1, 2-, 1, 3- and 1, 4-Cyclohexanedicarboxylates of Cd and Mn with chain and layered structures

Article abstract of DOI:10.1039/b512843a

A systematic study has been carried out on the three isomeric cyclohexanedicarboxylates (CHDCs) formed by cadmium and manganese with the three isomeric dicarboxylic acids, in the presence or absence of amines. The CHDCs have been prepared under hydrothermal conditions and their structures established by X-ray crystallography. We have been able to isolate two-dimensional layered structures of 1,2-, 1,3- and 1,4- cyclohexanedicarboxylates and chain structures of 1,3- and 1,4- cyclohexanedicarboxylates. The infinite metal-oxygen-metal linkages are observed only in the case of the 1,2-dicarboxylate. In all the three isomeric cyclohexanedicarboxylates, the e,e conformation is most favored, although the 1,4-CHDCs often contain rings in both the e,e and the a,e conformations. The Royal Society of Chemistry 2006.

Full text of DOI:10.1039/b512843a

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PAPER
www.rsc.org/dalton | Dalton Transactions
1, 2-, 1, 3- and 1, 4-Cyclohexanedicarboxylates of Cd and Mn with chain and
layered structures†
A. Thirumurugan, M. B. Avinash and C. N. R. Rao*
Received 9th September 2005, Accepted 21st November 2005
First published as an Advance Article on the web 24th November 2005
DOI: 10.1039/b512843a
A systematic study has been carried out on the three isomeric cyclohexanedicarboxylates (CHDCs)
formed by cadmium and manganese with the three isomeric dicarboxylic acids, in the presence or
absence of amines. The CHDCs have been prepared under hydrothermal conditions and their
structures established by X-ray crystallography. We have been able to isolate two-dimensional layered
structures of 1,2-, 1,3- and 1,4-cyclohexanedicarboxylates and chain structures of 1,3- and
1,4-cyclohexanedicarboxylates. The infinite metal–oxygen–metal linkages are observed only in the case
of the 1,2-dicarboxylate. In all the three isomeric cyclohexanedicarboxylates, the e,e conformation is
most favored, although the 1,4-CHDCs often contain rings in both the e,e and the a,e conformations.
Introduction
Experimental
Other than the aluminosilicates and phosphates, metal carboxy-
All the Cd and Mn CHDCs were synthesized by hydrothermal
methods by heating the corresponding homogenized reaction
mixture in a 23 ml PTFE-lined bomb at 180 ◦C (150 ◦C for
VIII) for 72 h under autogenous pressure. The pH of the starting
reaction mixture was generally in the range 5–6. The pH after the
reaction did not show appreciable change. The products of the
hydrothermal reactions were vacuum filtered and dried under am-
bient conditions. The starting compositions for the different new
CHDCs synthesized by us are as follows, I [Cd(H2O)2(C8H10O4)],
1 Cd(OAc)2·2H2O (0.272 g, 1 mM) : 1 (1,4-CHDC) (0.176 g,
1 mM) : 1 piperidine (0.1 ml, 1 mM) : 278 H2O (5 ml,
278 mM); II [Cd(C8H10O4)(C10H8N2)]·H2O, 2 Cd(OAc)2·2H2O
(0.136 g, 0.5 mM) : 2 (1,4-CHDC) (0.088 g, 0.5 mM) : 1 (2,2ꢀ-
bipy) (0.04 g, 0.25 mM) : 2 piperidine (0.05 ml, 0.5 mM) :
1111 H2O (5 ml, 278 mM); III [Cd3(C8H10O4)3(C12H8N2)2]·4H2O,
2 Cd(OAc)2·2H2O (0.136 g, 0.5 mM) : 1 (1,4-CHDC) (0.088 g,
0.5 mM) : 1 (1,10-phen) (0.0.05 g, 0.25 mM) : 2 NaOH (0.1 ml
of 5 M solution, 0.5 mM) : 1111 H2O (5 ml, 278 mM);
IV [Mn3(C8H10O4)3(C12H8N2)2]·4H2O, 2 MnCl2·4H2O (0.102 g,
0.5 mM) : 1 (1,4-CHDC) (0.088 g, 0.5 mM) : 1 (1,10-phen)
(0.0.05 g, 0.25 mM) : 2 piperidine (0.0.05 ml, 0.5 mM) :
1111 H2O (5 ml, 278 mM); V [Mn3(C8H10O4)3(C12H8N2)2]·4H2O,
2 Mn(OAc)2·4H2O (0.124 g, 0.5 mM) : 1 (1,3-CHDC) (0.088 g,
0.5 mM) : 1 (1,10-phen) (0.05 g, 0.25 mM) : 2 piperidine
lates constitute a large family of open framework structures.1–18
A
variety of metal carboxylates has been studied for their interesting
properties such as porosity, sorption, catalysis, non-linear optics,
luminescence and magnetism.19–30 In particular, the benzenedicar-
boxylic acids have been found to be the ideal ligands for design-
ing coordination polymers and open framework structures.1–9,13
Cyclohexanedicarboxylic acids would similarly be expected to
be useful ligands, considering that they also occur in different
conformations. There have, however, been very few metal cyclo-
hexanedicarboxylates (CHDCs) reported in the literature.31–34 We
have been investigating the compounds formed by cadmium and
manganese with 1,2-, 1,3- and 1,4-cyclohexanedicarboxylic acids
in the presence and absence of organic amines, with a view to
examine the structure, conformation as well as dimensionality.
In 1,2 derivatives, the equatorial, equatorial (e,e) and the axial,
equatorial (a,e) conformers are known as the cis isomers. The
axial, axial (a,a) conformer is known as the trans isomer. In 1,3
derivatives, the (e,e) and the (a,a) conformers are known as the
cis isomers. The (a,e) conformer is known as the trans isomer. In
1,4 derivatives, the (e,e) and the (a,a) conformers are known as
the trans isomers. The (a,e) conformer is known as the cis isomer.
It is to be noted that the e,e form is most stable in the 1,2-, 1,3-
and 1,4-CHDCs and the a,a form is least stable. The a,e form is
reasonably stable in the 1,4-CHDCs. The present study has enabled
us to isolate several isomeric CHDCs of Cd and Mn with chain
and layered structures, where the e,e conformation dominates in
all except the 1,4-derivatives. In the latter, the a,e conformation
also occurs.
(0.0.05 ml, 0.5 mM)
: 1111 H2O (5 ml, 278 mM); VI
[Cd(H2O)2(C8H10O4)]·2H2O, 1 Cd(OAc)2·2H2O (0.272 g, 1 mM) :
1 (1,3-CHDC) (0.176 g, 1 mM) : 2 NaOH (0.4 ml of 5 M solution,
2 mM) : 278 H2O (5 ml, 278 mM). VII [Cd(C8H10O4)(C12H8N2)],
1 Cd(OAc)2·2H2O (0.272 g, 1 mM) : 1(1,3-CHDC) (0.176 g,
1 mM) : 1 (1,10-phen) (0.199 g, 1 mM) : 2 NaOH (0.4 ml
of
5 M solution, 2 mM) : 278 H2O (5 ml, 278 mM;
VIII [Mn(H2O)(C8H10O4)(C12H8N2)], 2 Mn(OAc)2·4H2O (0.124 g,
0.5 mM) : 1 (1,3-CHDC) (0.088 g, 0.5 mM) : 1 (1,10-phen) (0.05 g,
0.25 mM) : 2 piperidine (0.0.05 ml, 0.5 mM) : 1111 H2O (5 ml,
278 mM); IX [Cd(C8H10O4)], 1 Cd(OAc)2·2H2O (0.272 g, 1 mM) :
1 (anhydride of 1,2-CHDC) (0.162 g, 1 mM) : 1 piperidine (0.1 ml,
1 mM) : 278 H2O (5 ml, 278 mM). Powder XRD patterns of
Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Ad-
vanced Scientific Research, Jakkur P. O., Bangalore, 560064, India. E-mail:
cnrrao@jncasr.ac.in; Fax: +91-80-22082766, 22082766
† Electronic supplementary information (ESI) available: Tables S1–S9:
Selected bond distances and angles for I–IX. Fig. S1: Plots of experimental
leff vs. T and 1/vm vs. T of IV, V and VIII. Fig. S2: Photoluminescence
spectra of I–IX. See DOI: 10.1039/b512843a
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the products were recorded using Cu-Ka radiation (Rich-Seifert,
3000TT). The patterns agreed with those calculated for single-
crystal structure determination.
located from the difference Fourier maps, but not stable during
refinement, hence these hydrogen atoms are excluded from the final
refinement. Details of the structure solution and final refinements
for the compounds I–IX are given in Tables 1–3. The powder
XRD patterns of I–IX were recorded and were consistent with the
patterns generated from single-crystal structure determination.
CCDC reference numbers 283059–283067.
Thermogravimetric analysis (TGA) was carried out (Mettler-
Toledo) in oxygen atmosphere (flow rate = 50 ml min−1) in
◦
the temperature range 25–900 ◦C (heating rate = 5 C min−1).
Infra-red (IR) spectroscopic studies have been carried out in
the mid-IR region using KBr pellets (Bruker IFS-66v). The
spectra show characteristic bands of the carboxylate units. Room
temperature photoluminescence spectra of samples were recorded
on powdered samples. A Perkin-Elmer spectrometer (LS-55) with
a single beam set-up was employed using a xenon lamp (50 watt)
as the source and a photo-multiplier tube as the detector. The
temperature-dependent magnetic susceptibilities of IV, V and
VIII were measured from 5 to 300 K in a constant magnetic field of
0.5 T.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b512843a
Results and discussion
We have been able to synthesize the cadmium derivatives of all the
three isomeric cyclohexanedicarboxylic acids and the manganese
derivatives of the 1,3- and 1,4-cyclohexanedicarboxylic acids. In
the case of the 1,3- and 1,4-CHDCs, we have found both one-
dimensional chain and two-dimensional layered structures. We
have isolated only a layered Cd 1,2-CHDC. The conformation of
the cyclohexanedicarboxylate acid in the different metal deriva-
tives is an important aspect of the study. In the 1,4-CHDCs, the
e,e conformer (trans structure) is the most stable form, while the
a,a conformer (trans structure) is the least stable form because
of the 1,3-diaxial hindrance. The stability of the a,e conformer
(cis structure) falls in between the a,a and e,e forms. In the 1,3-
CHDCs, the e,e conformer (cis structure) is more stable than
the a,a conformer (cis structure) and the a,e conformer (trans
structure) is chiral. In the 1,2-CHDCs, the e,e conformer (trans
structure) is most stable. In what follows, we discuss the structures
of the Cd and Mn CHDCs along with their conformations.
A suitable single crystal of each compound was carefully
selected under a polarizing microscope and glued to a thin glass
fiber. Crystal structure determination by X-ray diffraction was
performed on a Siemens Smart-CCD diffractometer equipped
with a normal focus, 2.4 kW sealed tube X-ray source (Mo-
˚
Ka radiation, k = 0.71073 A) operating at 40 kV and 40 mA.
An empirical absorption correction based on symmetry equiva-
lent reflections was applied using the SADABS program.35 The
structure was solved and refined using the SHELXTL-PLUS suite
of program.35 All the hydrogen atoms of the carboxylic acids were
located in the difference Fourier maps. For the final refinement the
hydrogen atoms on the carboxylic acid were placed geometrically
and held in the riding mode. Final refinement included atomic
positions for all the atoms, anisotropic thermal parameters for all
the non-hydrogen atoms except C(53)–C(57) in VII and C(2) in IX,
and isotropic thermal parameters for the hydrogen atoms. All the
hydrogen atoms were included in the final refinement for I, II, IV,
VII, VIII and XI. The hydrogen atoms associated with the water
molecules (coordinated or lattice water) of III, V, and VI were
1,4-Cyclohexanedicarboxylates
The cadmium 1,4-cyclohexanedicarboxylate [Cd(H2O)2(C8H10-
O4)], I, is a one-dimensional chain structure consisting of octa-
hedral CdO6 units connected by the carboxylate groups (Fig. 1),
Table 1 Crystal data and structure refinement parameters for 1,4-CHDCs I, II and III
I
II
III
Empirical formula
Mr
C8H14CdO6
318.59
Monoclinic
C2/c (no. 15)
11.5724(3)
5.4816(2)
16.7944(4)
90
102.941(2)
90
1038.30(5)
4
2.038
2.110
C18H20CdN2O5
456.76
Monoclinic
C2/c (no. 15)
17.3563(4)
11.8464(3)
18.3098(5)
90
97.1720(10)
90
3735.22(16)
8
1.624
1.200
C48H54Cd3N4O16
1280.15
Crystal system
Space group
Triclinic
¯
P1 (no. 2)
˚
a/A
8.9419(2)
11.9987(3)
12.4863(2)
102.4650(10)
91.7580(10)
111.7710(10)
1205.70(5)
1
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
3
˚
V/A
Z
Dc/g cm−3
1.763
1.387
l/mm−1
Total data collected
Unique data
Observed data [I > 2r(I)]
Rmerg
R indexes [I > 2r(I)]
R indexes (all data)
2104
753
735
0.0376
7651
2676
2438
0.0304
5149
3440
3118
0.0179
R1 = 0.0357;a wR2 = 0.901b
R1 = 0.0300;a wR2 = 0.0805b
R1 = 0.0210a; wR2 = 0.553b
R1 = 0.03704;a wR2 = 0.913b
R1 = 0.0327;a wR2 = 0.0827b
R1 = 0.0232a; wR2 = 0.0561b
ꢀ
ꢀ
ꢀ
ꢀ
a R1 = ꢁFo| − |Fcꢁ/ |Fo|. b wR2 = { [w(Fo − Fc2)2]/ [w(Fo2)2]}1/2; w = 1/[r2(Fo)2 + (aP)2 + bP], P = [max.(Fo2,0) + 2(Fc)2]/3, where a = 0.545
and b = 4.8788 for I, a = 0.0394 and b = 10.4253 for II, and a = 0.0321 and b = 0.0 for III.
2
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Table 2 Crystal data and structure refinement parameters for 1,4- and 1,3-CHDCs IV, V and VI
IV
V
VI
Empirical formula
Mr
C48H54Mn3N4O16
1107.77
C48H54Mn3N4O16
1107.77
Monoclinic
C2/c (no. 15)
8.5210(4)
21.5643(10)
26.7853(12)
90
91.0070(10)
90
4921.0(4)
4
1.495
0.833
C8H16CdO7
336.61
Orthorhombic
Pccn (no. 56)
13.1510
20.4388(4)
8.5602(2)
90
Crystal system
Space group
Triclinic
¯
P1 (no. 2)
˚
a/A
8.8827(15)
11.856(2)
12.321(2)
76.791(2)
87.930(3)
68.309(2)
1172.1(3)
1
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
90
90
3
˚
V/A
2300.81(7)
8
1.943
Z
Dc/g cm−3
1.569
0.874
l/mm−1
1.916
Total data collected
Unique data
Observed data [I > 2r(I)]
Rmerg
R indexes [I > 2r(I)]
R indexes (all data)
13718
5463
4366
0.0281
10308
3546
2749
0.0418
8944
1654
1479
0.0329
R1 = 0.0384;a wR2 = 0.0907b
R1 = 0.05777;a wR2 = 0.1542b
R1 = 0.0309;a wR2 = 0.0670b
R1 = 0.0519a; wR2 = 0.0954b
R1 = 0.0779a; wR2 = 0.1694b
R1 = 0.0373;a wR2 = 0.0705b
ꢀ
ꢀ
ꢀ
ꢀ
a R1 = ꢁFo| − |Fcꢁ/ |Fo|. b wR2 = { [w(Fo − Fc2)2]/ [w(Fo2)2]}1/2; w = 1/[r2(Fo)2 + (aP)2 + bP], P = [max.(Fo2,0) + 2(Fc)2]/3, where a =
2
0.0505 and b = 0.0 for IV, a = 0.0845 and b = 16.1649 for V, and a = 0.0185 and b = 7.0434 for IV.
Table 3 Crystal data and structure refinement parameters for 1,3- and 1,2-CHDCs VII, VIII and IX
VII
VIII
IX
Empirical formula
Mr
C40H36Cd2N4O8
925.53
Monoclinic
P21/n (no. 14)
11.6099(2)
17.0455(2)
18.5687(2)
104.8900
3551.29(8)
4
1.731
1.259
C40H40Mn2N4O10
846.64
Monoclinic
P21/c (no. 14)
9.8431(5)
17.6527(9)
11.6066(5)
104.0900(10)
1956.06(16)
2
1.437
0.708
C8H10CdO4
282.56
Monoclinic
C2/c (no. 15)
27.349(7)
4.9842(12)
12.627(3)
96.163(4)
1711.3(7)
8
2.193
2.528
Crystal system
Space group
˚
a/A
˚
b/A
˚
c/A
b/◦
3
˚
V/A
Z
Dc/g cm−3
l/mm−1
Total data collected
Unique data
Observed data [I > 2r(I)]
Rmerg
R indexes [I > 2r(I)]
R indexes (all data)
14758
5076
4509
0.0416
8107
2804
2282
0.0326
4868
1994
1575
0.040
R1 = 0.0500;a wR2 = 0.1336b
R1 = 0.0718;a wR2 = 0.1430b
R1 = 0.0843;a wR2 = 0.2058b
R1 = 0.0556;a wR2 = 0.1375b
R1 = 0.0889;a wR2 = 0.1504b
R1 = 0.1004;a wR2 = 0.2136b
ꢀ
ꢀ
ꢀ
ꢀ
a R1 = ꢁFo| − |Fcꢁ/ |Fo|. b wR2 = { [w(Fo − Fc2)2]/ [w(Fo2)2]}1/2; w = 1/[r2(Fo)2 + (aP)2 + bP], P = [max.(Fo2,0) + 2(Fc)2]/3, where a =
0.0665 and b = 13.3409 for VII, a = 0.0271 and b = 4.6127 for VIII, and a = 0.1345 and b = 0.0 for IX.
2
˚
with the asymmetric unit containing eight non-hydrogen atoms.
The cadmium atom sits on the twofold axis, on an inversion center,
4e. This cadmium atom is in a distorted octahedral environment
molecules and the carboxylate oxygen (H · · · O 1.85(3)–1.90 (3) A,
◦
˚
O · · · O 2.708(3)–2.731(2) A and ∠O–H · · · O 168(2)–173(2) ).
The cadmium 1,4-cyclohexanedicarboxylate [Cd(C8H10O4)-
(C10H8N2)]·H2O, II, is a two-dimensional layer structure (Fig. 2),
formed by the connectivity of Cd2N4O8 dimers and the carboxylate
groups. The asymmetric unit of II contains 27 non-hydrogen
atoms. The cadmium atom is in a distorted pentagonal bipyrami-
dal environment (CdN2O5) with the Cd–O bond distances in the
˚
(CdO6) with the Cd–O bond distances in the 2.295(4)–2.404(4) A
range. Two of the oxygens in the CdO6 polyhedron are from the
coordinated water molecules and the remaining four oxygens are
from two different carboxyl groups with (11) connectivity.36 The
polyhedra are connected to each other by the dicarboxylates with
(1111) connectivity,36 resulting in a one-dimensional infinite zigzag
chain. The cyclohexane ring lies about an inversion center. The two
carboxylate groups are in equatorial position (e,e), the torsional
angle (h) between the two being 180◦. The structure is stabilized
by inter chain hydrogen bonding interaction between the water
˚
2.269(3)–2.624(3) A range and Cd–N bond distances are 2.342(3)
˚
and 2.349(3) A. The two nitrogens of the CdN2O5 polyhedron
are from the terminal 2,2ꢀ-bipy molecule and the oxygens are
from three different carboxylic acid groups with (11) or (21)
connectivity.36 Two such polyhedra form an edge-sharing dimer
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◦
˚
by interlayer p–p interaction (3.663(4) A, 3.77(5) ) between the
adjacent bipy molecules, besides hydrogen bonding between the
lattice water molecules and the carboxylate oxygens (H · · · O 1.8(2)
◦
˚
˚
A, O · · · O 2.834(6) A and ∠O–H · · · O 164 ).
The cadmium 1,4-cyclohexanedicarboxylate, [Cd3(C8H10O4)3-
(C12H8N2)2]·4H2O, III, is a two-dimensional layer structure con-
sisting of one-dimensional infinite chains made up of trinuclear
Cd3N4O12 units connected by the carboxylate groups (Fig. 3).
The asymmetric unit contains 36 non-hydrogen atoms. Two Cd
atoms are in crystallographically independent sites with Cd(1) in
an octahedral environment (CdO6) and Cd(2) is in a distorted
pentagonal bipyramidal environment (CdN2O5). The Cd(1) atom
sits on the twofold axis, on an inversion center, 1b. The Cd–O bond
˚
distances are in the 2.240(2)–2.602(3) A range and the Cd–N bond
˚
distances are 2.331(2) and 2.377(2) A. The oxygens of the Cd(1)O6
polyhedron are from six different carboxyl groups with either
(11) or (21) connectivity.36 The two nitrogens of the Cd(2)N2O5
polyhedron are from the terminal 1,10-phen molecule and the five
oxygens are from three different carboxyl groups with either (11)
or (21) connectivity.36 The Cd(1)O6 polyhedron is connected to
two different Cd(2)N2O5 polyhedra by sharing the edges to form
a trinuclear Cd3N4O12 unit. Four of the l2 oxygen atoms from
four tridentate carboxylates (21) connect the three polyhedra. The
trinuclear unit gets connected to two other similar units by four
different carboxylates (2121) on either side giving rise to an infinite
one-dimensional chain structure. Between the two carboxylate
groups with (2121) connectivity,36 one is in axial position and
the other is in equatorial position (a,e) and the torsional angle
between the two carboxyl groups is 5.84(3)◦. The infinite one-
dimensional chains are connected with each other resulting in
Fig. 1 (a) Structure of [Cd(H2O)2(C8H10O4)], I and (b) the packing
arrangement in I, viewed along the a axis.
Fig. 2 (a) Structure of [Cd(C8H10O4)(C10H8N2)]·H2O, II and (b) view of
the layered structure of II along the b axis.
by sharing the l2 oxygen atom from a tridentate carboxylate (21).
These dimers are connected to four other dimers by four acid
molecules of two types with (2111) connectivity.36 Two of the
carboxylate groups are in equatorial position (e,e), with a torsional
angle (h) of 7.83(4)◦ between the two carboxyl groups. The other
is the (e,e) conformation with h = 168.61(4)◦. The 2,2ꢀ-bipy rings
projects on both the sides of the layer and the structure is stabilized
Fig. 3 (a) Structure of [Cd3(C8H10O4)3(C12H8N2)2]·4H2O, III viewed
along the a axis and (b) structure of III viewed along the c axis (the
rings in 1,10-phen molecules are not shown).
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the infinite two-dimensional layer structure. The two carboxylate
groups in the connecting acid with (1111) connectivity36 are in
equatorial position (e,e) with a torsional angle of 180◦. The lattice
water molecules are between the layers and hydrogen bonded to
the carboxylate oxygens. The ◦structure is stabilized by interlayer
˚
p–p interaction (3.43(1) A, 0.4 ) between the 1,10-phen molecules.
We have also prepared a manganese derivative of 1,4-
cyclohexanedicarboxylic acid, [Mn3(C8H10O4)3(C12H8N2)2]·4H2O,
IV, where all the Mn(II) ions are six coordinated. IV has a two-
dimensional structure similar to that of III (see Fig. 4). The Mn–O
˚
bond distances in IV are in the 2.121(2)–2.371(2) A range and the
˚
Mn–N bond distances are 2.247(2) and 2.299(2) A. Here the a,e
conformer is with (2111) connectivity36 whereas it is (2121) in III.
At 300 K, the leff of Mn in IV is 3.35 lB, larger than the expected
3.13 lB for a magnetically isolated Mn(II) ions in the trinuclear
model. The magnetic susceptibility, vm, fitted to the Curie–Weiss
law, gave a Weiss temperature, h, of −25.7 K for IV, which indicates
weak antiferromagnetic interaction between the Mn(II) centres.
Fig. 5 (a) Structure of [Mn3(C8H10O4)3(C12H8N2)2]·4H2O, V, viewed
along the a axis and (b) structure of V, viewed along the b axis.
˚
bond distances are 2.245(5) and 2.255(5) A. The six oxygens of
the Mn(1)O6 polyhedron are from six different carboxyl with
(11) or (21) connectivity.36 The two nitrogens of the Mn(2)N2O4
polyhedron are from the terminal 1,10-phen molecule and the
oxygens are from three different carboxyl groups with (11) or
(21) connectivity.36 The Mn(1)O6 polyhedron is connected to two
different Mn(2)N2O4 polyhedra by the sharing of two corners, thus
forming the trinuclear Mn3N4O12 unit. Two l2 oxygen atoms from
two tridentate carboxylate (21) connect the three polyhedra. The
trinuclear unit gets connected to two other similar units by six
different carboxylates (2111) on either side resulting in the infinite
one-dimensional chain structure. The connecting acid units are
in two conformations with one having the two carboxylates in
equatorial position (e,e) (torsional angle, 1.05◦) and other acid unit
appearing to have a flattened chair conformation due to the
disorder. The lattice water molecules are between the chains and
are hydrogen bonded to the carboxylate oxygens. The structure is
◦
˚
stabilized by interchain p–p interaction (3.6 A, 0 ) between the
1,10-phen molecules. At 300 K, the leff of Mn in V is 3.59 lB,
larger than the expected 3.13 lB for a magnetically isolated Mn(II)
ions in the trinuclear model (similar to that for IV). Up to 300 K,
the magnetic susceptibility, vm, would be fitted to the Curie–Weiss
law, with a h of −18.2 K, which indicates weak antiferromagnetic
interaction between the Mn(II) centres.
Fig. 4 (a) Structure of [Mn3(C8H10O4)3(C12H8N2)2]·4H2O, IV viewed
along the a axis and (b) the layered structure of IV (the rings in 1,10-phen
molecules are not shown).
1,3-Cyclohexanedicarboxylates
The manganese 1,3-cyclohexanedicarboxylate, [Mn3(C8H10O4)3-
(C12H8N2)2]·4H2O, V, has an infinite one-dimensional chain
structure consisting of the trinuclear Mn3N4O12 unit connected
by the carboxylate groups (Fig. 5), with the asymmetric unit
containing 36 non-hydrogen atoms. Two of the Mn atoms are
in two crystallographically independent sites with Mn(1) in
an octahedral environment (MnO6) and Mn(2) in a distorted
octahedral (MnN2O4) environment. The Mn(1) atom sits on
the twofold axis, on an inversion center, 4e. The Mn–O bond
The cadmium 1,3-cyclohexanedicarboxylate, [Cd(H2O)2-
(C8H10O4)]·H2O, VI, has a two-dimensional layer structure
(Fig. 6) formed by the connectivity between Cd2O13 dimers and the
carboxylate groups. The asymmetric unit of VI contains 17 non-
hydrogen atoms. The cadmium atom is in a distorted pentagonal
bipyramidal environment (CdO7) with Cd–O bond distances in
the 2.258(4)–2.607(4) A range. The seven oxygens of the CdO6
polyhedron are from two coordinated water molecules and four
different carboxylic acid groups with (2111) connectivity.36 Each
˚
˚
distances are in the 2.141(6)–2.424(4) A range and the Mn–N
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The TGA curve of VI shows two weight losses. The first weight loss
◦
of 16.93% around 120 C and the second weight loss of 49.26%
around 380 ◦C match well with the loss of water molecules, and the
cyclohexanedicarboxylate (calc. 16.04% and 50.50% respectively).
The cadmium 1,3-cyclohexanedicarboxylate [Cd(C8H10O4)-
(C12H8N2)], VII, is also a two-dimensional layer structure con-
sisting of an infinite two-dimensional network formed by the
connectivity of Cd2N4O8 dimers and carboxylate groups (Fig. 8).
The asymmetric unit contains 54 non-hydrogen atoms. The cad-
mium atom is in a distorted pentagonal bipyramidal environment
(CdN2O5) with Cd–O bond distances in the 2.233(5)–2.702(5)
˚
˚
A range and Cd–N bond distances in the 2.362(4)–2.405(4) A
range. The two nitrogens of the CdN2O5 polyhedron are from
the terminal 1,10-phen molecule and the oxygens are from three
different carboxyl groups with (11) or (21) connectivity.36 Two
such polyhedra form an edge-sharing dimer by sharing the l2
oxygen atom from a tridentate carboxylate (21). The dimers get
connected with four other dimers by the acid units of two types. In
one type, two of the carboxylate groups are in equatorial position
(e,e) with a torsional angle of 7.83(2)◦. The other acid molecule
appears as though they have a flattened chair conformation due
to the disorder. The 1,10-phen rings project on both the sides of
Fig. 6 Structure of [Cd(H2O)2(C8H10O4)]·H2O, VI, viewed along the b
axis.
CdO7 polyhedron shares an edge with another CdO7 polyhedron
forming the Cd2O13 dimer. The dimers are connected with four
other dimers by a carboxylate group with (11) connectivity,36 form-
ing the infinite two-dimensional network. The cyclohexane rings
project on both the sides of the layer. Both the carboxylate groups
of the 1,3-cyclohexanedicarboxylate are in equatorial position (e,e)
with a torsional angle of 6.11◦. The two lattice water molecules are
between the layers forming four-membered water clusters (Fig. 7).
The O · · · O distances between the water molecules are in the
˚
2.03(1)–2.59(1) range. The short O · · · O distance (2.03 A) is due to
the higher thermal parameter of the oxygen atoms (O100 and O200
with 0.5 occupancy factor). The O · · · O · · · O angles are 83.04(2)
and 92.57(2)◦. The adjustant clusters are twisted with respect to
◦
˚
each other by 55.01(3) and separated by a distance of 2.59(4) A.
Fig. 7 (a) The packing arrangement in [Cd(H2O)2(C8H10O4)]·H2O, VI
and (b) the view of the water clusters in VI. The water molecules are
connected by the dotted lines.
Fig. 8 (a) Structure of [Cd(C8H10O4)(C12H8N2)],VII and (b) packing
arrangement of in VI, viewed along the a axis.
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the layer. The structure is stabilized by intralayer p–p interaction
boxylate groups (Fig. 10). The asymmetric unit contains 13
non-hydrogen atoms. The Cd atom is in a distorted octahedral
environment with Cd–O bond distances in the 2.227(7)–2.413(6)
◦
˚
(3.546(4) A, 7.19(1) ) between the 1,10-phen molecules.
We have also obtained a zero-dimensional 1,3-cyclohexanedi-
carboxylate, [Mn(H2O)(C8H10O4)(C12H8N2)], VIII, containing 28
non-hydrogen atoms in the asymmetric unit. The Mn atom here
is in a distorted octahedral environment (MnN2O4) with Mn–O
˚
A range. The six oxygens of CdO6 polyhedron are from five
different carboxyl groups with (2121) connectivity.36 Each CdO6
polyhedron sharing its edge with another CdO6 octahedron to
form a edge-shared Cd2O11 dimer. These dimers are connected with
four other dimers by sharing the corners, thus forming the infinite
two-dimensional metal–oxygen–metal network, grafted with the
carboxylate groups. The cyclohexane rings in IX project on both
the sides of the layer. Both of the carboxylate groups of the 1,2-
cyclohexanedicarboxylate are in equatorial position (e,e) with a
torsional angle of 60.59(1)◦.
˚
bond distances in the 2.097(4)–2.264(5) A range and the Mn–N
˚
bond distances are 2.244(5) and 2.265(5) A. The two nitrogens
of the MnN2O4 polyhedron are from the terminal 1,10-phen
molecule. The oxygens are from one terminal coordinated water
and the three remaining oxygens are from two different carboxylic
acid groups with (11) or (10) connectivity.36 Two such polyhedra
form a dimer (Fig. 9) with two dicarboxylates (1110 connectivity),
where the two carboxylate groups are in equatorial position (e,e)
with a torsional angle of 4.16(2)◦. The struct◦ure is stabilized by
˚
intermolecular p–p interaction (3.89(1) A, 0.56 ) between the 1,10-
phen molecules and intermolecular CH · · · p interaction between
◦
˚
cyclohexane and 1,10-phen rings (3.24(1) A, 5.83 ). At 300 K, the
leff of Mn in VIII is 4.18 lB, larger than the expected 3.84 lB for a
magnetically isolated Mn(II) ions in the model. Up to 300 K, the
magnetic susceptibility, vm, could be fitted to the Curie–Weiss law,
with a h of −1.5 K. The small h value suggests that compound
is essentially paramagnetic with little or no antiferromagnetic
interaction between the Mn ions.
Fig. 10 (a) Structure of [Cd(C8H10O4)],IX along the
(b) structure of IX, showing the infinite M–O–M linkage.
b axis and
Conclusions
We have successfully prepared 1,4-, 1,3- and 1,2-CHDCs of
cadmium besides 1,4- and 1,3-CHDCs of manganese. In the case
of 1,4-CHDCs, we find only the e,e conformation in the one-
dimensional compound, and a coexistence of the e,e and a,e
conformations in the layered compounds formed by Cd and Mn.
Only the e,e conformation (cis structure) occurs in the 1,3-CHDCs
of Cd and Mn. However, some of the 1,3-compounds also contain
the CHDC in a flattened chair conformation due to the disorder.
The Cd 1,2-CHDC also has e,e conformation. Another aspect
of interest is the formation of the metal–oxygen–metal infinite
Fig.
9
(a) Structure of [Mn(H2O)(C8H10O4)(C12H8N2)], VIII and
(b) packing arrangement in VIII viewed along the a axis.
1,2-Cyclohexanedicarboxylate
The cadmium 1,2-cyclohexanedicarboxylate, [Cd(C8H10O4)], IX,
is a two dimensional layered structure consisting of a two-
dimensional metal–oxygen–metal network grafted by the car-
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linkages. In the light of the available literature,31–34 it appears that
the metal–oxygen–metal infinite linkages are most favored in the
1,2-dicarboxylates. Metal–oxygen–metal networks are known to
occur in 1,2-cyclohexenedicarboxylates.37 The three-dimensional
structures, however, seem to be favored in the 1,4-CHDCs. In
benzenedicarboxylates also, it is the 1,4-isomer that forms three-
dimensional structures.38
The four-membered ring in VIII is reminiscent of the
four-membered secondary building unit in open framework
phosphates.39–42 Whether the four-membered dicarboxylate VIII
can transform to chain, layered and three-dimensional structures is
to be explored. It is noteworthy that the zero- and one-dimensional
metal carboxylates have been found to transform to two- and
three-dimensional structures recently.38,43,44
All the CHDCs, I–IX, exhibit characteristic photoluminescence
(PL) spectra while excited at 268 nm. The parent acids themselves
show luminescence bands in the 350–385 nm region, while the
aromatic amines show a emission band around 450 nm. The main
PL band maxima of the Cd CHDCs are as follows: I, 460 nm, II,
422 nm, III, 389 nm, VI, 422 nm, VII, 390 nm, IX, 460 nm. The
main PL band maxima of all the Mn CHDCs (IV, V and VIII) were
at 422 nm. The Cd and Mn CHDCs exhibit a bathochromic shift
with respect to the acids and a hypsochromic shift with respect
to the amines. The hypsochromic shift of the emission bands of
the compounds with respect to the 1,10-phen and 2,2ꢀ-bipy, may
be because chelation of the ligand to the metal ion increases the
rigidity, thereby reducing the loss of energy by radiationless decay
of the intraligand emission excited state.
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Acknowledgements
The authors thank the Department of Science and Technology and
DRDO (India) for research support and Dr A. Sundaresan for the
help with the magnetic measurements. A. T. thanks the Council of
Scientific and Industrial Research (CSIR), Government of India,
for the award of the Senior Research Fellowship.
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