SURMOF Induced Morphological Crystal Engineering of Substituted

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SURMOF induced morphological crystal engineering of the substituted bezamides Geetha Bolla, and Allan S. Myerson Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.8b01214 • Publication Date (Web): 11 Sep 2018 Downloaded from http://pubs.acs.org on September 13, 2018

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Crystal Growth & Design

SURMOF induced morphological crystal engineering of the substituted bezamides Geetha Bolla, Allan S. Myerson* Department of Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, E19-502b, Cambridge, Massachusetts 02139, United States.

Abstract: Well established self-assembled monolayers are further explored and extended to SURMOFs as basic template hetero surfaces by using a basic stranded HKUST MOF as an example. The prepared SURMOF was used to study the morphological crystal engineering of the substituted bezamides. Prepared SURMOF substrates surfaces here are analyzed by SEM, and confirmed through thin film XRD. Here we proved that the MOF surface exhibited adsorption of substituted benzamides nucleus during both nucleation and growth directed due to the weak supramolecular interactions. MOF induced nucleation investigated here and showed control over the substituted benzamides for morphological engineering. Hence the concept of MOF induced morphological crystal engineering adapted to the field of morphology crystal engineering and showed additional advantage of heterogeneous nucleation. Introduction: A crystal cannot be formed instantaneously i.e. nucleation occurs at first, followed by growth, during growth and each crystal has its own growth history. Hence, understanding crystal structure and morphology crystal engineering of the small organic molecules become the grand challenge for solid-state chemists last couple of decades through various methods.1-3 However, the fundamental understanding with proper examples on molecular faces and ability to design their crystals with desired properties the whole concept falls under the umbrella of Crystal Engineering is still at rudimentary level in organic or inorganic crystals, hence there is emergence in need due to their potential applications.4-6 In addition, that has been developed to understand or control of the bio-minerals crystal formation mechanism with optical properties entitled as Biomineralization7-9 became fascinating with dual advantage in improved fabrication of synthetic materials and further to solve many serious pathological problems involving mineralization. Consequently, numerous methods were developed to understand the crystal growth, among them ‘tailor-made’ additive (a molecule very similar in structure) induced crystal mechanism due to surface adsorption of particular crystal face via weak supramolecular interaction in solution was initiated recently based on crystal engineering principles.3 Reported results dictate that such additives showed a dramatic effect on crystal growth and habit due to the preferential adsorption of the additive on specific crystal faces called as an active site for nucleation and growth. In fact, generally, bounded additive perturbs the regular growth of upcoming layers based on attachment energies and allow them in different directional growth, which finally leads changes

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in crystal morphology. Hence an efficient method for kinetic resolution of racemic conglomerates by crystallization in the presence of “tailor-made” additives was described and explained stereo selective adsorption of the additive at the surface of the growing crystals of the enantiomer resulting in a drastic decrease in their rate of growth which thus leads preferential crystallization of the opposite enantiomer (“rule of reversal”).2 This was proved by the crystallization of the conglomerates (R, S)-gIutamic acid hydrochloride, (R, S)-threonine, (R, S)-p-hydroxypheny1) glycine p-toluene sulfonate, and (R, S)asparagine hydrate in the presence of other amino acids as additives. Next example, dramatic change in morphology in presence of carboxylic acid additives on amide crystals, RCONH2/RCO2H eg: Asparagine/Aspartic acid was proved because the carboxyl O atom is a much weaker proton acceptor than the corresponding amide O atom. Hence there is a large energy loss in replacing an amide-amide hydrogen bond by an amide-acid hydrogen bond at the site of the additive. The system aspartic acid as an additive was added on asparagine and the crystals are prismatic in shape induces growth of {010} as plates due to retardation of growth along the b axis. Often this method limited in practical experiments due to the act of additive as an impurity and an excess amount of additive need.10 In another direction recently heterogeneous surface medication methods were developed extensively through self-assembled monolayers (SAM) for polymorph screening and morphological crystal engineering due to the presence of foreign surface in a crystallizing system can influence pathway of crystallization for the simple reason that nucleation barrier can be lowered as reduction in the interfacial free energy occurred but they are limited in success rate. 11-15 Here we have extended SAMs to SURMOFs (SAM+MOFs, Figure 1) which are principally deposition of the metal organic frame works on SAM hetero surface. Recently there was a prominent increment observed and proved that MOFs are highly porous and showed applications in various directions of the science.16-20 SURMOFs have been studied recently with different applications such as photovoltaics, CO2 reduction, memory devices, supercapacitors and batteries.17 The advantage of controlled orientation of the MOFs on the basis of the ground SAM functional group would allow preferential growth of the target functional group small organic molecules, but this young branch of chemistry not yet been explored in the direction morphological engineering. As MOFs are highly porous crystalline materials, their impact and the contribution on the surface as a heterogeneous layer are quite effective when compared with the usual SAM surface. In addition, they can lead to different nucleation and growth direction than usual crystallization path. With this prime idea, here we started our studies and discussed, how SURMOF can influence the crystal morphological crystal engineering of the benzamides. Supreme selection of the benzamides was justified due to their no complexation nature during crystallization time with selected HKUST MOF.


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(b) (a) Figure 1. (a) SURMOFs basic design with multiple layers in present study. (b) Preparation method for SURMOF used in present study and this was entitled as Dipping Layer By Layer (LBL-D).

Results and discussion: The template SURMOF crystallization method involved three major steps. As the first step, the self-assembled monolayers preparation using gold substrates, thiol solutions and second a well-known reported 3D HKUST MOF21, which consists of trimestic acid (H3BTC) and copper acetate, was formed from solutions using Layer By Layer Dipping16 (LBL-D). These SURMOF substrates were designed to investigate how the template functionalization of these inorganic, ordered, highly porous self-assemble layers of MOF on the surface (SURMOF) can influence the nucleation of functional organic molecules, all the preparation details discussed in supporting information section 1. The prepared SURMOF was confirmed by thin film X-ray diffraction (Figure S1a, b) and topo-chemical analysis was carried out by scanning electron microscopy and atomic force microscopy was reported recently in our earlier paper.22 However, here also we have confirmed the surface again with SEM analysis for different batches (Figure 2). The images of the Figure 2a, b are the one batch for 10 layers, showed the porous MOF surface distribution and Figure 2c to f are different batches in lower to higher magnification suggests that uniform distribution. In addition, various places on the surface SEM image analysis suggests that whole the substrate film was distributed in an uniform way. However, they are in micrometer in length.



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(a)

(b)

(c)

(d)

(e)

(f)

Figure 2. SEM images of the prepared SURMOF thin film surface in different experiments. Which showed that surface is in micro level with uniform MOF distribution. As part of our efforts, the third step is crystallization of small organics and to double check the viability of our SURMOF approach here we have chosen Benzamide (BZA), 4-Amino benzamide (ABZA),


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4-Hydroxy benzamide (HBZA). Indeed, there is no complexation was observed between benazamides, pristine HKUST MOF during slurry experiments at room temperature in 4-6 h (Figure S1). However, in our previous result, Acetamiophen (APAP) was chosen as an example organic to explore crystalline forms as a proof-of-concept and reported the crystallization of APAP Form II with block morphology for the first time.22 In an extended direction here we have studied the morphological changes and crystal growth directions of the benzamides (Figure 2) on SURMOF surface discussed in detail.

Scheme 1. The model systems such as benzamides used in this study. Example 1. Benzamide: The morphology of a matured crystal is defined by its relative rates of growth in different directions, which means the faster the growth in a given direction would lead smaller the face at perpendicular. Hence, if growth is inhibited in a direction perpendicular to a particular crystal face, the area of that face expected to increase relative to the areas of other faces of the same crystal. Addadi et al., reported benzamide, crystallizes from ethanol as plate-like crystals but in presence of additive as benzoic acid they observed retardation of crystal face growth along the crystallographic b axis was achieved and ended as needle crystals.1 In detail, BZA (compared with reported Refcode BZAMID11) crystallizes in the monoclinic crystal system (P21/c) with cyclic homo dimer motifs to form stable (001) layers with major morphological importance. Further phenyl C–H, π functional interacting via weak van der Waals interactions between phenyl groups along the other directions and ended as plate-like crystals. If in case present an additive for example, benzoic acid the formation of acid-amide hetero synthon possible through energy loss at active site which can lead an overall loss in energy BZA along b, hence morphology transformed 2D crystals into 1D. Apart with benzoic acid there are few more other additives was studied like o/m-toluamide and resulted in inhibition of growth along the crystallographic a direction due to the adsorption in the b direction.1 Here we have calculated morphology based on attachment energy and next BFDH predictions (Figure 3a, b) suggests plate morphology of the BZA. BZA crystals were grown solution crystallization in EtOH (1-10 mg/ml) and further on the surface of the designed SURMOF substrate was considered for face



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indexing experiments. Solution crystallization without MOF surface resulted in single crystals showed plate morphology with (001), (011), (101) morphological importance faces as major whereas crystals grown on the surface of the MOF crystallization suggests needle morphology with (001), (011) morphological importance faces as major and (101) was retarded. Packing of the BZA clearly showed the (001) face along the b direction benzamide dimers N‒H‧‧‧O and along the crystallographic a direction N‒H‧‧‧O catemers of the BZA extended via supramolecular interaction (hydrogen bond). Hence the SURMOF induced BZA crystal were morphologically engineered by stopping the (001) crystal face along the b direction. This might attribute due to the weak interactions between HKUST MOF porous surface, amide C=ONH 2. However, calculated 2D slice crystal faces in Material Studio showed (Figure 4a, b) (001) face of the BZA faces are exposed with amide as out next (011) faces (Figure 4c, d) were no hydrogen bond groups whereas (101) crystal face showed alternatively amide group (Figure 4e, f). Calculated attachment energies (Table 1) are (001), (011), (101): -14.9, -44.50, -47.89 Kcal/mol which showed the growth rate of second, third crystal faces difference is not high (~3 Kcal/mol). Hence controlling one face with modified SURMOF surface crystallization is an alternative to the additive induced crystallization as the result matches to attain plate to needle crystals of BZA. BZA

(a)

(b) Crystal 1 without MOF


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(c)

(d) Crystal 2 with MOF

(e)

(f)

Figure 3. (a) Morphology calculated based on attachment energy. (b) calculated morphology with hydrogen bond preferences in face based on BFDH predictions. Single crystal face indexing experiment results of the BZA. (c), (d) Face indexing of the BZA single crystals with their faces grown on solution crystallization without MOF surface suggests plate morphology with (001), (011), (101) morphological importance faces as major. (e), (f) Face indexing of the BZA crystals grown on the surface of the MOF crystallization suggests needle morphology with (001), (011) morphological importance faces as major and (101) was decreased.

(a) (001)a

(b) (001)b

(c) (011)a

(d) (011)b



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(e) (101)a

(f) (101)b

Figure 4. (a, b) View of the crystal face (001), (c, d) view of the crystal face (011), (e, f) view of the crystal face (101), calculated form Material Studio. This suggest that decreasing the morphological importance of the (101) face due to the lack in hydrogen bond polar groups. Table 1. Attachment energy calculations of the BZA crystal Form I by using dreiding force field method. Crystal face

Eatt(Total) kcal/mol -14.91 -44.50 -49.70 -47.89 -43.55

(0 0 2) (0 1 1) (1 0 -1) (1 0 1) (0 1 2)

Eatt(vdW) kcal/mol -13.37 -30.93 -30.32 -29.36 -36.24

Eatt(Electrostatic) kcal/mol -1.54 -13.57 -19.38 -18.52 -7.31

Total facet area 1.537996e+004 4.453315e+003 2.069583e+003 3.309268e+003 1.604570e+003

% Total facet area 57.35217626 16.60650455 7.71751644 12.34032763 5.98347513

Example 2. 4-Amino benzamide: ABZA crystals grown initially without substrate in EtOH (1–10 mg/ml) solvent through solution crystallization and the observed crystals showed prismatic, block morphology with (100), (110) as major morphological importance crystal faces. This results are further supported by attachment energy and BFDH morphology predictions and showed block habit (100) as a major crystal face (Figure 5a, b). Crystals

1,

2

and

3

are

grown

from

low,

medium,

high

concentrated

solutions

without HKUST MOF surface and picked for faces monitoring experiments. ABZA crystallizes in monoclinic, P21 through primary amide chains N‒H‧‧‧O along the b axis. Further, these opposite chains interact to form 2D sheets, these sheets form next N‧‧‧H‒O interactions with the amine to give 3D structure (Figure 5b). Here we have recollected the single crystal data of the ABZA as the reported data unit cell orientation unique axis is different from the present studies, all the crystallographic data were displayed at Table S1. Hence it is a trivial situation that hetero substrate can interact in three different motifs like at inertial chains, second at opposite chains site and finally third at amide active site at the time of birth of crystal (nucleation time). Interestingly these crystals showed initially (100) face as the major face and (110), (111), (010), (101), (001), (111) as minor faces at low dilution. Further (100) crystal faces started disappearing and started growing the (110) face as the major face at a higher concentration; (111), finally ended as block morphology (Figure 5c-h). As our main stream is to understand the crystal morphology


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influence

due

to MOF surface,

here

we

have

grown ABZA crystals

on

the

surface

of

the SURMOF heterogeneous substrate through solution phase epitaxy crystallizations method. The grown crystals labeled as 4, 5, 6, 7, 8 (Figure 5i to r) showed needles on surface and block morphology at edges, (111) as the major face and (001), (110), (100), (011), (010). Which clearly confirmed the nucleation of the ABZA on MOF surface is different from normal solvent crystallization experiments and did not follow the attachment energy during the crystal growth (Table 2). This results suggest that the N–H‧‧‧O interactions of the amide chains and amide to amine were acted as active sites with MOF surface which finally directed the crystal faces which are high attachment energies ended as needle morphology (retarded along the b axis and allowed along the crystallographic a axis). Indeed, at the edge grown crystals showed needle morphology with (100) face as the primary face and also further (111) faces as minor morphological importance. ABZA

(a)

(b) Crystal 1 without MOF at low to medium dilution

(d)

(c) Crystal 2 without MOF at medium dilution



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(f)

(e) Crystal 3 without MOF at high concentration

(g)

(h)

Crystal 4 with MOF at surface

(i)

(j) Crystal 5 with MOF at surface


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(k)

(l) Crystal 6 with MOF at surface

(n)

(m) Crystal 7 with MOF at edge

(o)

(p) Crystal 8 with MOF at edge



(q)

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(r)

Figure 5. ABZA crystal morphology experiments through predictions and face indexing experiments with, without SURMOF surface. We have calculated the hkl slices of the ABZA faces to understand the growth mechanism. The crystal faces which were attributed through solution crystallization (100), (001), (110) crystal faces (from low to high concentrations) exhibited amide and amide group motifs towards surface (Figure 6). Hence MOF pores can block their surface which allows other faces to grow further leads different growth compared to normal experiments. ABZA

(a) 100a

(b) 100b

(c) (001)a

(d) (001)b


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(e) (110)a

(f) (110)b

(g) (111)a

(h) (111)b

Figure 6. View of the ABZA crystal faces calculated form Material Studio. Table 2. Attachment calculations of the ABZA Crystal face (0 0 1) (1 0 0) (1 0 -1) (1 0 1) (0 1 1) (0 -1 1) (1 1 0) (1 -1 0) (1 1 -1) (1 -1 -1)

Eatt(Total) kcal/mol -16.53 -13.55 -17.56 -23.57 -25.36 -25.36 -19.55 -19.55 -23.15 -23.15

Eatt(vdW) kcal/mol -3.89 -9.06 -9.40 -10.93 -14.90 -14.90 -14.80 -14.80 -15.13 -15.13

Eatt(Electrostatic) kcal/mol -12.64 -4.48 -8.15 -12.64 -10.45 -10.45 -4.74 -4.74 -8.01 -8.01

Total facet area 1.357478e+003 1.407212e+003 725.36305004

% Total facet area 24.27382879 25.16313667 12.97062225

38.15940387 38.15940387 819.04188985 819.04188985 193.94900169 193.94900169

0.68234964 0.68234964 14.64574597 14.64574597 3.46811054 3.46811054

Example 3. 4-Hydroxy benzamide: HBZA crystals

(compared

with

reported

Refcode

VIDMAx)

were

grown

initially

without substrate in EtOH (1–10 mg/ml) through solution crystallization as such as BZA, ABZA and the observed well grown single crystals showed rod morphology with (001), (011), (010) with equal morphological importance crystal faces and crystal grew along the crystallographic a axis. This results are further supported by attachment energy and BFDH morphology predictions and showed block habit (100) as a major crystal face (Figure 7a, b). At first, crystals 1, 2 are grown from solutions without HKUST MOF surface and showed (001), (010), (011) face as major faces with equal importance, growth happened in a axis via N‒H‧‧‧O (Figure 7b-ii) supramolecular interactions.



Secondly,

crystals

on

the

surface

of

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the SURMOF heterogeneous

substrate

through solution phase epitaxy crystallizations method were studied carefully with multiple crystals at various places of the designed surface. These crystals showed plate morphology as (001) major and (011), (010), (100), (101) with minor morphological importance. This clearly dictates the MOF induced grown crystals labeled as 3, 4 (Figure 7) are extended along the crystallographic c axis through N‒H‧‧‧O on surface and block morphology at edges. Edge crystals were balanced of MOF and solution crystallization faces ended with similar morphological importance of the existing crystal faces. Which clearly confirmed the nucleation of the HBZA on MOF surface was happened along the c axis whereas in solution crystal grew along the crystallographic a axis. Controlling the growth was successful here by using our designed SURMOFs. All the faces exposure towards the surface and their attachment energies were shown in Figure 8 and Table 3. Indeed, here MOF surface grew crystals did not show the attachment energy calculated stable faces (001), (011) are -56.49, -48.40 kcal/mol. Further, all the crystals studied here are in detailed displayed in supporting information section 2 and 3. HBZA

(a)

(b-i)

(b-ii)

Crystal 1 without MOF

(d)

(c) Crystal 2 with out MOF


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(f)

(e) Crystal 3 with MOF surface

(g)

(h) Crystal 4 with MOF

(i)

(j) Crystal 5 with MOF at edge



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(l)

(k) Crystal 6 with MOF at edge

(m)

(n)

Figure 7. (a), (b) HBZA crystal faces calculated form Material Studio by attachment energy and BFDH morphology along with their interactions. (c-n) Single crystal face indexing experiments of the HBZA crystals grown with and without MOF substrate. This suggests that, solution crystallization gave rod morphology with near growth rate of (011), (010), (001) whereas with MOF small to big plates (001) as major face. In addition, at the edge all the faces are in equal growth rate ended with block morphology. HBZA

(b) (001)b

(a) (001)a


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(d) (011)b

(c) (011)a

(f) (100)b

(e) (100)a

(h) (010)b

(g) (010)a

(i) (110)a

(j) (110)b

(k) (111)a

(l) (111)b

(m) (11-1)a

(n) (110)b

Figure 8. View of the HBZA crystal faces calculated form Material Studio. Table 3. Attachment energies of the ABZA crystal faces calculated form Material Studio.



Crystal face (0 0 2) (0 1 1) (1 0 0) (0 2 0) (1 1 0) (1 1 -1) (1 0 2) (1 1 1)

Eatt(Total) kcal/mol -56.49 -48.40 -62.41 -49.29 -64.09 -76.85 -64.72 -68.14

Eatt(vdW) kcal/mol -19.31 -19.67 -44.25 -35.98 -40.71 -43.19 -38.66 -41.43

Eatt(Electrostatic) kcal/mol -37.17 -28.73 -18.16 -13.30 -23.38 -33.65 -26.06 -26.71

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Total facet area 1.005028e+004 2.126161e+004 5.937345e+003 4.085920e+003 8.319058e+003

% Total facet area 18.37105511 38.86442752 10.85296318 7.46871626 15.20653285

4.290678e+003 762.23955157

7.84299574 1.39330935

Powder X-ray diffraction analysis: In order to know the 2D orientation growth of BZA, ABZA, HBZA bulk crystals, thin film XRD experiments were performed. Crystals grown from solution crystallization showed plate morphology and resulted in PXRD with (001), (011), (101); (2θ ~ 7, 17, 18) crystal faces as major morphological importance. A gradual decrease and selective diffraction of the of the (002), 2θ of BZA at 7.851 was observed for the crystals grown on surface MOF this confirmed 1D growth (Figure 9a). ABZA crystals were grown at low dilution showed unique (00l) 2theta values and further at medium to high concentrated solution crystallization experiments resulted in (hk0) 2theta peaks (Figure 9b) which supported the single crystal face indexing experiments (Figure 5). However, the thin films and the crystals grown on designed surface was resulted in an additional 2theta which are corresponding to others crystals and confirmed the retardation of the previous existed faces (Figure 9c). Further the same was went ahead for HBZA and confirmed that the growth of the crystals in solution ended with (0kl), (00l) faces where as in the presence of the SURMOF crystals grew (00l) as major face exclusively (Figure 9d, e).

(b)

(a)


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(d)

(c)

(e) Figure 9. Powder, single crystal, film XRD comparison studies. (a) A change in relative peak intensities was observed from 2D plate crystals of BZA to needles. (b) ABZA commercial and crystals grown at low to high concentration comparison suggests the growth of (110) face. LC=Low Concentration, HC= High Concentration. (c) ABZA crystals and film on surface confirmed the induced faces of (00l). (d, e) HBZA single crystals grown from solution and on surface and also films. Which are again confirmed the (00l) face, crystal morphology rod (with equal relative growth in 001, 011) to 2D plates with (001) face was observed. Morphological crystal engineering and possible growth on hetero surface: It is a well-established fact that many of the organic molecules are crystalline and they have welldefined external and internal structures. The internal structure deals with the arrangement of molecules in the crystal lattice and this is entitled as polymorphism.23 The second one is the external structure which reveals the morphology of the crystal, stating the shape of crystal without changing the internal structure and this is entitled as morphological crystal engineering.1-2 It is also a well-known fact that the alteration of external and internal structure could further affect the physicochemical stability of the Active Pharmaceutical Ingredients (API).24-28 This phenomenon of altering the internal and external structure with crystal engineering principles gain huge attention in scientific community in recent days due to their



applications ranging from biochemistry to optoelectronics. If consider a molecule as A which can undergo for crystallization with n number of molecules, at first it forms nucleus at birth place then it will grow to form single crystal. In addition, it can form polymorphs and able to produce changes in morphology, hence the displayed image Figure 10a depicts MOF surface how it can influence for crystal formation. Normally if the crystal is like plate shape: Model I, with two growth rates consider as K1, K2 (K1=K2) to result faces f with surface S, it can adsorb tailor made additive or hetero surface at active crystal face and finally will give new morphology generally needles (K1≠K2) Figure 10b. In addition, if consider other model as Model II, if crystal grow in prismatic or acicular shape where the possible growth rates K1=K2, K1>>K2, K1

SURMOF Induced Morphological Crystal Engineering of Substituted

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