Magnetism and crystal structure of an N3O3‐coordinated iron(II) complex

The reaction of [FeL(MeOH)₂] {where L is the tetradentate N₂O₂‐coordinating Schiff base‐like ligand (E,E)‐diethyl 2,2′‐[1,2‐phenylenebis(nitrilomethylidyne)]bis(3‐oxobutanoate)(2−) and MeOH is methanol} with 3‐aminopyridine (3‐apy) in methanol results in the formation of the octahedral complex (3‐aminopyridine‐κN¹){(E,E)‐diethyl 2,2′‐[1,2‐phenylenebis(nitrilomethylidyne)]bis(3‐oxobutanoato)(2−)‐κ⁴O³,N,N′,O^3′}(methanol‐κO)iron(II), [Fe(C₂₀H₂₂N₂O₆)(C₅H₆N₂)(CH₄O)] or [FeL(3‐apy)(MeOH)], in which the Fe^II ion is centered in an N₃O₃ coordination environment with two different axial ligands. This is the first example of an octahedral complex of this multidentate ligand type with two different axial ligands, and the title compound can be considered as a precursor for a new class of complexes with potential spin‐crossover behavior. An infinite two‐dimensional hydrogen‐bond network is formed, involving the amine NH group, the methanol OH group and the carbonyl O atoms of the equatorial ligand. T‐dependent susceptibility measurements revealed that the complex remains in the high‐spin state over the entire temperature range investigated.     

Inner metal complexes of tetradentate Schiff base: Synthesis,characterization, biological activity and molecular docking studies

A novel Schiff base ligand, namely 2,2′‐((1E,1′E)‐(1,3‐phenylenebis(azanylylidene))bis(methanylylidene))diphenol (H₂L), was synthesized by condensation of m‐phenylenediamine and 2‐hydroxybenzaldehyde (in 1:2 ratio). Series of complexes were obtained from the reaction of La(III), Er(III) and Yb(III) chlorides with H₂L. The ligand and complexes were characterized using elemental analysis, infrared, ¹H NMR, UV–visible and mass spectroscopies, magnetic susceptibility and conductivity measurements and thermal analysis. Infrared and ¹H NMR spectra indicated the coordination of the azomethine nitrogens and deprotonated phenolic oxygen atoms in a tetradentate manner (ONNO). The thermal behaviour of the complexes was studied from ambient temperature to 1000°C. The complexes were found to have water molecules of hydration and coordinated water molecules. The complexes were found to possess high biological activities against various organisms compared to the free ligand (Gram‐positive bacteria Staphylococcus aureus and Bacillus subtilis, Gram‐negative bacteria Salmonella sp., Escherichia coli and Pseudomonas aeruginosa and fungi Aspergillus fumigatus and Candida albicans). The more effective and probable binding modes between H₂L with different active sites of colon cancer (PDB code: 2hq6) and lung cancer (PDB code: 1x2j) receptors were investigated using molecular docking studies.     

Bis[μ3‐cis‐N‐(2‐aminopropyl)‐N′‐(2‐carboxylatophenyl)oxamidato(3–)]bis(2,2′‐bipyridine)dichloridotetracopper(II) dihydrate

The title complex, bis[μ₃‐cis‐N‐(2‐aminopropyl)‐N′‐(2‐carboxylatophenyl)oxamidato(3−)]‐1:2:4κ⁷N,N′,N′′,O:O′,O′′:O′′′;2:3:4κ⁷O′′′:N,N′,N′′,O:O′,O′′‐bis(2,2′‐bipyridine)‐2κ²N,N′;4κ²N,N′‐dichlorido‐1κCl,3κCl‐tetracopper(II) dihydrate, [Cu₄(C₁₂H₁₂N₃O₄)₂Cl₂(C₁₀H₈N₂)₂]·2H₂O, consists of a neutral cyclic tetracopper(II) system having an embedded centre of inversion and two solvent water molecules. The coordination of each Cu^II atom is square‐pyramidal. The separations of Cu^II atoms bridged by cis‐N‐(2‐aminopropyl)‐N′‐(2‐carboxylatophenyl)oxamidate(3−) and carboxyl groups are 5.2096 (4) and 5.1961 (5) Å, respectively. A three‐dimensional supramolecular structure involving hydrogen bonding and aromatic stacking is observed.     

Synthesis,characterization and crystal structures of the bidentate Schiff base N,N′‐bis(2‐nitrocinnamaldehyde)ethylenediamine and its complex with CuNCS and triphenylphosphane

Reaction of copper(I) thiocyanate and triphenylphosphane with the bidentate Schiff base N,N′‐bis(trans‐2‐nitrocinnamaldehyde)ethylenediamine {Nca₂en, (1); systematic name (1E,1′E,2E,2′E)‐N,N′‐(ethane‐1,2‐diyl)bis[3‐(2‐nitrophenyl)prop‐2‐en‐1‐imine]}, C₂₀H₁₈N₄O₄, in a 1:1:1 molar ratio in acetonitrile resulted in the formation of the complex {(1E,1′E,2E,2′E)‐N,N′‐(ethane‐1,2‐diyl)bis[3‐(2‐nitrophenyl)prop‐2‐en‐1‐imine]‐κ²N,N′}(thiocyanato‐κN)(triphenylphosphane‐κP)copper(I)], [Cu(NCS)(C₂₀H₁₈N₄O₄)(C₁₈H₁₅P)] or [Cu(NCS)(Nca₂en)(PPh₃)], (2). The Schiff base and copper(I) complex have been characterized by elemental analyses, IR, electronic and ¹H NMR spectroscopy, and X‐ray crystallography [from synchrotron data for (1)]. The molecule of (1) lies on a crystallographic inversion centre, with a trans conformation for the ethylenediamine unit, and displays significant twists from coplanarity of its nitro group, aromatic ring, conjugated chain and especially ethylenediamine segments. It acts as a bidentate ligand coordinating via the imine N atoms to the Cu^I atom in complex (2), in which the ethylenediamine unit necessarily adopts a somewhat flattened gauche conformation, resulting in a rather bowed shape overall for the ligand. The NCS⁻ ligand is coordinated through its N atom. The geometry around the Cu^I atom is distorted tetrahedral, with a small N—Cu—N bite angle of 81.56 (12)° and an enlarged opposite angle of 117.29 (9)° for SCN—Cu—P. Comparisons are made with the analogous Schiff base having no nitro substituents and with metal complexes of both ligands.     

A novel three‐dimensional zinc(II) coordination polymer based on 3,3′‐{[1,3‐phenylenebis(methylene)]bis(oxy)}dibenzoic acid and 1,4‐bis(pyridin‐4‐yl)benzene: synthesis,crystal structure and photocatalytic properties

A novel three‐dimensional (3D) Zn^II coordination polymer, namely, poly[[[1,4‐bis(pyridin‐4‐yl)benzene](μ₃‐3,3′‐{[1,3‐phenylenebis(methylene)]bis(oxy)}dibenzoato)zinc(II)] 1,4‐bis(pyridin‐4‐yl)benzene], {[Zn(C₂₂H₁₆O₆)(C₁₆H₁₂N₂)]·C₁₆H₁₂N₂}_n or {[Zn(PMBD)(DPB)]·DPB}_n, 1 , where H₂PMBD is 3,3′‐{[1,3‐phenylenebis(methylene)]bis(oxy)}dibenzoic acid and DPB is 1,4‐bis(pyridin‐4‐yl)benzene, has been synthesized by self‐assembly using zinc nitrate, a semi‐rigid dicarboxylic acid and a nitrogen‐containing ligand. The single‐crystal X‐ray structure determination indicates that 1 possesses an intriguing 3D architecture with a 4‐connected uninodal cds topology, which is constructed from dinuclear {Zn₂} clusters and V‐shaped PMBD^2? linkers. Compound 1 exhibits excellent photocatalytic activity on the degradation of the organic dyes Rhodamine B (RhB), Rhodamine 6G (Rh6G) and Methyl Red (MR).     

Designing a heterotrinuclear CuII—NiII—CuII complex from a mononuclear CuII Schiff base precursor with dicyanamide as a coligand: synthesis,crystal structure,thermal and photoluminescence properties

Schiff bases are considered `versatile ligands' in coordination chemistry. The design of polynuclear complexes has become of interest due to their facile preparations and varied synthetic, structural and magnetic properties. The reaction of the `ligand complex' [CuL] {H₂L is 2,2′‐[propane‐1,3‐diylbis(nitrilomethanylylidene)]diphenol} with Ni(OAc)₂·4H₂O (OAc is acetate) in the presence of dicyanamide (dca) leads to the formation of bis(dicyanamido‐1κN¹)bis(dimethyl sulfoxide)‐2κO,3κO‐bis{μ‐2,2′‐[propane‐1,3‐diylbis(nitrilomethanylylidene)]diphenolato}‐1:2κ⁶O,O′:O,N,N′,O′;1:3κ⁶O,O′:O,N,N′,O′‐dicopper(II)nickel(II), [Cu₂Ni(C₁₇H₁₆N₂O₂)₂(C₂N₃)₂(C₂H₆OS)₂]. The complex shows strong absorption bands in the frequency region 2155–2269 cm⁻¹, which clearly proves the presence of terminal bonding dca groups. A single‐crystal X‐ray study revealed that two [CuL] units coordinate to an Ni^II atom through the phenolate O atoms, with double phenolate bridges between Cu^II and Ni^II atoms. Two terminal dca groups complete the distorted octahedral geometry around the central Ni^II atom. According to differential thermal analysis–thermogravimetric analysis (DTA–TGA), the title complex is stable up to 423 K and thermal decomposition starts with the release of two coordinated dimethyl sulfoxide molecules. Free H₂L exhibits photoluminescence properties originating from intraligand (π–π*) transitions and fluorescence quenching is observed on complexation of H₂L with Cu^II.     

Masking of Lewis acidity trends in the solid‐state structures of trichlorido‐ and tribromido(2,2′:6′,2′′‐terpyridine‐κ3N,N′,N′′)gallium(III)

The molecular structures of trichlorido(2,2′:6′,2′′‐terpyridine‐κ³N,N′,N′′)gallium(III), [GaCl₃(C₁₅H₁₁N₃)], and tribromido(2,2′:6′,2′′‐terpyridine‐κ³N,N′,N′′)gallium(III), [GaBr₃(C₁₅H₁₁N₃)], are isostructural, with the Ga^III atom displaying an octahedral geometry. It is shown that the Ga—N distances in the two complexes are the same within experimental error, in contrast to expected bond lengthening in the bromide complex due to the lower Lewis acidity of GaBr₃. Thus, masking of the Lewis acidity trends in the solid state is observed not only for complexes of group 13 metal halides with monodentate ligands but for complexes with the polydentate 2,2′:6′,2′′‐terpyridine donor as well.     

Synthesis and crystal structure of the dinuclear copper(II) Schiff base complex μ‐hydroxido‐μ‐chlorido‐bis{[bis(trans‐2‐nitrocinnamaldehyde)ethylenediamine]chloridocopper(II)} dichloromethane sesquisolvate

Transition metal complexes of Schiff base ligands have been shown to have particular application in catalysis and magnetism. The chemistry of copper complexes is of interest owing to their importance in biological and industrial processes. The reaction of copper(I) chloride with the bidentate Schiff base N,N′‐bis(trans‐2‐nitrocinnamaldehyde)ethylenediamine {Nca₂en, systematic name: (1E,1′E,2E,2′E)‐N,N′‐(ethane‐1,2‐diyl)bis[3‐(2‐nitrophenyl)prop‐2‐en‐1‐imine]} in a 1:1 molar ratio in dichloromethane without exclusion of air or moisture resulted in the formation of the title complex μ‐chlorido‐μ‐hydroxido‐bis(chlorido{(1E,1′E,2E,2′E)‐N,N′‐(ethane‐1,2‐diyl)bis[3‐(2‐nitrophenyl)prop‐2‐en‐1‐imine]‐κ²N,N′}copper(II)) dichloromethane sesquisolvate, [Cu₂Cl₃(OH)(C₂₀H₁₈N₄O₄)₂]·1.5CH₂Cl₂. The dinuclear complex has a folded four‐membered ring in an unsymmetrical Cu₂OCl₃ core in which the approximate trigonal bipyramidal coordination displays different angular distortions in the equatorial planes of the two Cu^II atoms; the chloride bridge is asymmetric, but the hydroxide bridge is symmetric. The chelate rings of the two Nca₂en ligands have different conformations, leading to a more marked bowing of one of the ligands compared with the other. This is the first reported dinuclear complex, and the first five‐coordinate complex, of the Nca₂en Schiff base ligand. Molecules of the dimer are associated in pairs by ring‐stacking interactions supported by C—H…Cl interactions with solvent molecules; a further ring‐stacking interaction exists between the two Schiff base ligands of each molecule.     

Structural studies of (prop‐2‐en‐1‐yl)bis[(pyridin‐2‐yl)methylidene]amine hetero‐scorpionate copper complexes

The structures of five compounds consisting of (prop‐2‐en‐1‐yl)bis[(pyridin‐2‐yl)methylidene]amine complexed with copper in both the Cu^I and Cu^II oxidation states are presented, namely chlorido{(prop‐2‐en‐1‐yl)bis[(pyridin‐2‐yl)methylidene]amine‐κ³N,N′,N′′}copper(I) 0.18‐hydrate, [CuCl(C₁₅H₁₇N₃)]·0.18H₂O, (1), catena‐poly[[copper(I)‐μ₂‐(prop‐2‐en‐1‐yl)bis[(pyridin‐2‐yl)methylidene]amine‐κ⁵N,N′,N′′:C²,C³] perchlorate acetonitrile monosolvate], {[Cu(C₁₅H₁₇N₃)]ClO₄·CH₃CN}_n, (2), dichlorido{(prop‐2‐en‐1‐yl)bis[(pyridin‐2‐yl)methylidene]amine‐κ³N,N′,N′′}copper(II) dichloromethane monosolvate, [CuCl₂(C₁₅H₁₇N₃)]·CH₂Cl₂, (3), chlorido{(prop‐2‐en‐1‐yl)bis[(pyridin‐2‐yl)methylidene]amine‐κ³N,N′,N′′}copper(II) perchlorate, [CuCl(C₁₅H₁₇N₃)]ClO₄, (4), and di‐μ‐chlorido‐bis({(prop‐2‐en‐1‐yl)bis[(pyridin‐2‐yl)methylidene]amine‐κ³N,N′,N′′}copper(II)) bis(tetraphenylborate), [Cu₂Cl₂(C₁₅H₁₇N₃)₂][(C₆H₅)₄B]₂, (5). Systematic variation of the anion from a coordinating chloride to a noncoordinating perchlorate for two Cu^I complexes results in either a discrete molecular species, as in (1), or a one‐dimensional chain structure, as in (2). In complex (1), there are two crystallographically independent molecules in the asymmetric unit. Complex (2) consists of the Cu^I atom coordinated by the amine and pyridyl N atoms of one ligand and by the vinyl moiety of another unit related by the crystallographic screw axis, yielding a one‐dimensional chain parallel to the crystallographic b axis. Three complexes with Cu^II show that varying the anion composition from two chlorides, to a chloride and a perchlorate to a chloride and a tetraphenylborate results in discrete molecular species, as in (3) and (4), or a bridged bis‐μ‐chlorido complex, as in (5). Complex (3) shows two strongly bound Cl atoms, while complex (4) has one strongly bound Cl atom and a weaker coordination by one perchlorate O atom. The large noncoordinating tetraphenylborate anion in complex (5) results in the core‐bridged Cu₂Cl₂ moiety.     

Two nickel(II) bis[(pyridin‐2‐yl)methyl]amine complexes with homophthalic and benzene‐1,2,4,5‐tetracarboxylic acids

Two new Ni^II complexes involving the ancillary ligand bis[(pyridin‐2‐yl)methyl]amine (bpma) and two different carboxylate ligands, i.e. homophthalate [hph; systematic name: 2‐(2‐carboxylatophenyl)acetate] and benzene‐1,2,4,5‐tetracarboxylate (btc), namely catena‐poly[[aqua{bis[(pyridin‐2‐yl)methyl]amine‐κ³N,N′,N′′}nickel(II)]‐μ‐2‐(2‐carboxylatophenyl)aceteto‐κ²O:O′], [Ni(C₉H₆O₄)(C₁₂H₁₃N₃)(H₂O)]_n, and (μ‐benzene‐1,2,4,5‐tetracarboxylato‐κ⁴O¹,O²:O⁴,O⁵)bis(aqua{bis[(pyridin‐2‐yl)methyl]amine‐κ³N,N′,N′′}nickel(II)) bis(triaqua{bis[(pyridin‐2‐yl)methyl]amine‐κ³N,N′,N′′}nickel(II)) benzene‐1,2,4,5‐tetracarboxylate hexahydrate, [Ni₂(C₁₀H₂O₈)(C₁₂H₁₃N₃)₂(H₂O)₂]·[Ni(C₁₂H₁₃N₃)(H₂O)₃]₂(C₁₀H₂O₈)·6H₂O, (II), are presented. Compound (I) is a one‐dimensional polymer with hph acting as a bridging ligand and with the chains linked by weak C—H...O interactions. The structure of compound (II) is much more complex, with two independent Ni^II centres having different environments, one of them as part of centrosymmetric [Ni(bpma)(H₂O)]₂(btc) dinuclear complexes and the other in mononuclear [Ni(bpma)(H₂O)₃]²⁺ cations which (in a 2:1 ratio) provide charge balance for btc⁴⁻ anions. A profuse hydrogen‐bonding scheme, where both coordinated and crystal water molecules play a crucial role, provides the supramolecular linkage of the different groups.     

Three heterotrinuclear Schiff base complexes of nickel(II) with cobalt(II), copper(II) and manganese(II)

The title compounds, bis­(di­methyl­form­amide)‐1κO,3κO‐bis{μ‐2,2′‐[2,2′‐di­methyl­propane‐1,3‐diyl­bis­(nitrilo­methylidyne)]­diphenolato}‐1κ⁴N,N′,O,O′:2κ²O,O′;2κ²O,O′:3κ⁴N,N′,O,O′‐di‐μ‐nitrito‐1:2κ²N:O;2:3κ²O:N‐dinickel(II)­cobalt(II), [CoNi₂(NO₂)₂(C₁₉H₂₂N₂O₂)₂(C₃H₇NO)₂], (I), ‐copper(II), [CuNi₂(NO₂)₂(C₁₉H₂₂N₂O₂)₂(C₃H₇NO)₂], (II), and ‐manganese(II), [MnNi₂(NO₂)₂(C₁₉H₂₂N₂O₂)₂(C₃H₇NO)₂], (III), consist of centrosymmetric linear heterotrinuclear metal complexes. The three complexes are isostructural. There are three bridges across the Ni–M atom pairs (M is Co²⁺, Cu²⁺ or Mn²⁺) in each complex, involving two O atoms of a μ‐N,N′‐bis­(salicyl­idene)‐2,2′di­methyl‐1,3‐propane­diaminate ligand and an N—O moiety of a μ‐nitrito group. The coordination sphere around each metal atom, whether Co²⁺, Cu²⁺, Mn²⁺ or Ni²⁺, can be described as distorted octahedral. The Ni?M distances are 2.9988 (5) Å in (I), 2.9872 (5) Å in (II) and 3.0624 (8) Å in (III).     

Two new zinc(II) and mercury(II) complexes based on N,N′‐(cyclohexane‐1,2‐diylidene)bis(4‐fluorobenzohydrazide): synthesis,crystal structures and antibacterial activities

Reaction of N,N′‐(cyclohexane‐1,2‐diylidene)bis(4‐fluorobenzohydrazide), C₂₀H₁₈F₂N₄O₂, ( L^F ), with zinc chloride and mercury(II) chloride produced different types and shapes of neutral coordination complexes, namely, dichlorido[N,N′‐(cyclohexane‐1,2‐diylidene)bis(4‐fluorobenzohydrazide)‐κ²N,O]zinc(II), [ZnCl₂(C₂₀H₁₈F₂N₄O₂)], ( 1 ), and dichlorido[N,N′‐(cyclohexane‐1,2‐diylidene)bis(4‐fluorobenzohydrazide)‐κ⁴O,N,N′,O′]mercury(II), [HgCl₂(C₂₀H₁₈F₂N₄O₂)], ( 2 ). The organic ligand and its metal complexes are characterized using various techniques: IR, UV–Vis and nuclear magnetic resonance (NMR) spectroscopies, in addition to powder X‐ray diffraction (PXRD), single‐crystal X‐ray crystallography and microelemental analysis. Depending upon the data from these analyses and measurements, a typical tetrahedral geometry was confirmed for zinc complex ( 1 ), in which the Zn^II atom is located outside the bis(benzhydrazone) core. The Hg^II atom in ( 2 ) is found within the core and has a common octahedral structure. The in vitro antibacterial activities of the prepared compounds were evaluated against two different bacterial strains, i.e. gram positive Bacillus subtilis and gram negative Pseudomonas aeruginosa bacteria. The prepared compounds exhibited differentiated growth‐inhibitory activities against these two bacterial strains based on the difference in their lipophilic nature and structural features.     

The crystal and molecular structures of three copper‐containing complexes and their activities in mimicking galactose oxidase

The structures of three copper‐containing complexes, namely (benzoato‐κ²O,O′)[(E)‐2‐({[2‐(diethylamino)ethyl]imino}methyl)phenolato‐κ³N,N′,O]copper(II) dihydrate, [Cu(C₇H₅O₂)(C₁₃H₁₉N₂O)]·2H₂O, 1 , [(E)‐2‐({[2‐(diethylamino)ethyl]imino}methyl)phenolato‐κ³N,N′,O](2‐phenylacetato‐κ²O,O′)copper(II), [Cu(C₈H₇O₂)(C₁₃H₁₉N₂O)], 2 , and bis[μ‐(E)‐2‐({[3‐(diethylamino)propyl]imino}methyl)phenolato]‐κ⁴N,N′,O:O;κ⁴O:N,N′,O‐(μ‐2‐methylbenzoato‐κ²O:O′)copper(II) perchlorate, [Cu₂(C₈H₇O₂)(C₁₂H₁₇N₂O)₂]ClO₄, 3 , have been reported and all have been tested for their activity in the oxidation of d ‐galactose. The results suggest that, unlike the enzyme galactose oxidase, due to the precipitation of Cu₂O, this reaction is not catalytic as would have been expected. The structures of 1 and 2 are monomeric, while 3 consists of a dimeric cation and a perchlorate anion [which is disordered over two orientations, with occupancies of 0.64 (4) and 0.36 (4)]. In all three structures, the central Cu atom is five‐coordinated in a distorted square‐pyramidal arrangment (τ parameter of 0.0932 for 1 , 0.0888 for 2 , and 0.142 and 0.248 for the two Cu centers in 3 ). In each species, the environment about the Cu atom is such that the vacant sixth position is open, with very little steric crowding.     

Synthesis and Characterization of Various Benzyl Diethylenetriaminepentaacetic Acids (dtpa) and Their Paramagnetic Complexes,Potential Contrast Agents for Magnetic Resonance Imaging

Four derivatives of diethylenetriaminepentaacetic acid (=3,6,9‐tris(carboxymethyl)‐3,6,9‐triazaundecanedioic acid (H₅dtpa)), potential contrast agents for magnetic resonance imaging (MRI), carrying benzyl groups at various positions of the parent structure were synthesized and characterized by a thorough multinuclear NMR study, i.e., the (S)‐ and (R)‐stereoisomers 1a and 1b of 4‐benzyl‐3,6,9‐tris(carboxymethyl)‐3,6,9‐triazaundecanedioic acid (H₅[(S)‐(4‐Bz)dtpa] and H₅[(R)‐(4‐Bz)dtpa], the diamide derivative N,N″‐bis[(benzylcarbamoyl)methyl]diethylenetriamine‐N,N′,N″‐triacetic acid (=3,9‐bis[2‐(benzylamino)‐2‐oxoethyl]‐6‐(carboxymethyl)‐3,6,9‐triazaundecanedioic acid; H₃[dtpa(BzA)₂]; 2 ), and the diester derivative N,N″‐bis{[(benzyloxy)carbonyl]methyl}diethylenetriamine‐N,N′,N″‐triacetic acid (=3,9‐bis[2‐(benzyloxy)‐2‐oxoethyl]‐6‐(carboxymethyl)‐3,6,9‐triazaundecanedioic acid; H₃[dtpa(BzE)₂]; 3 ). From the ¹⁷O‐NMR chemical shift of H₂O induced by their dysprosium complexes with ligands 1 – 3 , it was concluded that only one H₂O molecule is contained in the first coordination sphere of these lanthanide complexes. The rotational correlation times (τ_R) of the complexes were estimated from the ²H‐NMR longitudinal relaxation rate of the deuterated diamagnetic lanthanum complexes. The exchange time of the coordinated H₂O molecule (τ_M) was studied through the temperature dependence of the ¹⁷O‐NMR transverse relaxation rate. As compared to [Gd(dtpa)]²⁻, the H₂O‐exchange rate is faster for [Gd{(S)‐(4‐Bz)dtpa}]²⁻ and [Gd{(R)‐(4‐Bz)dtpa}]²⁻‐, slower for [Gd{dtpa(BzA)₂}], and almost identical for [Gd{dtpa(BzE)₂}]. The analysis of the ¹H‐relaxivity of the gadolinium complexes recorded from 0.02 to 300 MHz established that i) the relaxivity of [Gd{dtpa(BzE)₂}] is similar to that of [Gd(dtpa)]²⁻, ii) the slightly slower molecular rotation of [Gd{dtpa(BzA)₂}] induces a mild enhancement of its relaxivity, and iii) the marked increase of relaxivity of [Gd{(S)‐(4‐Bz)dtpa}]²⁻ and [Gd{(R)‐(4‐Bz)dtpa}]²⁻ mainly results from an apparently shorter distance between the gadolinium ion and the H₂O protons of the coordinated H₂O molecule.     

Effect of pH on the construction of CdII coordination polymers involving the 1,1′‐[1,4‐phenylenebis(methylene)]bis(3,5‐dicarboxylatopyridinium) ligand

Changing the pH value of a reaction system can result in polymers with very different compositions and architectures. Two new coordination polymers based on 1,1′‐[1,4‐phenylenebis(methylene)]bis(3,5‐dicarboxylatopyridinium) (L^2?), namely catena‐poly[[[tetraaquacadmium(II)]‐μ₂‐1,1′‐[1,4‐phenylenebis(methylene)]bis(3,5‐dicarboxylatopyridinium)] 1.66‐hydrate], {[Cd(C₂₂H₁₄N₂O₈)(H₂O)₄]·1.66H₂O}_n, (I), and poly[{μ₆‐1,1′‐[1,4‐phenylenebis(methylene)]bis(3,5‐dicarboxylatopyridinium)}cadmium(II)], [Cd(C₂₂H₁₄N₂O₈)]_n, (II), have been prepared in the presence of NaOH or HNO₃ and structurally characterized by single‐crystal X‐ray diffraction. In polymer (I), each Cd^II ion is coordinated by two halves of independent L^2? ligands, forming a one‐dimensional chain structure. In the crystal, these chains are further connected through O—H…O hydrogen bonds, leading to a three‐dimensional hydrogen‐bonded network. In polymer (II), each hexadentate L^2? ligand coordinates to six Cd^II ions, resulting in a three‐dimensional network structure, in which all of the Cd^II ions and L^2? ligands are equivalent, respectively. The IR spectra, thermogravimetric analyses and fluorescence properties of both reported compounds were investigated.     

Synthesis,structural characterization and thermal properties of a new copper(II) one‐dimensional coordination polymer based on bridging N,N′‐bis(2‐hydroxybenzylidene)‐2,2‐dimethylpropane‐1,3‐diamine and dicyanamide ligands

The design and synthesis of polymeric coordination compounds of 3d transition metals are of great interest in the search for functional materials. The coordination chemistry of the copper(II) ion is of interest currently due to potential applications in the areas of molecular biology and magnetochemistry. A novel coordination polymer of Cu^II with bridging N,N′‐bis(2‐hydroxyphenyl)‐2,2‐dimethylpropane‐1,3‐diamine (H₂L‐DM) and dicyanamide (dca) ligands, catena‐poly[[[μ₂‐2,2‐dimethyl‐N,N′‐bis(2‐oxidobenzylidene)propane‐1,3‐diamine‐1:2κ⁶O,N,N′,O′:O,O′]dicopper(II)]‐di‐μ‐dicyanamido‐1:2′κ²N¹:N⁵;2:1′κ²N¹:N⁵], [Cu₂(C₁₉H₂₀N₂O₂)(C₂N₃)₂]_n, has been synthesized and characterized by CHN elemental analysis, IR spectroscopy, thermal analysis and X‐ray single‐crystal diffraction analysis. Structural studies show that the Cu^II centres in the dimeric asymmetric unit adopt distorted square‐pyramidal geometries, as confirmed by the Addison parameter (τ) values. The chelating characteristics of the L‐DM²⁻ ligand results in the formation of a Cu^II dimer with a double phenolate bridge in the asymmetric unit. In the crystal, the dimeric units are further linked to adjacent dimeric units through μ_1,5‐dca bridges to produce one‐dimensional polymeric chains.     

Magnetic Ordering in Iron(II) Complexes due to a 2D Network of Hydrogen Bonds

The magnetic properties of two octahedral iron(II) complexes with Schiff base like equatorial N₂O₂ coordinating ligands and methanol (MeOH) as axial ligand are reported. Both compounds [FeL1(MeOH)₂] ( 1 ) and [FeL2(MeOH)₂] ( 2 ) (with L1 = [3,3′]‐[1,2‐phenylenebis(iminomethylidyne)‐bis(2,4‐pentanedionato)(2‐)‐N,N′,O²,O²′] and L2 = [E,E]‐[{diethyl 2,2′‐1,2‐phenylenebis(iminomethylidyne)bis(3‐oxo‐3‐phenylpropanato)} (2‐)‐N,N′,O3,O3′]) show a weak spontaneous magnetization below T_C = 10 K. Results from X‐ray structure analysis of 1 indicate, that this is due to 2D network of hydrogen bonds as previously discussed for a similar complex.     

[Cu(C8H16N4O2)0.5{N(CN)2}]n,a novel ladder‐like coordination polymer

A new polymeric copper complex, viz.catena‐poly[[[μ‐N,N′‐bis(3‐amino­propyl)oxa­mid­ato‐κ⁶N,N′,O:N′′,N′′′,O′]­dicopper(II)]‐di‐μ‐dicyan­amido‐1:1′κ²N¹:N⁵;2:2′κ²N¹:N⁵], [Cu₂(C₈H₁₆N₄O₂)(C₂N₃)₂]_n or [Cu(oxpn)_0.5{N(CN)₂}]_n [where H₂oxpn is N,N′‐bis(3‐amino­propyl)­ox­amide], has been ­synthesized by the reaction of Cu(oxpn), [Cu(ClO₄)₂]·6H₂O and NaN₃. In the crystal structure, the Cu atom is five‐coordinate and has a square‐pyrimidal (SP) configuration. In the polymer, dicyan­amide (dca⁻) groups link Cu^II cations in a μ‐1,5‐bridging mode, generating novel ladders in which each step is composed of dimeric [Cu₂(oxpn)]²⁺ cations. Abundant hydrogen bonds connect the polymer ladders into a two‐dimensional network structure.     

X‐ray and DFT studies of a mono‐ and binuclear copper(II) ionic compound containing a Schiff base

In the structure of trans‐bis(ethanol‐κO)tetrakis(1H‐imidazole‐κN³)copper(II) bis[μ‐N‐(2‐oxidobenzylidene)‐D,L‐glutamato]‐κ⁴O¹,N,O^2′:O^2′;κ⁴O^2′:O¹,N,O^2′‐bis[(1H‐imidazole‐κN³)cuprate(II)], [Cu(C₃H₄N₂)₄(C₂H₆O)₂][Cu₂(C₁₅H₁₄N₃O₅)₂], both ions are located on centres of inversion. The cation is mononuclear, showing a distorted octahedral coordination, while the anion is a binuclear centrosymmetric dimer with a square‐pyramidal copper(II) coordination. An extensive three‐dimensional hydrogen‐bonding network is formed between the ions. According to B3LYP/6–31G* calculations, the two equivalent components of the anion are in doublet states (spin density located mostly on Cu^II ions) and are coupled as a triplet, with only marginal preference over an open‐shell singlet.     

Four copper(II) complexes with potentially tetradentate tripodal ligands

The four title Cu^II compounds are chloro­[(2‐furyl­methyl)­bis(2‐pyridyl­methyl)­amine‐N,N′,N′′]copper(II) perchlorate, [CuCl(C₁₇H₁₇N₃O)]ClO₄, (I), chloro{2‐[bis(2‐pyridyl­methyl)­amino]­ethano­lato‐N,N′,N′′,O}­copper(II) hemi­[tetra­chloro­copper(II)], [CuCl(C₁₄H₁₇N₃O)][CuCl₄]_1/2, (II), chloro­[(2‐morpholino­ethyl)­bis(2‐pyridyl­methyl)­amine‐N,N′,N′′,N′′′]copper(II) perchlorate, [CuCl(C₁₈H₂₄N₄O)]ClO₄, (III), and chloro­[(2‐piperidinyl­ethyl)­bis(2‐pyridyl­methyl)­amine‐N,N′,N′′,N′′′]­copper(II) hexa­fluoro­phosphate, [CuCl(C₁₉H₂₆N₄)]­PF₆, (IV). They have tripodal potentially tetradentate ligands. In (I), the O atom of the furan moiety weakly coordinates to the Cu atom at a distance of 2.750 (3) Å.