Hydrogen-Bond Directed Cyanide-Bridged Molecular Magnets Derived from Polycyanidemetalates and Schiff Base Manganese(III) Compounds: Synthesis, Structures, and Magnetic Properties

Versatile applications of transition metal incorporating quinoline Schiff base metal complexes: An overview

Since the last decade, research on quinoline Schiff base metal complexes has risen substantially due to their versatile applications across many significant fields. Schiff bases are also known as azomethines, aldimines, and imines. Quinoline Schiff base-derived metal complexes are intriguing to study topics. These complexes are employed in biological, analytical, and catalytic fields. Researchers have found that Schiff bases are more biologically active when coordinated with metal ions. Research in the biological sciences has shown that heterocyclic compounds like quinoline and its derivatives are important. Because of their broad spectrum of activity, quinoline derivatives have been discovered to be effective therapeutic agents for various disorders. Even though various classical synthetic pathways mentioned in the literature are still in use, there is an urgent need for a new, more effective method that is safer for the environment, has a higher yield, generates less hazardous waste, and is easier to use. This highlights the critical need for a safe, eco-friendly approach to quinoline scaffold synthesis. This review focuses exclusively on Schiff base metal complexes derived from quinoline, fabricated and studied in the past ten years, and having anticancer, antibacterial, antifungal, antioxidant, antidiabetic, antiproliferative, DNA-intercalation, and cytotoxic activities.

Synthesis, crystal structure and magnetic properties of mer-tricyanidoiron(III) precursor-based 1D heterobimetallic complexes

Three new cyanide-bridged heterometallic complexes {{[Cu(S,S-Chxn)2][Fe(bbp)(CN)3]}2·2 H2O} n (1), {{[Cu(R,R-Chxn)2][Fe(bbp)(CN)3]}2·2 H2O} n (2) and {{[Cu(Cycam)][Fe(bbp)(CN)3]}·CH3OH·2 H2O} n (3) (bbp = bis(2-benzimidazolyl)pyridine dianion, Chxn = 1,2-diaminocyclo hexane, cyclam = 1,4,8,11-tetraazacyclodecane) have been assembled from the rarely used mer-tricyanidoiron(III) building block [PPh4]2[Fe(bbp)(CN)3] and three copper(II) compounds. The complexes have been characterized by elemental analysis, IR spectroscopy and single crystal X-ray diffraction. For the chiral enantiomers 1 and 2, the circular dichroism (CD) spectrum was also investigated. X-ray structural analyses revealed that the structures of the cyanide-bridged Fe-Cu complexes 1 and 2 are characterized by two crystallographically independent but structurally very similar homochiral neutral chains, each consisting of the repeating units {[Cu(S,S-Chxn)2][Fe(bbp)(CN)3]} (1) or {[Cu(R,R-Chxn)2][Fe(bbp)(CN)3]} (2). The crystal structure of 3 likewise is build up of chains consisting of {[Cu(Cyclam)][Fe(bbp)(CN)3]} building blocks. The temperature-dependent magnetic susceptibility and field dependent magnetization of the complexes showed antiferromagnetic interactions in complex 1 between the Fe(III) and Cu(II) ions, while complex 3 is ferromagnetic, indicating that the magnetic coupling through cyanide linkage is very sensitive to the structure parameters around the paramagnetic metal ions. These results have been further confirmed by fitting of the experimental data using a uniform chain model, leading to the coupling constants J = −6.35 cm−1, g = 2.08, R = 4.42 × 10−4 and J = 1.24 cm−1, g = 2.09, R = ∑(χ obsd T − χ cald T)2/∑(χ obsd T)2 = 4.67 × 10−4 for complexes 1 and 3, respectively.

Experimental and theoretical insights into the formation of weak hydrogen bonds and H⋯H bonding interactions in the solid-state structure of two eucalyptol derivatives

We report the synthesis and X-ray solid-state structure of two eucalyptol derivatives. Both compounds form self-assembled dimers establishing C–H⋯O hydrogen bonds and H⋯H bonding interactions.

A theoretical insight into the formation of chalcogen bonding (ChB) interactions involving coordinated DMSO molecules as σ-hole donors and benzoate groups as σ-hole acceptors in a dinuclear copper(ii) complex

The formation of two chalcogen bonding (ChB) interactions involving coordinated DMSO molecules as σ-hole donors and the O atoms of carboxylate groups as acceptors in a dimeric copper(ii) complex has been described.

Syntheses, Structures, and Catalytic Hydrocarbon Oxidation Properties of N-Heterocycle-Sulfonated Schiff Base Copper(II) Complexes

Reaction of the o-[(o-hydroxyphenyl)methylideneamino]benzenesulfonic acid (H2L) (1) with CuCl2·2H2O in the presence of pyridine (py) leads to [Cu(L)(py)(EtOH)] (2) which, upon further reaction with 2,2’-bipyridine (bipy), pyrazine (pyr), or piperazine (pip), forms [Cu(L)(bipy)]·MeOH (3), [Cu2(L)2(μ-pyr)(MeOH)2] (4), or [Cu2(L)2(μ-pip)(MeOH)2] (5), respectively. The Schiff base (1) and the metal complexes (2–5) are stabilized by a number of non-covalent interactions to form interesting H-bonded multidimensional polymeric networks (except 3), such as zigzag 1D chain (in 1), linear 1D chain (in 2), hacksaw double chain 1D (in 4) and 2D motifs (in 5). These copper(II) complexes (2–5) catalyze the peroxidative oxidation of cyclic hydrocarbons (cyclooctane, cyclohexane, and cyclohexene) to the corresponding products (alcohol and ketone from alkane; alcohols, ketone, and epoxide from alkene), under mild conditions. For the oxidation of cyclooctane with hydrogen peroxide as oxidant, used as a model reaction, the best yields were generally achieved for complex 3 in the absence of any promoter (20%) or in the presence of py or HNO3 (26% or 30%, respectively), whereas 2 displayed the highest catalytic activity in the presence of HNO3 (35%). While the catalytic reactions were significantly faster with py, the best product yields were achieved with the acidic additive.

MnIII-FeIII Heterometallic Compounds within Hydrogen-Bonded Supramolecular Networks Promoted by an [Fe(CN)5(CNH)]2- Building Block: Structural and Magnetic Properties

The reaction of [Fe(CN)₆]^3- and [Mn(acacen)]⁺ (H₂acacen = N, N'-bis(acetylacetone)ethylenediamine) building units in the presence of supramolecular cations, [(F-Anil)(18-crown-6)]⁺ (F-Anil⁺ = 3-fluoroanilinium) or [(Me-F-Anil)(18-crown-6)]⁺ (Me-F-Anil⁺ = 3-fluoro-4-methylanilinium), affords two new bimetallic compounds, [(F-Anil)(18-crown-6)][Mn(acacen)Fe(CN)₅(CNH)]·MeOH (1) and [(Me-F-Anil)(18-crown-6)][Mn(acacen)(MeOH)Fe(CN)₅(CNH)]·MeOH (2), respectively. Compound 1 exhibits a one-dimensional topology, while compound 2 is a dinuclear discrete system due to the coordination of a MeOH molecule at the axial position of the [Mn(acacen)]^- unit. For both systems, the acidity of the corresponding supramolecular cation triggers the protonation of the Fe^III moiety as [Fe(CN)₅(CNH)]^2-. Moreover, the resulting -CNH ligand induces hydrogen bonding interactions connecting the chains for 1 or the molecules for 2 into higher dimensional supramolecular networks. Magnetic properties of compounds incorporating these [Fe(CN)₅(CNH)]^2- building blocks were, for the first time, thoroughly investigated, indicating a three-dimensional antiferromagnetic order of single-chain magnets for 1 and an antiferromagnetically interacting S = 3/2 spin ground state for 2.

Indirect effect of hydrogen bonds on the magnetic coupling on Mn(iii) dinuclear compounds

Hydrogen bonds between the cationic complex and counteranion weaken the antiferromagnetic interaction.

Substitute Group-Tuned Schiff-Base Manganese(III)-Based Cyanide-Bridged Bimetallic Complexes: Synthesis, Crystal Structures and Magnetic Properties

The trinuclear cyanide-bridged heterometallic Pd(II)–Mn(III) complexes {[Mn(L1)(H2O)]2[Pd(CN)4]} and {[Mn(L2)(H2O)]2[Pd(CN)4]}·2H2O (L1 = N,N‘-1,2-propylene-bis(3-methoxysalicylideneiminate; L2 = N,N′-1,2-propylene-bis(3-ethoxysalicylideneiminate) were obtained and structurally and magnetically characterised. X-ray diffraction revealed their cyanide-bridged trinuclear core nature with a conformational difference. The magnetic susceptibilities of the two complexes revealed overall weak antiferromagnetic interactions between the adjacent Mn(III) ions.

Unprecedented ferromagnetic Gdnitronyl nitroxide coupling through a hydrogen bonding bridge

A novel lanthanide(iii)-nitronyl nitroxide chain {[Gd(hfac)₃(Nit-Ph-3,5-bIm)(H₂O)]·C₄H₁₀O}_n (1) was prepared and characterized. Strikingly, an unexpected ferromagnetic coupling between the Gd(iii) ion and the nitroxide group mediated by hydrogen bonding has been observed for the first time.

Synthesis, crystal structures and magnetic characterisation of two 2p–3d metallic coordination polymers

The coordination polymers {Mg[Fe(L)(CN)5]}n·0.5nH2O and {MgCu2(CH3COO)6}n [L = bis( N-imidazolyl)methane] have been synthesised. X-ray diffraction revealed that {Mg[Fe(L)(CN)5]}n·0.5nH2O has a one-dimensional neutral chain structure consisting of alternating [Mg(L)2(H2O)2)]2+ species and [Fe(L)(CN)5]2– building blocks, which can be further linked into a three-dimensional supramolecular structure by inter-chain p–p interactions. {MgCu2(CH3COO)6}n has a three-dimensional network with the [MgCu2(CH3COO)6] unit as neutral core extended by Mg–O bonds. Magnetic susceptibility studies on {MgCu2(CH3COO)6}n revealed antiferromagnetic interactions between adjacent Cu(II) ions.

Unfolding biological properties of a versatile dicopper(II) precursor and its two mononuclear copper(II) derivatives

Synthesis, inter-conversions and biological study of the dichloro bridged dicopper(II) compound [CuLCl]₂ (1) and its two mononuclear derivatives [CuLCl(H₂O)]·H₂O (2) and [CuLCl(py)] (3) (HL=2-(2-pyridylmethyleneamino)benzenesulfonic acid) are described. The dimeric compound 1 collapses into monomers 2 and 3 in the presence of coordinating solvents, water and pyridine, respectively, and 1 is regenerated upon simple stirring of 2 or 3 in methanol. The reactions of 1 with neutral (present study) and charged (earlier studies) ligands result in monomeric and multimeric compounds, respectively, attesting that it is a versatile dicopper(II) precursor. The anticancer activity of these copper complexes (1-3) was screened against lung (A-549) and breast (MDA-MB-231) human cancer cell lines. The IC₅₀ (half maximal inhibitory concentration) value for one (3) of the compounds suggests preferential cytotoxicity against breast cancer MDA-MB-231 cell line. Furthermore, the IC₅₀ value obtained for complex 3 is found to be almost two-fold times cytotoxic than the standard drug cisplatin. In addition, the underlying possible mechanism of its apoptosis-inducing efficacy in MDA-MB-231 cells has been rationalized by using flow cytometry (FACS) and Hoechst 33342/propidium iodide (PI) fluorescence staining. The stimulation of apoptotic induction for complex 3 has further been affirmed by reactive oxygen species (ROS) generation and mitochondrial aggregations studies.

Cyanide-bridged heterobimetallic magnetic complexes based on metalloporphyrinate and tricyanometalate building blocks

Three novel cyanide-bridged metalloporphyrinate complexes were synthesized and characterized, and their magnetic properties have also been systematically investigated.

Three Chiral Schiff-Base-Manganese(III)-Based Complexes: Synthesis, Structures and Magnetic Properties

Three chiral manganese(III) Schiff-base complexes [Mn(R,R-Salcy)(CH3OH)(N3)], [Mn(S,S-Salcy)(DMF)(N3)] (both monomers by X-structure determination) and the trinuclear complex (X-ray structure) {[Mn(R,R-Salcy)(H2O)]2[μ-Ni(CN)4]}·3CH3OH·H2O [Salcy = N,N′-(1,2-cyclohexanediylethylene)bis(salicylideneiminato)dianion)] have been synthesised. The trimeric complex shows weak antiferromagnetic interactions between the adjacent Mn(III) ions.

Single-molecule magnet behavior in three cyano-bridged heterometallic Fe(III)-Ni(II) clusters

One trinuclear and two tetranuclear cyanide-bridged Fe(III)-Ni(II) complexes were synthesized via treatment of a tricyanometallate with divalent Ni salts in the presence of 1-butylimidazole, 2,2-bipyrimidyl and 1,10-phenanthroline, respectively. Magnetic property studies demonstrated that the three complexes exhibit single-molecule magnet behavior as a result of strong intracluster ferromagnetic coupling and weak intercluster magnetic interactions.

Sulfonated Schiff base copper(ii) complexes as efficient and selective catalysts in alcohol oxidation: syntheses and crystal structures

Alcohol oxidation properties of four copper complexes (2–5) derived from the sulfonated Schiff base H₂L·3H₂O (1) are described. A quantitative conversion of 1-phenylethanol was obtained with 4 within 20 min of low power MW irradiation.

Synthesis, Structures and Magnetic Properties of Hydrogen-bond Directed 2D Heterobimetallic Cyanide-bridged Coordination Polymers

The complexes {[Mn(L1)(H2O)]2[Pd(CN)4]}·2CH3CN and {[Mn(L2)(H2O)]2[Pd(CN)4]}2·H2O [L1 = N,N-ethylene-bis(5-bromicsalicylideneiminate); L2 = N,N-ethylene-bis(5-methxysalicylideneiminate)] have been obtained from [Pd(CN)4]2- and the corresponding Schiff-base manganese(III) compounds. X-ray diffraction reveals that the complexes are constructed into two-dimensional supramolecular networks through intermolecular O–H…O and O–H…N hydrogen bond interactions. The magnetic susceptibilities of the two complexes reveal overall weak antiferromagnetic interactions between the adjacent Mn(III) ions.

Heterometallic complexes combining [MnIII(salpn)]+ and [Fe(CN)6]4− units as the products of reactions between [MnIII(salpn)(H2O)C(CN)3] and [Fe(CN)6]3−/4−

The tricyanomethanide ligand reduces Fe(iii) to Fe(ii) yielding the discrete and chain complexes.

Pressure induced transition from spin glass-like behavior to a metamagnet exhibiting weak ferromagnetism observed for decamethylferrocenium hexacyanobutadienide, [FeCp*2]˙+ [HCBD]˙-

The magnetic properties of [Fe(III)Cp*2]˙(+)[HCBD]˙(-) (Cp* = pentamethylcyclopentadienide; HCBD = hexacyanobutadienide, C4(CN)6) and [Fe(III)Cp*2]˙(+)[DDQ]˙(-) (DDQ = 2,3-dichloro-5,6-dicyanoquinonide) were measured at ambient and applied hydrostatic pressures up to 11.4 and 9.2 kbar, respectively. At ambient pressure [FeCp*2][HCBD] exhibits spin glass-like behavior with a freezing temperature, Tf, of 2.93 K from the peak in χ'(T) at 10 Hz, but magnetic ordering is not evident due to the lack of a remnant magnetization, bifurcation temperature, and hysteresis. Above 3.1 kbar, [FeCp*2][HCBD] magnetically orders as a metamagnet with an antiferromagnetic ground state with an ordering temperature, Tc, of 2.46 K determined from the Fisher specific heat, which increases linearly to 4.80 K at 11.4 kbar at a rate of 0.28 K kbar(-1). Upon application of pressure metamagnetic-like behavior with hysteresis indicative of a weak ferromagnet (canted antiferromagnet) was observed at and above 3.1 kbar, with a coercive field, Hcr, of 65 Oe, which increases exponentially to 795 Oe at 11.4 kbar. [FeCp*2]˙(+)[DDQ]˙(-) did not magnetically order above 2 K, and magnetic order was not observed up to 9.2 kbar. The pressure dependencies are reversible.

Synthesis, Crystal Structures and Magnetic Properties of Cyanide-bridged Trinuclear and Ion-pair Heterometallic Complexes

A cyanide-bridged, trinuclear, heterometallic Pd(II)–Mn(III) complex [{Mn(L)(H2O)}2{(μ-CN)2Pd(CN)2}] and an ion-pair complex [Co(Phen)2(H2O)2][Pd(CN)4]·MeOH have been synthesised (L = N,N-ethylene-bis(3-ethoxysalicylideneiminate; Phen = 1,10-phenanthroline). Single X-ray diffraction analysis reveals the neutral trinuclear complex is self-complementary through coordinated aqua ligands from one complex and the free O4 compartments from the neighbouring complex, thereby giving a 1D single chain supramolecular structure. The ion-pair complex forms a three-dimensional network via intermolecular O…H–N hydrogen bond interactions. Magnetic susceptibility studies show overall weak antiferromagnetic coupling between adjacent Mn(III) ions in the trimeric complex.