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RADIOCHEMISTRY, STABLE ISOTOPES,
NUCLEAR ANALYTICAL METHODS, GENERAL CHEMISTRY
93
drate (Mg[(C 5 H 3 N 2 O 2 )(H 2 O)] 2·2H 2 O) is composed
of monomeric molecules in which the magnesium(II)
ion at the centre of symmetry is coordinated
by two ligand molecules, each via its N,O
bonding moiety [Mg-N 2.177(2) Å, Mg-O 2.041(1)
Å]. The ligand molecules and the metal ion form
a trans-planar configuration (rms 0.0001 Å). Two
water oxygen atoms [Mg-O 2.091(1) Å], above and
below the plane, complete a slightly distorted octahedron
(Figs.1 and 2). A network of hydrogen bonds
operating between the solvation water molecules
acting as donors and unbonded carboxylate oxygen
atoms and unbonded hetero-ring nitrogen
atoms holds the monomers together.
X-ray diffraction data collection was carried out
on a KUMA KM4 four circle diffractometer at the
Institute of Nuclear Chemistry and Technology.
Structure solution and refinement was performed
using SHELXL programme package.
CRYSTAL CHEMISTRY OF COORDINATION COMPOUNDS
WITH HETEROCYCLIC CARBOXYLATE LIGANDS.
PART LVI. THE CRYSTAL AND MOLECULAR STRUCTURES
OF TWO CALCIUM(II) COMPLEXES
WITH IMIDAZOLE-4,5-DICARBOXYLATE AND WATER LIGANDS
Wojciech Starosta, Janusz Leciejewicz, Thathan Premkumar 1/ , Subbian Govindarajan 1/
1/
Department of Chemistry, Bharathiar University, Coimbatore, Tamilnadu, India
Fig.2. The packing diagram of Ca(4,5-IDA)(H 2 O) 4·H 2 O
showing the alignment of the molecular layers along
the c axis.
late oxygen atom O3 [d(Ca-O3)=2.325(1) Å], the
hetero-ring nitrogen atom [d(Ca-N2)=2.523(1)Å]
Fig.1. A fragment of the molecular sheet constituting the
structure of Ca(4,5-IDA)(H 2 O) 4·H 2 O with atom labelling
scheme. Non-hydrogen atoms are drawn at
the 50% probability level. For clarity, hydrogen atoms
are not shown.
The structure of poly-diaqua(µ-imidazole-4,5-dicarboxylato-N,O;O’;
-O’’, O’’’)calcium(II) monohydrate
([Ca(C 5 H 2 N 2 O 4 )(H 2 O) 2·H 2 O]) is built of
molecular sheets in which imidazole-4,5-dicarboxylate
ligand molecules (4,5-IDA) bridge the metal
ions using both their carboxylate groups, each acting
in a bidentate mode. Figure 1 shows the structural
unit with atom labelling scheme, Fig.2 – the
packing diagram. Calcium(II) ion is coordinated
by six oxygen atoms and one hetero-ring nitrogen
atom distributed at the apices of a capped trigonal
pyramid. The basal plane of the prism is formed by
two carboxylate oxygen atoms [d(Ca-O2=2.374(1)
Å, d(Ca-O4)=2.412(1) Å] and two water oxygen
atoms [d(Ca-O5)=2.384(1) Å, d(Ca-O6)=2.455(1)
Å], the capped position is occupied by the carboxy-
Fig.3. The coordination the calcium(II) ion in the structure
of Ca(4,5-IDA)(H 2
O) 4·H 2
O.