Syntheses, characterization and reactivity of Lewis acid-base adducts based on B-N dative bonds

Article abstract of DOI:10.1016/j.jorganchem.2013.08.022

Three Lewis acid-base adducts [(PhBO)₃·2hmt] (1), [(PhBO)₃-hmt-(PhBO)₃] (2) and [{(F-Ph)BO} ₃·hmt] (3) (hmt = hexamethylenetetramine) were prepared by the treatment of phenylboronic acid [PhB(OH)₂] or

Full text of DOI:10.1016/j.jorganchem.2013.08.022

Journal of Organometallic Chemistry 745-746 (2013) 329e334
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Syntheses, characterization and reactivity of Lewis acidebase adducts
based on BeN dative bonds
Sudeshna Saha a, Ravi Kumar Kottalanka b, Tarun K. Panda b, Klaus Harms c,
,
Stefanie Dehnen c, Hari Pada Nayek a
*
a Department of Applied Chemistry, Indian School of Mines, Dhanbad 826004, Jharkhand, India
b Department of Chemistry, Indian Institute of Technology, Hyderabad, Ordnance Factory Estate, Yeddumailaram 502205, Andhra Pradesh, India
c Fachbereich Chemie, Philipps Universität Marburg, Hans Meer-wein Strasse, Marburg, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Three Lewis acidebase adducts [(PhBO)3$2hmt] (1), [(PhBO)3ehmte(PhBO)3] (2) and [{(F-Ph)BO}3$hmt]
(3) (hmt ¼ hexamethylenetetramine) were prepared by the treatment of phenylboronic acid [PhB(OH)2]
or 4-fluorophenylboroxine [{(F-Ph)BO}3] with hexamethylenetetramine (hmt) in methanol or acetone.
The solid state structures of all the compounds were established by single crystal X-ray diffraction
analysis. Crystal structure determination indicates the formation of boroxine ring through ligand-
mediated dehydration of arylboronic acids. Triphenylboroxine acts as a bridge between two hmt mol-
ecules in 1, whereas hmt plays the role of a bridging ligand between two triphenylboroxine rings in 2.
Compound 1 is rare 1:2 adduct of triphenylboroxine and hmt whereas compound 2 and 3 are 1:2 and 1:1
adducts of triphenylboroxine or 4-fluorophenylboroxine and hmt respectively. The lability of the BeN
bond in solution was confirmed by NMR spectroscopy as well as by chemical reaction of 1 with
[Co(H2O)6](ClO4)2, resulting in the formation of [Co(H2O)6](ClO4)2$(hmt)2$2H2O (4), a boroxine free
hydrogen bonded framework structure.
Received 15 July 2013
Received in revised form
3 August 2013
Accepted 12 August 2013
Keywords:
Dative bonds
Boroxine
Lewis acidebase
1:2 Boroxine-base adduct
Hexamethylenetetramine
X-ray diffraction
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
preferably [2]. For instance, very recently, the Fischer group re-
ported the synthesis of covalent organic frameworks from 1,4-
In recent years, boron compounds were extensively utilized as
building blocks for the construction for macrocyclic two or three
dimensional assemblies and frameworks [1e4]. In this context, the
BeOH moieties of alkyl and arylboronic acids, RB(OH)2 (R ¼ organic
group) were condensed to BeOeB and BeOR functions, resulting in
the formation of boroxines with six-membered B3O3 ring struc-
tures or boronic esters on treatment with alcohols [5,6]. Boroxines
are Lewis acidic compounds. It can be found from literature that
boroxine can form adducts with N-donor ligands via formation of
N / B dative bonds extensively in 1:1 M ratio and adducts with 1:2
or 1:3 M ratio of boroxine and ligand are rare since they are ther-
modynamically unfavourable [7,8]. The boroxine-base adducts can
be easily obtained by two different methods. One is a chemical
dehydration process of boronic acids followed by derivatizations of
the base and the other method is a ligand-mediated dehydration of
boronic acids (Scheme 1). The latter method, ligand-mediated tri-
merization have been investigated for the construction of macro-
molecular architectures and frameworks featuring boroxines cores
benzenediboronic acid via an ammonia-assisted pathway [5]. A
series of hetero-arylboroxines have also been reported [9]. A large
number of macro cycles, 1D- and 2D polymers have been synthe-
sized based on N / B bonds. These were mainly synthesized by
treatment of boronate esters with pyridyl based ligands [10e15].
Molecular cages, for example, have been obtained by condensation
of a tetraboronic acid with a dicatechol linker or by condensation of
triboronic acids with tetra-ols and hexaols [16].
One of our recent research interests is to synthesize supramo-
lecular structures based on N / B bonds using hexamethylenetet-
ramine (hmt) as Lewis base. A recent review by Kirillov group on hmt
clearly indicates the versatile nature of hmt ligand as it can adopt
many coordination modes from monodentate-to-bridging-bi-, tri-
and -tetradentate on treatment with transition metals. Thus,
resulting coordination polymers possessing a large variety of topol-
ogies ranging from one-, two-, three-dimensional frameworks as
well as honeycomb, diamondoid complex networks [17]. Inspired by
flexible coordination mode of hmt, we report herein the synthesis of
three Lewis acidebase adducts [(PhBO)3$2hmt] (1), [(PhBO)3ehmte
(PhBO)3] (2) and [{(F-Ph)BO}3$hmt] (3) exhibiting 1:2, 2:1 and 1:1
boroxineehmt interactions. They can be prepared in good yields and
* Corresponding author.
E-mail address: hpnayek@yahoo.com (H.P. Nayek).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.08.022

330
S. Saha et al. / Journal of Organometallic Chemistry 745-746 (2013) 329e334
11B{1H} NMR spectra were recorded on a BRUKER AVANCE III-400
R
B
spectrometer. IR spectra in KBr (4500e500 cmꢀ1) were recorded
using a PerkineElmer RXI FT-IR spectrophotometer. Elemental
analyses were performed on a Vario Micro cube for C, H, N, S
Analyser by Elemental Analyser System GMBH. Phenylboronic
acid, 4-fluorophenylboronic acid, cobalt carbonate, perchloric
acid, hexamine were purchased from Spectrochem, India and used
as such. [Co(H2O)6](ClO4)2 was prepared by reacting cobalt car-
bonate with perchloric acid. [(F-Ph)BO]3 was synthesized by
condensation of 4-fluorophenylboronic acid in toluene using dean
stark apparatus. The NMR solvent CDCl3 was purchased from
Sigma Aldrich.
OH
OH
O
B
O
B
+ 3 H2O
R
B
3
R
O
R
NR'n
-NR'n
R
NR'n
O
B
OH
OH
O
B
NR'n
+ 3 H2O
R
B
3
B
R
2.2. Syntheses
-NR'n
R
O
2.2.1. Preparation of [(PhBO)3$2hmt] (1)
0
Scheme 1. Adduct formation of boroxine with N-donor ligands, NRn
.
Phenylboronic acid (0.250 g, 2.05 mmol) was dissolved in 10 mL
of methanol. Hexamethylenetetramine (0.144 g, 1.025 mmol) was
added to the methanolic solution. The solution was warmed in
water bath for 5 min, filtered and left in a conical for slow evapo-
ration of the solvent. Colourless crystals were collected by filtration
after 11 days. Yield: 0.350 g, 87%. 1H NMR (CDCl3, 25 ꢁC, 400 MHz):
high purity from phenylboronic acid [PhB(OH)2] (1 and 2) or 4-
fluorophenylboroxine [(F-Ph)BO]3 (3) and hmt in presence (2) or
absence (1, 3) of manganese perchlorate hexahydrate respectively. In
solution, all the compounds show equivalent boron atoms in the
boroxine rings, indicating according equilibria, and thus the labile
nature of the BeN bonds in solution. The reaction of compound 1
with cobalt perchlorate hexahydrate leads to the formation of
[Co(H2O)6](ClO4)2$(hmt)2$2H2O (4). We present and discuss syn-
thetic routes, spectroscopic studies and the solid state structures
of 1e4.
d
4.52 (s, 24H, CH2), 7.28e7.37 (m, 9H, Ph), 7.89e7.96 (m, 6H, Ph)
ppm; 13C NMR (CDCl3, 25 ꢁC, 100 MHz):
73.6 (CH2), 127.4 (Ph),
129.7 (Ph), 134.2 (Ph), 137.0 (Ph) ppm; 11B NMR (CDCl3, 25 ꢁC,
128 MHz):
18.9 ppm. IR data (KBr, cmꢀ1): 2975 (w), 2931 (w),1596
d
d
(m),1465 (m),1444 (s), 1410 (m),1376 (s), 1319 (s), 1251 (s), 1231 (s),
1189 (s), 1147 (m), 1069 (s), 996 (s), 908 (w), 827 (s), 738 (s), 655 (s),
621 (s), 592 (m). Anal. calcd for C30H39B3N8O3: Calc. C 60.85, H 6.64,
N 18.92; found C 60.23, H 6.29, N 18.70.
2. Experimental section
2.1. General consideration
2.2.2. Preparation of [(PhBO)3e(m2-hmt)e(PhBO)3] (2)
Phenylboronic acid (0.250 g, 2.05 mmol) and Mn(ClO4)$6H2O
(0.370 g, 1.025 mmol) were dissolved in 10 mL of methanol. The
solution was stirred for 10 min. Hexamethylenetetramine (0.144 g,
All manipulations were performed under aerobic condition.
Methanol, acetone were distilled prior to use. 1H NMR, 13C{1H} and
Ph
N
OH
N
N
N
B
N
MeOH
O
B
O
B
+
Ph
B
N
N
N
N
- 3 H2O
N
N
N
OH
Ph
O
Ph
1
MeOH
Mn(ClO4)2. 5 H2O
Ph
B
Ph
B
N
O
B
O
O
B
O
N
N
N
B
B
Ph
O
Ph
O
Ph
N
Ph
F
F
2
N
N
B
B
Acetone
F
N
O
B
O
O
B
O
B
N
+
N
N
B
N
O
O
F
F
F
3
Scheme 2. Synthesis of 1 (top), 2 (centre) and 3 (bottom).

S. Saha et al. / Journal of Organometallic Chemistry 745-746 (2013) 329e334
331
2.2.3. Preparation of [{(F-Ph)BO}3$hmt] (3)
4-Fluorophenylboroxine (0.100 g, 0.273 mmol) was dissolved in
5 mL of acetone. Hexamethylenetetramine (0.077 g, 0.546 mmol)
was added to the solution. The solution was stirred at room tem-
perature for 14 h, filtered and left in a conical for slow evaporation
of the solvent. Colourless crystals were obtained after 2 days. Yield:
0.100 g, 72%. 1H NMR (CDCl3, 25 ꢁC, 400 MHz):
d
4.66 (s, 12H, CH2),
7.06e7.11 (m, 6H, Ph), 7.93e7.97 (m, 6H, Ph) ppm; 13C NMR (CDCl3,
25 ꢁC, 100 MHz):
74.0 (CH2), 114.4, 114.6 (d, JCeF ¼ 19.7 Hz, Ph),
136.1,136.2 (d, JCeF ¼ 7.7 Hz, Ph),163.2,165.7 (d, JCeF ¼ 248.3 Hz, Ph)
d
ppm; 11B NMR (CDCl3, 25 ꢁC, 128 MHz):
d
19.5 ppm; 19F NMR
(CDCl3, 25 ꢁC, 376 MHz):
d
ꢀ111.0 ppm. IR data (KBr, cmꢀ1): 2975
50
40
30
20
10
0
-10
-20
(w), 2931 (w), 1590 (s), 1502 (w), 1428 (m), 1411 (s), 1379 (m), 1327
(s), 1288 (s), 1256 (m), 1211 (m), 1182 (w), 1154 (w), 1119 (w), 1084
(w), 1007 (s), 834 (m), 785 (w), 750 (s), Anal. calcd for
Fig. 1. 11B{1H} NMR spectrum of compound 1.
C
24H24B3N4O3F3: Calc. C 56.97, H 4.78, N 11.07; found C 56.81, H
1.025 mmol) was added to the methanolic solution. The solution
was refluxed for 1 h. Colourless crystals were appeared on slow
evaporating of the solution. Yield: 0.200 g, 77%. IR data (KBr, cmꢀ1):
3069 (w), 3021 (w), 1600 (s), 1494 (m), 1442 (s), 1380 (s), 1317 (s),
1252 (s), 1230 (m), 1195 (s), 1177 (m), 1127 (m), 1089 (w), 1064 (m),
1008 (m), 952 (w), 911 (m), 845 (m), 798 (w), 770 (m), 733 (s), 711
(s), 627 (m). Anal. calcd for C42H42B6N4O6: Calc. C 66.06, H 5.54, N
7.34; found C 65.24, H 5.43, N 7.18.
4.64, N 10.92.
2.2.4. Preparation of [Co(H2O)6](ClO4)2$(hmt)2$2H2O (4)
Compound 1 (0.050 g, 0.08 mmol) was dissolved in 5 mL MeOH.
A 5 mL of methanolic solution of Co(ClO4)2$6H2O (0.030 g,
0.08 mmol) was added to it and again 5 mL of MeOH was added to
the solution. The solution was stirred for 1 h, kept in conical. After
ꢁ
ꢀ
Fig. 2. Solid state structure of compound 1 (top left), 2 (bottom) and 3 (top right) and selected bond lengths [A] and bond angles [ ]; 1: B1eO11.4323(14), B1eO2 1.4564(16) B2eO2
1.3584(12), B1eN1 1.7196(16), B1eC1 1.6191(17), B2eC7 1.575(3), O1eB1eO2 115.70(10), B1eO2eB2 121.30(11), O2eB2eO20 122.72(16), O1eB1eN1 104.49(9), C1eB1eN1
107.02(9); 2: B1eO11.443(3), B1eO3 1.451(2), B2eO11.350(3), B2eO2 1.386(3), B3eO2 1.383(3), B3eO3 1.356(3), B4eO4 1.455(3), B4eO6 1.448(3), B5eO4 1.347(3), B5eO5 1.383(3),
B6eO5 1.385(3), B6eO6 1.348(3) B1eN1 1.688(3), N3eB4 1.704(3), O1eB1eO2 115.70(10), B1eO2eB2 121.30(11), O2eB2eO20 122.72(16), O1eB1eN1 104.49(9), C1eB1eN1
107.02(9); 3: B1eO1 1.454(3), B1eO3 1.454(3) B2eO2 1.386(3), B1eN6 1.658(4), B1eC11 1.614(3), B2eC17 1.553(4), O1eB1eO3 113.61(19), B1eO1eB2 122.91(19), O2eB3eO3
121.28(2), O1eB1eN6 103.56(19), C11eB1eN6 111.05(19).

332
S. Saha et al. / Journal of Organometallic Chemistry 745-746 (2013) 329e334
30 days pink coloured crystals were appeared. Yield: 0.035 g, 62.5%.
IR data (KBr, cmꢀ1): 3444 (br), 1643 (m), 1461 (w), 1236 (m), 1140
(s), 1107 (s), 1086 (s), 1011 (m), 690 (w), 623 (m). Anal. calcd for
C
12H40N8O16Cl2Co: Calc. C 21.10, H 5.86, N 16.41; found C 20.86, H
5.76, N 16.09.
Scheme 3. Synthesis of 4.
2.3. X-ray crystallography
Single crystals of compounds 1 and 2 were mounted on a
CryoLoop (Hampton Research Corp.) with a layer of light mineral
oil and placed in diffractometer at 298(2) K. Measurements of 1
4-fluorophenylboroxine, [{(F-Ph)BO}3] with hmt in acetone
(Scheme 2). Detailed synthesis procedures are provided
in Experimental section. All the compounds were characterized by
standard analytical/spectroscopic techniques and the solid-state
structures were established by single crystal X-ray diffraction
analysis.
and 2 were made on an Oxford Supernova Eos CCD detector with
ꢀ
graphite-monochromatic Cu-K
a
(1.54184 A) radiation. The data
of compound 3 and 4 were collected on a Bruker D8 Quest
diffractometer equipped with a Photon 100 CMOS area detector
The structures of [(PhBO)3$2hmt] (1), [(PhBO)3ehmte(PhBO)3]
(2) and [{(F-Ph)BO}3$hmt] (3) reveal the existence of two of the
three boron atoms in a chemically distinct environment. Conse-
quently, different chemical shifts due to two types of phenyl groups
and two types of methylene groups of hmt were anticipated for
both 1H and 13C NMR spectra of compounds 1, 2 and 3 respectively.
It is well established that N / B bond dissociates in solution and
the ligand undergoes fast exchange over the boron atoms. There-
fore, compound 1 and 3 exhibit only one set of distinct signals in
both 1H and 13C NMR spectra in solution at ambient temperature
implying the magnetic equivalence of all three boron atoms [18].
This is further supported by 11B NMR which shows only one signal
at 18.3 ppm (1) or 19.5 ppm (3) respectively and by 19F NMR which
also shows one signal at ꢀ111.0 (3) [19,20]. Fig.1 shows the 11B NMR
spectrum of 1. Compound 2 was not soluble in all common solvents
at room temperature. Hence, its characterization by solution NMR
measurements was not possible.
According to single crystal X-ray structure analyses, compound
1 and 2 crystallize in the monoclinic space group C2/c and P21/c
respectively, with four formula units in the unit cell; compound 3
crystallizes in the triclinic space group P-1 with two formula units
in the unit cell. Fig. 2 shows the molecular structures of 1e3. Table 1
summarizes details of the X-ray analyses. The molecular structures
of 1, 2 and 3 confirm the formation of boroxine ring through
condensation of phenylboronic acid or 4-fluorophenylboronic acid.
system, using MoKa radiation with graphite monochromatiza-
ꢀ
tion (
l
¼ 0.71073 A) at T ¼ 103 (2) K. The structures were solved
by direct methods (SIR92) [24] and refined on F2 by full-matrix
least-squares methods; using SHELXL-97 [25,26]. Non-
hydrogen atoms were anisotropically refined. H-atoms were
included in the refinement on calculated positions riding on
P
their carrier atoms. The function minimized was [ w(Fo2
ꢀ
Fc2)2] (w ¼ 1/[s2 (Fo2) þ (aP)2 þ bP]), where P ¼ (Max(Fo2,0) þ
2Fc2)/3 with
s
2(Fo2) from counting statistics. The function R1
and wR2 were (SjjFoj ꢀ jFcjj)/SjFoj and [Sw(Fo2 ꢀ Fc2)2/S(wFo4)]1/2
,
respectively.
3. Results and discussions
3.1. Syntheses and characterizations
Compounds 1 and 2 were prepared by the treatment of phe-
nylboronic acid [PhB(OH)2] with hexamethylenetetramine (hmt) in
methanol in absence or presence of manganese perchlorate hexa-
hydrate respectively (Scheme 2). The synthesis of 2 was not
possible in absence of manganese perchlorate hexahydrate under
identical reaction condition. We assume it reacts with hmt and
reduces the concentration of hmt in the reaction mixture, thus
favouring the synthesis of 2. Compound 3 was obtained by reacting
Table 1
Crystal data and experimental details of the single-crystal X-ray analyses of compounds 1e4.
Compound
1
2
3
4
Empirical formula
Formula weight/g molꢀ1
Crystal system
C30H39B3N8O3
592.12
Monoclinic
C2/c
17.0023(8)
10.8153(5)
16.3825(6)
C42H42B6N4O6
763.66
Monoclinic
P 21/c
12.5746(6)
19.6788(9)
20.2832(10)
C24H24B3N4O3F3
505.90
Triclinic
P-1
10.910(4)
11.238(4)
11.295(4)
80.469(12)
62.890(12)
72.457(12)
1174.7(7)
2
1.430
0.109
5e51
12,636
4345
0.0946
3004
C12H40Cl2N8O16Co
682.35
Triclinic
P-1
8.2075(10)
9.0886(13)
10.6609(14)
93.679(4)
104.312(3)
114.091(3)
691.05(16)
1
1.640
0.898
5e51
7658
2566
0.0276
2167
Space group
ꢀ
a/A
ꢀ
b/A
ꢀ
c/A
ꢁ
ꢁ
a
/
b
/
103.504(4)
127.970(3)
ꢁ
/
g
3
ꢀ
V/A
2929.2(2)
4
1.343
0.702
8e142
5663
2764
0.0195
2447
3956.8(3)
4
1.282
Z
rcalc/g cmꢀ3
m
(Cu a or MoKa)/mmꢀ1
0.664
K
2
Q
range/ꢁ
8e142
11,322
6603
0.0373
5011
Reflections measured
Independent reflections
R(int)
Ind. reflections (I > 2
s(I))
Parameters
201
503
430
228
R1 (I > 2
wR2 (all data)
s
(I))
0.0388
0.1106
1.055
0.0520
0.1518
1.016
0.0600
0.1853
1.019
0.391/-0.349
0.0281
0.0657
GooF (all data)
1.058
Max. peak/hole/ee 10ꢀ6pmꢀ3
0.254/-0.222
0.247/-0.233
0.362/e0.313 ee
A
.
ꢀꢀ3

S. Saha et al. / Journal of Organometallic Chemistry 745-746 (2013) 329e334
333
Table 2
The solid state structures also confirm that compound 1 is an
ꢁ
ꢀ
Distances (A) and angles ( ) within the hydrogen bonds of compound 4.
adduct of triphenylboroxine-hmt in 1:2 M ratio, which was found
to be rare. Triphenylboroxine acts as bridge between two hmt
molecules in 1, whereas hmt plays the role of a bridging ligand
between two triphenylboroxine rings in 2. A common feature of all
compounds is the formation of planar or nearly planar B3O3 rings.
The sums of angles within the ring are 720ꢁ, 718ꢁ and 719.4ꢁ in 1, 2
and 3 respectively, confirming planarity (1) or near-planarity (2, 3)
of the boroxine rings. In the structure of 1, two boron atoms, B1 and
B10 reveal a tetrahedral environment as a result of the coordination
by two hmt ligands. One boron atom B2 adopts a trigonal coordi-
nation geometry. In spite of the existence of two tetrahedrally co-
ordinated boron atoms, the planarity of the boroxine ring in 1 is
achieved due to the coordination of the two hmt’s molecules from
opposite site of the B3O3 ring, thus balancing the effects of N / B
bond formation. The atoms B1 and B4 in 2 are in tetrahedral
environment leaving other boron atoms in trigonal geometrical
environment. In compound 3, B1 possesses a tetrahedral coordi-
nation geometry, whereas B2 and B3 have a trigonal ligand envi-
ronment. The average BeO bond length, OeBeO and BeOeB angles
DeH/A
DeH
D/ A
H/A
:DeH/A
O1eH1C/N1*
O4eH4B/N3
O5eH4A/N4$
O3eH11B/N2#
0.77(3)
0.83(3)
0.81(3)
0.87(3)
2.854(3)
2.773(2)
2.827(3)
2.744(3)
2.09(3)
1.97(3)
2.02(3)
1.88(3)
175(3)
165(3)
174(2)
173(3)
Symmetry element * ¼ ꢀ1 ꢀ x, 1 ꢀ y, ꢀz; $ ¼ x, ꢀ1 þ y, z and # ¼ 1 ꢀ x, 1 ꢀ y, 1 ꢀ z;
D, donor; H, hydrogen; A, acceptor.
Compound 4 was obtained as pink crystals with colourless by-
product which was separated mechanically and identified by
NMR spectroscopy to be triphenylboroxine. Compound 4 is iso-
structural with its manganese and nickel analogues, which were
synthesized by reacting the corresponding metal perchlorate
hexahydrate with hmt in water [22].
The solid state structure of compound 4 was established by
single crystal X-ray analysis which shows that it crystallizes in the
triclinic space group P-1 with one formula unit in the unit cell. The
cobalt ion is located at the inversion centre and coordinated by six
ꢁ
ꢀ
were reported to be 1.382 A and 119.3, 120.3 respectively for tri-
phenylboroxine, [(PhBO)3] [21]. Compared to the latter, the corre-
sponding OeB1eO bond angles decreases by 3.6ꢁ in 1, 5.17ꢁ, 5.49ꢁ
in 2 and 5.7ꢁ in 3 at the tetrahedral boron atoms. The average OeBe
O angle of the trigonal boron atoms increases by an average of 2.5ꢁ,
0.9ꢁ and 0.7ꢁ in 1, 2 and 3 respectively.
ꢀ
water molecules with CoeO distances of 2.0643(15)e2.1162(15) A
which is identical with the reported values [23]. It can be found
from the structure that hmt and perchlorate anion are free from
metal, remaining outside the coordination shell. Additionally, two
non-coordinating water molecules were found in the structure. The
six coordinated water molecules are further connected to the six
free hmt molecules and each hmt is connected to three coordi-
nating and one free water molecules through intermolecular
hydrogen bonds. Fragments of the resulting hydrogen bonding
framework is illustrated in Fig. 3 besides the unit cell of 4. Details of
the hydrogen bonding are given in Table 2.
3.2. Reactivity
Compound 1 was reacted with [Co(H2O)6](ClO4)2 in methanol. It
acts as a mild hmt-donating species at room temperature resulting
in the formation of [Co(H2O)6](ClO4)2$(hmt)2$2H2O (4) (Scheme 3).
Fig. 3. Fragments of the crystal structure of 4: Unit cell (top left) OeH/N hydrogen bonds per formula unit (top right) and part of the hydrogen bonding framework (bottom). Large
black spheres ¼ Co, blue ¼ N, red ¼ O, green ¼ Cl, grey ¼ C, small black spheres ¼ H). (For interpretation of the references to colour in this figure legend, the reader is referred to the
web version of this article.)

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S. Saha et al. / Journal of Organometallic Chemistry 745-746 (2013) 329e334
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Acknowledgements
This work was financially supported by the DST, India under
FAST Track Scheme (Order No. SR/FT/CS-96/2011, dated 15/06/
2012) and ISM Dhanbad (Project No. ISM/Acad/AC/31.4/2011, dated
21/09/2011) Dhanbad. We thank Prof. V. K. Saxena (Dept. Of
Chemical Engineering) and Dr. Shouvik Chattopadhyay (Jadavpur
University, Kolkata) for proving elemental analysis and IR facilities
respectively.
Appendix A. Supplementary material
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