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Synthesis and structural characterization of new ladder-like organostannoxanes derived from carboxylic acid derivatives: [C5H4N(p-CO2)]2[Bu2Sn]4(μ3-O)2(μ2-OH)2, [Ph2CHCO2]4[Bu2Sn]4(μ3-O)2, and [(p-NH2)-C6H4-CO2]2[Bu2Sn]4(μ3-O)2(μ2-OH)2

Synthesis and structural characterization of new ladder-like organostannoxanes derived from... 1IntroductionDuring the past few decades, research on the synthesis and characterization of coordination polymers has intrigued scientists not only for their fascinating structures but also for their potential applications (Gielen et al., 2005; Kemmer et al., 2000; Willem et al., 1997). It has become apparent that coordination polymers may be prepared by the appropriate selection of metal and multifunctional ligands (Chandrasekhar et al., 2002, 2005; Diop et al., 2021). Among these materials, organotin(iv) carboxylate complexes have been actively investigated by a large number of researchers due to their significant reduction in tumor growth rates (Vieira et al., 2010), interesting topologies, and various structural types including monomers, dimers, tetramers, oligomeric ladders, and hexameric drums (Arjmand et al., 2014; Banti et al., 2019). The organostannoxanes have received special attentions, particularly in view of their immense structural diversity. Several products, such as ladders (Wen et al., 2018; García-Zarracino et al., 2009), cubes (Cavka et al., 2008), hexameric (Baul et al., 2017), and polymeric drums (Ma et al., 2003), have been isolated. Ladder-shaped tetranuclear organotin compounds (Wang et al., 2013) have also been isolated. Tetranuclear crystal structures [(n-Bu2Sn)4(O)2(OH)2(O3SC6H4-NH2-4)2] (Wen et al., 2018), [(Me2Sn)4(O)2(OH)2(O3SC6H4-NH2-4)2] (Wen et al., 2018), and [(n-Bu2Sn)4(μ3-O)2(μ2-OCH3)2(O2CC6H4-SO2NH2-4)2 (Wang et al., 2019) with the ladder as structural motif were previously described in the literature. Many butylstannoxanes were prepared using carboxylate ligands (Baul et al., 2017; Shankar and Dubey, 2020; Valcarcel et al., 2012; Wang et al., 2019). These molecular structures of compounds display hexameric Sn6O6 clusters with drum-like or tetrameric structures revealing Sn4O2 cores with ladder-type structural motifs. In our previous work, we reported a series of butylstannoxanes carboxylate complexes using carboxylic acid ligands such as pyridine-4-carboxylic acid, diphenylacetic acid, and 4-aminocarboxylic acid. The synthesis and structural characterization of three new organostannoxanes are reported as follows: [C5H4N(p-CO2)]2[Bu2Sn]4(μ3-O)2(μ2-OH)2 (1), [Ph2CHCO2]4[Bu2Sn]4(μ3-O)2 (2), and [(p-NH2)-C6H4-CO2]2[Bu2Sn]4(μ3-O)2(μ2-OH)2 (3).2Results2.1Crystallographic data and experimental detailsCrystal data, data collection, and structure refinement details for the complex are summarized in Table 1.Table 1Crystal data and structure refinement of 1 and 212FormulaC44H82N2O8Sn4C88H116O10Sn4MoietyC44H82N2O8Sn4C88H116O10Sn4T (K)175175SpacegroupP21/nP-1Crystal systemMonoclinicTriclinica (Å)13.0597(5)15.6908(7)b (Å)12.2041(6)15.7536(8)c (Å)17.0979(6)19.4517(8)α (°)9083.718(4)β (°)96.017(4)75.218(4)γ (°)9064.601(5)V (Å3)2710.09(19)4199.7(4)Z22P (g cm−3)1.5221.430Mr (g mol−1)1241.961808.65µ (mm−1)1.8671.231Rint0.0650.084θmax (°)29.09129.464Resolution (Å)0.790.82Ntot (measured)18,16452,524Nref (unique)6,38119,770Nref (I > 2σ (I))4,46210,858Nref (least-squares)4,46210,858Npar285928<σ(I)/I> 0.08070.1165R1 (I > 2σ(I))0.09010.0689wR2 (I>2σ(I))0.03900.0887R1 (all)0.13250.1292wR2 (all)0.04880.01682GOF1.42611.1410Δρ (e Å−3)−1.56/3.26−1.70/3.72Crystal size (mm)0.12 × 0.15 × 0.200.22 × 0.25 × 0.303Discussion3.1ReactionsThe general chemical reactions in methanol are shown for complexes 1 and 3 Eq. (1) and for complex 2 Eq. (2):(1)2HL+4n-Bu2Sn(OCH3)2+4H2O→L2[Bu2Sn]4(μ3-O)2(μ2-OH)2+8MeOHHL=pyridine-4-carboxylicacid(1)or4-aminobenzenecarboxylicacid(3),\begin{array}{c}2\text{HL}\hspace{.25em}+\hspace{.25em}4n{\text{-Bu}}_{2}\text{Sn}{({\text{OCH}}_{3})}_{2}\hspace{.25em}+\hspace{.25em}4{\text{H}}_{2}O\to {\text{L}}_{2}{{[}{\text{Bu}}_{2}\text{Sn}]}_{4}{({{\mu }}_{3}\text{-O})}_{2}{({{\mu }}_{2}\text{-OH})}_{2}\hspace{.25em}+\hspace{.25em}8\text{MeOH}\\ \text{HL}\hspace{.25em}=\hspace{.25em}\text{pyridine-}4\text{-carboxylic}\hspace{.5em}\text{acid}\hspace{.5em}({\bf{1}})\hspace{.5em}\text{or}\hspace{.5em}\hspace{2.5em}4\text{-aminobenzenecarboxylic}\hspace{.5em}\text{acid}\hspace{.5em}({\bf{3}}),\end{array}(2)4Ph2CHCO2H+4n-Bu2Sn(OCH3)2+2H2O→[Ph2CHCO2]4[Bu2Sn]4(μ3-O)2+8MeOH.4{\text{Ph}}_{2}{\text{CHCO}}_{2}H\hspace{.25em}+\hspace{.25em}4n\text{-}{\text{Bu}}_{2}\text{Sn}{({\text{OCH}}_{3})}_{2}\hspace{.25em}+\hspace{.25em}2{\text{H}}_{2}O\to {{[}{\text{Ph}}_{2}{\text{CHCO}}_{2}]}_{4}{{[}{\text{Bu}}_{2}\text{Sn}]}_{4}{({\text{&#x03BC;}}_{3}\text{-}\text{O})}_{2}\hspace{.25em}+\hspace{.25em}8\text{MeOH}\text{.}After synthesis, the complexes are characterized by elemental analyses, Fourier-transform infrared spectroscopy and nuclear magnetic resonance (1H, 13C) experiments, and, for 1 and 2, single-crystal X-ray diffraction.3.2Spectroscopic studies3.2.1FT-IR spectraThe explicit feature in the FTIR spectra is the absence of a broadband in the region 3,400–2,800 cm−1, which appears in the free ligands for the COOH group, indicating the removal of COOH protons and the formation of Sn–O bonds through this site (Li et al., 2010; Zhang et al., 2012). The strong absorption appearing at 444 (1), 436 (2), and 433 (3) cm−1 is assigned to ν(Sn–O) (Xiao et al., 2013). The intense absorption maximum in the 623–630 cm−1 region is assigned to an Sn–O–Sn stretching vibration (Li et al., 2015). In the infrared spectra of this complex, the Δν(C(O)O) [ν(C(O)O)asym – ν(C(O)O)sym] values are 299 cm−1 for 1 and 273 cm−1 for 3, larger than 200 cm−1, which stands for the monodentate coordination mode of the carboxylate groups (Hanif et al., 2010), and this behavior is also consistent with the X-ray structure. The two Δν magnitudes (νasymCOO – νsymCOO) 254 and 143 cm−1 for (2) show that two distinct coordination modes for carboxylate ligands are present in the structure (Eng et al., 2007). One carboxylate fragment is symmetrically bridged between two Sn ions, and another carboxylate acts as a bis-monodentate ligand for Sn atoms (Scheme 2). The presence of a νsSnBu2 band at 617 cm−1 (1), 615 cm−1 (2), and 613 cm−1 (3) indicates a nonlinear SnBu2 residue (Nakamoto, 1997; Beckman et al., 2004) (Schemes 1 and 2). The conclusions drawn from the IR data are very much consistent with those of the X-ray crystallography studies.Scheme 1Structures of [C5H4N(p-CO2)]2[Bu2Sn]4(μ3-O)2(μ2-OH)2 (1) or [(p-NH2)-C6H4-CO2]2[Bu2Sn]4(μ3-O)2(μ2-OH)2 (3).Scheme 2Structure of [Ph2CHCO2]4[Bu2Sn]4(μ3-O)2 (2).3.2.2NMR spectraThe 1H and 13C NMR data of the complexes are given in the experimental part, and the observed resonances have been assigned based on the chemical shift values. In the 1H NMR spectra, the expected signals in the 10–13 ppm region of the carboxylic acid hydrogens are not present in the complexes, indicating the replacement of the carboxylic acid protons with organotin(iv) moieties (Najafi et al., 2014; Xiao et al., 2013). The order of the 1H chemical shifts of the CHngroups in the Sn–butyl substituents was found to be (α, β) > (γ, δ) for the Bu2Sn complexes (SnCH2(α)CH2(β)CH2(γ)CH3(δ)) (Pruchnik et al., 2013). Multiplet signals in the 1.50–1.86, 1.25–1.43, and 0.92–0.93 ppm ranges are attributed to (m, α-CH2, β-CH2), (m, γ-CH2), and (t, δ-CH3), respectively. The multiplet signals at 8.12–6.77 ppm are assigned to aromatic protons. In the 13C NMR spectra of all the complexes, peaks at 167.41 (1), 175.1 (2), and 179.34 (3) ppm attributed to COO− groups show a downfield shift of all the carbon resonances compared to the free carboxylates. These conclusions are consistent with those of the IR data and the X-ray crystal structures.The structures for complexes 1, 2, and 3 are Sn4O4 tetramers with either monodentate or bridging carboxylate ligands (Schemes 1 and 2).3.3Crystal structure of complex 1A perspective view of the molecular structure of complex 1 is illustrated in Figures 1 and 2. Selected bond lengths (Å) and angles (°) are listed in Table 2. The structure consists of the hydroxide-bridged tetrameric organostannoxane ladder and two deprotonated pyridine-4-carboxylic ligands. The complex adopts tetranuclear tin(iv) ladder-like structure containing two deprotonated ligands linked by three alternate Sn2O2 four-membered rings. As is shown in 1, the molecular structure is a centrosymmetric ladder-like structure consisting of the Sn4(μ3-O)2(μ2-OH)2 group and two deprotonated ligands. As is the case for other usual tetrameric organostannoxanes (Li et al., 2015), the structure is based on a centrosymmetric Sn2O2 unit connected to a pair of exocyclic Sn atoms via bridging µ3-O atoms. Triply bridged μ3-O atoms, which share their electrons with three tin(iv) centers, have distorted tetrahedral configurations. All the Sn atoms are five-coordinated, showing a trigonal bipyramid configuration in two different chemical environments: SnBu2O2(OH) and SnBu2O(OH)[C5H4N(p-CO2)]. For Sn(1) atom (exocyclic), the basal plane is defined by C(33), C(27), and O(2), and the axial sites occupied by the O(2i) and O(16) atoms, which form an angle of 147.95 (14)°, deviating from a linear arrangement. The carboxylate moiety COO– of the ligand is bonded as a monodentate mode with Sn(3)–O(18) (2.176 Å) way as depicted in Table 2. These bond lengths are in accordance with those of the reported di-n-butyltin(iv) carboxylates (Xiao et al., 2013; Zhu et al., 2011).Figure 1Tetranuclear structure of [C5H4N-(p-CO2)]2[Bu2Sn]4(μ3-O)2(μ2-OH)2 (1).Figure 2Crystal structure in an infinite chain of [C5H4N-(p-CO2)]2[Bu2Sn]4(μ3-O)2(μ2-OH)2 (1) with O–H⋯N intermolecular hydrogen bonds. Only Cipso of the n-butyl groups are shown for clarity.Table 2Geometric parameters (Å and °) of complex 1Lengths (Å)Angles (°)Sn1–O2i2.128 (3)O2i–Sn1–O2 74.51 (17)Sn1i–O2–Sn3143.67 (18)Sn1–O2 2.062 (4)O2i–Sn1–Sn3 108.55 (10)Sn1–O2–Sn3 110.83 (15)Sn1–O16 2.139 (4)O2i–Sn1–O16 147.95 (14)O2–Sn3–C6 112.9 (2)Sn1–C27 2.106 (7)O2–Sn1–O16 73.44 (14)O2–Sn3–C9 112.2 (3)Sn1–C33 2.139 (7)O2i–Sn1–C27 95.6 (2)C6–Sn3–C9 134.7 (3)O2–Sn3 2.005 (4)O2–Sn1–C27 115.2 (3)O2–Sn3–O16 73.80 (15)Sn3–C6 2.087 (7)O16–Sn1–C27 98.3 (3)C6–Sn3–O16 91.8 (2)Sn3–C9 2.166 (8)O2i–Sn1–C33 99.2 (2)C9–Sn3–O16 96.3 (3)Sn3–O16 2.173 (4)O2–Sn1–C33 115.8 (3)O2–Sn3–O18 80.31 (14)Sn3–O18 2.176 (4)O16–Sn1–C33 94.2 (3)C6–Sn3–O18 99.1 (2)C27–Sn1–C33 129.0 (3)C9–Sn3–O18 92.6 (2)Sn1i–O2–Sn1 105.49 (17)O16–Sn3–O18 154.09 (16)Symmetry code: (i) −x, −y, −z + 1.Intermolecular O–H···N hydrogen bonds, involving the bridging hydroxy group and the N atom of the ligand, connect the discrete units into a two-dimensional (2D) network (Figure 2). For the O–H···N intermolecular interactions and C–H⋯O intramolecular interactions (Figure 3), the H(161)···N(24ii) and H(341)⋯O(18i) distances are 2.06(4) and 2.59 Å, respectively. The O(16)–H(161)···N(24ii) and C(34)–H(341)⋯O(18i) angles are 153(8) and 145° (Table 3). The hydrogen-bond geometry is close to the values reported for [(n-Bu2Sn)2(μ3-O)(µ-OH)L]2 (Li et al., 2015). The crystallographic study confirms the spectroscopic conclusions.Figure 3Crystal structure in infinite chain of [C5H4N-(p-CO2)]2[Bu2Sn]4(μ3-O)2(μ2-OH)2 (1) with intermolecular hydrogen bonds O–H···N (color code: blue) and intramolecular hydrogen bonds C–H⋯O (color code: greenish). Only Cipso of the n-butyl groups are shown for clarity.Table 3: Hydrogen-bond geometry (Å and °) of complex 1D–H···AD–HH···AD···AD–H···AO16–H161···N24ii0.82 (2)2.06 (4)2.810 (14)153 (8)C34–H341···O18i0.982.593.440 (14)145Symmetry codes: (i) −x, −y, −z + 1; (ii) x + 1/2, −y − 1/2, z − 1/2.3.4Crystal structure of complex 2The asymmetric unit features linkage of neighboring monomers by hydrogen–bond interactions [C–H⋯O and C–H⋯π], giving rise to the formation of organotin(iv) aggregate (Figure 4). Selected bond lengths (Å) and angles (°) are listed in Table 4. The conformations of the two independent molecules are almost the same, except for small differences in angles and bond lengths. The crystal structure is very similar to that reported by Zhang et al. (2012). The structure is a tetranuclear centrosymmetric dimer of an oxoditin(iv) unit having a central four-member ring composed of Sn(3)–O(2)–Sn(3i)–O(2i). In this complex, the central Sn2O2 core is fused with two four-member and two six-member rings. The four-member rings, that is, [Sn2O2, i.e., O(28)–Sn(1)–O(2)–Sn(3 i) and O(28i)–Sn(1i)–O(2i)–Sn(3)], are due to the bridging of the monodentate ligand through O atoms, O(28)–Sn(1), and O(28I)–Sn(1i), respectively. Two six-member rings [Sn2O3C; i.e., Sn(1)–O(6)–C(5)–O(4)–Sn(3)–O(2), Sn(1i)–O(6i)–C(5i)–O(4i)–Sn(3i)–O(2i)] also overlap central Sn2O2. As is the case for other usual tetrameric organostannoxane (Li et al., 2015), the structure is based on a centrosymmetric Sn2O2 unit connected to a pair of exocyclic Sn atoms via bridging µ3-O atoms. There are two distinct carboxylate ligands in the structure. The first carboxylate, defined by the O(4) and O(6) atoms, symmetrically bridges the exocyclic Sn(3) and endocyclic Sn(1) atoms. The second carboxylate is a bis-monodentate coordinating ligand to the exocyclic Sn(3) and endocyclic Sn() via µ-O(28) atom (Figure 4). The endocyclic Sn(3) exists in a distorted octahedron geometry with the four O atoms [O(4), O(6), O(2), and O(28i)] defining the basal plan. The axial position is occupied by C(20) and C(24) which form an angle C(20)–Sn(3)–C(24) of 143.7 (5) (Table 4). The exocyclic Sn(1) atoms are five coordinated and show distorted trigonal bipyramid geometry with the basal plan defined by the µ3–O(2) atom, the C(48) and C(44) atoms. The axial angle of O(6)–Sn(1)–O(28i) is 169.9°(3).Figure 4The ladder structure of aggregate complex 2 (hydrogen atoms bonded to carbon atoms are omitted, and only the α-carbon of the butyl groups has been drawn for clarity).Table 4Geometric parameters (Å and °) of complex 2Lengths (Å)Angles (°)Sn1–O2 2.044 (8)O2–Sn1–O6 91.7 (3)O28i–Sn3–O4 127.7 (3)Sn1–O6 2.276 (9)O2–Sn1–O28 78.3 (3)O2i–Sn3–C20 100.0 (4)Sn1–O28 2.198 (8)O6–Sn1–O28 169.9 (3)O2–Sn3–C20 105.2 (4)Sn1–C44 2.143 (12)O2–Sn1–C44 112.0 (4)O28i–Sn3–C20 79.4 (4)Sn1–C48 2.128 (13)O6–Sn1–C44 84.4 (4)O2i–Sn3–C24 99.6 (4)O2–Sn3i 2.143 (7)O28–Sn1–C44 98.2 (4)O2–Sn3–C24 108.8 (4)O2–Sn3 2.061 (8)O2–Sn1–C48108.4 (4)O28i–Sn3–C24 80.8 (4)Sn3–O28i 2.669 (9)O6–Sn1–C48 89.2 (4)O4–Sn3–C20 85.3 (5)Sn3–O4 2.262 (9)O28–Sn1–C48 95.0 (4)O4–Sn3–C24 83.2 (5)Sn3–C20 2.137 (13)C44–Sn1–C48 139.2 (5)C20–Sn3–C24 143.7 (5)Sn3–C24 2.117 (12)Sn3i–O2–Sn1 119.4 (3)Sn3–O4–C5 138.9 (8)Sn52–O53 2.218 (8)Sn3i–O2–Sn3 103.0 (3)O2–Sn3–O488.6 (3)Sn52–O57 2.047 (8)Sn1–O2–Sn3 137.6 (4)O2i–Sn3–O4165.5 (3)Sn52–O80 2.203 (7)O2i–Sn3–Sn3i 37.6 (2)O2i–Sn3–O28i66.7 (3)Sn52–C96 2.119 (14)O2i–Sn3–O2 77.0 (3)Sn52–C100 2.113 (14)O2–Sn3–O28i 143.6 (3)O55–Sn56, 2.298 (10)Sn56–O57ii 2.126 (8)Symmetry codes: (i) −x + 1, −y + 1, −z; (ii) −x + 1, −y + 2, −z + 1.Intermolecular C–H⋯O and C–H⋯π hydrogen bonds are recognized in complex 2, which link the molecular structure into 2D network. For the C–H⋯O interactions, the distances [H⋯O, in the 2.35–2.60 Å ranges] and [H⋯π, in the 2.40–2.60 Å ranges] (Table 5) are all close to the values reported by Li et al. (2015).Table 5Hydrogen-bond geometry (Å and °) of complex 2D–H···AD–HH···AD···AD–H···AC12–H121···C61ii0.932.403.11 (3)134C19–H191···O40.932.473.09 (3)124C37–H371···O300.932.443.05 (3)124C44–H442···O82iii0.972.603.37 (3)136C79–H791···O550.932.353.00 (3)127C89–H891···O820.932.433.05 (3)124C96–H962···O30iv0.972.563.26 (3)129C103–H1031···C621.052.603.54 (3)149Symmetry codes: (ii) −x + 1, −y + 2, −z + 1; (iii) x, y − 1, z; (iv) x, y + 1, z.4ConclusionCarboxylate clusters with a Sn4O4 ladder framework and a centrosymmetric Sn2O2 dimer as structural motifs have been successfully synthesized and characterized by elemental analyses, FTIR, NMR spectra, and X-ray single-crystal diffraction. These three ladder-shaped organostannoxane compounds reveal rich supramolecular structures as a result of intermolecular hydrogen bonds. In the crystalline state, the center Sn(iv) atoms of complexes 1 and 2 adopt five-, six-coordination mode, display trigonal bipyramid and octahedron geometry, and reveal rich supramolecular structures by intermolecular hydrogen–bonding interactions. The carboxylates are either bidentate bridging or monodentate.ExperimentalSynthesis of [C5H4N(p-CO2)]2[Bu2Sn]4(μ3-O)2(μ2-OH)2 (1)A methanolic solution containing 0.20 g (0.16 mmol) of pyridine-4-carboxylic acid, C5H4N-(p-CO2H), was added to a methanolic solution which contains 0.1 g (0.32 mmol) of di(n-butyl)dimethoxystannane, n-Bu2Sn(OCH3)2. The mixture was stirred at room temperature for more than 4 h. After the slow evaporation of the solvent, a white crystal was collected and characterized as [C5H4N(p-CO2)]2[Bu2Sn]4(μ3-O)2(μ2-OH)2, yield: 60%; IR (ATR, cm−1): 1,643 ν(OCO)asym, 1,408 ν(OCO)sym, 299 ∆ν, 1,601/1,557 νC═ C/C═N, 709 νaSnC2, 625 νs(Sn–O–Sn), 617 νsSnC2, 444 νSn–O. 1H NMR (CDCl3, ppm): SnCH2CH2CH2CH3, δ = 1.78–1.60 (m, CH2–CH2); 1.43–1.25 (m, CH2); 0.93 (t, CH3). Ligand, 7.5 (m, aromatic protons), 6.87 (m, aromatic protons). 13C NMR (CDCl3, ppm): SnCH2CH2CH2CH3, 31.60[Sn–CH2], 28.00[CH2], 25.31[CH2], 15.23[CH3]. Carbons of the ligands, 167.41 (CO2); 130.6, 128.61, 127.83 (aromatic carbons). Anal. calc. for: C46H86N2O8Sn4 (1,241.91): C, 42.53%; H, 6.50%; N, 2.20%. Found: C 42.55%; H, 6.65%; N, 2.26%.Synthesis of [Ph2CHCO2]4[Bu2Sn]4(μ3-O)2 (2)The preparation of [Ph2CHCO2]4[Bu2Sn]4(μ3-O)2 is similar to that of complex 1 with diphenylacetic acid 0.20 g (0.11 mmol) as carboxylate ligand 1:1 molar ratio. The mixture was stirred for around 3 h at room temperature and upon slow solvent evaporation, white-colored, prismatic crystals suitable for X-ray diffraction analysis have grown. Yield: 64%; IR (ATR, cm−1): 1,550 ν(OCO)asym, 1,386/1,497 ν(OCO)sym, 254/143 ∆ν, 1,571 νC═C, 709 νaSnC2, 623 νs(Sn–O–Sn), 615 νsSnC2, 436 νSn–O. 1H NMR (CDCl3, ppm): SnCH2CH2CH2CH3, δ = 1.86 (m, CH2–CH2); 1.59 (m, CH2); 0.92 (t, CH3). Ligand, 7.8 (s, CH), 7.5 (m, aromatic protons), 6.60 (m, aromatic protons). 13C NMR (CDCl3, ppm): SnCH2CH2CH2CH3, 28.7[Sn–CH2], 26.5[CH2], 27.7[CH2], 13.5[CH3]. Carbons of the ligands, 175.1 (CO2); 153.1 (CH); 128.64, 127.56, 127.17 (aromatic carbons). Anal. calc. for: C88H116O10Sn4 (1,808.7): C, 58.75%; H, 6.44%. Found: C, 58.44%; H, 6.44%.Synthesis of [(p-NH2)-C6H4-CO2]2[Bu2Sn]4(μ3-O)2(μ2-OH)2 (3)The preparation of [(p-NH2)-C6H4-CO2]2[Bu2Sn]4(μ3-O)2(μ2-OH)2 (3) followed that of complex 1, with (p-NH2)-C6H4-CO2 0.21 g (0.16 mmol) used as carboxylic acid in 1:2 molar ratio. The mixture was stirred for around 3 h at room temperature, and upon slow solvent evaporation, a white powder resulted. Yield: 53%; IR (ATR, cm−1): 1,623 ν(OCO)asym, 1,350 ν(OCO)sym, 273 ∆ν, 1,588 νC═C/C═N, 630 νs(Sn–O–Sn), 701 νaSnC2, 613 νsSnC2, 433 νSn–O. 1H NMR (CDCl3, ppm): SnCH2CH2CH2CH3, δ = 1.70–1.65 (m, CH2–CH2); 1.35–1.20 (m, CH2); 0.95 (t, CH3). Ligand, 7.5 (m, aromatic protons); 6.87 (m, aromatic protons). 13C NMR (CDCl3, ppm): SnCH2CH2CH2CH3, 31.46[Sn–CH2], 29.32[CH2], 26.36[CH2], 14.10[CH3]. Carbons of the ligands, 179.34 (CO2); 128.64, 127.56, 127.17 (aromatic carbons). Anal. calc. for: C46H86N2O8Sn4 (1,270.02): C, 43.50%; H, 6.83%; N, 2.21%. Found: C, 42.75%; H, 6.53%; N, 2.40%.Materials and methodsSynthesis and spectroscopic materialsPyridine-4-carboxylic acid, p-aminobenzoic acid, diphenylacetic acid, n-Bu2Sn(OCH3)2, and solvents were obtained from Aldrich and were used without further purification. Elemental analysis (C, H, and N) was performed using a Perkin–Elmer model 2400 CHN elemental analyzer. IR spectra in the range 4,000–400 cm−1 were recorded using FT-IR spectrophotometer Nicolet 710 TF-IR operated by the OMNIC software. 1H and 13C NMR spectra were recorded in CDCl3 solution on BRUKER DPX-300 and BRUKER AVANCE II 400 spectrometers with Topspin 2.1 as software. The spectra were acquired at room temperature (298 K). 13C NMR spectra are broadband-proton-decoupled. The chemical shifts were reported in ppm with respect to the references and were stated relative to external tetramethylsilane for 1H and 13C NMR.X-Ray crystallographyThe X-ray crystallographic data were collected using a Rigaku Oxford-Diffraction Gemini-S diffractometer. All data were collected with graphite monochromated Mo-Kα radiation (λ = 0.71073 Å) at 175 K. CrysAlis PRO (released on August 13, 2014, CrysAlis171.NET) (compiled on August 13, 2014, 18:06:01); cell refinement: CrysAlis PRO, Agilent Technologies, Version 1.171.37.35 (released on August 13, 2014, CrysAlis171.NET) (compiled on August 13, 2014, 18:06:01); data reduction: CrysAlis PRO, Agilent Technologies, Version 1.171.37.35 (released on August 18, 2014, CrysAlis171.NET) (compiled on August 13, 2014, 18:06:01); program(s) used to solve structure: Superflip (Palatinus and Chapuis, 2007); program(s) used to refine structure: CRYSTALS (Betteridge et al., 2003); molecular graphics: CAMERON (Watkin et al., 1996). Programs used for the representation of the molecular and crystal structures were Olex2 (Dolomanov et al., 2009) and Mercury (Macrae et al., 2008).Accession codesCCDC 2053062 (1) and 2053063 (2) contain the supplementary crystallographic data for this article. Copies can be obtained free of charge from the Cambridge Crystallographic Data Centre (CCDC), 12 Union Road, Cambridge CB2 1EZ, UK (fax: int. Code +44 1223 336 033; e-mail: deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk). http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Main Group Metal Chemistry de Gruyter

Synthesis and structural characterization of new ladder-like organostannoxanes derived from carboxylic acid derivatives: [C5H4N(p-CO2)]2[Bu2Sn]4(μ3-O)2(μ2-OH)2, [Ph2CHCO2]4[Bu2Sn]4(μ3-O)2, and [(p-NH2)-C6H4-CO2]2[Bu2Sn]4(μ3-O)2(μ2-OH)2

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de Gruyter
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© 2022 Tidiane Diop et al., published by De Gruyter
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10.1515/mgmc-2022-0008
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Abstract

1IntroductionDuring the past few decades, research on the synthesis and characterization of coordination polymers has intrigued scientists not only for their fascinating structures but also for their potential applications (Gielen et al., 2005; Kemmer et al., 2000; Willem et al., 1997). It has become apparent that coordination polymers may be prepared by the appropriate selection of metal and multifunctional ligands (Chandrasekhar et al., 2002, 2005; Diop et al., 2021). Among these materials, organotin(iv) carboxylate complexes have been actively investigated by a large number of researchers due to their significant reduction in tumor growth rates (Vieira et al., 2010), interesting topologies, and various structural types including monomers, dimers, tetramers, oligomeric ladders, and hexameric drums (Arjmand et al., 2014; Banti et al., 2019). The organostannoxanes have received special attentions, particularly in view of their immense structural diversity. Several products, such as ladders (Wen et al., 2018; García-Zarracino et al., 2009), cubes (Cavka et al., 2008), hexameric (Baul et al., 2017), and polymeric drums (Ma et al., 2003), have been isolated. Ladder-shaped tetranuclear organotin compounds (Wang et al., 2013) have also been isolated. Tetranuclear crystal structures [(n-Bu2Sn)4(O)2(OH)2(O3SC6H4-NH2-4)2] (Wen et al., 2018), [(Me2Sn)4(O)2(OH)2(O3SC6H4-NH2-4)2] (Wen et al., 2018), and [(n-Bu2Sn)4(μ3-O)2(μ2-OCH3)2(O2CC6H4-SO2NH2-4)2 (Wang et al., 2019) with the ladder as structural motif were previously described in the literature. Many butylstannoxanes were prepared using carboxylate ligands (Baul et al., 2017; Shankar and Dubey, 2020; Valcarcel et al., 2012; Wang et al., 2019). These molecular structures of compounds display hexameric Sn6O6 clusters with drum-like or tetrameric structures revealing Sn4O2 cores with ladder-type structural motifs. In our previous work, we reported a series of butylstannoxanes carboxylate complexes using carboxylic acid ligands such as pyridine-4-carboxylic acid, diphenylacetic acid, and 4-aminocarboxylic acid. The synthesis and structural characterization of three new organostannoxanes are reported as follows: [C5H4N(p-CO2)]2[Bu2Sn]4(μ3-O)2(μ2-OH)2 (1), [Ph2CHCO2]4[Bu2Sn]4(μ3-O)2 (2), and [(p-NH2)-C6H4-CO2]2[Bu2Sn]4(μ3-O)2(μ2-OH)2 (3).2Results2.1Crystallographic data and experimental detailsCrystal data, data collection, and structure refinement details for the complex are summarized in Table 1.Table 1Crystal data and structure refinement of 1 and 212FormulaC44H82N2O8Sn4C88H116O10Sn4MoietyC44H82N2O8Sn4C88H116O10Sn4T (K)175175SpacegroupP21/nP-1Crystal systemMonoclinicTriclinica (Å)13.0597(5)15.6908(7)b (Å)12.2041(6)15.7536(8)c (Å)17.0979(6)19.4517(8)α (°)9083.718(4)β (°)96.017(4)75.218(4)γ (°)9064.601(5)V (Å3)2710.09(19)4199.7(4)Z22P (g cm−3)1.5221.430Mr (g mol−1)1241.961808.65µ (mm−1)1.8671.231Rint0.0650.084θmax (°)29.09129.464Resolution (Å)0.790.82Ntot (measured)18,16452,524Nref (unique)6,38119,770Nref (I > 2σ (I))4,46210,858Nref (least-squares)4,46210,858Npar285928<σ(I)/I> 0.08070.1165R1 (I > 2σ(I))0.09010.0689wR2 (I>2σ(I))0.03900.0887R1 (all)0.13250.1292wR2 (all)0.04880.01682GOF1.42611.1410Δρ (e Å−3)−1.56/3.26−1.70/3.72Crystal size (mm)0.12 × 0.15 × 0.200.22 × 0.25 × 0.303Discussion3.1ReactionsThe general chemical reactions in methanol are shown for complexes 1 and 3 Eq. (1) and for complex 2 Eq. (2):(1)2HL+4n-Bu2Sn(OCH3)2+4H2O→L2[Bu2Sn]4(μ3-O)2(μ2-OH)2+8MeOHHL=pyridine-4-carboxylicacid(1)or4-aminobenzenecarboxylicacid(3),\begin{array}{c}2\text{HL}\hspace{.25em}+\hspace{.25em}4n{\text{-Bu}}_{2}\text{Sn}{({\text{OCH}}_{3})}_{2}\hspace{.25em}+\hspace{.25em}4{\text{H}}_{2}O\to {\text{L}}_{2}{{[}{\text{Bu}}_{2}\text{Sn}]}_{4}{({{\mu }}_{3}\text{-O})}_{2}{({{\mu }}_{2}\text{-OH})}_{2}\hspace{.25em}+\hspace{.25em}8\text{MeOH}\\ \text{HL}\hspace{.25em}=\hspace{.25em}\text{pyridine-}4\text{-carboxylic}\hspace{.5em}\text{acid}\hspace{.5em}({\bf{1}})\hspace{.5em}\text{or}\hspace{.5em}\hspace{2.5em}4\text{-aminobenzenecarboxylic}\hspace{.5em}\text{acid}\hspace{.5em}({\bf{3}}),\end{array}(2)4Ph2CHCO2H+4n-Bu2Sn(OCH3)2+2H2O→[Ph2CHCO2]4[Bu2Sn]4(μ3-O)2+8MeOH.4{\text{Ph}}_{2}{\text{CHCO}}_{2}H\hspace{.25em}+\hspace{.25em}4n\text{-}{\text{Bu}}_{2}\text{Sn}{({\text{OCH}}_{3})}_{2}\hspace{.25em}+\hspace{.25em}2{\text{H}}_{2}O\to {{[}{\text{Ph}}_{2}{\text{CHCO}}_{2}]}_{4}{{[}{\text{Bu}}_{2}\text{Sn}]}_{4}{({\text{&#x03BC;}}_{3}\text{-}\text{O})}_{2}\hspace{.25em}+\hspace{.25em}8\text{MeOH}\text{.}After synthesis, the complexes are characterized by elemental analyses, Fourier-transform infrared spectroscopy and nuclear magnetic resonance (1H, 13C) experiments, and, for 1 and 2, single-crystal X-ray diffraction.3.2Spectroscopic studies3.2.1FT-IR spectraThe explicit feature in the FTIR spectra is the absence of a broadband in the region 3,400–2,800 cm−1, which appears in the free ligands for the COOH group, indicating the removal of COOH protons and the formation of Sn–O bonds through this site (Li et al., 2010; Zhang et al., 2012). The strong absorption appearing at 444 (1), 436 (2), and 433 (3) cm−1 is assigned to ν(Sn–O) (Xiao et al., 2013). The intense absorption maximum in the 623–630 cm−1 region is assigned to an Sn–O–Sn stretching vibration (Li et al., 2015). In the infrared spectra of this complex, the Δν(C(O)O) [ν(C(O)O)asym – ν(C(O)O)sym] values are 299 cm−1 for 1 and 273 cm−1 for 3, larger than 200 cm−1, which stands for the monodentate coordination mode of the carboxylate groups (Hanif et al., 2010), and this behavior is also consistent with the X-ray structure. The two Δν magnitudes (νasymCOO – νsymCOO) 254 and 143 cm−1 for (2) show that two distinct coordination modes for carboxylate ligands are present in the structure (Eng et al., 2007). One carboxylate fragment is symmetrically bridged between two Sn ions, and another carboxylate acts as a bis-monodentate ligand for Sn atoms (Scheme 2). The presence of a νsSnBu2 band at 617 cm−1 (1), 615 cm−1 (2), and 613 cm−1 (3) indicates a nonlinear SnBu2 residue (Nakamoto, 1997; Beckman et al., 2004) (Schemes 1 and 2). The conclusions drawn from the IR data are very much consistent with those of the X-ray crystallography studies.Scheme 1Structures of [C5H4N(p-CO2)]2[Bu2Sn]4(μ3-O)2(μ2-OH)2 (1) or [(p-NH2)-C6H4-CO2]2[Bu2Sn]4(μ3-O)2(μ2-OH)2 (3).Scheme 2Structure of [Ph2CHCO2]4[Bu2Sn]4(μ3-O)2 (2).3.2.2NMR spectraThe 1H and 13C NMR data of the complexes are given in the experimental part, and the observed resonances have been assigned based on the chemical shift values. In the 1H NMR spectra, the expected signals in the 10–13 ppm region of the carboxylic acid hydrogens are not present in the complexes, indicating the replacement of the carboxylic acid protons with organotin(iv) moieties (Najafi et al., 2014; Xiao et al., 2013). The order of the 1H chemical shifts of the CHngroups in the Sn–butyl substituents was found to be (α, β) > (γ, δ) for the Bu2Sn complexes (SnCH2(α)CH2(β)CH2(γ)CH3(δ)) (Pruchnik et al., 2013). Multiplet signals in the 1.50–1.86, 1.25–1.43, and 0.92–0.93 ppm ranges are attributed to (m, α-CH2, β-CH2), (m, γ-CH2), and (t, δ-CH3), respectively. The multiplet signals at 8.12–6.77 ppm are assigned to aromatic protons. In the 13C NMR spectra of all the complexes, peaks at 167.41 (1), 175.1 (2), and 179.34 (3) ppm attributed to COO− groups show a downfield shift of all the carbon resonances compared to the free carboxylates. These conclusions are consistent with those of the IR data and the X-ray crystal structures.The structures for complexes 1, 2, and 3 are Sn4O4 tetramers with either monodentate or bridging carboxylate ligands (Schemes 1 and 2).3.3Crystal structure of complex 1A perspective view of the molecular structure of complex 1 is illustrated in Figures 1 and 2. Selected bond lengths (Å) and angles (°) are listed in Table 2. The structure consists of the hydroxide-bridged tetrameric organostannoxane ladder and two deprotonated pyridine-4-carboxylic ligands. The complex adopts tetranuclear tin(iv) ladder-like structure containing two deprotonated ligands linked by three alternate Sn2O2 four-membered rings. As is shown in 1, the molecular structure is a centrosymmetric ladder-like structure consisting of the Sn4(μ3-O)2(μ2-OH)2 group and two deprotonated ligands. As is the case for other usual tetrameric organostannoxanes (Li et al., 2015), the structure is based on a centrosymmetric Sn2O2 unit connected to a pair of exocyclic Sn atoms via bridging µ3-O atoms. Triply bridged μ3-O atoms, which share their electrons with three tin(iv) centers, have distorted tetrahedral configurations. All the Sn atoms are five-coordinated, showing a trigonal bipyramid configuration in two different chemical environments: SnBu2O2(OH) and SnBu2O(OH)[C5H4N(p-CO2)]. For Sn(1) atom (exocyclic), the basal plane is defined by C(33), C(27), and O(2), and the axial sites occupied by the O(2i) and O(16) atoms, which form an angle of 147.95 (14)°, deviating from a linear arrangement. The carboxylate moiety COO– of the ligand is bonded as a monodentate mode with Sn(3)–O(18) (2.176 Å) way as depicted in Table 2. These bond lengths are in accordance with those of the reported di-n-butyltin(iv) carboxylates (Xiao et al., 2013; Zhu et al., 2011).Figure 1Tetranuclear structure of [C5H4N-(p-CO2)]2[Bu2Sn]4(μ3-O)2(μ2-OH)2 (1).Figure 2Crystal structure in an infinite chain of [C5H4N-(p-CO2)]2[Bu2Sn]4(μ3-O)2(μ2-OH)2 (1) with O–H⋯N intermolecular hydrogen bonds. Only Cipso of the n-butyl groups are shown for clarity.Table 2Geometric parameters (Å and °) of complex 1Lengths (Å)Angles (°)Sn1–O2i2.128 (3)O2i–Sn1–O2 74.51 (17)Sn1i–O2–Sn3143.67 (18)Sn1–O2 2.062 (4)O2i–Sn1–Sn3 108.55 (10)Sn1–O2–Sn3 110.83 (15)Sn1–O16 2.139 (4)O2i–Sn1–O16 147.95 (14)O2–Sn3–C6 112.9 (2)Sn1–C27 2.106 (7)O2–Sn1–O16 73.44 (14)O2–Sn3–C9 112.2 (3)Sn1–C33 2.139 (7)O2i–Sn1–C27 95.6 (2)C6–Sn3–C9 134.7 (3)O2–Sn3 2.005 (4)O2–Sn1–C27 115.2 (3)O2–Sn3–O16 73.80 (15)Sn3–C6 2.087 (7)O16–Sn1–C27 98.3 (3)C6–Sn3–O16 91.8 (2)Sn3–C9 2.166 (8)O2i–Sn1–C33 99.2 (2)C9–Sn3–O16 96.3 (3)Sn3–O16 2.173 (4)O2–Sn1–C33 115.8 (3)O2–Sn3–O18 80.31 (14)Sn3–O18 2.176 (4)O16–Sn1–C33 94.2 (3)C6–Sn3–O18 99.1 (2)C27–Sn1–C33 129.0 (3)C9–Sn3–O18 92.6 (2)Sn1i–O2–Sn1 105.49 (17)O16–Sn3–O18 154.09 (16)Symmetry code: (i) −x, −y, −z + 1.Intermolecular O–H···N hydrogen bonds, involving the bridging hydroxy group and the N atom of the ligand, connect the discrete units into a two-dimensional (2D) network (Figure 2). For the O–H···N intermolecular interactions and C–H⋯O intramolecular interactions (Figure 3), the H(161)···N(24ii) and H(341)⋯O(18i) distances are 2.06(4) and 2.59 Å, respectively. The O(16)–H(161)···N(24ii) and C(34)–H(341)⋯O(18i) angles are 153(8) and 145° (Table 3). The hydrogen-bond geometry is close to the values reported for [(n-Bu2Sn)2(μ3-O)(µ-OH)L]2 (Li et al., 2015). The crystallographic study confirms the spectroscopic conclusions.Figure 3Crystal structure in infinite chain of [C5H4N-(p-CO2)]2[Bu2Sn]4(μ3-O)2(μ2-OH)2 (1) with intermolecular hydrogen bonds O–H···N (color code: blue) and intramolecular hydrogen bonds C–H⋯O (color code: greenish). Only Cipso of the n-butyl groups are shown for clarity.Table 3: Hydrogen-bond geometry (Å and °) of complex 1D–H···AD–HH···AD···AD–H···AO16–H161···N24ii0.82 (2)2.06 (4)2.810 (14)153 (8)C34–H341···O18i0.982.593.440 (14)145Symmetry codes: (i) −x, −y, −z + 1; (ii) x + 1/2, −y − 1/2, z − 1/2.3.4Crystal structure of complex 2The asymmetric unit features linkage of neighboring monomers by hydrogen–bond interactions [C–H⋯O and C–H⋯π], giving rise to the formation of organotin(iv) aggregate (Figure 4). Selected bond lengths (Å) and angles (°) are listed in Table 4. The conformations of the two independent molecules are almost the same, except for small differences in angles and bond lengths. The crystal structure is very similar to that reported by Zhang et al. (2012). The structure is a tetranuclear centrosymmetric dimer of an oxoditin(iv) unit having a central four-member ring composed of Sn(3)–O(2)–Sn(3i)–O(2i). In this complex, the central Sn2O2 core is fused with two four-member and two six-member rings. The four-member rings, that is, [Sn2O2, i.e., O(28)–Sn(1)–O(2)–Sn(3 i) and O(28i)–Sn(1i)–O(2i)–Sn(3)], are due to the bridging of the monodentate ligand through O atoms, O(28)–Sn(1), and O(28I)–Sn(1i), respectively. Two six-member rings [Sn2O3C; i.e., Sn(1)–O(6)–C(5)–O(4)–Sn(3)–O(2), Sn(1i)–O(6i)–C(5i)–O(4i)–Sn(3i)–O(2i)] also overlap central Sn2O2. As is the case for other usual tetrameric organostannoxane (Li et al., 2015), the structure is based on a centrosymmetric Sn2O2 unit connected to a pair of exocyclic Sn atoms via bridging µ3-O atoms. There are two distinct carboxylate ligands in the structure. The first carboxylate, defined by the O(4) and O(6) atoms, symmetrically bridges the exocyclic Sn(3) and endocyclic Sn(1) atoms. The second carboxylate is a bis-monodentate coordinating ligand to the exocyclic Sn(3) and endocyclic Sn() via µ-O(28) atom (Figure 4). The endocyclic Sn(3) exists in a distorted octahedron geometry with the four O atoms [O(4), O(6), O(2), and O(28i)] defining the basal plan. The axial position is occupied by C(20) and C(24) which form an angle C(20)–Sn(3)–C(24) of 143.7 (5) (Table 4). The exocyclic Sn(1) atoms are five coordinated and show distorted trigonal bipyramid geometry with the basal plan defined by the µ3–O(2) atom, the C(48) and C(44) atoms. The axial angle of O(6)–Sn(1)–O(28i) is 169.9°(3).Figure 4The ladder structure of aggregate complex 2 (hydrogen atoms bonded to carbon atoms are omitted, and only the α-carbon of the butyl groups has been drawn for clarity).Table 4Geometric parameters (Å and °) of complex 2Lengths (Å)Angles (°)Sn1–O2 2.044 (8)O2–Sn1–O6 91.7 (3)O28i–Sn3–O4 127.7 (3)Sn1–O6 2.276 (9)O2–Sn1–O28 78.3 (3)O2i–Sn3–C20 100.0 (4)Sn1–O28 2.198 (8)O6–Sn1–O28 169.9 (3)O2–Sn3–C20 105.2 (4)Sn1–C44 2.143 (12)O2–Sn1–C44 112.0 (4)O28i–Sn3–C20 79.4 (4)Sn1–C48 2.128 (13)O6–Sn1–C44 84.4 (4)O2i–Sn3–C24 99.6 (4)O2–Sn3i 2.143 (7)O28–Sn1–C44 98.2 (4)O2–Sn3–C24 108.8 (4)O2–Sn3 2.061 (8)O2–Sn1–C48108.4 (4)O28i–Sn3–C24 80.8 (4)Sn3–O28i 2.669 (9)O6–Sn1–C48 89.2 (4)O4–Sn3–C20 85.3 (5)Sn3–O4 2.262 (9)O28–Sn1–C48 95.0 (4)O4–Sn3–C24 83.2 (5)Sn3–C20 2.137 (13)C44–Sn1–C48 139.2 (5)C20–Sn3–C24 143.7 (5)Sn3–C24 2.117 (12)Sn3i–O2–Sn1 119.4 (3)Sn3–O4–C5 138.9 (8)Sn52–O53 2.218 (8)Sn3i–O2–Sn3 103.0 (3)O2–Sn3–O488.6 (3)Sn52–O57 2.047 (8)Sn1–O2–Sn3 137.6 (4)O2i–Sn3–O4165.5 (3)Sn52–O80 2.203 (7)O2i–Sn3–Sn3i 37.6 (2)O2i–Sn3–O28i66.7 (3)Sn52–C96 2.119 (14)O2i–Sn3–O2 77.0 (3)Sn52–C100 2.113 (14)O2–Sn3–O28i 143.6 (3)O55–Sn56, 2.298 (10)Sn56–O57ii 2.126 (8)Symmetry codes: (i) −x + 1, −y + 1, −z; (ii) −x + 1, −y + 2, −z + 1.Intermolecular C–H⋯O and C–H⋯π hydrogen bonds are recognized in complex 2, which link the molecular structure into 2D network. For the C–H⋯O interactions, the distances [H⋯O, in the 2.35–2.60 Å ranges] and [H⋯π, in the 2.40–2.60 Å ranges] (Table 5) are all close to the values reported by Li et al. (2015).Table 5Hydrogen-bond geometry (Å and °) of complex 2D–H···AD–HH···AD···AD–H···AC12–H121···C61ii0.932.403.11 (3)134C19–H191···O40.932.473.09 (3)124C37–H371···O300.932.443.05 (3)124C44–H442···O82iii0.972.603.37 (3)136C79–H791···O550.932.353.00 (3)127C89–H891···O820.932.433.05 (3)124C96–H962···O30iv0.972.563.26 (3)129C103–H1031···C621.052.603.54 (3)149Symmetry codes: (ii) −x + 1, −y + 2, −z + 1; (iii) x, y − 1, z; (iv) x, y + 1, z.4ConclusionCarboxylate clusters with a Sn4O4 ladder framework and a centrosymmetric Sn2O2 dimer as structural motifs have been successfully synthesized and characterized by elemental analyses, FTIR, NMR spectra, and X-ray single-crystal diffraction. These three ladder-shaped organostannoxane compounds reveal rich supramolecular structures as a result of intermolecular hydrogen bonds. In the crystalline state, the center Sn(iv) atoms of complexes 1 and 2 adopt five-, six-coordination mode, display trigonal bipyramid and octahedron geometry, and reveal rich supramolecular structures by intermolecular hydrogen–bonding interactions. The carboxylates are either bidentate bridging or monodentate.ExperimentalSynthesis of [C5H4N(p-CO2)]2[Bu2Sn]4(μ3-O)2(μ2-OH)2 (1)A methanolic solution containing 0.20 g (0.16 mmol) of pyridine-4-carboxylic acid, C5H4N-(p-CO2H), was added to a methanolic solution which contains 0.1 g (0.32 mmol) of di(n-butyl)dimethoxystannane, n-Bu2Sn(OCH3)2. The mixture was stirred at room temperature for more than 4 h. After the slow evaporation of the solvent, a white crystal was collected and characterized as [C5H4N(p-CO2)]2[Bu2Sn]4(μ3-O)2(μ2-OH)2, yield: 60%; IR (ATR, cm−1): 1,643 ν(OCO)asym, 1,408 ν(OCO)sym, 299 ∆ν, 1,601/1,557 νC═ C/C═N, 709 νaSnC2, 625 νs(Sn–O–Sn), 617 νsSnC2, 444 νSn–O. 1H NMR (CDCl3, ppm): SnCH2CH2CH2CH3, δ = 1.78–1.60 (m, CH2–CH2); 1.43–1.25 (m, CH2); 0.93 (t, CH3). Ligand, 7.5 (m, aromatic protons), 6.87 (m, aromatic protons). 13C NMR (CDCl3, ppm): SnCH2CH2CH2CH3, 31.60[Sn–CH2], 28.00[CH2], 25.31[CH2], 15.23[CH3]. Carbons of the ligands, 167.41 (CO2); 130.6, 128.61, 127.83 (aromatic carbons). Anal. calc. for: C46H86N2O8Sn4 (1,241.91): C, 42.53%; H, 6.50%; N, 2.20%. Found: C 42.55%; H, 6.65%; N, 2.26%.Synthesis of [Ph2CHCO2]4[Bu2Sn]4(μ3-O)2 (2)The preparation of [Ph2CHCO2]4[Bu2Sn]4(μ3-O)2 is similar to that of complex 1 with diphenylacetic acid 0.20 g (0.11 mmol) as carboxylate ligand 1:1 molar ratio. The mixture was stirred for around 3 h at room temperature and upon slow solvent evaporation, white-colored, prismatic crystals suitable for X-ray diffraction analysis have grown. Yield: 64%; IR (ATR, cm−1): 1,550 ν(OCO)asym, 1,386/1,497 ν(OCO)sym, 254/143 ∆ν, 1,571 νC═C, 709 νaSnC2, 623 νs(Sn–O–Sn), 615 νsSnC2, 436 νSn–O. 1H NMR (CDCl3, ppm): SnCH2CH2CH2CH3, δ = 1.86 (m, CH2–CH2); 1.59 (m, CH2); 0.92 (t, CH3). Ligand, 7.8 (s, CH), 7.5 (m, aromatic protons), 6.60 (m, aromatic protons). 13C NMR (CDCl3, ppm): SnCH2CH2CH2CH3, 28.7[Sn–CH2], 26.5[CH2], 27.7[CH2], 13.5[CH3]. Carbons of the ligands, 175.1 (CO2); 153.1 (CH); 128.64, 127.56, 127.17 (aromatic carbons). Anal. calc. for: C88H116O10Sn4 (1,808.7): C, 58.75%; H, 6.44%. Found: C, 58.44%; H, 6.44%.Synthesis of [(p-NH2)-C6H4-CO2]2[Bu2Sn]4(μ3-O)2(μ2-OH)2 (3)The preparation of [(p-NH2)-C6H4-CO2]2[Bu2Sn]4(μ3-O)2(μ2-OH)2 (3) followed that of complex 1, with (p-NH2)-C6H4-CO2 0.21 g (0.16 mmol) used as carboxylic acid in 1:2 molar ratio. The mixture was stirred for around 3 h at room temperature, and upon slow solvent evaporation, a white powder resulted. Yield: 53%; IR (ATR, cm−1): 1,623 ν(OCO)asym, 1,350 ν(OCO)sym, 273 ∆ν, 1,588 νC═C/C═N, 630 νs(Sn–O–Sn), 701 νaSnC2, 613 νsSnC2, 433 νSn–O. 1H NMR (CDCl3, ppm): SnCH2CH2CH2CH3, δ = 1.70–1.65 (m, CH2–CH2); 1.35–1.20 (m, CH2); 0.95 (t, CH3). Ligand, 7.5 (m, aromatic protons); 6.87 (m, aromatic protons). 13C NMR (CDCl3, ppm): SnCH2CH2CH2CH3, 31.46[Sn–CH2], 29.32[CH2], 26.36[CH2], 14.10[CH3]. Carbons of the ligands, 179.34 (CO2); 128.64, 127.56, 127.17 (aromatic carbons). Anal. calc. for: C46H86N2O8Sn4 (1,270.02): C, 43.50%; H, 6.83%; N, 2.21%. Found: C, 42.75%; H, 6.53%; N, 2.40%.Materials and methodsSynthesis and spectroscopic materialsPyridine-4-carboxylic acid, p-aminobenzoic acid, diphenylacetic acid, n-Bu2Sn(OCH3)2, and solvents were obtained from Aldrich and were used without further purification. Elemental analysis (C, H, and N) was performed using a Perkin–Elmer model 2400 CHN elemental analyzer. IR spectra in the range 4,000–400 cm−1 were recorded using FT-IR spectrophotometer Nicolet 710 TF-IR operated by the OMNIC software. 1H and 13C NMR spectra were recorded in CDCl3 solution on BRUKER DPX-300 and BRUKER AVANCE II 400 spectrometers with Topspin 2.1 as software. The spectra were acquired at room temperature (298 K). 13C NMR spectra are broadband-proton-decoupled. The chemical shifts were reported in ppm with respect to the references and were stated relative to external tetramethylsilane for 1H and 13C NMR.X-Ray crystallographyThe X-ray crystallographic data were collected using a Rigaku Oxford-Diffraction Gemini-S diffractometer. All data were collected with graphite monochromated Mo-Kα radiation (λ = 0.71073 Å) at 175 K. CrysAlis PRO (released on August 13, 2014, CrysAlis171.NET) (compiled on August 13, 2014, 18:06:01); cell refinement: CrysAlis PRO, Agilent Technologies, Version 1.171.37.35 (released on August 13, 2014, CrysAlis171.NET) (compiled on August 13, 2014, 18:06:01); data reduction: CrysAlis PRO, Agilent Technologies, Version 1.171.37.35 (released on August 18, 2014, CrysAlis171.NET) (compiled on August 13, 2014, 18:06:01); program(s) used to solve structure: Superflip (Palatinus and Chapuis, 2007); program(s) used to refine structure: CRYSTALS (Betteridge et al., 2003); molecular graphics: CAMERON (Watkin et al., 1996). Programs used for the representation of the molecular and crystal structures were Olex2 (Dolomanov et al., 2009) and Mercury (Macrae et al., 2008).Accession codesCCDC 2053062 (1) and 2053063 (2) contain the supplementary crystallographic data for this article. Copies can be obtained free of charge from the Cambridge Crystallographic Data Centre (CCDC), 12 Union Road, Cambridge CB2 1EZ, UK (fax: int. Code +44 1223 336 033; e-mail: deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).

Journal

Main Group Metal Chemistry – de Gruyter

Published: Jan 1, 2022

Keywords: diphenylacetate¸ pyridine-4-carboxylate; 4-aminobenzenecarboxylate; ladder and organostannoxanes

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