Tailoring Structural Diversity in Dimethyltin Carboxylates by the pH

Article Cite This: Inorg. Chem. 2019, 58, 10955−10964

pubs.acs.org/IC

Tailoring Structural Diversity in Dimethyltin Carboxylates by the pHControlled Hydrothermal Approach Ravi Shankar,*,† Archishmati Dubey,† Amanpreet Kaur Jassal,† Ekta Jakhar,† and Gabriele Kociok-Köhn‡ †

Department of Chemistry, Indian Institute of Technology Delhi, Delhi 110016, India Department of Chemistry, University of Bath, Bath BA2 7AY, U.K.

‡

Downloaded via UNIV PARIS-SUD on August 19, 2019 at 14:46:59 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

S Supporting Information *

ABSTRACT: The study presents a rational synthesis of new dimethyltin carboxylates, Me 2Sn(H2 btec) (1), Me2Sn(btec) 0.5 (2), [Me 2 Sn(H 2 O) 2 (btec) 0.5 ]·H 2 O (3), and [{Me2SnOSn(OH)Me2}(Me2SnOH)(btec)0.5]·H2O (4), derived from tetratopic 1,2,4,5-benzenetetracarboxylic acid (H4btec). The method relies upon hydrothermal reaction (130 °C, 72 h) of dimethyltin dichloride and H4btec under optimized pH (2 < pH < 8) conditions that allow control over dimethyltin speciation in aqueous medium as well as degree of deprotonation of the tetrafuntional carboxylic acid. The formation of a three-dimensional assembly in 1 is assisted by the bridging bidentate (μ2) mode of the carboxylate and O−H···O hydrogen bonds involving −COOH groups. The structure represents a unique example of the diorganotin framework derived from a partially deprotonated polyfuntional carboxylic acid. The structure of 2 adopts a three-dimensional motif wherein each pair of μ2-carboxylate groups (designated by C1 and C4) of the tetraanionic ligand form different spatial arrangements. For 3, the formation of one-dimensional motif with eight-coordinated tin atoms is assisted by the anisobidentate character of the carboxylate groups. The structure of 4 includes linear chains comprised of [Me2Sn(μ2−OH)]2 and the carboxylate ligand which extend to a layered motif with symmetrically substituted ladder-like distannoxanes acting as linkers. The underlying nets of 1, 2, and 4 exhibit sqc11, scu(sqc170), and sql topologies, respectively. Notably, these assemblies are extremely robust and show no sign of degradation upon exposure to neutral as well as weakly acidic/basic aqueous medium for 7 days.

■

INTRODUCTION In recent years, there has been growing interest in the design and synthesis of coordination polymers/metal−organic frameworks derived from multifunctional aromatic carboxylate-based ligands.1 Research activities in this field have advanced progressively with the realization that immense possibilities exist to tailor structural attributes and network topologies by a judicious choice of metal ion and an assortment of available polytopic ligands. For practical applications in diverse fields including gas sorption, ion exchange, and catalysis, among others, these solids meet the prerequisites of being robust with respect to their vulnerability toward phase change, loss of crystallinity, and decomposition under hydrolytic conditions.2 In this respect, MOFs derived from trivalent (Al3+, Ga3+, In3+) and tetravalent metal ions (Ti4+, Zr4+) have received a great deal of attention.3,4 The strong interactions between the higher valent metal ions/metal oxo-clusters and the carboxylate linkers are in accordance with Pearson’s hard/soft acid−base principle. In addition to thermodynamic considerations, the stability of the framework structures is also governed by kinetic factors. It has been amply demonstrated that higher connectivity between the oxo/hydroxo metal node and steric © 2019 American Chemical Society

attributes of the linker can provide a significant energy barrier to overcome and tend to reduce the attack of H2O, H3O+, or OH− guest molecules/ions.2 Despite these developments, there have been no systematic studies on rational synthesis of two-/three-dimensional coordination frameworks in an otherwise well-studied class of organotin carboxylates which are considered as potentially bioactive compounds against cancer cells.5,6 This paucity is partly attributed to their affinity to undergo structural changes in solution which implicates dynamic processes such as ligand exchange and associative−dissociative equilibrium due to the rather weak nature of the Sn−O coordinate bond. For the construction of macrocycles, cryptands, and one-/two-/threedimensional coordination motifs, studies primarily deal with di-/tri-substituted aromatic carboxylate linkers in the presence or absence of auxiliary N-donor ligands.7 Particularly noticeable are the structures built on dicarboxylatotetraorganodistannoxane-based frameworks.8 Classical methods such as azeotropic dehydration or salt metathesis reaction between an Received: May 14, 2019 Published: August 5, 2019 10955

DOI: 10.1021/acs.inorgchem.9b01387 Inorg. Chem. 2019, 58, 10955−10964

Article

Inorganic Chemistry

pH specific conditions and offers promise to design −COOH functionalized framework structures.10 In addition, different spatial arrangements of the carboxylate groups with respect to the plane of the phenyl ring occur due to steric reasons and offer a tool-kit to build structurally diverse coordination assemblies. Following this approach, we have synthesized new dimethyltin carboxylates of compositions Me2Sn(H2btec) (1), Me2Sn(btec)0.5 (2), [Me2Sn(H2O)2(btec)0.5]·H2O (3), and [{Me2SnOSn(OH)Me2}(Me2SnOH)(btec)0.5]·H2O (4) with interesting network topologies. Notably, these coordinationdriven self-assemblies exhibit exceptional hydrolytic stability over a wide pH range.

organotin precursor and a carboxylic acid are widely employed to construct such assemblies. Our previous studies have been devoted to develop new methods for the synthesis of higher-dimensional diorganotin(IV) coordination assemblies derived from mixed-ligand phosphonate and sulfonate ligands.9 The method relies upon a two-step approach involving the synthesis of diorganotin(alkoxy)alkanesulfonates, [R2Sn(OR)OSO2R]n (R = alkyl), and subsequent reaction of these reactive precursors with phosphonic acid under mild conditions. A unique example of a secondary building unit accessible by this approach is the trinuclear tin phosphonate cluster, [(R2Sn)3(O3PR1)2{OS(O)2R}2] (R, R1 = alkyl), with appended sulfonate groups which function as a linker to afford novel three-dimensional motifs. The study presented herein is directed toward the synthesis of diorganotin(IV) coordination assemblies derived from tetratopic 1,2,4,5-benzenetetracarboxylic acid under hydrothermal conditions by optimizing the pH (2 < pH < 8) of the reaction medium. The choice of the ligand is primarily driven by a large difference in the pKa values (pK1 = 1.92, pK2 = 2.87, pK3 = 4.49, pK4 = 5.63). This property favors partial or complete deprotonation of the carboxylic acids under

■

RESULTS AND DISCUSSION Synthesis and Characterization. The synthesis of 1−4 is achieved from the reaction of Me2SnCl2 and H4btec under hydrothermal conditions (130 °C, 72 h) by optimizing the initial pH of the reaction medium to 2−3 (for 1), 5−6 (for 2, 3), and 7.5−8.5 (for 4). Each reaction was performed in three different sets to establish the reproducibility of the protocol. The reactions can be represented as follows.

pH 2−3

Me2SnCl 2 + H4btec + 2KOH ⎯⎯⎯⎯⎯⎯⎯→ Me2Sn(H 2btec) + 2KCl + 2H 2O (1) 2Me2SnCl 2 + H4btec + 4KOH pH 5−6

⎯⎯⎯⎯⎯⎯⎯→ Me2Sn(btec)0.5 + [Me2Sn(H 2O)2 (btec)0.5 ]·H 2O + 4KCl + 4H 2O (2) (3) 3Me2SnCl 2 + 0.5H4btec + 6KOH pH 7.5−8.5

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯→ [{Me2SnOSnMe2(OH)}(Me2Sn(OH))(btec)0.5 ]·H 2O + 6KCl + 3H 2O (4)

The formation of 1 bearing uncoordinated −COOH groups in the structural framework necessitates a strong acidic pH (2− 3) to allow for partial deprotonation of the ligand. Compound 2 and its hydrated form 3 are formed as a mixture under pH 5−6 and were separated on the basis of their distinct crystal morphologies (parallelepiped and needles), as evident from SEM studies (Supporting Information, Figure S1). These compounds are separated in phase-pure form under a microscopic view and analyzed by powder X-ray diffraction (vide infra). Since the formation of oxo/hydroxo organotin species in 1−3 is not observed, it is surmised that hydrated dimethyltin cation, [Me2Sn(H2O)x]2+, persists as the dominant species in solution under acidic conditions (pH 2−6). The results find an analogy with the behavior of dimethyltin dichloride in aqueous medium under acidic pH and varying substrate concentration.11 This notion is further substantiated by a few crystallographically authenticated examples of discrete hydrated diorganotin cations, [R2Sn(H2O)4]2+ (R = Me, nBu), associated with weakly coordinating arenesulfonate anions.12 The formation of tetraorganodistannoxane in 4 relies upon basic reaction conditions (pH ∼ 8), for which there exists ample precedence in the literature.13 It is noteworthy to mention that the influence of pH conditions on the coordination-driven self-assembly process in organotin chemistry has not been addressed prior to this work, despite its wellknown relevance in metal−organic frameworks.14

□

Compounds 1−4 are insoluble in most of the common organic solvents. The phase purity in each case was established by comparison of the X-ray powder diffraction pattern of the bulk samples with the simulated one from single crystal X-ray structures (Figure 6). The infrared spectra (KBr) identify characteristic absorptions in the 1500−1700 cm−1 region and provide valuable information on the bonding behavior of the carboxylate groups (Supporting Information, Figure S2). For 1, three distinct absorptions appear at 1700, 1556, and 1410 cm−1 due to hydrogen bonded −COOH, νasCO2, and νsCO2 vibrations, respectively. The difference between the latter two values (Δν) on the order of 146 cm−1 suggests a bridging bidentate character of the carboxylate groups.15 A similar trend in the Δν (168 cm−1) value is observed for 2. For 3 and 4, the νasCO2 and νsCO2 absorptions appear at 1612−1590 and 1350−1365 cm−1 with a large Δν value on the order of 224− 262 cm−1. These results resemble closely a number of reported examples of diorganotin carboxylates with the anisobidentate coordination mode of the ligand.5 A broad band in the region of 3400−3500 cm−1 is assigned to lattice and/or coordinated water molecules. Thermogravimetric analysis (Supporting Information, Figure S3) reveals that 1 and 2 are stable up to 250 and 400 °C, respectively, while 3 shows an initial weight loss corresponding to one lattice and one coordinated water molecule (obsd, 9.8; calcd, 10.9%) up to 95 °C with subsequent appearance of a stable phase up to 330 °C. 10956


Article

Inorganic Chemistry

Figure 1. ORTEP diagrams (50% probability) and atomic numbering schemes of 1−4. All hydrogen atoms except COOH and OH groups are omitted for clarity.

[∠O1−C1−C2−C3 = −70.95(3)° and ∠O4−C5−C4−C3 = 12.17(34)°]. These attributes allow the layered structure to propagate in a three-dimensional motif via O−H···O hydrogen bonding between the neighboring −COOH groups. The relevant metrical parameters associated with these hydrogen bonds include O4−H4 = 0.820(2), H4···O3 = 1.832(2), O4··· O3 = 2.651(3) Å, ∠O4−H4···O3 = 176.65(16)°. Notably, compound 1 represents a unique example of a threedimensional assembly adorned with −COOH groups in the family of organotin carboxylates. Topological analysis of the framework structure was performed by contracting the ligand to its centroid while maintaining its connectivity, following the concept of the simplified underlying net.1c,16 While considering the layered structure, the dimethyltin moiety and the ligand can be logically designated as a 4-c uninodal net that belongs to sql topology with point symbol (44.62). Following a similar approach, the 3D structure can be designated as a 4,6-c two nodal net with sqc11 topology and point symbol (44.610.8)(44.62). Compound 2 crystallizes in the monoclinic P21/n space group. The structure differs from 1 with respect to the involvement of one tetraanionic ligand, [btec], and two dimethyltin cations in the repeat unit. The pair of carboxylate groups designated by C1 and C4 subtend torsional angles of −42.86 and −33.11, respectively, with respect to the phenyl ring and act in a syn−anti bidentate bridging mode. The subtle difference in the torsional angles allows the construction of a three-dimensional structure featuring two distinct arrays of eight-membered [Sn−O−C−O]2 puckered cyclic rings along the ac-plane (Figure 3). Each tin atom adopts a distorted

Compound 4 reveals loss of two water molecules from the lattice (obsd, 5.2; calcd, 5.6%) up to 150 °C after which it undergoes two successive weight losses at 350 and 530 °C. The char yield at 800 °C is nearly 38%. Structural Description. Single crystals of 1−4 suitable for X-ray crystallography were obtained directly from the hydrothermal reactions. A perspective ORTEP view of the repeat unit of each compound along with the atomic numbering scheme is shown in Figure 1. The crystallographic data are summarized in Table 1, while selected bond lengths and angles of 1−4 are given in Tables S1−S4, respectively (Supporting Information). Compound 1 crystallizes in the triclinic P1 space group. The repeat unit is composed of one dimethyltin cation and one [H2btec] ligand. Each tin atom is associated with four different ligands by virtue of the syn−anti bridging bidentate mode (Supporting Information, Figure S4) of the carboxylate groups [Sn1−O1, Sn1−O1#1 = 2.245(16), Sn1−O2#2, Sn1−O2#3 = 2.252(19) Å]. The bonding situation assists the formation of a layered structure composed of arrays of eight-membered [Sn− O−C−O]2 puckered cyclic rings with a chairlike conformation wherein the aromatic groups act as linkers (Figure 2). The geometry at each tin atom is distorted octahedron with the SnO4 core occupying the equatorial plane [∠O1#1−Sn1− O2#2, ∠O1−Sn1−O2#3 = 85.27(7)°; ∠O1−Sn1−O2#2, ∠O1#1−Sn1−O2#3 = 94.73(7); Σ360°] and axially disposed methyl groups [∠C6#1−Sn1−C6 = 180.00(8)°]. A noticeable feature is the observed difference in the spatial orientations of carboxylate (COO−) and uncoordinated −COOH groups with respect to the phenyl ring, as evident from the torsional angles 10957


Article

Inorganic Chemistry Table 1. Summary of Crystallographic Data of 1−4 crystal data

1

2

3

4

empirical formula formula weight temperature (K) wavelength (Å) crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dcalcd (g cm−1) μ (mm−1) F(000) crystal size (mm) θ range (deg) reflections collected independent reflections [R(int)] goodness-of-fit on F2 completeness to theta (%) max. and min. transmission data/restraints/parameters final R1, wR2 [I > 2sigma (I)] final R1, wR2 (all data) largest diff. peak and hole (e·Å−3)

C12H10O8Sn 400.89 300(2) 0.71073 triclinic P1 4.7971(3) 7.1710(4) 9.7105(5) 72.3410(10) 85.0520(10) 75.2660(10) 307.82(3) 1 2.163 2.2116 196 0.135 × 0.069 × 0.028 2.201−24.991 7593 1087 [0.0982] 1.01 99.9 0.942 and 0.839 1087/0/99 0.0183, 0.0477 0.0183, 0.0477 0.524 and −0.490

C7H7O4Sn 273.82 300(2) 0.71073 monoclinic P21/n 4.9060(3) 14.5672(9) 11.3934(7) 90 95.237 90 810.85(9) 4 2.243 3.12 524 0.086 × 0.033 × 0.032 2.275−30.908 14706 2329 [0.0270] 1.11 99.9 0.902 and 0.887 2329/0/112 0.0151, 0.0371 0.0173, 0.0379 0.464 and −0.418

C7H13O7Sn 327.86 299(2) 0.71073 monoclinic C2/c 11.1195(9) 13.0270(11) 15.7407(13) 90 98.341(2) 90 2256.0(3) 8 1.931 2.279 1288 0.127 × 0.124 × 0.046 2.423−28.391 19935 2819 [0.1410] 1.109 100 0.900 and 0.756 2814/16/174 0.0377, 0.0990 0.0414, 0.1038 1.360 and −1.683

C11H23O8Sn3 639.36 302(2) 0.71073 triclinic P1 9.0358(7) 10.1730(8) 11.3811(9) 96.033(2) 104.204(2) 94.120(2) 1003.38(14) 2 2.116 3.734 606 0.109 × 0.061 × 0.013 1.861−28.351 17931 4999 [0.0728] 1.002 100 0.953 and 0.761 4999/0/221 0.0291, 0.0483 0.0697, 0.0545 0.590 and −0.635

Figure 2. Perspective view of 1. (a) Layered structure. (b) 3D structure showing O−H···O hydrogen bonding interactions. All hydrogen atoms except COOH groups are omitted for clarity. The inset shows the chair conformation of the [Sn−O−C−O]2 ring. (c, d) Topological representations of the underlying nets.

octahedral geometry with an equatorially disposed SnO4 core (∠O2#1−Sn1−O4#2 = 95.08(5), ∠O2#1−Sn1−O1 = 85.46(4), ∠O4#2−Sn1−O3#3 = 88.44(6), ∠O1−Sn1−O3#3 = 91.01(7); Σ360 ± 01°) and trans C−Sn−C fragment

[∠C7−Sn1−C6 = 176.28(7)°]. A perspective view along the a-axis reveals the formation of rectangular grids with the aromatic rings acting as the vertices. The presence of methyl groups minimizes the solvent accessible void to 4.4% per unit 10958


Article

Inorganic Chemistry

Figure 3. Perspective view of 2. 3D structure (a) along the ac-plane and (b) along the bc-plane. All hydrogen atoms are omitted for clarity. (c) Topological representation of the underlying net.

cell, as calculated using PLATON.17 The overall structure can be regarded as a 4,8-connected two-nodal network that belongs to scu (sqc170) topology with the point symbol (416.612)(44.62)2. Compound 3 crystallizes in the monoclinic C2/c space group. The repeat unit is composed of two hydrated dimethyltin(IV) cations, [Me2Sn(H2O)2]2+, and one tetraanionic [btec]ligand. The structure adopts a one-dimensional assembly formed by covalent attachment of each tin atom with the carboxylate groups of two adjacent ligands [Sn−O2 = 2.112(3), Sn−O4 = 2.217(2) Å]. This results in the formation of an array of 14-membered macrocyclic rings containing ditin units with the aromatic groups acting as the spacers (Figure 4). The oxygen atoms, O5(C7) and O3(C3), are coordinated with the tin atom in an anisobidentate mode [Sn−O5 = 2.756(3), Sn−O3 = 3.168(3) Å]. The latter bond distance is considerably longer than the covalent sum of 2.13 Å but shorter than the sum of van der Waals radii (3.70 Å) between Sn and O atoms. The oxygen atoms (O1, O7) from coordinated water and (O2, O4, O5) from the carboxylate groups lie in a plane [Σ∠O−Sn−O = 360 ± 01°]. Accordingly, the geometry at the tin center can be better described as monocapped distorted pentagonal bipyramidal with a SnO5 core occupying the equatorial plane, while the O3 atom occupies an additional site. This unusual coordination geometry is supported by a large distortion of the O−Sn−O bond angles with the smallest and largest being 51.15(8) and 82.68(12)°, respectively, as well as a large deviation of the C1−Sn−C2 angle [150.92(2)°] from linearity. The Sn−O1 and Sn−O7 bond lengths of the coordinated water are 2.268(3) and 2.653(6) Å, respectively, and are in agreement with those reported for cationic diorganotin(IV) hydrates.11 To our knowledge, the coordination geometry of the tin atom as found in 3 has not been reported earlier in the family of organotin carboxylates. Strong O−H···O hydrogen bonding

interaction between the coordinated water molecules (O1, O7) and the carboxylate oxygen atoms (O3, O5) extends the one-dimensional assembly to a three-dimensional supramolecular motif. The relevant metrical parameters are as follows: O1−H1D = 0.80(6), H1D···O3#4 = 1.92(6), O1··· O3#4 = 2.711(4) Å, ∠O1−H1D···O3#4 = 170.0(6)°; O7− H7B = 0.84, H7B···O5#6 = 1.88, O7···O5#6 = 2.723(6) Å, ∠O7−H7B···O5#6 = 173.0°. The lattice water molecules are disordered and occupy the voids within the framework. Compound 4 crystallizes in the triclinic P1 space group. The structure is built from a repeat unit comprised of [Me2SnOSnMe2(OH)]2 (A), [{Me2Sn(μ2−OH)}2] (B), and [btec] ligand (Figure 5). The symmetrically substituted distannoxane (A) is constructed on a central Sn2O2 fourmembered ring (designated by Sn1) with two bridging hydroxyl groups of the Me2SnOH (designated by Sn2) units providing connectivity between Sn1 and Sn2 atoms [Sn−O = 2.183(3)−2.176(3) Å]. The self-assembly of A and B is accomplished by the distinct bonding preference of the tetraanionic ligand. The oxygen atoms (O4) of the adjacent carboxylate ligands are covalently linked with the Sn3 atoms of [Me2Sn(μ2−OH)]2 (B) to afford the formation of linear chains [Sn3−O4 = 2.159(2) Å]. These chains are held together by the distannoxane units via O6 oxygen atoms of the carboxylate groups [Sn2−O6 = 2.187(3) Å]. These bonding attributes afford the formation of a layered structure along the bc plane. The carboxylate oxygen atoms, O5, O6, and O7, form weak contacts with Sn3, Sn1#2, and Sn2, respectively [Sn3− O5 = 2.972(3), Sn1#2−O6 = 3.265(5), Sn2−O7 = 3.480(4) Å] and lie within the Van der Waals radii between the Sn and O atoms. Accordingly, the geometry at each tin atom is best described as distorted bicapped tetrahedron comprised of two Sn−C and two covalent Sn−O bonds (Sn−O = 1.986−2.17 Å), while O1−O6, O1−O7, and O3−O5 pairs define the capped faces around Sn1, Sn2, and Sn3 atoms, respectively. 10959


Article

Inorganic Chemistry

Figure 4. Perspective view of 3. (a) 1D structure. All hydrogen atoms and lattice water molecules are omitted. (b) 3D structure showing O−H···O hydrogen bonding interactions. All hydrogen atoms of methyl and lattice water are omitted for clarity.

Figure 5. Perspective view of 4. (a) 2D structure. All methyl groups, hydrogen atoms except for −OH groups, and lattice water molecules are omitted. (b) Topological representation. (c) 3D structure showing O−H···O hydrogen bonding. All methyl groups and hydrogen atoms except OH and water are omitted for clarity.

considered two-connected linkers and the tetratopic ligand as four-connected nodes. The resulting underlying net can be classified as 4-c uninodal sql topology defined by point symbol (44.62). The layered structure exhibits O−H···O type hydrogen bonding interactions involving OH (O1, O3), lattice water (O8), and carboxylate oxygen (O5, O7) atoms [O······O = 2.720−2.865 Å, ∠O−H···O = 171.49−179.47°] and directs

For example, the atoms forming the tetrahedron around Sn1 (C1, C2, O2, O2#2) display C1−Sn1−O2 and C2−Sn1−O2 angles on the order of 111.82(16) and 114.28(16), respectively, and form two angles that show at least in part the effect of capping atoms [O2−Sn1−O2#2 = 72.69(11); C1−Sn1−C2 = 133.9(2)]. To derive the topology of the twodimentional net, the oxo/hydroxo dimethyltin units are 10960


Article

Inorganic Chemistry

Figure 6. Powder X-ray differaction patterns of 1−4: simulated (black), primitive sample (red), and after hydrothermal treatment (green).

In conclusion, the study demonstrates for the first time a significant role of pH as a variable in rational synthesis of new dimethyltin carboxylates, 1−4, derived from H4btec ligand under hydrothermal conditions. Depending upon the pH of the reaction medium, dimethyltin species of varying compositions such as [Me 2 Sn] 2+ , [Me 2 Sn(H 2 O) 2 ] 2+ , [Me2SnOSn(OH)Me2]22+, and [Me2Sn(OH)]22+ remain an integral part of the framework structures. The method also allows a control over the degree of deprotonation of the ligand, and their coordination preferences direct the construction of one-/two-/three-dimensional motifs. The underlying nets of 1, 2, and 4 exhibit sqc11, scu (sqc170), and sql topologies, respectively. An interesting revelation is the exceptional stability of these polymers under extreme hydrothermal conditions, including acidic and basic medium. Further studies are in progress to harness this approach toward the synthesis of porous organotin-based coordination polymers and applications derived from there.

the assembly to a three-dimensional supramolecular motif. The solvent accessible void as calculated using PLATON is 9.27% per unit cell. Powder X-ray Diffraction. To evaluate hydrolytic stability, the primitive samples were heated under hydrothermal conditions (130 °C, 3 days) and studied by PXRD thereafter (Figure 6). No phase transition or framework collapse was observed. In addition, the primitive samples were immersed in aqueous HCl and KOH solutions of pH 3 and 10 separately for 7 days. The final unit cell parameters of the treated samples obtained from single crystal X-ray diffraction data remain identical to those obtained for the untreated samples. These results suggest the retention of crystallinity and structural integrity of these assemblies even under extreme aqueous conditions. While a plausible reason for the unique stability of these compounds is yet to be understood, an intuitive rationale can be put forth by considering high coordination number and imposed steric effects by the carboxylate ligand on each metal center, thus preventing the attack by H2O, H3O+, and OH− species. The strong donor− acceptor interactions in 1−4 can be considered promising to minimize deleterious side effects which are known to originate from the complexing ability of the Lewis acidic tin centers with various biochemically important molecules and initiate a cascade of events disrupting normal biological behavior.18

■

EXPERIMENTAL SECTION

Dimethyltin dichloride and 1,2,4,5-benzenetetracarboxylic acid were purchased from Sigma-Aldrich and used as procured. Fourier transform infrared (FTIR) spectra were recorded on a PerkinElmer Frontier FTIR spectrometer in the range 4000−400 cm−1 using a KBr pallet. Elemental analysis (C, H) was performed on a PerkinElmer model 2400 CHN elemental analyzer. Thermogravimetric analysis (TGA) was carried out in a nitrogen atmosphere between 30 and 800 10961


Article

Inorganic Chemistry °C at a heating rate 10 °C/min on a PerkinElmer Thermal analysis system. Powder X-ray diffraction (XRD) data were collected on a Bruker Advance machine using Cu Kα radiation. Each powder pattern was recorded in the 5−50° range (2θ) with a 0.5 s/step scan, corresponding to an approximate duration of 25 min. Synthetic Methods. Synthesis of Me2Sn(H2btec) (1). An aqueous solution (5.0 mL) of dimethyltin dichloride (0.219 g, 1.0 mmol) was added slowly to a preheated solution (10 mL, 80 °C) of H4btec (0. 254 g, 1.0 mmol) in water. The resulting clear solution with a pH of 1.5 was treated with aqueous KOH until a pH of 2−3 was attained. The content was then transferred to a 50 mL Teflon-lined autoclave and heated at 130 °C for 72 h. Upon cooling, a crop of crystalline solid of 1 was obtained which was washed with deionized water and ethanol. Yield: 88%. IR (KBr, cm−1): 1556 (νasymCO2); 1411 (νsymCO2); 1700 (νCOOH). Anal. Calcd for C12H10O8Sn: C, 35.92; H, 2.49. Found: C, 35.84; H, 2.47. Synthesis of Me2Sn(btec)0.5(2) and [Me2Sn(H2O)2(btec)0.5]·H2O (3). Following the procedure as described for 1, the solution containing dimethyltin dichloride (0.219 g, 1.0 mmol) and H4btec (0. 254 g, 1.0 mmol) was treated with aqueous KOH to attain a pH of 5−6. Hydrothermal treatment (130 °C, 72 h) of the mixture yields a crop of crystalline solid. The SEM micrographs reveal two distinct crystal morphologies (parallelepiped and needles) which were separated under a microscopic view and identified as pure phases of 2 and 3, respectively. For 2. Yield: 40%. IR (KBr, cm−1): 1550 (νasymCO2); 1382 (νsymCO2). Anal. Calcd for C7H7O4Sn: C, 30.68; H, 2.56. Found: C, 30.72; H, 2.61. For 3. Yield: 45%. IR (KBr, cm−1): 1612 (νasymCO2); 1350 (νsymCO2); 3400−3500 (br, νO−H). Anal. Calcd for C7H13O7Sn: C, 25.62; H, 3.96; Found: C, 25.71; H, 4.02. Synthesis of [{Me2SnOSnMe2(OH)}(Me2Sn(OH))(btec)0.5]·H2O (4). The synthesis of 4 was achieved by following a procedure similar to that described for 1 using dimethyltin dichloride (0.219 g, 1.0 mmol) and H4btec (0. 254 g, 1.0 mmol) at pH 8.0. The reaction was performed under hydrothermal conditions (130 °C, 72 h). Upon slow cooling, a crop of crystalline solid was obtained and identified as 4. Yield: 50%. IR (KBr, cm−1): 1591 (νasymCO2); 1367 (νsymCO2); 3400−3500 (br, νO−H, H 2 O and OH). Anal. Calcd for C11H23O8Sn3: C, 20.64; H, 3.59; Found: C, 20.21; H, 3.62. X-ray Crystallography. Intensity data of 1−4 were collected on a Bruker APEX-III CCD, using graphite monochromated Mo Kα radiation (λ = 0.71073 Å). Cell parameters, data reduction, and absorption corrections were performed using Bruker SAINT, using SAINT and SADABS.19 The structure was solved by direct methods using SHELXT and refined by a full-matrix least-squares method based on F2 using SHELXL-2016 (for 1, 2, and 4) and SHELXL2018/3 (for 3).20 Calculations were performed using ShelXle.21 All non-hydrogen atoms were refined anisotropically. All hydrogen atoms were placed in geometrically calculated positions using a riding model except for coordinated/lattice water, −OH, and −COOH groups which were located in the difference Fourier map and refined with bond length restraints and fixed Uij. For 3, the hydrogen atoms (H1A, H1B) on O1 were refined with free Uij. The lattice water molecule (O8) is disordered over two sites in the ratio of 1:1. Graphics were created using the Diamond program.22

■

cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Ravi Shankar: 0000-0002-4991-7018 Archishmati Dubey: 0000-0002-1329-404X Amanpreet Kaur Jassal: 0000-0003-2810-1762 Ekta Jakhar: 0000-0002-2469-0830 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work is supported by CSIR, India [Grant No. 01(2651)/ 12/EMR-II]. We are grateful to UGC, India, and IIT Delhi for providing senior research fellowships to A.D. and E.J., respectively. A.K.J. acknowledges DST(SERB), India, for a postdoctoral fellowship. The authors thank DST-India for providing a grant for the single crystal X-ray instrument.

■

REFERENCES

(1) (a) Zhou, H.-C.; Long, J. R.; Yaghi, O. M. Introduction to MetalOrganic Frameworks. Chem. Rev. 2012, 112, 673−674. (b) Stock, N.; Biswas, S. Synthesis of Metal-Organic Frameworks (MOFs): Routes to Various MOF Topologies, Morphologies, and Composites. Chem. Rev. 2012, 112, 933−969. (c) O’Keeffe, M.; Yaghi, O. M. Deconstructing the Crystal Structures of Metal-Organic Frameworks and Related Materials into Their Underlying Nets. Chem. Rev. 2012, 112, 675−702. (d) Gu, J.; Wen, M.; Liang, X.; Shi, Z.; Kirillova, M. V.; Kirillov, A. M. Multifunctional Aromatic Carboxylic Acids as Versatile Building Blocks for Hydrothermal Design of Coordination Polymers. Crystals 2018, 8, 83−98. (e) Lu, W.; Wei, Z.; Gu, Z.-Y.; Liu, T.-F.; Park, J.; Park, J.; Tian, J.; Zhang, M.; Zhang, Q.; Gentle III, T.; Bosch, M.; Zhou, H.-C. Tuning the structure and function of metal−organic frameworks via linker design. Chem. Soc. Rev. 2014, 43, 5561−5593. (2) Burtch, N. C.; Jasuja, H.; Walton, K. S. Water Stability and Adsorption in Metal-Organic Frameworks. Chem. Rev. 2014, 114, 10575−10612. (3) (a) Aguirre-Díaz, L. M.; Reinares-Fisac, D.; Iglesias, M.; Gutiérrez-Puebla, E.; Gándara, F.; Snejko, N.; Monge, M. Á . Group 13th metal-organic frameworks and their role in heterogeneouscatalysis. Coord. Chem. Rev. 2017, 335, 1−27. (b) Devic, T.; Serre, C. High valence 3p and transition metal based MOFs. Chem. Soc. Rev. 2014, 43, 6097−6115. (4) Yuan, S.; Qin, J.-S.; Lollar, C. T.; Zhou, H.-C. Stable MetalOrganic Frameworks with Group 4 Metals: Current Status and Trends. ACS Cent. Sci. 2018, 4, 440−450. (5) (a) Tiekink, E. R. T. Structural chemistry of organotin carboxylates: a review of the crystallographic literature. Appl. Organomet. Chem. 1991, 5, 1−23. (b) Wengrovius, J. H.; Garbauskas, M. F. Solution and Solid-State Structures of Several Dialkyltin Dicarboxylate Complexes, [R2Sn(O2CR’CO2)]x: Polymorphic Organotin Polymers. Organometallics 1992, 11, 1334−1342. (c) Lockhart, T. P. Solution and Solid-State Structures of Di-nbutyltin 3-Thiopropionate. X-ray Crystal Structure Determination of the Cyclic Hexamer. Organometallics 1988, 7, 1438−1443. (d) Lockhart, T. P.; Calabrese, J. C.; Davidson, F. Structural Studies of Diorganotin(IV) Carboxylates. X-ray and NMR Structures of Me 2 Sn(OAc) 2 and a 7-Coordinate Tin Anion, Me 2 Sn(OAc)3−NMe4+.2CHCl3. Organometallics 1987, 6, 2479−2483.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.9b01387. SEM micrographs for 2 and 3, IR spectra and TGA of 1−4, and tables (S1−S4) containing selected bond lengths and bond angles (PDF) Accession Codes

CCDC 1891967−1891969 and 1915262 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/ 10962


Article

Inorganic Chemistry (6) (a) Gielen, M. Tin based antitumour drugs. Coord. Chem. Rev. 1996, 151, 41−51. (b) Sirajuddin, M.; Ali, S.; Mckee, V.; Sohail, M.; Pasha, H. Potentially bioactive organotin(IV) compounds: Synthesis, characterization, in vitro bioactivities and interaction with SS-DNA. Eur. J. Med. Chem. 2014, 84, 343−363. (c) Sirajuddin, M.; Mckee, V.; Tariq, M.; Ali, S. Newly designed organotin(IV) carboxylase with peptide linkage: Synthesis, structural elucidation, physiochemical characterizations and pharmacological investigations. Eur. J. Med. Chem. 2018, 143, 1903−1918. (7) (a) Garcia-Zarracino, R.; Ramos-Quinones, J.; Hopfl, H. SelfAssembly of Dialkyltin(IV) Moieties and Aromatic Dicarboxylates to Complexes with a Polymeric or a Discrete Trinuclear Macrocyclic Structure in the Solid State and a Mixture of Fast Interchanging Cyclooligomeric Structures in Solution. Inorg. Chem. 2003, 42, 3835− 3845. (b) García-Zarracino, R.; Höpfl, H. A 3D Hybrid Network Containing Large Spherical Cavities Formed through a Combinationof Metal Coordination and Hydrogen Bonding. Angew. Chem., Int. Ed. 2004, 43, 1507−1511. (c) García-Zarracino, R.; Höpfl, H. SelfAssembly of Diorganotin(IV) Oxides (R = Me, nBu, Ph) and 2,5Pyridinedicarboxylic Acid to Polymeric and Trinuclear Macrocyclic Hybrids with Porous Solid-State Structures: Influence of Substituents and Solvent on the Supramolecular Structure. J. Am. Chem. Soc. 2005, 127, 3120−3130. (d) Chandrasekhar, V.; Mohapatra, C.; Butcher, R. J. Synthesis of One- and Two-Dimensional Coordination Polymers Containing Organotin Macrocycles. Reactions of (n-Bu3Sn)2O with Pyridine Dicarboxylic Acids. Structure-Directing Role of the Ancillary 4,4′-Bipyridine Ligand. Cryst. Growth Des. 2012, 12, 3285−3295. (e) Ma, C.; Wang, Q.; Zhang, R. Self-Assembly and Characterization of a Novel 2D Network Polymer Containing a 60-Membered Organotin Macrocycle. Inorg. Chem. 2008, 47, 7060−7061. (f) Chandrasekhar, V.; Thirumoorthi, R. Reactions of 3,5Pyrazoledicarboxylic Acid with Organotin Chlorides and Oxides. Coordination Polymers Containing Organotin Macrocycles. Organometallics 2009, 28, 2096−2106. (g) Chandrasekhar, V.; Mohapatra, C.; Banerjee, R.; Mallick, A. Synthesis, Structure, and H2/CO2 Adsorption in a Three-Dimensional 4-Connected Triorganotin Coordination Polymer with a sqc Topology. Inorg. Chem. 2013, 52, 3579−3581. (h) Gong, Y.-Q.; Wang, R.-H.; Lou, B.-Y.; Hong, M.-C. catena- Poly[[dimethyltin(IV)]-μ-benzene-1,4-dicarboxylato]. Acta Crystallogr., Sect. E: Struct. Rep. Online 2005, E61, m1226−m1227. (i) Ndoye, D.; Diop, L.; Molloy, K. C.; Kociok-Köhn, G. X-ray crystal structures of[(Cy2NH2)]3[C6H3(CO2)3].4H2O and [i-Bu2NH2][(Me3SnO2C)2C6H3CO2]. Main Group Met. Chem. 2013, 36, 215− 219. (j) Ma, C.; Han, Y.; Zhang, R.; Wang, D. Self-Assembled Triorganotin(IV) Moieties with 1,3,5 BenzenetricarboxylicAcid: Syntheses and Crystal Structures of Monomeric, Helical, and Network Triorganotin(IV) Complexes. Eur. J. Inorg. Chem. 2005, 3024−3033. (k) Ndoye, D.; Diop, L.; Molloy, K. C.; Kociok-Kö hn, G. Supramolecular organotin tris-carboxylates: crystal and molecular structure of [Cy2NH2]2[1-Me3(H2O)SnOCO-3,5-(OOC)2C6H3]· EtOH. Main Group Met. Chem. 2012, 35, 59−61. (8) (a) Chandrasekhar, V.; Thirumoorthi, R.; Azhakar, R. New Structural Forms of Organostannoxane Macrocycle Networks. Organometallics 2007, 26, 26−29. (b) García-Zarracino, R.; Höpfl, H.; Güizado-Rodríguez, M. Bis(tetraorganodistannoxanes) as Secondary Building Block Units(SBUs) for the Generation of Porous Materials − A Three-Dimensional Honeycomb Architecture Containing Adamantane-type Water Clusters. Cryst. Growth Des. 2009, 9, 1651−1654. (c) Zhang, R.- F.; Wang, Q.-F.; Yang, M.-Q.; Wang, Y.R.; Ma, C.-L. Five new dicarboxylate organotin complexes under hydrothermal condition: Syntheses, characterization and crystal structures of 1D, 2D and 3D polymers constructed from dimeric tetraorganodistannoxane units. Polyhedron 2008, 27, 3123−3131. (d) Sougoule, A. S.; Mei, Z.; Xiao, X.; Balde, C. A.; Samoura, S.; Dolo, A.; Zhu, D. A novel macrocyclic organotin carboxylate containing a penta-nuclear long ladder. J. Organomet. Chem. 2014, 758, 19−24. (e) Wang, R.-H.; Hong, M.-C.; Luo, J.-H.; Cao, R.; Weng, J.-B. Synthesis and Crystal Structures of the First Two Novel Dicarboxylate

Organotin Polymers Constructed from Dimeric Tetraorganodistannoxane Units. Eur. J. Inorg. Chem. 2002, 2082−2085. (9) (a) Shankar, R.; Jain, A.; Singh, A. P.; Kociok-Köhn, G.; Molloy, K. C. Facile Synthesis of Novel Two- And Three-Dimensional Coordination Polymers Containing Dialkyltin Phosphonate-Based Tri/Tetra-Nuclear Clusters with Appended Sulfonate Groups. Inorg. Chem. 2009, 48, 3608−3616. (b) Shankar, R.; Singla, N.; Asija, M.; Kociok-Köhn, G.; Molloy, K. C. Synthesis and Structural Studies of Diorganotin(IV)-Based Coordination Polymers Bearing Silaalkylphosphonate Ligands and Their Transformation into Colloidal Domains. Inorg. Chem. 2014, 53, 6195−6203. (c) Shankar, R.; Jain, A.; Kociok-Köhn, G.; Molloy, K. C. Diorganotin-Based Coordination Polymers Derived from Sulfonate/Phosphonate/Phosphonocarboxylate Ligands. Inorg. Chem. 2011, 50, 1339−1350. (d) Shankar, R.; Mendiratta, S.; Singla, N.; Kociok-Köhn, G.; Lutter, M.; Jurkschat, K. Reactivity of Elemental Tin and Zinc toward Organophosphonic Acid Dialkyl Esters: A New One-Pot Recipe for the Synthesis of Coordination Assemblies Derived from O-Alkylorganophosphonate Ligands. Inorg. Chem. 2017, 56, 721−724. (10) (a) Atallah, H.; Mahmoud, M. E.; Jelle, A.; Lough, A.; Hmadeh, M. A highly stable indium based metal organic framework for efficient arsenic removal from water. Dalton Trans 2018, 47, 799−806. (b) Volkringer, C.; Loiseau, T.; Guillou, N.; Férey, G.; Haouas, M.; Taulelle, F.; Elkaim, E.; Stock, N. High-Throughput Aided Synthesis of the Porous Metal-Organic Framework-Type Aluminum Pyromellitate, MIL-121, with Extra Carboxylic Acid Functionalization. Inorg. Chem. 2010, 49, 9852−9862. (c) Xiao, X.; Du, D.; Han, X.; Liang, J.; Tian, M.; Zhu, D.; Xu, L. Self-assembly of triorganotin(IV) moieties with 1,2,4,5-benzenetetracarboxylic acid: Syntheses, characterizations and influence of solvent on the molecular structure. J. Organomet. Chem. 2012, 713, 143−150. (11) Tobias, R. S.; Yasuda, M. Studies on the Soluble Intermediates in the Hydrolysis of Dimethyltin Dichloride. Can. J. Chem. 1964, 42, 781−793. (12) (a) Chandrasekhar, V.; Boomishankar, R.; Singh, S.; Steiner, A.; Zacchini, S. Synthesis and X-ray Crystal Structure of the Novel Organotin Dication [n-Bu2Sn(H2O)4]2+: A Lamellar Layered Structure Assisted by Intermolecular Hydrogen Bonding. Organometallics 2002, 21, 4575−4577. (b) Hippel, I.; Jones, P. G. Blaschette, A. Charakterisierung des Kations [Me2Sn(H2O)4]2+ imkristallinenZus t a n d : B i l d u n g u n d R ö n t g e n s t r u k t u r a n a l y s e v o n Tetraaquadimethylzinn(IV)-bis(1,1,3,3-tetraoxo-1,3,2-benzodithiazolid). J. Organomet. Chem. 1993, 448, 63−67. (13) Beckmann, J.; Henn, M.; Jurkschat, K.; Schürmann, M. Hydrolysis of Bis((trimethylsilyl)methyl)tin Dihalides. Crystallographic and Spectroscopic Study of the Hydrolysis Pathway. Organometallics 2002, 21, 192−202 and references cited therein . (14) Long, L.-S. pH effect on the assembly of metal-organic architectures. CrystEngComm 2010, 12, 1354−1365. (15) (a) Deacon, G. B.; Phillips, R. J. Relationships Between the Carbon-Oxygen Stretching Frequencies of Carboxylato Complexes and the Type of Carboxylate Coordination. Coord. Chem. Rev. 1980, 33, 227−250. (b) Pretsch, E.; Bühlmann, P.; Affolter, C. Structure Determination of Organic Compounds; Springer-Verlag: Berlin, Heidelberg, 2000. (16) (a) Blatov, V. A.; Shevchenko, A. P.; Proserpio, D. M. Applied Topological Analysis of Crystal Structures with the Program Package Topos Pro. Cryst. Growth Des. 2014, 14, 3576−3586. (b) Blatov, V. A. Multipurpose crystallochemical analysis with the program package TOPOS. IUCr Comp Comm Newsl. 2006, 7, 4. (17) Spek, L. Single-crystal structure validation with the program PLATON. J. Appl. Crystallogr. 2003, 36, 7−13. (18) Vargas, D. G.; Magaña, A. -M; Sharma, H. K.; Whalen, M. M.; Gilbert, T. M.; Pannell, K. H. A potential “green” organotin: Bis(methylthiopropyl)tin dichloride, [MeS(CH2)3]2SnCl2. Inorg. Chim. Acta 2017, 468, 125−130. (19) (a) SAINT; Bruker AXS Inc.: Madison, WI, 2003. (b) SADABS; Bruker AXS Inc.: Madison, WI, 2002. 10963


Article

Inorganic Chemistry (20) (a) SHELXL-2018/3; 2018. (b) Sheldrick, G. M. A Short History of SHELX. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, A64, 112−122. (c) Sheldrick, G. M. SHELXS and SHELXL; University of Göttingen: Göttingen, Germany, 1997. (21) Hübschle, C. B.; Sheldrick, G. M.; Dittrich, B. ShelXle: aQt graphical user interface for SHELXL. J. Appl. Crystallogr. 2011, 44, 1281−1284. (22) Klaus, B. DIAMOND, version 1.2c; University of Bonn: Bonn, Germany, 1999.

10964


Tailoring Structural Diversity in Dimethyltin Carboxylates by the pH

Recommend Documents