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Cite this: DOI: 10.1039/c4dt01312c
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Retention of single crystals of two Co(II)
complexes during chemical reactions and
rearrangement†
Shaikh M. Mobin* and Akbar Mohammad
Monomeric [CoII(hep-H)(H2O)4]SO4 [1]SO4 and [CoII(hep-H)2(H2O)2](NO3)2 [2](NO3)2 have been developed from 2-(2-hydroxyethyl)pyridine (hep-H) and CoSO4·7H2O/Co(NO3)2·6H2O, respectively, at 298 K.
On exposure to heat (120 °C), the light orange single crystal of [1]SO4 transforms to a pink single crystal
corresponding to the neutral sulfato bridged dimeric complex [(CoII(hep-H)(H2O)2(µ2-sulfato-O,O’))2](3).
However, the orange single crystal of [2](NO3)2 transforms to the single crystal of monomeric [CoII(hep-H)2(NO3)]NO3 [4]NO3 (orange) upon exposure to heat (110 °C) where one of the NO3− counter anions in [2]
(NO3)2 moves to the coordination sphere. The facile SCSC transformations of [1]SO4 (orange) → 3 ( pink)
Received 2nd May 2014,
Accepted 24th June 2014
and [2](NO3)2 (orange) → [4]NO3 (orange) involve intricate multiple bond breaking and bond forming pro-
DOI: 10.1039/c4dt01312c
cesses without losing the crystallinity. Moreover, the immersion of the pink single crystal of 3 in 1 N HCl
results in a green single crystal of ionic monomeric [CoII(H2O)6]·SO4[5]SO4, which indeed demonstrates
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the unprecedented unique two-step SCSC transformations.
Introduction
The recent upsurge in the field of single-crystal-to-singlecrystal (SCSC) transformations has revealed a new generation
of materials with fascinating properties.1–5 The SCSC transformation of discrete and polymeric molecules by heat,1a–d,6–12
vapor8b,13–15 or light16,17 has gained considerable interest due
to its potential application in sensor technology,18a,b magnetic
materials,18c–f catalysis18g,h and gas storage materials.19 SCSC
transformation, involving bond breaking and bond formation,
while retaining its crystallinity has been recognised as a challenging process.1–3,20,21 The SCSC transformation includes diverse
processes such as thermally induced rearrangement,1a–d,6–12
hydration–rehydration,2a,21,22 absorption–resorption,23,24 vapor
diffusion13–15 and removal or uptake of guest molecules.2a,18b,25
Though the SCSC process with MOFs is well documented, only a
few reports are known at the discrete molecular level.13,22,26 The
reversible or irreversible dehydration of coordinated or lattice
water molecules by heating or by the vapor diffusion method at
the SCSC level is reported to undergo the change in dimen-
Discipline of Chemistry, School of Basic Sciences, Indian Institute of Technology
Indore, Khandwa Road, Indore 452017, India. E-mail: [email protected];
Tel: +91 731 2438 762
† Electronic supplementary information (ESI) available. CCDC 986620–986624.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c4dt01312c
This journal is © The Royal Society of Chemistry 2014
sionality of the porous polymeric structures.2a,21 In contrast, only
two examples of SCSC transformation at the discrete neutral molecular level involving coordinated water molecules are known: (i)
reversible exchange of a coordinated water molecule by methanol
without change in colour or structural motif in the tri-iron
system,27 and (ii) our recent work with irreversible SCSC transformation involving a change in structural motif from a dimeric
blue copper(II) complex to a tetrameric green copper(II) complex
upon dehydration of coordinated water molecules by using a
simple vapour diffusion technique.13
As a part of our ongoing research program, the present
article demonstrates unique examples of facile SCSC transformations of discrete monomeric ionic Co(II) complexes, incorporating two different oxyanions via the influence of heat.
Experimental section
Materials
Commercially available starting materials, CoSO4·7H2O, Co(NO3)2·6H2O, 2-(2-hydroxyethyl)pyridine (hep-H), hydrochloric
acid (35%) and reagent grade solvents were used as received.
Physicochemical characterizations
Infrared spectra were obtained with a Bio-Rad FTS 3000MX
instrument using KBr pellets. Thermogravimetric analysis
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(TGA) was performed on a METTLER TOLEDO (TGA/DSC 1)
using software STARe System. Powder X-ray diffraction for complexes was recorded on a Rigaku SmartLab X-ray diffractometer
using monochromated CuKα radiation (0.154 nm). Solid-state
UV-vis spectra were measured on a Perkin Elmer Lambda 35
UV-VIS spectrophotometer at room temperature. Single crystal
X-ray structural studies of complexes ([1]SO4/3/[5]SO4/[2](NO3)2/[4]NO3) were performed on a CCD equipped SUPERNOVA diffractometer from Agilent Technologies with Oxford
Instruments low-temperature attachment.
Synthesis of [1]SO4. To a methanolic solution (15 cm3) of
hep-H (0.123 g, 1 mmol) a solution of CoSO4·7H2O (0.281 g,
1 mmol) in methanol (15 cm3) was added and the resultant
mixture was stirred magnetically for 6 h at 298 K. To remove
unreacted materials, the solution was then passed through
filter paper (Whatman filter paper, 70 mm). The filtrate was
allowed to stand at room temperature for crystallization.
Orange-coloured, block-shaped crystals of [1]SO4 were
obtained within a week by slow evaporation of the solvent. A
crystal was then subjected to X-ray analysis, which confirmed
the identity of the crystal as [1]SO4. IR (KBr, cm−1): 3226(br),
2898(w), 2840(w), 2742(w), 2658(w), 2227(w), 2007(w), 1942(w),
1900(w), 1611(m), 1571(m), 1492(m), 1443(m), 1427(w),
1365(w), 1336(m), 1314(w), 1145(m), 1101(m), 1029(m),
985(m), 859(m), 785(w), 766(m), 630(m), 582(w). TGA: temperature range °C (% weight loss): 80–150 (21.53); 150–382 (35.95);
382–713 (32.55).
Synthesis of [2](NO3)2. To a methanolic solution (15 cm3) of
hep-H (0.123 g, 1 mmol) a solution of Co(NO3)2·6H2O (0.291 g,
1 mmol) in methanol (15 cm3) was added and the resultant
mixture was stirred magnetically for 6 h at 298 K. To remove
unreacted materials, solution was then passed through the
filter paper (Whatman filter paper, 70 mm). The filtrate was
allowed to stand at room temperature for crystallization.
Orange coloured crystals of [2](NO3)2 were obtained within
10 days by slow evaporation of the solvent. A crystal was then
subjected to X-ray analysis, which confirmed the identity of
the crystal as [2](NO3)2. IR (KBr, cm−1): 3322(w), 3214(w),
3170(w), 2748(w), 2665(w), 2422(w), 1618(m), 1488(w), 1433(w),
1383(s), 1156(w), 1075(m), 1025(m), 856(m), 769(m), 704(w),
628(w), 587(w), TGA: temperature range °C (% weight loss):
30–100(8); 100–150 (50.13); 150–610 (28.32).
Heat driven single-crystal-to-single-crystal (SCSC)
transformation of [1]SO4 to 3
Orange-coloured crystals of [1]SO4 were exposed to a temperature of 120 °C for 1 h, which led to the transformation of the
monomeric complex structure to the dimeric complex structure, as it showed a distinct change in colour of the crystals
from orange to pink without a loss in crystallinity. A crystal was
then subjected to X-ray analysis, which confirmed the identity
of the crystal as 3. The exposure of [1]SO4 above 120 °C temperature resulted in an immediate loss in crystallinity. IR (KBr,
cm−1): 3321(br), 2972(w), 2855(w), 2757(w), 2695(w), 2519(w),
2360(w), 2340(w), 2133(w), 2009(w), 1937(w), 1857(w), 1608(m),
Dalton Trans.
Dalton Transactions
1572(m), 1492(m), 1446(s), 1364(m), 1342(m), 1321(m), 1136(m),
1059(m), 1023(m), 981(m), 886(m), 856(w), 791(s), 627(m),
609(m), 515(m). TGA: temperature range °C (% weight loss):
130–190 (11.27); 190–393 (37.4); 393–797 (28.84).
Acid driven single-crystal-to-single-crystal (SCSC)
transformation of 3 to [5]SO4
Pink-coloured crystals of 3 were placed on a glass slide containing a few drops of 1 N HCl (aq. HCl) at room temperature.
Within 10 min, a distinct colour change of the crystals from
pink to green was observed with loss of crystal size. A transformed crystal was subjected to X-ray analysis, which confirmed the structure of the crystal as a [5]SO4. The exposure of
3 above 1 N concentration leads to dissolving of crystal.
Heat driven single-crystal-to-single-crystal (SCSC)
transformation of [2](NO3)2 to [4]NO3
Orange-coloured crystals of [2](NO3)2 were exposed to a temperature of 110 °C for 1 h which led to the transformation of a
monomeric complex structure to another monomeric complex
structure. A crystal was then subjected to X-ray analysis, which
confirmed the identity of the crystal as [4]NO3. The exposure of
[2](NO3)2 above 110 °C temperature resulted in an immediate
loss in crystallinity. IR (KBr, cm−1): 3322(w), 3179(w), 2954(w),
2869(w), 2749(w), 2656(w), 2401(w), 2340(w), 1764(w), 1616(s),
1486(w), 1383(s), 1155(m), 1074(m), 1024(m), 856(s), 827(m),
768(m), 703(w), 631(w), 585(w), TGA: temperature range °C
(% weight loss): 70–404 (63.7); 404–600 (29.54).
X-ray crystallographic determination
Single crystal X-ray structural studies of complexes ([1]SO4/3/[5]SO4/[2](NO3)2/[4]NO3) were performed on a CCD equipped
SUPERNOVA diffractometer from Agilent Technologies with a
low-temperature attachment. Data for ([1]SO4, 3, [2](NO3)2)
were collected at 150(2) K using graphite-monochromated Mo
Kα radiation (λα = 0.71073 Å) and data for ([5]SO4 and [4]NO3)
was collected at 150(2) K using Cu Kα radiation λα = 1.5418 Å.
The strategy for the data collection was evaluated by using
CrysAlisPro CCD software. The data were collected by standard
‘phi-omega’ scan techniques, and they were scaled and
reduced using CrysAlisPro RED software. The structures were
solved by direct methods using SHELXS-97 and refined by full
matrix least squares with SHELXL-97, refining on F2.28 In the
case of [4]NO3, the crystal was not of good quality after
transformation.
The positions of all the atoms were obtained by direct
methods. All non-hydrogen atoms were refined anisotropically.
The remaining hydrogen atoms were placed in geometrically
constrained positions and refined with isotropic temperature
factors, generally 1.2 × Ueq of their parent atoms. All the
H-bonding interactions, mean plane analyses, and molecular
drawings were obtained using the program Diamond (ver
3.1d). The crystal and refinement data is summarized in
Table 1, and selected bond distances and bond angles are
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Table 1
Paper
Crystallographic parameters of all complexes
Identification code
[1]SO4
3
[5]SO4
[2](NO3)2
[4]NO3
Empirical
formula
Formula weight
Temperature
Wavelength (Å)
Crystal system,
space group
Unit cell parameter
a/Å
b/Å
c/Å
α/°
β/°
γ/°
V/Å3
Z, dcalcd (mg m−3)
μ/mm−1
F(000)
Crystal size (mm3)
θ range
Index ranges
C7H17CoNO9S
C14H26Co2N2O14S2
H24Co2O20S2
C14H22CoN4O10
C14H18CoN4O8
350.21
150(2) K
0.71073
Monoclinic, P21
628.35
150(2) K
0.71073
Monoclinic, P21/n
526.17
150(2) K
1.5418
Monoclinic, C2/c
465.29
150(2) K
0.71073
ˉ
Triclinic, P1
429.25
150(2) K
1.5418
Orthorhombic, Pbcn
9.3343(4)
6.9370(2)
10.5740(4)
90
92.156(4)
90
684.20(4)
2, 1.700
1.446
362
0.28 × 0.26 × 0.21
3.51 to 24.99
−11 ≤ h ≤ 11
−8 ≤ k ≤ 8
−12 ≤ l ≤ 12
4116/2304
[R(int) = 0.0215]
Semi-empirical from
equivalents
0.7511 and 0.6877
7.1858(7)
23.0471(15)
7.5389(7)
90
117.044(13)
90
1112.01(17)
2, 1.877
1.755
644
0.28 × 0.25 × 0.20
3.16 to 24.99
−8 ≤ h ≤8
−21 ≤ k ≤ 27
−8 ≤ l ≤ 8
7742/1956
[R(int) = 0.0636]
Semi-empirical from
equivalents
0.7204 and 0.6583
10.0401(8)
7.2224(6)
24.274(2)
90
98.265
90
1741.9(3)
4, 2.006
18.103
1080
0.26 × 0.22 × 0.18
3.68 to 72.26
−6 ≤ h ≤ 12
−8 ≤ k ≤ 8
−28 ≤ l ≤ 29
3276/1687
[R(int) = 0.0310]
Semi-empirical
from equivalents
0.1598 and 0.0740
7.7747(6)
8.2003(5)
8.8496(8)
96.823(6)
113.416(8)
109.189(6)
468.28(6)
1, 1.650
0.980
241
0.34 × 0.30 × 0.27
3.13 to 24.99°
−9 ≤ h ≤ 9
−9 ≤ k ≤ 9
−10 ≤ l ≤ 10
4269/1642
[R(int) = 0.0242]
Semi-empirical from
equivalents
0.7778 and 0.7318
12.6998(12)
8.8157(9) A
33.412(3)
90
90
90
3740.7(6)
8, 1.524
7.655
1768
0.33 × 0.30 × 0.25
4.37 to 61.13°
−14 ≤ h ≤ 14
−8 ≤ k ≤ 10
−37 ≤ l ≤ 37
19 829/2868
[R(int) = 0.2515]
Semi-empirical from
equivalents
0.3395 and 0.2408
Full-matrix
least-squares on F2
2304/10/210
Full-matrix
least-squares on F2
1956/5/174
Full-matrix
least-squares on F2
1687/0/159
Full-matrix
least-squares on F2
1642/0/145
Full-matrix
least-squares on F2
2868/0/253
1.109
R1 = 0.0260,
wR2 = 0.0690
R1 = 0.0279,
wR2 = 0.0699
0.401 and −0.421
1.257
R1 = 0.0745,
wR2 = 0.1707
R1 = 0.0778,
wR2 = 0.1723
1.072 and −0.707
1.070
R1 = 0.0465,
wR2 = 0.1231
R1 = 0.0488,
wR = 0.1267
0.630 and −1.101
1.145
R1 = 0.0233,
wR2 = 0.0604
R1 = 0.0277,
wR2 = 0.0618
0.244 and −0.380
0.951
R1 = 0.0682,
wR2 = 0.0945
R1 = 0.1917,
wR2 = 0.1299
0.304 and −0.355
986620
986622
986624
986621
986623
Reflections collected/
unique
Absorption correction
Max. and min.
transmission
Refinement method
Data/restraints/
parameters
GOF, F2
R1, wR2 [I > 2σ(I)]
R1, wR2 (all data)
Largest diff. peak
and hole (e Å−3)
CCDC no.
shown in Table S1,† and hydrogen bonding interactions are
shown in Table S2.†
Results and discussions
The monomeric ionic cobalt(II) complexes [CoII(hep-H)(H2O)4]SO4[1]SO4 and [CoII(hep-H)2(H2O)2](NO3)2[2](NO3)2 were synthesised via the reactions of CoSO4·7H2O and Co(NO3)2·6H2O
with the ligand hep-H (2-(2-hydroxyethyl)pyridine) (Scheme 1).
The newly synthesised complexes were characterised by standard methods (Experimental).
This article demonstrates unique examples of facile SCSC
transformations of discrete monomeric ionic Co(II) complexes
incorporating two different oxyanions via the influence of
heat: [1]SO4 (orange) → 3 ( pink) and [2](NO3)2 (orange) →
[4]NO3 (orange) (Schemes 2 and 3).
Moreover, on immersion of a pink single crystal of 3 in 1 N
HCl results in a green single crystal of [CoII(H2O)6]·SO4 [5]SO4
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(Green) via the elimination of hep-H ligand from 3
(Scheme 2).29,30 However, no such transformation was
observed with orange single crystals of [4]NO3.
To the best of our knowledge, the present work demonstrates the first example of two-step SCSC transformations of
an ionic monomeric complex to a neutral dimeric complex to
an ionic monomeric (different) complex (Scheme 2).
[1]SO4 and [2](NO3)2 crystallized in non-centrosymmetric
ˉ space
monoclinic P21 and centrosymmetric triclinic P1
groups, respectively (Table 1). The perspective views of the
molecular structures of [1]SO4 and [2](NO3)2 are shown in
Fig. 1 and 2. The asymmetric unit of [1]SO4 consists of one
CoII ion, one bidentate hep-H ligand and four water molecules.
The charge of the complex ion is balanced by the SO42− ion.
The pyridine N(1) and alcohol O(1) donors of hep-H and
two water molecules constitute the basal plane, the other
two water molecules occupy the axial position with elongated bond lengths, forming distorted octahedral geometry.
The Co(1)–N(1), Co(1)–O(1), Co(1)–O(5) and Co(1)–O(3) bond
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Scheme 1
Synthetic route of [1]SO4 and [2](NO3)2.
Scheme 2
Schematic representation of stepwise SCSC transformation of [1]SO4 (orange) → 3 ( pink) → [5]SO4 (green).
Scheme 3
Schematic representation of the SCSC transformation of [2](NO3)2 (orange) → [4]NO3 (orange).
distances are 2.123(2), 2.063(3), 2.074(2) and 2.113(3) Å,
respectively, and the elongated apical bond distances are
2.131(3) Å for Co(1)–O(2) and 2.106(3) Å for Co(1)–O(4)
(Table S1†).
[2](NO3)2 consists of one CoII ion, two bidentate hep-H
ligands and two water molecules and the charge of complex
ion is neutralized by NO3− ions. The pyridine N(1) and N(2)
and alcohol O(1) and O(2) donors of two hep-H ligands form
the basal plane and the two coordinated water molecules
occupy the elongated axial position forming distorted octa-
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hedral geometry. The Co(1)–N(1), Co(1)–O(1), and Co(1)–O(2)
bond distances are 2.1489(14), 2.0897(12), 2.1081(12) Å,
respectively (Table S1†).
[1]SO4 and [2](NO3)2 differ with respect to ligand composition around the metal ions with one ligand with four water
molecules in the former and two ligands and two water molecules in the later as well as counter anions, i.e. SO42− versus
NO3−.
The packing diagram of [1]SO4 reveals strong intermolecular hydrogen bonding interactions between the coordinated
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Fig. 1
Perspective view of [1]SO4.
Fig. 2
Perspective view of [2](NO3)2.
water molecules of the cationic monomeric CoII unit and the O
atoms of the sulfate anion, leading to the formation of hydrogen-bonded dimeric units as shown in Fig. 3 (Table S2†).
[2](NO3)2 shows strong intermolecular hydrogen bonding
interactions between the two coordinated water molecules and
O atoms of two nitrate anions forming a hydrogen-bonded 1Dpolymeric chain in which the two water molecules are
arranged in a trans fashion to each monomeric unit (Fig. 4a).
Each polymeric chain is further connected to a neighboring
Fig. 3
Hydrogen-bonded 2D network in [1]SO4.
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Paper
chain via O–H⋯O interactions between the third O atom of
the NO3 anion and the hydroxyl OH group of the hep-H ligand,
leading to the formation of a 2D-network (Fig. 4b) (Table S2†).
The packing diagrams of [1]SO4 and [2](NO3)2 reveal that in
[1]SO4 the two cis water molecules form a hydrogen-bonded
dimer, while [2](NO3)2 yields a linear 1D polymeric chain due
to the involvement of two coordinated apical water molecules
which are arranged in a trans fashion in the chain.
The involvement of the counter sulfate or nitrate anion in
the formation of the hydrogen-bonded dimeric unit or polymeric chain in the packing of [1]SO4 or [2](NO3)2, respectively,
has instigated the exploration of the effect of heat on the
single crystals of [1]SO4 or [2](NO3)2.
Upon heating the single crystals of [1]SO4 at 120 °C, a
drastic colour change from orange to pink occurred with the
retention of crystallinity. The single crystal X-ray structure of
the pink crystal established its identity as a neutral sulfate
bridged dimeric Co(II) complex, [(CoII(hep-H)(H2O)2(µ2-sulfatoO,O′))2] (3) (Fig. 5).
Although heating the orange crystals of [2](NO3)2 at 110 °C
did not cause any colour change the crystal structure revealed
the formation of a new ionic monomer [4]NO3, where one of
the counter NO3− groups moved into the coordination sphere
and linked to the metal ion in a bidentate fashion (Fig. 6).
Thus, the SCSC transformations of [1]SO4 (orange) → 3 ( pink)
and [2](NO3)2 (orange) → [4]NO3 (orange) under the influence
of heat involved simultaneous several bond breaking and bond
forming processes in each case.
3 possesses a monoclinic, P21/n space group with a crystallographically imposed inversion center (Table 1). Each hexa-coordinated CoII ion in 3 is bonded to pyridine N1 and alcohol
O1 donors of a bidentate hep-H ligand, two O atoms of two
different sulfate ions in the apical position and two water
molecules at the axial site, forming a distorted octahedral geometry (Table S1,† Fig. 5).
The packing diagram of 3 reveals moderately strong inter
and intra-molecular O–H⋯O hydrogen bonding interactions.
The intra-molecular H-bonding involves H-atoms of coordinated water molecules and uncoordinated O-atoms of
sulfate ions. The intermolecular hydrogen bonding involves
the H-atoms of coordinated water molecules and alcohol (OH)
H-atom to two uncoordinated O-atoms of sulfate ions of neighboring dimers, resulting in a hydrogen bonded tetramer,
which continues along the c-axis to form a hydrogen-bonded
1D-polymeric chain (Fig. 7 and Table S2†). Furthermore, the
1D-polymeric chains extend via C–H⋯π interactions along the
c-axis leading to the formation of a 2D-network (Fig. S1†).
[4]NO3 possesses an orthorhombic, Pbcn space group
(Table 1). The CoII ion in [4]NO3 is coordinated to two hep-H
ligands and one nitrate in a bidentate fashion. The pyridine
N(1)/N(2) and alcohol O(1)/O(2) donors of two bidentate hep-H
ligands and one nitrate ion O(3)/O(4) are coordinated to the
central CoII ion, forming a distorted octahedral geometry
(Table S1† and Fig. 6).
The packing diagram of [4]NO3 shows intermolecular
O–H⋯O hydrogen bonding interactions between two O-atoms
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Fig. 4
(a) Hydrogen-bonded 1D polymeric chain in [2](NO3)2. (b) Hydrogen-bonded 2D network in [2](NO3)2.
Fig. 5
Perspective view of 3.
Fig. 6
of the anionic nitrate group and the hydroxyl OH group of
hep-H ligands of two neighboring monomeric units, forming a
1D polymeric chain (Fig. 8a). Each 1D polymeric chain is
further connected to neighboring chains via the third O atom
of anionic NO3 to the CH of the pyridine ring and methylene
group to form a hydrogen-bonded 3D network (Table S2† and
Fig. 8b).
[5]SO4 crystallizes in a monoclinic C2/c space group with a
crystallographically imposed inversion centre (Table 1). The
CoII ion in [5]SO4 consists of successive layers of hexa-aqua coordinated octahedral geometry as a cation and independent
tetrahedra sulfate ions as anions. Although the crystal struc-
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Perspective view of [4]NO3.
ture of [5]SO4 has been reported, we were able to generate it by
the SCSC transformation of 3. All the bond distances and
angles in [5]SO4 are similar to the reported values (Table S1,
Fig. S2a and S2b†).
Significantly, in 3 the two CoII ions and two sulfate ions are
separated by 5.178 and 4.093 Å, respectively, leading to an
8-membered metallacyclic ring (Fig. S3†). This prompted us to
explore the feasibility of encapsulating solvent or other anions
inside the metallacyclic ring. However, exposure of 3 to the
vapor of different solvents such as MeOH, EtOH, iPrOH,
acetone and acetonitrile yielded no further transformation.
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Fig. 7
Hydrogen-bonded linear 1D-chain along c-axis in 3.
Fig. 8
(a) 1D Polymeric chain in [4]NO3. (b) Hydrogen-bonded 3D network of [4]NO3.
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However, immersion of the pink crystal of 3 in 1 N HCl (HCl +
H2O) resulted in the formation of a green crystal corresponding to monomeric hexahydrate CoII sulfate [5]SO4. The
crystal structure of [5]SO4 was in agreement with the reported
structure (Table 1, S1, Fig. S2a and S2b†).29,30 The SCSC transformation of 3 to [5]SO4 also caused a loss in size of the crystal
by about 20% due to the removal of the hep-H ligand. Moreover, the attempt to remove water molecules in 3 by heat led to
a loss in crystallinity.
The vibrational frequencies of the complexes ([1]SO4,
[2](NO3)2, 3 and [4]NO3) correspond to coordinated water and
coordinated/uncoordinated SO4 and NO3 groups in their IR
spectra and appear in the ranges of 3400–3200 cm−1 and
1600–1100 cm−1, respectively (Fig. S4–S7†). Thermogravimetric
analysis (TGA) for all samples was performed under N2. TGA of
[1]SO4 revealed stepwise dehydration of four water molecules
between 80 and 150 °C and losses beyond 150 °C corresponded to hep-H and sulfate (Fig. S8 and S9†). The loss of four
water molecules in 3 occurred at a slightly higher temperature
up to 190 °C, whereas the losses of hep-H and sulfate took
place in the temperature range of 190–700 °C (Fig. S8 and
S10†). The TGA study of [2](NO3)2 revealed the loss of a total of
∼8% in the temperature range of 30–100 °C, which corresponded to the removal of two coordinated water molecules.
The loss of hep-H took place from 100 to 150 °C (Fig. S8 and
S11†), whereas no such weight loss was observed for [4]NO3 up
to 70 °C. The loss of the ligands (hep-H and nitrate) in [4]NO3
was observed to take place around 70 to 600 °C (Fig. S8 and
S12†).
The PXRD patterns of bulk [1]SO4, 3, [2](NO3)2 and[4]NO3
are consistent with the simulated PXRD patterns generated
from single-crystal data, which indicates the structural identity
as well as the phase purity of the bulk products (Fig. S13a and
b and Fig. S14a and b†).
The solid state absorption spectra of [1]SO4/3/[5]SO4 and
[2](NO3)2/[4](NO3) at 298 K were recorded in the range of
400–800 nm (Fig. S15†). The complexes exhibited multiple
moderately intense to weak absorptions in the visible region,
which are tentatively assigned to metal/ligand derived charge
transfer transitions, due to the presence of different types of
ligands around the metal ion in each case.31
Conclusions
We have demonstrated for the first time a facile, two-step SCSC
transformations of an ionic monomeric Co(II) complex ([1]SO4)
to a neutral dimeric Co(II) complex (3) to a different ionic
monomeric Co(II) complex ([5]SO4) via simultaneous several
bond breaking and bond forming processes. Furthermore, we
described the SCSC transformation of [2](NO3)2 to [4]NO3 via
the shifting of one NO3− counter anion to the coordination
sphere with the simultaneous breaking of Co–OH2 bonds. The
article thus highlights the role of varying the oxyanions (SO42−/
NO3−) in stabilizing different complex frameworks in [1]SO4
Dalton Trans.
Dalton Transactions
and [2](NO3)2 and altogether different modes of SCSC
transformations.
Acknowledgements
We would like to acknowledge CSIR, New Delhi, India for
funding and Sophisticated Instrumentation Centre (SIC), IIT
Indore for providing the characterization facility. A.M. would
like to thank to MHRD, New Delhi, India for providing
fellowship.
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