Diimide Ligands Research Articles

Inorganic anion-induced structural diversity and structural transformation in a metal-negative ligand system containing Cd(II) ion and naphthalene diimide ligand

The coordination of a new 1,4,5,8-naphthalenediimides-based ligand N,N-di-(5-tetrazol)-1,4,5,8-naphthalenetetracarboxydiimide (H2dtNDI) with CdSO4 afforded mixtures containing {[Cd(dtNDI)(DMF)2.5]·DMAc}n (1) and {[Cd2(dtNDI)2(DMAc)2]·DMAc}n (2) as components. Whereas the coordination of H2dtNDI with CdX2 (x=ClO4−, NO3− and I−) afforded pure coordination polymer, namely, {[Cd(dtNDI)(H2O)2.5]·DMAc}n (3). All the compounds contain binuclear M2L2 ring as secondary building block (SBU). Compound 1 is a 1D chain composed of the binuclear SBUs and dimeric Cd(II) MBBs. Compound 2 exhibit a 2D network with (4·82) topology based on a binuclear SBUs. Compound 3 possess a five-fold interpenetrating 3D dia framework with tetrameric Cd(II) MBBs as nodes and binuclear SBUs as linkers. Although the inorganic anions are not appeared in the final frameworks of compounds 1–3, they play an important role in the structural formation during assembly process. In addition, the mixtures composed of compounds 1–2 can transfer to pure compounds 3via solvent-mediated process.

Synthesis and characterization of a photochromic magnesium(II) coordination polymer based on a naphthalene diimide ligand.

Naphthalene diimides, which are planar, chemically robust and redox-active, are an attractive class of electron-deficient dyes, which can undergo a single reversible one-electron reduction to form stable radical anions in the presence of electron donors upon irradiation. This makes them excellent candidates for organic linkers in the construction of photochromic coordination polymers. Such a photochromic one-dimensional linear coordination polymer has been prepared using N,N'-bis(3-carboxyphenyl)naphthalene-1,8:4,5-tetracarboximide (H2BBNDI). Crystallization of H2BBNDI with magnesium nitrate in an N,N'-dimethylformamide (DMF)/ethanol/H2O mixed-solvent system under solvothermal conditions afforded the one-dimensional coordination polymer catena-poly[[bis(dimethylformamide-κO)magnesium(II)]-bis[μ-N-(3-carboxylatophenyl)-N'-(3-carboxylphenyl)naphthalene-1,8:4,5-tetracarboximide-κ2O:O']], [Mg(C28H13N2O8)2(C3H7NO)2]n. The asymmetric unit contains half of a magnesium cation, one HBBNDI- ligand and one DMF molecule. Two partially deprotonated HBBNDI- ligands bridge two magnesium cations to form a one-dimensional chain. Strong inter-chain π-π interactions between the naphthalene rings of the HBBNDI- ligand and the imide rings of adjacent chains provide a two-dimensional structure. The supramolecular three-dimensional framework is stabilized by π-π interactions between naphthalene rings of neighbouring two-dimensional supramolecular networks. The complex exhibits a reversible photochromic behaviour, which may originate from the photoinduced electron-transfer generation of radicals in the HBBNDI- ligand.

Divalent Naphthalene Diimide Ligands Display High Selectivity for the Human Telomeric G-quadruplex in K+ Buffer.

Selective G‐quadruplex ligands offer great promise for the development of anti‐cancer therapies. A novel series of divalent cationic naphthalene diimide ligands that selectively bind to the hybrid form of the human telomeric G‐quadruplex in K+ buffer are described herein. We demonstrate that an imidazolium‐bearing mannoside‐conjugate is the most selective ligand to date for this quadruplex against several other quadruplex and duplex structures. We also show that a similarly selective methylpiperazine‐bearing ligand was more toxic to HeLa cancer cells than doxorubicin, whilst exhibiting three times less toxicity towards fetal lung fibroblasts WI‐38.

Frontispiece: The First Lanthanide Complexes with a Redox‐Active Sulfur Diimide Ligand: Synthesis and Characterization of [LnCp*2(RN=)2S], Ln=Sm, Eu, Yb; R=SiMe3

Frontispiece: The First Lanthanide Complexes with a Redox‐Active Sulfur Diimide Ligand: Synthesis and Characterization of [LnCp*₂(RN=)₂S], Ln=Sm, Eu, Yb; R=SiMe₃

A robust metallomacrocyclic motif for the formation interpenetrated coordination polymers

The reproducibility of an M2L2 metallomacrocyclic synthon containing L-alanine substituted naphthalene diimide ligands (AlaNDI), and its ability to form both catenane and rotaxane motifs, has been demonstrated in a series of nine homochiral coordination polymers. The planes of the NDIs that comprise the metallomacrocycle are ∼7 A apart, an ideal distance for an aromatic group to reside within the ring with multiple parallel π-interactions. The tendency for these systems to be dominated by π-interactions appears to be a driving force for interpenetration of these coordination polymers by either the formation of catenanes between two {M2(AlaNDI)2} metallomacrocycles or the formation of rotaxanes by dipyridyl coligands passing through metallomacrocycles (4,4′-bipyridine, dipyridylethene and dipyridylnaphthalenediimide). Due to both of these interpenetration motifs being facilitated by parallel π-interactions, the interpenetration of the individual networks does not typically lead to increased dimensionality in the structures, with the exception of one material in which a 1D chain interpenetrates in a 1D → 2D manner. Two of the reported coordination polymers, both containing dipyridylnaphthalenediimide (4PyNDI), are not interpenetrated with π-interactions present between the 4PyNDI ligands themselves rather than engaging with the macrocycles. Overall the reproducibility of the metallomacrocycle, and the relatively common occurrence of catenane and rotaxane motifs, suggests that this is a promising synthon for further crystal engineering applications.

The First Lanthanide Complexes with a Redox-Active Sulfur Diimide Ligand: Synthesis and Characterization of [LnCp*2 (RN=)2 S], Ln=Sm, Eu, Yb; R=SiMe3.

The first lanthanide complexes with a redox-active sulfur diimide ligand, [LnCp*2 (Me3 SiN=)2 S] (Ln=Sm, Eu, Yb; Cp*=η5 -C5 Me5 ), are reported. The complexes were synthesized by using [LnCp*2 (THF)2 ] and (Me3 SiN=)2 S and have been thoroughly characterized by single-crystal X-ray diffraction, EPR spectroscopy, UV/Vis/NIR electronic absorption spectroscopy and SQUID magnetometry. The results, as interpreted by CASSCF/SOC-RASSI calculations providing a non-perturbative treatment of spin-orbit coupling, indicate that these paramagnetic complexes are best described as Ln3+ and [(Me3 SiN=)2 S]-. adducts. As such, these complexes contain the first isolated and structurally characterized acyclic [(RN=)2 S]-. radical anions.

Ferrocenyl naphthalene diimides as tetraplex DNA binders

Seven ferrocenyl naphthalene diimide (FND) ligands were synthesized. Each had a higher affinity for tetraplex DNA than for either single- or double-stranded DNA. The FND binding affinities were >105M−1 in 0.10M AcOH-AcONa or AcOH-AcOK (pH5.5) containing 0.10M NaCl or KCl. The FNDs with the highest binding affinities for tetraplex DNA showed 23- or 8-times higher preference for tetraplex DNA than for single- or double-stranded DNA, respectively. The current signals generated from the seven FNDs bound to the tetraplex DNA immobilized on the electrode were found to correlate with the binding affinities of these ligands for the tetraplex DNA. Furthermore, using the telomerase repeat amplification protocol assay, the FND ligands could be categorized into three groups: (a) inhibiting both telomerase and Taq polymerase, (b) inhibiting telomerase alone, and (c) inhibiting neither telomerase nor Taq polymerase.

Transparent-to-Dark Electrochromic Behavior in Naphthalene-Diimide-Based Mesoporous MOF-74 Analogs

Summary The deliberate insertion of redox-active naphthalene diimide ligands into the versatile family of metal-organic frameworks known as MOF-74 (CPO-27) gives rise to a mesoporous electrochromic MOF that can be switched from transparent to dark, a desirable feature in electrochromic devices such as smart windows. Specifically, we report two new materials that have the MOF-74 topology and display redox activity stemming from a naphthalene diimide salicylic acid (NDISA) ligand. We show that these materials can be deposited as thin films on fluorine-doped tin oxide glass. The surprisingly different morphologies of MOF films obtained from Mg 2+ and Ni 2+ ions is likely controlled by the nucleation kinetics of Mg 2 (NDISA) and Ni 2 (NDISA), respectively. Both materials exhibit well-behaved quasi-reversible redox events associated with the [NDI]/[NDI] ·– and [NDI] ·– /[NDI] 2– redox couples, which are also responsible for the electrochromic switching.

Molecular recognition of naphthalene diimide ligands by telomeric quadruplex-DNA: the importance of the protonation state and mediated hydrogen bonds.

In depth Monte Carlo conformational scans in combination with molecular dynamics (MD) simulations and electronic structure calculations were applied in order to study the molecular recognition process between tetrasubstituted naphthalene diimide (ND) guests and G-quadruplex (G4) DNA receptors. ND guests are a promising class of telomere stabilizers due to which they are used in novel anticancer therapeutics. Though several ND guests have been studied experimentally in the past, the protonation state under physiological conditions is still unclear. Based on chemical intuition, in the case of N-methyl-piperazine substitution, different protonation states are possible and might play a crucial role in the molecular recognition process by G4-DNA. Depending on the proton concentration, different nitrogen atoms of the N-methyl-piperazine might (or might not) be protonated. This fact was considered in our simulation in terms of a case by case analysis, since the process of molecular recognition is determined by possible donor or acceptor positions. The results of our simulations show that the electrostatic interactions between the ND ligands and the G4 receptor are maximized in the case of the protonation of the terminal nitrogen atoms, forming compact ND G4 complexes inside the grooves. The influence of different protonation states in terms of the ability to form hydrogen bonds with the sugar-phosphate backbone, as well as the importance of mediated vs. direct hydrogen bonding, was analyzed in detail by MD and relaxed force constant (compliance constant) simulations.

Mercury- and cadmium-assisted [2 + 2] cyclodimerization of tert-butylselenium diimide.

The complexes [MCl2{N,N'-(t)BuNSe(μ-N(t)Bu)2SeN(t)Bu}] [M = Cd (1), Hg (2)] were obtained in high yields by the reaction of tert-butylselenium diimide Se(IV)(N(t)Bu)2 with CdCl2 or HgCl2 in tetrahydrofuran. Recrystallization of 1 and 2 from acetonitrile (MeCN) afforded yellow crystals of 1·MeCN and 2·MeCN, respectively. Isomorphic 1·MeCN and 2·MeCN contain an unprecedented dimeric selenium diimide ligand, which is N,N'-chelated to the metal through exocyclic imido groups. In addition to the complexes 1 and 2, the (77)Se NMR spectra of acetonitrile solutions of 1·MeCN and 2·MeCN indicated the presence of the dimeric (t)BuNSe(μ-N(t)Bu)2SeN(t)Bu, monomeric Se(IV)(N(t)Bu)2, and cyclic selenium imides. Density functional theory calculations at the PBE0/def2-TZVPP level of theory were used to assign the (77)Se resonances of the dimer. A comparison of Gibbs energies of formation of some metal dichloride complexes [MCl2{N,N'-Se(IV)(N(t)Bu)2}] and [MCl2{N,N'-(t)BuNSe(μ-N(t)Bu)2SeN(t)Bu}] (M = Zn, Cd, Hg) indicated that the formation of complexes containing a dimeric selenium diimide ligand is favored over those containing a monomeric ligand for the group 12 metals. In the case of the group 10 metal halogenides (M = Ni, Pd, Pt), the Gibbs energies of the complexes with monomeric Se(IV)(N(t)Bu)2 ligands are close to those containing dimeric (t)BuNSe(μ-N(t)Bu)2SeN(t)Bu ligands. A plausible reaction pathway with a low activation energy involves the initial formation of [MCl2{N,N'-Se(IV)(N(t)Bu)2}] (M = Zn, Cd, Hg), which then reacts with another molecule of Se(N(t)Bu)2, leading to the final [MCl2{N,N'-(t)BuNSe(μ-N(t)Bu)2SeN(t)Bu}] complex. Without the presence of group 12 metal halogenides, the [2 + 2] cyclodimerization of Se(IV)(N(t)Bu)2 is virtually thermoneutral, but the activation energy is relatively high, which accounts for the kinetic stability of (t)BuNSe(μ-N(t)Bu)2SeN(t)Bu in solution. A minor byproduct, [Cd7Cl14{N,N'-Se(II)(NH(t)Bu)2}6]·4CH2Cl2, was identified by X-ray crystallography as a heptanuclear cluster with selenium(II) diamide ligands N,N'-chelated to the cadmium centers.

Synthesis, fluorescence, and sorption properties of cobalt coordination polymers of the N,N′-bis(4-pyridylmethyl)naphthalene diimide ligand

Three cobalt coordination polymers, namely {[Co(4-pmntd)2(CF3SO3)(H2O)]·(CF3SO3)·(C2H5OH)·0.5(HCCl3)·H2O} n (1), {[Co(4-pmntd)(H2O)4]·(NO3)2·H2O} n (2), and {[Co(4-pmntd)(pta)(CH3OH)2]·2(CHCl3)} n (3) (4-pmntd = N,N′-bis(4-pyridylmethyl)-naphthalene diimide; pta = terephthalate), have been synthesized by reactions of 4-pmntd with Co(CF3SO3)2·4H2O, Co(NO3)2·6H2O, and Co(pta), respectively. The complexes have been characterized by elemental analyses, powder X-ray diffraction, thermogravimetric analyses, IR spectroscopy, and single-crystal X-ray diffraction. In complex 1, the ligand adopts U-mode, resulting in a dumbbell-like 2D (4, 4)-sql net structure in a non-interpenetrating edge-to-edge arrangement. The Z-mode ligand arrangement leads to 1D zigzag chains for complex 2, and a 2D twofold interpenetrating bat-like (4, 4)-sql net for complex 3. A solution of complex 2 in DMF showed a change in color and remarkably enhanced fluorescence upon the addition of two equivalents of acetate, whereas other anions did not induce a color change. Hence, complex 2 can act as a highly promising acetate-detecting reagent. Their thermal and the gas adsorption properties of complexes 1 and 3 were investigated. Three 1D and 2D cobalt coordination polymers have been synthesized; their structural diversity in these complexes is attributed to different coordination abilities, geometries of counter-anions, and the different conformations adopted by the ligand. A solution of complex 2 showed a change in color and remarkably enhanced fluorescence upon the addition of two equivalents of acetate, whereas other anions did not induce a color change. Hence complex 2 can act as a highly promising acetate-detecting reagent. Their thermal properties and the gas adsorption property of complexes 1, 3 were investigated.

Thermodynamics of binding of di- and tetrasubstituted naphthalene diimide ligands to DNA G-quadruplex.

Naphthalene diimide ligands have the potential to stabilize human telomeric G-quadruplex DNA via noncovalent interactions. Stabilization of G-quadruplex high order structures has become an important strategy to develop novel anticancer therapeutics. In this study four naphthalene diimide based ligands were analyzed in order to elucidate the principal factors determining contributions to G-quadruplex-ligand binding. Three possible modes of binding and their respective Gibbs free energies for two naphthalene diimide based di-N-alkylpyridinium substituted ligands have been determined using a molecular docking technique and compared to experimental results. The structures obtained from the molecular docking calculations, were analyzed using the ab initio based fragment molecular orbital (FMO) method in order to determine the major enthalpic contributions to the binding and types of interactions between the ligand and specific residues of the G-quadruplex. A computational methodology for the efficient and inexpensive ligand optimization as compared to fully ab initio methods based on the estimation of binding affinities of the naphthalene diimide derived ligands to G-quadruplex is proposed.

Broadband visible-light-harvesting trans-bis(alkylphosphine) platinum(II)-alkynyl complexes with singlet energy transfer between BODIPY and naphthalene diimide ligands.

A heteroleptic bis(tributylphosphine) platinum(II)-alkynyl complex (Pt-1) showing broadband visible-light absorption was prepared. Two different visible-light-absorbing ligands, that is, ethynylated boron-dipyrromethene (BODIPY) and a functionalized naphthalene diimide (NDI) were used in the molecule. Two reference complexes, Pt-2 and Pt-3, which contain only the NDI or BODIPY ligand, respectively, were also prepared. The coordinated BODIPY ligand shows absorption at 503 nm and fluorescence at 516 nm, whereas the coordinated NDI ligand absorbs at 594 nm; the spectral overlap between the two ligands ensures intramolecular resonance energy transfer in Pt-1, with BODIPY as the singlet energy donor and NDI as the energy acceptor. The complex shows strong absorption in the region 450 nm-640 nm, with molar absorption coefficient up to 88 000 M(-1) cm(-1) . Long-lived triplet excited states lifetimes were observed for Pt-1-Pt-3 (36.9 μs, 28.3 μs, and 818.6 μs, respectively). Singlet and triplet energy transfer processes were studied by the fluorescence/phosphorescence excitation spectra, steady-state and time-resolved UV/Vis absorption and luminescence spectra, as well as nanosecond time-resolved transient difference absorption spectra. A triplet-state equilibrium was observed for Pt-1. The complexes were used as triplet photosensitizers for triplet-triplet annihilation upconversion, with upconversion quantum yields up to 18.4 % being observed for Pt-1.

Bis(quinolin-2-ylcarbon-yl)amido-κ(3) N,N',N'']bromido-(N,N-di-methyl-formamide-κO)copper(II).

In the mononuclear title complex, [CuBr(C20H12N3O2)(C3H7NO)], synthesized from the quinoline-derived reduced Schiff base 4-(quinolin-2-ylmeth­yl)amino­phenol, the coordination geometry around Cu2+ is distorted square-pyramidal, comprising a bromide anion at the apex [Cu—Br = 2.4671 (5) Å]. The base of the pyramid is built up from one di­methyl­formamide O-atom donor [Cu—O = 2.078 (2) Å] and three N-atom donors from the monoanionic, tridentate bis­(quinolin-2-ylcarbon­yl)di­imide ligand [Cu—Ndi­imide = 1.941 (3) Å, and Cu—Nquinol­yl = 2.060 (3) and 2.049 (3) Å]. An intra­molecular C—H⋯O occurs. In the crystal, weak methyl and aromatic C—H⋯Br and formyl C—H⋯Ocarbon­yl hydrogen-bonding inter­actions generate an overall layered structure lying parallel to (001).

Enhancing selective CO2 adsorption via chemical reduction of a redox-active metal–organic framework

A new microporous framework, Zn(NDC)(DPMBI) (where NDC = 2,7-naphthalene dicarboxylate and DPMBI = N,N'-di-(4-pyridylmethyl)-1,2,4,5-benzenetetracarboxydiimide), containing the redox-active benzenetetracarboxydiimide (also known as pyromellitic diimide) ligand core has been crystallographically characterised and exhibits a BET surface area of 608.2 ± 0.7 m(2) g(-1). The crystallinity of the material is retained upon chemical reduction with sodium naphthalenide (NaNp), which generates the monoradical anion of the pyromellitic diimide ligand in the framework Zn(NDC)(DPMBI)·Na(x) (where x represents the molar Na(+)/Zn(2+) ratio of 0.109, 0.233, 0.367 and 0.378 from ICP-AES), as determined by EPR, solid state Vis-NIR spectroelectrochemistry and UV-Vis-NIR spectroscopy. The CO2 uptake in the reduced materials relative to the neutral framework is enhanced up to a Na(+)/Zn(2+) molar ratio of 0.367; however, beyond this concentration the surface area and CO2 uptake decrease due to pore obstruction. The CO2 isosteric heat of adsorption (|Q(st)|) and CO2/N2 selectivity (S), obtained from pure gas adsorption isotherms and Ideal Adsorbed Solution Theory (IAST) calculations, are also maximised relative to the neutral framework at this concentration of the alkali metal counter-ion. The observed enhancement in the CO2 uptake, selectivity and isoteric heat of adsorption has been attributed to stronger interactions between CO2 and both the radical DPMBI ligand backbone and the occluded Na(+) ions.

New insights from molecular dynamic simulation studies of the multiple binding modes of a ligand with G-quadruplex DNA

G-quadruplexes are higher-order DNA and RNA structures formed from guanine-rich sequences. These structures have recently emerged as a new class of potential molecular targets for anticancer drugs. An understanding of the three-dimensional interactions between small molecular ligands and their G-quadruplex targets in solution is crucial for rational drug design and the effective optimization of G-quadruplex ligands. Thus far, rational ligand design has been focused mainly on the G-quartet platform. It should be noted that small molecules can also bind to loop nucleotides, as observed in crystallography studies. Hence, it would be interesting to elucidate the mechanism underlying how ligands in distinct binding modes influence the flexibility of G-quadruplex. In the present study, based on a crystal structure analysis, the models of a tetra-substituted naphthalene diimide ligand bound to a telomeric G-quadruplex with different modes were built and simulated with a molecular dynamics simulation method. Based on a series of computational analyses, the structures, dynamics, and interactions of ligand-quadruplex complexes were studied. Our results suggest that the binding of the ligand to the loop is viable in aqueous solutions but dependent on the particular arrangement of the loop. The binding of the ligand to the loop enhances the flexibility of the G-quadruplex, while the binding of the ligand simultaneously to both the quartet and the loop diminishes its flexibility. These results add to our understanding of the effect of a ligand with different binding modes on G-quadruplex flexibility. Such an understanding will aid in the rational design of more selective and effective G-quadruplex binding ligands.

Mechanism of the antiproliferative activity of some naphthalene diimide G-quadruplex ligands.

G-quadruplexes are higher-order nucleic acid structures that can form in G-rich telomeres and promoter regions of oncogenes. Telomeric quadruplex stabilization by small molecules can lead to telomere uncapping, followed by DNA damage response and senescence, as well as chromosomal fusions leading to deregulation of mitosis, followed by apoptosis and downregulation of oncogene expression. We report here on investigations into the mechanism of action of tetra-substituted naphthalene diimide ligands on the basis of cell biologic data together with a National Cancer Institute COMPARE study. We conclude that four principal mechanisms of action are implicated for these compounds: 1) telomere uncapping with subsequent DNA damage response and senescence; 2) inhibition of transcription/translation of oncogenes; 3) genomic instability through telomeric DNA end fusions, resulting in mitotic catastrophe and apoptosis; and 4) induction of chromosomal instability by telomere aggregate formation.

Improving the affinity of naphthalene diimide ligand to telomeric DNA by incorporating Zn2+ ions into its dipicolylamine groups

N,N′-bis[3-[3-(2,2′-dipicolyl)methylaminopropyl]-methylaminopropyl]naphthalene-1,4,5,8-tetracarboxylic acid diimide, 1, and its complex with zinc ions, 2, were investigated against telomeric sequences, [TAGGG(TTAGGG)3] and [AGGG(TTAGGG)3], which reveal different G-quadruplex structures depending on the conditions. Spectrophotometric, SPR, and CD techniques revealed that both ligands showed large binding constants to hybrid-type G-quadruplexes formed in the presence of K+ ions. Moreover, 2 revealed higher affinity to investigated oligonucleotides suggesting that complex of naphthalene diimide derivative with Zn2+, comparing to 1, provided additional electrostatic or coordination interactions between positively charged zinc ions and condensed negative charged phosphate anions from G4 DNA.

Perylene ligand wrapping G-quadruplex DNA for label-free fluorescence potassium recognition

A perylene ligand, N,N-bis-(1-aminopropyl-3-propylimidazol salt)-3,4,9,10-perylene tetracarboxylic acid diimide ligand (PDI), which consisted of π-conjugated perylene moiety and hydrophilic side chains with positively charged imidazole rings, was used to wrap G-quadruplex for fluorescence turn-on K+ recognition. Electrostatic attraction between PDI's positively charged imidazole rings and DNA's negatively charged phosphate backbones enabled PDI to accumulate on DNA. Upon trapping K+, these G-rich DNA sequences transitioned to G-quadruplex. Subsequently, PDI ligands wrapped G-quadruplex, in which the flat aromatic core of PDI ligand interacted with G-quartet through π–π stacking and the side chains were positioned in grooves through electrostatic interactions. Consequently, the interaction mode change and conformational transition from PDI stacked G-sequence to PDI wrapped G-quadruplex led to PDI fluorescence enhancement, which was readily monitored as the detection signal. This strategy excluded the sequence tagging step and exhibited high selectivity and sensitivity towards K+ ion with the linear detection range of 10–150nM. Besides, PDI ligands may hold diagnostic and therapeutic application potentials to human telomere and cancer cells.

Synthesis, structural characterization and in vitro cytotoxicity of diorganotin (IV) diimido complexes

Reactions of the diorganotin with two N–OH diimide ligands (N-hydroxyphthalimide and N-hydroxysuccinimide) yielded five new dimeric tetraorganostannoxanes formulated as R8Sn4O2L2X2. The crystal structures of the complexes reveal the formation of the tetranuclear species contains a planar Sn4O4 core, consisting of three adjacent rhombs with bridging oxo and N–OH diimide ligands. The central tin atoms are five-coordinated to assume a distorted trigonal bipyramidal configuration and the N–OH diimide ligands act as monodentate O-bound planar. In vitro cytotoxic activities of the title compounds have been determined against three cell lines (A549, HCT-8 and HL-60). Studies reveal that three di-n-butyltin(IV) diimido complexes show higher cytotoxic activities than cisplatin. The structure–activity relationship of the cytotoxicity of the title complexes has also been discussed.