Four complexes with a bulky carboxylate ligand: syntheses,crystal structures,and luminescent properties

Abstract  

Four complexes of 3,3-diphenylpropanoate (L) and 4,4′-bipyridine as auxiliary bridging ligands were synthesized and characterized, namely [Zn(L)₂(4bpy)(EtOH)₂]_∞ (1), [Co(L)₂(4bpy)(EtOH)₂]_∞ (2), [Ni(L)₂(4bpy)(EtOH)₂]_∞ (3), and [Cu(L)₂(4bpy)(H₂O)]_∞ (4) (4bpy = 4,4′-bipyridine). X-ray single-crystal diffraction analyses show that complexes 1–4 all take one-dimensional (1D) fishbone-like structures incorporating bridging 4bpy ligands. The complexes show different supramolecular frameworks interlinked via intermolecular hydrogen bonds, π···π stacking, and/or C–H···π supramolecular interactions. Complex 3 only has a simple one-dimensional fishbone-like chain, whereas complexes 1 and 2 show two-dimensional supramolecular structures by interchain C–H···O hydrogen bonds. Complex 4 is assembled into two-dimensional layers and then an overall three-dimensional framework by a combination of interchain O–H···O hydrogen bonds and C–H···π supramolecular interactions. The luminescent properties of the ligands and their complexes were investigated.     

Two 3-D supramolecular architecture based on the linkages of Co(II) complexes and lattice water molecules

Two new 3-D supramolecular compounds [Co(phen)(tdc)(H₂O)₃]·5H₂O (1) and [Co(phen)(Htdc)(H₂O)₃]·(Htdc)·2H₂O (2, phen = 1,10-phenanthroline, H₂tdc = thiophene-2,5-dicarboxylate) have been hydrothermally synthesized and structurally characterized. In 1, the neutral [Co(phen)(tdc)(H₂O)₃] complexes behave as pillars to join the water layers to make an overall 3-D supramolecular architecture by H-bond interactions. In 2, similar 2-D water layer is not observed, which could be due to one uncoordinated Htdc ligand instead of three lattice water molecules of 1. The thermal stabilities of 1 and 2 were investigated by thermogravimetric measurements.     

Self-assembly of two zinc(II) supramolecular architectures with carboxylate and chelating aromatic amine ligands: [Zn(nba)2(phen)(H2O)] and [Zn(nip)(phen)]n (nba = 4-nitrobenzoic acid, nip = 5-nitroisophthalic acid)

Two new zinc(II) compounds, [Zn(nba)₂(phen)(H₂O)] (1) and [Zn(nip)(phen)] _n (2) [nba = 4-nitrobenzoic acid, nip = 5-nitroisophthalic acid, phen = 1,10-phenanthroline] have been hydrothermally synthesized by reaction of zinc acetate and phen with the ligands nba and nip, respectively. Compound (1) consists of mononuclear zinc(II) molecules which forms a 2D supramolecular structure based on hydrogen bonds between the hydroxyl groups (and aromatic groups as well) and carboxylate oxygen atoms. Compound (2) displays 1D zigzag chains which are combined to 1D supramolecular double-chains by π–π stacking and further assembled into a 3D supramolecular framework through hydrogen bonds.     

Coexistence of two conformational isomeric chains in a zinc(II) phosphonate induced by π···π stacking interactions

Hydrothermal reaction of zinc acetate with diethyl [(phenylsulfonyl)methyl]phosphonate as well as 1,10-phenanthroline (phen) afforded a novel zinc(II) phosphonate with the formula of [Zn₄(PhSO₂CH₂PO₃)₄(phen)₂(H₂O)₂]·2H₂O. Such compound features two conformational isomeric 1D chains which are regulated by two different π···π stacking interactions. In addition, it exhibits broad blue fluorescent emission band at 387 nm.     

Syntheses,Structures, and Properties of Mono‐ and Tetranuclear Nickel(II) Complexes Derived from a Tridentate Schiff Base Ligand

Three new nickel(II) complexes constructed with N‐(2‐hydroxybenzyl)‐β‐alanine (H₂L), namely [NiL(phen)H₂O]·H₂O ( 1 ) (phen = 1.10‐phenanthroline), [Ni₄L₄(H₂O)₄]·5H₂O ( 2 ) and K[Ni₄L₄(NCS)(H₂O)₅]·5.42H₂O ( 3 ) have been synthesized and characterized by single‐crystal X‐ray diffraction analysis. Complex 1 exhibits a discrete structure, and the structures are bound together through hydrogen bonding to a one‐dimensional chain in ladder‐like fashion. Complexes 2 and 3 contain similar [Ni₄(μ₂‐O)₆] cores with “zig‐zig” arrangement. In complex 3 , the tetranuclear nickel units [Ni₄L₄(H₂O)₄] and [Ni₄L₄(NCS)(H₂O)] are alternately bridged by potassium atoms to a one‐dimensional chain. The neighboring chains are further linked up by {K₂O₂} units to a two‐dimensional layer structure. Moreover, the IR, XRD, TGA and the temperature‐dependent magnetic susceptibility for 2 and 3 have also been studied.     

Monomeric and polymeric structures derived from 3,3′,4,4′-biphenyltetracarboxylic acid, phenanthroline and metal ions

Under similar hydrothermal synthetic conditions, the reactions of Fe(NO₃)₃/FeCl₂, CuCl₂, NiCl₂, and CdCl₂ with phenanthroline (phen) and 3,3′,4,4′-biphenyltetracarboxylic acid (H₄BPTC) afforded complexes [Fe(phen)₃](H₃BPTC)₂ (1), [Cu(phen)(BPTC)_0.5 · H₂O] · H₂O (2), [Ni₃(phen)₃(BPTC)_1.5(H₂O)₅] · 4H₂O (3) and [Cd(phen)(BPTC)_0.5] · H₂O (4). The short Fe–N distance in the monomeric Fe(phen)₃(H₃ BPTC)₂ (1) shows that the Fe(II) is in a low-spin state. H₃ BPTC⁴⁻ acts as a counter-ion in this complex. In [Cu(phen)(BPTC)_0.5 · H₂O] · H₂O (2), the central Cu(II) is five-coordinated in a square-pyramidal geometry. The ligand BPTC⁴⁻ is centrosymmetric and the four deprotonated carboxylic groups of BPTC⁴⁻ are coordinated to four different copper ions to form a 1D ladder complex indicating a comparatively strong coordination. In [Ni₃(phen)₃(BPTC)_1.5(H₂O)₅] · 4H₂O (3), all nickel(II) atoms are in an octahedral coordination environment. There are two different BPTC⁴⁻ ligands; one is centrosymmetric and the other is asymmetric. Metal ions are linked through fully deprotonated BPTC⁴⁻ ligands to form a 2D metal-organic sheet. [Cd(phen)(BPTC)_0.5] · H₂O (4) has a 3D metal-organic framework. TG, IR, and fluorescence data for the complexes are presented.     

Synthesis,crystal structures,and biological activities of silver(I) and cobalt(II) complexes with an azole derivative ligand

Abstract  Two new complexes, [Ag(L)₂](NO₃) · (H₂O) (1) and [Co(L)₂Cl₂] (2) [L = 1-(imidazol-1-yl-methyl)-benzotriazole], have been synthesized and structurally characterized by X-ray diffraction techniques. In complex (1), the Ag(I) atom adopts a linear coordination geometry involving the imidazole nitrogens of two ligands. The [Ag(L)₂] units are developed into a three-dimensional structure by intermolecular hydrogen bonds, π–π interactions, and Ag···O interactions. In complex (2), the Co(II) atom is in a distorted tetrahedral environment with two imidazole nitrogens and two chloride ligands. The [Co(L)₂Cl₂] units are assembled into a three-dimensional structure by intermolecular hydrogen bonds and π–π interactions. The bioactivities of both complexes have been studied, and the results indicate that complex (1) exhibits excellent radical-scavenging (RS) and fungicidal (FG) activities while complex (2) only has weak fungicidal activity. Graphical abstracts   Synthesis, crystal structures and biological activities of silver(I) and cobalt(II) complexes with an azole derivative ligand. Chang-Xue An, Xin-Li Han, Peng-Bang Wang, Zhi-Hui Zhang*, Hai-Ke Zhang and Zhi-Jin Fan Two novel complexes, [Ag(L)₂](NO₃) · (H₂O) (1) and [Co(L)₂Cl₂] (2) [L = 1-(imidazol-1-yl-methyl)-benzotriazole] have been synthesized and structurally characterized. The molecules of complexes (1) and (2) are extended to 2-D and 3-D structures by the non-coordinated bonds. The ligand and complex (1) exhibit excellent radical-scavenging and fungicidal activities. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis, structures and luminescent properties of Co(II) and Ni(II) metal-organic frameworks with semirigid diphthalic ligands

A series of transition metal coordination polymers [Co(H₃L)₂(4,4′- bpy)(H₂O)₂]_n?n(4,4′-bpy) (1), [Ni(H₂L)(4,4′-bpy)(H₂O)₂]_n (2), [Co₂(L)(phen)₂(H₂O)₄]_n?(H₂O)_2n (3), and [Ni₂(L)(phen)₂(H₂O)₄]_n?(H₂O)_2n (4) have been assembled from a semirigid multicarboxylate ligand 3,3′-(1,4-phenylenebis(oxy))diphthalic acid (H₄L) with the help of 4,4′-bipyridine (4,4′-bpy) ligand or 1,10-phenanthroline (phen) ligand. X-ray single crystal diffraction analysis reveals that complex 1 crystallizes in the space group of P − 1 and displays a one-dimensional (1D) chain structure constructed from 4,4′-bpy ligand and H₃L ligand, which was further interlinked to form a three-dimensional network via hydrogen bonds. In complex 2, Ni(II) atoms are coordinated by L ligand in monodentate fashion to form alternate left- and right-helices, which are further bridged together by the coordination interactions between Ni(II) atoms and 4,4′-bpy, leading to a 2-fold (4, 4)-connected interpenetrating network. Isostructural complexes 3 and 4 belong to the space group P − 1 and display a 1D chain structure constructed from phen and L ligands, which was further interlinked to form a 2D plane via π–π interactions. In addition, their thermal and luminescent properties were also investigated.     

Five new cobalt(II) complexes based on indazole derivatives: synthesis,DNA binding and molecular docking study

Five cobalt(II) complexes based on 1H-indazole-3-carboxylic acid (H₂L), [Co(phen)(HL)₂]·2H₂O (1), [Co(5,5′-dimethyl-2,2′-bipy)(HL)₂] (2), [Co(2,2′-bipy)₂(HL)₂]·5H₂O (3), [Co₂(2,9-dimethyl-1,10-phen)₂(L)₂] (4) and [Co₂(6,6′-dimethyl-2,2′-bipy)₂(L)₂]·H₂O (5) (2,2'-bipy = 2,2′-bipyridine, phen = 1,10-phenanthroline), have been synthesized and structurally characterized by elemental analyses, IR and UV-vis spectroscopies and single-crystal X-ray crystallography. The results indicate that 1–3 possess mononuclear Co(II) structures, while 4 and 5 exhibit binuclear structure. 1D water tape which is linked by the multiple hydrogen bonds was embedded in the 3D motif of complex 3. Complexes 4 and 5 show two orthogonal planes of motif that was constituted by phen/2,2′-bipy and indazole acid, respectively. The intermolecular interactions including hydrogen bonding and π-π stacking interactions are stabilizing these complexes. The interactions of the synthesized complexes with calf-thymus DNA (CT-DNA) have been investigated by UV-vis absorption titration, ethidium bromide displacement assay and viscosity measurements. The results reveal that the complexes could interact with CT-DNA via a groove binding mode. Their behavior rationalization was further theoretically studied by molecular docking.     

The synthesis,crystal structure and thermal studies of a mixed-ligand 1,10-phenanthroline and hexamethylenetetramine complex of lanthanum nitrate. Insight into coordination sphere geometry changes of lanthanide(III) 1,10-phenanthroline complexes

The structure of tetraaqua-bis(nitrato-O,O′)-(1,10-phenanthroline-N,N′)-lanthanum(III) 1,3,5,7-tetraazatricyclo[3.3.1.1^3,7]decane nitrate dihydrate, [La(NO₃)₂ · phen · (H₂O)₄]⁺ · hmt · NO ₃ ⁻ · 2H₂O, is presented. The lanthanum ion exhibits tenfold coordination and the polyhedron can be described as tetradecahedron. The complex cations, nitrate ions, water and hexamethylenetetramine molecules are assembled via hydrogen bonds, H–π rings and π–π stacking interactions into 3D supramolecular network. The bond strength of coordination sphere was calculated by means of the bond-valence method. The influence of La:phen stoichiometry and additional ligand on the changes of lanthanum(III) coordination sphere geometry in ten-coordinated complexes with 1,10-phenanthroline was discussed. The infrared spectrum of structure optimised by means of quantum mechanical calculations was analysed and compared with measured one. The obtained compound was characterised by thermogravimetric analysis in conjunction with evolved gases in the air atmosphere.     

Synthesis, structural characterization and thermal properties of three copper(II) complexes based on aryl hydrazide ligands

The thiosemicarbazide and hydrazide Cu(II) complexes, [Cu₃L₂¹(py)₄Cl₂] (1), [Cu(HL²)py] (2) and [Cu(HL³)py] (3), (H₂L¹ = 1-picolinoylthiosemicarbazide, H₃L² = N′-(2-hydroxybenzylidene)-3-hydroxy-2-naphthohydrazide, H₃L³ = 2-hydroxy-N′-((2-hydroxy-naphthalen-1-yl)methylene)benzohydrazide) have been prepared and characterized through physicochemical and spectroscopic methods as well as X-ray crystallography. Complex 1 has a centrosymmetric structure with –N–N– bridged Cu₃ skeleton. Neighboring molecules are linked into a 3D supermolecular framework by π–π stacking interactions, N–H···Cl and C–H···Cl hydrogen bonds. Complexes 2 and 3 have similar planar structures but different dimers formed by concomitant Cu···N and Cu···O interactions, respectively. Solvent accessible voids with a volume of 391 ?³ are included in the structure of complex 2, indicating that this complex is a potential host candidate. Thermogravimetric analysis shows that the three complexes are stable up to 100 °C.     

Synthesis,structure and luminescent properties of Cd(II) and Zn(II) complexes constructed from 3,5-dimethyl-2, 6-pyrazinedicarboxylic acid

[Cd₂(phen)₂(DPZDA)₂(H₂O)₂] · 8H₂O (1) and [Zn(phen)(DPZDA)(H₂O)] · 2H₂O (2) have been synthesized by reaction of Cd(NO₃)₂/Zn(NO₃)₂ with phen and DPZDA (where phen = 1,10-phenanthroline, H₂DPZDA = 3,5-dimethyl-2,6-pyrazinedicarboxylic acid) in aqueous ethanol solution. Elemental analysis, IR spectra, thermal analyses and X-ray single crystal diffraction were carried out to determine the composition and crystal structure of 1 and 2. In 1, a 2D supramolecular network containing a novel metal-water decamer were formed by hydrogen bonds. In 2, a 2D supramolecular structure was constructed from hydrogen bonds and π·· · π interactions. Moreover, 1 and 2 displayed photoluminescent properties in the blue range at room temperature.     

Two manganese(II) complexes based on anthracene-9-carboxylate: Syntheses,crystal structures,and magnetic properties

Abstract  To explore the influence of the anthracene ring skeleton, with a large conjugated π-system, on the structures and properties of its complexes, two Mn^II complexes with anthracene-9-carboxylate ligand were synthesized and structurally characterized: {[Mn(L)₂(H₂O)₂](H₂O)}_∞ (1) and [Mn₂(L)₄(phen)₂(μ-H₂O)](CH₃OH) (2) (L = anthracene-9-carboxylate and phen = 1,10-phenanthroline). Complex (1) has a one-dimensional (1D) chain structure that is further assembled to form a two-dimensional (2D) sheet, and then an overall three-dimensional (3D) network by π···π stacking and/or C–H···π interactions. Complex (2) makes a dinuclear structure by incorporating the chelating phen ligand, which is further interlinked via inter-molecular π···π stacking and C–H···π interactions to generate a higher-dimensional supramolecular network along the different crystallographic directions. The results reveal that the bulky anthracene ring skeleton in L, by virtue of intra- and/or inter-molecular π···π stacking and C–H···π interactions, plays an important role in the formation of complexes (1) and (2). The magnetic properties of (1) and (2) were further investigated. As expected, the very long inter-metallic separations result in weak magnetic coupling, with the corresponding coupling constant values of J = −10 cm⁻¹ for (1) and J = −2.46 cm⁻¹ for (2). Graphical abstract  The constructions of two new Mn^II complexes comprising 1D chain (1) and dinuclear subunit (2) structures have been successfully achieved by using a bulky anthracene-9-carboxylic acid (HL), together with incorporating the chelating 1,10-phenanthroline as a co-ligand for (2). The result reveals that the bulky anthracene ring skeleton of HL, by virtue of intra- and/or inter-molecular π···π stacking and C–H···π interactions, plays an important role in the formation of the supramolecular architectures of (1) and (2). Moreover, magnetic properties of the complexes have been investigated.      

Multi‐Dimensional Cobalt(II) and Nickel(II) Coordination Polymers

A series of metal coordination polymers, [Co₂(NB)₄(bpp)₂(H₂O)]·H₂O ( 1 ), [Co₂(e,e‐trans‐chdc)(e,a‐cis‐chdc)(bpp)₂] ( 2 ), [Ni(e,e‐trans‐chdc)(bpp)(H₂O)₂] ( 3 ), [Ni₂(PDA)₂(bpp)₂(H₂O)₃]·H₂O ( 4 ), and [Ni‐(mBDC)(bpp)] ( 5 ) (NB = 3‐nitrobenzoate anion; bpp = 4,4′‐trimethylene dipyridine; chdc = cyclohexane‐1,4‐dicarboxylate anion; PDA = 1,4‐phenylenediacetate anion; mBDC = 1,3‐benzene dicarboxylate anion), were synthesized from metal ions and organic mixed‐ligands by hydrothermal reactions. The single crystal structure analysis revealed that 1, 3, and 4 were 2D sheets with bilayer (1 and 4) and 2‐fold interpenetrated layers (3), 2 is a 3D binodal (4,5)‐connected framework, and 5 is a 1D chains. The non‐covalent interactions of H‐bonds and π–π stacking caused this conformation of highly cross‐linked networks. Compounds 1‐5 were further characterized by thermal gravimetric analysis, powder X‐ray diffraction, UV‐vis, infrared, and PL spectroscopy.     

Studies on the magnetic properties of two cobalt(II) complexes bearing 1,4-phenylenediacetate ligands

One reported compound [Co(PDA)(4,4′-bipy)]_n·nH₂O and one new compound [Co(PDA)(Im)₂(H₂O)₂]_n·nH₂O were prepared by the reactions of Co(NO₃)₂·6H₂O or Co(OH)₂ with 1,4-phenylenediacetic acid (H₂PDA) in the presence of the ancillary ligands 4,4′-bipyridine (4,4′-bipy) or imidazole (Im), and their magnetic properties were investigated. The presence of 4,4′-bipy in [Co(PDA)(4,4′-bipy)]_n·nH₂O results in a μ ₃-bridging mode of the PDA²⁻ ligand with one μ ₂-carboxylato group and one chelating carboxylato group and the construction of a 2D framework as reported in the literature. The introduction of Im ligand in [Co(PDA)(Im)₂(H₂O)₂]_n·nH₂O helps to construct a one dimensional chain with the two carboxylato groups of PDA²⁻ ligand in monodentate coordination modes. The magnetic studies reveal the presence of dominant antiferromagnetic interaction in [Co(PDA)(4,4′-bipy)]_n·nH₂O with a field-induced magnetic transition due to spin-flop. Magnetically, [Co(PDA)(Im)₂(H₂O)₂]_n·nH₂O presents a mononuclear structure. This work reveals that the introduction of ancillary ligands in the Co(II)-PDA system adjusts the linking modes of PDA²⁻ and therefore the resulting frameworks and their magnetic properties.     

Synthesis,crystal structures,and magnetic properties of cobalt(II) and nickel(II) complexes of 2,2′-bipyridine-6,6′-dicarboxylate: three three-dimensional networks formed via hydrogen bonding interactions

Three Co(II) and Ni(II) complexes, namely [Co(bpdc)(H₂O)₂] (1), [Ni(bpdc)(H₂O)₂] (2), and [Co₂(bpdc)₂(prz)_0.5(H₂O)₃]·0.5H₂O (3) (H₂bpdc = 2,2′-bipyridine-6,6′-dicarboxylic acid and prz = piperazine), have been synthesized from H₂bpdc and the corresponding metal salts under hydrothermal conditions. The complexes were characterized by physico-chemical and spectroscopic methods, as well as by X-ray crystallography. Compounds 1 and 2 both consist of neutral mononuclear molecules, of [Co(bpdc)(H₂O)₂] and [Ni(bpdc)(H₂O)₂], respectively. Compound 3 consists of a mononuclear molecule of [Co(bpdc)(H₂O)₂] and a binuclear molecule of [Co₂(bpdc)₂prz (H₂O)₂]. The discrete neutral complexes 1–3 further extend their structures into three-dimensional supramolecular architectures by intermolecular O–H⋯O and C–H⋯O hydrogen bonds as well as π–π stacking interactions. Magnetic susceptibility measurements show that complex 3 exhibits weak ferromagnetic interactions between the two Co(II) ions bridged by the prz ligand, with C = 5.41 cm³ mol⁻¹ K and θ = +27.6 K, respectively.     

Two cadmium(II) addition compounds with 3-hydroxy-2,7-naphthalenedisulfonate containing aromatic diamines and their 3-D net

{[CdCl(2,2′-bipy)₂(H₂O)]⁺·[Cd(3-O^?-2,7-NDS)(2,2′-bipy)₂]^?·3H₂O} (1) and {[Cd(phen)₃]²⁺·2[Cd(3-O^?-2,7-NDS)(phen)₂]^?·8.5H₂O} (2) (3-OH-2,7-NDS?=?3-hydroxy-2,7-naphthalenedisulfonate, phen?=?1,10-phenanthroline, and 2,2′-bipy?=?2,2′-bipydine) were prepared and characterized by X-ray single-crystal diffraction. Compound 1 contains a discrete coordination cation [CdCl(2,2′-bipy)₂(H₂O)]⁺ and a coordination anion [Cd(3-O^?-2,7-NDS)(2,2′-bipy)₂]^?; 2 contains a discrete coordination cation [Cd(phen)₃]²⁺ and two coordination anions [Cd(3-O^?-2,7-NDS)(phen)₂]^?. There are numerous weak interactions among the coordination cation, coordination anion, and free water molecules, such as O–H?···?O hydrogen bonds, π?···?π stacking, and Cl^??···?π interactions in 1 and π?···?π stacking and C–H?···?π interactions in 2. The cations and anions as building blocks are connected to construct different 3-D supramolecular architectures via weak intermolecular interactions. Particularly, the capsule structure of 1 was observed.     

Supramolecularly assembled water layers stabilized by sebacic anions in complexes of Zn(II) and Co(II)

Two three-dimensional supramolecular water architectures, [Zn(phen)₃]₂·[Zn(C₁₀H₁₆O₄)·(H₂O)₃]·(C₁₀H₁₆O₄)₂·20H₂O (1) and [Co(phen)₃]₂·[Co(H₂O)₆]·(C₁₀H₁₆O₄)₃·30H₂O (2) [phen = 1,10-Phenanthroline, C₁₀H₁₆O₄ = sebacic dianion], have been synthesized and characterized by IR, elemental analysis, thermogravimetric analysis, and single-crystal X-ray diffractions. The two structures both contain extensive hydrogen bonding between water molecules as well as between water molecules and sebacic anions. The water molecules and sebacic acid O atoms assembled 2D supramolecular corrugated sheets with different morphology in the two complexes.     

Syntheses and crystal structures of two 2D coordination polymers of cobalt(II) and nickel(II) with the Malonate Dianion Ligand

Two 2D complexes, [Co(mal)(phen)(H₂O)₂] (1) and [Ni(mal)(phen)(H₂O)₂] (2) (mal?=?malonate dianion; phen?=?1,10-phenanthroline), have been synthesized by the reaction of Co(ClO₄)₂·6H₂O and Ni(ClO₄)₂·6H₂O with disodium malonate and 1,10-phenanthroline in MeOH/H₂O solution. Their crystal structures have been determined by X-ray diffraction. The structures of Complexes 1 and 2 show that each metal ion is coordinated by one 1,10-phenanthroline, two water molecules and a malonate ligand forming a distorted octahedral environment and each mononuclear fragment forms a 2D supramolecular network through H-bonding interactions.     

Synthesis,structural characterization and substituent effects of two copper(II) complexes with benzaldehyde ortho-oxime ligands

Two new Cu(II) complexes, [Cu(L¹)₂] (1) and [Cu(L²)₂] (2) (HL¹ = (E)-3-bromo-5-chloro-2-hydroxy benzaldehyde O-methyl oxime; HL² = (E)-3-bromo-5-chloro-2-hydroxy benzaldehyde O-ethyl oxime), have been synthesized and characterized by physicochemical and spectroscopic methods. X-ray crystallographic analyses show that complexes 1 and 2 have similar structures, consisting of one Cu(II) atom and two L⁻ units. In both complexes, the Cu(II) atom, lying on an inversion center, is four-coordinated in a trans-CuN₂O₂ square-planar geometry by two phenolate O and two oxime N atoms from two symmetry-related N,O-bidentate oxime ligands. Moreover, both complexes form an infinite three-dimensional supramolecular structure involving intermolecular C–H···Br hydrogen bonds and π···π stacking interactions between the metal chelate rings and aromatic rings. Substituent effects in the two complexes are discussed.