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Monocarboxylic Acid driven Structural Transformation in Manganese based Metal-Organic Frameworks K. S. Asha, Rajeev Khoj, Niyaz Ahmed, Ramesh Nath, and Sukhendu Mandal Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.6b01168 • Publication Date (Web): 24 Jan 2017 Downloaded from http://pubs.acs.org on January 24, 2017

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Crystal Growth & Design

Monocarboxylic

Acid

driven

Structural

Transformation in Manganese based Metal-Organic Frameworks K. S. Asha,a Rajeev Khoj,a N. Ahmed,b R. Nath*b and Sukhendu Mandal*a [a]

School of Chemistry

Indian Institute of Science Education and Research Thiruvananthapuram, Thiruvananthapuram, Kerala, India, 695016 E-mail: [email protected] [b]

School of Physics

Indian Institute of Science Education and Research Thiruvananthapuram, Thiruvananthapuram, Kerala, India, 695016 E-mail: [email protected] KEYWORDS. Chirality. Magnetism. Mechanism. Monocarboxylic acid. Structural transformation. ABSTRACT:

The use of monocarboxylic acid along with dicarboxylic acid significantly influences the nucleation- growth- transformation process in crystals of Metal - Organic Frameworks (MOFs). Usually the acetic acid is being used as coordination modulator to control the morphology and size of crystals. We have explored here the effect of acetic acid on the structures where the SBU is a

ACS Paragon Plus Environment

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trimer. The acetic acid binds with the metal ion and induces structural transformation with anisotropic crystal growth. The acetic acid bonded structures are found to have magnetic long range ordering at low temperature. Moreover the bonding fashion of the acetate ion creates a chiral center in the framework due to spontaneous resolution of the achiral building units. We have proposed a possible mechanism for this acetic acid driven transformation by analyzing the powder X-ray diffraction patterns and singe crystal structure. Thus this work not only provides a strategy to synthesize new designed structures using mixed carboxylic acid ligands but also shed light towards the structural transformation and magnetic properties.

Introduction Over the past few decades research on MOFs have received a great attention owing to their plethora of applications in various fields of science.1-5 The overall control on synthesis of these hybrid materials is challenging due to several controlling parameters. It is generally accepted that the factors like molar ratio of the starting materials, metal source, solvent, temperature, and pH of the reaction medium control the size and morphology of the crystals and dimensionality of the structure.6-8 The morphogenesis and downsizing of MOF crystals to micro/ nano regime have attracted more attention due to their diverse applications in material science. Use of mono dentate ligands like acetic acid, benzoic acid, formic acid, trimethylamine, and pyridine etc. has been explored as a modulator or template to control the growth of single crystals through the coordination modulation method.9-12 The modulators exhibit a competing interaction with the ligand which is used for the synthesis of MOFs and thus limit the growth in a particular direction. The control of morphology and size has great interest in sensing, gas adsorption, and biological applications, etc.13-15


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There are many reports where the role of mono dentate ligand, metal coordination and stability of metal - oxo clusters in tuning the morphology and size of crystals have been discussed.16-18 Kitagawa and coworkers have shown how acetic acid acts as a coordination modulator to downsize the crystals of [Cu2(ndc)2(dabco)] (where, ndc = 1, 4-naphthalene dicarboxylate, dabco = diazabicyclo [2.2.2]octane) to the nano regime.16 In this case the acetic acid competes with ndc2linkers which are connected to the Cu-based paddle-wheel units and limits the growth in that particular direction but does not affect the growth along the pillaring direction. Behrens and coworkers used same technique for the synthesis of nanoscale Zr- based MOFs where Zr forms a cluster in a square-antiprismatic geometry by bridging with μ3-O, μ3-OH, and carboxylate groups.17 However, the use of acetic acid plays a different role where the SBU is linear dimer or trimer. Recently Kasel and coworkers have shown that acetic acid acts as a co-ligand instead of modulator in the case of MOF with trimer as secondary building unit.18 From these observations we may conclude that the coordination mode and rigidity of metal - oxo cluster determine the role of acetic acid. The paddle - wheel and cage like metal - oxo clusters are highly rigid and robust due to their specific geometry. Therefore, acetic acid cannot bind to those clusters, which will be energetically unfavorable. Whereas the dimeric or trimeric clusters are more labile, hence the acetic acid binds to the metal ion. MOFs with mixed ligands have reached a new level of rational design and construction that involves the synergetic coordination of different ligands and metal ions. Some quite interesting structures can be formed only with combination of mixed ligands and this implies the importance and success of the mixed ligands strategy. Due to mixed ligand’s synergistic effect it creates not only the structural hierarchy but also the interesting chemical and physical properties for many potential applications.


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We have synthesized four Mn based MOFs using dicarboxylate and monocarboxylate ligands and studied their structural and magnetic properties. The as synthesized compounds were labelled as:

1,

[Mn3(BDC)3(DMA)4];

[(CH3)2NH2][Mn2(BDC)2(CH3COO)].

2, 2

DMA;

[Mn3(OH-BDC)3(DMA)4]; and

2a,

1a,

[(CH3)2NH2][Mn2(OH-

BDC)2(CH3COO)]. H2O. The compounds 1 and 2, where a similar structure to compound 1 has been reported by Li et al in 2011,19 form a trimer metal cluster unit, which is linked by the dicarboxylate ligand forming the two - dimensional structure, while the compounds 1a and 2a form the infinite one - dimensional (1D) chain as SBU unit through Mn – O – Mn bonding, which are then connected by dicarboxylate ligands to form the three - dimensional structure. The detailed structural investigation and the similarities in the synthetic procedure prompted us to explore the transformation from 1 to 1a and 2 to 2a, respectively. We have proposed a possible mechanism for this transformation. Magnetic properties of all these compounds have also investigated and correlated with their structural features. Experimental Synthesis Compound 1: 0.137 g (0.53 mmol) of Mn(NO3)2. 4 H2O was dissolved in 3 mL methanol and mixed with 0.089 g (0.5 mmol) of terephthalic acid in 3 mL DMA (N, N’-dimethylacetamide). Then the whole mixture was taken in a closed glass vial and kept at 100 °C in oven for three days. The colorless crystals were formed, washed with DMF (N, N’-dimethylformamide) many times and dried under vacuum for further use. Compound 2: 0.137 g (0.53 mmol) of Mn(NO3)2.4 H2O was dissolved in 3 mL methanol and mixed with 0.098 g (0.5 mmol) of 2-hydroxy terephthalic acid in 3 mL DMA and sonicated for five minutes. The whole mixture was taken in a closed glass vial and kept at 100 °C in oven for


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three days. The colorless crystals were formed, washed with DMF many times and dried under vacuum for further use. Compound 1a: 0.137 g (0.53 mmol) of Mn(NO3)2.4 H2O was dissolved in 3 mL methanol and 2 mL acetic acid was added to this. The solution was kept undisturbed for some time. Then 0.089 g (0.5 mmol) of terephthalic acid dissolved in 3 mL DMA was added to it and sonicated for five minutes. The whole mixture was taken in a closed glass vial and kept at 100 °C in oven for six days. The colorless crystals were formed, washed with DMF many times and dried under vacuum for further use. Compound 2a: To the solution of 0.137 g (0.53 mmol) Mn(NO3)2.6 H2O dissolved in 3 mL Methanol, 2 mL acetic acid was added and kept undisturbed for some time. Then 0.098 g (0.5 mmol) of 2-hydroxy terephthalic acid dissolved in 3 mL DMA was added to it and sonicated for five minutes. The whole mixture was taken in a closed glass vial and kept at 100 °C in oven for three days. The collected colorless crystals were washed with DMF many times and dried under vacuum for further use. Transformation of 1 to 1a: Crystals of compound 1 was taken in a glass vial and then 2 mL acetic acid was added. The mixture were kept at 100 °C for six days. The needle shaped crystals were formed. Transformation of 2 to 2a: The crystals of compound 2a were synthesized by immersing the crystals of compound 2 in 2 mL acetic acid in a glass vial and then heated at 100 °C six days.


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Results and Discussion Structural description These four compounds can be classified into two categories; the compounds 1 and 2 can be grouped into one category since those compounds have resemblance in their structural features. These compounds have same kind of metal and ligand connectivity and network topology. Compound 1 was crystallized in triclinic crystal system with P-1 space group whereas 2 was crystallized in monoclinic system with P21/n space group. The asymmetric unit of structure 1 consists of three metal ions, three ligand molecules and four coordinated organic solvent molecules and 2 consists of one and half of metal ion, one and half ligand and two coordinated dimethylacetamide molecules (Figure 1a and 1b). The inorganic cluster in both the compounds is Mn3(OCO)6 unit, which is linked via bidentate functionalized organic linker molecules forming a two - dimensional (2D) network (Figures 1c). In the trimer unit, there are two crystallographically independent Mn ions, both have the coordination number six and adopt a distorted octahedral geometry. One Mn2+ ion is coordinated to six carboxylate oxygen atoms whereas other Mn2+ which is symmetry generated to form the two terminal centers, coordinated to four carboxylate oxygen atoms and two oxygen atoms from solvent molecules. The structural features of compound 2 is similar to that of compound 1, except terephthalic acid is replaced by 2-hydroxy-terephthalic acid (Figures S1 and S2). These two-dimensional layers in both the compounds are connected by noncovalent interactions between the coordinated solvent molecules (Figure S3). Each trimer unit is connected to six other trimer units via ligand molecules forming 6-c connected network (Figure 1d and 1e).


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The compounds 1a and 2a are classified to another category. Those were crystallized in orthorhombic system with space group P212121 and C2221, respectively. These are structurally similar with one - dimensional Mn - O - Mn chain as SBU (Figure 2a). (a)

(b)

(d)

(c)

η1

Mn2

(e)

μ2

Mn1

Mn2

Figure 1. (a) and (b) The asymmetric unit present in compounds 1 and 2, respectively; (c) SBU unit Mn3 (OCO)6 of compound 1; (d) and (e) the 6-c connected network in compounds 1 and 2, respectively.

The one - dimensional chains are interconnected by linker molecules to form the three dimensional network (Figure 2b). The metal ions are six coordinated and among six, four come from dicarboxylate organic linker molecules and two from acetic acid. There are two kinds of metal ions with different coordination environment. Mn1 is bonded to one acetic acid whereas


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Mn2 is bonded with two acetic acid molecules (Figures 2a and S4 - S5). The acetate ion bridges the metal centers to form the one-dimensional infinite Mn – O – Mn chain. The phase purity of all structures were checked using powder X-ray diffraction studies. The PXRD pattern of all as-synthesized compounds was exactly matching with that of simulated one (Figure S6). The IR and TGA measurements also have been carried out for more structural information (Figures S7 and S8). The first step of weight loss in the compounds 1 and 2 are due to the loss of coordinated solvent molecules, and that in compounds 1a and 2a are due to lattice solvent and organic cation molecules. The chirality in crystalline materials is very important and it brings vital attention in various applications.20-24 The chiral metal organic compounds can be synthesized either by the use of homochiral molecular building blocks (MBBs) or by spontaneous resolution of chiral centers and chiral nets comprised of achiral MBBs.25-31 Use of homochiral ligand to synthesize a chiral compound is an expensive method. Hence it is still a challenge to design an

Mn1

Mn2

μ1

μ2

(b)

(a)

Figure 2. (a) One-dimensional Mn - O - Mn chain in 1a and (b) three-dimensional network structure of compound 1a.


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organic ligand combining both flexibility and directionality that can induce chirality through spontaneous resolution during the controlled assembly by local destruction of achiral asymmetric unit. Bulk chirality can be created in MOFs which exhibits a network topology that is inherently chiral because of the spatial organization of achiral building blocks.32 But unfortunately, spontaneous resolution sometimes leads to the formation of racemic mixtures or conglomerates.33 In the present work two compounds were crystallized with chiral space group containing 21 screw axis and they are optically inactive. These were formed with intertwined helical connectivity and it may be due to the racemic twined crystals. The compounds 1a and 2a were crystallized in chiral space group and it might be due to the absence of symmetry around the metal asymmetric center (Figure S9). The analysis of the optical activity of compounds 1a and 2a using the circular dichroism (CD) spectroscopy show that these are optically inactive, because the spectrum does not have any significant spectral behavior corresponds to the enantiomeric excess (Figure S10). We have investigated the structure in more detail to understand what could be the reason for optical inactivity. Then we realized that in all the compounds one-dimensional chain is connected by ligands to form two different helices in the network (Figures 2b and S5). The way by which the ligands are connected to the one-dimensional chain leads to the formation of helical structure (Figure 3). Interestingly we observed that both the right handed and left handed helices exist in the same structure leading to a conglomerate which lacks the optical activity. The high flack parameter (0.33(2) for 1a and 0.32(3) for 2a) of both the structures (without TWIN refinement) also proved that the compounds were not formed with absolute structure (See ESI, Table S11 and S12). One can have a chemical control over the growth of different facets to facilitate the anisotropic crystal growth. We have reported here the potential use of monocarboxylic acid as structure-


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directing agent which induces the structural transformation as well as chirality. The only difference in the synthetic conditions of compounds 1a and 2a compared to compounds 1 and 2 is the use of acetic acid. This observation excited us to explore the possibility of structural transformation between the above mentioned two categories of structures by using the acetic acid. So we have done it by immersing the crystals of 1 and 2 in acetic acid and heated at 100 0C for few days and we have observed the formation of crystals of 1a and 2a (See ESI and Figure 4). It is very clear from the crystal images that the acetic acid has important role in controlling the morphology also. We have selected acetic acid since it has high metal binding ability and directionality. Usually monocarboxylic acids are used to control the rate of nucleation in crystal growth and thus to control the shape and size of MOF particle.34-37 But for the first time we have shown that acetic acid can be used for the structural transformation and that can induce the chirality also. However the reports on post synthetic modification of achiral MOF to form the design targeted chiral MOF have been reported.38


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Figure 3. The helical structure of compound 1a.

In the present case when the metal ions react with dicarboxylate linkers alone under solvothermal conditions the crystals with irregular shape were formed. But after transformation crystals were formed with specific needle-like shape. This may be due to the controlled nucleation and oriented growth of crystals. During crystallization process the metal ion interacts with the acetate ion much faster than dicarboxylate ion due to its strong coordination ability. This might lead to the destruction of SBU of the original structures and induces transformation.


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Figure 4. The microscopic images of compounds 1 to 2 and 1a to 2a.

Monocarboxylate (here acetic acid) impedes the coordination between metal and dicarboxylate linkers. The metal acetate diffuses into the framework and breaks the SBU. The metal acetate binds to the terminal metal ion of the trimer unit and blocks the further growth in that particular direction (Figure S13). The new metal center also adopts an octahedral coordination geometry with dicarboxylate ligands and then connects to other trimer units forming the one - dimensional chain. Thus the impeded metal acetate forms a bridge between the two trimer units. The coordinated solvent molecules were also removed and the dicarboxylate ligand molecules fill the remaining coordination sites of the new metal center. One can assume that the transformation essentially results in anisotropic growth and here the acetic acid triggers the growth mechanism by varying the crystal growth rates along different facets.39 The prediction of crystal morphology can be done


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by considering the relative growth rates of the different crystal faces. In principle, a crystal should grow in a particular direction unless the energetics is changed along a particular facet. Thus the growth rates of facets in different orientations are proportional to the attachment energy of growth units.40 The final morphology of the crystal is often determined by the consequence of competitive growth of (hkl), (h00) and (hk0) faces and the structure is formed with facets at slower growth rate.40-44 As shown in figures S14 - S15, for compounds 1 and 2 the dominating facets are either two of (hk0), (0kl), and (h0l) planes. The growth in these orientations is slower than other planes. Whereas for compounds 1a and 2a the slower growth happens in either one of those orientations only, therefore it results in the formation of long needles not the blocks or plates. Magnetic Studies Among those two categories, one set of structures contain Mn-trimer cluster and other set contain Mn – O – Mn chain as SBU. In order to analyse the influence of structural features on the magnetic properties, we have performed the magnetic measurements on all the compounds and correlated with the corresponding structures. Compounds 1 and 1a: χ(T) of compounds 1 and 1a measured at an applied field H = 1T is shown in Fig. 5(a) and 5(b), respectively. At high temperatures, χ(T) of both the compounds increases with decreasing temperatures, following the Curie-Weiss (CW) behaviour as expected in the paramagnetic regime. At Tmax ≃ 3.16 K and 8.66 K, it passes through a broad maximum for 1 and 1a, respectively, indicating short - range magnetic ordering which is a typical behaviour of low - dimensional magnets. Compound 1 does not show any signature of magnetic long – range ordering down to 2.1 K whereas, compound 1a undergoes a magnetic long – range ordering at TN ≃ 4.5 K, as evident from the splitting of Zero Field Cooled (ZFC) and Field Cooled (FC) susceptibilities.


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In order to extract the magnetic parameters, we have performed a CW fit to the 1/χ vs. T data at high temperatures using the following expression: 𝜒(𝑇) = 𝜒0 +

𝐶 𝑇+𝜃CW

, ------------------------------ (1)

where χ0 is temperature independent parameters which includes contributions of core diamagnetic susceptibility (χcore) and Van - Vleck paramagnetism (χvv). The second term is the CW law with C being the Curie constant and θCW the characteristic CW temperature. The parameters were obtained by fitting Eq. (1) to the high temperature data (T ≥ 50 K for 1 and T ≥ 100 K for 1a) are tabulated in Table 1.

Figure 5. Magnetic susceptibility (χ) vs. temperature (T) for 1 and 1a measured at an applied magnetic field of H = 1 T. The solid line represents the 1-D fit as described in the text. Lower inset in 5(a): 1/χ vs. T fitted by a CW law using Eq. (1) as shown by the red solid line; Upper inset in 5(b): The ZFC and FC susceptibilities measured under an applied field of 100 Oe in the low temperature region.


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Compounds 2 and 2a (OH substituted): Figures 6 (a) and 6 (b) show the χ(T) of 2 and 2a, respectively measured at H = 1 T. Both the compounds exhibit a pronounced broad maximum at Tmax ≃ 8.5 K and 11.67 K, respectively. No magnetic long – range ordering was observed for 2 while ZFC and FC susceptibilities for compound 2a show a bifurcation at TN ≃ 4.5 K, indicating the occurrence of magnetic long – range ordering. The parameters obtained from the fit of Eq. (1) to the high temperature data (T ≥ 50 K for 2 and T ≥ 200 K for 2a) are shown in Table 1.

2a

2

Figure 6. Magnetic susceptibility (χ) vs. temperature (T) for 2 and 2a measured at an applied magnetic field of H = 1 T. The solid line represents the 1-D fit as described in the text. Lower inset in 6(a): 1/χ vs. T fitted by a CW law using Eq. (1) as shown by the red solid line; Upper inset in 6(b): The ZFC and FC susceptibilities measured under an applied field of 100 Oe in the low temperature region.


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Table 1. Magnetic parameters obtained from the CW fit [Eq. (1)] to the χ(T) data in the high temperature regime for all the compounds. Compound

χ0 (cm3/mol/Mn)

C (cm3 K/mol Mn)

θCW (K)

µeff (µB)

𝒈

1

-2.77x10-4

4.43

1.92

5.95

2.01

1a

-5.75x10-4

3.73

26.80

5.46

1.85

2

-2.36x10-4

3.75

13.50

5.47

1.85

2a

-4.08x10-4

3.66

28.04

5.41

1.82

3𝑘B 𝐶

The effective moment (𝜇eff = √

𝑁A

) calculated for 𝑆= 5/2 from the value of 𝐶 and the

corresponding value of 𝑔 (𝜇eff = 𝑔√𝑆(𝑆 + 1)) are also tabulated.

Heat Capacity: The heat capacity (Cp) was measured for compounds 1a and 2a in the low temperature region at zero applied field to detect the occurrence of magnetic long - range ordering. Figure 7 shows the Cp(T) for both the compounds. A clear anomaly at 4.36 K and 4.94 K for compounds 1a and 2a, respectively, confirms the onset magnetic long – range ordering, consistent with the χ(T) measurements.


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2a

T (K)

Figure 7. Cp vs T measured for compounds 1a and 2a in zero applied magnetic field. The downward arrows point to the transition anomalies.

For all the compounds, the calculated effective moment 𝜇eff is close to the expected spin only value of 𝜇eff = 𝑔√𝑆(𝑆 + 1) μB ≃ 5.92 μB for Mn2+ (𝑆 = 5/2), assuming 𝑔 = 2. Small variation is likely due to a slight change in 𝑔-value as indicated in the last column of Table 1. For the compounds 1, 1a, 2, and 2a, broad maximum in χ(T) data indicates low dimensional character. The χ(T) data were fitted using one-dimensional chain model (See ESI). The parameters obtained from the fit are listed in Table 2. The transformation from compounds 1 and 2 to 1a and 2a, respectively, results in a reduction in inter atomic distance between Mn2+ ions. Thus, the trimer arrangement in compounds 1 and 2 with large inter - trimer distance transforms into a uniform spin chain of Mn2+ ions. As seen in Table 2, the 1D spin chain model fits to the χ(T) data [ESI, Eq. (2)] giving a higher value of exchange interaction (J/kB) for 1a and 2a compared to compounds 1 and 2, respectively.


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Table 2. Magnetic parameters obtained from the 1-D chain model [ESI, Eq. (2)] fit to the χ(T) data for compounds 1, 1a, 2, and 2a, respectively. The temperature ranges used for fitting are (3 K – 380 K), (4 K – 380 K), (7 K – 380 K), (7.3 K – 380 K), and (8.3 K – 380 K) for compounds 1, 1a, 2, and 2a, respectively.

Compounds

χ0 (cm3/mol Mn)

J/kB (K)

1

-4.63x10-3

0.30

2

7.32x10-4

1.02

1a

1.33x10-4

1.56

2a

6.47x10-4

1.66

In real 1-D systems, in addition to the dominant intra - chain interaction, there exists a weak inter - chain coupling, due to which the system undergoes a magnetic long – range ordering at a finite temperature. The compounds 1a and 2a undergo a magnetic long – range ordering at TN ≃ 4.36 K and 4.94 K, respectively, due to the weak inter - chain (𝐽⊥) interaction. Using the Oguchi criterion45, one can estimate the strength of inter - chain interaction as 𝑘B 𝑇 N |𝐽|

=

4𝑆(𝑆+1) 3𝐼(𝜂)

, ----------------------------------------------- (4)

where η = 𝐽⊥ /𝐽 and I(η) is the a triple integral with different components of the wave vector q. The numerical values of I(η) for different values of η are found out by simulating the data in Table 1. Using the appropriate values of TN and J, the value of I(η) was found to be 4.176 and 3.92, for 1a and 2a, respectively. From these values of η, J/kB was calculated to be 0.0884 K and 0.0996 K for compounds 1a and 2a, respectively.


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Conclusions We have synthesized four new structures based on Mn2+ as metal source and functionalized terephthalate as ligand. It was very interesting to observe how the acetic acid acts as a ligand rather than modulator over here. We noted that the acetic acid which is a well-known capping agent was the main driving force for the structural transformation. The morphogenesis due to anisotropic growth in crystals also was examined using PXRD and microscopic imaging studies. We have also analyzed how acetate bonding creates chirality in the framework structures. The possible mechanistic pathway for the transformation was proposed based on the structural information. The structural transformation leads to a significant increase in the exchange interactions between Mn2+ ions and the occurrence of magnetic long – range ordering at low temperature in the structures. A detailed analysis of the magnetic data underscored the structure-property relationship.

ASSOCIATED CONTENT The supporting information includes the materials and methods, crystallographic data table, structures, PXRD, IR, TGA, CD spectra, scheme of proposed mechanism, and the magnetic χ vs. T fitting of all compounds.

AUTHOR INFORMATION Corresponding Author Sukhendu Mandal* School of Chemistry


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Indian Institute of Science Education and Research Thiruvananthapuram, Thiruvananthapuram, Kerala, India, 695016 E-mail: [email protected] R. Nath* School of Physics Indian Institute of Science Education and Research Thiruvananthapuram, Thiruvananthapuram, Kerala, India, 695016 E-mail: [email protected] Funding Sources Science and Engineering Research Board (SERB), Govt. of India, through a grant SB/S1/IC14/2013 ACKNOWLEDGMENT We are grateful to Prof. V. Ramakrishnan for the encouragement and support. AKS acknowledges CSIR for the fellowship. REFERENCES References 1.

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Table of contents

2

1

R

L

Acetic acid

2a 1a

The role of monocarboxylic acid in modifying the structure of Metal-Organioc Frameworks has been explored. The acetic acid bridges the trimer secondary building units and forming a onedimensional chain. The structural transformation has been studied in single crystals. This transformation leads to introduce long range magnetic ordering in those compounds. Authors: K. S. Asha,a Rajeev Khoj,a N. Ahmed,b R. Nath*b and Sukhendu Mandal*a Title: Monocarboxylic Acid driven Structural Transformation in Manganese based Metal-Organic Frameworks


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Monocarboxylic Acid Driven Structural ... - ACS Publications

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