2Fe(MeOH)(Cl)]Cl (2)
Under a nitrogen atmosphere, 115 mg (0.25 mmol) of 2,6-diace-
tylpyridinebis(phenylthiosemicarbazone) and 41 mg (0.25 mmol)
of anhydrous FeCl3 were combined in 40 mL of dry methanol to
give a green solution. The volume was reduced to 10 mL and upon
standing at room temperature gave a green microcrystalline pre-
cipitate of 2 (108 mg, 0.175 mmol, 70%). X-ray quality crystals
were grown by slow evaporation of a solution in 50/50 metha-
nol/acetonitrile. Elem. Anal. Calc. for C24H27N7S2Cl2OFe: C, 46.47;
H, 4.39; N, 15.81. Found: C, 46.28; H, 4.12; N, 16.00%. E-chem:
E1/2 = 75 mV ðEcp ꢁ Epa ¼ 210 mVÞ, irr. waves at 1000 mV,
Fig. 1. Thiosemicarbazone ligands showing the common bonding modes of the
neutral and anionic ligand.
ꢁ1270 mV. UV–Vis, nm (
e): 252 (70500), 343 (45200), 753 (sh,
400). Mass Spec. (positive mode): 585/587 (M+).
2.4. Bis(2-acetylphenylthiosemicarbazone-6-acetylpyridine)iron(III)
0
perchlorate [(L2 )2Fe]ClO4 (3)
To 60 mL of methanol was added 230 mg (0.50 mmol) of 2,6-
diacetylpyridinebis(phenylthiosemicarbazone)
and
230 mg
(0.50 mmol) of Fe(ClO4)3, giving rise to a brown precipitate which
was washed with methanol and diethyl ether to give 300 mg
(0.30 mmol, 60%) of 3 as a brown powder. X-ray quality crystals
were grown by slow cooling of a DMF solution. IR (KBr pellet,
cmꢁ1): 3420br, 3079w, 1713m, 1598m, 1549m, 1507vs, 1458m,
1441s, 1399m, 1364m, 1318m, 1192w, 1158m, 1115s, 810m,
747m, 691m, 622m, 584w, 505w. Elem. Anal. Calc. for (C32H30N8O2-
Fe)ClO4 ꢀ H2O: C, 48.29; H, 4.05; N, 14.08. Found: C, 47.75; H, 3.89;
N, 14.30%. E-chem: E1/2 = 0.0 mV ðEc ꢁ Ea ¼ 78 mVÞ. UV–Vis, nm
Fig. 2. Mercury drawings downloaded from the Cambridge Crystallographic
Database [8] for structures from references [11a,11c,11e] and [12a–c] representing
the seven structural types in the literature for 2,6-diacetylpyridinebis(thiosemicar-
bazone) complexes and indicating the metals for which structures have been
reported.
p
p
(e): 226 (246500), 390 (30600), 669 (240), 850 (sh, 220). Mass
spec.: 678 (M+).
purification. 2,6-Diacetylpyridinebis(thiosemicarbazone) [10]
(H2L1) and 2,6-diacetylpyridinebis(phenylthiosemicarbazone)
[13] (H2L2) were synthesized as previously described. IR spectra
were recorded on a Nicolet Avatar 360 FTIR. Electrochemical char-
acterization was performed in acetonitrile with [NEt4ClO4] as sup-
porting electrolyte using a PAR 263A potentiostat/galvanostat with
a Pt disk working electrode and a Ag/AgCl reference electrode.
Potentials are quoted with respect to Ag/AgCl. UV/Visible spectra
were obtained using a Hitachi U-2010 spectometer. Mass spectra
were obtained on a Varian 1200 LC/MS using ESI ionization tech-
nique. Conductivity measurements were made with a Systronics
(India) direct reading conductivity meter (model 304) and mag-
netic susceptibility measurements were carried out on a PAR 155
vibrating sample magnetometer. The data were corrected for dia-
magnetic susceptibilities using Pascal’s constants. Elemental anal-
yses were obtained from M-H-W Laboratories, Phoenix, AZ.
2.5. Bis[2,6-diacetylpyridinebis(thiosemicarbazone)
(acetonitrile)cobalt(II)] perchlorate [H2L1Co(CH3CN)]2(ClO4)4 (4)
To 50 mL of methanol was added 155 mg (0.50 mmol) of 2,6-
diacetylpyridinebis(thiosemicarbazone) and 180 mg (0.50 mmol)
of Co(ClO4)2. The mixture was heated for 1 h, giving rise to a
brownish-orange solution. The resulting mixture was reduced to
10 mL and upon sitting at room temperature, 210 mg (0.175 mmol,
70%) of 4 was isolated as a dark orange crystalline material. X-ray
quality crystals were grown by slow evaporation of a solution in
acetonitrile/methanol. IR (KBr pellet, cmꢁ1): 3417br, 1617s,
1558m, 1472w, 1384w, 1307w, 1274w, 1193m, 1121vs, 1108vs,
1083vs, 1031s, 625s, 521s. Elem. Anal. Calc. for (C26H36N16S4Co2)
(ClO4)4: C, 25.67; H, 2.98; N, 18.42. Found: C, 26.17; H, 3.35; N,
17.60%. E-chem: irr. waves at ꢁ580 mV and ꢁ1440 mV. UV–Vis,
nm (
multiplets at 1113 [M(ClO4)3]+, 1073 [(M–CH3CN)(ClO4)3]+, 1032
[(M–2CH3CN)(ClO4)3]+, 466.5 [(M–2CH3CN)(ClO4)2]2+
e): 320 (43500), 447 (sh, 13000). Mass spec. (positive mode):
2.2. 2,6-Diacetylpyridinebis(thiosemicarbazone)dichloro iron(III)
.
chloride [H2L1FeCl2]Cl (1)
2.6. Bis[2,6-diacetylpyridinebis(phenylthiosemicarbazone) cobalt(III)]
In 50 mL of methanol were combined 155 mg (0.50 mmol) of
H2L1 and 135 mg (0.50 mmol) of FeCl3 ꢀ 2.5H2O The mixture was
heated at reflux for 1 h, resulting in a greenish-brown crystalline
precipitate which was isolated and washed with methanol and
diethyl ether to give 215 mg (0.41 mmol, 82%) of 1 as a greenish-
brown crystalline material. X-ray quality crystals were grown by
slow evaporation of a methanol solution. IR (KBr pellet, cmꢁ1):
3314s, 3255s, 3127s, 2907m, 1602vs, 1552vs, 1464m, 1403m,
1366m, 1191s, 1107m, 815w, 799w, 599w. Elem. Anal. Calc. for
C11H15N7FeCl3 ꢀ 3H2O: C, 25.14; H, 4.03; N, 18.66. Found: C,
25.00; H, 3.87; N, 18.70%. E-chem: irr. wave at ꢁ960 mV. UV–Vis,
nitrate [L2Co]2(NO3)2 (5)
To 50 mL of methanol were added 230 mg (0.50 mmol) of 2,6-
diacetylpyridinebis(phenylthiosemicarbazone)
and
150 mg
(0.50 mmol) of Co(NO3)2. The mixture was heated at reflux for
1 h and reduction of the volume to 10 mL gave 255 mg (0.21 mmol,
84%) of 5 as a brown powder. X-ray quality crystals were grown by
slow evaporation of a solution in 50/50 methanol/acetonitrile. IR
(KBr pellet, cmꢁ1): 3425br, 1652m, 1616m, 1581m, 1539s,
1496m, 1441m, 1384vs, 1318m, 1253m, 1194m, 1155m, 1120m,
811w, 753m, 691m, 578w, 498w. Elem. Anal. Calc. for
(C46H42N14S4Co2)(NO3)2 ꢀ 2H2O: C, 46.16; H, 3.87; N, 18.72. Found:
C, 46.35; H, 3.65; N, 19.00%. E-chem: irr. wave at ꢁ800 mV. UV–Vis,
nm (
e): 238 (262800), 319 (67700), 718 (246). Mass Spec. (positive
mode): 363 [M–2HCl]+.

1350
A. Panja et al. / Inorganica Chimica Acta 362 (2009) 1348–1354
nm (
e
): 388 (32700), 257 (74000), 205 (134800). Mass spec. (po-
were refined using anisotropic thermal parameters. Pertinent de-
tails are given in Table 1.
sitive mode): 1035 [M–H]+.
2.7. (2,6-Diacetylpyridinebis(phenylthiosemicarbazone))cyano-
3. Results and discussion
cobalt(III) [L2Co(CN)] (6)
Two ligands were employed in this study, both derived from the
condensation of two equivalents of a thiosemicarbazide with 2,6-
diacetyl pyridine – L1 employs unsubstituted thiosemicarbazide
and L2 has a phenyl group substituted on the terminal N atoms.
To 40 mL of methanol were added 150 mg (0.125 mmol) of 5
and 20 mg (0.25 mmol) of KCN. The mixture was stirred overnight
and the solvent was removed. The resulting brown solid was
washed with water and dried to yield 110 mg (0.19 mmol, 78%)
of 6 as a brown solid. IR (KBr pellet, cmꢁ1): 3470br, 3068w,
2122m, 1598s, 1495vs, 1460s, 1439vs, 1402s, 1371m, 1318m,
1253m, 1160m, 1090m, 807w, 753m, 692m, 503w. Elem. Anal. Calc.
for C24H21N8S2Co ꢀ H2O: C, 51.25; H, 4.12; N, 19.92. Found: C,
51.28; H, 3.60; N, 19.82%. E-chem: irr. wave at ꢁ1130 mV. UV–
3.1. Iron chemistry
Using the unsubstituted ligand and FeCl3, we isolated the
mononuclear Fe(III) complex [H2L1FeCl2]Cl (1). Room temperature
magnetic susceptibility and conductivity measurements (Table 4)
are consistent with this formulation. An ORTEP drawing of the cat-
ion in 1 is shown in Fig. 3, with data collection and structure solu-
tion parameters in Table 1 and selected bond distances and angles
in Tables 2 and 3. The complex sits on a general position in the
orthorhombic space group Pbca and crystallizes with three water
molecules in the asymmetric unit. The structure is of type I, with
pentagonal bipyramidal coordination around the Fe(III); the five
donor atoms of the essentially planar ligand comprise the equato-
rial pentagonal plane and two chloride ligands are in the axial posi-
tions. The chloride counterion is involved in a hydrogen bond with
Vis, nm (e): 207 (137000), 260 (133000), 381 (57000). Mass spec.
(positive mode): 518 [M–CN]+.
2.8. X-ray crystallography
Data for 1 were collected using a Bruker APEX diffractometer
(Cu K
perature apparatus. Data for 2–5 were collected using a Bruker
Kappa APEXII diffractometer (Mo K , k = 0.71069 Å) equipped with
a, k = 1.54178 Å) equipped with Bruker KRYO-FLEX low-tem-
a
an Oxford Cryosystems Cryostream 700 low-temperature appara-
tus. Suitable crystals were identified under a polarizing microscope
and affixed with oil in a Hampton Research Cryoloop and trans-
ferred to the coldstream of the diffractometer. Data reduction
was performed using Bruker SAINT [14] software, structure solution
(direct methods) and refinement (full-matrix least-squares) using
SHELXS-97 and SHELXL-97 [15] within the Bruker SHELXTL suite. Data
were corrected for Lorentz and polarization effects and for absorp-
tion using the Bruker SADABS [14] program (multiscan for 1, face
indexing for 2–5). Hydrogen atoms were placed at calculated ide-
alized positions and were not refined. All non-hydrogen atoms
Table 1
X-ray data collection and structure solution parameters for 1–5
1
2
3
4
5
Formula
Mol. wt.
C11H21N7O3S2Cl3Fe
525.67
C24H27N7OS2Cl2Fe
620.40
C41H51N11O9S2ClFe
997.34
C26H36N16Cl4Co2O16S4
1216.60
C46H46N16Co2O8S4
1197.07
Color
Habit
brown
block
green
block
dark
block
dark orange
block
dark red
block
Temperature (K)
Diffractometer
Crystal System
Radiation
100
Bruker APEX
orthorhombic
Cu K
Pbca
150
150
150
150
Bruker K-APEXII
monoclinic
Mo K
Bruker K-APEXII
monoclinic
Mo K
Bruker K-APEXII
triclinic
Bruker K-APEXII
monoclinic
Mo Ka
a
a
a
Mo K
a
ꢀ
Space group
P21/n
P2/c
P1
C2/c
0
a (AÅ)
12.6799(4)
14.2998(5)
22.3519(7)
90
90
90
4052.8(2)
8
1.723
13.146(5)
11.186(5)
19.496(5)
90
108.910(5)
90
2712.2(17)
4
1.519
14.545(5)
10.644(5)
14.951(5)
90
94.010(5)
90
2309.0(16)
2
1.434
8.588(5)
25.241(5)
16.298(5)
13.478(5)
90
112.246(5)
90
5132(3)
2
1.544
0.879
0
b (AÅ)
12.079(5)
12.741(5)
62.893(5)
71.769(5)
81.909(5)
1117.4(9)
1
0
c (AÅ)
a
(°)
b (°)
c
(°)
0
V (AÅ3)
Z
Dcalc (g cmꢁ3
)
1.808
1.254
l
(mmꢁ1
)
11.801
0. 940
0.540
F(000)
2152
1280
1024
618
2448
Dimension (mm)
h Range (°)
Reflections/unique (Riint
>2r(I)/parameters
.09 ꢂ .09 ꢂ .02
3.96–63.76
35986/3144 (0.0428)
2520/263
93.9
0.18 ꢂ 0.30 ꢂ 0.38
1.65–26.72
52125/5747 (0.0590)
4202/353
99.8
.20 ꢂ .20 ꢂ .20
1.40–26.54
37759/4752 (0.0957)
3460/305
98.5
.30 ꢂ .28 ꢂ .18
1.87–27.14
45929/4874 (0.0615)
3433/360
98.5
.38 ꢂ .20 ꢂ .10
1.52–23.64
36047/3828 (0.1090)
2396/345
99.2
)
Completeness to hmax
Goodness-of-fit
1.028
1.099
1.065
0.953
1.035
R1/wR2 (I > 2
R1/wR2 (all)
Ext. Coefficient
Peak/hole (eÅꢁ3
r
(I))
0.0389/0.0980
0.0535/0.1072
none
0.951/ꢁ0.337
0.0401/0.1039
0.0626/0.1182
none
0.472/ꢁ0.348
0.0592/0.1778
0.0811/0.1913
0.0012(10)
0.650/ꢁ0.457
0.0580/0.1651
0.0897/0.1915
none
1.145/ꢁ0.990
0.0538/0.1302
0.1095/0.1684
none
0.557/ꢁ0.653
)

A. Panja et al. / Inorganica Chimica Acta 362 (2009) 1348–1354
1351
including Zn [11a], Fe [11c], and Mn [11b,11d]. The Zn, Fe, and
one of the Mn structures are entirely analogous to that of 1, with
a neutral unsubstituted ligand and two anionic ligands in the axial
positions, while the structure of [LMn(EtOH)2] has the ligand dou-
bly deprotonated with two neutral ethanol ligands in the axial
positions. Interestingly, in the mass spectrum, the only detectable
ion corresponds to a loss of two molecules of HCl, i.e., double
deprotonation of the ligand to produce the [L1Fe]+ ion. The extent
of planarity of the ligand can be defined by the dihedral angles be-
tween two planes: (i) the plane of the three coordinated N atoms
and (ii) the plane containing the metal, a coordinated S atom,
and the coordinated N atom nearest to it. All of the previous struc-
tures, along with that of 1, feature relatively planar ligands, with
dihedral angles ranging from 0.72° to 11.30°. In 1, these dihedral
angles are both equal to 1.00° giving the most planar ligand of all
reported complexes of this type.
When the phenyl-substituted ligand L2 was employed, a mono-
nuclear complex was also isolated, but crystallographic character-
ization (confirmed by elemental analysis) unexpectedly identified
it as an Fe(II) complex, although the reductant has not been iden-
tified. It should be noted that [H2L1FeII(SCN)2] was also prepared by
reaction of H2L1 with FeCl3 [11c]. An ORTEP drawing of [H2L2Fe
(MeOH)(Cl)]Cl (2) is shown in Fig. 4, with data collection and struc-
ture solution parameters in Table 1 and selected bond distances
and angles in Tables 2 and 3. Also displaying type I, the molecule
sits on a general position in the monoclinic space group P21/n with
the methanol ligand engaging in0hydrogen bonding with the chlo-
ride counterion (Cl2ꢀ ꢀ ꢀO1 3.104 AÅ). Both the coordinated and non-
coordinated Cl’s also form hydrogen bonds with the two N atoms
bound to the C–S moiety, giving rise to a chain of Fe molecules held
Fig. 3. ORTEP drawing of the cation in 1, showing 50% ellipsoids. H atoms omitted
for clarity.
0
one terminal amine (Cl3ꢀ ꢀ ꢀN7 3.240 ÅA). A hydrogen bonding net-
work involving all three water molecules links the Fe-containing
cations together. Bond lengths are within the 0 normal range for
Fe(III) and the Fe–S bonds (2.494 and 2.529 ÅA) and C–S bonds
0
(1.685 and 1.687 ÅA) are consistent with a neutral ligand containing
C–S double bonds.
The structure of 1 is similar to others that have been reported
for mononuclear complexes of divalent transition metal ions,
together by hydrogen bonding. Bond lengths are within the normal
range for Fe(II) and the Fe–S bonds (2.581 and 2.668 ÅA) and C–S
0
Table 2
0
Selected bond distances (AÅ) for 1–5
1
2
3
M–S bonds
Fe(1)–S(1)
Fe(1)–S(2)
Fe(1)–N(4)
Fe(1)–N(5)
Fe(1)–N(3)
2.5292(10)
2.4934(10)
2.184(3)
2.254(3)
2.295(3)
Fe(1)–S(1)
Fe(1)–S(2)
Fe(1)–N(4)
Fe(1)–N(3)
Fe(1)–N(5)
2.5806(11)
2.6678(9)
2.224(2)
2.286(2)
2.310(2)
Fe(1)–S(1)
2.2025(12)
M–Npy bonds
M–Naxo bonds
Fe(1)–N(2)
Fe(1)–N(1)
1.925(3)
2.036(3)
4
5
M–S bonds
Co(1)–S(2)
Co(1)–S(1)
Co(1)–S(10)
Co(1)–N(4)
Co(1)–N(5)
Co(1)–N(3)
2.525(2)
2.592(2)
2.629(2)
2.160(3)
2.253(4)
2.278(4)
Co(1)–S(1)
Co(1)–S(2)
Co(1)–S(20)
Co(1)–N(4)
Co(1)–N(3)
Co(1)–N(5)
2.292(2)
2.227(2)
2.300(2)
1.845(4)
1.903(4)
1.887(4)
M–Npy bonds
M–Naxo bonds
Table 3
Selected bond angles (°) for 1–5
1
2
3
N(4)–Fe(1)–N(3)
N(4)–Fe(1)–S(1)
N(3)–Fe(1)–S(1)
S(2)–Fe(1)–S(1)
Cl(1)–Fe(1)–Cl(2)
70.43(10)
144.00(8)
73.59(7)
70.47(3)
168.09(4)
N(4)–Fe(1)–N(3)
69.79(8)
144.02(6)
74.25(6)
75.21(3)
174.78(5)
N(2)–Fe(1)–N(1)
N(2)–Fe(1)–S(1)
N(1)–Fe(1)–S(1)
N(10)–Fe(1)–S(1)
N(20)–Fe(1)–S(1)
S(10)–Fe(1)–S(1)
79.95(11)
84.91(9)
163.16(8)
91.10(9)
87.94(9)
95.70(6)
N(4)–Fe(1)–S(1)
N(3)–Fe(1)–S(1)
S(1)–Fe(1)–S(2)
O(1)–Fe(1)–Cl(1)
4
5
N(4)–Co(1)–N(3)
N(4)–Co(1)–S(1)
N(3)–Co(1)–S(2)
S(2)–Co(1)–S(1)
N(8)–Co(1)–S(10)
S(1)–Co(1)–S(10)
70.65(14)
141.70(11)
142.98(11)
73.37(5)
171.20(11)
84.15(4)
N(4)–Co(1)–N(5)
N(4)–Co(1)–N(3)
N(5)–Co(1)–S(2)
S(2)–Co(1)–S(1)
S(2)–Co(1)–S(20)
82.28(18)
80.90(18)
86.07(13)
84.60(6)
84.87(6)
N(4)–Co(1)–S(1)
N(5)–Co(1)–S(1)
N(3)–Co(1)–S(1)
N(3)–Co(1)–S(2)
S(1)–Co(1)–S(20)
103.71(15)
103.29(14)
75.85(15)
111.17(14)
157.35(6)

1352
A. Panja et al. / Inorganica Chimica Acta 362 (2009) 1348–1354
Table 4
and angles in Tables 2 and 3. The complex sits on a twofold axis
in the monoclinic space group P2/c and crystallizes with two mol-
ecules of DMF, one of which is disordered. Each ligand maintains
the intact thiosemicarbazone on one side of the pyridine ring,
but has been hydrolyzed on the other side to reform the ketone
functionality. The ligand acts in a tridentate manner with coordi-
nation through the pyridine and azomethine N atoms and the S
atom. Two ligands complete the octahedral coordination environ-
Room temperature magnetic moments and molar conductivity data
Complex Magnetic moment per nucleus
(B.M.)
Molar conductivity
ꢁ1 cm2 molꢁ1
(
X
)
1
3
4
5
6
5.85
5.95
4.70
diamagnetic
diamagnetic
90 (1:1)
77 (1:1)
285 (1:4)
148 (1:2)
0
0
8 (non-electrolyte)
ment of the Fe(III) complex. Fe–S (2.203 ÅA) and C–S (1.751 ÅA) bonds
in this case are consistent with a monodeprotonated ligand. The
ordered DMF molecule forms a hydrogen bond with an N–H group
on the Fe complex. Infrared spectra clearly show stretches for both
the imine (m m
CN = 1598 cmꢁ1) and ketone ( CO = 1713 cmꢁ1) func-
tionalities, confirming the ligand hydrolysis.
3.2. Cobalt chemistry
While the iron chemistry of these ligands leads to the isolation
of mononuclear species, the chemistry with cobalt is dominated by
dinuclear species. Two different dinuclear species were isolated
depending, once again, on the particulars of the ligand substituents
and the cobalt salt.
Using the unsubstituted ligand in combination with Co(ClO4)2,
the Co(II) complex {[H2L1Co(CH3CN)]2}(ClO4)4 (4) is isolated. Mag-
netic susceptibility measurements are consistent with previous re-
ports of significant orbital contributions to high-spin Co(II)
complexes, which yield magnetic moments in the 4.7–5.2 B.M.
range [17]. Conductivity measurements are consistent with a 1:4
electrolyte. An ORTEP drawing of the cation in 4 is shown in Fig
6, with data collection and structure solution parameters in Table
1 and selected bond distances and angles in Tables 2 and 3. The di-
meric molecule displays structure type V, and is situated on an
Fig. 4. ORTEP drawing of 2, showing 50% ellipsoids. H atoms omitted for clarity. The
thin line between Cl(2) and O(1) indicates the hydrogen bonding interaction.
0
bonds (1.668 and 1.676 ÅA) are again consistent with a neutral li-
gand with a C–S double bond. Once again, the ligand in 2 is very
planar, with dihedral angles involving the planes described above
of 10.8° and 3.06°.
A seemingly trivial change involving a switch from FeCl3 to Fe
(ClO4)3 resulted in a surprising result. The only complex that could
be isolated was found to be one in which the ligand had been par-
tially hydrolyzed. There is precedence for the hydrolysis of one side
of a 2,6-pyridinebis(imine) ligand [16]. Magnetic susceptibility and
conductivity measurements are consistent with an S = 5/2 species
ꢀ
inversion center in the triclinic space group P1. Each Co atom in
4 is in a pentagonal bipyramidal coordination geometry, similar
to the Fe atom in 1, with the pentadentate ligand occupying the
equatorial pentagonal plane. One axial position is occupied by an
CH3CN ligand, while the second axial position is filled by a sulfur
atom from the centrosymmetrically related ligand. Until recently,
this structural type had not been reported for a complex of a
bis(thiosemicarbazone) ligand, but Souza and coworkers reported
a similar Zn complex in 2005.[12a] Unlike the Zn dimer, 4 exhibits
a symmetric Co2S2 core, with bond lengths between Co and the two
and
a 1:1 electrolyte. An ORTEP drawing of the cation in
0
[(L2 )2Fe]ClO4 (3) is shown in Fig. 5, with data collection and struc-
ture solution parameters in Table 1 and selected bond distances
Fig. 5. ORTEP drawing of the cation in 3, showing 50% ellipsoids. H atoms omitted
Fig. 6. ORTEP drawing of the cation in 4, showing 50% ellipsoids. H atoms omitted
for clarity.
for clarity.

A. Panja et al. / Inorganica Chimica Acta 362 (2009) 1348–1354
1353
0
bridging sulfur atoms of 2.604 and 2.605 ÅA.0 Bond lengths to the
rotation about the N(2)–N(3) bond such that the torsional angle
C(8)–N(3)–N(2)–C(7) is 54° (compared with 6° on the other arm
of the ligand). The result is that the carbamate portion on one side
of the ligand is almost perpendicular to the rest of the ligand. Using
the interplanar dihedral angle measurement defined earlier, 5
shows, by far, the largest such angle, 72.48°, of any reported struc-
ture involving this class of ligand, especially in those complexes
where all five donor atoms are coordinated to the same metal.
The resulting coordination geometry still deviates significantly
from octahedral symmetry, most notably in that the non-bridging
thiolate is tilted towards the open end of the ligand, such that the
‘‘trans” S(1)–Co(1)–S(20) angle is only 157°. The geometry of the
non-bridging sulfur atom are shorter (2.526 ÅA), as expected. These
0
Co–S bond lengths and the C–S bond lengths (1.676 and 1.708 ÅA)
are consistent with a C–S double bond and a neutral ligand. The li-
gand in 4 is still quite planar, but shows a slight helical twist, with
0
the non-bridging thiolate situated 0.333 ÅA above the plane defined
by the Co and the three coordinated N atoms and the bridging thio-
0
late situated 0.506 ÅA below this plane, towards the other Co. One
perchlorate is ordered, while the other has been modeled with
one full occupancy O atom and six partially occupied O sites. The
disordered perchlorate forms hydrogen bonds to the Co dimer, pro-
ducing a chain of dimers.
A second type of dimer is isolated when the phenyl-substituted
ligand is treated with Co(NO3)2. An ORTEP drawing of the cation in
the Co(III) complex [L2Co]2(NO3)2 (5) is shown in Fig. 7 with data
collection and structure solution parameters in Table 1 and se-
lected bond distances and angles in Tables 2 and 3. The dimer is sit-
uated on a twofold axis in the monoclinic space group C2/c and
crystallizes with two water molecules per dimer. One water mole-
cule and the nitrate counterion are involved in hydrogen bonds
with each other and with the Co dimer. Each Co ion is in a distorted
octahedral coordination sphere with the five donor atoms of one
dianionic ligand and a S from the symmetrically related ligand pro-
viding the ligation. This is the first example of a ligand of this type
occupying five positions in an octahedral coordination sphere. In
order to form this compound, the normally planar ligand must
deviate from planarity to an extent not previously observed. This
deviation is manifest in two areas. The first, less drastic deviation,
is a slight bending of one side of the ligand from planarity. Thus, if
one defines a plane containing Co, the pyridine N atom N(4) and
Co2S2 core is more asymmetric than that in 4, with a bond length
0
of 2.226 ÅA to the thiolate from the same ligand (Co(1)–S(2)) and
0
2.300 ÅA to the thiolate from the opposing ligand (Co(1)–S(20)).
The difficulty with which this ligand wraps around an octahedral
geometry is further manifest in the relatively long bond distance
0
between Co and the terminal thiolate (Co(1)–S(1) 2.292 ÅA. All of
the Co–S and C–S bond distances, however, are consistent with
the ligand being in the deprotonated form.
Compound 5 thus represents a new structural type for this class
of ligands. It is similar to three other dimeric species which have
been synthesized as precursors to models for the active site of co-
balt-containing nitrile hydratase. Mascharak and coworkers have
2ꢁ
published the synthesis and characterization of ½CoPyPSꢃ2 with
a tetraanionic pentadentate N3S2 ligand utilizing one pyridine
and two amide nitrogen donors and two thiolate sulfur donors
2þ
[18]. We have synthesized ½CoðtsaltpÞꢃ2 and a related dimer, both
with N2S3 ligands containing two imine nitrogen donors, two thio-
late sulfur donors, and one thioether sulfur donor [5b,19]. The
2ꢁ
C(8) and C(9), one finds that the coordinated azomethine N atom
geometry of 5 is very similar to that of ½CoPyPSꢃ2 with the three
0
N(3) is 0.14 ÅA out of the plane and the carbamate N atom N(2) is
backbone donor atoms (pyridine N and two amide or azomethine
N) spanning the meridian of the octahedral coordination sphere,
one thiolate S occupying an axial site and the other thiolate S in
the same plane of the backbone donors and bridging to the other
0
0.61 ÅA out of the plane. This compares with N(5) and N(6) on the
0
other side of the ligand, both of which are only 0.04 ÅA out of the
analogous plane. The second deviation is much more severe – a
2þ
Co atom. ½CoðtsaltpÞꢃ2 differs in that the backbone donors (one
thioether S and two imine N) occupy one trigonal face.
The two Co dimers, 4 and 5, show very different electrochemical
responses. The pentagonal bipyramidal dimer 4 has a pseudo-
reversible couple at ꢁ475 mV versus Ag/AgCl, likely corresponding
to a CoIII/II couple and an irreversible couple at ꢁ1440 mV, which is
in the range that has been seen for CoII/I couples in related com-
plexes [20]. The pseudo-octahedral dimer 5, on the other hand,
shows only an irreversible CoIII/II couple at ca. ꢁ800 mV. This
behavior is very similar to that in ½CoðtsaltpÞꢃ22þ, which is also a
pseudo-octahedral dimer and has an irreversible electrochemical
response at ca. ꢁ800 mV.
2þ
2ꢁ
It has been shown that both ½CoðtsaltpÞꢃ2 and ½CoðPyPSÞꢃ2
can be cleaved by addition of cyanide ion to give mononuclear spe-
cies of the form [LCoCN] (neutral species for tsaltp2ꢁ complex and
dianion for PyPS4ꢁ complex). [Co(PyPS)CN]2ꢁ has been further
shown to be able to catalyze the hydrolysis of acetonitrile to acet-
amide,[18] while [Co(tsaltp)CN] has not yet been shown to serve
this function at pH < 12. Treatment of 5 with KCN results in the iso-
lation of 6, which, although not yet structurally characterized, dis-
plays a CN stretch in the infrared spectrum at 2122 cmꢁ1 and
analyzes satisfactorily for [L2CoCN]. With four such species now
in hand with different donor sets, it is possible to more thoroughly
investigate the geometric and electronic features which bear on
the ability of a Co(III) species to catalyze the controlled hydrolysis
of the nitrile bond.
4. Conclusions
New iron and cobalt complexes of bis(thiosemicarbazone) li-
Fig. 7. ORTEP drawing of the cation in 5, showing 50% ellipsoids. H atoms omitted
gands have been synthesized and characterized. Complex 3 shows
for clarity.

1354
A. Panja et al. / Inorganica Chimica Acta 362 (2009) 1348–1354
[7] (a) S.W. Ragsdale, M. Kumar, Chem. Rev. 96 (1996) 2515;
(b) S.W. Ragsdale, L.G. Ljungdahl, D.V. DerVartanian, Biochem. Biophys. Res.
Commun. 115 (1983) 658;
an unexpected hydrolysis of the ligand, while complex 5 displays
an unprecedented amount of deviation from planarity, enabling
the ligand, for the first time, to occupy five sites of a distorted octa-
hedral coordination sphere. Complex 6 adds to the growing num-
ber of octahedral Co(III) complexes with mixed N/S coordination
geometries that are being synthesized as model complexes for
the active site of Co nitrile hydratase. Further studies are being car-
ried out to characterize the reactivity of this and related species.
(c) S.W. Ragsdale, L.G. Ljungdahl, D.V. DerVartanian, Biochem. Biophys. Res.
Commun. 108 (1982) 658;
(d) P.A. Lindahl, E. Munck, S.W. Ragsdale, J. Biol. Chem. 265 (1990) 3873;
(e) C.M. Gorst, S.W. Ragsdale, J. Biol. Chem. 266 (1991) 20687;
(f) C. Fan, C.M. Gorst, S.W. Ragsdale, B.M. Hoffman, Biochemistry 30 (1991)
431;
(g) S.P. Cramer, M.K. Eidsness, W.H. Pan, T.A. Morton, S.W. Ragsdale, D.V.
DerVartanian, L.G. Ljungdahl, R.A. Scott, Inorg. Chem. 26 (1987) 2477;
(h) J. Xia, J. Dong, S. Wang, R.A. Scott, P.A. Lindahl, J. Am. Chem. Soc. 117 (1995)
7065;
Acknowledgement
(i) C.Y. Ralston, H. Wang, S.W. Ragsdale, M. Kumar, N.J. Spangler, P.W. Ludden,
W. Gu, R.M. Jones, D.S. Patil, S.P. Cramer, J. Am. Chem. Soc. 122 (2000) 10553;
(j) D. Qiu, M. Kumar, S.W. Ragsdale, T.G. Spiro, Science 264 (1994) 817;
(k) M. Kumar, D. Qiu, T.G. Spiro, S.W. Ragsdale, Science 270 (1995) 628;
(l) T.I. Doukov, T.M. Iverson, J. Seravalli, S.W. Ragsdale, C.L. Drennan, Science
298 (2002) 567;
This work was supported by NIH COBRE Award P20 RR017708
from the National Center for Research Resources (D.M.E.). We
thank Dr. Colin Thomas for assistance in checking the synthetic
procedures.
(m) C. Darnault, A. Volbeda, E.J. Kim, P. Legrand, X. Vernede, P.A. Lindahl, J.C.
Fontecilla-Camps, Nat. Struct. Biol. 10 (2003) 271.
[8] Range established by a search of the Cambridge Structural Database: F.H. Allen,
Acta Crystallogr., Sect. B 58 (2002) 380–388.
Appendix A. Supplementary data
[9] (a) W. Huang, J. Jia, J. Cummings, M. Nelson, G. Schneider, Y. Lindqvist,
Structure 5 (1997) 691;
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2008.06.031.
(b) S. Nagashima, M. Nakasako, N. Dohmae, M. Tsujimura, K. Takio, M. Odaka,
M. Yohda, N. Kamiya, I. Endo, Nat. Struct. Biol. 5 (1998) 347.
[10] M. Mohan, P. Sharma, M. Kumar, N.K. Jha, Inorg. Chim. Acta 125 (1986) 9.
[11] (a) A. Bino, N. Cohen, Inorg. Chim. Acta 210 (1993) 11;
(b) A.H. Othman, K.-L. Lee, H.-K. Fun, B.-C. Yip, Acta Crystallogr., Sect. C 52
(1996) 602;
References
[1] E.J. Blanz, F.A. French, Cancer Res. 28 (1968) 2419.
[2] (a) S.P. Mittal, S.K. Sharma, R.V. Singh, J.P. Tandon, Curr. Sci. 50 (1981) 483;
(b) E. Bermejo, R. Carballo, A. Castiñeiras, R. Dominguez, A.E. Liberta, C.
Maichle-Mössmer, M.M. Salberg, D.X. West, Eur. J. Inorg. Chem. 965 (1999).
[3] (a) A.S. Dobeck, D.L. Klayman, E.J. Dickson, J.P. Scovill, E.C. Tramont,
Antimicrob. Agents Chemother. 18 (1980) 27;
(b) N.C. Kasuga, K. Sekino, C. Koumo, N. Shimada, M. Ishikawa, K. Nomiya, J.
Inorg. Biochem. 84 (2001) 55.
[4] J.C. Logan, M.P. Fox, J.H. Morgan, C.J. Pfau, J. Gen. Virol. 28 (1975) 271.
[5] (a) D.M. Eichhorn, N. Goswami, Comm. Inorg. Chem. 24 (2003) 1–13;
(b) B.W. Smucker, M.J. Van Stipdonk, D.M. Eichhorn, J. Inorg. Biochem. 101
(2007) 1537–1542.
(c) G. Dessy, V. Fares, Cryst. Struct. Commun. 10 (1981) 1025;
(d) R. Pedrido, M.R. Bermejo, M.J. Romero, M. Vazquez, A.M. Gonzalez-Noya, M.
Maneiro, M.J. Rodriguez, M.I. Fernandez, Dalton Trans. (2005) 572;
(e) C.A. Brown, W. Kaminsky, K.A. Claborn, K.I. Goldberg, D.X. West, J. Braz.
Chem. Soc. 13 (2002) 10.
[12] (a) A.I. Matesanz, I. Cuadrado, C. Pastor, P. Souza, Z. Anorg. Allgem. Chem. 631
(2005) 780;
(b) G.F. de Sousa, D.X. West, C.A. Brown, J.K. Swearingen, J. Valdes-Martinez,
R.A. Toscano, S. Hernandez-Ortega, M. Homer, A.J. Bortoluzzi, Polyhedron 19
(2000) 841;
(c) M.R. Bermejo, A.M. Gonzalez-Noya, R.M. Pedrido, M.J. Romero, M. Vazquez,
Angew. Chem., Int. Ed. Engl. 44 (2005) 4182;
(d) E. Labisbal, A. Castineiras, C.A. Brown, D.X. West, Z. Naturforsch., B 56
(2001) 229;
(e) M.S. Shongwe, H.N.R. Kharousi, H. Adams, M.J. Morris, E. Bill, Inorg. Chem.
45 (2006) 1103.
[6] (a) T. Nagasawa, H. Nanba, K. Ryuno, K. Takeuchi, H. Yamada, Eur. J. Biochem.
162 (1987) 691;
(b) M. Odaka, T. Noguchi, S. Nagashima, M. Yohda, S. Yabuki, M. Hoshino, Y.
Inoue, I. Endo, Biochem. Biophys. Res. Commun. 221 (1996) 146;
(c) M. Odaka, K. Fujii, M. Hoshino, T. Noguchi, M. Tsujimura, S. Nagashima, M.
Yohda, T. Nagamune, Y. Inoue, I. Endo, J. Am. Chem. Soc. 119 (1997) 3785;
(d) T. Nagasawa, K. Ryuno, H. Yamada, Biochem. Biophys. Res. Commun. 139
(1986) 1305;
(e) M.J. Nelson, J. Jin, I.M. Turner, G. Grove, R.C. Scarrow, B.A. Brennan, L. Que, J.
Am. Chem. Soc. 113 (1991) 7072;
(f) T. Nagasawa, K. Takeuchi, H. Yamada, Biochem. Biophys. Res. Commun. 155
(1988) 1008;
(g) T. Nagasawa, K. Takeuchi, H. Yamada, Eur. J. Biochem. 196 (1991) 581;
(h) B.A. Brennan, G. Alma, M.J. Nelson, L.T. Durney, R.C. Scarrow, J. Am. Chem.
Soc. 118 (1996) 9194;
(i) M.S. Payne, S. Wu, R.D. Fallon, G. Tudor, B. Stieglitz, I.M. Turner, M.J. Nelson,
Biochemistry 36 (1997) 5447;
[13] G.F. DeSousa, V.M. Deflon, E. Niquet, A. Abras, J. Braz. Chem. Soc. 12 (2001) 493.
[14] APEX2 User Manual, Bruker AXS, Inc., Madison, WI, 2006.
[15] G.M. Sheldrick, Institüt für Anorganische Chemie der Universität,
Tammanstrasse 4, D-3400 Göttingen, Germany, 1998.
[16] B. Le Gall, F. Conan, J.-M. Kerbaol, M.M. Kubicki, E. Vigier, Y. Le Mest, J.S. Pala,
Inorg. Chim. Acta 336 (2002) 87–90.
[17] (a) M. Juric, B. Peric, N. Brnicevic, P. Planini, D. Pajic, Z. Kreso, G. Giester, B.
Kaitner, Dalton Trans. (2008) 742;
(b) G. Vuckovic, V. Stanic, S.P. Sovilj, M. Antonijeic-Nikolic, J. Mrozinski, J. Serb.
Chem. Soc. 70 (2005) 1121.
[18] J.C. Noveron, M.M. Olmstead, P.K. Mascharak, J. Am. Chem. Soc. 121 (1999)
3553.
[19] C.E. Moore, D.M. Eichhorn, unpublished work.
[20] A.K. Singh, R. Mukherjee, Dalton Trans. (2008) 260.
(j) A. Miyanaga, S. Fushinobu, K. Ito, T. Wakagi, Biochem. Biophys. Res.
Commun. 288 (2001) 1169.