Cobalt(III) complexes with tridentate hydrazone ligands: Protonation state and hydrogen bond competition

Article abstract of DOI:10.1039/c5ra22068h

Cobalt(iii) complexes of the type [Co(HL)(L)] were synthesized under solvothermal conditions staring from [Co(C₅H₇O₂)₃] and the corresponding ligand H₂L (salicylaldehyde 4-hydroxybenzhydrazone, 3-meth

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Cobalt(III) complexes with tridentate hydrazone ligands: protonation
state and hydrogen bonds competition
Višnja Vrdoljak,*a Gordana Pavlović,b Tomica Hrenar,a Mirta Rubčić,a Patrizia Siega,c Renata Dreosc
and Marina Cindrića
5
Received (in XXX, XXX) Xth XXXXXXXXX 200X, Accepted Xth XXXXXXXXX 200X
First published on the web Xth XXXXXXXXX 200X
DOI: 10.1039/b000000x
Cobalt(III) complexes of the type [Co(HL)(L)] were synthesized under solvothermal conditions
staring from [Co(C5H7O2)3] and the corresponding ligand H2L (salicylaldehyde
10 4ꢀhydroxybenzhydrazone, 3ꢀmethoxysalicylaldehyde 4ꢀhydroxybenzhydrazone,
4ꢀmethoxysalicylaldehyde 4ꢀhydroxybenzhydrazone, salicylaldehyde benzhydrazone,
3ꢀmethoxysalicylaldehyde benzhydrazone, 4ꢀmethoxysalicylaldehyde benzhydrazone). The
presence of differently protonated forms of the same ligand in complexes was supported by IR and
NMR spectroscopy as well as by the single crystal Xꢀray diffraction method. The effect of weak
15 interactions on the supramolecular architecture and their role on the ligand form stabilization has
been analysed. Molecular interactions within the unit cells were investigated and quantified by
extensive quantum chemical analysis on models built from crystal structures using density
functional theory and empirical dispersion. Ligands used in this study were prepared under
environmentally friendly conditions by the mechanochemical synthesis. Their thermal behaviour
20 and phase transitions were investigated using TG and DSC analysis and the powder Xꢀray
diffraction method.
methoxybenzilidene)ꢀbenzohydrazide, respectively, represent
such examples.
Introduction
The chemistry of hydrazones has been receiving an ongoing
attention in various fields, ranging from organic synthesis1–3
25 and medicinal chemistry4–6 to supramolecular and
coordination chemistry.7–12 The hydrazone moiety can
undergo reversible structural changes upon photochemical
treatment and triggers like pH or temperature changes.13–17
Different arrangements or conformations can lead to
30 significant changes in physical and chemical properties of
hydrazones and their complexes which make them attractive
materials in connection with their potential applications.18−22
55 Inspired by the previously mentioned facts in this work we
were interested to investigate mononuclear cobalt(III)
complexes which bear tridentate ONO hydrazone ligands in
different protonation states. Such complexes can be
formulated as [Co(HL)(L)], where HL denotes singly
60 deprotonated ligand and L doubly deprotoneted one. In this
comprehensive study we employed Xꢀray crystallography, IR
and NMR spectroscopy as well as quantum chemical
calculations to analyze: (i) structural and electronic changes
of the hydrazone moiety depending on the protonation state of
65 ligand; (ii) importance of nonbonding interactions in the
stabilization of particular ligand form and (iii) potential role
of N–H···O/N or O–H···O/N hydrogen bonds in the overall
stabilization of the crystal structure.
Metal
complexes
with
aroylhydrazone
ligands
ArC=N−NH−(C=O)−R are usually mononuclear or dinuclear.
35 Some examples of structurally characterized complexes are
[Sn(L)(Ph)2]ꢁEtOH,23
[Cd(HL)2],24
[Cu2(L)2(py)2],25
[Cu2(HL)2(H2O)2](NO3)2,26
[Co(HL)2]ClO4ꢁH2OꢁCH3CN,27
[Co(L)2]2[Co(H2O)4(OPPh3)2],28 [Co(L)2]Cl,29 [Co(L)2]ꢁH2O,30
or [Co(L)(HL)2](NO3)2ꢁH2OꢁCH3OH.31 In these compounds,
40 the hydrazone ligand is in the singlyꢀdeprotonated HL–, or in
doublyꢀdeprotonated L2– form, Scheme 1. The protonation
state of these ligands in metal complexes plays an important
role since it offers fineꢀtuning of properties such as
electrochemical, photophysical or catalytic.32–34
45 Although numerous transition metal complexes with
aroylhydrazone derivatives are known, related cobalt(III)
complexes are rare. Only seven such structures have been
published to date.27–39 In addition, complexes based on
differently deprotonated ligand are even more scarce. The
50 structures of the complexes [Fe{H(3,5ꢀtBu2)salbh}{(3,5ꢀ
tBu2)salbh}],40 and [Fe(L)(HL)],41 containing the 3,5ꢀdiꢀtertꢀ
70 Scheme 1 Tautomerism of hydrazone ligand and reversible deprotonation
butylsalicylidene
benzoylhydrazine,
or
Nꢀ(2ꢀoxoꢀ3ꢀ
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Table 1 Synthesis of hydrazone ligands.
As a part of this study we also aimed to investigate synthesis
of aroylhydrazone ligands under more environmentally
friendly conditions. For this purpose we employed
mechanochemical synthesis which has been extensively
investigated lately as a "green" synthetic route.42,43 It has been
applied to various organic reactions, including condensation
reactions, nucleophilic additions, Diels–Alder reactions, etc.44
The first synthesis of hydrazones using ballꢀmilling method
was reported by Kaupp and coworkers.45,46 Baltas et al.
Ligand
Aldehydea
Hydrazideb
Milling
time/min
H2L1
Sal
HBOH
HBOH
HBOH
HB
HB
HB
40
20
60
30
30
60
H2L2ꢁH2O
H2L3ꢁH2O
H2L4
3ꢀOMeꢀSal
4ꢀOMeꢀSal
Sal
3ꢀOMeꢀSal
4ꢀOMeꢀSal
5
H2L5ꢁH2O
H2L6 ꢁH2O
a Sal (slicylaldehyde), 3ꢀOMeꢀSal (3ꢀmethoxysalicylaldehyde), 4ꢀOMeꢀ
35 Sal (4–methoxysalicylaldehyde); b HBOH (4ꢀhydroxybenzhydrazide),
HB (benzhydrazide)
10 recently reported solventꢀfree mechanochemical route for
pharmaceutically attractive phenol hydrazones using
a
vibratory ball mill with an average reaction time of four
hours.47
Compounds H2L1 and H2L4 were found to be unsolvated,
whereas H2L2ꢁH2O, H2L3ꢁH2O, H2L5ꢁH2O and H2L6ꢁH2O were
40 obtained in their hydrated forms. They were analyzed by
PXRD (Fig. 1) thermogravimetric (TG) and differential
scanning calorimetric measurements (DSC, see ESI Figs.
S1−S6†). PXRD patterns for prepared hydrazones were
compared to those calculated from the previously reported
45 single crystal Xꢀray crystallography studies, Fig. 1 ((a) H2L1,
CSD code YIFPAF01;48 (b) H2L2ꢁH2O, CSD code ROGFEZ;49
(c) H2L3ꢁH2O, CSD code MOKRUA;50 (d) H2L4, CSD code
ZAYQAR;51 (e) H2L5ꢁH2O, CSD code TEZMER52 and (f)
H2L6ꢁH2O, CSD code MIQXUH).53 The appearance of
50 experimental diffraction patterns is consistent with those
simulated for all compounds.
Results and Discussion
15 Synthesis of hydrazone ligands
Synthesis of ligands was carried out using equimolar amounts
of
the
corresponding
aldehyde
(salicylaldehyde,
3ꢀmethoxysalicylaldehyde or 4ꢀmethoxysalicylaldehyde) and
hydrazide (4ꢀhydroxybenzhydrazide or benzhydrazide) under
20 mechanochemical conditions, Scheme 2. Reactions were
performed by liquidꢀassisted grinding of the reagents in
presence of a small amount of methanol and acetanhydride.
The powder Xꢀray diffraction (PXRD) revealed the complete
disappearance of reflections corresponding to starting
25 compounds after 20–60 min (Table 1). It should be noted that
the addition of acetanhydride/methanol mixture led to a
significant reduction of the reaction time comparing to the
results obtained when catalyst was not added to the reaction
mixture.
30
Scheme 2 Synthesis of hydrazone ligands H2L1ꢀ6
.
Fig. 1 Comparison of the PXRD patterns for mechanochemically
prepared ligands (the green lines: (a) H2L1; (b) H2L2ꢁH2O; (c) H2L3ꢁH2O;
55
(d) H2L4; (e) H2L5ꢁH2O and (f) H2L6ꢁH2O), and calculated from the
deposited crystal structure (the black lines with CSD code).
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Their thermal behaviour and phase transitions were
investigated using TG and DSC analysis and the powder Xꢀ
ray diffraction method. The first mass loss in the TG curves of
H2L2ꢁH2O, H2L3ꢁH2O, H2L5ꢁH2O and H2L6ꢁH2O was related to
the water molecule release (6.1%, 5.0%, 6.7% and 6.0%,
respectively). The dehydration process was observed as a
broad endothermic peak in DSC thermograms. Afterward, an
exothermic peak appeared in thermograms of H2L3 and H2L5
5
(Figs. S3 and S5) suggesting
a
solidꢀtoꢀsolid phase
Scheme 3. The structural formula of [Co(HL)(L)] complex (showing
60
hydrazonato HL– form and hydrazidato L2– form).
10 transformation (see ESI Figs. S7 and S8†). On the other hand,
in the case of H2L2ꢁH2O and H2L6ꢁH2O an exothermic peak
during the heating process was not observed (Figs. S2 and
S6†). To inspect in detail, samples were heated from the
ambient temperature at various heating rates (2, 10, 20 and 50
15 °C min−1). Again, no peaks were observed up to the
temperature associated with melting endotherm. As seen form
PXRD patterns the absence of the solvent molecule in H2L2
induced certain shifts in the peak position whereas in case of
H2L6 the unsolvated compound showed a diffractogram
20 significantly different from that of H2L6ꢁH2O (see ESI Figs.
S9 and S10†). Additionally, the resulting materials obtained
by the solid state desolvation of H2L5ꢁH2O and H2L6ꢁH2O
exhibited PXRD patterns consistent with those simulated
from the singleꢀcrystal data for the anhydrous H2L5 and H2L6,
25 respectively (Fig. S8 and S10).
The melting endotherms of the anhydrous hydrazones are very
sharp, occurring over a narrow temperature interval thus
indicating purity of the compounds. From DSC measurements
it follows that the melting points for H2L1–6 were 268 °C
30 (ꢀfusH = 37 kJ mol–1), 194 °C (ꢀfusH = 25 kJ mol−1), 229 °C
(ꢀfusH = 31 kJ mol–1), 179 °C (ꢀfusH = 22 kJ mol–1), 191°C
(ꢀfusH = 32 kJ mol–1) and 181 °C (ꢀfusH = 25 kJ mol–1),
respectively.
In all compounds formed after chelation, the ligands were
found to exist in differently deprotonated forms (Scheme 3).
The protonation state and formation of [Co(HL)(L)] was
supported by IR and NMR spectroscopy as well as by the
65 single crystal Xꢀray diffraction method.
Molecular and crystal structures of the H2L3, H2L5 and H2L6
ligands
Crystals of the anhydrous hydrazones H2L3, H2L5 and H2L6
70 suitable for single crystal Xꢀray diffraction (SCXRD) were
obtained from ethanol.54 In the crystal structures of all three
ligands, hydrazone molecules are found in the same
tautomeric form. As it is evident from the relevant bond
distances (see ESI, Table S1†),55 aldehyde residues of the
75 molecules adopt the enolꢀimino form, while their hydrazone
−(C=O)− linkages assume the keto form. In each case, the
molecular structure is stabilized by a strong intramolecular
hydrogen bond of the O–HꢁꢁꢁN type, characteristic for the
oꢀhydroxy Schiff bases (Table S1).
80 H2L3 molecules adopt a synꢀconfiguration, when taking into
consideration relative position of O1 and O2 oxygen atoms
(Fig. 2 a)). The 4ꢀmethoxysalicylidene residue and the central
hydrazone linkage, =N−NH−(C=O)−, are essentially coplanar,
while the terminal 4ꢀhydroxybenzene ring is twisted in such a
85 way to form a dihedral angle of 39.94(6)° with respect to the
plane of the aldehyde ring. Crystal structure of H2L3 unveils a
complex hydrogen bonding network formed by two types of
intersecting hydrogenꢀbonded chains (see ESI, Fig. S12†).
The first type corresponds to infinite zigꢀzag hydrogenꢀbonded
90 C(8) chains that grow parallel to bꢀaxis and are realized
through O3–H3OꢁꢁꢁO1 hydrogen bonds. As each molecule
additionally associates with the neighbouring ones via N2–
H2NꢁꢁꢁO2 hydrogen bonds, it leads to formation of the second
type of hydrogenꢀbonded chain, C(7) one, which runs along
95 the cꢀaxis. Supramolecular assembly formed in such a way is
further stabilized and extended into a threeꢀdimensional
network through C–HꢁꢁꢁO interactions (Fig. S12).
Synthesis of cobalt(III) complexes with hydrazone ligands
35 The mononuclear cobalt(III) complexes [Co(HL1–6)(L1–6)]
(1−3) were prepared solvothermally in methanol by the
reaction of [Co(acac)3] with the corresponding hydrazone
ligand H2L1–6 in a 1:2 metal to ligand ratio. Reactions were
also performed in methanol under refluxing conditions.
40 However, they resulted in a significantly lower yield even
after longer reaction time. All complexes are dark red
crystalline solids soluble in coordinating solvents such as dmf
or dmso and only moderately soluble in pyridine, picoline or
methanol. Thermal stability of these complexes was
45 investigated in the atmosphere of pure oxygen. The first step
in the thermogravimetric curve of 6ꢀMeOH was related to the
loss of MeOH molecule (131–155 °C) and was followed, on
further heating, by significant weight loss at 291 °C due to
ligand decomposition. For TG measurement, the crystals of
50 2·0.7MeOH were stored into a desiccator and then placed in a
freezer (at −15 °C). TG measurement showed gradual mass
loss in the range 159–285 °C ascribed to loss of methanol (see
ESI Fig. S11(a)†). Desolvation of 2·0.7MeOH also occurred
upon prolonged standing at room temperature and afforded the
55 stable crystalline form of 2 as the final residue (Fig. S11(b)).
Compounds 1–6 started to decompose at 317 °C for 1, 330°C
for 2, 331 °C for 3, 347 °C for 4, 297 °C for 5, 291 °C for 6.
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As opposed to molecules of H2L3, those of H2L5 assume an
antiꢀconfiguration when considering the position of O1 and
O2 atoms (Fig. 2 b)). While the inner hydrazone portion and
25 the aldehyde part of the molecule remain planar, the terminal
benzene ring is tilted 62.30(8)° away from this plane. The
adopted antiꢀconfiguration with favourable alignment of
hydrogen bond donors and acceptors allows formation of
2
centrosymmetric hydrogenꢀbonded dimers, displaying a R2 (8)
30 motif which is accomplished through N2–H2NꢁꢁꢁO1 hydrogen
bonds (see ESI, Fig. S13†). The dimers associate via C7–
H7ꢁꢁꢁO2 interactions into endless chains which run along the
bꢀaxis. Such chains are joined into layers via C5–H5ꢁꢁꢁO3
interactions, which are finally stacked through van der Waals
35 interactions (Fig. S13).
4ꢀmethoxysalicylaldehyde benzhydrazone (H2L6) crystallizes
in the space group Pc with two molecules per asymmetric
unit. As can be seen from Fig. 3 the two molecules differ
substantially in the orientation of the methoxy moiety on the
40 position four of the salicylaldehyde ring. Moreover, there is
an apparent difference in the conformation of the molecules
(Fig. 3), while both of them adopt a synꢀconfiguration when
referring to O1 and O2 atoms. In the crystal, molecules
connect via N–HꢁꢁꢁO hydrogen bonds, each independent
45 molecule with its own kind, thus forming hydrogenꢀbonded
chains C(4) motifs which spread along the cꢀaxis. Such chains
are stabilized and mutually connected through C–HꢁꢁꢁO
interactions (see ESI, Fig. S14†).
Fig. 2. Mercuryꢀrendered ORTEP view of molecular structures of: a)
H2L3, and b) H2L5. The displacement ellipsoids are drawn at the 50%
probability level at 296(2) K while the hydrogen atoms are drawn as
spheres of arbitrary radius. Intramolecular hydrogen bonds of the O–HꢁꢁꢁN
type, yielding a S(6) motif, are shown as orange dashed line.
5
50 Molecular and crystal structure of 2
The asymmetric unit of 2 contains complex molecule in
general crystallographic position and loosely bound 0.7
methanol of crystallization per complex molecule (Fig. 4).
The methanol molecules are arranged within channels of the
55 crystal structure along the a axis (Fig. S15, see ESI†). The
Co(III) ion is octahedrally coordinated via two ONO
tridentate ligands which differ in their protonation state, see
Scheme 3) preserving electroneutrality of the complex
molecule as a whole. The imino nitrogen atoms are axially
60 positioned (Co1−N11 1.880(2) Å and Co1−N21 1.867(2) Å)
and four oxygen atoms constitute equatorial plane of the
octahedron. The deformation from ideal octahedral geometry
is manifested in trans octahedral bond angles values which
amount 171.65(10)°, 177.53(9)° and 178.75(9)° and cis
65 octahedral bond angles values which are in the range
83.18(10)° − 94.87(10)°.
The Co−O(phenolate) bonds values amount 1.879(2) Å and
1.899(2) Å for Co1−O12 and Co1−O22 bonds, respectively,
and the Co−O cobaltꢀtoꢀ(hydrazonato) oxygen atoms bond
70 distance values amount: Co1−O11 1.928(2) Å and Co1−O21
1.884(2) Å. One ligand acts in a hydrazonato HL– form, while
the other is in the hydrazidato L2– form (at O12 in the first
ligand, and O22 and O21 in the second one). Since the ligand
molecule labelled as first one is in the singlyꢀdeprotonated
75 form, the trend that Co1−O11 bond distance (1.928(2) Å) is
longer than Co1−O12 bond distance (1.879(2) Å) in the same
ligand is expected.
Fig. 3. a) Mercuryꢀrendered ORTEP view of molecular structures of the
two molecules constituting the asymmetric unit of H2L6 (topꢀmolecule 1;
bottomꢀmolecule 2). For clarity, molecules are not shown in their true
position within the asymmetric unit. The displacement ellipsoids are
drawn at the 30% probability level at 296(2) K. The hydrogen atoms are
drawn as spheres of arbitrary radius. Intramolecular hydrogen bonds of
the O–HꢁꢁꢁN type are shown as orange dashed lines. b) Overlapping
10
15 diagram of the two molecules comprising the asymmetric unit of H2L6
(light brownꢀmolecule 1; blueꢀmolecule 2). The diagram was constructed
by overlying O11, C11, N12 and N11 atoms with O21, C21, N22 and
N21 atoms, respectively. Dihedral angle between the planes of the
aldehyde and the benzene rings is 26.9(3)° for molecule 1, and 35.5(3)°
20
for molecule 2.
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45
Fig. 5. The alternated assembling of two supramolecular hydrogen
bonded rings via O13−H13O···N22 (ring A) and O23−H23O···O12 (ring
B) intermolecular hydrogen bonds in the crystal structure of 2.
Fig. 4. Mercury–rendered ORTEP view of the molecular structure of
complex 2ꢀ0.7MeOH. The displacement ellipsoids are drawn at the 50%
probability level at 296(2) K after use of SHELXLꢀ2013 SQUEEZE
instruction. The atomꢀnumbering crystallographic scheme has been
applied. The hydrogen atoms are drawn as spheres of arbitrary radius.
5
On the other hand, comparing bond distances within the
coordination sphere, the O21 atom of the doubly deprotonated
ligand (Co1−O21 bond distance of 1.884(2) Å within the fiveꢀ
10 membered chelate ring fragment) is found to be more tightly
bound to the Co(III) ion than the O11 atom of the singlyꢀ
deprotonated ligand (Co1−O11 1.928(2) Å). The similar trend
one can observe for Co1−N11 1.880(2) Å and Co1−N21
1.867(2) Å bonds exhibiting stronger bond with the nitrogen
15 atom of the doublyꢀdeprotonated hydrazonato ligand enhanced
by more pronounced delocalization.
50
Fig. 6. Bifurcation of N12−H12N group at two proton donors in 2
between two proton acceptors: the phenolate O22 atom and the methoxy
O24 atom thus forming two hydrogen bonds: N12−H12N···O22 of the
distance value 3.066(3) Å and N12−H12N···O24 2.770(4) Å.
The coexistence of both forms within a complex is evidenced
by the bond distances values (see ESI Table S3a†) in the
region of fiveꢀmembered chelate ring which is in agreement
20 with the position of the electron density maximum
corresponding to the H12N hydrogen atom of the hydrazone
NH group. Therefore, the keto C11−O11 bond distance values
amounts 1.278(3) Å, on the contrary to the value of 1.309(3)
Å for the O21−C21 bond distance value. The N12−C11 bond
25 distance of 1.333(4) Å is more σ in character opposite from
N22−C21 which is shortened to the value of 1.315(4) Å.
The proton of the hydroxyl O23−H23O is bifurcated between
two proton acceptors; one is phenolate oxygen O12 atom and
the other is methoxy O14 atom, Fig. 5. The supramolecular
30 centrosymmetrical ring is formed via O23−H23O···O12
intermolecular hydrogen bond between hydroxyl group and
phenolate O12 donor atom (see ESI Fig. S16, Table S4†). The
O13−H13O···N22 intermolecular hydrogen bond of 2.734(4)
Å between hydroxyl O13−H13O group and the nonꢀdonor
35 nitrogen atom N22 forms another supramolecular hydrogen
bonded ring which alternates within crystal structure of 2 with
the former (Fig. 5, Table S4†). Bifurcation of the N12−H12N
protonꢀdonor group in 2 between two proton acceptors: the
phenolate O22 atom and the methoxy O24 atom are shown in
40 Fig. 6. Therefore, two intermolecular hydrogen bonds are
formed: N12−H12N···O22 and N12−H12N···O24 (Table
S4†). The formation of 3D hydrogen bonded network
including all above mentioned types of hydrogen bonds is
given in ESI, Fig. S17.
55 Molecular and crystal structure of 1 and 6·MeOH
The Co(III) ion in and 6·MeOH is situated at
1
crystallographically imposed twoꢀfold axis (Fig. S18, Fig.
S19, see ESI†). In this way, the asymmetric unit contains half
of the complex molecule. The coordination around Co(III) ion
60 in both complexes is best described as a distorted octahedron
formed by two condensed chelate rings comprising tridentate
ONO aroylhydrazone ligands. From the crystallographical
point of view, both ligands are represented as an average of
hydrazonato HL– and hydrazidato L2– forms, which is
65 achieved by occupational factor of H12N atom to be set up as
0.5 during crystallographic refinement. Therefore, the request
for
symmetry
and
simultaneously
for
complex
electroneutrality is preserved.
In complex 1 each of the two ligands coordinate to Co(III) ion
70 with the hydrazone oxygen (Co1−O1 1.892(2) Å), phenolate
oxygen (Co1−O2 1.884(2) Å) and imine nitrogen donor atoms
(Co1−N1 1.874(3) Å) being in axial positions, to form two
chelate rings: sixꢀmembered with the O2 and N1 donor atoms
and fiveꢀmembered with the N1 and O1 donor atoms. The
75 deformation from ideal octahedral geometry is manifested in
trans octahedral bond angles values which amount 172.05(18)
and 178.70(10)° and cis octahedral bond angles values which
are in the range 83.68(11)° − 95.24(11)° (Table S3(b)).
The structurally analogous complex 6 exhibits comparable
80 geometrical parameters: (Co1−O1 1.921(2) Å, Co1−O2
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1.886(2) Å and Co1−N1 1.876(2) Å) (Table S3(b)). In the
region of fiveꢀmembered chelate ring, which is most
dependent on the type of forms, HL– or L2–, the C1−O1 bond
distance of 1.289(4) and 1.285(3) Å in 1 and 6·MeOH,
checking the dominant molecular interactions in crystal
structures of 1 and 2.
According to the calculated values (Table 2) crystal structures
of 1 and 2 were more stable than 1' and 2', respectively. The
5
respectively, and N2−C1 bond distance of 1.325(4) and 55 presence O–H···O and N–H···N hydrogen bonds in 1 was
1.331(4) Å in 1 and 6·MeOH, respectively, are an average of
the HL– and L2– fiveꢀmembered chelate rings (Table S3b).
In complex 1 the coꢀexistence of two ligand forms, which
differ in their protonation states, is maintained by the
shown to be a stability factor in contrast to O–H···N and N–
H···O hydrogen bonds in 1' (Fig. 8). Likewise, the presence
of O–H···N hydrogen bond and bifurcated hydrogen bond
between N–H group of singlyꢀdeprotonated ligand and
10 intermolecular hydrogen bond N2−H12N···N2 (Table S4). 60 phenolate and methoxy oxygen atoms in 2 was shown to be
The hydrogen bond distance value of 2.811(4) Å and bond
angle value of 163(7)° (for the N2−H12N···N2 angle) are
both within expected range values for N−H···N type of
hydrogen bond. This hydrogen bond assembles complex
15 molecules into infinite 1D chain along a axis (Fig. 7).
The H13O hydrogen atom of the hydroxyl group of
4ꢀhydroxybenzhydrazone ligand is bifurcated thus forming
two intermolecular hydrogen bonds with the phenolate O2 and
imine N1 atoms (Table S4†) with the former bond being
20 expectedly stronger and more linear. The O3–H13O···O2
intermolecular hydrogen bonds forms infinite 2D chains of
fused rings spreading along b axis in a zigꢀzag manner (see
ESI; Fig. S20†).
more stable than N–H···N hydrogen bond and bifurcated
hydrogen bond between the O–H group and phenolate and
methoxy oxygen atoms in 2', respectively (Fig. 9, Table 2).
The crystal structure of 6·MeOH is dominated by the
25 N−H···O type of intermolecular hydrogen bond (Table S4).
The other hydrogen bonds are of the C–H···O type and
include all oxygen atoms O1, O2, O3 and O4 (see ESI; Fig.
S21†).
65 Fig. 8. Tetrameric model of a) crystal structure of 1 and b) 1' (1 with the
same packing as in 2).
30 Fig. 7. Fraction of crystal structure of complex 1 showing assembling of
complex molecules in ac plane into 1D infinite chains via N2–H12N···N2
intermolecular hydrogen bond (denoted as orange dashed line).
Quantum chemical calculations
In order to investigate and quantify molecular interactions
35 within the unit cells, extensive quantum chemical analysis was
performed. Firstly, models of four complexes of 1 and four
complexes of
2 were built from crystal structures and
geometry optimization were performed using B3LYP hybrid
functional and D3 version of Grimme’s dispersion with
40 BeckeꢀJohnson damping56 with 6ꢀ31g(d) basis set (Figs. 8a
and 9a). After that the model 1' of four complexes of 1 with
the same packing of structure 2 was built by removing
methoxy groups from ligands in the optimized structure of 2
(Figs. 8b). Vice versa, the model 2' of four complexes of 2
45 with the same packing of structure 1 was built by adding
methoxy groups on the optimized structure of 1 (Fig. 9b).
Additional geometry optimizations and harmonic frequency
calculations were performed. The goal of this analysis was to
establish the quantitative relationship between the structures
50 by comparing standard Gibbs energies of formation and
Fig. 9. Tetrameric model of a) crystal structure of 2 and b) 2' (2 with the
same packing as in 1).
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Table 2. Standard Gibbs energies of formation for four complexes of 1
are suitable for accommodation of the methanol molecules
(Fig. S15†).
50 Although, both complexes 2 and 6·MeOH contain –OCH3
group; in complex 6·MeOH it acts as proton acceptor in the
formation of the C–H···O type of the hydrogen bond, and not
and 2 and models 1' and 2' build from their crystal structures calculated
with B3LYP and D3 version of Grimme’s dispersion with BeckeꢀJohnson
damping with 6ꢀ31g(d) basis set.
Compound
ꢂrG°/kJ mol–1 ꢂrG°/kJ mol–1
in
the
formation
of
hydrogen
bond
with
(relative to 1)
(relative to 2)
–NH group, like in 2. Thus, the supramolecular role of MeOH
55 solvent molecule of crystallization in the stabilization of
hydrogen bonding is evident considering its competition with
–OCH3 group for hydrogen bond formation with the –NH
group.
1 (built from crystal structure)
1' (built from crystal structure of 2)
2 (built from crystal structure)
0.0
190.41
–
–
–
–
0.0
2' (built from crystal structure of 1)
145.82
5
Comparative structural analysis
The molecular structures of 1 and 6·MeOH exhibit metrical
parameters resemblance. Namely, both complexes contain
Co(III) ion positioned at twoꢀfold axis and thus both forms,
10 singlyꢀ and doublyꢀdeprotonated form of the particular ligand,
are present as an averaged structure preserving
electroneutrality of the complex molecule as a whole. On the
contrary, the asymmetric unit of
2 reveals Co(III) ion
coordinated by HL− and L2− ligand forms, separately. This is
15 crystalographically evidenced as the averaged metrics of two
different ligand forms in 1 and 6·MeOH in comparison with
two ligand forms in 2 (Table 3).
Table 3. Comparison of bond distances within fiveꢀmembered chelate
ring (Å) in 1, 2 and 6·MeOH
HL− ligand in 2
L2− ligand in 2
Bond
1
6·MeOH
N1−N2 1.403(4) 1.405(3) N11−N12 1.380(3) N21−N22 1.385(4)
N2−C1 1.325(4) 1.331(4) N12−C11 1.333(4) N22−C21 1.315(4)
C1−O1 1.289(4) 1.285(3) O11−C11 1.278(3) O21−C21 1.309(3)
60
Fig. 10. Channels in the structure of 1 spreading in aꢀaxis direction
(similar is in bꢀ and cꢀaxis directions).
20
Although, ligand skeleton is highly delocalized π system
(particularly that which is doublyꢀdeprotonated), it is apparent
that O11−C11 bond distance in 2 reflects dominantly double
character, while O21−C21 in 2 is dominantly σ in character.
25 As opposed, the C1−O1 bond distances in 1 and 6·MeOH are
intermediates between a carboxyl C−O single (1.31 Å) and
C=O double bond (1.21 Å). The shortest C=N bond distance
value is expectedly found in the doublyꢀdeprotonated form
(N22ꢀC21 1.315(4) Å in 2), while the analogous bond distance
30 in the singlyꢀdeprotonated form (N12−C11 1.333(4) Å in 2) is
in accordance with its more pronounced singleꢀbond
character.
The presence of both ligand forms HL− and L2− in 1 and
6·MeOH is stabilized via supramolecular assembling by
35 means of the N2−H12N···N2 intermolecular hydrogen bond
in 1 or N2−H12N···O4 in 6·MeOH with MeOH molecule. In
both cases, 1D infinite chains are formed resulting in channels
that spread in each space dimension of the crystal structure
(Fig. 10).
40 This stabilization occurs in 2 in the way that the proton donor
N12−H12N group of HL– ligand forms hydrogen bonded
centrosymmetrical dimers with the methoxy oxygen atom of
the adjacent complex molecule showing bifurcation by
forming additional hydrogen bond with the phenolate oxygen
45 atom. This additional bond is responsible for the
interconnected structure with smaller number of channels
(Fig. 11). The channels that are formed in the structure of 2
65 Fig. 11. Channels in the structure of 2 spreading in cꢀaxis direction (there
are no similar channels in other directions).
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NMR spectroscopy
Complexes 1−6 were characterized via 1D and 2D 1H NMR
spectroscopy in DMSOꢀd6 (see ESI, Fig. S22ꢀS27). The 1H
NMR spectra of all the complexes, recorded immediately after
dissolution, show only one set of signals, in agreement with a
centrosymmetric configuration of the complexes. The signals
due to the C10ꢀOH and to =N−NH are absent in the spectra of
the coordinated chelates, indicating that the ligands undergo
deprotonation and that the protons involved in the
5
10 intermolecular hydrogen bonds exchange fast in solution. The
N=CH resonance is shifted downfield of about 0.3 ppm
relative to the free ligand, as a result of the electronic
redistribution consequent to complexation, as it was
previously observed for the related Mo complexes.57 These
15 data indicate that the coordination mode found in the crystal
structures is retained in solution. The signals of the C5ꢀOH
protons in complexes 1−3 are broad and they are likely
involved in a chemical exchange process.
1
The H NMR spectra of 1 and 4 did not change with time. On
20 the contrary, a second set of signals, corresponding to the free
ligand, developed in the spectra of the other complexes. This
second set increased with time, reaching after about 10 days
an integrated intensity, relative to the signals of the starting
complexes, of 3% and 6% for 2 and 5, respectively, and of 7%
25 and 23% for 3 and 6. The above results suggest a different
stability of the complexes in DMSOꢀd6 solution, the
complexes with the H2L1,4 ligands being more stable than
those with H2L2,5 and those with H2L3,6 being the least
stable.
Fig. 12 1H NMR spectrum of complex 1 in DMSOꢀd6 (a) with a ratio
[NaOH]/ [complex ] = 1.1, recorded (a) immediately after the addition;
60 (b) after 15 min. Successive spectra were recorded at intervals of 5 min.
30 In order to investigate the acidꢀbase behaviour of the
1
complexes in solution, a H NMR titration was carried out on
1 and 5. The complexes dissolved in DMSOꢀd6 (about 5×10−3
mmol in 0.8 mL of solvent) were titrated in the NMR tube
with a 0.5 M solution of NaOH dissolved in D2O. The
35 chemical shift changes relative to the starting complex (ꢀδ)
were plotted at different [NaOH]/[complex] ratios. For 5, all
the resonances are shifted upfield up to the addition of about a
1:1 amount of NaOH (see ESI, Fig. S28(a)†), whereas
successive additions do not cause a further shift, indicating
40 that the complex behaves as a monoprotic acid. A parallel
experiment carried out on 1 (see ESI, Fig. S28(b)†) shows a
similar behavior for additions up to 1:1, but the signals keep
moving upfield for further additions of NaOH (up to about a
3:1 ratio). This second acidꢀbase process affects mainly the
45 resonances of the protons closer to C5ꢀOH, indicating that the
deprotonation occurs at the phenolic protons.
Fig. 13 PC1 scores obtained by principal component analysis of NMR
spectra presented on Fig. 12 in dependence of time.
65
IR spectroscopy
It is worth of noting that, for [NaOH]/[complex] ratios
ranging from about 1 to about 3, the upfield shift is associated
with a severe broadening of the signals at 6.75 ppm (C4ꢀH and
50 C6ꢀH) and 7.74 ppm (C3ꢀH and C7ꢀH), which become sharp
again with time (Fig. 12, see ESI, Fig S29†). In this pH range,
the complex reacts to give the double and triple deprotonated
species: a fast deprotonation followed by a relatively slow
equilibration between the species may explain the evolution of
55 the signals with time. Reaction profile obtained by principal
component analysis is presented on Fig. 13.
The spectra of all complexes show two set of bands in
agreement with formulation of complexes 1−6 as
[Co(HL)(L)], with singlyꢀ and doublyꢀdeprotonated ligands
70 (Scheme 3). Assignments are corroborated with high level
quantum chemical calculations. The band characteristic for
the C=O group at ca. 1645 cm−1 (seen in the IR spectrum of
H2L) is shifted to 1545−1515 cm−1 in the spectra of the
complexes, suggesting coordination of hydrazonato HL–
75 ligand through the carbonyl oxygen atom. On the other hand,
the presence of a new band in the range of 1385–1280 cm−1,
due to stretching vibrations of the C−O bond, suggests
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tautomerism
(=N−NH−(C=O)−
ꢀ
=N−N=(C−OH)−),
modes: 1D infinite chains in
centrosymmetrical dimers in 2.
The preferred formation of O–H···O and N–H···N hydrogen
1
and 6·MeOH, and
deprotonation and coordination of hydrazidato L2– form
through the oxygen atom.
In the IR spectra of the ligands vibration bands belonging to 60 bonds in 1 over the O–H···N and N–H···O hydrogen bonds,
5
C=Nimine and C−Ophenolic groups are found at ca. 1630 and
1355 cm−1, respectively. In the case of HL– ligand these bands
are shifted to 1614−1606 cm−1 and 1386−1380 cm−1. For L2–
ligand they are found at lower wavenumbers (in the range
results in channels that spread in each space dimension of the
crystal structure. On the contrary, when formation of O–H···N
and N–H···O in 2 is more stable than O–H···O and N–H···N,
than the reaction favours the formation of interconnected
1607–1598 cm–1 and 1285–1241 cm−1). This finding clearly 65 structure with channels that spread only in one direction.
10 indicates coordination of the ligands to the metal centre
through the nitrogen and oxygen atoms of these two groups.
Such channels that are formed in the structure of 2 are suitable
for the accommodation of the methanol molecules.
UVꢁVis spectroscopy
Experimental section
The electronic absorption spectrum of the ligands H2L1 and
H2L4 exhibit several absorption bands with distinct maxima at
15 290, 300 and 328 nm and at 289, 300 and 329 nm,
respectively. These transitions are assigned to the intraꢀligand
charge transfer transitions.58,59 Similar results are observed for
H2L2 and H2L5 (at 303, 312 and 342 nm and at 303, 311 and
341 nm, respectively) as well as for H2L3 and H2L6 (at 291,
20 302 and 331 nm and at 292, 302 and 332 nm, respectively).
The cobalt(III) complexes display absorptions with maxima at
402 and 421 nm (1), 400 and 421 nm (2), 392 and 413 nm
(3), 405 and 423 nm (4), 410 and 429 nm (5), and at 398 and
416 nm (6). These transitions correspond to the ligandꢀtoꢀ
25 metal charge transfer transitons.60 Each complex displays
additional bands in the higher energy region characteristic for
intraꢀligand transitions.
Preparative part. All starting materials, reagents, and metal
70 salt were purchased from commercial sources and used as
received. The starting complex [Co(C5H7O2)3] (C5H7O2
acetylacetonate) was prepared as described in the literature.61
=
Mechanochemical synthesis of H2L1ꢁꢁ6
75 All reactions were carried out using a Retsch MM200 ball mill
operating at 25 Hz frequency. 4ꢀHydroxybenzhydrazide or
benzhydrazide (1 mmol), and the appropriate aldehyde (1
mmol of salicylaldehyde, 3ꢀmethoxyꢀsalicylaldehyde or
4ꢀmethoxysalicylaldehyde),
methanol
(40
ꢃL)
and
80 acetanydride (5 ꢃL) were placed with two 7 mm grinding balls
in a 10 mL stainless steel jar. The reactants were ground for
40 min to obtain H2L1, 20 min to obtain H2L2ꢁH2O, 60 min to
obtain H2L3ꢁH2O, 30 min to obtain H2L4, 30 min to obtain
H2L5ꢁH2O and 60 min to obtain H2L6ꢁH2O. Then, the samples
85 were left in air at room temperature.
Conclusions
The work presented here demonstrates the mechanochemical
30 strategy as a successful route for the preparation of the
aroylhydrazone ligands. We have indicated the importance of
catalytic amounts of methanol/acetanhydride for their
synthesis via liquid assisted grinding procedure. Desolvation
of hydrates and polymorph interꢀconversion of the hydrazones
35 result in the formation of the unsolvated forms, three of which
have been structurally characterized via single crystal Xꢀray
diffraction method.
Solvothermal synthesis of cobalt(III) complexes
A mixture of [Co(C5H7O2)3] (0.42 mmol) and the appropriate
aroylhydrazone (0.84 mmol) in methanol (25 mL) was
suspended in a 35 mL Teflon liner, which was sealed in an
90 autoclave and heated at 110 °C for 5 h. The solution was
allowed to cool slowly, resulting in the formation of dark red
almost black product. The obtained product was filtered and
dried up to constant weight.
The mononuclear complexes [Co(HL)(L)] containing
differently deprotonated aroylhydrazone ligands have been
40 obtained by the reaction of the corresponding ligand H2L and
[Co(acac)3] under solvothermal conditions. The molecular and
crystal structures analyses of 1, 2 and 6·MeOH revealed
octahedral arrangement of the tridentate ONO ligands via
formation of two condensed chelate rings and the presence of
45 both forms of the particular ligand (HL– and L2–) in the same
complex molecule. The bond distances values in the
coordination sphere of Co(III) are influenced by many factors
such as charge, degree of the ligand deprotonation and
involvement of the donor atom into hydrogen bond formation.
50 The stabilization of the particular ligand form in the complex
molecules occurs via intermolecular hydrogen bond formation
between the –NH group of the singlyꢀdeprotonated ligand
form and the nitrogen atom of the doublyꢀdeprotonated form
(in 1), with the phenolate and methoxy oxygen atoms (in 2) or
55 with the solvent methanol molecule (in 6·MeOH). These
hydrogen bonds shape different supramolecular assembling
95 [Co(HL1)(L1)] (1). Yield: 0.23 g, 84%. Calc. for
C28H21CoN4O6 (568.422): C, 59.2; H, 3.7; N, 9.9. Found: C,
58.9; H, 3.8; N, 9.7%. TG: calc. Co3O4 14.1%, found 14.0%.
Selected IR data (cm−1): 1609 (C=NHL), 1600 (C=NL), 1590
(ring C=C), 1545 (C=OHL), 1389 (C–NHL), 1380 (C–
100 Ophenolate,HL), 1278 (C−OL), 1241 (C–Ophenolate,L). UVꢀ
1
Vis(dmso):
λ
/nm: 274, 302, 338, 402 and 421. H NMR (400
MHz, DMSOꢀd6, TMS): δ = 6.54 (t, 1H; C13ꢀH), 6.60 (m, 1H;
C11ꢀH ), 6.75 (d, 2H; C4ꢀH and C6ꢀH), 6.94 (t, 1H; C12ꢀH),
7.59 (d, 1H; C14ꢀH), 7.74 (d, 2H; C3ꢀH and C7ꢀH), 8.89 (s,
105 1H; C8ꢀH), 10.21 (br s, 1H; C5ꢀOH).
[Co(HL2)(L2)] (2). 0.22 g, 85%. Crystals of the compound
2ꢀ0.7MeOH lose solvated molecules at room temperature and
were analyzed as unsolvated species. Calc. for C30H25CoN4O8
110 (628.474): C, 57.3; H, 4.0; N, 8.9. Found: C, 57.7; H, 4.3; N,
8.5%. TG: calc. Co3O4 12.8%, found 13.1%. Selected IR data
(cm−1): 1608 (C=NHL), 1607 (C=NL), 1592 (ring C=C), 1530
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Physical methods
(C=OHL), 1392 (C–NHL), 1384 (C–Ophenolate,HL), 1281 (C−OL),
1242 (C–Ophenolate,L). UVꢀVis(dmso): /nm: 275, 302, 339,
400 and 421. H NMR (400 MHz, DMSOꢀd6, TMS): δ = 3.61
(s, 3H; OCH3), 6.16 (m, 2H; C11ꢀH and C13ꢀH), 6.74 (d, 2H;
C4ꢀH and C6ꢀH), 7.49 (d, 1H; C14ꢀH), 7.73 (d, 2H; C3ꢀH and
C7ꢀH), 8.79 (s, 1H; C8ꢀH), 10.23 (br s, 1H; C5ꢀOH).
λ
Elemental analyses were provided by the Analytical Services
60 Laboratory of the Ruđer Bošković Institute, Zagreb.
Thermogravimetric (TG) analysis was carried out with a
1
5
MettlerꢀToledo
TGA/SDTA851e
thermobalance using
aluminum crucibles. All experiments were recorded in a
dynamic atmosphere with a flow rate of 200 cm3 min−1.
65 Heating rates of 5 K min−1 were used for all investigations.
Differential scanning calorimetry (DSC) measurements were
carried out with a MettlerꢀToledo DSC823e calorimeter and
analyzed by the Mettler STARe 9.01. software. Fourier
Transform Infrared spectra (FTꢀIR) were recorded in KBr
70 pellets with a PerkinꢀElmer 502 spectrophotometer. Spectra
were recorded in the spectral range between 4500−450 cm−1.
[Co(HL3)(L3)] (3). Yield: 0.21 g, 81%. Calc. for
C30H25CoN4O8 (628.474): C, 57.3; H, 4.0; N, 8.9. Found: C,
10 57.7; H, 4.3; N, 8.5%. TG: calc. Co3O4 12.8%, found 13.2%.
Selected IR data (cm−1): 1614 (C=NHL), 1606 (C=NL), 1588
(ring C=C), 1536 (C=OHL), 1388 (C–NHL), 1384 (C–
Ophenolate,HL), 1286 (C−OL), 1241 (C–Ophenolate,L). UVꢀ
1
Vis(dmso):
λ
/nm: 274, 339, 392 and 413. H NMR (400 MHz,
15 DMSOꢀd6, TMS): δ = 3.36 (s, 3H; OCH3), 6.42 (t, 1H; C13ꢀ
H), 6.54 (d, 1H; C12ꢀH), 6.72 (d, 2H; C4ꢀH and C6ꢀH), 7.21
(d, 1H; C14ꢀH), 7.72 (d, 2H; C3ꢀH and C7ꢀH), 8.88 (s, 1H;
C8ꢀH), 10.18 ( br s, 1H; C5ꢀOH).
1
1D and 2D H NMR spectra were recorded on a Jeol EXꢀ400
instrument (1H at 400 MHz and 13C at 100.4 MHz). Electronic
absorption spectra were recorded at 25 °C on a Cary 100 UVꢀ
75 Vis Spectrophotometer.
20 [Co(HL4)(L4)] (4). Yield: 0.18 g, 82%.
Calc. for
XꢁRay Crystallography. Powder diffraction.
C28H23CoN4O4 (536.424): C, 62.7; H, 3.9; N, 10.4. Found: C,
62.3; H, 3.8; N, 10.25%. TG: calc. Co3O4 15.00%, found
14.65%. Selected IR data (cm−1): 1606 (C=NHL), 1598
(C=NL), 1593 (ring C=C), 1519 (C=OHL), 1389 (C–NHL), 1386
The powder Xꢀray diffraction data were collected by the
Panalytical X’Change powder diffractometer in the Braggꢀ
Brentano geometry using CuKα radiation. The sample was
80 contained on a Si sample holder. Patterns were collected in
25 (C–Ophenolate,HL), 1283 (C−OL), 1282 (C–Ophenolate,L). UVꢀ
the range of 2θ = 5 − 50° with the step size of 0.03° and at 1.5
1
Vis(dmso):
λ
/nm: 270, 300, 336, 405 and 423. H NMR (400
s per step. The data were collected and visualized using the
X'Pert programs Suite.62
MHz, DMSOꢀd6, TMS): δ = 6.49 (t, 1H; C13ꢀH), 6.53 (d, 1H;
C11ꢀH ), 6.89 (t, 1H; C12ꢀH), 7.36 (d, 2H; C4ꢀH and C6ꢀH),
7.45 (m, 1H; C5ꢀH), 7.57 (d, 1H; C14ꢀH), 7.87 (d, 2H; C3ꢀH
30 and C7ꢀH), 8.91 (s, 1H; C8ꢀH).
XꢁRay Crystallography. Single crystal diffraction.
85 The SCXRD data collection for all three ligands and complex
6·MeOH were conducted with an Oxford Xcalibur
diffractometer equipped with 4ꢀcircle kappa geometry and
CCD Sapphire 3 detector graphite–monocromated MoKα
[Co(HL5)(L5)] (5). Yield: 0.18 g, 73%. Calc. for
C30H25CoN4O6 (598.491): C, 60.4; H, 4.2; N, 9.4. Found: C,
59.9; H, 3.4; N, 9.1%. TG: calc. Co3O4 13.5%, found 13.8%.
35 Selected IR data (cm−1): 1606 (C=NHL), 1599 (C=NL), 1592
(ring C=C), 1514 (C=OHL), 1391 (C–NHL), 1384 (C–
radiation (λ = 0.71073 Å) at 296(2) K using ωꢀscans. Singleꢀ
90 crystal Xꢀray diffraction data collection for structures 1 and 2
was performed on Oxford Xcalibur Gemini diffractometer
equipped with Sapphire CCD detector and graphite–
Ophenolate,HL), 1285 (C−OL), 1282 (C–Ophenolate,L). UVꢀ
1
Vis(dmso):
λ
/nm: 269, 305, 339, 410 and 429. H NMR (400
monocromated CuKα radiation (
λ = 1.5418 Å) at 296(2) K
MHz, DMSOꢀd6, TMS): δ = 3.63 (s, 3H; OCH3), 6.17 (s, 1H;
40 C11ꢀH), 6.20 (d, 1H; C13ꢀH), 7.39 (m, 2H; C4ꢀH and C6ꢀH),
7.48 (m, 2H; C5ꢀH and C14ꢀH), 7.86 (d, 2H; C3ꢀH and C7ꢀH),
8.86 (s, 1H; C8ꢀH).
using ωꢀscans. The data for complex 2 has been later collected
95 again with the Oxford Xcalibur diffractometer at 150(2) K in
order to verify the presence of residual density which has been
interpreted as the solvent voids capable to fit certain amount
of MeOH molecule.
[Co(HL6)(L6)] (6ꢀMeOH). Yield: 0.18 g, 71%. Calc. for
45 C31H29CoN4O7 (598.491): C, 59.05; H, 4.95; N, 8.9. Found: C,
59.2; H, 4.7; N, 8.7%. TG: calc. for MeOH 5.1%, found 5.2%;
TG: calc. Co3O4 12.8%, found 13.0%. Selected IR data
(cm−1): 1606 (C=NHL), 1598 (C=NL), 1591 (ring C=C), 1514
(C=OHL), 1389 (C–NHL), 1384 (C–Ophenolate,HL), 1295 (C−OL),
Data collection for all structures has been performed by
100 applying the CrysAlis Software system.63 The Lorentzꢀ
polarization effect was corrected and the intensity data
reduced and the empirical absorption correction (by the multiꢀ
scanning method) were performed, all with the CrysAlis
software package.63 The diffraction data have been scaled for
105 absorption effects by the multiꢀscanning method. Structures
solutions were accomplished by using direct methods
followed by differential Fourier syntheses. Structure
refinement was performed on F2 by weighted fullꢀmatrix
leastꢀsquares. Programs SHELXSꢀ201364 and SHELXLꢀ201364
110 integrated in the WinGX65 software system (Version 2013.3)
were used to solve and refine structures. All nonꢀhydrogen
atoms were refined anisotropically. Hydrogen atoms not
involved in hydrogen bonding were placed in geometrically
50 1261 (C–Ophenolate,L). UVꢀVis(dmso): λ/nm: 267, 342, 398 and
1
416. H NMR (400 MHz, DMSOꢀd6, TMS): δ = 3.38 (s, 3H;
OCH3), 6.45 (t, 1H; C13ꢀH), 6.56 (d, 1H; C12ꢀH), 7.25 (d,
1H; C14ꢀH), 7.38 (d, 2H; C4ꢀH and C6ꢀH), 7.48 (m, 1H; C5ꢀ
H), 7.87 (d, 2H; C3ꢀH and C7ꢀH), 8.97 (s, 1H; C8ꢀH).
55
10
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idealized positions and they were constrained to ride on their
The complex 6·MeOH contains disordered MeOH molecule
parent atoms [Csp2−ꢀH 0.93 Å with Uiso(H) = 1.2 Ueq(C) and 25 with two possible spatial orientation of MeOH molecule
Csp3ꢀH 0.96 Å with Uiso(H) = 1.5 Ueq(C)], while the others are
found as a peaks of small electronꢀdensities in difference
electronꢀdensity Fourier maps and refined with the restrained
OꢀH (0.82 Å) and N−H (0.86 Å) distances and assigned
within unit cell. This is imposed by the crystallographically
determined setting of the carbon C16 atom at the 2ꢀfold
rotation axis. Therefore, the occupancy factors of the carbon
C16 and oxygen O4 atom have been refined necessarily as
5
isotropic displacement parameters being 1.2 times larger than 30 fixed value of 0.5. The assignment of the type of atom has
the equivalent isotropic displacement parameters of the parent
atoms.
been performed on the basis of the type of disorder as well as
by participation of the oxygen O4 atom in the hydrogen bonds
formation with protonꢀdonor groups of complex molecule
(N2ꢀH12N, C7ꢀH7 and C8ꢀH8; see ESI Table S3a). No
10 As the compound H2L6 crystallizes in nonꢀcentrosymmetric
space groups (Pc) due to the absence of significant anomalous
scattering, the absolute structure could not be determined 35 hydrogen atoms have been assigned to the atoms of MeOH
reliably and the corresponding Flack parameter was omitted
from the final cif file (Flack parameter refined to a value of
15 0.8(10)).
In the complex 2·0.7CH3OH the refinement of occupancy
factors for the O1 and C1 methanol atoms gave value of 0.7. 40 made
molecule.
The molecular geometry calculations were performed by
PLATON (Version 130614)66 and PARST programs67
integrated in the WinGX software system. Drawings were
using
Mercury68
and
POVꢀRay69.
Selected
Due to that, the performance of data collection at 150(2) K is
undertaken in order to confirm the presence of residual
20 density in the crystal voids and it is also interpreted, but more
reliably, as the 0.7 MeOH molecule per complex molecule.
crystallographic and refinement data for structures obtained
via singleꢀcrystal Xꢀray diffraction are summarized in Tables
4 and 5. Main geometrical features (selected bond distances
and angles) along with hydrogen bond geometry for the
The final refinement procedure has been performed by 45 structures are given in Table S1−S3, respectively.
PLATON SQUEEZE instruction at 296(2) K data.
Table 4. Crystal data and structure refinement for ligands H2L3, H2L5 and H2L6
Ligand
H2L3
H2L5
H2L6
Chemical formula
C15H14N2O4
286.28
monoclinic, colourless, block
0.21 x 0.31 x 0.45
P21/c(No. 14)
4
C15H14N2O3
270.28
monoclinic, pale yellow, prism
0.08 x 0.18 x 0.36
P21/n(No. 14)
C15H14N2O3
Mr
270.28
monoclinic, colourless, prism
0.11 x 0.19 x 0.38
Pc(No. 7)
Crystal system, color and habit
Crystal dimensions (mm3)
Space group
Z
4
4
Unit cell parameters:
a /Å
b /Å
c /Å
15.1547(3)
8.3437(2)
10.9630(2)
90
101.307(2)
90
1359.33(5)
1.399
0.103
9.1617(5)
6.1414(4)
23.4795(12)
90
11.4472(6)
12.6502(9)
9.4907(5)
90
97.657(5)
α
/°
94.806(5)
β
/°
90
90
γ
/°
V /Å3
1316.45(13)
1.364
1362.09(14)
1.318
Dcalc /g cm–3
0.097
568
0.093
568
ꢁ
/mm–1
F(000)
600
Index range
h: –19 to 20,
k: –11 to 11,
l: −14 to 14
18347
h:–11 to 9,
k: –7 to 7,
l: –22 to 29
h:–14 to 14,
k: –16 to 16,
l: –11 to 12
15072
Reflections collected
Independent reflections
8242
3447 [R(int) = 0.019]
2778
3447/ 3/200
R1 = 0.0402; wR2 = 0.1044
2848 [R(int) = 0.027]
1832
2848 / 2 / 188
R1 = 0.0458; wR2 = 0.0940
R1 = 0.0862; wR2 = 0.1078
5950 [R(int) = 0.055]
3419
5950/ 6 / 375
R1 = 0.0644; wR2 = 0.1456
R1 = 0.1190; wR2 = 0.1735
Number of reflections with [I>2σ(I)]
Data / restraints / parameters
Final Ra indices [I>2σ(I)]
Rb indices (all data)
R1 = 0.0514; wR2 = 0.1122
a R = Σ||Fo| – |Fc||/ Σ|Fo|; b wR = {Σ[w(Fo2 – Fc2)2]/Σ[w(Fo )2]}1/2
2
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Table 5. Crystal data and structure refinement for complexes 1, 2 and 6·MeOH
Complex
1
2
6·MeOH
Chemical formula
Mr
C28H21CoN4O6
568.42
C30H25CoN4O8
628.47
C30H25CoN4O6· CH3OH
624.48
Crystal system, color and habit
Orthorhombic, dark red plate
Triclinic, dark red, irregular beaked Monoclinic, dark red cube block
plate
Crystal dimensions (mm3)
0.22 × 0.19 × 0.07
I b c a (No. 73)
8
0.51 × 0.29 × 0.17
0.63 × 0.49 × 0.47
Space group
C 2/c (No.15)
P 1(No. 2)
Z
2
4
Unit cell parameters:
a /Å
b /Å
c /Å
11.5874(6)
18.9530(9)
23.1420(14)
90
90
90
5082.4(5)
1.486
5.737
10.2428(4)
12.2495(4)
13.1323(6)
102.594(3)
107.080(4)
97.463(3)
1503.55(11)
1.388
21.903(4)
10.2910(8)
12.5225(8)
90
98.436(10)
90
2792.0(5)
1.486
0.672
α
/°
β
/°
γ
/°
V /Å3
Dcalc /g cm–3
4.953
648
ꢁ
/mm–1
F(000)
2336
1288
Index range
h: −7 to 14,
k: −20 to 23,
l: −27 to 28
8906
h: −12 to 12,
k: −14 to 14,
l: −15 to 15
14096
h: −27 to 27,
k: −13 to 13,
l: −15 to 14
7034
Reflections collected
Independent reflections
Number of reflections with [I>2σ(I)]
2410 [R(int) = 0.0785]
1742
5693[R(int) = 0.0465]
4808
2915[R(int) = 0.0313]
2383
100.0 %
99.9 %
96.0%
Completeness to
θ = 67.68°
(25.24° for 6·MeOH)
Data / restraints / parameters
Final Ra indices [I>2σ(I)]
Rb indices (all data)
2410 / 2 / 183
R1 = 0.0512; wR2 = 0.1151
R1 = 0.0736;wR2 = 0.1305
5693 / 3 / 399
R1 = 0.0530; wR2 = 0.1485
R1 = 0.0628;wR2 = 0.1568
2915/2/204
R1 = 0.0502; wR2 = 0.1184
R1 = 0.0635; wR2 = 0.1248
2
a R = Σ||Fo| – |Fc||/ Σ|Fo|; b wR = {Σ[w(Fo2 – Fc2)2]/Σ[w(Fo )2]}1/2
Computational Methods
30 † Electronic Supplementary Information (ESI) available: (1) DSC
thermograms, (2) PXRD patterns, (3) TG curves, (4) figures for
compounds (6) Tables of selected bond distances and angles and of
hydrogen bonds parameters and (7) 1H NMR spectra. Crystallographic
data sets for the structures H2L3, H2L5, H2L6, 1, 2, 2·0.7MeOH and
35 6ꢀMeOH are available through the Cambridge Structural Data base with
deposition numbers 1432533ꢀ1432539. See DOI: 10.1039/b000000x/
5
Geometry optimizations for the unit cells were performed
using the hybrid functional using B3LYP hybrid functional
and D3 version of Grimme’s dispersion with BeckeꢀJohnson
damping70 with 6ꢀ31g(d) basis set in combination with the 6ꢀ
31G(d) basis set starting from crystallographically determined
10 structures. Additionally, to quantitatively determine the
standard Gibbs energies of binding, harmonic vibrational
frequencies were calculated. All quantum chemical
calculations were carried out using the Gaussian 09 program
package.71
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a University of Zagreb, Faculty of Science, Department of Chemistry,
Horvatovac, 102a, 10000 Zagreb, Croatia, Fax: ++ 385ꢀ1ꢀ4606341; Tel:
++385ꢀ1ꢀ4606353; Eꢀmail: visnja.vrdoljak@chem.pmf.hr
b University of Zagreb, Faculty of Textile Technology, Division of Applied
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c Department of Chemical and Pharmaceutical Sciences, University of
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Table of contents entry
Differently protonated ligands in [Co(HL)(L)] are stabilized via
supramolecular assembling through O–H···O/N and N–H···N/O
hydrogen bonding. Channels spreading either in each space
dimension or predominantly in one direction are formed.