Dioxidomolybdenum(VI) complexes of tridentate ONO donor aroylhydrazones: Syntheses, spectral and structural characterization

Article abstract of DOI:10.1016/j.poly.2016.11.033

Four dioxidomolybdenum(VI) complexes, [MoO₂(L¹)(H₂O)] (1), [MoO₂(L¹)(H₂O)]·(4,4′-bipy) (2), [(MoO₂(L¹))₂(4,4′-bipy)]·2H₂O (3) and [MoO₂

Full text of DOI:10.1016/j.poly.2016.11.033

Accepted Manuscript
Dioxidomolybdenum(VI) complexes of tridentate ONO donor aroylhydra-
zones: Syntheses, spectral and structural characterization
A. Ambili Aravindakshan, Bibitha Joseph, U.L. Kala, M.R. Prathapachandra
Kurup
PII:
S0277-5387(16)30624-6
DOI:
http://dx.doi.org/10.1016/j.poly.2016.11.033
POLY 12341
Reference:
Polyhedron
To appear in:
Received Date:
Revised Date:
Accepted Date:
3 October 2016
9 November 2016
13 November 2016
Please cite this article as: A. Ambili Aravindakshan, B. Joseph, U.L. Kala, M.R. Prathapachandra Kurup,
Dioxidomolybdenum(VI) complexes of tridentate ONO donor aroylhydrazones: Syntheses, spectral and structural
characterization, Polyhedron (2016), doi: http://dx.doi.org/10.1016/j.poly.2016.11.033
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

1
Dioxidomolybdenum(VI) complexes of tridentate ONO donor
aroylhydrazones: Syntheses, spectral and structural characterization
A. Ambili Aravindakshana, Bibitha Josepha, U.L. Kalab, M.R. Prathapachandra
Kurupa,*
aDepartment of Applied Chemistry, Cochin University of Science and Technology, Kochi
682 022, Kerala, India
bDepartment of Chemistry, Sree Narayana College, Nattika, Thrissur, Kerala, India
Abstract
Four
dioxidomolybdenum(VI)
complexes,
[MoO2(L1)(H2O)]
(3)
(1),
[MoO2(L1)(H2O)]·(4,4′-bipy)
(2),
[(MoO2(L1))2(4,4′-bipy)]·2H2O
and
[MoO2(L2)(DMF)] (4), of two tridentate ONO donor aroylhydrazones, H2L1 and H2L2
(where H2L1 = 3-methoxy-2-hydroxybenzaldehyde-2-furoic acid hydrazone and H2L2 = 4-
benzyloxy-2-hydroxybenzaldehyde-4-nitrobenzoic hydrazone), have been synthesized and
characterized by partial elemental analyses, molar conductivity measurements, FT-IR and
electronic spectral studies. A distorted octahedral geometry was established for all the
complexes using single crystal XRD studies. In all the complexes, the aroylhydrazone
coordinates to the MoO22+ core through the phenolate oxygen, azomethine nitrogen and
iminolate oxygen atoms, furnishing a vacant coordination site that can be utilized for
binding of substrates like solvents or heterocyclic bases. The monomeric complexes
[MoO2(L1)(H2O)] (1) and [MoO2(L2)(DMF)] (4) were formed by the stoichiometric
reaction of MoO2(acac)2 with the respective aroylhydrazones. The reaction of H2L1 with
MoO2(acac)2 and 4,4′-bipyridine in an equimolar ratio yielded the 4,4′-bipyridine adduct
[MoO2(L1)(H2O)]·(4,4′-bipy) (2), whereas the binuclear complex [(MoO2(L1))2(4,4′-
bipy)]·2H2O (3) was formed, in which 4,4′-bipyridine acts as a conjugated bidentate
* Corresponding author
E mail address: mrpcusat@gmail.com, mrp_k@yahoo.com (M.R. Prathapachandra Kurup)
Phone: +91-484-2862423
Fax: +91-484-2575804

2
linker between two molybdenum centers, by taking twice the molar concentration of 4,4′-
bipyridine.
Keywords: Aroylhydrazones; Dioxidomolybdenum(VI) complexes; Heterocyclic bases;
IR spectra; Crystal structures
1. Introduction
Aroylhydrazones and their transition metal complexes have fascinated researchers
on account of their potential implications in multifarious fields like medicine [1-3],
catalysis [4], non-linear optics [5], magnetism etc [6]. Among the transition metals,
molybdenum is a versatile biometal which has the ability to promote facile electron-
transfer pathways, a consequence of the easy inter-convertibility of the different
oxidation states, and permits facile ligand exchange reactions through the formation of
stable and labile complexes with nitrogen, oxygen or/and sulfur donor atoms [7,8]. This
intrinsic feature enables molybdenum to form complexes that function as efficient
catalysts in oxotransferase reactions [9] as well as excellent models for molybdoenzymes
[10]. Molybdenum complexes of the dibasic tridentate ligand system are especially
significant and have been widely studied because they afford MoO2L or MoOL
complexes with accessible coordination sites that can be exploited for substrate binding
[8,11,12]. Dioxidomolybdenum complexes have been reported to show remarkable
catalytic activities in several organic transformation reactions which are employed in
industrial processes such as epoxidation of olefins [13], oxidation of sulfides and olefins
[14], oxidative cleavage of glycols [15] etc. Dioxidomolybdenum complexes have also
been investigated for their biological relevance [16-19] and they occupy a significant
place within the scope of the fundamental chemistry of this metal.
The design and development of synthetic methodologies for compounds with
diverse structures and supramolecular architectures are quite interesting as well as
challenging too. Coordination frameworks extending from mononuclear to multinuclear
centres can be assembled by controlling reaction parameters like the inherent
coordination geometry of the metal ion, nature and bonding versatility of the ligands
used, metal-ligand ratio, pH values of the reaction medium and solvents employed
[20,21]. The syntheses of binuclear complexes derived from a dibasic ligand system can

3
be achieved by employing neutral linear N,N′-bidentate spacers like 4,4′-bipyridine (4,4′-
bipy), trans-1,2 bis(4-pyridyl)ethane, trans-1,2 bis(4-pyridyl)ethane, 4,4′-bipyridine-
N,N′-dioxide etc. as bridging ligands [22,23]. These extended polypyridyl type bridging
ligands are found to be excellent and have the ability to connect two coordinatively
unsaturated metal centers, which in turn produce mixed-valence complexes as well as
molecular wires [24]. The supramolecular frameworks in the crystal lattices are
stabilized through various intermolecular and non-covalent forces like hydrogen bonds,
π···π and C–H···π interactions [25].
In this paper, we report the syntheses as well as structural characterization of four
dioxidomolybdenum(VI) complexes of the aroylhydrazones H2L1 and H2L2 (where H2L1
= 3-methoxy-2-hydroxybenzaldehyde-2-furoic acid hydrazone and H2L2 = 4-benzyloxy-2-
hydroxybenzaldehyde-4-nitrobenzoic hydrazone), in which three of them are mononuclear
and the remaining one is binuclear in nature. The supramolecular interactions present in
structures of the complexes, arising from different solvents (DMF and H2O) as well as the
heterocyclic bidentate linker 4,4′-bipy which was added to complete the sixth labile
coordination site of the dioxidomolybdenum(VI) complexes, have been also discussed.
2. Experimental section
2.1. Materials
3-Methoxy-2-hydroxybenzaldehyde
(Alfa
Aesar),
4-benzyloxy-2-
hydroxybenzaldehyde (Sigma-Aldrich), 2-furoic acid hydrazide (Sigma-Aldrich), 4-
nitrobenzoic hydrazide (Sigma-Aldrich), MoO2(acac)2 (Sigma-Aldrich) and the
heterocyclic base, like 4,4′-bipyridine (Sigma-Aldrich), were of Analar grade and
purchased from commercial sources. The solvents methanol (Spectrochem) and DMF
(Spectrochem) were used without further purification. The ligand H2L1 was obtained by
the condensation of equimolar mixtures of methanolic solutions of 3-methoxy-2-
hydroxybenzaldehyde and 2-furoic acid hydrazide and the product was formed in situ.
The ligand H2L2 was prepared and isolated as H2L2·C3H7NO by an earlier reported
method [26]. The structural formulae of the aroylhydrazones H2L1 and H2L2 are
represented in Scheme 1.

4
Scheme 1
2.2.1. Syntheses of the dioxidomolybdenum(VI) complexes
2.2.2.1. Synthesis of [MoO2(L1)(H2O)] (1)
Methanolic solutions of 3-methoxy-2-hydroxybenzaldehyde (0.1521 g, 1 mmol)
and 2-furoic acid hydrazide (0.1261 g, 1 mmol) were mixed and refluxed in a water bath
for six hours. To this solution, MoO2(acac)2 (0.3262 g, 1 mmol) dissolved in hot
methanol and 4 drops of con. HCl were added and the resulting orange colored solution
was refluxed for six hours. The solution was then kept for evaporation at room
temperature and an orange precipitate formed. Single crystals of the compound were
isolated by recrystallization from a DMF-methanol mixture within four weeks. The
product obtained was filtered and dried. Yield: 0.2222 g (55%).
2.2.2.2. Synthesis of [MoO2(L1)(H2O)]·(4,4′-bipy) (2)
Methanolic solutions of 3-methoxy-2-hydroxybenzaldehyde (0.1521 g, 1 mmol)
and 2-furoic acid hydrazide (0.1261 g, 1 mmol) were mixed and refluxed in a water bath
for six hours. To this solution, 4,4′-bipyridine (0.1561 g, 1 mmol) and MoO2(acac)2
(0.3262 g, 1 mmol) dissolved in hot methanol were added and the resulting orange
colored solution was refluxed for 6 hours. An orange colored precipitate separated out
and single crystals of the compound were isolated by recrystallization from a DMF-
methanol mixture within three weeks. The product obtained was filtered and dried.
Yield: 0.4090 g (73%)
2.2.2.3. Synthesis of [(MoO2(L1))2(4,4′-bipy)]·2H2O (3)
Methanolic solutions of 3-methoxy-2-hydroxybenzaldehyde (0.1521 g, 1 mmol)
and 2-furoic acid hydrazide (0.1261 g, 1 mmol) were mixed and refluxed in a water bath
for six hours. To this solution, 4,4′-bipyridine (0.3123 g, 2 mmol) and MoO2(acac)2
(0.3262 g, 1 mmol) dissolved in hot methanol were added and the resulting orange
colored solution was refluxed for 6 hours. An orange colored precipitate separated out
and single crystals of the compound were isolated by recrystallization from a DMF-
methanol mixture within four weeks. The product obtained was filtered and dried.
Yield: 0.6814 g (72%).

5
2.2.2.4. Synthesis of [MoO2(L2)(DMF)] (4)
To a solution of aroylhydrazone, H2L2 (0.4640 g, 1 mmol) in DMF, MoO2(acac)2
(0.3260 g, 1 mmol) in DMF was added. The resultant solution was refluxed for 4 hours.
This was cooled and the orange colored crystalline complex that formed was collected,
washed with methanol, followed by ether and dried over P4O10 in vacuo. Single crystals
of [MoO2(L2)(DMF)] (4) were obtained by recrystallization of the compound from DMF.
Yield: 0.3956 g (67%).
2.3. Physical measurements
Carbon, hydrogen and nitrogen analyses were carried out using a Vario EL III
CHNS analyzer. Infrared spectra were recorded on a JASCO FT-IR-5300 spectrometer
in the range 4000-400 cm-1 using KBr pellets. Electronic spectra were recorded on a
Thermo Scientific Evolution 220 model UV-Visible spectrophotometer in the 50000-
10000 cm-1 range using solutions in DMF. Molar conductivities of the complexes in
DMF solutions (10-3 M) at room temperature were measured using a Systronic model 303
direct reading conductivity meter.
2.4. X-ray crystallography
Single crystal of complexes 1-4 with suitable dimensions were selected and
mounted on a Bruker SMART APEXII CCD diffractometer, equipped with a graphite
crystal, incident-beam monochromator and a fine focus sealed tube with Mo Kα (λ =
0.71073 Å) radiation as the X-ray source. The unit cell dimensions were measured and
the data collection was performed at 292(2) K. The programs SAINT and XPREP were
used for data reduction and APEX2 and SAINT were used for cell refinement [27].
Absorption corrections were carried out using SADABS based on Laue symmetry using
equivalent reflections [28]. The structures were solved by direct methods and refined by
full-matrix least-squares refinement on F2 using SHELXL-97 and SHELXL-2014/7 [29]
provided in WinGX [30]. The molecular and crystal structures were plotted using
DIAMOND version 3.2g [31].

6
In all the complexes, anisotropic refinements were performed for all non-hydrogen
atoms and all H atoms on C atoms were placed in calculated positions, guided by
difference maps, with C–H bond distances of 0.93-0.96 Å. H atoms were assigned as Uiso
= 1.2Ueq (1.5 for Me). The hydrogen atoms (H7A and H7B in 1 / H1 and H1' in 2 / H1D
and H1E in 3) attached to the oxygen atom of the coordinated water molecule in 1 and 2
as well as the lattice water molecule in 3 were located from difference maps and their
distances and angles were restrained using DFIX and DANG instructions with distance
restraints of O–H = 0.86 0.01 and H···H = 1.36 0.02 Å, followed by refinement of their
displacement parameters. The reflections (1 0 0), (-2 8 3) and (0 1 1) in 1, (0 0 1), (0 1
1), (1 1 0) and (1 0 1) in 2, (0 1 1), (0 0 1), (0 1 0) and (-1 1 4) in 3 and (0 0 1), (-1 1 1), (-
1 0 1) and (0 1 0) in 4 were omitted owing to bad disagreement. In
[MoO2(L1)(H2O)]·(4,4′-bipy) (2), the extinction coefficient has a value of 0.0127(11).
The crystallographic data and structure refinement parameters for compounds 1-4 are
given in Table 1.
Table 1
3.
Results and discussion
Four dioxidomolybdenum(VI) complexes of two different tridentate ONO
aroylhydrazones were synthesized and characterized. Complexes 1 and 4 were afforded
by the stoichiometric reaction of MoO2(acac)2 with the aroylhydrazones in DMF-
methanol or DMF reaction media. The reaction of an aroylhydrazone, MoO2(acac)2 and
4,4′-bipyridine in equimolar ratios yielded the 4,4′-bipyridine adduct of
dioxidomolybdenum(VI), complex 2, whereas when the ratio of the reactants was
changed from 1:1:1 to 1:1:2, the binuclear complex 3 was formed in which 4,4′-
bipyridine acts as linker between two molybdenum centers. The complexes were
characterized by various physico-chemical methods, such as partial elemental analyses,
molar conductivity measurements, FT-IR and electronic spectral analyses. We were also
successful in isolating single crystals of compounds 1-4 and their structures were
established by single crystal X-ray diffraction studies.
All the dioxidomolybdenum(VI) complexes are soluble in solvents like DMF and
DMSO, partially soluble in acetonitrile and insoluble in solvents like methanol and ethanol.

7
The analytical data of the complexes are given in Table 2. The partial elemental analyses
of the complexes suggest that all the complexes are analytically pure and correspond to
mononuclear complex motifs with the general formula [MoO2(L)(X)], where L is the
bideprotonated aroylhydrazone and X is the solvent (H2O or DMF), for all the complexes
except 3 in which two [MoO2(L)] moieties are connected by a conjugated bidentate 4,4′-
bipyridine linker, resulting in a dimeric complex.
In all the complexes, the
aroylhydrazone ligand is coordinated in the bideprotonated iminolate form, which is
evident from the IR spectral analyses. The molar conductivity measurements of all the
compounds in DMF (10-3 M) at room temperature suggests that all the complexes are
non-electrolytic in nature and remain undissociated in DMF [32].
Table 2
3.1. IR spectra
The tentative assignments for the significant IR spectral bands of the
dioxidomolybdenum(VI) complexes are presented in the Table S1. The aroylhydrazones
H2L1 and H2L2 displayed distinct bands in the regions 1597-1609, 1680-1580, 3067-3186,
3377-3505 and 1102-1127 cm-1, corresponding to the ν(C=N), ν(C=O), ν(N–H), ν(O–H)
and ν(N–N) stretching vibrations, which are indicative of the existence of the amido form
of the ligand in the solid state [33,34]. The bands due to ν(C=O) and ν(N–H) are absent
in the complexes, suggesting the occurrence of amido-iminol tautomerization following
the deprotonation of the ligands during complexation [34a,34d]. The shift of the ν(C=N)
absorption towards lower frequency in all the complexes indicates the coordination of the
azomethine nitrogen atom to the metal center [34a,34d]. The disappearance of the
intense bands attributed to –C=O stretching vibrations along with appearance of new
bands in the 1543-1630 cm-1 region due to the asymmetric stretching vibration of the
newly formed C=N bond justifies the iminolization of the aroylhydrazone ligand in these
complexes [35]. The presence of lattice water in complex 3 was confirmed from the
broad band obtained above 3400 cm-1 [36,37].
All the dioxidomolybdenum(VI) complexes exhibit two bands in the 890-915 and
920-970 cm-1 regions and can be assigned to symmetric and asymmetric vibrations
respectively, characteristic of cis-MoO2 cores as reported in the literature [12,38]. The

8
weak band in the 550-610 cm-1region in the metal complexes has been assigned to the
ν(Mo–N) vibration mode [18,39]. The medium intensity bands at 814, 1217 and 1405
cm-1 in 2 and 1226 and 1407 cm-1 in 3 corresponds to the stretching vibrations of the free
as well as coordinated bidentate 4,4′-bipyridine ligand respectively [40].
3.2. Electronic spectra
The electronic spectral assignments of the dioxidomolybdenum(VI) complexes in
DMF solution are summarized in Table S2.
The electronic spectra of the
aroylhydrazones show bands in the 32600-38200 cm-1 region due to n→π*/π→π*
transitions [8,34b,34c]. These bands suffer a considerable shift in intensity and
wavelength on coordination [8,34a,34d]. The complexes show broad bands in the 21110-
29000 cm-1 region which may be assigned to ligand to metal charge transfer transitions
[8].
3.3. Description of the crystal structures
3.3.1. General features in the molecular structures of [MoO2(L1)(H2O)] (1),
[MoO2(L1)(H2O)]·(4,4′-bipy) (2), [(MoO2(L1))2(4,4′-bipy)]·2H2O (3) and
[(MoO2(L2)(DMF)] (4)
The coordination geometry around the molybdenum(VI) atom shows a distorted
octahedral environment with an NO5 (for 1, 2 and 4) or N2O4 (for 3) chromophore. The
coordination geometry was satisfied by the bideprotonated tridentate ONO donor
aroylhydrazone ligand, through the phenolate oxygen, azomethine nitrogen and iminolate
oxygen atoms, and terminal oxo groups. The sixth labile site is occupied by an oxygen
atom of solvent water in 1 and 2, a nitrogen atom of the heterocyclic bidentate linker in 3
and an oxygen atom of solvent DMF in 4. The equatorial positions of the octahedron are
defined by the donor atoms of the aroylhydrazone ligand and one of the terminal oxo
oxygen atoms, whereas the axial positions are occupied by another terminal oxo oxygen
atom and the oxygen atom of the solvent water/nitrogen atom of the heterocyclic base. In
all the complexes, the aroylhydrazone ligand is coordinated to the cis-MoO22+ core in a
2+
meridional fashion, forming five and six membered metallocycles involving the MoO2
center. The large as well as weak Mo–X distances (X = oxygen atom of the solvent

9
molecule in 1, 2 and 4 or the nitrogen atom of the heterocyclic base in 3), in comparison
with the other Mo–N, Mo–O bond distances in the complex, substantiate the respective
position to hold the possibility of functioning as a substrate binding site. In all cases the
Mo atom is displaced by 0.3-0.5 Å from the square plane towards the terminal oxo
oxygen atom at a distance of 1.9-2.1 Å from this plane, leading to the shrinking of the
bond length of the trans oxo oxygen atom as well as lengthening the Mo–X bond. The
Mo–O, Mo–N and Mo=O bonds are within their normal ranges and are comparable to
those observed in other similar dioxidomolybdenum(VI) complexes [19,22,23,35]. The
aroylhydrazone ligand is coordinated in the iminolate form in the complexes, which is
evidenced by the bond distances C9–O3 (1.30-1.33 Å) and N2–C9 (1.29-1.32 Å) [8].
The bond lengths C=Nazo and Nazo–Nimine also show the extensive delocalization in the
coordinated hydrazine ligand. The cis-MoO22+ unit forms five and six membered chelate
rings with bite angles in the range 70-82° (Ophenolate–Mo–Nazo and Oiminolate–Mo–Nazo).
The bond distances about the Mo center reveal the magnitude of the distortions, as can be
seen in Table 3. The angular distortion in the octahedral environment around the Mo
atom comes from the five and six membered chelate rings with the hydrazone ligand, so
that the trans angles and cis angles significantly deviate from the ideal values of 180 and
90° respectively.
3.3.1.1. Crystal structure of [MoO2(L1)(H2O)] (1)
The molecular structure of complex 1 along with the atom numbering scheme is
shown in Fig. 1 and significant bond distances and bond angles are shown in Table 3.
The complex crystallizes into the monoclinic space group, P21/c with four molecules in
the unit cell.
Fig. 1
Ring puckering analysis and least square plane calculations [41] show that in
complex 1 the ring Cg(1), comprising of the atoms Mo(1), O(3), C(9), N(1) and N(2), is
puckered with puckering amplitude Q(2) = 0.0788(19) Å and φ(2) = 15.4(18)º. The
puckering of the five membered metallocycle was also calculated in terms of the
pseudorotation parameter P and τm [42], and it was found that the metallocycle adopts
twisted conformation with P = 190.7(13)º and τ = 7.7(1)º for reference bond Mo(1)–O(3)

10
in Cg(1). The metallocycle Cg(3), comprising of atoms Mo(1), O(2), C(7), C(6), C(8)
and N(1), is also found to be puckered in complex 1 with puckering amplitude Q =
0.266(2) Å, θ = 117.4(4)° and φ = 223.6(6)º.
3.3.1.2. Crystal structure of [MoO2(L1)(H2O)]·(4,4′-bipy) (2)
Orange block shaped single crystals of [MoO2(L1)(H2O)]·(4,4′-bipy) (2) were
isolated by slow evaporation of its mother liquor. The asymmetric unit of the compound
consists of a [MoO2(L1)(H2O)]·molecule and half of a 4,4′-bipyridine molecule. There is
an inversion center at the midpoint of the C14···C14A bond of the 4,4′-bipyridine
molecule. The complex is crystallized as the 4,4′-bipyridine adduct in the triclinic space
ꢀ
group, P1. The bond lengths and bond angles are comparable to similar
dioxidomolybdenum(VI) complexes in which 4,4′-bipyridine is present in the crystal
lattice [11,43]. The molecular structure of complex 2 along with the atom numbering
scheme is shown in Fig. 2.
Fig. 2
The ring puckering analysis and least square plane calculations [41] of complex 2
show that the six membered metallocycle Cg(3), comprising of atoms Mo(1), O(2), C(7),
C(6), C(8) and N(1), is puckered with puckering amplitude Q = 0.300 Å, θ = 117.7(4)º
and φ = 207.8(6)º. Conformational analyses [44] show that this six membered
metallocycle Cg(3) adopts the S-form (screw-boat) conformation.
3.3.1.3. Crystal structure of [(MoO2(L1))2(4,4′-bipy)]·2H2O (3)
Reddish orange block shaped single crystals of [(MoO2(L1))2(4,4′-bipy)]·2H2O (3)
were isolated by slow evaporation of its mother liquor. This complex crystallizes in the
ꢀ
triclinic space group, P1, possessing a crystallographic center of inversion. The
molecular structure of complex 3, along with the atom numbering scheme, is shown in
Fig. 3 and the description of the structure is limited to half of the molecule.
Fig. 3
Two [MoO2(L)] units in complex 3 are bridged together through the nitrogen
atoms of the 4,4′-bipyridyl ligand to form a dinuclear dioxidomolybdenum(VI) complex
with a Mo···Mo separation of 11.9865(5) Å; this is comparable to similar binuclear

11
dioxidomolybdenum(VI) complexes in which the metal centers are connected by a 4,4′-
bipyridine linker [19,22,23,45]. Ring puckering analysis and least square plane
calculations [41] show that the ring Cg(3) in complex 3, comprising of atoms Mo(1),
O(2), N(1), C(6), C(7) and C(8), is puckered with puckering amplitude Q = 0.3500(18) Å,
θ = 119.2(3)° and φ = 189.2(5)º.
3.3.1.4. Crystal structure of [MoO2(L2)(DMF)] (4)
The molecular structure of the complex 4, with the atom numbering scheme, is
shown in Fig. 4 and relevant bond distances and angles are presented in Table 3. The
ꢀ
complex crystallizes in the triclinic space group P1. There are two crystallographically
independent molecules in the asymmetric unit of the compound (Fig. 4) with bond
lengths and angles which agree with each other.
Fig. 4
Ring puckering analysis and least square plane calculations [41] show that the
rings Cg(2) and Cg(7) in complex 4, involving the Mo(1) and Mo(2) centers, are found to
be puckered. The six membered metallocycle Cg(2), comprising of the atoms Mo(1),
O(2), C(10), C(11), C(14) and N(1), is puckered with puckering amplitude Q = 0.250(2)
Å, θ = 60.3(7)° and φ = 21.4(8)º. Similarly, the six membered metallocycle Cg(7),
comprising of the atoms Mo(2), O(10), C(34), C(35), C(38) and N(5), is also puckered
with puckering amplitude Q = 0.294(2) Å, θ = 116.4(6)° and φ = 190.2(7)º.
3.3.2.Supramolecular features in complexes 1-4
The interaction parameters for complexes 1-4 are listed in Table S3. In
[MoO2(L1)(H2O)] (1), the oxygen atom of the coordinated water molecule acts as a
hydrogen bond donor and is involved in intermolecular hydrogen bonds, namely O(7)–
H(7A)···O(1), O(7)–H(7B)···O(4) and O(7)–H(7B)···N(2). These hydrogen bonds
connect the molecules to form a supramolecular chain which propagates in the b direction
when viewed along the crystallographic a axis (Fig. 5). The hydrogen atom H7B attached
to O7 is involved in bifurcating hydrogen bonds with two acceptors, N2 and O4.
Fig. 5

12
Non-conventional hydrogen bonding interactions, like C(1)–H(1B)···O(5),
C(12)–H(12)···O(3) and C(13)–H(13)···O(6), are also present in the crystal lattice of 1.
The hydrogen bonds, C(1)–H(1B)···O(5) and C(12)–H(12)···O(3) link adjacent
molecules (Fig. S1). The hydrogen bond C(13)–H(13)···O(6), observed at a H···A
distance of 2.33 Å and <(DHA) = 150.5°, connects the molecules in a linear fashion
propagating along the b direction (Fig. 6).
Fig. 6
The crystal lattice packing in complex 1 is also further supported by π···π as well
as O–H···π bonding interactions (Table S4). The six membered aromatic ring Cg(4)
(comprising of atoms C2, C3, C4, C5, C6 and C7) of one aroylhydrazone moiety interacts
with the five membered furan ring Cg(2) (comprising of atoms O4, C10, C11, C12 and
C13) of another aroylhydrazone moiety through a π···π interaction with a distance of
3.6756 Å (Fig. S2). The hydrogen atom H7A attached to the O7 atom of the coordinated
water molecule is involved in a O–H···Cg(1) interaction, in which Cg(1) is a five
membered metallocycle comprising of atoms Mo1, O2, C9, N3 and N2. The unit cell
crystal lattice packing is viewed along the b direction (Fig. S3).
The crystal packing of [MoO2(L1)(H2O)]·(4,4′-bipy) (2) is enriched with strong
classical intermolecular hydrogen bonds (Fig. 7), in which the oxygen (O1W) atom of the
coordinated water molecule acts as a donor for two different acceptors, N2 (imine
nitrogen atom) and N3 (nitrogen atom of 4,4′-bipyridine). The hydrogen bond O(1W)–
H(1)···N(2) connects adjacent molecules into dimers. One of the complex motifs in these
dimers is connected to the nitrogen atom of a nearby 4,4′-bipyridine molecule through an
O(1W)–H(1′)···N(3) hydrogen bond. There is a weak non-conventional C–H···O
hydrogen bonding interaction involving the hydrogen atom H18 attached to the C18 atom
of the 4,4′-bipyridine molecule and the oxo oxygen atom O6.
Fig. 7
The crystal lattice packing in complex 2 is also further supported by π···π as well
as O–H···π interactions (Table S4) which is the same as observed in the case of complex
1. The Cg(4) (comprising of atoms C2, C3, C4, C5, C6 and C7) and Cg(2) (comprising
of atoms O4, C10, C11, C12 and C13) rings of adjacent aroylhydrazone moieties interact

13
with a distance of 3.873(2) Å. The O1W–H1···Cg(1) interaction is observed at a H···Cg
distance of 2.66(3) Å, in which Cg(1) is a five membered metallocycle comprising of the
atoms Mo1, O2, C9, N3 and N2. The unit cell crystal packing of 2 as viewed along the
crystallographic a axis is given in Fig. S4.
The unit cell packing of [(MoO2(L1))2(4,4′-bipy)]·2H2O (3), featuring sliding H
shaped complex motifs when viewed along the crystallographic a axis, is shown in Fig. 8.
The crystal packing of complex 3 is strengthened by classical and non-classical inter- or
intramolecular hydrogen bonds present in the lattice. The intramolecular hydrogen bonds
C(14)–H(14)···O(6), C(18)–H(18)···N(1) and O(1S)–H(1E)···O(5) impart rigidity to the
complex motif (Fig. S5).
Fig. 8
In complex 3, the oxygen atom of the lattice water molecule, O1S, participates
in bifurcating hydrogen bonds with two acceptors, atoms N2 and O4, through the
hydrogen atom H1D. The non-conventional intermolecular hydrogen bonds C(8)–
H(8)···O(5), O(15)–H(15)···O(1) and O(18)–H(18)···O(1S) assemble the complex motifs
and form a one dimensional layer type chain in the crystal packing which propagates
along the bc plane when viewed along the crystallographic a axis (Fig. 9). The trans oxo
oxygen atom O5 serves as an acceptor for both conventional intramolecular (O(1S)–
H(1E)···O(5)) as well as non-conventional intramolecular (C(8)–H(8)···O(5)) hydrogen
bonding interactions. Similarly, the carbon atom attached to the 4,4′-bipyridine molecule
is involved in the bifurcating hydrogen bonds with two acceptors, atoms N1 and O1S, for
the formation of non-conventional intra as well as intermolecular hydrogen bonding
interactions.
Fig. 9
In complex 3, two π···π (between Cg(1)···Cg(4) and Cg(2)···Cg(2)) and two
C(1)–H(1A)···Cg(5) and C(12)–H(12)···Cg(4) bonding interactions (Table S4) are
observed in the crystal structure. There exists a weak π···π interaction between Cg(4)
(comprised of atoms N3, C14, C15, C16, C17 and C18) interacting with Cg(1)

14
(comprised of atoms Mo1, O1, C9, N2 and N1) at a distance of 3.9660(13) Å. Another
π···π interaction is observed between the furan rings (Cg(2)···Cg(2)) of adjacent
molecules (Fig. S6). Weak C(1)–H(1A)···Cg(5) and C(12)–H(12)···Cg(4) bonding
interactions are observed in the crystal packing (Fig. S7).
In [MoO2(L2)(DMF)] (4), there are no conventional hydrogen bonds present in the
molecular system. However, some weak interactions like π···π, C–H···π and C–H···O
(Table S4) are observed in the crystal structure. The adjacent molecules are linked into
chains by non-conventional hydrogen bonding interactions, as shown in Fig. 10. Rings
Cg(9) and Cg(10) of neighboring molecules are involved in π···π stacking with a distance
of 3.808(2) Å (Fig. S8). C–H···π interactions exist between H(1) and Cg(10) [C(40),
C(41), C(42), C(43), C(44), C(45)] and H(42) and Cg(3) [C(1), C(2), C(3), C(4), C(5),
C(6)] (Fig. S9). Weak N–O···π interactions are also present in the complex. The π···π, C–
H···π and N–O···π interactions support the packing stability in the absence of strong
conventional hydrogen bonds.
Fig. 10
Conclusion
Four dioxidomolybdenum(VI) complexes using two different ONO tridentate
aroylhydrazones were synthesized, then spectroscopically and structurally characterized.
All the complexes exhibit a distorted octahedral geometry whose sixth labile coordination
site is occupied by a solvent molecule (water or DMF) or a heterocyclic base (4,4′-
bipyridine). We were also able to synthesize mononuclear (2) as well as binuclear (3)
complexes using the same reactants, but differing their molar ratios. Large Mo–X bond
lengths (X = labile site) in the complexes can be used for application purposes and among
the complexes synthesized, [(MoO2(L1))2(4,4′-bipy)]·2H2O (3) has the highest Mo–X
bond length (2.439(2) Å). The different packing arrangements of the complex motif and
supramolecular architectures formed by the influence of hydrogen bonding and weak
non-covalent forces were also investigated.

15
Supporting Information
The tables and figures, including hydrogen bonding and non-bonding interactions,
IR and UV-Vis spectra are included.
Acknowledgments
AAA and BJ acknowledge CSIR for the award of a Senior Research Fellowship.
The ULK acknowledges UGC for the financial support. The authors are thankful to the
Sophisticated Analytical Instrumentation Facility, Cochin University of Science and
Technology, Kochi, India for elemental analyses and single crystal X-ray diffraction
measurements.
Appendix A. Supplementary data
Crystallographic data for the structural analyses have been deposited with the Cambridge
Crystallographic Data Center as CCDC 1506862, 1506864, 1506869 and 1506904 for the
complexes [MoO2(L1)(H2O)] (1), [MoO2(L1)(H2O)]·(4,4′-bipy) (2), [(MoO2(L1))2(4,4′-
bipy)]·2H2O (3) and [(MoO2(L2)(DMF)] (4) respectively. Copies of this information may
be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html or from the
Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: +44-1223-336-033; e-
mail: deposit@ccdc.cam.ac.uk).
References
[1]
S.Y. Ebrahimipour, I. Sheikhshoaie, J. Simpson, H. Ebrahimnejad,
M. Dusek, N. Kharazmi, V. Eigner, New J. Chem. 40 (2016) 2401-
2412.
[2]
[3]
[4]
J. Deng, Y. Gou, W. Chen, X. Fu, H. Deng, Bioorg. Med. Chem. 24 (2016) 2190-
2198.
X. Zhao, X. Chen, J. Li, J. Chen, G. Sheng, F. Niu, D. Qu, Y. Huo, H. Zhu, Z.
You, Polyhedron 97 (2015) 268-272.
M. Sutradhar, E.C.B.A. Alegria, K.T. Mahmudov, M.F.C.G. da Silva,
A.J.L. Pombeiro, RSC Adv. 6 (2016) 8079-8088.

16
[5]
[6]
[7]
I. Sheikhshoaie, S.Y. Ebrahimipour, M. Sheikhshoaie, H.A. Rudbari, M.
Khaleghi, G. Bruno, Spectrochim. Acta 124A (2014) 548-555.
R. Bikas, N. Noshiranzadeh, L. Sieroń, J.M. Barandiaran, T. Lis, J. Alanso, Inorg.
Chem. Commun. 67 (2016) 85-89.
M.A. Hussein, T.S. Guan, R.A. Haque, M.B.K. Ahamed, A.M.S.A. Majid, Inorg.
Chim. Acta 421 (2014) 270-283.
[8]
[9]
N. Mathew, M.R.P. Kurup, Spectrochim. Acta A78 (2011) 1424-1428.
M.E. Judmaier, C.H. Sala, F. Belaj, M. Volpe, N.C. Mösch-Zanetti,
New J. Chem. 37 (2013) 2139-2149.
[10] H. Sugimoto, M. Sato, L.J. Giles, K. Asano, T. Suzuki, M.L. Kirk,
S. Itoh, Dalton Trans. 42 (2013) 15927-15930.
[11] K. Užarević, G. Pavlović, M. Cindrić, Polyhedron 52 (2013) 294-300.
[12] E.B. Seena, M.R.P. Kurup, Polyhedron 26 (2007) 3595-3601.
[13] M. Bagherzadeh, M.M. Haghdoost, A. Ghanbarpour, M. Amini, H.R. Khavasi, E.
Payab, A. Ellern, L.K. Woo, Inorg. Chim. Acta 411 (2014) 61-66.
[14] G. Romanowski, J. Kira, Polyhedron 117 (2016) 352-358.
[15] N. García, R. Rubio-Presa, P. García-García, M.A. Fernández-Rodríguez, M.R.
Pedrosa, F.J. Arnáiz, R. Sanz, Green Chem. 18 (2016) 2335-2340.
[16] S. Rakshit, D. Palit, S.K.S. Hazari, S.Rabi, T.G. Roy, F.Olbrich, D. Rehder,
Polyhedron 117 (2016) 224-230.
[17] M.A. Hussein, T.S. Guan, R.A. Haque, M.B.K. Ahamed, A.M.S.A. Majid,
Polyhedron 85 (2015) 93-103.
[18] D. Biswal, N.R. Pramanik, S. Chakrabarti, N. Chakraborty, K.
Acharya, S.S. Mandal, S. Ghosh, M.G.B. Drew, T.K. Mondal, S.
Biswas, New J. Chem. 39 (2015) 2778-2794.
[19] S. Pasayat, S.P. Dash, Saswati, P.K. Majhi, Y.P. Patil, M. Nethaji, H.R. Dash, S.
Das, R. Dinda, Polyhedron 38 (2012) 198-204.
[20] R.J. Kunnath, M. Sithambaresan, A.A. Aravindakshan, A. Natarajan, M.R.P.
Kurup, Polyhedron 113 (2016) 73-80.

17
[21] M. Đaković, D.V.-Viçosa, M.J. Calhorda, Z. Popović, Cryst. Eng.
Comm. 13 (2011) 5863-5871.
[22] N.R. Pramanik, M. Chakraborty, D. Biswal, S.S. Mandal, S. Ghosh,
S. Chakrabarti, W.S. Sheldrick, M.G.B. Drew, T.K. Mondal, D.
Sarkar, Polyhedron 85 (2015) 196-207.
[23] N.K. Ngan, K.M. Lo, C.S.R. Wong, Polyhedron 33 (2012) 235-251.
[24] M.D. Ward, Chem. Soc. Rev. 24 (1995) 121-134.
[25] V. Vrdoljak, B. Prugovečki, D. Matković-Čalogović, T. Hrenar, R.
Dreos, P.Siega, Cryst. Growth Des. 13 (2013) 3773-3784.
[26] B. Joseph, M. Sithambaresan, M.R.P. Kurup, Acta Cryst. E69 (2013)
o1160-o1161.
[27] SMART and SAINT, Area Detector Software Package and SAX Area Detector
Integration Program, Bruker Analytical X-ray, Madison, WI, USA, 1997.
[28] SADABS, Area Detector Absorption Correction Program; Bruker Analytical X-ray;
Madison, WI, 1997.
[29] G.M. Sheldrick, Acta Cryst. C71 (2015) 3-8.
[30] L.J. Farrugia, J. Appl. Cryst. 45 (2012) 849-854.
[31] K. Brandenburg, Diamond Version 3.2g, Crystal Impact GbR, Bonn, Germany, 2010.
[32] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81-122.
[33] M. Nandy, S. Shit, C. Rizzoli, G. Pilet, S. Mitra, Polyhedron 88
(2015) 63-72.
[34] (a) B.N.B. Raj, M.R.P. Kurup, E. Suresh, Spectrochim. Acta 71A
(2008) 1253-1260.
(b) M. Kuriakose, M.R.P. Kurup, E. Suresh, Spectrochim. Acta 66A
(2007) 353-358.
(c) B.N.B. Raj, M.R.P. Kurup, Spectrochim. Acta 66A (2007) 898-
903.

18
(d) B.N.B. Raj, M.R.P. Kurup, E. Suresh, Struct. Chem. 17 (2006)
201-208.
[35] S.Y. Ebrahimipour, H. Khabazadeh, J. Castro, I. Sheikhshoaie, A. Crochet, K.M.
Fromm, Inorg. Chim. Acta 427 (2015) 52-61.
[36] V. Stefov, V.M. Petrusevski, B. Soptrajanov, J. Mol. Struct. 293
(1993) 97-100.
[37] K. Jayakumar, M. Sithambaresan, A.A. Aravindakshan, M.R.P. Kurup,
Polyhedron 75 (2014) 50-56.
[38] K. Nakamoto, Infrared and Raman Spectra of Inorganic and
Coordination Compounds, 5th ed., John Wiley & Sons, NewYork, 1997,
p.86.
[39] S. Sinha, M. Chakraborty, N.R. Pramanik, T.K. Raychaudhuri, T.K.
Mondal, D. Sarkar, M.G.B. Drew, S. Ghosh, S.S. Mandal, Polyhedron
55 (2013) 192-200.
[40] J. Metz, O. Schneider, M. Hanack, Spectrochim. Acta. 38A (1982) 1265-1273.
[41] D. Cremer, J.A. Pople, J. Am. Chem. Soc. 97 (1975) 1354-1358.
[42] S.T. Rao, E. Westhof, M. Sundaralingam, Acta Cryst. A37 (1981)
421-425.
[43] N.K. Ngan, R.C.S. Wong, K.M. Lo, S.W. Ng, Acta Cryst. E67 (2011)
m747.
[44] G.G. Evans, J.A. Boeyens, Acta Cryst. B45 (1989) 581-590.
[45] (a) R. Dinda, S. Ghosh, L.R. Falvello, M. Tomás, T.C.W. Mak,
Polyhedron 25 (2006) 2375-2382.
(b) S. Alghool, C. Slebodnick, Polyhedron 67 (2014) 11-18.

19
3-Methoxy-2-hydroxybenzaldehyde-2-furoic acid hydrazone (H2L1)
4-Benzyloxy-2-hydroxybenzaldehyde 4-nitrobenzoic hydrazone (H2L2)
Scheme 1. Structures of the tridentate ONO donor aroylhydrazones.
Table 1. Crystallographic data and structure refinement for 1, 2, 3 and 4
Parameters
1
2
3
4
C13H12MoN2O7
404.19
C18H16MoN3O7 C36H32Mo2N6O14
Empirical formula
Formula weight
Crystal system
Space group
C24H22MoN4O8
590.40
482.28
964.56
Monoclinic
P21/c
Triclinic
Triclinic
Triclinic
ꢀ
P1
P1
P1
Cell parameters
a (Å)
9.3396(7)
10.1066(7)
15.5078(12)
90
8.0905(4)
10.2535(5)
12.8847(7)
76.608(3)
75.849(2)
69.484(2)
7.6833(3)
10.2972(4)
12.4364(5)
71.555(2)
79.260(2)
88.556(2)
14.0681(12)
14.0982(12)
15.2049(12)
95.301(3)
b (Å)
c (Å)
α (°)
β (°)
97.872(2)
90
114.053(3)
111.047(3)
γ (°)

20
Volume V (Å3)
Z
1450.01(19)
958.08(9)
2
916.43(6)
1
2467.2(4)
4
4
1.852
1.672
1.748
Calculated density (ρ)
(Mg m-3)
1.589
0.944
808
0.731
486
0.765
486
Absorption
coefficient, µ (mm-1)
0.588
1200
F(000)
Crystal size (mm3)
θ range for data
collection
0.40 x 0.32 x 0.28 0.35 x 0.30 x 0.30 0.30 x 0.25 x 0.20
0.40 × 0.35 × 0.30
1.80 to 27.00°
2.652 to 28.307°
2.73 to 25.05°
2.700 to 28.337°
Limiting indices
-12 ≤ h ≤ 10
-8 ≤ k ≤ 13
-9 ≤ h ≤ 9
-12 ≤ k ≤ 12
-14 ≤ l ≤ 15
5779 / 3395
-9 ≤ h ≤ 10
-12 ≤ k ≤ 13
-16 ≤ l ≤ 16
7334 / 4571
-14≤ h ≤ 17,
-18 ≤ k ≤ 12,
-19 ≤ l ≤ 19
17880/10768
-20 ≤ l ≤ 20
10490 / 3614
Reflections collected/
Unique Reflections
(Rint)
[R(int) = 0.0360] [R(int) = 0.0196] [R(int) = 0.0224] [R(int) = 0.0204]
Completeness to θ
Absorption correction
25.242 (99.7%)
Semi-empirical
from equivalents
0.740 and 0.560
25.05 (99.3%)
Semi-empirical
25.242 (98.5%)
Semi-empirical
27.00 (98.0%)
Semi-empirical
from equivalents from equivalents from equivalents
0.803 and 0.774 0.820 and 0.750 0.838 and 0.790
Maximum and
minimum
transmission
3557 / 0 / 217
1.012
10548 / 0 / 672
1.031
Data / restraints /
3370 / 3 / 272
0.946
4446 / 3 / 271
1.042
parameters
Goodness-of-fit on F2
Final R indices
[I > 2σ (I)]
R1 = 0.0316,
wR2 = 0.0700
R1 = 0.0436,
R1 = 0.0238,
wR2 = 0.0641
R1 = 0.0270,
wR2 = 0.0695
R1 = 0.0334,
wR2 = 0.0761
R1 = 0.0417,
wR2 = 0.0807
R1 = 0.0377,
wR2 = 0.0919
R indices (all data)
R1 = 0.0573,
wR2 = 0.1059
wR2 = 0.0781
0.572 and -1.056
0.433 and -0.432 0.438 and -0.408 1.063 and -0.649
Largest difference
peak and hole (e Ǻ-3)
2
2 2 1/2
R1 = Σ||Fo| - |Fc|| / Σ|Fo|
wR2 = [Σw(Fo -Fc2)2 / Σw(Fo ) ]

21
Table 2. Colors, partial elemental analyses and molar conductivity measurements of the
dioxidomolybdenum(VI) complexes of ONO donor aroylhydrazones
Found (Calc.) %
Compounds
Color
Λ*M
C
H
N
[MoO2(L1)(H2O)] (1)
Orange
38.06 (38.63)
49.10 (49.30)
45.10 (44.83)
48.98 (48.82)
2.43 (2.99)
3.63 (3.60)
3.63 (3.34)
3.93 (3.76)
6.81 (6.93)
9.81 (10.00)
8.81 (8.71)
9.87 (9.49)
4
6
[MoO2(L1)(H2O)]·(4,4′-bipy) (2)
[(MoO2(L1))2(4,4′-bipy)]·2H2O (3)
Orange
Dark red
Orange
6
[MoO2(L2)(DMF)] (4)
11
* 10-3 M solutions in DMF
Table 3. Selected bond lengths (Å) and bond angles (°) of compounds 1-4
Bond lengths (Å)
[MoO2(L1)(H2O)] (1)
[MoO2(L1)(H2O)]·(4,4′-bipy)
[(MoO2(L1))2(4,4′-bipy)]·2H2O
[MoO2(L2)(DMF)] (4)
(2)
(3)
Mo1–O2
Mo1–N1
Mo1–O3
Mo1–O5
Mo1–O6
Mo1–O7
C8–N1
1.9918(18)
Mo1–O2
Mo1–N1
Mo1–O3
Mo1–O5
Mo1–O6
Mo1–O1W
C8–N1
1.9209(18)
2.242(2)
Mo1–O2
Mo1–N1
Mo1–O3
Mo1–O5
Mo1–O6
Mo1–N3
C8–N1
1.9288(18)
2.232(2)
2.0088(18)
1.701(2)
1.6978(17)
2.439(2)
1.288(3)
1.394(3)
1.298(3)
1.327(3)
Mo1–O2
1.923(2)
2.217(2)
2.009(2)
1.705(2)
1.689(2)
2.341(2)
1.289(4)
1.391(3)
1.292(4)
1.316(3)
2.252(2)
2.0018(18)
1.682(2)
1.699(2)
2.320(2)
1.292(3)
1.398(3)
1.306(3)
1.318(3)
Mo1–N1
Mo1–O3
Mo1–O6
Mo1–O7
Mo1–O8
C14–N1
N1–N2
2.0157(17)
1.6880(18)
1.6995(18)
2.2425(18)
1.291(3)
N1–N2
N1–N2
1.391(3)
N1–N2
C9–N2
C9–N2
1.298(3)
C9–N2
C15–N2
C15–O3
C9–O3
C9–O3
1.306(3)
C9–O3

22
Mo2–O10
Mo2–N5
Mo2–O11
Mo2–O14
Mo2–O15
Mo2–O16
C38–N5
1.923(2)
2.218(2)
2.007(2)
1.682(2)
1.701(2)
2.351(2)
1.292(4)
1.392(3)
1.294(4)
1.313(3)
N5–N6
C39–N6
C39–O11
Bond angles (°)
[MoO2(L1)(H2O)] (1)
[MoO2(L1)(H2O)]·(4,4′-bipy)
(2)
O5–Mo1–O1W
[(MoO2(L1))2(4,4′-
[MoO2(L2)(DMF)] (4)
bipy)]·2H2O (3)
O5–Mo1–O7 169.53(11)
O6–Mo1–N1 158.89(11)
170.28(8)
158.08(8)
151.60(8)
105.38(9)
102.88(9)
98.33(8)
97.82(9)
95.07(8)
94.49(9)
83.89(9)
83.44(8)
81.64(7)
79.98(8)
75.66(7)
71.83(7)
O5–Mo1–N3
172.69(8)
159.23(8)
148.94(8)
105.51(9)
105.04(8)
98.79(9)
98.51(9)
94.88(8)
92.46(9)
81.88(8)
81.80(8)
80.61(8)
80.36(7)
78.98(8)
71.78(7)
O7–Mo1–O8
O6–Mo1–N1
O2–Mo1–O3
O6–Mo1–O7
O6–Mo1–O2
O7–Mo1–O2
O6–Mo1–O3
O7–Mo1–O3
O7–Mo1–N1
O6–Mo1–O8
O2–Mo1–O8
O2–Mo1–N1
O3–Mo1–O8
N1–Mo1–O8
O3–Mo1–N1
170.90(9)
O6–Mo1–N1
O2–Mo1–O3
O5–Mo1–O6
O6–Mo1–O2
O6–Mo1–O3
O5–Mo1–O2
O5–Mo1–N1
O5–Mo1–O3
O2–Mo1–O1W
O6–Mo1–O1W
O2–Mo1–N1
O3–Mo1–O1W
N1–Mo1–O1W
O3–Mo1–N1
O6–Mo1–N1
O2–Mo1–O3
O5–Mo1–O6
O6–Mo1–O2
O5–Mo1–O2
O5–Mo1–O3
O6–Mo1–O3
O5–Mo1–N1
O2–Mo1–N1
O6–Mo1–N3
O3–Mo1–N3
N1–Mo1–N3
O2–Mo1–N3
O3–Mo1–N1
158.54(10)
149.74(9)
104.84(11)
102.31(9)
99.95(12)
97.19(9)
97.10(11)
95.07(10)
83.13(9)
82.29(9)
81.64(9)
77.29(8)
76.46(8)
72.07(9)
O2–Mo1–O3
149.79(8)
O5–Mo1–O6 105.65(13)
O6–Mo1–O2 102.50(10)
O5–Mo1–O2
O6–Mo1–O3
O5–Mo1–O3
O5–Mo1–N1
O6–Mo1–O7
O2–Mo1–N1
O2–Mo1–O7
O3–Mo1–O7
N1–Mo1–O7
O3–Mo1–N1
99.18(10)
97.38(9)
97.07(10)
93.91(10)
84.49(12)
81.83(8)
80.98(8)
78.53(8)
75.72(9)
71.78(8)
O14–Mo2–O16 170.79(10)
O15–Mo2–N5 159.40(11)
O10–Mo2–O11 149.27(9)
O14–Mo2–O15 104.87(12)
O15–Mo2–O10 102.52(10)
O14–Mo2–O10 100.83(12)
O15–Mo2–O11 97.47(10)
O14–Mo2–O11 96.23(11)
O14–Mo2–N5
94.12(10)

23
O15–Mo2–O16 83.52(10)
O10–Mo2–N5 81.23(9)
O10–Mo2–O16 80.67(10)
O11–Mo2–O16
N5–Mo2–O16
O11–Mo2–N5
78.65(9)
77.07(8)
72.16(8)

24
Fig. 1. Molecular structure of [MoO2(L1)(H2O)] (1), along with the atom numbering
scheme.
Fig. 2. Molecular structure of [MoO2(L1)(H2O)]·(4,4′-bipy) (2), along with the atom
numbering scheme.

25
Fig. 3. Molecular structure of [(MoO2(L1))2(4,4′-bipy)]·2H2O (3), along with the atom
numbering scheme. Two solvent water molecules are omitted for clarity.

26
Fig. 4. Asymmetric unit of [MoO2(L2)(DMF)] (4) (hydrogen atoms are omitted for
clarity), along with the atom numbering scheme.
Fig. 5. Conventional hydrogen bonding interactions present in [MoO2(L1)(H2O)] (1).

27
Fig. 6. C–H···O hydrogen bonding interactions in 1 connecting the molecules in a linear
fashion propagating along the b direction.
Fig. 7. Conventional hydrogen bonding interactions present in [MoO2(L1)(H2O)]·(4,4′-
bipy) (2).

28
Fig. 8. The H-shaped complex motifs of [(MoO2(L1))2(4,4′-bipy)]·2H2O (3) packed in
the crystal lattice when viewed along the crystallographic a axis.

29
Fig. 9. The hydrogen bonding interactions in [(MoO2(L1))2(4,4′-bipy)]·2H2O (3)
connecting the molecules when viewed along the crystallographic a axis.
Fig. 10. Supramolecular chain mediated by non-conventional hydrogen bonding
interactions in [MoO2(L2)(DMF)] (4).