Supramolecular complexes obtained from the interaction of violuric acid with manganese ion and nitrogenous ligands

Article abstract of DOI:10.1016/j.molstruc.2014.04.032

This work describes the synthesis, spectroscopic characterization (Raman and infrared) and structural arrangement of three new supramolecular complexes named [Mn(H₂Vi)₂(H₂O)₄)](bpy) ₂ (1), [Mn(bpa)₂(H₂O)₄](H ₂Vi)₂ (2) and [Mn(bpp)₂(H₂Vi) ₂]·(bpp)₂(H₂O)₂ (3); these compounds have been obtained making use of different building blocks such as 4,4′-bipyridyne (bpy), 1,2-bis(4-pyridyl)ethane (bpa) and 4,4′-trimethylene-dipyridine (bpp) acting as spacers with violuric acid and manganese ion, presenting behavior related to processes of molecular self-assembling and self-organization, very common in studies of supramolecular systems. In all these compounds the violurate anion appears in the crystalline arrangement as monodentate, anionic and chelate forms for 1, 2 and 3, respectively. The important to note is that monodentate coordination in 1 and chelate in 3 through O2 and O3 oxygen atoms from the oxime group can be considered the first example in literature involving violuric acid, both in coordination or interaction with manganese ion. Moreover, it can be seen a good agreement between the structural results and the spectroscopic data; for instance the presence of an intense band in the Raman spectrum around 1603 and 1012 cm^-1 in all obtained compounds, assigned to the ν(CC)/ν(CN) and ν(ring)modes of the pyridyl ligand, respectively. Other important band can be observed in 1031 cm^-1 only for compound 3, assigned to the ν(NO) mode of the violurate ligand; the band at 1284 cm ^-1 referring to the ν(NO) mode, very characteristic of violurate species is not seen in the spectrum, thus confirming the coordination of this building block by the oxime moiety.

Full text of DOI:10.1016/j.molstruc.2014.04.032

Journal of Molecular Structure xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Supramolecular complexes obtained from the interaction of violuric acid
with manganese ion and nitrogenous ligands
Humberto C. Garcia a, Renata Diniz a, Nivaldo L. Speziali b, Luiz Fernando C. de Oliveira a,
⇑
a Núcleo de Espectroscopia e Estrutura Molecular, Departamento de Química, Universidade Federal de Juiz de Fora, Campus Universitário s/n, Martelos, Juiz de Fora,
MG 36036-900, Brazil
b Departamento de Física, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
ꢀ
Three new complexes obtained from
violuric acid, manganese ion and
nitrogenous ligands.
Building blocks
ꢀ
ꢀ
X-ray diffraction and vibrational data
to understand the crystal structure.
[Mn(H2Vi)2(H2O)4)](bpy)2 (1)
presents violuric acid in a
monodentate coordination.
[Mn(bpa)2(H2O)4](H2Vi)2 (2) presents
violuric acid as counter ion.
[Mn(bpp)2(H2Vi)2]ꢁ(bpp)2(H2O)2 (3)
presents violuric acid in a chelate
form.
ꢀ
ꢀ
Monodentate
Counter ion
Chelate
a r t i c l e i n f o
a b s t r a c t
Article history:
This work describes the synthesis, spectroscopic characterization (Raman and infrared) and structural
arrangement of three new supramolecular complexes named [Mn(H2Vi)2(H2O)4)](bpy)2 (1), [Mn(bpa)2
(H2O)4](H2Vi)2 (2) and [Mn(bpp)2(H2Vi)2]ꢁ(bpp)2(H2O)2 (3); these compounds have been obtained mak-
ing use of different building blocks such as 4,40-bipyridyne (bpy), 1,2-bis(4-pyridyl)ethane (bpa) and
4,40-trimethylene-dipyridine (bpp) acting as spacers with violuric acid and manganese ion, presenting
behavior related to processes of molecular self-assembling and self-organization, very common in studies
of supramolecular systems. In all these compounds the violurate anion appears in the crystalline arrange-
ment as monodentate, anionic and chelate forms for 1, 2 and 3, respectively. The important to note is that
monodentate coordination in 1 and chelate in 3 through O2 and O3 oxygen atoms from the oxime group
can be considered the first example in literature involving violuric acid, both in coordination or interac-
tion with manganese ion. Moreover, it can be seen a good agreement between the structural results and
the spectroscopic data; for instance the presence of an intense band in the Raman spectrum around 1603
Received 24 February 2014
Received in revised form 8 April 2014
Accepted 8 April 2014
Available online xxxx
Keywords:
Violuric acid
Manganese ion
4,40-Bipyridyne
1,2-Bis(4-pyridyl)ethane
1,3-Bis(4-pyridyl)propane
Hydrogen bonds
and 1012 cmꢂ1 in all obtained compounds, assigned to the
ligand, respectively. Other important band can be observed in 1031 cmꢂ1 only for compound 3, assigned
to the (N@O) mode, very
(NAO) mode of the violurate ligand; the band at 1284 cmꢂ1 referring to the
m(CC)/m(CN) and m(ring)modes of the pyridyl
m
m
characteristic of violurate species is not seen in the spectrum, thus confirming the coordination of this
building block by the oxime moiety.
Ó 2014 Elsevier B.V. All rights reserved.
⇑
Corresponding author. Tel./fax: +55 (32) 3229 3310.
E-mail address: luiz.oliveira@ufjf.edu.br (L.F. C. de Oliveira).
http://dx.doi.org/10.1016/j.molstruc.2014.04.032
0022-2860/Ó 2014 Elsevier B.V. All rights reserved.
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2
H.C. Garcia et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
engineering for presenting aliphatic chains different sizes separat-
Introduction
ing two pyridyl rings, thus acting as a spacer ligand in the produc-
tion of new arrangements that can provide cavities of different
sizes.
During the past 60 years the assembly and study of new crystal-
line systems, based on molecules called building blocks have
attracted attention of several research groups, receiving the sug-
gestive name of crystal engineering; firstly introduced by Pepinsky
[1]. A better understanding of this type of study and the growing
number of works in this area are closely related to the chemistry
and crystallography of small molecules [2]. The main advantage
of the synthesis of such systems is the obtaining of new structural
arrangements, which have a composition and spatial ordering pre-
viously defined by each one of the used building blocks as well as
the metal ions. These new materials may be presenting different
functionalities such as optical, electronic, magnetic and catalytic
processes [3,4].
This work aims the synthesis, structural and spectroscopic char-
acterization of three new compounds obtained from the interac-
tion between violuric acid and nitrogenous ligands (bpy, bpa and
bpp) with manganese ion, trying to understand the influence of
the spacers in the obtained structures, as well as to develop an
understanding about the characteristics of possible different forces
involved in the supramolecular interactions in each one of the
obtained compounds. In this sense, X-ray diffraction together with
infrared and Raman vibrational techniques were used to determine
the solid state assembly for each one of the synthesized
compounds.
In all the studies involving crystalline engineering the weak
non-covalent interactions such as hydrogen bonding, electrostatic
Experimental section
interaction, CAHꢁ ꢁ ꢁ
p, p-stacking and hydrophobic interactions
are the main responsible for the solid assembling, being defined
by Lehn as ‘‘the chemistry beyond the molecule’’ [5,6]. Such inter-
actions are also responsible for the stability of many physical and
biological systems, especially in solid small molecular arrange-
ments, acting in the construction of complicated extended arrays
of molecular self-organization [7], as will be addressed and dis-
cussed for different systems synthesized in this investigation.
Among the building blocks used in this work it can be men-
tioned as [2,4,6(1H,3H)-pyrimidinetrione-5-oxime, H3Vi] or violu-
ric acid (Scheme 1). H3Vi and its derivatives have been used in
the spectrophotometric determination of transition metal ions,
due their strong complexing character; as an example it can men-
tioned the work of Awadallah and coworkers [8], who synthesized
different salts of violurate with alkaline and transition metals,
including manganese ion which is rarely mentioned in this build-
ing block literature. Another well-known property of this building
block is its acid–base equilibrium; the first ionization of H3Vi
occurs in a pK1 = 4.35 although the oxime group deprotonates eas-
ily, generating the violurate anion H2Viꢂ, the second and third ion-
ization occurs in a pK2 = 9.64 and pK3 = 14.2, respectively, since the
NH groups are much weaker acid species, giving rise to HVi2ꢂ and
Vi3ꢂ, respectively [9]. It is straightforward to note that when this
chemical species loses its protons, its solution presents a very
intense purple coloration, caused by the electronic transitions
Chemicals and reagents
All chemicals were used as purchased without further purifica-
tion: violuric acid monohydrate (C4H3N3O4ꢁH2O, 97.0%, Sigma
Aldrich), 4,40-bipyridyl (C10H8N2, 98.0%, Sigma Aldrich), 1,2-bis(4-
pyridyl)ethane (C12H12N2, 99.0%, Sigma Aldrich), 4,40-trimethyl-
ene-dipyridine (C13H14N2, 98.0%, Sigma Aldrich), MnSO4ꢁH2O
(98.0%, Vetec), MnCl2ꢁ4H2O (98.0%, Vetec), Na2CO3 (99.0%, Sigma
Aldrich) and AgNO3 (99.0%, Sigma Aldrich).
Synthesis
For compounds 1 and 2 the synthesis procedure was similar:
10.0 mL of an aqueous colorless solution containing 96 mg
(0.55 mmol) of violuric acid (H3Vi) was neutralised with 29 mg
(0.27 mmol) of sodium carbonate, resulting in a purple solution.
To this purple solution was added under stirring 10.0 mL of an eth-
anolic solution containing 85 mg (0.55 mmol) of bpy (for com-
pound 1) and 100 mg (0.55 mmol) of bpa (for compound 2). To
this solution it was slowly added 5.0 mL of an aqueous solution
containing 92 mg (0.55 mmol) of manganese sulfate; the resulting
solution was kept for few days to crystallize. To obtain compound 3
the synthesis procedure was divided into three steps: First step – A
20 mL of
a colorless aqueous solution containing 288 mg
p– p in the visible region of the electromagnetic spec-
p* and n–
(1.65 mmol) of H3Vi was added to 10 mL of a solution containing
280 mg (1.65 mmol) of AgNO3, resulting in a reddish precipitate
(AgH2Vi), partially insoluble, and a solution of the same color; it
is noteworthy that the synthesis involving silver salt must be con-
ducted in an darkness environment, in order to prevent reduction
of the silver. Second step – The AgH2Vi precipitate was filtered and
used to react with 20 mL of an aqueous solution containing 170 mg
(0.86 mmol) of MnCl2ꢁ4H2O; the white AgCl precipitate was dis-
carded and a resulting reddish solution of Mn(H2Vi)2 was obtained.
Third step –10 mL of an ethanolic solution containing 171 mg
(0.86 mmol) of bpp was slowly added to the previous reddish
trum, and also by the different resonance canonic structures [10].
Furthermore, from the supramolecular chemistry point of view it
can be seen through Scheme 1 that H3Vi provides multiple sites
of coordination and interactions, such as the AC@O, @NAOH and
ANAH groups, thus resulting in a greater stability in the formed
structural arrangement.
Another class of well-known building blocks is the nitrogenous
ligands; in this work it has been used 4,40-bipyridyl (bpy), 1,2-
bis(4-pyridyl)ethane (bpa) and 4,40-trimethylene-dipyridine (bpp)
[11–13]. This is a class of compounds widely used in crystal
Scheme 1.
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H.C. Garcia et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
3
solution to allow diffusion between them. After three days the
Results and discussion
formation of a reddish crystalline material was obtained, which
was filtered, washed and dried. Elemental analysis: [Mn(H2Vi)2
(H2O)4)](bpy)2 (1): Calcd.: C, 44.75%; H, 3.76%; N, 18.64%; Found:
C, 44.85%; H, 3.89%; N, 18.24% [yield = 42%]; [Mn(bpa)2(H2O)4]
(H2Vi)2 (2): Calcd.: C, 47.59%; H, 4.49%; N, 17.34%; Found: C,
47.63%; H, 4.81%; N, 17.13% [yield = 63%];[Mn(bpp)2(H2Vi)2]-
ꢁ(bpp)2(H2O)2 (3): Calcd.: C, 60.14%; H, 5.55%; N, 16.37%; Found:
C, 60.60%; H, 5.00%; N, 15.70% [yield = 33%].
The crystalline nature of supramolecular compounds 1, 2 and 3
obtained from reactions involving H3Vi, the pyridyl nitrogenous
ligands (bpy, bpa and bpp) and manganese ion have been revealed
by X-ray single crystal analysis; the crystal data and some bond
distances, bond angles and hydrogen interactions are displayed
in Tables 1 and 2, respectively. Compound 1 crystallizes in a tri-
clinic system presenting Pꢂ1 space group; Fig. 1 represents the
repetition unit of the structure, formed by three neutral blocks.
One of blocks is constituted by the metal ion exhibiting slightly
distorted octahedral coordination geometry, defined by four aqua
ligands (two O5 and two O6) in the equatorial positions and two
anionic H2Viꢂ which are bonded in monodentate geometry
through the oxygen atoms in an axial position, neutralizing the
charge in the block. It is interesting to notice that this coordination
mode appears to be the first reported in literature, since previous
works have shown that the chelate coordination mode through
the N5 and O6 atoms (see Scheme 1) are the common geometry
[20–22]. The other two building blocks are formed by the uncoor-
dinated bpy in its neutral form. A hydrogen bond of 2.842(3) Å,
which can be classified as weak [23], is observed between the
nitrogen atoms (N1AHN1ꢁ ꢁ ꢁN4) of H2Viꢂ and bpy blocks. Due to
the presence of several groups considered proton acceptors and
donors, many other hydrogen bonds are observed for this struc-
ture, all of them are displayed in Table 2. The supramolecular
structural arrangement of this compound can be seen in more
details in Fig. 2, where it can be seen that at each vertex of the uni-
tary cell is a bpy moiety. This same ligand appears involved in a
Physical measurements
Infrared spectra were obtained using a Bomem MB-102 spec-
trometer fitted with a CsI beam splitter, with the samples prepared
as KBr pellets and the spectral resolution was acquired at 4 cmꢂ1
;
good signal-to-noise ratios were obtained from the accumulation
of 128 spectral scans. Fourier-transform Raman spectroscopy was
performed using a Bruker RFS 100 instrument, equipped with a
Nd3+/YAG laser operating at 1064 nm in the near-infrared region
and a InGaAs detector cooled with liquid N2; good signal-to-noise
ratios were obtained from 2000 scans that were accumulated over
a period of 30 min with a spectral resolution of 4 cmꢂ1. All spectra
were obtained at least twice to show reproducibility, and there
were no changes in the band positions or intensities observed. Sin-
gle crystal X-ray diffraction data were collected using an Oxford
GEMINI A Ultra diffractometer with Mo Ka (k = 0.71073 Å) for every
compound. Data collection, reduction and cell refinement were per-
formed by CrysAlis RED, Oxford diffraction Ltda, Version
1.171.32.38 program [14]. The structures were solved and refined
using SHELXL-97 [15]. The empirical isotropic extinction parameter
x was refined according to the method previously described by
Larson [16], and a Multiscan absorption correction was applied
[17]. The structures were drawn by ORTEP-3 for windows [18]
and Mercury [19] programs. CCDC 958393, 958394 and 971466
contained the supplementary crystallographic data for compounds
1, 2 and 3 respectively. These data can be obtained free of charge at
<http://www.ccdc.cam.ac.uk> or from the Cambridge Crystallo-
graphic Data Centre, 12, Union Road, Cambridge CB2 IEZ, UK [Fax:
(internat.) 1 44 1223/336-033; E-mail: deposit@ccdc.cam.ac.uk].
supramolecular interaction of the type CAHꢁ ꢁ ꢁ
p
(Cꢁ ꢁ ꢁ
p dis-
tance = 3.659(3) Å) with other bpy block (which is crystallograph-
ically different from the previous bpy), located inside the unitary
cell. A set of hydrogen bonds of medium intensity can be observed
through the coordination of the water molecules and the bpy
located at the vertex of the unitary cell, specifically
O5AH5Bꢁ ꢁ ꢁN5 = 2.766(3) Å. Another non-covalent interaction
occurs through the aromatic ring of the bpy building block and
the H2Viꢂ moiety, being classified as
centroid–centroid distance of 3.670(2) Å [24]. It can said that the
p-stacking and presenting
Table 1
Crystal data of [Mn(bpy)2(H2O)4]ꢁ(H2Vi)2 (1), [Mn(bpa)2(H2O)4]ꢁ(H2Vi)2 (2) and [Mn(bpp)2(H2Vi)2]ꢁ(bpp)2(H2O)2 (3) compounds.
Compound
[Mn(bpy)2(H2O)4]ꢁ(H2Vi)2 (1)
28H28MnN10O12
[Mn(bpa)2(H2O)4]ꢁ(H2Vi)2 (2)
C32H35MnN10O12
806.64
Triclinic
P1
9.4388(3)
9.9758(2)
10.3210(3)
76.536(2)
83.520(3)
63.365(3)
844.78(5)
1
[Mn(bpp)2(H2Vi)2]ꢁ(bpp)2(H2O)2 (3)
Formula
C
C60H56MnN14O10
1188.13
Triclinic
Pꢂ1
Formula weight/g molꢂ1
751.54
Crystal system
Space group
a/Å
b/Å
c/Å
a
b
Triclinic
Pꢂ1
8.6117(5)
9.5665(5)
11.3309(7)
85.769(5)
67.885(5)
69.349(5)
807.36(9)
1
9.1274(6)
9.8119(5)
17.4463(11)
101.742(5)
104.758(5)
92.248(5)
1472.42(16)
1
c
V/Å3
Z
Crystal size/mm
0.55 ꢃ 0.25 ꢃ 0.18
0.44 ꢃ 0.20 ꢃ 0.13
0.39 ꢃ 0.12 ꢃ 0.08
D
calc/g cmꢂ3
1.546
1.586
1.340
l(Mo K
a
)/cmꢂ1
0.489
0.473
0.295
Transmission factors (min/max)
0.864/0.917
13183/3300
2754
0.892/0.943
43028/6904
5052
0.957/0.978
10921/6024
3584
Reflections measured/unique
Observed reflections [F2o > 2 (Fo2)]
r
N°. of parameters refined
257
504
476
R[Fo > 2
r
(Fo)]
r
0.0399
0.0961
0.0672
0.1748
0.0802
0.1876
wR[F2o > 2
(Fo)2]
S
1.050
1.041
1.034
RMS peak/
0.065
0.128
0.078
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4
H.C. Garcia et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
Table 2
Select bond distances (in Å) and hydrogen interactions of [Mn(bpy)2(H2O)4]ꢁ(H2Vi)2 (1), [Mn(bpa)2(H2O)4]ꢁ(H2Vi)2 (2) and [Mn(bpp)2(H2Vi)2]ꢁ(bpp)2(H2O)2 (3).
Bond distance/Å
[Mn(bpy)2(H2O)4]ꢁ
(H2Vi)2 (1)
Bond distance/Å
[Mn(bpa)2(H2O)4]ꢁ
(H2Vi)2 (2)
Bond distance/Å
[Mn(bpp)2(H2Vi)2]ꢁ
(bpp)2(H2O)2 (3)
Mn1AO1
Mn1AO5
Mn1AO6
N3AC3
2.273(1)
2.146(2)
2.121(2)
1.333(2)
1.380(3)
Mn1AO5
Mn1AO6
Mn1AO7
Mn1AO8
Mn1AN4
Mn1AN5
O1AC1
O2AC2
O3AN3
O4AC4
2.170(5)
2.168(6)
2.134(6)
2.190(6)
2.269(6)
2.263(7)
1.188(9)
1.268(9)
1.289(6)
1.232(10)
Mn1AO2
Mn1AO3
2.113(2)
2.184(3)
N3AC3
Mn1AN4
1.375(5)
2.259(3)
N2AC2
O1AC1
O2AC2
O3AN3
O4AC4
1.229(2)
1.229(2)
1.271(2)
1.218(2)
O1AC1
O2AC2
O3AN3
O4AC4
1.215(5)
1.236(4)
1.229(4)
1.230(6)
Hydrogen bond (D. . .A/Å)
N1AHN1ꢁ ꢁ ꢁN4
N2AHN2ꢁ ꢁ ꢁO2
O5AH5Aꢁ ꢁ ꢁN3
O5AH5Bꢁ ꢁ ꢁN5
O6AH6Aꢁ ꢁ ꢁO2
O6AH6Aꢁ ꢁ ꢁO3
06AH6Bꢁ ꢁ ꢁO3
Hydrogen bond (D. . .A/Å)
N10AHN10ꢁ ꢁ ꢁN6
N2AHN2ꢁ ꢁ ꢁN7
N1AHN1ꢁ ꢁ ꢁO11
N8AHN8ꢁ ꢁ ꢁO3
O5AH5Aꢁ ꢁ ꢁO3
O5AH5Aꢁ ꢁ ꢁO4
O5AH5Bꢁ ꢁ ꢁO9
Hydrogen bond (D. . .A/Å)
N2AHN2ꢁ ꢁ ꢁN6
2.842(3)
2.857(3)
2.852(3)
2.766(3)
2.806(2)
2.913(3)
2.640(3)
2.829(10)
2.780(10)
2.748(8)
2.770(9)
2.721(7)
2.825(9)
2.765(9)
2.724(7)
2.798(8)
2.806(8)
2.768(9)
2.784(9)
2.773(8)
2.803(5)
2.796(5)
N1AHN1ꢁ ꢁ ꢁN5
O6AH6Aꢁ ꢁ ꢁO1
O6AH6Bꢁ ꢁ ꢁO10
O6AH6Bꢁ ꢁ ꢁO11
O7AH7Aꢁ ꢁ ꢁO2
O7AH7Bꢁ ꢁ ꢁO10
O8AH8Aꢁ ꢁ ꢁO4
Fig. 1. ORTEP view of [Mn(bpy)2(H2O)4]ꢁ(H2Vi)2 (1) crystal structure. Ellipsoids are
drawn at the 50% probability level, except for hydrogen atoms which are
represented by circles of arbitrary radius. The water molecules of crystallization
are omitted for clarity. Symmetry code: (i) ꢂx, 1 ꢂ y, 1 ꢂ z; (ii) ꢂ1 + x, y, ꢂ1 + z; (iii)
1 ꢂ x, 1 ꢂ y, 2 ꢂ z.
Fig. 3. ORTEP view of [Mn(bpa)2(H2O)4]ꢁ(H2Vi)2 (2) crystal structure. Ellipsoids are
drawn at the 50% probability level, except for hydrogen atoms which are
represented by circles of arbitrary radius. The water molecules of crystallization
are omitted for clarity. Symmetry code: (i) x, ꢂ1 + y, 1 + z.
Fig. 3 exhibits the asymmetric units of complex 2, being consti-
tuted by a cationic block formed by the metal ion covalently
bonded to four aqua ligands in equatorial positions, and two bpa
species in axial and terminal positions, giving rise to a slightly dis-
torted octahedral geometry. Neutralizing each cationic bock it can
be observed the presence of two uncoordinated violurate anions.
The presence of different donor and acceptor protons blocks favors
the appearance of hydrogen bonds; due to these interactions, it can
be observed the presence of a supramolecular cavity formed
through hydrogen bonds and classified as N1 ¼ R32ð12Þ, where the
symbol R is related to a ring, whereas the numbers indicate the
number of donor (subscript) and acceptor (superscript) moieties
and the number in parentheses indicates the number of atoms
involved in the arrangement in each set [25]. Fig. 4 shows the
supramolecular arrangement involved in the plane perpendicular
to the bc diagonal, with the formation of weak and medium
hydrogen bonds between [Mn(H2O)4(bpa)2]2+ and H2Viꢂ building
blocks, thus generating a two-dimensional network described as
Fig. 2. Supramolecular interactions: hydrogen bonds,
[Mn(bpy)2(H2O)4]ꢁ(H2Vi)2 (1) compound.
p-stacking and CAHꢁ ꢁ ꢁp for
stability of this supramolecular arrangement becomes more effec-
tive and evident due to the large variety and the high number of
different interactions present in the system, such as hydrogen
bonds,
p-stacking and CAHꢁ ꢁ ꢁ
p.
N2 ¼ Cð19Þ2R2ð10ÞR4ð38Þ. Another
p-stacking supramolecular
2
4
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H.C. Garcia et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
5
Fig. 4. Supramolecular interactions: hydrogen bonds and
[Mn(bpa)2(H2O)4]ꢁ(H2Vi)2 (2) compound.
p-stacking for
Fig. 6. Supramolecular interactions: hydrogen bonds and CAHꢁ ꢁ ꢁ
p
of compound
[Mn(bpp)2(H2Vi)2]ꢁ(bpp)2(H2O)2 (3).
main driving forces responsible for the arrangement could be
accessed and solved.
The bi-dimensional array of compound 3 can be seen across
Fig. 6, formed by [Mn(bpp)2(H2Vi)2] building blocks interacting
via N1AHN1ꢁ ꢁ ꢁN5 = 2.796(5) Å hydrogen bonds, between the
H2Viꢂ and bpp ligands, respectively, and classified as of medium
intensity [23]. This type of supramolecular interaction in the zigzag
form observed in these structures for bpp and H2Viꢂ ligands, giving
rise to geometrical figures such as a rectangle, is common in the lit-
erature involving only the coordination of bpp ligand [27]. As an
example it can mentioned the work of Garcia et al. [28] describing
a bis-monodentate bpp coordination which occurs through the two
nitrogen atoms of the ligand; in that structure the counter ion ami-
nosalicylate is not influencing the bpp coordination mode. In this
investigation, since the H2Viꢂ coordination occurs as a chelate to
the metal site, it happens an hindering of the bis-monodentate
coordination in the zigzag form, being only observed the monoden-
tate coordination of bpp, leaving the (N5) nitrogen atom uncoordi-
nated to perform a hydrogen interaction with the other (N1)
nitrogen atom of the violurate moiety. Another important supra-
Fig. 5. ORTEP view of [Mn(bpp)2(H2Vi)2]ꢁ(bpp)2(H2O)2 (3) crystal structure. Ellip-
soids are drawn at the 50% probability level, except for hydrogen atoms which are
represented by circles of arbitrary radius. The water molecules of crystallization are
omitted for clarity. Symmetry code: (i) 1 ꢂ x, ꢂy, 1 ꢂ z.
interaction can be observed across the two pyridyl rings of the bpa
ligand, presenting centroid–centroid distance of 3.786(2) Å.
Although it is possible to note the presence of several rings in
the macro structure, only the effective approximation of two bpa
ligands are responsible for observing the
p-stacking interaction.
molecular interaction called CAHꢁ ꢁ ꢁ
p = 3.752(2) Å can be noted
between the hydrogen atom of an aliphatic chain and the pyridyl
This fact can be explained by the presence of the aliphatic chain
(ACH2ACH2A) in the molecular structure of the nitrogenous
ligand, showing a steric effect that disfavors the approach of the
pyridyl rings. This same aliphatic chain only allows the formation
ring, from distinct bpp ligands. To connect the layers observed in
Fig. 6, it can be seen the presence of
p-stacking interactions
between the rings of the coordinated and uncoordinated pyridyl
ligands presenting centroid–centroid distance of 3.531(3) Å. Other
hydrogen bonding interaction between the layers occurs involving
the nitrogen atom (N6) of the uncoordinated bpp and the nitrogen
atom (N2) atom of the violurate anion, N2AHN2ꢁ ꢁ ꢁN6 = 2.803(5) Å.
The vibrational spectra of the building blocks and complexes 1,
2 and 3 are shown in Figs. 7 and 8, related to infrared and Raman
of CAHꢁ ꢁ ꢁ
p
interaction of 3.586(3) Å (Cꢁ ꢁ ꢁ
p distance) for the ring
from the H2Viꢂ building block. The interaction between two differ-
ent planes in Fig. 4 occurs via hydrogen bonds between the
carbonyl group with the coordinated water molecule,
O5AH5Bꢁ ꢁ ꢁO9 = 2.765(9) Å, and through the NH and the oximato
groups, N1AHN1ꢁ ꢁ ꢁO11 = 2.748(8) Å.
Fig. 5 displays the repeating unit of compound 3; it comprises a
neutral block formed by manganese ion in a slightly distorted octa-
hedral geometry coordinated to two nitrogen atoms from bpp in
the axial position, adopting a conformation Trans–Trans (or TT)
with N-to-N separation distances of 9.632(2) Å, or by the Trans
arrangement between the ACH2 groups of the aliphatic chain
[26]. Completing the coordination sphere, it can be observed the
presence of two H2Viꢂ, violurate anions, originating a chelate
through the O2 and O3 oxygen atoms from the carbonyl and oxime
groups, respectively; such structure forms two five-member rings,
which contributes to increase the thermodynamical stability of the
structure. Due to the chelate formation, it can be observed a lower
O3AN3 = 1.229(4) Å bond distance for compound 3 when com-
pared to 1.271(2) Å and 1.289(6) Å for the compounds 1 and 2,
respectively; this fact can be attributed to a decrease in this bond
order between these two atoms, via a new bond which is respon-
sible for the appearance of such ring. Completing the compound
3 repeating unit it can be mentioned the presence of two neutral
bpp and two water molecules of crystallization, which due to the
complexity of arrangement they are not shown in Fig. 5. Moreover,
the two uncoordinated bpp species present the nitrogen and car-
bon atoms (N7A, C24A, C25A, C26A, C27A, C28A C29A and C30A)
from one of its pyridyl rings in a disordered position; despite this
disorder, the main features of the solid state structure and the
Fig. 7. Infrared spectra of [Mn(bpy)2(H2O)4]ꢁ(H2Vi)2 (1), [Mn(bpa)2(H2O)4]ꢁ(H2Vi)2
(2) and [Mn(bpp)2(H2Vi)2]ꢁ(bpp)2(H2O)2 (3) compounds; for comparison purposes,
the spectra of the ligands (bpy and NaH2Vi) are also displayed.
Please cite this article in press as: H.C. Garcia et al., J. Mol. Struct. (2014), http://dx.doi.org/10.1016/j.molstruc.2014.04.032

6
H.C. Garcia et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
m(ring) + d(NHi.p.) coupled mode, after the proton loss. The assign-
ment of this band is important in this work in order to observe
the type of coordination and/or interaction of this building block
in the supramolecular unit: as a counter ion, monodentate or che-
late species, since the degree of electronic delocalization over the
structure is responsible for changes in position and wavenumber
for such vibrational mode. On the other hand, for the three nitro-
gen spacers bpy, bpa and bpp, although the difference in their
structures occurs due to the insertion of the aliphatic chain, it
can be observed the presence of some bands in their spectra that
occur in similar positions, and related to the pyridyl group which
is the common chemical group in all these building blocks. As an
example it can be cited the bpy ligand which presents an intense
band occurring at 1591 cmꢂ1 assigned to the
m(CC)/m(CN) mode
of the pyridyl ring; for bpa and bpp this same band appears at
1597 and 1605 cmꢂ1, respectively. Thus this band can be consid-
ered as very important in the vibrational spectroscopy analysis of
these species, acting as marker; it is also clear that shifts to a dif-
ferent wavenumber by the coordination process with the metal
site, caused by an increasing of the bond order due to the use the
electrons pair non-bonding in the formation bond metal ligand,
can be expected. Other important band occurs at 1408, 1414 and
Fig. 8. Raman spectra (excited at 1064 nm) of [Mn(bpy)2(H2O)4]ꢁ(H2Vi)2 (1),
[Mn(bpa)2(H2O)4]ꢁ(H2Vi)2 (2) and [Mn(bpp)2(H2Vi)2]ꢁ(bpp)2(H2O)2 (3) compounds;
for comparison purposes, the spectra of the ligands (bpy and NaH2Vi) are also
displayed.
1416 cmꢂ1, assigned to
m(ring) mode of the bpy, bpa and bpp spe-
techniques, respectively. The main vibrational modes and the
respective assignments have been based on similar chemical sys-
tems [29–31], and are listed in Table 3. Each vibrational spectrum
presents some characteristic bands which are related to different
coordination modes of H2Viꢂ as well the nitrogen ligands, and will
be discussed below.
cies respectively; however, for this band there are no observed
shifts caused by any coordination processes.
For the compounds 1, 2 and 3 the infrared spectrum presents
one broad band in the 3600–3400 cmꢂ1 region, assigned to the
m
(NH) and m
(OH) modes of the H2Viꢂ and H2O building blocks,
respectively. Other strong band, observed at 1670, 1688 and
1726 cmꢂ1, can be assigned to the stretching of the carboxyl group
In the infrared spectrum of hydrated NaH2Vi violurate salt can
be observed the presence of a set of three bands at 1732, 1701
m(CO) of the violurate ion building block. It can be said that the
and 1676 cmꢂ1, all of them assigned to the
m(C@O) mode of differ-
high wavenumber shift observed for this band occurs for com-
pound 1; this fact can be explained by the coordination of this
building block via the oxygen atom of the carboxyl group (AC@O),
thus weakening the bond and consequently shifting the band to
lower wavenumber. Furthermore in this region the spectrum of
compound 1 is more defined with a smaller number of bands,
which can be related to the CO stretching mode overlap after coor-
dination of one of the carbonyl groups. For compound 2 the shift of
ent carbonyl groups present in this building block. In an earlier
work by de Oliveira et al. [29], analyzing the Raman spectra of dif-
ferent violurate species, no significant changes in wavenumbers
were observed, suggesting the proton loss by O5 atom has no influ-
ence on the bond order of these chemical bonds. An important
band, that can be attributed as a characteristic marker of this struc-
ture, occurs at 1277 cmꢂ1
, and can be assigned to the
Table 3
Raman (R) and infrared (IR) wavenumbers (in cmꢂ1) and tentative assignment of the most important bands observed for [Mn(bpy)2(H2O)4]ꢁ(H2Vi)2 (1), [Mn(bpa)2(H2O)4]ꢁ(H2Vi)2
(2) and [Mn(bpp)2(H2Vi)2]ꢁ(bpp)2(H2O)2 (3) compounds.
NaH2Vi
bpy/bpa/bpp
[Mn(bpy)2(H2O)4]ꢁ(H2Vi)2
[Mn(bpa)2(H2O)4]ꢁ(H2Vi)2
[Mn(bpp)2(H2Vi)2ꢁ(bpp)2(H2O)2
Tentative assignment
(1)
(2)
(3)
IR
R
IR
R
IR
R
IR
R
IR
R
518 m
571 m
516 m
570 m
655 vs
728 w
513 m
571 m
512 w
564 w
657 s
515 m
567 m
512 w
565 w
655 s
517 m
561 m
518 m
562 w
653 s
d(ring) + d(C@O)i.p.
d ring)
Ring Breathing
d(N@O)o.p. +d(C@O)o.p
d (NH)o.p
729 w
785 w
826 w
723 w
785 w
806 w
731 w
788 w
829 w
800 w
793 w
816 w
792 w
825 m
m
m
m
m
m
m
m
m
(ring) + d(ring)
(ring)
(N–O)
989 m
1000 s
1012 vs
1016 vs
1011 vs
1031s
1142 m 1144 w
1130 w
1219 m 1218 m 1221 m
1141 w
1130 w
1230 s
(ring)(
(ring) + d(CH)
(ring)( C–C)
mC–N)
1224 sh
1233 s
1216 s
1234 s
1218 vs
1241 m
1227 s
1277 s
1228 vs
1287 s
1227 s
1271 s
1296 vs
m
1279 s
1296 sh
(ring) + d(NH)i.p.
(N@O)
1285 vs
1414 vs
1284 m
1410 vs
1406 s
1438 s
1436 sh
1433 w
1595
1649 s
1670 vs
1437 sh
1609 m
1655 s
1688 s
1436 sh
1609 vs
1636 s
1693 s
1726 s
m
m
m
m
m
m
m
(ring)(
mC–N) + d(NH)i.p.
1591 s
1606 s
1603 vs
1650 s
1695 s
1615 s
1652 m
1698 s
1608 s
1637 m
1695 s
1722 s
2928 m
3058 vs
(CC)/ (CN)
m
1676 vs 1646 sh
1701 vs 1681 s
1732 vs 1726 sh
(C@O)
(C@O)
(C@O)
(CH)aliphatic
(CH)aromatic
2926 m
3064 s
3073 m
Abbreviations: vs, very strong; s, strong; m, medium; w, weak; sh, shoulder; i.p., in plane; o.p., out of plane.
Please cite this article in press as: H.C. Garcia et al., J. Mol. Struct. (2014), http://dx.doi.org/10.1016/j.molstruc.2014.04.032

H.C. Garcia et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
7
this same vibrational mode is due to appearance of different reso-
nance canonic structures originated from the H2Viꢂ building block
as a counter ion, and the broadening band in this region can be
attributed to the CO groups of the building block under different
1722 cmꢂ1 for compound 3, which shows a wavenumber shift less
pronounced when compared to the violuric acid (1737 cmꢂ1), since
the chelate coordination of the structure makes difficult the forma-
tion of resonance structures when compared to the other com-
pounds. Another important band can be observed at 1285 and
1284 cmꢂ1 for compounds 1 and 2, respectively, assigned to the
chemical environments. For compound
3 the carboxyl bond
appears stronger when compared to the other compounds; this
fact could be explained by the chelate coordination appearing in
the structure, thus preventing the formation of a resonance struc-
ture in the ring, which is responsible for wakening this band. Fur-
thermore the similarity in this region between compound 3 and
NaH2Vi suggests that coordination of such compound and its pre-
cursor may be the almost the same. Another important band can
be observed at 1433, 1437 (shoulder) and 1436 (shoulder) cmꢂ1
for compounds 1, 2 and 3 respectively, and attributed to a set of
m(N@O) mode. It can be seen that the presence of this band corrob-
orates with the presence of this building block in a monodentate
geometry and also as a counter ion for these compounds. The
important to be noted in this mode is the absence of this band
for compound 3, which strengthens its coordination by the (O5)
oxygen atom, which can be verified by the appearance of a new
band at 1031 cmꢂ1 and attributed to the
m(NAO) mode. Another
band that can be used as a marker for these building blocks
appears at 655 cmꢂ1 for each compound, referring to the ring
breathing mode; such band appears shifted to a higher wavenum-
ber values when compared to the precursor (645 cmꢂ1), due to the
bond strengthening caused by the proton loss. The presence of a
pyridyl ligand in the formation of supramolecular complexes can
be confirmed through two important marker bands at 1603 and
coupled modes [
1271 cmꢂ1 for compounds 1 and 2 respectively, which are assigned
to the [ (ring) + d(NH)i.p.] coupled mode, are also important to
mring + m(CAN) + d(NH)i.p.]. Bands at 1279 and
m
characterize such compounds, since are related to the electronic
delocalization over the ring. This same vibration does not appear
in compound 3 spectrum, strongly suggesting the inexistence of
electronic delocalization, as seen for compounds 1 and 2, due to
coordination in chelate form. To confirm the presence of bpy, bpa
and bpp nitrogenous ligands in the synthesized structures, only
two bands can be analyzed: the one at 1595, 1609 and
1012 cmꢂ1, assigned to the
m(CC)/m(CN) and m(ring) modes, respec-
tively. The band at 1600 cmꢂ1 is very important because its huge
shift to higher wavenumber values strongly suggest the coordina-
tion of the nitrogen ligand to the metal site in the same geometry
as compound 2; a small wavenumber shift can suggest the exis-
tence of intermolecular forces or even the uncoordination of this
building block.
1609 cmꢂ1, assigned to the
m(CC)/m(CN) mode and presenting a
small wavenumber shift when compared to the free ligand for
compounds 1 and 3, suggesting the presence of uncoordinated spe-
cies in their neutral form in these structures, which is confirmed by
structural analysis. Another important set of bands that can be
observed to confirm the nitrogen ligands bpy, bpa and bpp in the
formation of compounds occur around 1408 cmꢂ1, assigned to
the coupled modes m(ring)/d(CH); however, this region is not used
for assignments, due to the presence of bands relative to the other
building block (NaH2Vi) used in this study.
As a final remark it can be said that these results demonstrate
the importance in choosing the appropriate ligands in crystal engi-
neering, related to the formation of different supramolecular
arrangements. For compound 3 it can be said that the adopted syn-
thesis procedure favored the formation of the chelate complex, fol-
lowed by bpp coordination in replacing the water molecules as
well as the presence of other bpp in the neutral form for complet-
ing the crystal lattice. The synthesis procedures for compounds 1
and 2 were similar, and this reflects the existence of weak intermo-
lecular forces for both compounds; for compound 1 the hydrogen
bond formed between the N4 atom of bpy and N1 atom of H2Viꢂ
favors the violurate anion coordination through the carboxyl
group, whereas for compound 2 the bpa coordination is the
responsible for the stabilization of the complex formed, preventing
the coordination water molecules exit which plays an important
role in the formation of hydrogen bond with other violurate anions.
In the NaH2Vi Raman spectrum (Fig. 8) some characteristic
bands can also be observed, as for instance a broad band featuring
shoulders at 1726, 1681 and 1646 cmꢂ1, assigned to different
m(CO)
modes of the violurate species. Such bands appear shifted to lower
wavenumbers when compared to violuric acid, which can be
explained by the proton exit producing a bond weakening due to
the formation of different resonance canonic structures. Another
fact which contributes to this discussion is the appearance of an
intense band at 1287 cmꢂ1, assigned to the
m
(N@O) mode, that is
not present in its precursor spectrum, just showing up an intense
band at 1577 cmꢂ1 concerning
m(C@N). In the same way, the pres-
ence of an intense band at 655 cmꢂ1 shifted to higher wavenumber
when compared to the free violuric acid (645 cmꢂ1), assigned to the
Conclusions
ring breathing mode,
m
(ring) [29].
It has been described the synthesis, spectroscopic (Raman and
infrared) and structural characterization of three novel supramo-
lecular arrangements: [Mn(H2Vi)2(H2O)4)](bpy)2 (1), [Mn(bpa)2
(H2O)4](H2Vi)2 (2) and [Mn(bpp)2(H2Vi)2]ꢁ(bpp)2(H2O)2 (3),
obtained through diffusion or precipitation techniques. The
formation of these new compounds can be considered the first
investigation involving the interaction and coordination between
manganese ion and violurate ligand in three different forms:
monodentate, chelate and counter ion. Compound 3 presents the
chelate coordination form through O2 and O3 oxygen atoms, a type
of coordination which has not been described in literature for this
building block; compound 2 presents the bpa ligand coordinated to
the manganese ion, whereas for compound 1 the inverse can be
seen, i.e., the coordination from violurate ion, both presenting a
monodentate form of coordination. Additionally the use of crystal
engineering in the formation of these new compounds is only pos-
sible due to the presence of manganese central ion, which shows
the importance and especially the great affinity of this metal ion
with the building blocks used in synthesis of the different
In general, the Raman spectra of bpy, bpa and bpp exhibit char-
acteristic bands which can be discussed together the obtained
complexes. Among the main vibrational bands it can be mentioned
the ones at ca. 1600 and 1000 cmꢂ1, assigned to the
m
(CC)/m(CN)
and
m(ring) modes, respectively. These two modes are important
band markers for these compounds, since their coordination to
the metal ion can be observed through their shift to higher wave-
number values, thus being related to an increase in the bond order
by means of ligand coordination. Other important band appears at
1297, 1216 and 1218 cmꢂ1 for bpy, bpa and bpp, respectively,
being assigned to [d(ring) + d(CH)] coupled modes. It is important
to note that this vibrational mode in particular does not present
a pronounced shift in the process of ligand coordination.
Compounds 1, 2 and 3 exhibit one set of intense bands in the
region of 1720–1650 cmꢂ1, assigned to the
m(C@O) mode of differ-
ent carbonyl groups. Due to the different coordination and interac-
tion of these compounds it can be observed the shift of such
different bands. As an example, it can be mentioned the band at
Please cite this article in press as: H.C. Garcia et al., J. Mol. Struct. (2014), http://dx.doi.org/10.1016/j.molstruc.2014.04.032

8
H.C. Garcia et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
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