Second-sphere coordination complexes via hydrogen bonding: Synthesis, characterization of [Co(NH3)6](XO3)3·nH2O (X=Br, I) and single crystal X-ray structure determination of [Co(NH3)6<

Article abstract of DOI:10.1016/j.molstruc.2005.11.027

Single crystals of [Co(NH₃)₆](BrO₃)₃·0.5H₂O and peach coloured precipitate of [Co(NH₃)₆](IO₃)₃·3H₂O were obtained by reacting hexaamminecobalt(II

Full text of DOI:10.1016/j.molstruc.2005.11.027

Journal of Molecular Structure 788 (2006) 49–54
www.elsevier.com/locate/molstruc
Second-sphere coordination complexes via hydrogen bonding: Synthesis,
characterization of [Co(NH ) ](XO ) $nH O (XZBr, I) and single crystal
3
6
3 3
2
X-ray structure determination of [Co(NH ) ](BrO ) $0.5H O
2
3
6
3 3
a,
a
a
b,
c
Raj Pal Sharma
*
, Ritu Bala , Rajni Sharma , Julio Perez **, Daniel Miguel
a
Department of Chemistry, Panjab University, Chandigarh 160014, India
Departamento de Qu ´ı mica Org a´ nica e Inorg a´ nica-IUQOEM, Universidad de Oviedo-CSIC, Oviedo 33006, Spain
b
c
Departamento de Qu ´ı mica Inorg a´ nica, Universidad de Valladolid, Valladolid 47071, Spain
Received 13 October 2005; received in revised form 13 November 2005; accepted 13 November 2005
Available online 4 January 2006
Abstract
3 6 3 3 2 3 6 3 3 2
Single crystals of [Co(NH ) ](BrO ) $0.5H O and peach coloured precipitate of [Co(NH ) ](IO ) $3H O were obtained by reacting
hexaamminecobalt(III) chloride with appropriate silver halate in 1:3 molar ratio in hot aqueous medium. These hexaamminecobalt(III) complexes
have been characterized by spectroscopic studies (e.g. UV–vis and IR). Single crystal X-ray structure determination of title complex salt revealed
3
C
K
the presence of discrete ions, i.e. cation [Co(NH
3
)
6
]
, three anions, BrO and half water molecule in the solid state. Crystal lattice is stabilized by
3
K
K
electrostatic forces of attractions and hydrogen bonding interactions (N–H/O , O–H/O ). The formation of salts of definite composition with
halate ions and solubility product data suggest that purely inorganic hexaamminecobalt(III) cation may be used as an anion receptor for these
weakly coordinating inorganic oxo-anions.
q 2005 Elsevier B.V. All rights reserved.
Keywords: Anion receptor; Cobalt(III); Coordination chemistry; Inorganic synthesis; Halates; X-ray crystallography
1
. Introduction
The hexaamminecobalt(III) tripositive cation is a stable
complex known since 1798. Its stability, kinetically inert, high
symmetry and large number of N–H bonds make it ideally
suited to serve as a building block for the construction of 3D
networks. However, examples of its use as a supramolecular
synthon are rare. Thus, Stoddart [2] investigated its second-
sphere complexation with crown ethers, and Shimizu [3]
studied the 3D network formed with the trianion 1,3,5-
tris(sulfomethyl)benzene. From the point of view of the
potential use of a specific class of molecules as building
block of H-bonded architectures for crystal engineering,
amidinium ion and its derivatives appear to be very promising
as they very easily form acid–base complexes with carboxylate
or other oxygenate anions which are linked by strong Co–N–
The use of hydrogen bonding in the design of 3D networks
received considerable attention in the last decades. In most
cases, purely organic building blocks have been employed;
however, the application of metal complexes is becoming
increasingly important [1]. In these species, the hydrogen bond
donor atoms are usually part of organic ligands. Chelating
ligands are often chosen in order to impart a higher stability to
the complexes. The hydrogen bond acceptors are either polar
molecules or anions. Since these species feature lone electron
pairs and hence are potential ligands, highly stable complexes
are needed to prevent substitution reactions, i.e. to keep the
hydrogen bond acceptors in the second coordination sphere of
the metal atom.
C
K
H /O
charge assisted H-bonds (CAHB)
oxoanion
3
+
H
H
N
H
-
-
(NH3)5Co
N
H
H
+
O oxoanion
(NH3)5
Co
O oxoanion
H
*
Corresponding authors. Tel.: C91 0172 2534433; fax: C91 0172 2545074.
Tel.: C34 985 103465; fax: C34 985 103446.
E-mail addresses: rpsharma@pu.ac.in (R.P. Sharma), japm@fq.uniovi.es
*
*
N–H/O bonds are the most abundant hydrogen bonds in
(
J. Perez).
biopolymer aggregates and the main factors for the secondary
struture of DNA or proteins, receptor–agent binding, etc. [4,5].
The supramolecular aggregates result from balance between
0022-2860/$ - see front matter q 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2005.11.027

50
R.P. Sharma et al. / Journal of Molecular Structure 788 (2006) 49–54
hydrogen bond interactions and electrostatic interactions
between the constituent ions [6].
for X-ray structure determination. The remaining clear
supernatant solution gave second crop of crystals. The
overall yield is nearly quantitative and the salt decomposes
at 463 K. Solubility 16.0 g/100 ml in water at 25 8C:
[Co(NH ) ](BrO ) $0.5H O, H, 3.43; N, 15.16; Co, 10.63.
K
Salts of monoanionic halates, XO , are used in the
manufacturing of dyes, matches, firework, explosives, herbi-
cide, antiseptic (mucous membrane) and as oxidizing agents
3
3
6
3 3
2
K1
[7]. Therefore, the study of the behaviour of halate anions as
components of 3D networks is of interest.
Found: H, 3.13; N, 15.02; Co, 10.01; IR (cm ): n 3186 (br),
s
d 1587 (br), d 1339 (s), r 862 (s), n 811 (sh), 768 (s). UV/vis
r
d
s
Although the synthesis and single crystal X-ray structure
determinations of a variety of hexaamminecobalt(III)
complex salts have been reported in the literature, only few
reports deal with the interaction between this cation and the
accompanying anions in the solid state [8]. We have recently
reported three complex salts of hexaamminecobalt(III) cation
(solution): lmaxZ474 (eZ54.5/mol l cm), 338 (eZ
45.2/mol l cm).
2.3. Synthesis of [Co(NH ) ](IO ) $3H O
3
6
3 3
2
Hexaamminecobalt(III) chloride (1 g, 0.0037 mol) was
dissolved in 50 ml hot water in which solid silver iodate
(3.189 g, 0.0112 mol) was added. The mixture was stirred and
heated (at70 8C)for15 minforcompletion of reaction and white
precipitate of silver chloride was filtered off. The reddish-orange
filtrate gave peach coloured precipitate on cooling, which were
filtered washed with ice-cold water followed by acetone and
dried in air. The overall yield is quantitative and the salt
decomposes at 480 K. Solubility 0.35 g/100 ml in water at
25 8C. Anal. Calcd for [Co(NH ) ](IO ) $3H O: H, 3.24; N,
K
K
with halate ions ðClO ; IO Þ [5a] in which only one of the
3
3
halide ions (Cl or Br) has been replaced by halate ion. The
present work reports a new methodology to synthesize
K
hexaamminecobalt(III) complex with halate ions ðBrO and
3
K
3
IO Þ in which all three chloride ions have been replaced by
halate ions and characterization of these newly synthesized
complex salts on the basis of elemental analyses and
spectroscopic studies. A single crystal X-ray structure of
[
Co(NH ) ](BrO ) $0.5H O was determined to conclusively
3 6 3 3 2
3 6
3 3
2
K1
establish the structure and composition. The 3D structure is
stabilized by extensive charge-assisted hydrogen bonding.
We have already reported the potential use of cationic
hexaamminecobalt(III) as anion receptor for inorganic oxo-
anions [8c–e], fluoro-anions [8f–g] and organic oxo-anions
11.35;Co, 7.96. Found:H, 3.14;N, 11.30;Co, 7.16;IR(cm ), n
3392 (sh), n 3260 (br), d 1593 (br), d 1325 (s), r 874 (s), n
as
d
s
r
793(s), 752 (sh), 737 (s); UV/vis (solution): lmaxZ474 (eZ
58.1/ml cm), 338 (eZ48.9/mol cm).
[
8h–k].
2.4. Crystal structure determination
2
. Experimental
A suitable crystal was attached to a glass fiber and
transferred to a Bruker AXS SMART 1000 diffractometer
with graphite monochromatized Mo Ka X-radiation and a
CCD area detector. Raw frame data were integrated with the
SAINT [11] program. The structure was solved by direct
methods with SHELXTL [12]. An empirical absorption
correction was applied with the program SADABS [13]. All
non-hydrogen atoms were refined anisotropically. Hydrogen
atoms were set in calculated positions and refined as riding
atoms. A peak was found at the two-fold axis, corresponding to
a disordered molecule of water (occupancy 0.5). Calculations
were made with SHELXTL and PARST [14]. Drawings were
made with SHELXTL and PLUTON [15] under WINGX [16].
All other information regarding the refinement is also recorded
in Table 1.
2
.1. General remarks
Analytical grade reagents were used without any further
purification. [Co(NH ) ]Cl has been prepared by air oxidation
3
6
3
of Co(II) salt in ammonical solution in the presence of
activated charcoal as a catalyst according to method described
by Bjerrum and McReynold [9]. Silver bromate and silver
iodate were prepared by reacting silver nitrate with appropriate
sodium salts of halate ions in 1:1 molar ratio in aqueous
medium. Cobalt was determined by standard gravimetric
method of estimation [10] and H, N were estimated micro
analytically by automatic PERKIN ELMER 2400CHN
elemental analyzer. UV–vis spectra were recorded using
HITACHI 330 spectrometer in water as solvent. Infrared
spectra of the title complex salts were recorded using Perkin
Elmer spectrum RX FT-IR system using Nujol mull in KBr
plates.
3. Results and discussion
3.1. Synthesis
2
.2. Synthesis of [Co(NH ) ](BrO ) $0.5H O
2
When hexaamminecobalt(III) halide and appropriate alkali
metal halates were reacted in 1:1 molar ratio in hot aqueous
medium, the complex salts [Co(NH ) ]Cl (ClO ), [Co(NH ) ]-
3
6
3 3
Hexaamminecobalt(III) chloride (1 g, 0.0037 mol) was
3
6
2
3
3 6
dissolved in 35 ml hot water in which solid silver bromate was
added (2.66 g, 0.0112 mol). The mixture was stirred for half
an hour for completion of reaction and white precipitate of
silver chloride was filtered off. The reddish-orange coloured
filtrate gave, after a week, red coloured single crystals suitable
Br (ClO ) and [Co(NH ) ]Cl (IO )$H O were obtained [8a].
2 3 3 6 2 3 2
In order to replace all three chloride ions with halate ions
(bromate and iodate) hexaamminecobalt(III) chloride was
reacted with silver halate in 1:3 molar ratio in hot aqueous
medium and filtering off the precipitated silver chloride as

R.P. Sharma et al. / Journal of Molecular Structure 788 (2006) 49–54
51
Table 1
Crystal data and structural refinement parameters of [Co(NH
Table 2
3 6 3 3 2
) ]BrO ) $0.5H O
sp
Solubility products (K ) of hexaamminecobalt(III) salts
Empirical formula
Formula weight
Temperature
H
18Br
553.87
296(2) K
3
CoN
6
O
9
$0.50H
2
O
Complex salts
Solubility (M)
Ksp
[
[
[
[
[
[
Co(NH
Co(NH
Co(NH
Co(NH
Co(NH
Co(NH
3
3
3
3
3
3
)
)
)
)
)
)
6
6
6
6
6
6
]Cl
]Cl
3
2
0.2605
0.3169
0.0692
0.0470
0.2898
0.0051
0.12
$ClO
$ClO
$IO $H
](BrO $0.5H
](IO $3H
3
0.04
˚
Wavelength
0.71073 A
Monoclinic
K5
K5
]Br
]Cl
2
3
9.19!10
1.96!10
0.19
Crystal system
Space group
2
3
2
O
2
C /c
3
)
3
2
O
˚
Unit cell dimensions
aZ26.236(4) A
bZ7.2274(10) A, bZ124.430(2)8
cZ18.710(3) A
2926.3(7) A
K8
3
)
3
2
O
1.87!10
˚
˚
3
˚
Volume
reported in the Section 2, when the appropriate amounts of the
hexaamminecobalt(III) chloride and silver iodate were mixed
in minimum amount of water peach colured precipitate of
complex salt [Co(NH ) ](IO ) $H O formed because ionic
Z
8
3
Density (calculated)
Absorption coefficient
F(000)
2.514 mg/m
K1
9.418 mm
2152
3
6
3 3
2
3
Crystal size
0.40!0.27!0.23 mm
1.880–23.258
products are greater than solubility products, K (Table 1). But
sp
Theta range for data collection
Index ranges
when hexaamminecobalt(III) chloride and silver bromate in
minimum amount of water reddish orange coloured crystals of
complex salt [Co(NH ) ](BrO ) $0.5H O formed after a week
K18%h%28, K8%k%7, K20%l%17
6237
Reflections collected
Independent reflections
Completeness to thetaZ23.258
Absorption correction
Max. and min. transmission
Refinement method
Data/restraints/parameters
2089 [R(int)Z0.0373]
99.7%
3 6
3 3
2
because ionic products are greater than solubility products, K
K
sp
SADABS
at the crystallization point. The binding of ClO ion is more in
3
1.000000 and 0.511754
complex salt [Co(NH ) ]Br $ClO as compared to
3 6
2
2
3
Full-matrix least-squares on F
[Co(NH ) ]Cl $ClO which shows the effect of co-anion also
3 6 2 3
2089/0/182
2
(Table 2).
.3. Spectroscopy
The vibrational spectra of the title complex salts show that
Goodness-of-fit on F
1.080
Final R indices [IO2sigma(I)]
R indices (all data)
R1Z0.0249, wR2Z0.0637
R1Z0.0291, wR2Z0.0651
0.0078(2)
3
Extinction coefficient
K3
˚
0.631 and K0.825 e A
Largest diff. peak and hole
the stretching vibration of the coordinated NH molecule are
3
given in equation:
lower than those of the free NH molecules for two reasons,
3
one is the effect of coordination and the other is the effect of the
K
½
CoðNH Þ ꢀCl C3AgXO /½CoðNH Þ ꢀðXO Þ C3AgC lY ;
3
6
3
3
3 6
3 3
K
3
counter ions, i.e. BrO or IO in the title complex salts. This is
3
due to the weakening of the N–H bond due to the formation of
K
X Z Br or I
N–H/O and O–H/O type of hydrogen bonds. It is seen that
the antisymmetric stretch and symmetric NH stretch, NH
3
3
The repeated attempts to prepare complex salt,
Co(NH ) ](BrO ) were unsucessfull even when using 1:3
degenerate deformation, NH symmetric deformation and NH
3
3
[
3
6
3 3
vibrations appear in the regions of 3400–3000, 1650–1550,
K1
370–1200 and 800–900 cm , respectively, for [Co(NH ) ]-
molar ratio of hexaamminecobalt(III) chloride and alkali metal
bromate in aqueous medium. The chemical compositions of
newly synthesized complex salts were initially indicated by
halate tests and subsequently confirmed by elemental analyses.
These hexaamminecobalt(III) complex salts are stable in air
and light, soluble in hot water but insoluble in organic solvents
and high melting solids.
1
Cl [17] which are comparable with those in the title complex
3 6
3
salts. The Infrared spectra of the sodium/potassium salts of
bromate and iodate ions [18] show strong sharp band close to
K1
the region 810–428 and 796–745 cm
for BraO and IaO
bond, respectively, but for title complex salts the stretching
band appeared in the region 811–768 (ClaO) and 793–737
(
K1
IaO) cm . The lowering in stretching frequency of BraO
3
.2. Solubility products
and IaO bonds in the title complex salts may be due to N–H/
O type of hydrogen bonding which weaken BraO and IaO
bonds.
Solubility of ionic salts in water differs to a great extent and
on the basis of solubility criterion, the salts are classified into
three categories: (a) solubilityO0.1 M (soluble), (b) solubility
between 0.01 and 0.1 M (slightly soluble) and (c) solubility!
The two transitions in the electronic spectra of
hexaamminecobalt(III) complexes are observed around 470
6
and 340 nm (d–d transitions typical for low spin Co(III) d
1
0
room temperature (Table 2) shows that [Co(NH ) ](IO ) $3-
.01 M (sparingly soluble). The solubility measurement at
octahedral complex) assigned to
1
A /T
1g
and
1
g
1
A / T , respectively, as reported in the literature [19].
3
6
3 3
1g
2g
H O is sparingly soluble in water but [Co(NH ) ](BrO ) $0.5-
2
The UV–vis spectrum of the aqueous solution of complex
salt, [Co(NH ) ](BrO ) $0.5H O shows two ligand field
3 6
3 3
H O and [Co(NH ) ]Cl are soluble in water. It is observed that
3 6
2
3
3 6
3 3
2
3C
the binding (association) of iodate ions with [Co(NH ) ] is
absorption at lmaxZ474 (3Z54.5/mol l cm) and 338
(3Z54.5/mol l cm). Similar pattern was observed for
[Co(NH ) ](IO ) $3H O complex salt, having lmaxZ474
3
6
much more as compared to bromate and chloride ions, i.e. the
K
K
3
K
3
binding affinities are in the order IO [Cl OBrO . As
3 6
3 3
2

52
R.P. Sharma et al. / Journal of Molecular Structure 788 (2006) 49–54
(
eZ58.1/mol l cm), 338 (eZ48.9/mol l cm). Strong absorp-
Table 3
3 6 3 3 2
Bond lengths (A) and angles (8) for [Co(NH ) ](BrO ) $0.5H O
˚
tion maxima observed for the title complex salts are also in
agreement with those of related salts such as hexaammine-
cobalt(III) di halide halate [8a].
Co(1)–N(6)
1.948(3)
Br(1)–O(12)
Br(2)–O(23)
Br(2)–O(21)
Br(2)–O(22)
Br(3)–O(31)
Br(3)–O(33)
Br(3)–O(32)
1.644(3)
1.628(3)
1.636(3)
1.652(3)
1.623(4)
1.653(3)
1.654(4)
Co(1)–N(1)
1.955(3)
Co(1)–N(2)
1.956(3)
Co(1)–N(5)
1.961(3)
4
. X-ray crystallography and packing
Co(1)–N(3)
1.966(3)
Co(1)–N(4)
1.969(3)
Br(1)–O(13)
1.631(3)
For the title complex salt, X-ray structure determination
revealed the presence of the following crystallographically
Br(1)–O(11)
1.638(3)
N(6)–Co(1)–N(1)
N(6)–Co(1)–N(2)
N(1)–Co(1)–N(2)
N(6)–Co(1)–N(5)
N(1)–Co(1)–N(5)
N(2)–Co(1)–N(5)
N(6)–Co(1)–N(3)
N(1)–Co(1)–N(3)
N(2)–Co(1)–N(3)
N(5)–Co(1)–N(3)
N(6)–Co(1)–N(4)
N(1)–Co(1)–N(4)
89.85(16)
179.35(15)
90.80(15)
89.03(15)
178.86(15)
90.32(15)
90.97(15)
89.76(15)
89.00(15)
90.07(15)
89.08(15)
89.82(15)
N(2)–Co(1)–N(4)
N(5)–Co(1)–N(4)
N(3)–Co(1)–N(4)
O(13)–Br(1)–O(11)
O(13)–Br(1)–O(12)
O(11)–Br(1)–O(12)
O(23)–Br(2)–O(21)
O(23)–Br(2)–O(22)
O(21)–Br(2)–O(22)
O(31)–Br(3)–O(33)
O(31)–Br(3)–O(32)
O(33)–Br(3)–O(32)
90.95(15)
90.36(14)
179.57(14)
105.6(2)
3
C
independent components in the solid state: [Co(NH ) ] ,
K
BrO and half water molecule (Fig. 1(a)). This conclusively
3
6
3
established the existence of [Co(NH ) ](BrO ) $0.5H O. The
3
6
3 3
2
105.88(19)
103.17(19)
106.3(2)
cobalt(III) metal ion is surrounded by six nitrogen atoms
originating from six coordinating ammonia molecules
resulting in a slightly distorted octahedral geometry
102.75(18)
103.04(18)
103.1(2)
(
Table 3). The Co–N bond distances are in the range
˚
.948(3)–1.969(3) A, in agreement with those found in the
1
103.5(3)
other hexaamminecobalt(III) dihalide halate salts recently
reported by us [8a]. The cis and trans N–Co–N bond angles
are in the range 89.08(15)8–90.97(15)8 and 178.86(15)8–
105.5(2)
Symmetry transformations used to generate equivalent atoms.
1
cobalt(III) complex salt are BrO3 anions. The Br–O bond
79.57(14)8 respectively. The counter anions of this
K
bond lengths and bond angles for the bromate anions present
in title complex salt are comparable with those of ionic
bromates reported in literature (Table 4) [20–23]. It is
obvious that there is no effect of three bromate ions on the
structural parameters of hexaamminecobalt(III) complex
cation as compared to two halide and one halate ions studied
previously [8a].
distance and O–Br–O bond angle are in the range 1.623(4)8–
1
˚
.654(4) A and 102.75(18)8–106.3(2)8, respectively. These
Apart from ionic constituents half water molecule is co-
crystallized with the complex salt resulting in composition
[Co(NH ) ](BrO ) $0.5H O. The H-bond donors groups are
3 6 3 3 2
ammine, while the acceptors are oxygens of bromate ions.
Fig. 1 shows the relative disposition of the bromate anions
and the hexaamminecobalt(III) cation. Dashed lines represent
H-bonds between oxygen atoms of bromate and hydrogen
atoms of coordinated ammonia groups. There is a one-half
molecule of water (placed in a symmetry element) per
hexaamminecobalt cation. Fig. 2 displays all components
(
cation, three anions and water) showing the main
interactions. There is an extensive network of hydrogen
bonds in the crystal lattice. In the view perpendicular to face
a–c, displayed in Fig. 3, it is possible to distinguish an
arrangement in puckered layers parallel to axis c, the layers
being connected only by hydrogen bonding through the water
molecules.
Table 4
˚
A comparison of bond lengths (A) and angles (8) for the bromate anion in
several salts and in the complex salt
BrOK3
X–O
References
O–X–O
NaBrO
3
1.648 (4)
1.648 (9)
1.640
104.1 (5)
104.1 (3)
105.5
[20]
[21]
[22]
[23]
A
[
Mg(H
2
O)
6 3 2
](BrO )
NH
4
BrO
3
Fig. 1. (a) ORTEP diagram of [Co(NH3)6](BrO3)3$0.5H2O (b) figure shows
the relative disposition of the bromate anions and the hexaamminecobalt(III)
cation. Dashed lines represent H-bonds between oxygen atoms of bromate and
hydrogen atoms of coordinated ammonia groups.
Hg(OH)BrO
Co(NH ](BrO
3
1.610 (5)
1.639 (3)
103 (3)
[
3
)
6
3
)
3
$0.5H
2
O
104.3 (2)
A, Present work.

R.P. Sharma et al. / Journal of Molecular Structure 788 (2006) 49–54
53
hydrogen bonding between the coordinated ammonia mol-
ecules and the halate ions as observed in earlier studies
involving other anions.
6. Supplementary data
Crystallographic data for the structure analysis of the title
compound has been deposited at the FIZ, 76344 Eggenstein-
Leopoldshafen (Germany) having CSD number 415732 (Tel.:
C49 7247 808 205; fax: C49 7274 808 666; E-mail:
crysdata@fiz-karlsruhe.de).
Acknowledgements
Ritu Bala thanks the CSIR, New Delhi, India for the
financial support (Grant No.01(1768)/02 /EMR-II). Daniel
Miguel acknowledges the funding of project BQU 2002-03414.
Fig. 2. All components (cation, three anions and water) present in complex salt
showing the main interactions.
References
[
1] (a) A.D. Burrows, C.-W. Chan, M.M. Chowdhry, J.E. McGrady,
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(
(
(
b) M. Tadokoro, K. Nakasuji, Coord. Chem. Rev. 198 (2000) 205.
c) M.W. Hosseini, Coord. Chem. Rev. 240 (2003) 157.
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1
968, pp. 443–465.
5
. Conclusion
The reactions between [Co(NH ) ]Cl and silver halates
bromate and iodate) in aqueous medium have provided an
[
[
6] A. Katrusiak, M. Szafranski, J. Mol. Struct. 378 (1996) 205.
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3
6
3
[8] (a) R.P. Sharma, R. Bala, R. Sharma, V. Ferretti, Inorg. Chim. Acta 358
(2005) 3457.
(
(
(
(
(
(
b) R.P. Sharma, R. Bala, R. Sharma, P. Venugopalan, J. Coord. Chem.
7 (2004) 1563.
efficient and quantitative method for the preparation of
hexaamminecobalt(III) halates. X-ray structure determination
of the bromate salt, [Co(NH ) ](BrO ) $0.5H O, revealed the
5
c) R.P. Sharma, R. Bala, R. Sharma, K.K. Bhasin, R.K. Chadha,
J. Coord. Chem. 57 (2004) 313.
3
6
3 3
2
presence of ionic constituents along with half molecule of
water in the crystal lattice. The hydrogen bonding between the
hydrogens of coordinated ammonia molecules and oxygens of
bromate ions is clearly shown, and the 3D structure as a result
of the hydrogen bonds involving water molecules is interesting.
The solubility difference due to the anions is also interesting. In
one case the iodate ions replaced all the chloride ions, while in
the other case only one chloride ion was replaced in spite of the
lower solubility of the complex triiodate. The formation of
d) R.P. Sharma, R. Bala, R. Sharma, J.M. Salas, M. Quiros, J. Coord.
Chem. 58 (2005) 217.
e) R.P. Sharma, R. Bala, R. Sharma, U. Rychlewska, B. Warzajtisc,
J. Fluorine Chem. 126 (2005) 967.
f) R.P. Sharma, R. Bala, R. Sharma, P. Venugopalan, J.M. Salas,
M. Quiros, J. Fluorine Chem., in press.
(g) R.P. Sharma, R. Bala, R. Sharma, P. Venugopalan, J. Mol. Struct. 229
(2004) 694.
(
h) R.P. Sharma, R. Bala, R. Sharma, K.N. Singh, V. Ferretti, J. Mol.
Struct., in press.
(
i) R.P. Sharma, R. Bala, R. Sharma, A.D. Bond, Acta. Crystallogr. C61
(2005) 356.
definite salts of composition of [Co(NH ) ](BrO ) $0.5H O
3
6
3 3
2
3
and [Co(NH ) ](IO ) $3H O shows that [Co(NH ) ] present
C
3
6
3 3
2
3 6
(j) R.P. Sharma, R. Bala, R. Sharma, B.M. Kariuki, U. Rychlewska,
B. Warzajtisc, J. Mol. Struct. 748 (2005) 143.
in [Co(NH ) ]Cl is a promising anion binding agent for
3
6
3
(
k) R.P. Sharma, R. Bala, R. Sharma, P. Venugopalan, J. Mol. Struct. 752
2005) 170.
9] J. Bjerrum, J.P. McReynold, Inorg. Synth. 2 (1946) 216.
weakly coordinating halate ions as well as other anions in
aqueous medium in contrast to other synthetic receptors which
are effective in non-aqueous solvents. The anion binding of
(
[
[
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Longmans, London, 1961.
3
C
cationic cobalt ammine, [Co(NH ) ] , is achieved by the
3
6

54
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[
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