Organization of Mn-Clusters in pcu and bcu Networks - American

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Organization of Mn-clusters in pcu and bcu networks: synthesis, structure and properties Srinivasan Natarajan, Aninda J Bhattacharyya, Saurav Bhattacharaya, and M. Gnanavel Cryst. Growth Des., Just Accepted Manuscript • Publication Date (Web): 27 Nov 2013 Downloaded from http://pubs.acs.org on December 2, 2013

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Crystal Growth & Design

Organization of Mn-Clusters in pcu and bcu Networks: Synthesis, Structure and Properties

Saurav Bhattacharya,a M. Gnanavel,b Aninda J. Bhattacharyyab and Srinivasan Natarajana*

a

Frameworks Solids Laboratory, Solid State and Structural Chemistry Unit, Indian Institute of Science,

Bangalore – 560012, India.

b

Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore – 560012, India.

*

Corresponding Author: e-mail: [email protected], [email protected]

ACS Paragon Plus Environment


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Abstract Two new anionic inorganic-organic hybrid compounds [H3O][Mn3(µ3-OH)(C14H8O6S)3(H2O)](DMF)5, I, and [H3O]2[Mn7(µ3-OH)4(C14H8O6S)6(H2O)4](H2O)2(DMF)8, II, have been prepared employing mild solvothermal methods. Both the compounds have three-dimensionally extended structures formed by Mn6 and Mn7 clusters, respectively. The connectivity between Mn6 and Mn7 clusters and 4,4’-sulfonyldibenzoic acid anions (SDBA2-) results in a six connected pcu network in I and an eight connected bcu network in II. The presence of hydronium ion (H3O+) along with the solvent molecules in the channels of both the compounds suggested proton conduction in the solids. Proton conductivity studies gave values of ~ 3x10-4 Ω-1cm-1 98% relative humidity in both the compounds. The high activation energies indicate a vehicle mechanism in the compounds, I and II. Magnetic studies indicate antiferromagnetic behavior in both the compounds.


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Introduction The synthesis of solids with tunable voids and channels is an important task for synthetic chemists. The advent of inorganic coordination polymers (CP) or metal organic framework (MOF) compounds provided an opportunity to explore such solids with open structures. Many a times, the prepared compounds have solvent molecules, either coordinated or free, occupying the voids and channels. It has been shown that the solvent molecules can be exchanged / removed by simple post-synthetic modifications, which render the compounds with exposed metal centers and open channels for the exploitation in many areas such as catalysis, sorption and separation processes.1 Recent studies indicate that the presence of solvent molecules, such as water, provide opportunities to explore proton conductivity behavior in some of the CP / MOF compounds. The interest in proton conducting materials are due to the ever increasing energy demand coupled with the dwindling natural resources of the world for cleaner as well as alternate energy sources. Fuel-cell technologies based on hydrogen provide a viable option in the conversion of chemical energy into other useful forms, notably the electrical energy.2 The product of the chemical process in fuel-cells is water and heat, which makes this technology environmentally benign. The implementation of the fuel-cell technology crucially depends on the efficiency of proton conduction. There have been considerable efforts towards this direction, which resulted in new compounds with reasonable proton conduction behavior.3 Modular porous materials such as the MOFs, with solvent molecules occupying channels and voids, have been examined as possible candidates for proton conduction as they can be operated over a range of temperatures (25 - 300°C).4 We have been interested in the assembly of polynuclear metal clusters as building blocks in new MOF structures as they provide fascinating structural arrangements.5 In addition, some of the compounds exhibit interesting magnetic behavior as well.6 In most of these compounds, -O-, -OH or –OH2 units connect more than two metal centers forming high nuclearity metal clusters.7

Such clusters are further joined by aromatic

carboxylates or N-containing ligands giving rise to structures of varying dimensionality. High nuclearity metal clusters forming interesting networks are rare8. This could be due to the coordination restrictions of the participating metal ion along with the steric hindrance posed by the bulky organic ligands employed in the assembly.9 In spite of these limitations, the preparation of high nuclearity metal clusters in extended framework structures could be rewarding for their interesting properties; viz., towards possible single molecule magnetic



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(SMM) behavior.10 As part of our efforts to investigate the formation of new framework compounds, we have explored the reactions between 4,4’-sulfonyldibenzoic acid (H2SDBA) and Mn2+ ions under solvothermal conditions. Our studies have been successful and we have isolated two new compounds, [H3O][Mn3(µ3OH)(C14H8O6S)3(H2O)](DMF)5, I and [H3O]2[Mn7(µ3-OH)4(C14H8O6S)6(H2O)4](H2O)2(DMF)8, II.

The

compounds have Mn6 (I) and Mn7 (II) clusters as part of the structures. The connectivity between the Mn6 and Mn7 clusters through the carboxylate linkers result in pcu (I) and bcu (II) network topologies. In this paper, we describe the synthesis, structure and properties of both these compounds.

Experimental Section Synthesis and Initial Characterization Synthesis of [H3O][Mn3(µ3-OH)(C14H8O6S)3(H2O)](DMF)5, I,: A mixture of MnCl2 (0.3 mmol) and H2SDBA (0.3 mmol) was dissolved in a solvent mixture of DMF/Ethanol (6 ml/2 ml) under constant stirring. 0.06 ml of HBF4 was added and the reaction mixture was homogenized at room temperature for about 10 min. The homogenized reaction mixture with the composition 1MnCl2 : 1H2SDBA : 78DMF : 34C2H5OH : 1HBF4 was transferred to a 23 ml PTFE lined stainless steel autoclave and heated to 110°C for 2 days. The resulting product contained pale Yellow block crystals, which were filtered, washed with dry ethanol and dried in vacuum. The initial and final pH of the reaction was measured to be 1.3 and 5.1, respectively. Elemental analysis (%) for [H3O][Mn3(µ3-OH)(C14H8O6S)3(H2O)](DMF)5 [Found (calcd): C 44.6 (45.7), H 4.7 (4.34), N 4.58 (4.68), S 6.63 (6.42)]. Synthesis of [H3O]2[Mn7(µ3-OH)4(C14H8O6S)6(H2O)4](H2O)2(DMF)8, II,: Compound II was prepared by employing an identical synthetic procedure, except for the addition of 0.023 ml of NH4OH. The reaction mixture with the composition, 1MnCl2: 1H2SDBA: 78DMF : 34C2H5OH : 1HBF4 : 1NH4OH, was homogenized and transferred to a 23 ml PTFE lined stainless steel autoclave and heated to 110°C for 2 days. The resulting product contained colorless block crystals were filtered, washed with dry ethanol and dried in vacuum. The initial and final pH of the reaction was measured to be 2.2 and 5.3, respectively. Elemental analysis (%) for [H3O]2[Mn7(µ3-OH)4(C14H8O6S)6(H2O)4](H2O)2(DMF)8 [Found (calcd): C 42.3 (43.07), H 4.52 (4.2), N 4.21 (3.72), S 6.35 (6.38)]. Initial characterizations were carried out by elemental analysis, powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), IR and UV-Vis spectroscopic studies. Elemental analysis (C, H, N) was


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carried out using a Thermo Finnigan EA Flash 1112 series instrument. PXRD data were recorded in the 2θ range of 5-50° using Cu-Kα radiation (Philips X’pert Pro). The powder XRD patterns were generated from the structures determined using single crystal XRD (simulated PXRD) by using Mercury software (version 1.4.1). The observed PXRD was found to be entirely consistent with the simulated PXRD patterns for both the compounds (ESI, Figure S1). IR spectra for both the compounds were recorded using KBr pellet method (PERKIN ELMER SPECTRUM 1000). The IR spectra exhibited sharp characteristics bands (ESI, Table S1, Figure S2). The IR spectra of compound I exhibited a broad band centered around 3600 – 3300 cm-1, which suggests the presence of water molecules and H3O+ ions. In compound II, distinct peaks corresponding to the lattice and coordinated water molecules as well as H3O+ ions were observed in the IR spectra (3581, 3454, 3342 cm-1, respectively).11 The bands at ~ 3088 cm-1 and ~ 3081 cm-1 for compounds I and II, respectively, correspond to the aromatic C-H stretching frequency of the benzene rings of SDBA2- ions. The bands at ~2972 cm-1and ~2865 cm-1 for I and at ~2939 and ~ 2872 cm-1 for II, respectively, could be due to the asymmetric and symmetric C-H stretching of the methyl groups of the lattice DMF molecules (ESI).11 The two sharp bands at ~1292 cm-1 and ~1217 cm-1 for I and at ~ 1300 cm-1 and ~1221 cm-1 for II correspond to the asymmetric and symmetric stretching of the S=O group of SDBA2- ions. The band at ~569 cm-1 for I and at ~ 577 cm-1 for II corresponds to the stretching frequency of C-S bond in SDBA2- ions.11

Single Crystal Structure Determination Suitable single crystal of I and II was mounted on the tip of a glass fibre using cyanoacrylate glue. .The data were collected at 120(2) K on an Oxford Xcalibur (Mova) diffractometer equipped with an EOS CCD detector. The X-ray generator was operated at 50 kV and 0.8 mA using Mo Kα (λ = 0.71073 Å). Cell refinements and data reductions were performed using Crysalis Red.12 The structure was solved using direct methods and refined employing SHELX97 present in the WINGX suite of programs (version 1.63.04a).13 The hydrogen positions could be assigned to the hydronium ion [O(23)] and the coordinated water molecule [O(13)] in I but not for the disordered solvent DMF molecules. In II, the hydrogen positions could not be assigned to the coordinated water molecules, lattice water molecule [O(23)] and the hydronium ion [O(24)]. In I, only two solvent DMF molecules were located whereas in II none of the solvent DMF molecules could be located. The number of DMF molecules in each compound was arrived at by combining the results of the elemental analysis, IR and TGA studies.

Final refinement included atomic positions for all the atoms, anisotropic thermal

parameters for all the non-hydrogen atoms and isotropic thermal parameters for all the hydrogen atoms. The



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full matrix least square refinement against |F2| were carried out using WinGx package of programs.14 The highly disordered solvent molecules in I and II were accounted for by using the SQUEEZE program present in the WinGX platon program.15 The details of the structure and final refinement parameters are given in Table 1. The CCDC numbers of compound I and II are respectively 928834 and 928835.

Results and Discussion Structure of [H3O][Mn3(µ3-OH)(C14H8O6S)3(H2O)](DMF)5, I The asymmetric unit of I consists of 79 non-hydrogen atoms [ESI, Figure S7(a)]. All the three crystallographically independent Mn2+ ions have distorted octahedral geometry; Mn(1) and Mn(2) have five carboxylate oxygens and a µ3-OH [(O3)] group, and Mn(3) has four carboxylate oxygens, one µ3-OH [O(3)] and a coordinated water molecule [O(13)]. The Mn-O bond distances are in the range 2.081(3) – 2.357(3) Å [av. 2.152 Å for Mn(1), 2.198 Å for Mn(2) and 2.169 Å for Mn(3)]. The O-Mn-O bond angles are in the range 56.90(9) – 179.80(12)°. The selected bond distances and bond angles are listed in the ESI (Tables S2, S3). The SDBA2- anions exhibit differences in the carboxylate bonding with the metal ions. Thus acid-1 has one of the carboxylate groups bonding in the µ2-η2:η1 mode while the other carboxylate has the µ2-η1:η1 mode. Acid-2 has one of the carboxylate groups bonded in the µ3-η1:η2 mode while the other carboxylate group has the µ2-η1:η1 mode. Acid-3 has both the carboxylates bonded with the µ2-η1:η1 mode [ESI, Figure S7(b)]. The Mn2+ ions are connected via the µ3-OH as well as through the six carboxylate groups to form a triangular [Mn3(µ3-OH)(CO2)6] unit, which gives rise to a hexamer [Mn6(µ3-OH)2(CO2)12] through symmetry translation (Figure 1a). The Mn6 clusters are connected to each other through pairs of SDBA2- anions forming a 2D layer (Figure 1b), which are cross linked to form the three dimensional structure possessing one dimensional channels [Figure 1c, S7(e)]. The connectivity between the Mn6 clusters and SDBA2- ions lead to an anionic framework, [Mn6(µ3-OH)(SDBA)6]‾. The charge could then be balanced by the protonation of one of the solvent water molecules present in the structure [Figures 1b, S7(d)]. Thus, the hydronium ions along with the DMF molecules occupy the one dimensional channels. The possibility of hydronium ions in the channels was confirmed from elemental analysis (C, H, N), IR spectroscopy as well as TGA analysis. The hydronium ion [O(23)] also participates in hydrogen bonding through O – H····O type interactions involving the coordinated water [O(13)] and DMF molecule [O(22)]. The O····O distances are in the range of 2.677(10) – 2.852(9) Å and O - H····O


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bond angles are in the range of 146 - 168° [ESI, Table S4]. Similar hydronium ions in the channels have been observed earlier in MOFs.16 From a topological view, each Mn6 cluster is connected to six other Mn6 clusters through pairs of SDBA2- ions. Considering each Mn6 clusters as a node and the pairs of SDBA2- as linkers, we arrive at a pcu (primitive cubic) net with a schläfli symbol of [412.63] (Figure 2).17 The structure can also be visualized by considering the Mn6 clusters as rigid molecular polygons or secondary building units (SBU) with the points of extension being the carboxylate carbon atoms joined together by the SDBA2- linkers, a concept developed by Yaghi et al.18 Each Mn6 clusters is composed of six octahedral Mn2+ ions connected peripherally by twelve carboxylate groups. .Considering the carbon atoms of the twelve carboxylate groups as vertices of a polygon, we arrive at a distorted cuboctahedra SBU with twelve points of extension (Figure 2a). Similar cuboctahedral SBUs have been observed earlier.18a The SDBA2- anions link each cuboctahedra through the edges giving rise to an overall six connected pcu net (Figure 2b,c).

Structure of [H3O]2[Mn7(µ3-OH)4(C14H8O6S)6(H2O)4](H2O)2(DMF)8, II Compound II has 73 non-hydrogen atoms in the asymmetric unit [ESI, Figure S8(a)]. There are four crystallographically independent Mn2+ ions, of which Mn(1) occupies a special position (2a) with a site multiplicity of 0.5. All the Mn2+ ions have distorted octahedral coordination geometry. Mn(1) is coordinated by two carboxylate oxygens and four µ3-OH groups [O(1), O(2)]. Mn(2) and Mn(4) are connected with four carboxylate oxygens, one coordinated water [O(12) for Mn(2) and O(7) for Mn(4)] and one µ3-OH group [O(2) for Mn(2) and O(1) for Mn(4)]. Mn(3) has four carboxylate oxygens and two µ3-OH groups [O(1) and O(2)]. The Mn – O bond distances are in the range 2.079(4) – 2.229(3) Å [av. 2.153 Å for Mn(1); 2.198 Å for Mn(2); 2.135 Å for Mn(3) and 2.168 Å for Mn(4)]. The O – Mn – O bond angles are in the range 78.57(9) - 180°. Selected bond distances and bond angles have been listed in the ESI (Tables S2, S3). The SDBA2- anions exhibit differences in the binding with the Mn2+ ions. Thus, acid-1 has one of the carboxylate groups binding in a µ2-η1:η1 mode while the second carboxylate group bonds with the µ3-η2:η1 mode. The other two SDBA2- anions (acid-2 and acid-3) have similar binding with the µ2-η1:η1 mode [ESI, Figure S8(b)]. The Mn centers are connected through the µ3-OH units forming a seven membered Mn7 cluster. In addition, the Mn centers are also connected through the carboxylate oxygens forming a [Mn7(µ3OH)4(CO2)12] building unit in II [Figure 3a]. The other way to look at this arrangement is to consider six Mn2+



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ions being arranged in a cyclic fashion that resembles a cyclohexane with the seventh Mn2+ [Mn(1)] ion occupying the center. The three dimensional structure of II can be understood by considering the connectivity between the Mn7 clusters and SDBA2- units one fragment at a time. Thus, a one dimensional chain results from the connectivity between Mn7 clusters and SDBA2- anions. Two such chains are oriented in a direction that is mutually perpendicular to each other forming the 2D layers [Figure 3b]. The layers are cross-linked by SDBA2ions giving rise to an anionic three dimensional structure, [Mn7(µ3-OH)4(SDBA)6(H2O)4]2- possessing one dimensional channels [Figures 3c, S8(e)]. The charge is balanced by the presence of a hydronium ions, H3O+, which occupies the one dimensional channels along with the water molecules and the DMF molecules [ESI, Figure S8(d)]. The presence of the hydronium ion was confirmed by a combination of elemental analysis (C, H, N), IR spectroscopy as well as TGA analysis. The hydronium ion [O(23)] would be expected to have O – H····O type hydrogen bond interactions with the carboxylate oxygens [O(4) and O(16)] and the µ3-OH oxygen [O(1)]. From a topological view, each Mn7 cluster is connected to four Mn7 clusters through four pairs of SDBA2- anions and to four other Mn7 clusters through single SDBA2- anions. Considering each Mn7 cluster as nodes and the SDBA2- anions as linkers, one arrives at an eight connected bcu net with a schläfli symbol of [424.64] (Figure 4).17 The structure can also be visualized by utilizing the concept of secondary building unit (SBU)18. Each Mn7 cluster is composed of seven distorted octahedral Mn2+ ions connected peripherally through twelve carboxylate groups. Considering the carbon atoms of the twelve carboxylate groups as vertices of a polygon, we arrive at an SBU with twelve points of extension resembling a highly distorted hexagonal prism (Figure 4a). Distorted hexagonal prismatic SBUs have been observed earlier.18a The SDBA2- anions then link the SBUs (pairs of SDBA2- ions connecting the edges and single SDBA2- ions connecting the corners) giving rise to an overall eight connected bcu net (Figure 4b,c).

Structural Comparison The two hybrid compounds [H3O][Mn3(µ3-OH)(C14H8O6S)3(H2O)](DMF)5, I and [H3O]2[Mn7(µ3OH)4(C14H8O6S)6(H2O)4](H2O)2(DMF)8, II were obtained by employing simple modifications in the synthesis procedure. Compound I was synthesized from a reaction mixture having an initial pH of 1.3 whereas compound II formed from a reaction mixture having an initial pH of 2.2, the higher could be the result of the addition of NH4OH.

The role of pH on the formation of inorganic-organic hybrid structures exhibiting different


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dimensionalities has been investigated.19 The role of pH on the formation of oxo clusters of Mo has been well known.19d In the present study, a marginal increase in the pH of the reaction mixture resulted in having Mn7 cluster in II as compared to the Mn6 cluster in I. It is likely that the variation in the pH could have resulted in an enhanced presence of hydroxide ion (OH‾) in the reaction medium, which leads to the binding of more metal centers forming the metal clusters. Stabilization of high nuclearity divalent transition metal clusters in hybrid structures have been known before and we have summarized the structures in Tables 2 (MII6 clusters) and 3 (MII7 clusters). Of these, the Co6 cluster, observed in [Co6(OH)2(ipa)5(H2O)5].8H2O20a, and the Co7 cluster observed in [Co7(ip)5(OH)4(bpp)2].2H2O21a appear to be related to the present clusters (Figure 5). The Co6 cluster has Co3 triangles formed by µ3-OH groups connected through the µ2-O oxygens of the carboxylate groups forming the cluster; but the main difference is that the cluster is built from a mixture of trigonal bipyramidal and ocatahedral geometries (Figure 5a). The Co7 cluster appears to be more closely related to the Mn7 cluster having the cyclical arrangement of Co2+ ions with the seventh Co2+ occupying the middle. The main difference between the present cluster and the Co7 cluster is that two of the peripheral Co2+ ions are tetrahedrally coordinated whereas all the Mn+2 ions have distorted octahedral coordination (Figure 5b). In terms of the SBU idea, both the Co6 and the Co7 clusters have ten carboxylate groups attached to them and hence form a SBU with ten points of extension. The Mn6 (I) and Mn7 (II) clusters have twelve carboxylate groups attached to them and hence have twelve points of extension (Figure 5). The inter-cluster connectivity gives pcu (I) and bcu (II) topologies (Figures 2c, 4c). The pcu topology is observed in many inorganic-organic hybrid structures, whereas the bcu is rare. Stabilization of bcu related topology using a Co4 cluster was realized from this laboratory.6a Inorganic-organic hybrids with pcu and bcu topologies formed by the connectivity between M6 and M7 clusters have been observed earlier.20a,21b

In

Co6(OH)2(ipa)5(H2O)5].8H2O,20a considering the Co6 clusters as nodes and the isophthalate anions as the linkers, one can visualize the evolution of a pcu network topology [Figure 6a]. In (EMIM)2[Zn7(µ4-O)2(1,4-ndc)6]21b, the connectivity between the heptanuclear Zn cluster (node) and 1,4-naphthalenedicarboxylates (1,4-ndc) (linker) leads to the formation of a bcu topology (Figure 6b). It may be noted that the connectivity between the high nucluarity clusters (M6 and M7 ) could lead to many framework topologies. The topology depends on the type of ligand that is employed in the connectivity between such clusters (Tables 2 and 3). The connectivity of each Mn6 cluster to six other Mn6 clusters in I through the SDBA linkers forms an octahedra (Figure 7a). The octahedra (six Mn6 clusters) can be visualized to form a ReO3-like structure. Of



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course, this visualization gives a macroscopic view of the arrangement of the six Mn6 clusters. Likewise, the interconnectivity between the cubes (eight Mn7 clusters) also gives a body centered cubic arrangement (Figure 7b).

Thermal Studies The thermal stability of the compounds were examined using thermogravimetric analysis (TGA). The studies were carried out under a flow of air (flow rate = 20 ml min-1) in the temperature range of 30 - 850°C (heating rate = 5°C min-1) (ESI, Table S5, Figures S9, S10). Compound I shows four distinct weight loss regions in the TGA curve. The first sharp weight loss of ~15% in the temperature range 50-150°C correspond to the loss of three DMF molecules. The second gradual weight loss of ~10.3% in the temperature range of 150350°C corresponds to the loss of two DMF molecules. The third sharp weight loss of ~54.8% in the temperature range 350-390°C may correspond to the destruction of the framework with the loss of SDBA2-, water and H3O+. The fourth weight loss of ~4.1% was very broad. Compound II also shows four weight loss regions in the TGA curve. The first weight loss of ~12% in the temperature range 95-160°C corresponds to the loss of five DMF molecules. The second gradual weight loss of ~7.4% in the temperature range 160-270°C correspond to the loss of three DMF molecules. The third weight loss of ~4.9% in the temperature range 270-390°C corresponds to the loss of water and H3O+. The fourth weight loss of 56.1% in the temperature range 390-670°C may correspond to the final destruction of the framework with the loss of the SDBA2- ions. The final products of TGA analysis in both the compounds were found to be Mn2O3 (JCPDS: 89-4836) and Mn3O4 (JCPDS: 24-0734). The stabilities of the compounds were also investigated employing the TGA and PXRD studies to probe the changes that accompany the desolvation and resolvation of the guest meolcules. To this end, the as-synthesized compounds were desolvated by heating them at 130°C (I) and 155°C (II) for four hours and then resolvated by immersing in DMF/Ethanol solvent mixtures at 80°C. TGA studies on the desolvated compounds did not exhibit any initial weight losses observed during the TGA studies of the as-synthesized compounds (ESI, Figures S9, S10). The weight losses observed on the desolvated compounds were comparable (~80%), which suggests that the compounds lose only the organic ligands. TGA studies of the resolvated I and II exhibit a behavior reminiscent of the as-synthesized compounds. This study suggests that the compounds on heating at 130°C (I) and at 155°C (II) retain the parent crystal structure. PXRD patterns of the desolvated I and II show reasonable framework stability with partial loss of crystallinity, and the compounds appear to regain their crystallinity during the resolvation step (ESI, Figures S9, S10).


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Water Sorption Studies From the TGA and PXRD studies, it appears that the occluded solvent molecules could be partially removed by heating the samples at 130°C (I) and 155°C(II). The PXRD studies of the compounds heated at these temperatures indicated that the solids retain their crystallinity suggesting that the gross structure remains largely unaltered.

This prompted us to examine the possibility of reversible water adsorption-desorption

behavior in I and II. We investigated the reversibility of water adsorption employing a modified TGA setup containing a port for introducing the water vapor. Samples were taken in a TGA crucible and heated to 130°C for I and 155°C for II in an atmosphere of flowing dry nitrogen (50mL/min). The samples were subsequently cooled to room temperature and nitrogen gas bubbling through water was allowed to pass into the system for possible rehydration for 60 min. During this process, we observed that both I and II exhibited only partial reabsorption of water molecules. Thus, 86.5% and 84.9% of the initial weight was absorbed from the dehydrated weights of 82.6% and 81%, which corresponds to ~ 3 moles and ~ 6 moles of water per mole of I and II, respectively (ESI, Figure S11). This dehydration-rehydration experiment was repeated on the same sample resulting in similar behavior. It may be noted that we could not reach the expected weight gain during the rehydration process, which may suggest that the water uptake is quite sluggish. In order to probe this behavior a little deeper, we sought to carry out an experiment by performing a water sorption isotherm. To this end, a preheated sample of I (130°C, four hours) and II (155°C, four hours) was employed and the water adsorption isotherms were measured at 298K. Both the compounds exhibited a slow but gradual uptake of water reaching a value of 160 mL/g (equivalent to 8 mole H2O/mole of I) and 200 mL/g (equivalent to 19 mole H2O/mole of II) at p/po = 0.9 (Figure 8). The water adsorption isotherm was completed over a period of 30 hours. The discrepancy in the uptake values between the cyclic TGA studies and water adsorption isotherms for both the compounds could be due to the longer duration of exposure to the saturated water vapor. Both the compounds exhibited a hysteresis in the adsorption-desorption cycle, which suggest that the water molecules are strongly adsorbed in the one-dimensional channels.

Proton Conductivity Studies The presence of a number of guest molecules exhibiting hydrogen bond interactions in I and II suggested the possibility of examining the proton mobility. To probe the proton conductivity behavior, acimpedance spectroscopy studies (Alpha, Novocontrol) were carried out by scanning the samples in the



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frequency range 0.1 – 106 Hz (signal amplitude: 0.12 V). The sample pellets were sandwiched between two stainless steel electrodes and exposed to different relative humidity values and different temperatures employing an indigenously fabricated cell. The compounds were exposed and equilibrated at different relative humidities for 24 hrs before the proton conductivity experiments. The PXRD studies on the samples exposed to 98% relative humidity for 24 hours did not reveal any noticeable changes (ESI, Figure S13). At 34°C and 98% relative humidity, we observed proton conductivity values of 3×10-4 and 3.44×10-4 Ω-1cm-1for I and II, respectively (Fig 9,10, Table 4). These values are higher than those reported for PCMOF-3 (3.5x10-5 Ω-1cm-1 at RT and 98% RH).4f The proton conductivity values are also comparable to the values observed in Gd3(H0.75O3PCHOHCOO)4.xH2O , (3.2x10-4 Ω-1cm-1 at 21°C and 98% RH).22 The values, however, are marginally lower than that found in (NH4)2(adp)[Zn2(ox)3].3H2O (8×10-3 Ω-1cm-1 at 25°C and 98% RH).23 The proton conductivity studies also reveal that both the compounds I and II exhibit profound dependence for the relative humidity, decreasing with lower relative humidity values. Thus, conductivity values of the order of ~10-5–10-6 Ω-1cm-1 at 85% humidity, ~10-7 Ω-1 cm-1 at 75% humidity and ~10-8 Ω-1 cm-1 at 51% humidity have been observed for both the compounds (Table 4). Marginally higher proton conductivity values were observed in II compared to I, which could be due to the presence of larger number of guest molecules in II. Two distinct mechanisms, Grotthus or vehicular mechanism,3c have been well known for the proton migration in solids. The activation energies for the proton migration give reasonable insight into the possible mechanism for the movement of protons in solids. In the present study, the activation energies at 51% humidity (the lowest observed proton conductivity values) are 0.52 eV for I and 0.68 eV for II (Figure 11). These values are higher than the activation energies observed in other compounds that follow the Grotthus mechanism (0.1 – 0.5 eV). In the vehicular mechanism, the activation energies are generally > 0.6 eV.4 From the present studies it is clear that the lowest values of activation energies are already higher than the general threshold values under the Grotthus mechanism. The activation energies at ~ 98% humidity were found to be 0.93 eV and 1.16 eV, respectively for I and II (Figure 11, Table 4). These values are typically observed for proton conductors that follow the vehicle mechanism.

Since the present structures contain (H3O)+ cations in the channels, it is

conceivable that the extra-framework hydronium ion act as the vehicle to transport the protons in these solids. Similar proton conduction in modular porous compounds has been observed.3a, 25


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Magnetic Studies Magnetic studies were carried out in the temperature range 5-300K using a SQUID magnetometer (Quantum Design Inc., USA) (Figures 12, 13). The studies indicate that the overall magnetic behavior is antiferromagnetic. The room temperature values of χmT per Mn3 units in I and Mn3.5 units in II were found to be 18.6 and 16.4 emu mol-1K, respectively. These values are larger than the expected spin-only values of 13.1 and 15.3 emu mol-1K, respectively, for the magnetically isolated high spin Mn2+ ions (S= 5/2) indicating strong magnetic interactions between the Mn2+ ions. The field-cooled (FC) and zero-field cooled (ZFC) susceptibilities did not exhibit any clear divergence even at low temperatures indicating the absence of any long range magnetic correlations between the Mn centers. From a fit of the magnetic susceptibility values in the high temperature region (75 - 300°C) for the Curie-Weiss law, θp values of -107.1 K and -54.1 K, were obtained for I and II, respectively. The high θp values suggest that the Mn2+ ions interact anti-ferromagnetically. Although both the compounds have clusters of Mn2+ ions, we did not observe any signatures suggestive of a single molecule magnetic behavior in I and II. The large separation of the magnetic clusters (Mn6 and Mn7) coupled with the isotropic nature of the spins of Mn2+ ions (d5) under an octahedral field could have contributed to the observed anti-ferromagnetic behavior in I and II.

Conclusion In conclusion, two new inorganic-organic hybrid compounds have been synthesized and characterized. Both the compounds are anionic and the structures have Mn6 (I) and Mn7 (II) clusters connected through SDBA2- anions. The charge compensation is through the H3O+ ions which are located in the one-dimensional channels. The connectivity between the building units (Mn6/Mn7 clusters) gives rise to pcu (I) and bcu (II) network topologies. Both the compounds exhibit good proton conductivity with values of ~ 3x10-4 Ω-1cm-1at 34°C and 98% RH. The proton conductivity values are comparable with some of the well established proton conducting hybrid compounds. The activation energies suggest a vehicle mechanism, which is not surprising as the channels contain H3O+ ions. Magnetic studies indicate predominantly antiferromagnetic behavior in both the compounds.



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Acknowledgements Authors thank Council of Scientific and Industrial Research (CSIR), Government of India for the award of a fellowship (SRF to SB) and a research grant (SN). SN thanks the Department of Science and Technology (DST), Government of India for a J.C. Bose National Fellowship and AJB thanks DST-Nano Mission for financial support.

Supporting Information Available IR, UV-Visible spectra of the compounds; PXRD patterns and TGA of the compounds; important bond distances, bond angles and hydrogen bond distances in the compounds and additional structural figures. This material is available free of charge via the internet at http://pubs.acs.org.


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Figure Captions Figure 1 (a) The Mn-Hexamer observed in compound I.. 2-

(b) The connectivity between the Mn6 clusters and SDBA units forming a 2D arrangement. Some of

the DMF molecules along with the hydronium ions are shown (c) The observed 3D structure of I. Figure 2 (a) The Mn6 cluster and the distorted cuboctahedral SBU observed in I (b) The connectivity between the cuboctahedral SBUs. Note the formation of the pcu net. (c) The pcu net Figure 3 (a) The Mn-Heptamer observed in compound II. Mn1 (green color) occupies the inversión center (see text). (b) The connectivity between the Mn7 clusters and SDBA

2-

units forming a 2D arrangement. The

solvent molecules are not shown for clarity. (c) The 3D structure of II. Figure 4 (a) The Mn7 cluster and the distorted hexagonal prism SBU observed in II. (b) The connectivity between the SBUs.

Note the formation of bcu topology (green lines =

connectivity through two SDBA2- anions, pink lines = connectivity through one SDBA2- anion. The blue lines are the guide to the the body centered arrangement). (c) The bcu net. Figure 5 (a) The Co6 cluster in Co6(OH)2(ipa)5(H2O)5].8H2O20a. Note the close similarity to the present Mn6 cluster (I) (b) The Co7 cluster in [Co7(ip)5(OH)4(bpp)2].2H2O21a. Note the close similarity to the Mn7 cluster (II). Figure 6 (a) The pcu topology observed in Co6(OH)2(ipa)5(H2O)5].8H2O20a. (b) The bcu topology observed in (EMIM)2[Zn7(µ4-O)2(1,4-ndc)6]21b.



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Figure 7 (a) The six Mn6 clusters forming a big octahedral structure, which are connected to form a ReO3 like structure.. (b) The eight Mn7 clusters forming a big cubic arrangement, which forms a body-centered cubic structure. The pink cube represents the body-center.. Figure 8 (a) Water vapor adsorption - desorption isotherms of compound I (b) Water vapor adsorption – desorption isotherms of compound II. Figure 9 Nyquist plots of proton condcution for the compound I at (a) 98%, (b) 85% and (c) 75% and (d) 51% relative humidities and at different temperatures. Figure 10 Nyquist plots of proton condcution for the compound II at (a) 98%, (b) 85% and (c) 75% and (d) 51% relative humidities and at different temperatures. Figure 11 (a) Activation energies for the proton conduction of compound I at different RH (b) Activation energies for proton conduction of compound II at different RH Figure 12 (a) FC – ZFC plots of compound I (b) χmT vs T plot of I. (Inset shows the 1/χm vs T plot of I) Figure 13 (a) FC-ZFC plots of compound II (b) χmT vs T plot of II. Inset shows the 1/χm vs T plot of II.


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Table 1: Crystal data and structure refinement parameters of compounds I and II. Structural Parameter

I

II

Empirical formula

C48H25N2O23S3Mn3

C84H48O48S6Mn7

Formula weight

1263.74

2402.16

Crystal system

Monoclinic

Monoclinic

Space group

P21/n (no.14)

P21/n (no.14)

a(Å)

15.9995(5)

18.0352(10)

b(Å)

18.1852(7)

25.8676(13)

c(Å)

24.8199(7)

18.0584(9)

α(°)

90

90

β(°)

102.917(3)

118.861(3)

γ(°)

90

90

Volume (Å3)

7038.7(4)

7378.3(7)

Z

4

2

Temperature(K)

120(2)

120(2)

ρcalcd (gcm-3)

1.193

1.081

µ (mm-1)

0.683

0.729

Wavelength (Å)

0.71073

0.71073

θ range (deg)

2.39 to 26.00

1.51 to 26.00

R index [I>2σ(I)]

R1 = 0.0647, wR2 = 0.1823

R1 = 0.0696, wR2 = 0.1820

R (all data)

R1 = 0.0883, wR2 = 0.1996

R1 = 0.1391, wR2 = 0.2040

R1 = Σ|| Fo | - | Fc || / Σ | Fo |; wR2 = {Σ [w (Fo2 – Fc2)]/Σ [w (Fo2) 2]}1/2 . w = 1/[ρ2(Fo)2+(aP)2+bP]. P = [max (Fo, O)+2(Fc) 2]/3, where a = 0.1036 and b = 0.0000 for I, a = 0.1121 and b = 0.0000 for II.



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Table 2: Comparison of the transition metal Hexanuclear (MII6) clusters reported in literature with the compound I Compoundsref

Cluster Unit

Connectivity within the MII6 cluster unit

Linkers and topology (using MII6

[Mn6(µ3-OH)2(COO)12]2-

Compound 1

cluster as node)

Six octahedral manganese connected

SDBA2- connects the Mn6

through corners and edges via µ3-OH

cluster nodes forming a six

and carboxylates

connected

net

with

pcu

topology

[Co6(µ3-OH)2(ipa)5(H2O)5].8H2O20a

Co(PAC)(HCOO)20b

[Co6(µ3-OH)2(COO)10]

[Co6(COO)12]

Four octahedral, one tetrahedral and

ipa connects the Co6 cluster

one trigonal bipyramidal Co centers

nodes

connected through edge and corner

connected

sharing.

topology.

Six corner shared distorted cobalt

PAC connects the Co6 clusters

octahedra

to form the six connected

connected

through

carboxylate groups to form a cyclic Co6

forming pcu

the

six

network

interpenetrated pcu topology

cluster.

Zn6(NDC)5(µ3-OH)2(DMF)2·4DMF20c

[Zn6(m-O3S-Ph-PO3)4(4,4’20d

bpy)6(H2O)4].18H2O

[Zn6(µ3-OH)2(COO)10]

[Zn6(PO3)4]4+

Two Zn3 triangles formed out of corner

NDC connects the Zn6 clusters

shared tetrahedral and octahedral zinc

to form the six connected

centers, bridged by carboxylate groups

network with pcu topology.

Two distorted octahedral and four

4,4’-bpy connects the Zn6

distorted

clusters forming a uninodal

tetrahedral

zinc

centers

connected through phosphonate groups

eight connected bcu topology


Illustrations (MII6 cluster and Framework topology)

Page 23 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48


[Zn12(µ6-O)2(TCOPM)4].3H2O.8NO3

[Zn6(µ6-O)(COO)6]4+

20e

.8DMF

Six distorted tetrahedral Zn centers are

TCOPM connects the Zn6

edge

clusters to form the binodal

shared

through

µ6-O

and

(3,6) connected network with

carboxylate oxygens.

pyr topology.

Cu6(µ3-O)(µ3-OH)(pyz)6(BTC)20f

[Cu6(µ3-O)(µ3-

Two Cu3 triangles formed out of three

BTB

OH)(pyz)6(COO)3]

distorted square planar Cu centers,

clusters to form a binodal (3,3)

connects

three pyrazolates and one µ3-O group

connected

bridged by three carboxylates.in a face

topology

net

each

with

Cu6 srs

to face mode

[(CH3)2NH2][Zn6(µ3-OH)(µ4-

[Zn6(µ3-OH)(µ4-


O)(H2O)2(BBS)5].DMFx20g

O)(H2O)2(COO)9]

distorted tetrahedral Zinc centers are

BBS connects the Zn6 clusters to form a 5 connected net with

connected through corners via µ3-OH,

sqp topology

µ4-O and carboxylate groups..

Co6(µ3-OH)2(PCN)1020h



Bridging PCN group leads to

distorted

the formation of a molecular

tetrahedral

Co

centers

connected via corner and edge sharing.

complex

[Zn9(BTB)4(odabco)3(µ3-O)3(µ2-

[Zn6(µ3-OH)2(odabco)2(µ2-

Six distorted octahedral Zinc centers

BTB connects the Zn6 clusters

H2O)6].16DEF20i

H2O)4(COO)8]

connected through faces and corners

to form the binodal (3,12)

via

connected net with

µ3-OH,

carboxylates.

odabco,

µ2-H2O

and

28

34 4

schläfli 3

symbol (4 .6 8 )3(4 )8



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

[Mn6(HCOO)6(BTC)2(DMF)6]20j

[Mn6(HCOO)6(COO)6]

Page 24 of 49

Six distorted octahedral manganese are

BTC connects the Mn6 cluster

connected in a cyclic fashion via

nodes

carboxylate oxygens

dimensional

to

form

connected

a

binodal net

two (3,6)

with

kgd

topology

[Co3(met)(µ3-

[Co6(µ3-

Four octahedral and two tetrahedral Co

Sip and datrz connect the Co6

OH)2(datrz)(sip)].2.25H2O20k

OH)4(COO)4(datrz)2]2+

centers connected through corner and

cluster nodes to form a binodal

edge sharing via µ3-OH, carboxylates

(3,8)

and bridging datrz groups

schläfli

connected

net

with

symbol

(4.5.6)2(42.56.611.76.82.9)

Co(PYNT)(H2O)220l

[Co6(COO)6(H2O)12]6+

Six distorted octahedral cobalt centers

PYNT

are connected by six carboxylate

clusters to form the binodal

connects

the

Co6

groups in a cyclic fashion

(3,18) connected net with schläfli symbol (43)(439.666.848)

Co3(BTB)1.5(Im)1.35(O)0.5(OH)0.5(H2O)1.65

[Co6(µ3-OH)2(COO)9]+

20m

[Mn6(O2CPh)10(µ4-OH)2(CH3OH)3 (H2O)].1.5(pz)20n

[Mn6(µ4-OH)2(COO)10]

Two Co3 triangles, formed by corner

BTB connects the Co6 clusters

sharing of two distorted Co octahedra

to

and one tetrahedral, bridged by three

connected net with

carboxylate groups

symbol (43)3(49.627)

form

a

binodal

(3,9) schläfli

Six distorted octahedral Mn centers are

The benzoate ligand bridges

edge

the manganese centers to form

shared

through

carboxylate groups.

µ4-OH

and

the

overall

structure.


molecular

Page 25 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

[Mn6(SPPA)4(phen)6(H2O)4].5H2O20o


[Mn6(PO3)4]4+

Four distorted octahedral and two

SPPA

distorted square pyramidal Mn centers

clusters

connects

corner shared through phosphonate

dimensional chains

to

the form

Mn6 one

groups

ipa = isophthalic acid; BTC = 1,3,5-benzenetricarboxylic acid; DMF = N,N’-dimethylformamide; met = metanol; datrz = 3,5-diaminotriazole; sip = 5-sulfoisophthalic acid; PYNT = 5-(3’-carboxylphenyl)nicotinic acid; BTB = Benzene-1,3,5-tribenzoate; Im = Imidazole; pyz = pyrazole; BBS = 4,4’-dibenzoic acid-2,2’-sulfone; PCN = phenylcinnamate; odabco = N-oxide-1,4-diazabicyclo[2.2.2]-octane; DEF = N,N’-diethylformamide; PAC = (E)-3-(pyridine-3-yl)acrylate; NDC = 1,4-naphthalenedicarboxylic acid; TCOPM = tris-(p-carboxyphenyl)-methane; SPPA = m-sulfophenylphosphonic acid; phen =- 1,10-phenanthroline; pz = pyrazine.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Page 26 of 49

Table 3: Comparison of the Transition metal Heptanuclear (MII7) clusters reported in literature with the compound II Compoundsref

Cluster Unit

Connectivity within the MII7 cluster unit

Linkers and topology (using MII7 cluster as node)

Compound II

[Mn7(µ3-

Seven

OH)4(COO)12]2-

connected through corners and edges

octahedral

manganese

SDBA2-

connects

the

Mn7

cluster nodes forming an eight connected

net

with

bcu

topology

[Co7(ipa)5(µ3-OH)4(bpp)2].2H2O21a


Five octahedral Mn and two tetrahedral Mn centers connected thrrough corners and edges via µ3-OH and carboxylate groups

Ipa and bpp connects the Mn7 cluster nodes to form an eight connected

net

with

sqc117

topology having the schläfli symbol [36.412.58.62]

(EMIM)2[Zn7(µ4-O)2(1,4-ndc)6]21b

[Zn7(µ4-O)2(COO)10

One

six

ndc connects the Zn7 clusters to

distorted tetrahedral Zinc centers corner

distorted

octahedral and

form the eight connected net

shared through µ4-O and carboxylate

with bcu topology

groups

Zn7(µ3-OH)2(btc-NO2)4(bpp)2(H2O)221c

Co7(µ3-OH)8(ox)3(ppz)321d

[Zn7(µ3-OH)2(COO)10]2+

[Co7(µ3-OH)8]6+

Two Zn3 triads, formed out of corner

btc-NO2 and bpp connect the

sharing of two distorted Zn tetrahedra

Zn7 clusters to form an eight

and one octahedra. are bridged by a

connected

distorted Zn octahedra

topology.

Seven distorted octahedral Cobalt edge

Ppz and ox connect the Co7

connected through µ3-OH groups

clusters to form a uninodal 12

net

with

connected net with a 18

42

6

symbol (3 .4 .5 )


bcu

schläfli

Illustrations (MII7 cluster and Framework topology)

Page 27 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

[Co8(tbip)6(µ3-OH)4(H2O)9]·12(H2O)21e


[Co7(µ3-OH)4(COO)9]+

cobalt

Tbip and mononuclear Co+2

centers corner and edge shared through

ions connect Co7 clusters to

µ3-OH and carboxylate groups

form a binodal (3,6) connected

Seven

distorted

octahedral

2D net with 3

9

schläfli symbol

6

(4 )(4 .6 )

Zn7(µ4-O)2(CH3CO2)10(bpe)21f

[Zn7(µ4-O)2(COO)10

One

distorted

octahedral and

six

Bpe connects the Zn7 clusters to

distorted tetrahedral Zinc centers corner

form

shared through µ4-O and carboxylate

chains

the

one

dimensional

groups [Mn7(trz)8(CH3CO2)4(µ3-OH)2].2.5H2O21g

[Mn7(µ3-

Two triads containing two octahedral

trz connects the Mn7 cluster

OH)2(COO)4(µ2-trz)8

Mn and one square pyramidal Mn

nodes

connected by an octahedral Mn through

connected net with hexagonal

corner sharing.

primitive topology

and

square

pyramidal

Bridging

forming

phen

an

and

eight

[Mn7(µ3-OH)2(OSPA)4(phen)8].10H2O.

[Mn7(µ3-OH)2(µ3-

Octahedral

OSPA

phen21h

ASO3)4(µ2-SO3)2]

manganese connected through corners

groups leads to the formation of

and edges via µ3-OH, sulfonates and

a molecular complex.

arsonates..

[Zn7(µ4-O)2(pda)5(H2O)2].5DMF.4EtOH. 6H2O21i

[Zn7(µ4-O)2(COO)10]

Four distorted tetrahedral and three

pda connects the Zn7 clusters to

distorted octahedral Zinc centers corner

form a six connected net with

and face shared through

pcu topology.

µ4-O and

carboxylate groups

[H3O][Zn7(µ3-OH)3(BBS)6].13DMF20g

[Zn7(µ3-OH)3(COO)9]2+

Three pairs of corner shared distorted

BBS connects the Zn7 clusters

tetrahedral

to form a six connected network

Zn

centers

are

linked

through a distorted octahedral Zn via

with a distorted pcu topology.

µ3-OH and carboxylate groups.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

[Zn7(µ4-O)2(bpdc)4(dmpp)2]·6DEF·10H2O21j

[Zn7(µ4-O)2(NN)2 (COO)8]

Distorted tetrahedral and octahedral Zn

Bpdc and dmpp connect the Zn7

µ4-O,

clusters to form a six connected

centers corner shared through dmpp and carboxylate groups

[Zn7(µ2-OH)8(DTA)3].H2O21k

[Zn7(µ2-OH)8]6+

net with pcu topology

Seven distorted tetrahedral Zn centers

DTA connects the Zn7 clusters

corner shared through the

to form the six connected net

µ2-OH

with pcu topology.

groups

[Zn7(trz)6(1,2,4,5-BTC)2(H2O)6].8H2O21l

[Zn7(trz)6]8+

Two

tetrahedral,

two

trigonal

pyramidal and three octahedral Zn centers linked by six triazole units

(HN(C2H5)3)4[Zn7(L)6]·2H2O21m

[Zn7(PO3)6]2+

Six distorted trigonalbipyramidal and one octahedral Zn centers corner shared through phosphonate groups

[Zn7(ipa)6(µ3-OH)4(H2O)2]·6DMF·4H2O20c

[Zn7(µ3-OH)4(COO)8]2+

Four tetrahedral and three octahedral Zn centers edge and corner shared through µ3-OH and carboxylate groups

[Co7(bzp)6(N3)9(CH3O)3].2ClO4.2H2O21n

[Co7(N3)9(CH3O)3]2+

Seven distorted octahedral Co centers edge shared through azide and methoxy groups

The BTC and triazole moieties connect the Zn7 clusters to form the binodal (4,10) connected net with schläfli symbol (3.43.52)2(34.48.514.616.7.82)

Bridging ligand L leads to the formation of the molecular complex

ipa connects the Zn7 clusters to form the six connected net with pcu topology.

Bzp bridges the cobalt centers forming the cyclic disc like molecular complex


Page 28 of 49

Page 29 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

[KCo7(µ3-OH)3(ipa)6(H2O)4]·12H2O21o


[Co7(µ3-OH)3(COO)12]-

Seven distorted octahedral Co centers edge and corner shared through µ3-OH and carboxylate groups

[Co7(µ3-OH)4(ina)4(ipa)3(H2O)2]·10H2O21p


Seven distorted octahedral Co centers corner and edge shared through µ3-OH and carboxylate groups

The connectivity between the Co7 clusters, ip and K+ ion leads to a NaCl net. Green lines indicate connectivity through isophthalate and K+ while yellow lines indicate connectivity through isophthalates only. ina and ipa connects the Co7 clusters to form the eight connected net with hexagonal primitive topology

ipa = isophthalic acid; bpp = 1,3-bis(4-pyridyl)propane; trz = 1,2,4-triazole; OSPA = o-sulfophenylarsonic acid; phen = 1,10-phenanthroline; ox = oxalic acid; ppz = piperazine; tbip = 5-tertiarybutylisophthalic acid; bpe = 1,2-bis(4-pyridyl)ethane; 1,4-ndc = 1,4-naphthalenedicarboxylic acid; btc-NO2 = 5-nitro-1,2,3-benzenetricarboxylic acid; bpp = 1,3-bi(4-pyridyl)propane; pda = p-phenylenediacrylic acid; BBS = 4,4’-dibenzoic acid-2,2’-sulfone; bpdc = 4,4’-biphenyldicarboxylic acid; dmpp = 3,5-dimethyl-4-(4’-pyridyl)pyrazole; DTA = 9,10-ditetrazolateanthracene; 1,2,4,5-BTC = 1,2,4,5-benzenetetracarboxylic acid; L = 1-C10H7CH2N(CH2COOH)(CH2PO3H2); bzp = 2-benzoylpyridine; ina = isonicotinic acid.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48


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Table 4: Proton conductivities and activation energies at 34°C and different relative humidities

Conductivity at 34°C and 98%

Compound I [σ = Ω-1cm-1] / Eact =

Compound II [σ = Ω-1cm-1] / Eact =

eV]

eV]

3×10-4 / 0.93

3.443× ×10-4 / 1.16

1.56 ×10-6 / 0.85

1.9 ×10-5 / 1.08

4.535×10-7 / 0.70

6.57× ×10-7 / 1.00

3.33 ×10-8 / 0.52

6.80× ×10-8 / 0.68

humidity / Eact Conductivity at 34°C and 85% humidity / Eact Conductivity at 34°C and 75% humidity / Eact Conductivity at 34°C and 51% humidity / Eact



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(a)

(b) Bhattacharya, et al. Figure 1


Page 33 of 49

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(c)

Bhattacharya, et al. Figure 1



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(a)

(b)


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Page 35 of 49

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(c)




1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 49

(a)

(b)



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(c)




1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(a)

(b)


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Page 39 of 49

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(c)




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Page 40 of 49

(a)

(b) Bhattacharya, et al. Figure 5


Page 41 of 49

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(a)

(b)




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Page 42 of 49

(a)

(b)



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(a)

(b)




1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 44 of 49

(a)

(b)

(c)

(d) Bhattacharya, et al. Figure 9


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(a)

(b)

(c)

(d) Bhattacharya, et al. Figure 10



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(a)

(b)



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(a)

(b)




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(a)

(b)



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For Table of Contents Use Only :

Organization of Mn-Clusters in pcu and bcu Networks: Synthesis, Structure and Properties Saurav Bhattacharya,1 M. Gnanavel,2 Aninda J. Bhattacharyya2 and Srinivasan Natarajan1*

Two new anionic inorganic-organic hybrid compounds [H3O][Mn3(µ3-OH)(C14H8O6S)3(H2O)](DMF)5, I, and [H3O]2[Mn7(µ3-OH)4(C14H8O6S)6(H2O)4](H2O)2(DMF)8, II, have been synthesized and characterized.

The

compounds consist of Mn6 and Mn7 clusters, respectively, connected by 4,4’-sulfonyldibenzoic acid anions resulting in a pcu network in I and a bcu network in II. Proton conductivity studies gave values of ~ 3x10-4 Ω1

cm-1 at 98% relative humidity in both the compounds with high activation energies indicating a vehicle

mechanism.


Organization of Mn-Clusters in pcu and bcu Networks - American

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