View PDF VersionPrevious ArticleNext Article
 
DOI: 10.1039/B512843A (Paper) Dalton Trans., 2006, 221-228

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 *
Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur P. O., Bangalore, 560064, India. E-mail: cnrrao@jncasr.ac.in; Fax: +91-80-22082766, 22082766

Received 9th September 2005 , Accepted 21st November 2005

First published on 24th November 2005

Abstract

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

Other than the aluminosilicates and phosphates, metal carboxylates 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 benzenedicarboxylic acids have been found to be the ideal ligands for designing 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 cyclohexanedicarboxylates (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.

Experimental

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 ambient conditions. The starting compositions for the different new CHDCs synthesized by us are as follows, I [Cd(H2O)2(C8H10O4)], 1[thin space (1/6-em)]Cd(OAc)2·2H2O (0.272 g, 1 mM) : 1[thin space (1/6-em)](1,4-CHDC) (0.176 g, 1 mM) : 1[thin space (1/6-em)]piperidine (0.1 ml, 1 mM) : 278[thin space (1/6-em)]H2O (5 ml, 278 mM); II [Cd(C8H10O4)(C10H8N2)]·H2O, 2[thin space (1/6-em)]Cd(OAc)2·2H2O (0.136 g, 0.5 mM) : 2[thin space (1/6-em)](1,4-CHDC) (0.088 g, 0.5 mM) : 1[thin space (1/6-em)](2,2′-bipy) (0.04 g, 0.25 mM) : 2[thin space (1/6-em)]piperidine (0.05 ml, 0.5 mM) : 1111[thin space (1/6-em)]H2O (5 ml, 278 mM); III [Cd3(C8H10O4)3(C12H8N2)2]·4H2O, 2[thin space (1/6-em)]Cd(OAc)2·2H2O (0.136 g, 0.5 mM) : 1[thin space (1/6-em)](1,4-CHDC) (0.088 g, 0.5 mM) : 1[thin space (1/6-em)](1,10-phen) (0.0.05 g, 0.25 mM) : 2[thin space (1/6-em)]NaOH (0.1 ml of 5 M solution, 0.5 mM) : 1111[thin space (1/6-em)]H2O (5 ml, 278 mM); IV [Mn3(C8H10O4)3(C12H8N2)2]·4H2O, 2[thin space (1/6-em)]MnCl2·4H2O (0.102 g, 0.5 mM) : 1[thin space (1/6-em)](1,4-CHDC) (0.088 g, 0.5 mM) : 1[thin space (1/6-em)](1,10-phen) (0.0.05 g, 0.25 mM) : 2[thin space (1/6-em)]piperidine (0.0.05 ml, 0.5 mM) : 1111[thin space (1/6-em)]H2O (5 ml, 278 mM); V [Mn3(C8H10O4)3(C12H8N2)2]·4H2O, 2[thin space (1/6-em)]Mn(OAc)2·4H2O (0.124 g, 0.5 mM) : 1[thin space (1/6-em)](1,3-CHDC) (0.088 g, 0.5 mM) : 1[thin space (1/6-em)](1,10-phen) (0.05 g, 0.25 mM) : 2[thin space (1/6-em)]piperidine (0.0.05 ml, 0.5 mM) : 1111[thin space (1/6-em)]H2O (5 ml, 278 mM); VI [Cd(H2O)2(C8H10O4)]·2H2O, 1[thin space (1/6-em)]Cd(OAc)2·2H2O (0.272 g, 1 mM) : 1[thin space (1/6-em)](1,3-CHDC) (0.176 g, 1 mM) : 2[thin space (1/6-em)]NaOH (0.4 ml of 5 M solution, 2 mM) : 278[thin space (1/6-em)]H2O (5 ml, 278 mM). VII [Cd(C8H10O4)(C12H8N2)], 1[thin space (1/6-em)]Cd(OAc)2·2H2O (0.272 g, 1 mM) : 1(1,3-CHDC) (0.176 g, 1 mM) : 1[thin space (1/6-em)](1,10-phen) (0.199 g, 1 mM) : 2[thin space (1/6-em)]NaOH (0.4 ml of 5 M solution, 2 mM) : 278[thin space (1/6-em)]H2O (5 ml, 278 mM; VIII [Mn(H2O)(C8H10O4)(C12H8N2)], 2[thin space (1/6-em)]Mn(OAc)2·4H2O (0.124 g, 0.5 mM) : 1[thin space (1/6-em)](1,3-CHDC) (0.088 g, 0.5 mM) : 1[thin space (1/6-em)](1,10-phen) (0.05 g, 0.25 mM) : 2[thin space (1/6-em)]piperidine (0.0.05 ml, 0.5 mM) : 1111[thin space (1/6-em)]H2O (5 ml, 278 mM); IX [Cd(C8H10O4)], 1[thin space (1/6-em)]Cd(OAc)2·2H2O (0.272 g, 1 mM) : 1[thin space (1/6-em)](anhydride of 1,2-CHDC) (0.162 g, 1 mM) : 1[thin space (1/6-em)]piperidine (0.1 ml, 1 mM) : 278[thin space (1/6-em)]H2O (5 ml, 278 mM). Powder XRD patterns of the products were recorded using Cu-Kα radiation (Rich-Seifert, 3000TT). The patterns agreed with those calculated for single-crystal structure determination.

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.

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-Kα radiation, λ = 0.71073 Å) operating at 40 kV and 40 mA. An empirical absorption correction based on symmetry equivalent 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 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.

Table 1 Crystal data and structure refinement parameters for 1,4-CHDCs I, II and III
  I II III
a R 1 = ∑‖Fo| − |Fc‖/∑|Fo|. b wR 2 = {∑[w(Fo2 − Fc2)2]/∑[w(Fo2)2]}1/2; w = 1/[σ2(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.
Empirical formula C8H14CdO6 C18H20CdN2O5 C48H54Cd3N4O16
M r 318.59 456.76 1280.15
Crystal system Monoclinic Monoclinic Triclinic
Space group C2/c (no. 15) C2/c (no. 15) P[1 with combining macron] (no. 2)
a/Å 11.5724(3) 17.3563(4) 8.9419(2)
b/Å 5.4816(2) 11.8464(3) 11.9987(3)
c/Å 16.7944(4) 18.3098(5) 12.4863(2)
α/° 90 90 102.4650(10)
β/° 102.941(2) 97.1720(10) 91.7580(10)
γ/° 90 90 111.7710(10)
V/Å3 1038.30(5) 3735.22(16) 1205.70(5)
Z 4 8 1
D c/g cm−3 2.038 1.624 1.763
µ/mm−1 2.110 1.200 1.387
Total data collected 2104 7651 5149
Unique data 753 2676 3440
Observed data [I > 2σ(I)] 735 2438 3118
R merg 0.0376 0.0304 0.0179
R indexes [I > 2σ(I)] R 1 = 0.0357;awR2 = 0.901b R 1 = 0.0300;awR2 = 0.0805b R 1 = 0.0210a; wR2 = 0.553b
R indexes (all data) R 1 = 0.03704;awR2 = 0.913b R 1 = 0.0327;awR2 = 0.0827b R 1 = 0.0232a; wR2 = 0.0561b

Table 2 Crystal data and structure refinement parameters for 1,4- and 1,3-CHDCs IV, V and VI
  IV V VI
a R 1 = ∑‖Fo| − |Fc‖/∑|Fo|. b wR 2 = {∑[w(Fo2 − Fc2)2]/∑[w(Fo2)2]}1/2; w = 1/[σ2(Fo)2 + (aP)2 + bP], P = [max.(Fo2,0) + 2(Fc)2]/3, where a = 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.
Empirical formula C48H54Mn3N4O16 C48H54Mn3N4O16 C8H16CdO7
M r 1107.77 1107.77 336.61
Crystal system Triclinic Monoclinic Orthorhombic
Space group P[1 with combining macron] (no. 2) C2/c (no. 15) Pccn (no. 56)
a/Å 8.8827(15) 8.5210(4) 13.1510
b/Å 11.856(2) 21.5643(10) 20.4388(4)
c/Å 12.321(2) 26.7853(12) 8.5602(2)
α/° 76.791(2) 90 90
β/° 87.930(3) 91.0070(10) 90
γ/° 68.309(2) 90 90
V/Å3 1172.1(3) 4921.0(4) 2300.81(7)
Z 1 4 8
D c/g cm−3 1.569 1.495 1.943
µ/mm−1 0.874 0.833 1.916
Total data collected 13718 10308 8944
Unique data 5463 3546 1654
Observed data [I > 2σ(I)] 4366 2749 1479
R merg 0.0281 0.0418 0.0329
R indexes [I > 2σ(I)] R 1 = 0.0384;awR2 = 0.0907b R 1 = 0.05777;awR2 = 0.1542b R 1 = 0.0309;awR2 = 0.0670b
R indexes (all data) R1 = 0.0519a; wR2 = 0.0954b R1 = 0.0779a; wR2 = 0.1694b R 1 = 0.0373;awR2 = 0.0705b

Table 3 Crystal data and structure refinement parameters for 1,3- and 1,2-CHDCs VII, VIII and IX
  VII VIII IX
a R 1 = ∑‖Fo| − |Fc‖/∑|Fo|. b wR 2 = {∑[w(Fo2 − Fc2)2]/∑[w(Fo2)2]}1/2; w = 1/[σ2(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.
Empirical formula C40H36Cd2N4O8 C40H40Mn2N4O10 C8H10CdO4
M r 925.53 846.64 282.56
Crystal system Monoclinic Monoclinic Monoclinic
Space group P21/n (no. 14) P21/c (no. 14) C2/c (no. 15)
a/Å 11.6099(2) 9.8431(5) 27.349(7)
b/Å 17.0455(2) 17.6527(9) 4.9842(12)
c/Å 18.5687(2) 11.6066(5) 12.627(3)
β/° 104.8900 104.0900(10) 96.163(4)
V/Å3 3551.29(8) 1956.06(16) 1711.3(7)
Z 4 2 8
D c/g cm−3 1.731 1.437 2.193
µ/mm−1 1.259 0.708 2.528
Total data collected 14758 8107 4868
Unique data 5076 2804 1994
Observed data [I > 2σ(I)] 4509 2282 1575
R merg 0.0416 0.0326 0.040
R indexes [I > 2σ(I)] R 1 = 0.0500;awR2 = 0.1336b R 1 = 0.0718;awR2 = 0.1430b R 1 = 0.0843;awR2 = 0.2058b
R indexes (all data) R 1 = 0.0556;awR2 = 0.1375b R 1 = 0.0889;awR2 = 0.1504b R 1 = 0.1004;awR2 = 0.2136b

CCDC reference numbers 283059–283067.

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 derivatives 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.

1,4-Cyclohexanedicarboxylates

The cadmium 1,4-cyclohexanedicarboxylate [Cd(H2O)2(C8H10O4)], I, is a one-dimensional chain structure consisting of octahedral CdO6 units connected by the carboxylate groups (Fig. 1), 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 (CdO6) with the Cd–O bond distances in the 2.295(4)–2.404(4) Å 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 (θ) between the two being 180°. The structure is stabilized by inter chain hydrogen bonding interaction between the water molecules and the carboxylate oxygen (H⋯O 1.85(3)–1.90 (3) Å, O⋯O 2.708(3)–2.731(2) Å and ∠O–H⋯O 168(2)–173(2)°).
(a) Structure of [Cd(H2O)2(C8H10O4)], I and (b) the packing arrangement in I, viewed along the a axis.
Fig. 1 (a) Structure of [Cd(H2O)2(C8H10O4)], I and (b) the packing arrangement in I, viewed along the a axis.

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 bipyramidal environment (CdN2O5) with the Cd–O bond distances in the 2.269(3)–2.624(3) Å range and Cd–N bond distances are 2.342(3) and 2.349(3) Å. The two nitrogens of the CdN2O5 polyhedron are from the terminal 2,2′-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 by sharing the µ2 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 (θ) of 7.83(4)° between the two carboxyl groups. The other is the (e,e) conformation with θ = 168.61(4)°. The 2,2′-bipy rings projects on both the sides of the layer and the structure is stabilized by interlayer π–π interaction (3.663(4) Å, 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) Å, O⋯O 2.834(6) Å and ∠O–H⋯O 164°).


(a) Structure of [Cd(C8H10O4)(C10H8N2)]·H2O, II and (b) view of the layered structure of II along the b axis.
Fig. 2 (a) Structure of [Cd(C8H10O4)(C10H8N2)]·H2O, II and (b) view of the layered structure of II along the b axis.

The cadmium 1,4-cyclohexanedicarboxylate, [Cd3(C8H10O4)3(C12H8N2)2]·4H2O, III, is a two-dimensional layer structure consisting 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) Å range and the Cd–N bond distances are 2.331(2) and 2.377(2) Å. 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 µ2 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 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 π–π interaction (3.43(1) Å, 0.4°) between the 1,10-phen molecules.


(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).
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).

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) Å range and the Mn–N bond distances are 2.247(2) and 2.299(2) Å. Here the a,e conformer is with (2111) connectivity36 whereas it is (2121) in III. At 300 K, the µeff of Mn in IV is 3.35 µB, larger than the expected 3.13 µB for a magnetically isolated Mn(II) ions in the trinuclear model. The magnetic susceptibility, χm, fitted to the Curie–Weiss law, gave a Weiss temperature, θ, of −25.7 K for IV, which indicates weak antiferromagnetic interaction between the Mn(II) centres.


(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).
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 distances are in the 2.141(6)–2.424(4) Å range and the Mn–N bond distances are 2.245(5) and 2.255(5) Å. 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 µ2 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 π–π interaction (3.6 Å, 0°) between the 1,10-phen molecules. At 300 K, the µeff of Mn in V is 3.59 µB, larger than the expected 3.13 µB for a magnetically isolated Mn(II) ions in the trinuclear model (similar to that for IV). Up to 300 K, the magnetic susceptibility, χm, would be fitted to the Curie–Weiss law, with a θ of −18.2 K, which indicates weak antiferromagnetic interaction between the Mn(II) centres.
(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.
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.

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) Å 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 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 forming 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 Å) 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) Å. 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).


Structure of [Cd(H2O)2(C8H10O4)]·H2O, VI, viewed along the b axis.
Fig. 6 Structure of [Cd(H2O)2(C8H10O4)]·H2O, VI, viewed along the b axis.

(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. 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.

The cadmium 1,3-cyclohexanedicarboxylate [Cd(C8H10O4)(C12H8N2)], VII, is also a two-dimensional layer structure consisting 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 cadmium atom is in a distorted pentagonal bipyramidal environment (CdN2O5) with Cd–O bond distances in the 2.233(5)–2.702(5) Å range and Cd–N bond distances in the 2.362(4)–2.405(4) Å 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 µ2 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 the layer. The structure is stabilized by intralayer π–π interaction (3.546(4) Å, 7.19(1)°) between the 1,10-phen molecules.


(a) Structure of [Cd(C8H10O4)(C12H8N2)],VII and (b) packing arrangement of in VI, viewed along the a axis.
Fig. 8 (a) Structure of [Cd(C8H10O4)(C12H8N2)],VII and (b) packing arrangement of in VI, viewed along the a axis.

We have also obtained a zero-dimensional 1,3-cyclohexanedicarboxylate, [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 bond distances in the 2.097(4)–2.264(5) Å range and the Mn–N bond distances are 2.244(5) and 2.265(5) Å. 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 structure is stabilized by intermolecular π–π interaction (3.89(1) Å, 0.56°) between the 1,10-phen molecules and intermolecular CH⋯π interaction between cyclohexane and 1,10-phen rings (3.24(1) Å, 5.83°). At 300 K, the µeff of Mn in VIII is 4.18 µB, larger than the expected 3.84 µB for a magnetically isolated Mn(II) ions in the model. Up to 300 K, the magnetic susceptibility, χm, could be fitted to the Curie–Weiss law, with a θ of −1.5 K. The small θ value suggests that compound is essentially paramagnetic with little or no antiferromagnetic interaction between the Mn ions.


(a) Structure of [Mn(H2O)(C8H10O4)(C12H8N2)], VIII and (b) packing arrangement in VIII viewed along the a axis.
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 carboxylate 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) Å 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)°.
(a) Structure of [Cd(C8H10O4)],IX along the b axis and (b) structure of IX, showing the infinite M–O–M linkage.
Fig. 10 (a) Structure of [Cd(C8H10O4)],IX along the b axis and (b) structure of IX, showing the infinite M–O–M linkage.

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 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 2,2′-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.

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.

References

  1. C. N. R. Rao, S. Natarajan and R. Vaidhyanathan, Angew. Chem., Int. Ed., 2004, 43, 1466 CrossRef CAS.
  2. O. M. Yaghi, H. L. Li, C. Davis, D. Richardson and T. L. Groy, Acc. Chem. Res., 1998, 31, 474 CrossRef CAS.
  3. M. Eddaoudi, J. Kim, D. Vodak, A. Sudik, J. Wachfer, M. O'Keeffe and O. M. Yaghi, Proc. Natl. Acad. Sci. USA, 2002, 99, 4900 CrossRef CAS.
  4. M. Eddaoudi, J. Kim, D. Vodak, A. Sudik, J. Wachfer, M. O'Keeffe and O. M. Yaghi, Science, 2002, 295, 4900.
  5. D. T. Vodak, M. E. Braun, J. Kim, M. Eddaoudi and O. M. Yaghi, Chem. Commun., 2001, 2532 RSC.
  6. H. Li, C. E. Davis, T. L. Groy, D. G. Kelley and O. M. Yaghi, J. Am. Chem. Soc., 1998, 120, 2186 CrossRef CAS.
  7. S. R. Miller, P. A. Wright, C. Serre, T. Loiseau, J. Marrot and G. Férey, Chem. Commun., 2005, 3850 RSC.
  8. K. Barthelet, J. Marrot, G. Férey and D. Riou, Chem. Commun., 2004, 520 RSC.
  9. K. Barthelet, K. Adil, F. Millange, C. Serre, D. Riou and G. Férey, J. Mater. Chem., 2003, 13, 2208 RSC.
  10. C. Serre, F. Taulelle and G. Férey, Chem. Commun., 2003, 2755 RSC.
  11. F. Millange, C. Serre and G. Férey, Chem. Commun., 2002, 822 RSC.
  12. C. Serre, F. Millange, C. Thouvenot, M. Noguès, G. Marsolier, D. Louër and G. Férey, J. Am. Chem. Soc., 2002, 124, 13519 CrossRef CAS.
  13. S. A. Bourne, J. Lu, A. Mondal, B. Moulton and M. J. Zawarotko, Angew. Chem., Int. Ed., 2001, 40, 2111 CrossRef CAS.
  14. B. Moulton, H. Abourahma, M. W. Bradner, J. Lu, G. J. McManus and M. J. Zaworotko, Chem. Commun., 2003, 1342 RSC.
  15. Z. Lin, F. Jiang, L. Chen, D. Yaun and M. Hong, Inorg. Chem., 2005, 44, 73 CrossRef CAS.
  16. Y.-Q. Sun, J. Zhang, Y.-M. Chen and G.-Y. Yang, Angew. Chem., Int. Ed., 2005, 44 DOI:10.1002/anie.200500453.
  17. M.-B. Zhang, J. Zhang, S.-T. Zheng and G.-Y. Yang, Angew. Chem., Int. Ed., 2005, 44, 1388 CrossRef.
  18. Q. Fang, G. Zhu, M. Xue, J. Sun, G. Tian, G. Wu and S. Qiu, Dalton Trans., 2004, 2202 RSC.
  19. B. Moulton and M. J. Zawarotko, Chem. Rev., 2001, 101, 1629 CrossRef CAS.
  20. B. Moulton, J. Lu, R. Hajndl, S. Hariharan and M. J. Zaworotko, Angew. Chem., Int. Ed., 2002, 41, 2821 CrossRef CAS.
  21. J. S. Seo, D. Whang, H. Lee, S. I. Jun, J. Oh, Y. J. Jeon and K. Kim, Nature, 2000, 404, 982 CrossRef CAS.
  22. P. M. Forster and A. K. Cheetham, Angew. Chem., Int. Ed., 2002, 41, 457 CrossRef CAS.
  23. R. Kitaura, K. Fujimoto, S. Noro, M. Kondo and S. Kitagawa, Angew. Chem., Int. Ed., 2002, 41, 133 CrossRef CAS.
  24. N. L. Rosi, J. Eukert, M. Eddaoudi, D. T. Vodak, J. Kim, M. O'Keeffe and O. M. Yaghi, Science, 2003, 300, 1127 CrossRef CAS.
  25. J. L. C. Rowsell, A. R. Millward, K. S. Park and O. M. Yaghi, J. Am. Chem. Soc., 2004, 126, 5666 CrossRef CAS.
  26. B. Paella and M. Hirscher, Adv. Mater., 2005, 17, 538 CrossRef.
  27. J. L. C. Rowsell and O. M. Yaghi, Angew. Chem., Int. Ed., 2005, 44, 4670 CrossRef CAS.
  28. D. S. Kim, P. M. Forster, R. L. Toquin and A. K. Cheetham, Chem. Commun., 2004, 2148 RSC.
  29. P. M. Forster, A. R. Burbank, C. Livage, G. Férey and A. K. Cheetham, Chem. Commun., 2004, 368 RSC.
  30. L. Yi, B. Ding, B. Zhao, P. Cheng, D.-Z. Liao, S.-P. Yan and Z.-H. Jiang, Inorg. Chem., 2004, 43, 33–43 CrossRef CAS.
  31. Y. J. Kim and D. Y. Jung, Chem. Commun., 2002, 908 RSC.
  32. M. Kurmoo, H. K. Kumagai, S. M. Hughes and C. J. Kepert, Inorg. Chem., 2003, 42, 6709 CrossRef CAS.
  33. Y. J. Qi, Y. H. Wang, C. W. Hu, M. H. Cao, L. Mao and E. B. Wang, Inorg. Chem., 2003, 42, 8519 CrossRef CAS.
  34. W. Bi, R. Cao, D. Sun, D. Yaun, X. Li, Y. Wang, X. Li and M. Hong, Chem. Commun., 2004, 2104 RSC.
  35. G. M. Sheldrick, SADABS Siemens Area Detector Absorption Correction Program, University of Göttingen, Gottingen, Germany, 1994 Search PubMed; G. M. Sheldrick, SHELXTL-PLUS Program for Crystal Structure Solution and Refinement, University of Gottingen, Gottingen, Germany, 1997 Search PubMed.
  36. For description of connectivity, see: D. Massiot, S. Drumel, P. Janvier, M. B-Doeuff and B. Buujoli, Chem. Mater., 1997, 9, 6 Search PubMed.
  37. D. S. Kim, P. M. Forster, G. D. de Delgado, S.-E. Park and A. K. Cheetham, Dalton Trans., 2004, 3365 RSC.
  38. A. Thirumurugan and C. N. R. Rao, J. Mater. Chem., 2005, 15, 3852 RSC.
  39. C. N. R. Rao, S. Natarajan, A. Choudhury, S. Neeraj and A. A. Ayi, Acc. Chem. Res., 2001, 34, 80 CrossRef CAS.
  40. A. A. Ayi, A. Choudhury, S. Natarajan, S. Neeraj and C. N. R. Rao, J. Mater. Chem., 2001, 11, 1181 RSC.
  41. M. Dan, D. Udayakumar and C. N. R. Rao, Chem. Commun., 2003, 2212 RSC.
  42. R. Murugavel, M. G. Walawalkar, M. Dan, H. W. Roesky and C. N. R. Rao, Acc. Chem. Res., 2004, 37, 763 CrossRef CAS.
  43. C. Serre, F. Millange, S. Surblé and G. Férey, Angew. Chem., Int. Ed., 2004, 43, 6285 CrossRef.
  44. M. Dan and C. N. R. Rao, Angew. Chem., Int. Ed., 2005 DOI:10.1002/anie.200502413.

Footnote

† Electronic supplementary information (ESI) available: Tables S1–S9: Selected bond distances and angles for I–IX. Fig. S1: Plots of experimental μeffvs. T and 1/χmvs. T of IV, V and VIII. Fig. S2: Photoluminescence spectra of I–IX. See DOI: 10.1039/b512843a
This journal is © The Royal Society of Chemistry 2006
Click here to see how this site uses Cookies. View our privacy policy here.