The first naphthosemiquinone complex of K+ with vitamin K3 analog: Experiment and density functional theory

Article abstract of DOI:10.1016/j.molstruc.2015.01.053

Synthesis and characterization of potassium complex of 2-hydroxy-3-methyl-1,4-naphthoquinone (phthiocol), the vitamin K3 analog, has been carried out using FT-IR, UV-Vis, ¹H and ¹³C NMR, EPR, cyclic voltammetry and single crystal X-ray diffraction experiments combined with the density functional theory. It has been observed that naphthosemiquinone binds to two K⁺ ions extending the polymeric chain through bridging oxygens O(2) and O(3). The crystal network possesses hydrogen bonding interactions from coordinated water molecules showing water channels along the c-axis. ¹³C NMR spectra revealed that the complexation of phthiocol with potassium ion engenders deshielding of C(2) signals, which appear at δ = ～14.6 ppm whereas those of C(3) exhibit up-field signals near δ ～ 6.9 ppm. These inferences are supported by the M06-2x based density functional theory. Electrochemical experiments further suggest that reduction of naphthosemiquinone results in only a cathodic peak from catechol. A triplet state arising from interactions between neighboring phthiocol anion lead to a half field signal at g = 4.1 in the polycrystalline X-band EPR spectra at 133 K.

Full text of DOI:10.1016/j.molstruc.2015.01.053

Accepted Manuscript
+
The first naphthosemiquinone complex of K with vitamin K3 analog: Experi-
ment and Density Functional Theory
Laxmi Kathawate, Shridhar P. Gejji, Sachin D. Yeole, Prakash L. Verma,
Vedavati G. Puranik, Sunita Salunke-Gawali
PII:
S0022-2860(15)00072-1
DOI:
http://dx.doi.org/10.1016/j.molstruc.2015.01.053
MOLSTR 21298
Reference:
Journal of Molecular Structure
To appear in:
Received Date:
Revised Date:
Accepted Date:
19 November 2014
30 January 2015
30 January 2015
Please cite this article as: L. Kathawate, S.P. Gejji, S.D. Yeole, P.L. Verma, V.G. Puranik, S. Salunke-Gawali, The
+
first naphthosemiquinone complex of K with vitamin K3 analog: Experiment and Density Functional Theory,
Journal of Molecular Structure (2015), doi: http://dx.doi.org/10.1016/j.molstruc.2015.01.053
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.

The first naphthosemiquinone complex of K+ with vitamin K3
analog: Experiment and Density Functional Theory
Laxmi Kathawatea, Shridhar P. Gejjia*,Sachin D. Yeolea, Prakash L.Vermaa,Vedavati G.
Puranikb, Sunita Salunke-Gawalia*
aDepartment of Chemistry, Savitribai Phule Pune University, Pune 411007, India
bCenter for Material Characterization, CSIR-National Chemical Laboratory, Pune 411008, India
Abstract
Synthesis and characterization of potassium complex of 2-hydroxy-3-methyl-1,4-
naphthoquinone (phthiocol), the vitamin K3 analog, has been carried out with FT-IR, UV-
1
visible, H and 13C NMR, EPR, cyclic voltammetry and single crystal X-ray diffraction
experiments combined with the density functional theory. It has been observed that
naphthosemiquinone binds to two K+ ions extending the polymeric chain through bridging
oxygens O(2) and O(3). The crystal network possesses hydrogen bonding interactions from
coordinated water molecules showing water channels along the c-axis.13C NMR spectra
revealed that complexation of phthiocol with the potassium ion engenders deshielding of
C(2)signals, which appear at δ=~14.6 ppm) unlike those of C(3) exhibiting up-field signals
near δ ~6.9 ppm. These inferences are supported by the M05-2x based density functional
theory. Electrochemical experiments further have shown that the reduction of
naphthosemiquinone results in only a cathodic peak from catechol. A triplet state arising from
interactions between neighboring phthiocol anion lead to half field signal at g= 4.1 in
polycrystalline X-band EPR spectra at 133 K.
.
Key Words: Vitamin K3, phthiocol, naphthosemiquinone, hydrogen bonding, 13C NMR,
DFT
*Corresponding author
E-mail: sunitas@chem.unipune.ac.in, spgejji@chem.unipune.ac.in
Tel. No. : +912025601397 -Ext-531, fax: +912025693981
1

Introduction
Synthesis and isolation of 2-hydroxy-3-methyl-1,4-naphthoquinone was carried out in
ether soluble constituents by saponification of acetone soluble fat of tubercule bacillus. The
compound [1] crystallizes as yellow prisms with molecular formula C11H8O3 that melts near
174 C forming deep red water soluble salts with alkali and other bases. The oxidation of [1]
with hydrogen peroxide in alkaline solution yield phthalic acid hence, the pigment was
named ‘phthiocol’ [1]. This yellow pigment possesses vitamin K like activity [2]. The
phthiocol can be obtained in the laboratory on epoxidation by hydrogen peroxide followed by
hydrolysis of vitamin K3 (2-methyl-1,4-naphthoquinone)[3,4] that belongs to the K group
vitamin and finds applications in medicine as antitumor, anticancer drug possessing anti-
oncogenic [5-7] and antihemorrhagic properties [8-9]. The antihemorrhagic activity of
vitamin K group depends on molecular structure [10] and reduction potential [11]. Besides
this K group vitamins act as cofactor in blood clotting.
O
O
8
5
1
4
OH
9
3
9
7
6
2
2
6
7
3
10
10
CH3
CH3
4
1
5
8
O
O
Vitamin K3
Menadione
Phthiocol
Phthiocol binds metal ion with bidentate/tridentate coordination yielding different
oxidation states as in: completely oxidized (form I), one electron reduced
naphthosemiquinone (form II) and two electron reduced catechol forms (form III), which are
shown in Scheme 1. Molecular structures of coordination complexes of phthiocol ligand with
the transition metal ions viz., Zn2+ [4], Cu2+ [13] and Mn2+ [15] have been reported. Phthiocol
engender coordination polymers with Sm3+ and Cd2+ ions [16-17]. To the best of our
knowledge the hitherto investigation is the first report on characterization of K+ complex of
naphthosemiquinone ligand.
2

O-
O
O
O-
OH
OH
1e-
1e-
1e-
1e-
CH3
CH3
CH3
O-
O
O
II
III
I
Scheme 1 Redox forms of 2-hydroxy-3-methyl-1,4-naphthoquinone. I, oxidized
naphthoquinone form (NQ); II, naphthosemiquinone form (NSQ2-.) and III, catechol form
(CAT)
Experimental
Analytical
grade
chemicals
are
used.
Menadione
(2-methyl-1,4-
naphthoquinone)obtained from Sigma Aldrich was recrystalized in methanol prior to
synthesis. Milli-Q water was used in flame photometry experiments. Anhydrous methanol
was purified using standard procedure [18].
Synthesis of Phthiocol
The preparation followed a slight modification of the published procedure [3].
Menadione (1.0 g; 5.8 mM) was dissolved in 10 ml methanol and chilled on an ice bath. A
solution of 0.2 g of anhydrous Na2CO3 and 1 ml of 30% H2O2 in 5 ml of water was then
added with the reaction mixture maintained at 0 C. Addition of 100 ml of chilled water
precipitates2-methyl-1,4-naphthoquinoneoxide as colorless crystals which were collected by
filtration and dried. The solid was treated with 5 ml concentrated H2SO4 and allowed to stand
for 10 minutes. Subsequent addition of 20 ml water gave a yellow precipitate which was
recrystallized with methanol containing a few drops of concentrated H2SO4. The crude
product was column chromatographed using 5% methanol in toluene.
Characterization of Phthiocol
Yellow solid, Yield: 0.84 g, 84%. FT-IR; (KBr, cm-1): 3371, 1660, 1591, 1456, 1392, 1344,
1301, 1276, 1211, 1178, 1074, 1228, 985, 900, 833, 788, 727, 684, 634, 534, 439, 412, 381.
1H NMR; (DMSO-d6, 300 MHz) δ/ppm: 1.956 (s, 3H), 7.969 (d, J = 6.3, 2H), 7.821 (t, J =
6.15, 2H), 7.778 (t, J = 6.3, 2H), 7.989 (d, J = 5.4, 2H), 10.900 (s, Ar-OH).13C NMR
3

(DMSO-d6, 500 MHz) δ/ppm: 8.97, 120.31, 126.03, 126.04, 130.38, 132.41, 133.7, 134.78,
155.83,181.02, 185.05. UV-Vis; (Methanol, λmax, nm): 295, 324, 479. UV-Vis; (Methanol,
λmax, nm): 287, 330, 388, 479. Anal. data calc. for [C11H8O3] (188.17 g): C, 70.21; H, 4.29 %.
Found: C, 70; H, 20 %, LC-MS (m/z): 188.
Synthesis of Phth-K2
1mM of phthiocol (0.188 g) was dissolved in 15 ml anhydrous methanol. 1 mM of
KOH (0.560 g) was dissolved in 10 ml of anhydrous methanol. The two solutions were mixed
with constant stirring for 20 minutes at 26C. The pH of the solution was found to be close to
7. The products precipitated products were filtered and washed with diethyl ether and dried
under vacuum. The synthesis of Phth-K2 was carried out at the room temperature (26C). The
+
mole ratio of naphthoquinone and KOH was retained to 1:1. The concentration of K ions
was determined by flame photometry. Thermogravimetric (TG) analysis confirmed the
presence of adsorbed as well as coordinated water molecules in the title complex. The residue
following complete decomposition of organic entity was found to be K2O.
Characterization of Phth-K2
Red orange solid, Yield: 0.22 g, 73 %. FT-IR (KBr; cm‒1): 3381, 3215, 1670, 1589, 1521,
1
1392, 1350, 1280, 1230, 1124, 952, 844, 734, 682, 621, 553, 422. H NMR (DMSO-d6, 500
MHz) δ/ppm: 1.748 (s, 3H), 7.799 (d, J = 7.5, 2H), 7.680 (d, J = 7.0, 2H), 7.560 (t, J = 7.5,
2H), 7.742 (t, J = 7.5, 2H). 13C NMR (DMSO-d6, 500 MHz) δ/ppm: 9.54, 113.41, 124.43,
124.59, 129.43, 131.52, 132.07, 136.12, 170.44, 178.57, 185.97.UV-Vis; (Methanol, λmax
,
nm): 295, 324, 479. Anal. data calc. for [K2C11H7O3] 2.5 H2O, (310.41 g): C, 42.56; H, 03.89
%., Found: C, 42.82; H, 03.86 %.
Physical Measurements
Elemental analysis was carried outon Thermo Finnigan EA 1112 Flash series
elemental analyzer. The concentration of K+ in Phth-K2 was determined on SYSTRONICS
flame photometer 128. AR grade KCl was standard for flame photometry analysis. UV-
Visible spectra of phthiocol ligand and the K+ complex were recorded on SHIMADZU UV
1650 in methanol between 200 to 800 nm.1H and13C NMR spectra of compounds were
recorded in DMSO-d6, on Varian 500 MHz NMR spectrophotometer with the
tetramethylsilane (TMS)as a reference. Liquid chromatograph mass spectrum of phthiocol
4

was recorded on Shimadzu, liquid chromatograph mass spectrophotometer,LC-MS-2010EV
with ESI as the source was used for ionization
Cyclic voltammetry studies
Electrochemical measurements were performed with CHI 6054E electrochemical
analyser equipped with a commercial platinum disc electrode (CHI Instruments, USA, 2 mm
diameter), AgNO3wire and platinum wire loop which serve as working, reference and counter
electrodes, respectively. After fixing the electrodes to the cell 0.513 g of tetra butyl
ammonium perchlorate (100 mM in 15 mL solution) was transferred to cell through high
purity argon gas. The blank or controlled voltammograms were acquired in tetra butyl
ammonium perchlorate–DMSO mixture prior to measurements. Sample dispersed in small
amount of solvent injected in cell for further measurement (analytic concentration 5 mg/15
mL). At the end of each set of experiments the potentials were calibrated with respect to the
normal hydrogen electrode (NHE) using the ferrocene as internal standard.
Single Crystal X-ray Crystallography
Single crystal of Phth-K2 was grown by slow evaporation of the solution in methanol.
Red coloured needle type crystal of approximate size 0.12 x 0.10 x 0.01 mm3, was mounted
for data collection on Bruker SMART APEX CCD diffractometer employing Mo K radiation
with fine focus tube of 50 kV and 30 mA. Crystal to detector distance 6.05 cm, 512 x 512
pixels/frame, multirun data acquisition, four data sets. Total frames = 1829, Oscillation /
frame -0.3º, exposure / frame = 25.0 sec / frame, maximum detector swing angle = –30.0º,
beam centre = (260.2, 252.5), in plane spot width = 1.24, SAINT integration, range = 1.10
to 24.75º, completeness to  of 24.75 º is 99.7 %. SADABS correction applied.
All the data were corrected for Lorentzian, polarisation and absorption effects. SHELX-
97 (ShelxTL) [19] was used for structure solution and full matrix least squares refinement on
F2. Carbon atom C(2)was thermally not stable and refined isotropically. Hydrogen atoms
were included in the refinement as per the riding model, the hydrogens of the water molecule
and those of O(2)H were thus determined by difference fourier and refined subsequently.
Data collection and refinement parameters are listed in Table 1.
Computational Method
The anion and Phth-K2 were optimized using the analytical gradient method relaxing
all the geometric parameters simultaneously. The density functional theory based on
5

dispersion corrected exchange correlation functional M06-2x [20] from the Minnesota group,
with the internally stored 6-31+G(d,p) basis set was employed. The Gaussian-09 program
[21] was used. Optimizations were performed with the SCF= ‘ultrafine’ grid option. The
vibrational frequencies were computed analytically using the second derivatives of energy
from the hessian matrix. The harmonic frequencies thus obtained were scaled by a factor of
0.9541 as recommended for the M06-2x functional [22].All the normal vibration frequencies
turned out to be real (no frequency was imaginary) hence, the optimized structures were
1
confirmed to be local minima on the potential energy surfaces. The H and 13C NMR
chemical shifts were computed by subtracting respective shielding constants from those of
the tetramethylsilane (TMS) which was used as the reference within the framework of the
gauge-independent atomic orbital (GIAO) method. The influence of solvent on1H and 13C
NMR chemical shifts was modeled through self-consistent reaction field (SCRF) theory
employing the polarized continuum model (PCM) in the presence of DMSO (solvent).
Results and Discussion
Single Crystal X-ray Crystallography
Single crystal X-ray data for Phth-K2 was collected at room temperature. The
molecular structure, ORTEP diagram has been depicted in Fig.1. Crystallographic data is
summarized in Table 1. Selected bond distances are reported in Table 2. An extensive data
has further been given in the Table S1 of the ESI† of supporting information. As shown in
Fig. 1 the potassium ion shows distorted octahedral geometry and coordinates to four
phthiocols and a H2O molecule. The extending polymeric chain resulted through binding of
phthiocol to metal ion via O(1), O(2) and O(3) as depicted in Fig.2. The potassium oxygen
contact distances in distorted octahedron around K+ vary from ~2.6 to 2.8 Å [23-33]. The
phthiocol facilitating hydrogen bonding interactions [(i) O(2)-H=0.96(7)Å, H∙∙∙O(5)=1.75Å,
O(2)∙∙∙O(5)=2.71(1)Å, O(2)-H∙∙∙O(5) = 179(7), (-1+x,y,z), (ii)O(4)∙∙∙O(5)=2.82(2)Å]
(Fig.3)engender water channels along the ‘c’ axis as depicted in Figure.
The C=O bond distances in the phthiocol complex are displayed in Table 2 are
relatively large compared to those observed in the complexes of phthiocol [4]. The C-C and
C=O bond distances of quinones are sensitive to oxidation state of ligands in their complexes
[34-41]. The bond distances in redox susceptible quinonoid ligands, have proven useful to
identifying the oxidation number of phthiocol in the complexes. The C=O distances in
catecholate complexes have been observed to be 1.32-1.39Å, whereas the C-C bond distances
in hexatomic carbon ring closer to those of aromatic systems with the average of these being
6

in the range 1.39-1.41 Å. The respective C=O and C-C bond distances in semiquinone
complexes usually are found to be1.28Å-1.31 Å and 1.42Å -1.45 Å.
Fig.1 ORTEP diagram of Phth-K2. Ellipsoids are drawn at 50 % probability
Fig.2 Polymeric chain of ‘K+’ formed due to bridged ligands in Phth-K2
Compared to these data, the neutral quinones complexes possess the carbonyl and C-
C bond distances to be ~1.23 Å and ~1.53 Å in [34-41]. Nonetheless, the bond distances do
not distinguish metal-quinone antiferromagnetic interactions and the quinonoid C=O
distances in 2-oxido-1,4-naphthoquinone anion are observed to be longer[42]. Furthermore
charge delocalization engenders relatively long C(2)-O(2) and C(4)-O(3) bonds. Besides the
7

C(1)-O(1) bond distance in the oxidized form of phthiocol anion are nearly unchanged and
turn out to be 1.23 Å [43]. Thus it may be conjectured that variation in oxidation state of
naphthoquinone emerge with its signature in C(1)-O(1) bond distances.
Fig.3 Packing viewed down ‘c’ axis. The ligand forms channels with water molecule
hydrogen bonded to the ligands in Phth-K2
Selected bond distances in phthiocol complex [4] and free phthiocol [43] are
compared in Table 3. The C=O bond distances in Phth-K2are longer than the corresponding
ones in the oxidized form of phthiocol. A comparison of catecholate and quinone has shown
that the carbonyl bond distances in the latter are relatively short. Observed C(2)-C(3)
distances (1.44Å) thus show intermediate C-C and C=C character. Thus, the presence of
dianion phthiocol radical as form II (cf. Scheme 1) in the titled K+ naphthosemiquinone
complex is evident. These inferences have further been supported by the EPR and
electrochemical experiments.
Electronic structure
Optimized structure along with selected bond distances (in Å) of Phth-K2 complex
from the M06-2x/6-31+G(d,p) theory has been displayed in Fig.4
8

Fig. 4 Optimized geometry of the Phth-K2 complex
Phth-K2 structure obtained from the M06-2x based density functional theory is in consonant
with that observed in the single crystal X-ray experiments. The separation between K+ and
carbonyl oxygens O(1) and O(2) was predicted to be ~ 2.54 Å in the complex.
1H and 13C NMR,FT-IR and Electronic Spectra
1H NMR spectra revealed six peaks for isolated phthiocol compared to five for the
Phth-K2 as displayed in Fig.S1 in ESI†. A singlet due to –OH, and -CH3, doublet from
C(5)H and C(8)H and triplet of C(6)H and C(7)H can also be noticed. Further the Phth-K2
protons on C(5) to C(8)and those from the methyl group exhibit upfield signals compared to
the phthiocol anion. It may further be remarked here that the complexation of phthiocol anion
with the metal can be monitored by measurements of the13C NMR chemical shifts. The
corresponding NMR signals in Phth-K2 complex (Fig.5) engender upfield signals for C(1),
C(3), C(5), C(6), C(7), C(8), C(9) and C(10)). As opposed to this the signals due to (CH3,
13
C(2), C(4))deshielding in the C NMR spectra in thePhth-K2complex.It is therefore, evident
that the complexation with the metal ion influences C(2) and C(3) signals significantly. A
large shielding of C(3) signals (δC 6.9 ppm) in the spectra further suggests paramagnetic
interaction.
9

As far as the methyl protons are concerned, the δH values from the M06-2x/6-
31+G(d.p) theory given in Table 4 refer to mean of those of individual protons in the group.
Theoretically calculated chemical shifts by and large, agree well with those observed in the
experiment.Experimental13C NMR chemical shifts further led to following inferences. The
C(4),C(1) and C(2) signals from 184 ppm to 170 ppm, are largely deshielded. A large up-
field signal of the methyl carbon (δc 9.5 ppm) has also been observed. As shown in Table 4,
the calculated chemical shifts are in accordance with the experiment. The largest shielding of
C(3) predicted from the present density functional theory concurs with the experimental data.
The infrared spectra in 3400cm-1 -2800 cm-1 region of phthiocol (Fig.S2 in ESI†)
shows a band at 3371 cm-1 arising from coupling of-OH and -CH stretchings, which becomes
broader on complexation. Two sharp peaks near 1591 cm-1 and 1660 cm-1of the anion were
assigned to carbonyl stretching [44]. The complexation of phthiocol has further been
accompanied by emergence of bands near1521 cm-1, 1589 cm-1 and 1670 cm-1 instead. A
sharp peak ~1521 cm-1assigned to those of carbonyl group of naphthosemiquinone phthiocol
[45].
Table S7 in ESI† reports vibrational frequencies of the isolated K2C11H12O5 complex
and those in Phth2-•from the MO6-2x based density functional theory. A band near 1536 cm-1
in the calculated spectra assigned to C=O stretching vibration comprising of strong coupling
from different internal coordinates corresponds to a broad band near the 1521 cm-1 and thus
suggests the presence of Phthiocol in semiquinone form in the complex [45]. Moreover,
computational studies revealed that C=O stretching vibration is diffused in different normal
vibrations from 1621 cm-1 -1508 cm-1(cf. Table S7 of ESI†). It has further been predicted that
the OH stretching near3718 cm-1 of the anion shifts to the lower wave number (3688 cm-1)
with a concomitant increase in its intensity on complexation.
10

O
O
133.48
132.07
181.02
155.83
120.31
178.57
OH
130.38
129.43
OH
126.03
126.04
124.43
124.59
170.44
113.41
132.41
131.52
CH3
CH3
185.05
185.97
134.78
136.12
8.97
9.54
O
O
Fig.5 13C NMR spectra of free phthiocol (top) and Phth-K2 (bottom)
UV-Visible spectra of phthiocol and Phth-K2 in methanol are displayed Fig.S3 in
ESI†. Two bands centered ~327 nm were assigned to * transition of quinonoid and
benzenoid rings, respectively [4, 46-47] are observed. The ~329 nm peak in Phth-K2 show
hyposochromic shift. A single broad band in the visible region arises from n* transition.
11

Table 1 Crystal data for Phth-K2.
Empirical formula
Formula weight
K2 C11H12O5
263.31
Temperature
273(2) K
Wavelength
0.71073 Å
Crystal system
Monoclinic
Space group
Pc
Unit cell dimensions
a = 3.9070(4) Å,  = 90°.
b = 18.510(2) Å,  = 111.347(2) °.
c = 8.6690(8) Å,  = 90°.
583.92(10) Å3
Volume
Z
2
Density (calculated)
Absorption coefficient
1.498 g/cc
0.461 mm-1
F(000)
274
0.12 x 0.10 x 0.01 mm3
1.10 to 24.75°.
Crystal size
Theta range for data collection
Index ranges
-4<=h<=4, -21<=k<=21, -9<=l<=9
4579
Reflections collected
Independent reflections
Completeness to theta = 24.75°
Max. and min. transmission
Refinement method
1950 [R(int) = 0.0790]
99.7 %
0.9949 and 0.9480
Full-matrix least-squares on F2
Data / restraints / parameters
1950 / 5 / 169
2
1.274
Goodness-of-fit on F
Final R indices [I>2sigma(I)]
R indices (all data)
R1 = 0. 1046, wR2 = 0.1728
R1 = 0.1252, wR2 = 0.1800
0.12(14)
Absolute structure parameter
Largest diff. peak and hole
0.391 and -0.481 e.Å-3
12

Table 2 Selected structural parameters (bond- lengths in Å] and -angles in °in Phth-K2.
Bonds
Bond lengths
[Å]
Bonds
angles [°]
K-O(3)#1
K-O(2)#2
K-O(3)#3
K-O(2)
K-O(4)
K-O(1)
2.616(7)
2.702(7)
2.727(7)
2.743(7)
2.761(9)
2.821(7)
3.412(8)
3.474(9)
1.230(10)
1.248(10)
2.702(7)
0.96(7)
O(3)#1-K-O(2)#2
O(3)#1-K-O(3)#3
O(2)#2-K-O(3)#3
O(3)#1-K-O(4)
O(2)#2-K-O(4)
O(3)#3-K-O(4)
O(2)-K-O(4)
O(3)#1-K-O(1)
O(2)#2-K-O(1)
O(3)#3-K-O(1)
O(2)-K-O(1)
88.4(2)
93.94(19)
173.2(2)
96.5(3)
89.1(3)
96.9(3)
89.8(3)
116.4(2)
87.5(2)
85.8(2)
57.3(2)
146.8(3)
118.9(10)
119.4(10)
121.7(8)
123.4(8)
119.4(8)
117.2(8)
120.1
K-C(4)#3
K-C(2)#2
O(1)-C(1)
O(2)-C(2)
O(2)-K#4
O(2)-H
O(3)-C(4)
C(1)-C(2)
C(1)-C(9)
C(2)-C(3)
C(3)-C(4)
C(5)-C(6)
C(5)-C(10)
C(6)-C(7)
C(7)-C(8)
C(8)-C(9)
C(9)-C(10)
O(4)-K-O(1)
1.268(10)
1.462(13)
1.482(12)
1.441(13)
1.407(14)
1.351(13)
1.370(12)
1.386(13)
1.375(13)
1.383(12)
1.375(12)
O(1)-C(1)-C(2)
O(1)-C(1)-C(9)
C(2)-C(1)-C(9)
O(2)-C(2)-C(3)
O(2)-C(2)-C(1)
C(3)-C(2)-C(1)
C(7)-C(8)-H(8)
C(9)-C(8)-H(8)
C(10)-C(9)-C(8)
120.1
120.7(8)
Symmetry transformations used to generate equivalent atoms:
#1 x-2,y,z-1 #2 x-1,y,z #3 x-1,y,z-1 #4 x+1,y,z #5 x+2,y,z+1 #6 x+1,y,z+1
Table 3Bond distances (in Å) of Phth-K2 and [Zn(Phthiocol)2(H2O)2] from the experiment
and M06-2x/6-31+G(d,p) theory.
Phth-K2
Expt.
Phthiocol
Expt.
[Zn(Phthiocol)2(H2O)2]
Bond
DFT
1.275
1.393
1.258
1.431
1.379
1.442
1.456
1.470
DFT
1.212
1.341
1.220
1.501
1.352
1.481
1.489
1.497
Expt.
DFT
1.241
1.303
1.222
1.501
1.368
1.469
1.470
1.505
C(1)-O(1) 1.230(10)
C(2)-O(2) 1.248(11)
C(4)-O(3) 1.268(10)
C(1)-C(2) 1.462(13)
C(2)-C(3) 1.441(14)
C(3)-C(4) 1.407(14)
C(1)-C(9) 1. 482(12)
C(4)-C(10) 1.461(12)
1.228(2)
1.346(2)
1.224(2)
1.486(2)
1.352(2)
1.477(2)
1.477(2)
1.493(2)
1.227(5)
1.292(4)
1.245(5)
1.509(5)
1.363(5)
1.449(5)
1.472(5)
1.494(6)
13

Table 4Comparison of 1Hand 13C NMR chemical shifts of Phthiocol anion and PhthK2
complex from the experiment and M06-2x/6-31+G(d,p) theory. The numbers in parenthesis
refer to those obtained from theory.
Types of
Phth-K2
Phth-K2
Phth
carbons/protons
δH
δc
δc
C(1)
178.57 (170.12)
170.44 (154.65)
113.41 (121.24)
181.02 (152.68)
155.83 (154.94)
120.31 (107.54)
C(2)-OH
C(3)-CH3
(3.7)
1.748 (2.1)
C(4)
185.97 (180.73)
185.05 (166.04)
C(5)H
C(6)H
C(7)H
C(8)H
C(9)
7.680 (9.2)
7.560 (8.5)
7.742 (8.3)
7.799 (8.7)
136.12 (141.65)
124.59 (139.42)
124.43 (140.06)
132.07 (139.64)
129.43 (143.87)
131.52 (142.56)
9.54 (15.54)
134.78 (139.61)
126.04 (113.61)
126.03 (120.40)
133.48 (138.11)
130.38 (145.51)
132.41(137.61)
8.97 (9.13)
C(10)
CH3
Electron Paramagnetic Resonance and Electrochemical Studies
EPR spectra of polycrystalline Phth-K2 were recorded at the room temperature (298
K) and at 133 K (Fig.S4 and Fig.S5 in ESI†). A broad signal near g = 2.00 and a weak triplet
near g ~ 4 was observed. The Phth-K2 being polymeric a triplet state possibly generated from
ferromagnetic interactions between neighboring radical spins in the complex [48]. With 1:1
mole ratio of KOH to phthiocol used in synthesis the hydroxyl group of Phth-
K2getsdeprotonated:
Phth- + Phth
2Phth- •
Disproportionate reaction between anionic phthiocol and protonated phthiocol generates
naphthosemiquinone dianion in Phth-K2. A similar mechanism was suggested in case of the
2-hydroxy-1,4-naphthoquinone [42]. It should be pointed out here that the generation of the
anion radical from menadione in the presence of alkali through disproportionate reaction was
conjectured earlier in the literature [48-57]. Alkali metal NaOH, KOH, KF are used in solvent
14

(0.1 NaOH, methanol/water, ethanol/water, ethanol (abs), methanol, DMSO, THF) generate
the anionic radical of menadione (MNQ-•). The observed ‘g’value in the presence of salt in
different solvents was found to be 2.00045 0.00002. The hydroquinone reacts with
potassium fluoride (KF) in methanolic solution producing the dipotassium salt. A
disproportionate reaction yields radical through:
MNQ2- + MNQ
2MNQ-•
Cyclic voltammogram of Phth-K2in DMSO (Fig.6 and Fig.S6 in ESI†) reveals
Cathodic quasi-reversible peak ~0.52 V vs NHE in free phthiocol [58]. No such a peak
observed in Phth-K2. The observed cathodic peak at ~1.10 V assigned to naphthosemiquinone
(form II in Scheme 1) stem from catechol (form III in Scheme 1) reduction. Anodic
irreversible peak at +0.88 V assigned to the reoxidation of coordinated phthiocol in Phth-K2
[58, 62]. Electrochemical studies hence, ascertain coordination of phthiocol in one electron
reduced naphthosemiquinone form.
2.0x10-5
Phth-K2
0.0
-2.0x10-5
-1.5 -1.0 -0.5 0.0 0.5 1.0
E/V (Vs NHE)
Fig.6 Cyclic voltammogram of Phth-K2 at 0.1 V/s scan rate.
Conclusions
A room temperature stable Phth-K2 complex was synthesized with phthiocol binds to K+ ions
1
in naphthosemiquinone form. The complex was characterized by FTIR, H and 13C NMR,
EPR, electrochemical, single crystal X-ray diffraction experiments. Polymeric Phth-K2 shows
metal ion located in the vicinity of four phthiocol neighbours. Naphthosemiquinone generated
15

in disproportion reaction of catechol and oxidised form of phthiocol ligand. Half field signal
observed ~g=4 at 133 K in the X-band EPR spectra of polycrystalline Phth-K2, attributed to
‘triplet state’ consequent to ferromagnetic interactions of neighbouring spins of phthiocol.
Supporting information available
Fig. S1 to S7, crystallographic Tables S1 to S7. Crystallographic data have been deposited
with the Cambridge Crystallographic Data Centre and may be obtained on request quoting
the deposition number 1034515from the CCDC, 12 Union Road, Cambridge CB21EZ, UK
(Fax: +44 1223 336 033; E-mail address: deposit@ccdc.cam.ac.uk).
Acknowledgement
LK is thankful to the Deparment of Science and Technology (DST), New Delhi, India for the
Senior Research Fellowship. SDY acknowledges the support from the University Grants
Commission, New Delhi for the award of D. S. Kothari postdoctoral fellowship. PLV thanks
Savitribai Phule Pune University, Pune, India for the award of fellowship through the
potential excellence scheme. A partial support through Young Scientist Scheme (SR/FT/CS-
030/2009) of DST, New Delhi, India to SSG has been gratefully acknowledged.
16

References
[1] R.J. Anderson, M. S. Newman, J. Biol. Chem., 103 (1933) 197-201.
[2] E.G. Ball, J. Biol.Chem., 106 (1934) 515-524.
[3] L.F. Fieser, J. Biol.Chem., 133 (1940) 391-396.
[4] L. Kathawate, S. Sproules, O. Pawar, G. Markad, S. Haram, V. Puranik, S. Salunke-
Gawali, J. Mol. Struct., 1048 (2013) 223-229.
[5] S. Rane, K. Ahmed, S. Salunke-Gawali, S. B. Zaware, D. Srinivas, R. Gonnade, M.
Bhadbhade, J. Mol. Struct., 892 (2008) 74–83.
[6] J.M. Jamison, J. Gilloteaux, M. Venugopal, J.A. Koch, C. Sowick, R. Shah, J.L.
Summers, Tissue. Cell, 28 (1996) 687-701.
[7] C. Chen, Y.Z. Liu, K.S. Shia, H.Y. Tseng, Bioorg. Med. Chem. Lett., 12 (2002)
2729–2732
[8] J.A. Duin, J.A. Jongejan, Annu. Rev. Biochem. 58 (1989) 403-406.
[9] D.M. Dooley, M.A. McGuirl, D.E. Brown, P.N. Turkowski, W.S. Mcintire, P.F.
Knowles, Nature, 349 (1991) 262-264.
[10] C.M. Jackson, Y. Nemerson, Ann. Rev. Biochem. 49 (1980) 765-811.
[11] S.A. Petrova, M.V. Kolodyazhny, O.S. Ksenzhek, J. Electroanal. Chem., 277 (1990)
189-196.
[12] O.S. Ksenzhek, S.A. Petrova, M.V. Kolodyazhny, S.V. Oleinik, Bioelectrochem.
Bioenerg., 4 (1977) 335-543.
[13] S. Salunke-Gawali, R. Dalvi, K. Ahmed, S. Rane, J. Therm. Anal. Cal, 76 (2004)
801–812.
[14] S. Salunke-Gawali, S.Y. Rane, K. Boukheddaden, E. Codjovi, J. Linares, F.Varret,
P.P. Bakare Ind. J. Chem.43A (2004) 2563-2567.
[15] M.P. Mulay, P. L. Garge, S.B. Padhye, R.L. Haltiwanger, L.A. deLearie, C.G.
Pierpont, J. Chem. Soc., Chem. Commun.,(1987) 581-582.
[16] P. Shinde, S. Nilakhe, V. Shinde, B.A. Kulkarni, V.R. Sapre, M.P. Wadekar, J. Appl.
Chem., 7 (2014) 33-40.
[17] S. Gaikwad, R. Kankariya, D. Shah, J. Appl. Chem., 3 (2014) 164-169.
[18] W.L. Armarego, D.D. Perrin, D.R. Perrin Purification of Laboratory Chemicals,
Pergamon Press. London, (1998) 260.
[19] G.M. Sheldrick, SHELX-97 Program for crystal structure solution and refinement,
University of Göttingen, Germany, 1997.
[20] Y. Zhao, D.G. Truhlar, Theor. Chem. Acc., 12 (2008) 215-241.
17

[21] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R.
Cheeseman, G Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H Nakatsuji, M
Caricato, X Li, H.P Hratchian, A.F Izmaylov, J Bloino,G .Zheng, J.L. Sonnenberg,
M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y.
Honda, O. Kitao, H. Nakai, T. Vreven, J.A. Montgomery, Jr, J.E Peralta, F. Ogliaro,
M. Bearpark, J.J. Heyd, E. Brothers, K.N. Kudin, V.N. Staroverov, R Kobayashi, J
Normand, K. Raghavachari, A Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M.
Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C.
Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A. J. Austin,. R.
Cammi, C. Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski,
G.A Voth, P. Salvador, J.J Dannenberg, S. Dapprich, A.D. Daniels, O. Farkas, J.B.
Foresman, J.V. Ortiz, J. J.Cioslowski, D.J. Fox,. Gaussian 09, Revision A.02;
Gaussian, Inc.: Wallingford CT, 2009.
[22] M. L. Laury, M. J. Carlson, A. K. Wilson, J. Comput. Chem. 33 (2012) 2380-2387.
[23] S. Margadonna, K. Prassides, Y. Iwasa, Y. Taguchi, M.F. Craciun, S. Rogge, A.F.
Morpurgo, Inorg. Chem., 45 (2006) 10472-10478.
[24] I. Fernandez, F. Breher, P. S.Pregosin, Z. Fei, P. J. Dyson, Inorg. Chem., 44 (2005)
7616-7623.
[25] C. Kayser, R. Fischer, J. Baumgartner, C. Marschner, Organomet., 21 (2002) 1023-
1030.
[26] I. Kobrsi, W. Zheng, J.E. Knox, M.J. Heeg, H.B. Schlegel, C.H. Winter, Inorg.
Chem., 45 (2006)8700-8710.
[27] R.E. Dinnebier, S. Vensky, M. Panthofer, M. Jansen, Inorg. Chem., 42 (2003) 1499-
1507.
[28] M. Westerhausen, M.W. Ossberger, P. Mayer, H. Piotrowski, H. Noth, Organomet.,
23 (2004) 3417-3424.
[29] Y. Shuku, R. Suizu, K. Awaga, Inorg. Chem., 50 (2011) 11859-11861.
[30] S. Gupta, M.V. Kirillova, M.C. Fatima, G. da Silva, A.J.L. Pombeiro, and A.M.
Kirillov, Inorg. Chem. 52 (2013) 8601-8611.
[31] K.T. Mahmudov, M. Fatima. G. da Silva, A.M. Kirillov, M.N. Kopylovich, A.
Mizar,J.L.P. Armando J. L. Pombeiro, Cryst. Growth. Des. 13 (2013) 5076-5084.
[32] I.A. Guzeia, M.H. Kima, R. Westa, Daltan. Trans. 21 (2013) 3722-3739.
[33] M.U. Anwar, L.N. Dawe, M.S. Alam, L.K. Thompson, Inorg. Chem. 51 (2012)
11241-11250.
18

[34] C.G. Pierpont, Coord. Chem. Rev., 219-221 (2001) 415-433.
[35] C.G. Pierpont, Coord. Chem. Rev., 216 -217 (2001) 99-195.
[36] M.W. Lynch, R.M. Buchanan, C. G. Pierpont, D.N. Hendrickson, Inorg. Chem., 20
(1981) 1038-1046.
[37] M.W. Lynch, D.N. Hendrickson, B.J. Fitzgerald, C.G. Pierpont, J. Am. Chem. Soc.,
106 (1984) 2041-2049.
[38] A.M. Barthram, Z.R. Reeves, J.C. Jeffery, M. D. Ward, J. Chem. Soc. Dalton Trans.,
(2000) 3162-3169.
[39] A.B.P. Lever, P.R. Auburn, E.S. Dodsworth, H. Masa-aki, W.Liu, M. Melnik, W.A.
Nevin, J. Am. Chem. Soc., 110 (1988) 8076-8084.
[40] G.A. Abakumov, V.K. Cherkasov, M.P. Bubnov, O.G. Ellert, Z.B. Dobrokhotova, L.
N. Zakharov and Y. T. Struchkov, Dokl. Akad. Nauk., 328 (1993) 12-15.
[41] C.G. Pierpont, H.H. Downs, Inorg. Chem., 16 (1977) 2970-2972.
[42] S. Salunke-Gawali, L. Kathawate, Y. Shinde, V.G. Puranik, J. Mol. Struct. 1010
(2012) 38-45.
[43] J. Gaultier, C. Hauw, Acta.Crystallogr., 19 (1965) 919-926.
[44] T. Satoh, T. Tsuji, H. Matsuda, S. Sudoh, Bull. Chem. Soc. Jpn. 80 (2007) 321-323.
[45] M. Mac, J. Wirz, Photochem Photobiol Sci. 1 (2002) 24-29.
[46] K.Y. Chu, J. Griffiths, J. Chem. Soc., Perkin Trans. 1 (1979) 696-701.
[47] M. Khan, Z. Khan, Spectrochim. Acta. Part. A. 61 (2005) 777-790.
[48] C. Frontana and I. Gonzalez, J. Electroanal. Chem., 603 (2007) 155-165.
[49] J.A. Pedersen, J. Chem. Soc., Perkin Trans., 2 (1973) 424-431.
[50] S.C. Sharma, K. Torssell, Acta Chem. Scand., Ser. B, 32 (1978) 437-446.
[51] P. Ashworth, W. T. Dixon, J. Chem. Soc., Perkin Trans., 2 (1974) 739-744.
[52] M.R. Das, H.D. Connor, D.S. Leniart, J.H. Freed, J. Am. Chem.Soc., 92 (1970) 2258-
2268.
[53] J.M. Fritsch, S.V. Tatwawadi, R.N. Adams, J. Phys. Chem., 71 (1967) 338-341.
[54] M. Adams, M.S. Blois, R.H. Sands, J. Chem. Phys., 28 (1958) 774-776.
[55] J.L. Huntington, D.G. Davis, J. Magn. Reson., 3 (1970) 456-467.
[56] J.A. Pedersen, Spectrochim. Acta. Part A., 58 (2002) 1257-1277.
[57] H. Joela, P. Lehtovuori, Phys. Chem. Chem. Phys., 1 (1999) 4003-4010.
[58] F.J. Gonzalez, Electroanalysis, 10 (1998) 638-642.
[59] F. González, J. Aceves, R. Miranda, I. González, J. Electroanal. Chem.,310(1991)
293-303.
19

[60] C. Amatore, J-M. Save´ant, J. Electroanal. Chem.,85(1977) 27-46.
[61] J. L. Ortiz, J. Delgado, A. Baeza, I. González, R. Sanabria, R. Miranda, J. Electroanal.
Chem., 411(1996)103-107.
[62] C. Amatore, G. Copobianco, G. Farnia, G. Sandona, J-M. Saveant, M. G. Severin, E.
Vianello, J. Am. Chem. Soc., 107(1985) 1815-1824.
20

Graphical Abstract
Highlights
 The first naphthosemiquinone coordination complex of vitamin K3 analog is reported.

Hydrogen bonded water channels to the phthiocol are observed.
 Redox couple naphthosemiquinone to catechol is evident in electrochemical studies.
13C NMR chemical shifts are in consonant with experiments.

21