Polymeric seven-coordinated organotin(IV) complexes derived from 5-amino-2-chlorobenzoic acid and in vitro anti-cancer studies

Cancer cases are alarmingly increasing worldwide, and newer chemotherapeutic agents are needed. Recent analogs of cisplatin (carboplatin, lobaplatin, nedaplatin and oxaliplatin) and their marketing as advanced chemotherapeutic drugs have furthered the interest in metal-based anti-cancer drugs. In the current study, two new polymeric organotin(IV) carboxylate complexes (1 and 2) have been synthesized and characterized. Spectroscopic studies showed that coordination took place via carboxylates. Furthermore, X-ray crystallographic study on 1 indicated that it possesses a monomeric structure and exists in polymeric formation due to additional Sn–N coordination, assigning seven coordinations to each metal ion. Both the complexes were tested against three cancerous (human colon cancer, HCT 116; breast cancer, MCF-7; and leukemia, K562) and one non-cancerous (3T3-L1) cell lines. Complex 1 showed exceptional cytotoxicity against cancerous cell lines (IC₅₀ = 1.0 μM for HCT 116; 258.7 nM for MCF-7; and 46.7 nM K562) and remained comparatively non-toxic against normal cells (IC₅₀ = 37.0?μM). This shows that both complexes have selective cytotoxicity against cancer cells.     

Review: structural diversity in organotin(IV) dithiocarboxylates and carboxylates

Organotin(IV) complexes are known for their outstanding structural diversity and applications. Organotin(IV) carboxylates and dithiocarboxylates form an important class of organotin(IV) compounds. The structural diversity of these compounds emanates from several features including flexibility in coordination geometries, coordination numbers, and versatility of the ligands to engage in different modes of chelation from monodentate to bidentate. Triorganotin(IV) complexes with various ligands mostly demonstrate tetrahedral or trigonal bipyramidal symmetry with some distortions, while diorganotin(IV) and chlorodiorganotin(IV) complexes have variation of geometries and coordination numbers. Some monoorganotin(IV) complexes have also been reported with pentagonal bipyramidal geometries.     

Macrocyclic organotin(IV) carboxylates based on benzenedicarboxylic acid derivatives: Syntheses, crystal structures and antitumor activities

Six new organotin carboxylates based on 1,3-benzenedicarboxylic acid and 1,4-benzenedicarboxylic acid derivatives, namely (Ph₃Sn)₂(2,5-L¹)(C₂H₅OH)₂ (1) (2,5-H₂L¹ = 2,5-dibenzoylterephthalic acid), (Ph₃Sn)₂(2,5-L²)(C₂H₅OH)₂ (2) (2,5-H₂L² = 2,5-bis(4-methylbenzoyl)terephthalic acid), (Ph₃Sn)₂(2,5-L³)(C₂H₅OH)₂ (3) (2,5-H₂L³ = 2,5-bis(4-ethylbenzoyl)terephthalic acid), [(n-Bu₂Sn)₄(4,6-L¹)O₂(OH)(OC₂H₅)]₂·2(C₂H₅OH) (4) (4,6- H₂L¹ = 4,6-dibenzoylisophthalic acid), [(n-Bu₂Sn)₄(4,6-L¹)O₂(OH)(OC₄H₉)]₂·2(C₄H₉OH) (5) and [(n-Bu₂Sn)₄(4,6-L²)O₂(OH)(OC₂H₅)]₂·2(C₂H₅OH) (6) (4,6-H₂L² = 4,6-bis(4-methylbenzoyl)isophthalic acid), have been synthesized. All the organotin carboxylates have been characterized by elemental analysis, IR, ¹H and ¹³C NMR spectroscopy and X-ray crystallography diffraction analyses. The structural analysis reveals that complexes 1-3 show similar structures, containing binuclear triorganotin skeletons. The significant intermolecular O-H?O hydrogen bonds linked the complexes 1-3 to form a novel 2D network polymer with 38-member macrocycles. In complexes 4-6, two Sn₄O₄ ladders are connected by two 1,3-benzenedicarboxylic acid derivatives to yield ladder-like octanuclear architectures and form macrocycle with 24 atoms. In addition, the antitumor activities of complexes 1-6 have been studied.     

Synthesis and structural characterization of organotin(IV) carboxylates based on different heterocyclic substituents

Six novel organotin(IV) carboxylates have been successfully synthesized, namely, the polymer (C₆H₅)₃Sn(L1)_∞ (1) [HL1 = 4-imidazolyl benzoic acid], the mononuclear (C₆H₅)₃Sn(L2) (2) [HL2 = 4-pyrazolylbenzoic acid], (C₆H₅)₃Sn(L3)·CH₃OH (3) [HL3 = 4-triazolylbenzoic acid] and (C₆H₅)₃Sn(L4) (4) [HL4 = 4-tetrazolyl benzoic acid] and the tetranuclear [(n-Bu₂Sn)₄(L2)₂O₂(OCH₃)₂] (5) and [(n-Bu₂Sn)₄(L3)₂O₂(OCH₃)₂] (6). X-ray diffraction analyses show 1D infinite chain of polymer 1, single molecular structures of isomorphous complexes 2 and 4, single molecule structures of complex 3 containing solvent CH₃OH molecule and similar ladder-type structures of complexes 5 and 6. The photoluminescence of ligands and 1-6 were also measured in the solid state at room temperature.     

Synthetic, structural and biological studies of organotin(IV) complexes of schiff bases derived from pyrrol-2-carboxaldehyde

Some new organotin(IV) complexes having general formulae R₂MCl[L] and R₂M[L]₂ were synthesized by the reactions of Me₂MCl₂ with Schiff bases [5-Mercapto-4-(pyrrolcarboxalideneamino)-s-triazole, 5-Mercapto-3-methyl-4-(2-pyrrolcarboxalideneamino)- s-triazole, 3-Ethyl-5-mercapto-4-(2-pyrrolcarboxalideneamino)-s-triazole] in 1:1 and 1:2 molar ratios. All of the compounds were characterized by elemental analysis, molar conductance, IR, UV, ¹H, ¹³C and ¹¹⁹Sn NMR spectral studies. The IR and ¹H NMR spectral data suggest the involvement of azomethine nitrogen in coordination with the central metal atom. With the help of the above-mentioned spectral studies, penta and hexacoordinated environments around the central metal atoms in the 1:1 and 1:2 complexes, respectively, have been proposed. Finally, the free ligands and their metal complexes were tested in vitro against some pathogenic bacteria and fungi to assess their antimicrobial properties.     

Synthesis,spectroscopic characterization,X-ray crystal structure,biological screening and catalytic studies of organotin(IV) carboxylates of 3-(4-cyanophenyl) acrylic acid

A series of six organotin(IV) carboxylates [Me₂SnL₂] (1), [n-Bu₂SnL₂] (2), [n-Oct₂SnL₂] (3), [Me₃SnL] (4), n-Bu₃SnL (5) and [Ph₃SnL] (6), where L = 3-(4-cyanophenyl) acrylic acid have been synthesized and characterized by elemental analysis, FT-IR and NMR (¹H, ¹³C). The complex (4) was also analyzed by single crystal X-ray analysis which showed distorted trigonal bipyramidal geometry with polymeric bridging behavior. The complexes 1–6 were screened for antimicrobial activities and cytotoxicity. The results showed significant activity with few exceptions. The catalytic activity of complexes was assessed in transesterification reaction of Brassica campestris oil (triglycerides) to produce biodiesel (fatty acid methyl esters). The results showed that triorganotin(IV) complexes exhibited good catalytic activity than their di-analogues.     

Synthesis, crystal structures, electrochemical studies and anti-tumor activities of three polynuclear organotin(IV) carboxylates containing ferrocenyl moiety

A novel ferrocene-containing ligand 3-trifluoromethyl-5-ferrocenyl -pyrazol-1-yl-acetic acid (LCOOH) and three organotin(IV) carboxylate derivatives [Ph₄Sn₂O(OCH₃)(OOCL)]₂(1), [BuSnO(OOCL)]₆(2) and [Bu₄Sn₂O(OOCL₂)₂] (3) have been synthesized and structurally characterized by means of FT-IR, elemental analysis, ¹H NMR, ¹¹⁹Sn NMR, X-ray crystallography and cyclic voltammetry. Both complexes 1 and 3 are centrosymmetric with ladder framework. Complex 2 is a hexanuclear one with drum structure. Furthermore, their anti-tumor activities were also evaluated, using HepG2 human hepatocellular liver carcinoma cells, A549 human lung carcinoma cells and B16-F10 melanoma cells. Complex 1 displayed the best cytotoxicity and can be pointed out as a promising substrate to be subject of further investigations.     

Carbon-13 NMR studies of some organotin(IV) compounds

The ¹³C chemical shifts and ¹³C−¹¹⁹Sn, ¹¹⁷Sn coupling constants for several organotin(IV) compounds R_xSnCl_4−x (R = Me, Buⁿ, Ph; x = 1−4) have been measured in both inert (CDCl₃) and donor (DMSO-d₆) solvents, as have ¹³C data for the compounds R_xSnR′_4−x (R = Me, Ph; R′ = Buⁿ and R = Me; R′ = Ph; x = 1−3) and the compounds Me₃SnX (X = pseudo halide). The δ and ¹J(C-Sn) values appear to depend mainly on the type and number of substituents on tin and the donor ability of the solvent. There are linear relationships between the number of substituents (x) and both δ and ¹J(C-¹¹⁹Sn) for almost the R_xSnX_4−x series (R = Me, Buⁿ, Ph; X = Cl and R = Me, Buⁿ; X = Ph; x = 1−4), when measured in a single solvent, e.g. CDCl₃. There is an excellent linear relationship between ¹J(C-¹¹⁹Sn) and ²J(¹HC-¹¹⁹Sn) for the compounds Me_xSnCl_4−x. Determination of ¹³C data for Me₃SnCl and Ph₃SnCl in a range of solvents reveals that the value of ¹J(C-Sn) increases with the donor ability of the solvent.The marked increase in the values of ¹J(C-¹¹⁹Sn) in DMSO-d₆ for the compounds R_xSnCl_4−x(R = Me, Buⁿ,Ph) on going progressively from x = 4 to x = suggest tin coordination numbers of 4, 5, 6 and 6, respectively. Some additional physical data are presented for the isolated complexes from DMSO and the compounds Ph_xSnCl_4−x(x = 1−3) and Me₃SnX with X = N₃ or OCOMe.     

Biological studies of organotin(IV) complexes with 2-mercaptopyrimidine

The known organotin(IV) complexes with 2-mercaptopyrimidine (L) [Me₂SnL₂] (1), [Buⁿ ₂SnL₂] (2), [Ph₂SnL₂] (3), and [Ph₃SnL] (4) were synthesized using a new approach. The effect of the synthesized compounds on peroxidation of fatty acids (oleic and linoleic) was studied. Complexes 1–4 promote the peroxidation of oleic acid. Their effect on the enzymatic peroxidation of linoleic acid with lipoxygenase was compared with that of cisplatin and in vitro cytoxicity against sarcoma cancer cells was determined. The antiproliferative effect of complexes 2–4 was demonstrated. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 737–743, April, 2007.     

Syntheses and structural characterization of organotin(IV) complexes derived from reaction of 2,3-diphenylpropionic acid and various alkyltin salts

Five new organotin(IV) complexes, [(R₃Sn)(O₂C₁₅H₁₃)] _n (R?=?Me: 1; nBu: 2), [RSn(O)(O₂C₁₅H₁₃)]₆ (R?=?Ph: 3), [(R₂Sn)₂(O₂C₁₅H₁₃)₂(μ ₃-O)]₂ (R?=?Me: 4), and [(R₂Sn)(O₂C₁₅H₁₃)₂] (R?=?nBu: 5), have been prepared by the reaction of 2,3-diphenylpropionic acid and the corresponding organotin chloride with sodium ethoxide in methanol. All the complexes were characterized by elemental analysis, FT-IR, NMR (¹H, ¹³C, ¹¹⁹Sn) spectroscopy, TGA, and X-ray crystallography. The structural analyses reveal that 1 and 2 are 1-D infinite polymeric chains with Sn in syn–anti conformation. Complex 3 has a drum structure with six Sn centers. Complex 4 has a supramolecular chain-like ladder through weak intermolecular Sn?···?O interactions. Complex 5 is a monomer, connected into a 1-D polymer through intermolecular C–H?···?O interactions. Complexes 1 and 5 crystallize in the orthorhombic space groups P212121 and P21212, which are chiral space groups.     

Biologically potent organotin(IV) complexes of 2-maleimidoacetic acid

The in vitro LD₅₀, anti-bacterial, anti-fungal and anti-yeast bio-tests are carried out, which proved them to be powerful biocides. The in vitro anti-tumour and analgesic activities also displayed excellent potential of the title compounds. Series of organotin(IV) complexes are synthesized and characterized. Based on spectroscopic analysis and literature evidences, the compound 1 is tetrahedral and 2 distorted octahedral or trigonal bipyramidal in nature wherein the compounds 3 and 4 are tetrahedral in solid and polymeric trigonal bipyramidal geometry in solution. Beside to ¹H, ¹³C and ¹¹⁹Sn NMR, the FT-IR is successfully applied to verify the bonding mode of endo and exo status of tin(IV) of compound 2.     

Equilibrium studies of organotin(IV) complexes with vitamin B(6)

The complex-formation equilibria of dimethyltin(IV), trimethyltin(IV) and tributyltin(IV) with pyridoxamine were investigated in dioxane-water mixtures and at different temperatures using a potentiometric technique. The stepwise formation constants of the complexes formed in solution were calculated using the non-linear least-square program MINIQUAD-75. The effect of dioxane as a solvent on the protonation constants of pyridoxamine and the formation constants of organotin(IV) complexes was discussed. The thermodynamic parameters DeltaH degrees and DeltaS degrees calculated from the temperature dependence of the equilibrium constants were investigated. The concentration distribution of the various complex species was evaluated as a function of pH.     

Synthetic, structural, and antimicrobial studies of organotin(IV) complexes of semicarbazone, thiosemicarbazone derived from 4-hydroxy-3-methoxybenzaldehyde

Reaction of dibutyltin dichloride, dimethyltin dichloride, and tributyltin chloride with ligands derived from thiosemicarbazone and semicarbazone leads to the formation of a new series of organotin(IV) complexes of general formula R₂SnCl₂·L and R₃SnCl·L (where L ligands derived from the condensation of thiosemicarbazide and semicarbazide with 4-hydroxy-3-methoxybenzaldehyde). The authenticity of these ligands and their metal complexes have been established on the basis of elemental analysis, conductance measurements, molecular weight determinations, infrared, ¹H NMR, ¹³C NMR, ¹¹⁹Sn NMR, and UV spectral studies. These studies showed that the ligands coordinate to the metal atom in a bidentate. An octahedral structure is proposed for the organotin(IV) complexes. The ligands and its metal complexes are screened for their antimicrobial activities against some Gram-positive and Gram-negative bacteria, and fungus. The studies demonstrated that metalation can increase the antimicrobial activity rather than the free ligands.     

Preparation and structural studies on organotin(IV) complexes with flavonoids

Fourteen complexes of di-n-butyltin(IV)²⁺ cations with flavonoid glycosides (rutin, hesperidin, 2′,4′,3-trihydroxy-5′,4-dimetoxychalkone 4-rutinoside) and flavonoid aglycones (quercetin, morin, hesperitin and sorte flavones) were prepared. The composition of the complexes was determined by standard analytical methods. The results showed that complexes containing diorganotin(IV)²⁺ moiety and the ligand in 1∶1, 2∶1 or 3∶1 ratio are formed. The FTIR spectra were consistent with the presence of Sn-O (phenol or carbohydrate) vibration in the compounds. The structure of the complexes was measured by Mössbauer spectroscopy. Comparison of the experimental quadrupole splitting with those calculated on the basis of partial quadrupole splitting concept revealed that the complexes are of four types: with the central tin atoms surrounded by donor atoms in a purely trigonal-bipyramidal, octahedral+trigonal-bipyramidal, trigonal-bipyramidal+tetrahedral and octahedral+tetrahedral arrangement. This procedure also distinguished between the different structural isomers of both trigonal-bipyramidal and octahedral complexes. Conclusions could therefore be drawn on the factors determining which of the isomers are formed in the systems. The Mössbauer parameters obtained for organotin(IV)-flavonoid complexes were compared with those measured for organotin(IV)-carbohydrate complexes.     

Biological activity studies on organotin(IV) complexes and parent compounds

This review summarized the literature and own data on the parent organotin(IV) compounds and complexes formed with biologically active ligands.     

Some new organotin(IV) complexes with kojic acid and maltol

Organotin(IV) complexes of kojic acid and maltol of the type R₃Sn(L) and R₂Sn(L)Cl [R=C₆H₅CH₂-,p-ClC₆H₄CH₂-; HL=kojic acid, maltol] have been synthesized in anhydrous THF. They were characterized by UV, IR,¹H NMR, and mass spectral studies. Their activityvs. E. coli, S. aureus and P. pyocyanea bacterial strains have been studied and the general order of activity is S. auresu>P. pyocyanea>E. coli. In all the complexes, the ligand acts as bidentate, forming a five membered chelate ring. All the complexes are 11 metal ligand complexes. Various thermodynamic parameters have been calculated for the first two decomposition steps using TG/DTA/DSC curves. (p-ClC₆H₄CH₂)₃Sn(L) complexes have the minimum and (C₆H₅CH₂)₂Sn(L)Cl complexes have the maximum activation energy.One of the authors (RJ) is grateful to CSIR, New Delhi, India for the award of a Senior Research Fellowship (S.R.F.).     

Biological evaluations and spectroscopic characterizations of 3-(4-ethoxyphenyl)-2-methylacrylate based organotin(IV) carboxylates derivatives

Six new organotin(IV) carboxylates, [Me₂SnL₂] (1), [n-Bu₂SnL₂] (2), [n-Oct₂SnL₂] (3), [Me₃SnL] (4), [n-Bu₃SnL] (5) and [Ph₃SnL] (6), where L = 3-(4-ethoxyphenyl)-2-methylacrylate, have been synthesized and characterized by FT-IR, NMR spectroscopy and elemental analyses. The synthesized compounds were tested for in vitro antibacterial and antifungal activities. The complexes 4–6 demonstrated higher activity than the complexes 1–3. UV-Vis absorption spectroscopy indicated that the ligand and its complexes interacted with DNA via partial intercalation as well as minor groove binding.