In situ synthesis and dielectric properties of copper(II) and nickel(II) chiral Schiff base complexes

Two chiral Schiff base-containing complexes, [Cu(L¹)](ClO₄)₂·H₂O (1, L¹ = (S,S)-N1,N2-bis((1H-imidazol-4-yl)methylene)cyclohexane-1,2-diamine) and [Ni(L²)₂](ClO₄)₂ (2, L² = (S,S)-N1-((1H-imidazol-4-yl)methylene)cyclohexane-1,2-diamine) were synthesized from the reaction mixture of 1H-imidazole-4-carbaldehyde, (S,S)-1,2-diaminocyclohexane and Cu(ClO₄)₂·6H₂O or Ni(ClO₄)₂·6H₂O in methanol. Single-crystal X-ray diffraction analyses reveal that the in situ generated chiral Schiff base ligands L¹ and L² are bisubstituted and monosubstituted, respectively, corresponding to the different metal ions Cu^II and Ni^II. Variable-frequency and -temperature dielectric properties of 1 and 2 have been studied.     

Synthesis and characterization of nickel(II) and copper(II) complexes with a tetramethyltetraaza macrocycle containing 2-pyridylmethyl pendant arms

The complexes [Ni(L²)](ClO₄)₂·H₂O (1) and [Cu(L²)]Cl₂·4H₂O (2) have been synthesized and characterized by X-ray crystallography, electronic absorption and cyclic voltammetry. The crystal structure of 1 reveals a distorted octahedral geometry with four nitrogen atoms of the macrocycle and two nitrogen atoms of the pendant pyridylmethyl groups. The structure of 2 shows that the complex is centrosymmetric and the metal center has a tetragonally distorted octahedral environment. The electronic spectra and electrochemical behaviors of the complexes are significantly affected by the presence of the pendant arms.     

Syntheses and X-ray crystal structures of [Zn(cyclen)–im–Zn(cyclen)](ClO4)3 and [Ni(cyclen)(imH)(ClO4)](ClO4) (cyclen=1,4,7,10-tetraazacyclododecane,im=imidazolate)

The imidazolate-bridged binuclear zinc(II) macrocyclic complex, [Zn(cyclen)–im–Zn(cyclen)](ClO₄)₃ (1) and the free imidazole coordinated mononuclear nickel(II) complex, [Ni(cyclen)(imH)(ClO₄)](ClO₄) (2) (cyclen=1,4,7,10-tetraazacyclododecane, im=imidazolate) have been synthesized. Complexes 1 and 2 have been characterized by single crystal structural analyses. In complex 1 both zinc(II) ions are five-coordinated with a distorted square pyramidal geometry composed of four nitrogen atoms from cyclen and one nitrogen atom from the bridging imidazolate ion with N₅ chromophore. Complex 2 is mononuclear nickel(II) having six-coordination with distorted octahedral geometry consisting of four nitrogen atoms from cyclen, one nitrogen atom from the imidazole molecule and one oxygen from one of the perchlorate ions to give a N₅O chromophore.     

Four-, six- and eight-coordinated lead(II) complexes with amine- or amide-type tripodal ligands

Three novel lead(II) complexes, [Pb(L¹)](ClO₄)₂ (1) (L¹ = tris(2-benzylaminoethyl)amine), [Pb(L²)₂](ClO₄)₂ (2) (L² = tris(4-phenyl-3-aza-2-oxobutyl)amine) and [Pb₂(L³)₂](ClO₄)₄ (3) (L³ = tris[3-aza-2-oxo-4-(2-pyridyl)butyl]amine) were synthesized and structurally characterized. All three complexes show different stoichiometries as well as coordination numbers of four in 1, eight in 2 and six in 3, respectively. Complex 1 displays a typical tripodal-type 1:1 (M:L) structure and 2 shows a sandwich-type 1:2 structure. The octa-dentate lead(II) ion in 2 is at the center of a dicapped trigonal prism. Complex 3 is revealed as a unique dinuclear 2:2 complex, in which two hexa-dentate lead(II) ions are linked by two carbonyl μ–O atoms forming a Pb₂(μ–O)₂ parallelogram-type moiety.     

A novel one-dimensional nickel(II) complex with a hydrogen-bond-link

A novel compound [Ni(L)(H₂O)₂]_0.5[Ni(L)(WO₄)₂]_0.5·4H₂O (1) (L=3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,0^1.18,0^7.12]docosane) has been structurally and magnetically characterized. The nickel(II) ions are shown to be in distorted octahedral environments with secondary amines of macrocycles in which two trans water molecules and two trans tungstate ions are assembled around each metal center. Two nickel(II) complexes are connected into a one-dimensional chain via hydrogen bonds. The magnetic susceptibility measurement for 1 indicates weak antiferromagnetic interaction (J=−1.01(2) cm⁻¹; H=−JΣS_i·S_i+1) between the S=1 nickel(II) paramagnetic centers.     

Synthesis, structure and magnetism of a μ3-carbonato bridged nickel(II) complex with 2,2′,2″-tris(2-aminoethyl)amine ligand: a new coordination mode of carbonato bridge

A novel bridged Ni(II) complex with tris(2-aminoethyl)amine (tren), [Ni₃(tren)₃(H₂O)₂(μ₃-CO₃)](ClO₄)₄ · 2H₂O, was obtained by bubbling CO₂ into an aqueous solution of μ₂-OH bridged Ni(II) complex. The X-ray structure analysis of the title complex shows that the three nickel atoms are asymmetrically bridged by one tetradentate carbonato ligand, which presents a new bridge mode. The further magnetochemistry study exhibits a strong antiferromagnetic coupling between nickel(II) ions with J₁ = −11.03 cm⁻¹, J₂ = −80.27 cm⁻¹ in the title compound.     

Mononickel(II), dimercury(II), and 1-D polymeric silver(I) complexes with a ditopic 18-membered N2O2S2-macrocycle

A ditopic 18-membered N₂O₂S₂-macrocycle (L) incorporating hard (NO₂) and soft (NS₂) binding sites in each side was employed and its three complexes (1–3) exhibiting different stoichiometries, geometries, and topologies have been prepared and structurally characterized. First, nickel(II) nitrate hexahydrate reacts with L to give a mononuclear complex [Ni(L)](NO₃)₂·2H₂O (1) in which the metal center locates inside the macrocyclic cavity adopting a hexa-coordinated octahedral geometry shielded by the strongly bound macrocycle from the anion and solvent. While, silver(I) tetrafluoroborate afforded a one-dimensional coordination polymer {[Ag(L)]BF₄}_n (2) with an L-Ag-L-Ag pattern. In 2, the silver(I) center is penta-coordinate with NO donors from one L and NS₂ donors from an adjacent L to form a sandwich-type adopting a distorted trigonal bipyramidal geometry. Mercury(II) chloride yielded a dinuclear complex [Hg₂(L)Cl₄] (3) in which two mercury(II) ions locate opposite side of L in a chair form. Each mercury(II) center in 3 is penta-coordinate, being bound to one pyridine N atom, two O(S) donors in the compositional disorder, and two chloride ions adopting a distorted square-pyramidal geometry. The comparative NMR studies show the preferential binding affinity of silver(I) over potassium(I) toward L.     

Delicate structural regulation and stepwise phase transformation of Cu(II) coordination assemblies directed by inorganic counterion

Assembly of 3-(2-pyridyl)-4-(4-pyridyl)-5-(3-pyridyl)-1,2,4-triazole (L²⁴³) with Cu(NO₃)₂ or Cu(ClO₄)₂ affords a mononuclear complex [Cu(L²⁴³)₂(H₂O)₂](NO₃)₂ (1) or a 1D linear coordination polymer {[Cu(L²⁴³)₂(H₂O)](ClO₄)₂(CH₃OH)}_n (3). Incorporating NaN₃ into such assembled systems under similar conditions will produce two distinct 2D layered networks with the formulas {[Cu(L²⁴³)(N₃)](NO₃)(H₂O)₂}_n (2) or {[Cu(L²⁴³)(N₃)](ClO₄)(H₂O)}_n (4), both of which contain dual inorganic-anions as the counterparts (NO₃⁻/N₃⁻ for 2 and ClO₄⁻/N₃⁻ for 4). Further, with a subtle change of reaction condition for 2 or 4, a 1D linear array [Cu(L²⁴³)(N₃)₂]_n (5) is obtained with only N₃⁻ equilibrating the positive charges. Significantly, stepwise structural transformations between such crystalline phases can also be achieved by the direction of azide anion.     

One-pot template synthesis and crystal structure of two new polyaza copper(II) complexes

A new 14-membered hexazamacrocyclic copper(II) complex [Cu(H₂L¹)](ClO₄)₄(L¹=1,8-bis(2-aminoethyl)-1,3,6,8,10,13-hexaazacyclotetradecane) has been prepared by the one-pot reaction of ethylenediamine and formaldehyde in the presence of the Cu(II) ion. The crystal structure of [Cu(H₂L¹)](ClO₄)₄ was determined by X-ray diffraction. It crystallizes in the triclinic space group P−1 with a=12.118(2) Å, b=12.438(2) Å, c=12.466(2) Å, α=102.26(1)°, β=112.82(1)°, γ=111.51(1)°, and Z=2. The coordination geometry around the copper(II) ions is axially elongated octahedral with four nitrogen atoms of the macrocycle [Cu–N 2.012(7) Å for Cu(1) and 2.013(6) Å for Cu(2), average value] and two oxygen atoms of two ClO₄⁻ anions [Cu–O=2.550 Å for Cu(1) and 2.601(6) Å for Cu(2)]. [CuL²](ClO₄)₂(L²=3,7-bis(2-aminoethyl)-1,3,5,7-tetraazabicyclo[3,3,2]decane) with a novel tetraazabicyclic ligand was obtained from the same reaction system as an additional product. Crystal structure of [CuL²](ClO₄)₂: monoclinic space group Cc, a=16.393(3) Å, b=8.8640(18) Å, c= 13.085(3) Å, β=105.01(3)°, and Z=4.     

Synthesis and characterization of palladium (II) complex of Schiff base ligand: CS bond cleavage and catalytic activity

Reaction of ligand, L-CH₂Ph with Pd(CH₃CN)₂Cl₂ in acetonitrile in presence of PPh₃ and subsequent addition of NaClO₄ yielded Pd(II) complex, [Pd(L)(PPh₃)](ClO₄) 1 due to the SC (CH₂Ph) bond cleavage during complexation. Complex 1 was characterized by spectral analysis and the structure was authenticated by single crystal X-ray diffraction. The diffraction analysis revealed that the monoanionic ligand binds with palladium (II) in (N, N, S) fashion in a distorted square planar geometry where the fourth position is occupied by one tri phenyl phosphine group. One ClO₄⁻ ion satisfies the charge of the former aggregate, [Pd(L)(PPh₃)]⁺. The complex [Pd(L)(PPh₃)](ClO₄), 1 exhibits a very good catalytic activity towards CC bond formation.     

A mononuclear copper(II) complex of a protonated unsymmetrical dinucleating Schiff base ligand

Reaction of the unsymmetrical and potentially dinucleating Schiff base ligand HL¹ with copper(II) salts has given mono- and dinuclear metal complexes. The structure of a mononuclear complex of diprotonated HL¹, [Cu(H₂L¹)(OH₂)](ClO₄)₃·H₂O·CH₃OH_, has been determined.     

Synthesis and crystal structure of a mononuclear Ni(II) complex with tetraazadiphenol macrocycle bearing cyclohexanes

The mononuclear tetraazadiphenol macrocyclic nickel(II) complex [Ni(H₂[20]-DCHDC)](ClO₄)₂ (II) {H₂[20]-DCHDC = 14,29-dimethyl-3,10,18,25-tetraazapentacyclo-[25,3,1,0^4,9,1^12,16,0^19,24] ditriacontane-2,10,12,14,16(32),17,27(31),28,30-decane-31,32-diol} has been synthesized by self-assembly and characterized by elemental analysis, conductance, IR and FAB-MS spectrum, and single crystal X-ray diffraction. In the mononuclear complex, the Ni(II) ion is coordinated with a square planar conformation by two phenolate groups and two iminic sites on one side of the macrocycle. The bond angles of O–Ni–O {85.37(19)°} and N–Ni–N {88.0(2)°} are smaller than 90°.     

Syntheses,characterization and properties of manganese,cobalt and copper complexes from chelate N-donor ligands

2-[(S)-4-isopropyl-2-oxazolyl]quinoline (L¹) and 2-[(S)-4-phenyl − 2-oxazolyl]quinoline (L²) react with manganese, cobalt and copper salts to yield four new complexes: [Mn₂(L¹)₂]Cl₂ (1), {[Co(L¹)₂]₂(OH)}(ClO₄)₃ (2), [Cu₂I₂(L¹)₂] (3), and {[Cu(L²)₂]₂(OH)}(BF₄)₃·H₂O (4), which were fully characterized by single-crystal and powder X-ray diffraction, IR, elemental and thermogravimetric analyses. Complexes 1–4 all show dinuclear structure. Two metal ions are bridged by Cl⁻ in 1, by OH^– in 2 and 4, and by I⁻ in 3. Moreover, non-linear optical, and ferroelectric and magnetic properties have been investigated.     

Structural evidence of a ketimine as the product of an amino acid with an aldehyde. An intermediate in the racemization and transamination of amino acids

The aldimine and ketimine forms of two Schiff base complexes formed by the condensation of two isomeric imidazole carboxaldehydes with an amino acid are reported. Reaction of L¹, the Schiff base condensate of 5-methyl-4-imidazolecarboxaldehyde (5Me4Im) and valine, with copper(II) perchlorate results in the isolation of [Cu(L¹)(5Me4Im)(ClO₄)] while the analogous reaction of L², the Schiff base condensate of 1-methyl-2-imidazolecarboxaldehyde (1Me2Im) with alanine, and nickel(II) results in the isolation of [Ni(L²)₂]. L¹ exhibits the expected aldimine form of the amino acid derived Schiff base, 5Me4Im-CH = N-CH(R)CO₂⁻, while L² exhibits the tautomeric ketimine form, 1Me2Im-CH₂–N = C(R’)CO₂⁻. Structural data clearly support the two tautomeric forms. The ketimine form, observed in [Ni(L²)₂], has been proposed as an intermediate in the racemization and transamination of amino acids.     

One-dimensional manganese(II) complex with only end-to-end azide ligands: Crystal structure and magnetic characterization

A novel one-dimensional azido-bridged manganese(II) complex of formula [Mn(L)₂(N₃)](ClO₄) 1 has been synthesized and characterized crystallographically and magnetically, where L is the bidentate Schiff base obtained from the condensation of pyridine-2-carbaldehyde with 4-methoxyl aniline. Complex 1 is of one-dimensional chain structure with single end-to-end azido bridges. Magnetic analysis reveals that the weak antiferromagnetic interaction is mediated by the single end-to-end azido bridge with the exchange parameter J = −6.60 cm⁻¹.     

Zirconium phosphonate immobilized chiral amino alcohol for heterogeneous enantioselective addition of diethylzinc to benzaldehyde

The chiral (1R,2S)-(−)-2-amino-1,2-diphenylethanol and (1S,2R)-(+)-2-amino-1,2-diphenylethanol had been immobilized on the layered frame of zirconium phosphate to obtain zirconium phosphonates (1R,2S)-(−)-4a and (1S,2R)-(+)-4b. The enantioselective addition of Et₂Zn to benzaldehyde using zirconium phosphonates (1R,2S)-(−)-4a and (1S,2R)-(+)-4b as heterogeneous catalysts yielded secondary alcohol in 80.1% yield and e.e. values of up to 54.3%, which was only 7.6% e.e. lower than that using the corresponding ligands (1R,2S)-(−)-2a and (1S,2R)-(+)-2b as homogeneous catalysts. The zirconium phosphonates (1R,2S)-(−)-4a and (1S,2R)-(+)-4b were characterized by IR, SEM, XRD and TG analysis. SEM and XRD data showed that the catalysts (1S,2R)-(+)-4b and (1R,2S)-(−)-4a were in aggregate and mesopore structure with the same interlayer spacing 2.48 nm and pore diameter 5.6 nm.     

Mono- and dinuclear silver(I) complexes of benzene- and pyridine-bearing 20-membered thiaoxaaza macrocycles

Two 20-membered penta- and hexadentate macrocycles containing one or two pyridine subunits, namely [20]aneNO₂S₂ (L¹) and [20]aneN₂O₂S₂ (L²), have been synthesized. Reaction of L¹ with silver(I) nitrate afforded a unique 2:2 (M:L) disilver(I) complex [μ₂-Ag₂(L¹)₂](NO₃)₂ (1) in which two four-coordinate Ag atoms bridge two ligands to form a cyclic dimer. In contrast, an endo-dentate 1:1 monosilver(I) complexes [AgL²]X; [X = ClO₄ (2) or PF₆ (3)] which show isomorphous structures were obtained from the reactions of L² with silver(I) salts.     

Interaction of copper(II) with N-substituted bis(2-pyridylmethyl)amine derivatives: New discrete and 1-D polymeric complex systems — The latter displaying ferromagnetic behaviour

Interaction of copper(II) with the N-substituted bis(2-pyridylmethyl)amine derivatives, (R)-N¹,N¹-bis(pyridine-2-ylmethyl)butane-1,2-diamine (L¹) and (R)-2-(bis(pyridin-2-ylmethyl)amino)butan-1-ol (L²), has led to isolation of optically active [Cu(L¹)Cl]PF₆ (1) and [Cu(L²)Cl]ClO₄ (2), respectively. The X-ray structures of (1) and (2) show that the copper is bound to all four heteroatoms of the respective ligands as well as to a chlorine atom in a distorted square pyramidal arrangement in which the three nitrogens of L¹ or L² occupy three positions of each basal plane while the fourth position is occupied by the chloro ligand; apical sites in each case are filled by the amine donor from the NH₂-substituted butane arm in L¹ or the (protonated) alcohol oxygen of the 2-aminobutane-1-ol substituent in L². To a first approximation the coordination geometry in 2 is distorted square pyramidal; however, the remaining (axial) site on each copper centre is involved in a long contact (2.96 Å) with a bound chloro ligand from an adjacent complex which connects individual complex units in a zigzag 1-D polymeric chain, so that the coordination geometry could also be seen as pseudo-octahedral. A temperature-dependent magnetic study revealed the presence of ferromagnetic exchange coupling between copper centres in the chain reflecting the orthogonal structure between the chloro-bridged copper(II) ions; in contrast, and as expected, the discrete complex 1 is magnetically dilute.     

A dinuclear nickel(II) complex bridged by tricyanomethanide: structure and magnetic properties

Complexation of Ni^II ion with triethylenetetramine (teta) and potassium tricyanomethanide KC(CN)₃ yielded a new binuclear complex, [(teta)Ni(C(CN)₃)₂Ni(teta)](ClO₄)₂ (1), where two nickel(II) centres are held together by two tricyanomethanide bridges. The dinuclear units are aggregated into ladders; four of them being identified inside the unit cell. The effective magnetic moment on the cooling exhibits a slight gradual increase until 25 K; below this limit a strong, abrupt ferromagnetic interaction culminating at 16 K appears.     

A unique 3-D 3d–4f heterometallic coordination polymer with double betaine ligand: Crystal structure and magnetic properties

A unique 3d–4f heterometallic coordination polymer with double betaine ligand, [GdCu₂(L¹)₄(H₂O)₂](ClO₄)₇ · 6H₂O 1 (L¹ = 1,3-bis(pyridinio-4-carboxylato)-propane), has been synthesized by the self-assembly of Cu(ClO₄)₂ and Gd(ClO₄)₃ with flexible double betaine ligand L¹, and structurally characterized by single-crystal X-ray diffraction. The structure of 1 can be regarded as being constructed by the cross-linkage of the vertex-sharing double-paddle-wheel-like trinuclear [Cu(COO)₄Gd(COO)₄Cu] units and L¹ ligands to produce an interesting cationic NaCl-like framework with a 4¹²6³ topology, which is counter-balanced by the perchlorate ions located in the interspaces of the framework. Variable-temperature magnetic susceptibilities of 1 show there is no magnetic interaction between the Cu(II) and Gd(III) ions.