Coordination polymers of Cu(II) and Cd(II) with bifunctional chelates of the type dipicolylamino-alkylcarboxylate, (NC5H4CH2)2N(CH2)nCO2H (n = 1, 2, 3 and 4)

A series of bifunctional chelates of the type dipicolylamino-alkylcarboxylate (NC₅H₄CH₂)₂N(CH₂)_nCO₂H (n = 1-4; HL¹-HL⁴, respectively) has been prepared. Reactions of the ligands in aqueous methanol/N,N-dimethylformamide with the appropriate Cu(II) salts yielded the compounds [CuL¹](NO₃)·H₂O (1·H₂O), [CuL²(H₂O)]BF₄·H₂O (2·H₂O), [Cu(HL³)(SO₄)]₂ (3) and [CuL⁴(NO₃)]·MeOH (4·MeOH). While compounds 1, 2 and 4 are one-dimensional, the detailed connectivities within the chains are quite distinct, depending on factors such as alkyl chain length and ligation of aqua ligands or anionic components. In contrast to 1, 2 and 4, the structure of 3 is molecular, a binuclear assembly of edge-sharing Cu(II) ‘4+2’ distorted octahedra. The Cd(II) species, [{CdL²}₂(SO₄)]·4H₂O (5·4H₂O), prepared from HL² and CdSO₄·nH₂O in aqueous methanol/N,N-dimethylformamide, is two-dimensional, with a network constructed from binuclear units of seven coordinate Cd(II), , linked through bridging SO₄²⁻ groups to produce an assembly of linked hexagonal rings [{CdL²}₂(SO₄)]₆.     

New macrocyclic Cu(II)-bischelates with paddle wheel Cu2-acetate cage

Two novel bolaamphiphile based dicarboxylic ligands L1H₂ and L2H₂ are synthesized by desymmetrizing aromatic anhydrides. The corresponding Cu(II) complexes [Cu(L1) · EtOH]₂ (1), [Cu(L2) · (CH₃CN)]₂ (2) are synthesized and characterized. The crystal structure obtained for (1) and (2) indicates that they are new class of tetralactone type macrocyclic Cu(II) chelate complexes with paddle wheel Cu₂-acetate cage structure. The 1:1, Cu(II) and ligand ratio leads into formation of a novel binuclear Cu(II) tetracarboxylate complexes. The macrocyclic chelate ring size in compounds 1 and 2 was altered from [15] membered to [19] membered by introducing phthalyl and diphenyl head groups as discussed in detail. The single crystal X-ray structure shows the Cu(II)?Cu(II) distance 2.613(13) Å for 1 and 2.626(13) Å for 2, the corresponding room temperature EPR spectra recorded for powdered polycrystalline samples indicate the existence of Cu(II)?Cu(II) dimeric system.     

Study of the coordination behaviour of (3,5-diphenyl-1H-pyrazol-1-yl)ethanol against Pd(II), Zn(II) and Cu(II)

A new easily synthetic route with a 96% yield of ligand 2-(3,5-diphenyl-1H-pyrazol-1-yl)ethanol (L) is obtained. The reactivity of L against Pd(II), Zn(II) and Cu(II) leads to [PdCl₂(L)₂] (1), [ZnCl₂(L)] (2) and [CuCl(L′)]₂ (3) (L′ is the ligand L without alcoholic proton), respectively. According to the different geometries imposed by the metallic centre and the capability of L to present various coordination links, it has been obtained complexes with square planar (1 and 3) or tetrahedral (2) geometry and different nuclearity: monomeric (1 and 2) or dimeric (3). Complete characterisation by analytical and spectroscopic methods, resolution of L and 1-3 by single-crystal X-ray diffraction and magnetic studies for complex 3 are presented.     

Cu(II) complexes with labile apical coordination: Synthesis, crystal structure, H NMR investigation, and oxidation properties of mononuclear [Cu(dien)(2-PhIm)(ClO4)] (1), [Cu(dien)(2-MeBzIm)] (2), complexes

The compounds [Cu(dien)(2-PhIm)(ClO₄)](ClO₄) (1); [Cu(dien)(2-MeBzIm)](ClO₄)₂ (2); where dien = diethylenetriamine, 2-PhIm = 2-phenylimidazole and 2-MeBzIm = 2-methylbenzimidazole, were synthesized and characterized. The complexes possessing [Cu(II)dien] moiety as common, the former containing 2-phenylimidazole, yielded square pyramidal geometry with apical perchlorate coordination [Cu1-O(5) = 2.449 Å], while the latter with 2-methylbenzimidazole formed square planar geometry with weak perchlorate contact [Cu1-O(8) = 2.596 Å] in its apical position. The effect of solvent and the variable temperature ¹H NMR investigation combinedly explore the geometrical rearrangement towards five coordination around Cu(II) metal center by accommodating the solvent molecule in its fifth coordination. Possessing easily labile perchlorate anion, both these complexes were investigated for their oxidation capability using 3,5-di-tert-butyl catechol (DTBC). The rate constant determined for the oxidation of DTBC to corresponding quinone indicates that they are catalytically quite similar and the k_cat of 1 ≈ 2. The crystal structure and the NMR investigations are discussed in detail.     

Electrochemical synthesis and crystal structure of iron(II), cobalt(II), nickel(II) and copper(II) complexes of dianionic tetradentate N4 Schiff base ligand

The electrochemical oxidation of anodic metal (iron, cobalt, nickel and copper) in an acetonitrile solution of the potentially chelating Schiff base N,N(dithiodiethylenebis-(aminylydenemethylydene)-bis(1,2-phenylene)ditosylamide (H₂L) afforded stable complexes of empirical formula [ML]. The compounds obtained have been characterized by microanalysis, IR spectroscopy and ES-MS mass spectrometry. The crystal and molecular structures of [FeL]·CH₃CN (1) [CoL]·CH₃CN (2), [NiL]·CH₃CN (3) and [CuL]·CH₃CN (4) have been determined by X-ray diffraction in all complexes, the metal atom is in a distorted tetrahedral environment with the Schiff base acting as a tetradentate N4 donor.     

Syntheses, structures and properties of copper(II) complexes containing N-(2-hydroxybenzyl)-amino amide ligands

Four copper(II) complexes containing the reduced Schiff base ligands, namely, N-(2-hydroxybenzyl)-glycinamide (Hsglym) and N-(2-hydroxybenzyl)-l-alaninamide (Hsalam) have been synthesized and characterized. The crystal structures of [Cu₂(sglym)₂Cl₂] (1), [Cu₂(salam)₂(NO₃)₂] · H₂O (3), [Cu₂(salam)₂(NO₃)(H₂O)](NO₃) · 1.5H₂O (4), [Cu₂(salam)₂](ClO₄)₂ · 2H₂O (5) show that the Cu(II) atoms are bridged by two phenolato oxygen atoms in the dimers. The sglym ligand bonded to Cu(II) in facial manner while salam ligand prefers to bind to Cu(II) in meridonal geometry. Variable temperature magnetic studies of 3 showed it is antiferromagnetic. These Cu(II) complexes and [Cu₂(sglym)₂(NO₃)₂] (2), exhibit very small catecholase activity as compared to the corresponding complexes containing acid functional groups.     

Synthesis, crystal structures and magnetic properties of the copper(II) complexes containing isophthalate anion as coligand

Two new dinuclear isophthalato-bridged copper(II) complexes [Cu₂(ntb)₂(μ-ipt)](ClO₄)₂·4CH₃OH·0.33H₂O (1), [Cu₂(bbma)₂(μ-ipt)(NO₃)(CH₃OH)]NO₃·CH₃OH (2) and one mononuclear complex [Cu(bbma)(ipt)(CH₃OH)_0.67(H₂O)_0.33]·2CH₃OH (3) containing tetradentate and tridentate poly-benzimidazole ligands were synthesized, where ntb is tris(2-benzimidazolylmethyl)amine, bbma is bis(benzimidazol-2-yl-methyl)amine and ipt is isophthalate dianion. All of the complexes were characterized by elemental analysis, IR spectra and X-ray crystallography. The structures of complexes 1 and 2 consist of μ-ipt bridging two Cu(II) centers in a bis(monodentate) bonding fashion. The coordination geometry around the Cu(II) ions of both compounds has a distorted square pyramidal geometry. The Cu···Cu distances are 9.142 and 10.435 Å for 1 and 2, respectively. Complex 3 has a distorted square pyramidal geometry achieved by the three N-atoms of the bbma ligand, one isophthalate-oxygen atom and one oxygen atom from a coordinated methanol molecule. The magnetic susceptibility measurements at variable temperature over the 2-300 K range for complexes 1 and 2 are reported, with J values to be −0.013 and −0.32 cm⁻¹, respectively. The results show that the two complexes exhibit very weak antiferromagnetic interactions between the dinuclear copper(II) centers.     

Synthesis, structure, and properties of monomeric Fe(II), Co(II), and Ni(II) complexes of neutral N-(aryl)-2-pyridinecarboxamides

We have prepared and structurally characterized six-coordinate Fe(II), Co(II), and Ni(II) complexes of types [M^II(HL¹)₂(H₂O)₂][ClO₄]₂ (M = Fe, 1; Co, 3; and Ni, 5) and [M^II(HL²)₃][ClO₄]₂ · MeCN (M = Fe, 2 and Co, 4) of bidentate pyridine amide ligands, N-(phenyl)-2-pyridinecarboxamide (HL¹) and N-(4-methylphenyl)-2-pyridinecarboxamide (HL²). The metal centers in bis(ligand)-diaqua complexes 1, 3 and 5 are coordinated by two pyridyl N and two amide O atoms from two HL¹ ligands and six-coordination is completed by coordination of two water molecules. The complexes are isomorphous and possess trans-octahedral geometry. The metal centers in isomorphous tris(ligand) complexes 2 and 4 are coordinated by three pyridyl N and three amide O atoms from three HL² ligands. The relative dispositions of the pyridine N and amide O atoms reveal that the pseudo-octahedral geometry have the meridional stereochemistry. To the best of our knowledge, this work provides the first examples of structurally characterized six-coordinate iron(II) complexes in which the coordination is solely by neutral pyridine amide ligands providing pyridine N and amide O donor atoms, with or without water coordination. Careful analyses of structural parameters of 1-5 along with that reported in the literature [M^II(HL¹)₂(H₂O)₂][ClO₄]₂ (M = Cu and Zn) and [Co^III(L²)₃] have allowed us to arrive at a number of structural correlations/generalizations. The complexes are uniformly high-spin. Spectroscopic (IR and UV/Vis) and redox properties of the complexes have also been investigated.     

Synthesis, structures, and magnetic properties of dicopper(II) and dinickel(II) complexes with a new bis(macrocycle), 7,7-(2-hydoxypropane-1,3-diyl)bis{3,7,11,17-tetraazabicyclo[11.3.1]- heptadeca-1(17),13,15-triene}

A new bis(macrocycle) ligand, 7,7^′-(2-hydoxypropane-1,3-diyl)-bis{3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene} (HL), and its dicopper(II) ([Cu₂(HL)Cl₂](NO₃)₂ · 4H₂O (4a), [Cu₂(HL)I₂]I₂ · H₂O (4b)) and dinickel(II) ([Ni₂(L)(OH₂)](ClO₄)₃ (5a), [Ni₂(L)(OH₂)]I₃ · 2H₂O (5b), [Ni₂(L)N₃](N₃)₂ · 7H₂O (5c)) complexes have been synthesized. The alkoxide bridged face-to-face structure of the dinickel(II) complex 5c has been revealed by X-ray crystallography, as well as the “half-opened clamshell” form of the bis(macrocyclic) dicopper(II) complex 4b. Variable temperature magnetic susceptibility studies have indicated that there exists intramolecular antiferromagnetic coupling (J=−33.8 cm⁻¹ (5a), −32.5 cm⁻¹ (5b), and −29.7 cm⁻¹ (5c)) between the two nickel(II) ions in the nickel(II) complexes.     

Synthesis, structures and magnetic properties of nicotinato-copper(II) complexes with polybenzimidazole and polyamine ligands

Four novel nicotinato-copper(II) complexes containing polybenzimidazole and polyamine ligands were synthesized with formula [Cu₂(bbma)₂(nic)₂](ClO₄)₂·CH₃OH·0.5H₂O (1), [Cu₂(dien)₂(nic)₂](ClO₄)₂·2CH₃OH (2), [Cu(ntb)(nic)]ClO₄·H₂O (3) and [Cu(tren)(nic)]BPh₄·CH₃OH·H₂O (4), in which bbma is bis(benzimidazol-2-yl-methyl)amine, dien is diethylenetriamine, ntb is tris(2-benzimidazolylmethyl)amine, tren is tris(2-aminoethyl)amine and nic is nicotinate anion. All of the complexes were characterized by elemental analysis, IR and X-ray diffraction analysis. Complexes 1 and 2 contain centrosymmetric dinuclear entity with the two Cu(II) atoms bridged by two nicotinate anions in an anti-parallel mode. The Cu···Cu separation is 7.109 Å for 1 and 6.979 Å for 2. Complexes 3 and 4 are mononuclear with nicotinate coordinated to Cu(II) ion by the carboxylate O atom in 3 and the pyridine N atom in 4. All of the complexes exhibit abundant hydrogen bonds to form 1D chain for 1, 3, 4 and 2D network for 2. Magnetic susceptibility measurements over the 2-300 K range reveal very weak ferromagnetic interaction between the two Cu(II) ions in 1 and antiferromagnetic interaction in 2 mediated by nicotinate ligand, with J value to be 0.15 and −0.19 cm⁻¹, respectively.     

Synthesis, structure, and catalytic activity of chiral Cu(II) and Ag(I) complexes with (S,S)-1,2-diaminocyclohexane-based N4-donor ligands

Condensation of (S,S)-1,2-cyclohexanediamine with 2 equiv. of 2-pyridine carboxaldehyde in toluene in the presence of molecular sieves at 70 °C gives N,N′-bis(pyridin-2-ylmethylene)-(S,S)-1,2-cyclohexanediamine (S,S-1) in 95% yield. Reduction of 1 with an excess of NaBH₄ in MeOH at 50 °C gives N,N′-bis(pyridin-2-ylmethyl)-(S,S)-1,2-cyclohexanediamine (S,S-2) in 90% yield. Reaction of 1 or 2 with 1 equiv. of CuCl₂ · 2H₂O in methanol gives complexes [N-(pyridin-2-ylmethylene)-(S,S)-1,2-cyclohexanediamine]CuCl₂ (3) and [Cu(S,S-2)(H₂O)]Cl₂ · H₂O (4), respectively, in good yields. Complex 4 can further react with 1 equiv. of CuCl₂ · 2H₂O in methanol to give [Cu(S,S-2)][CuCl₄] (5) in 75% yield. The rigidity of the ligand coupled with the steric effect of the free anion plays an important role in the formation of the helicates. Treatment of ligand S,S-1 with AgNO₃ induces a polymer helicate {[Ag(S,S-1)][NO₃]}_n (6), while reaction of ligand 2 with AgPF₆ or AgNO₃ in methanol affords a mononuclear single helicate [Ag(S,S-2)][PF₆] (7) or a dinuclear double helicate [Ag₂(S,S-2)₂][NO₃]₂ · 2CH₃OH (8) in good yields, respectively. All compounds have been characterized by various spectroscopic data and elemental analyses. Compounds 1, 3-5, 7 and 8 have been further subjected to single-crystal X-ray diffraction analyses. The Cu(II) complexes do not show catalytic activity for allylation reaction, in contrast to Ag(I) complexes, but they do show catalytic activity for Henry reaction (nitroaldol reaction) that Ag(I) complexes do not.     

New template reactions of salicylaldehyde S-methyl-isothiosemicarbazone with 2-formylpyridine promoted by Ni(II) or Cu(II) metal ions

The template reaction between salicylaldehyde S-methyl-isothiosemicarbazone and 2-formylpyridine in presence of nickel(II) or copper(II) salts yields two new coordination compounds with general formula [NiL¹]₂(1) and [CuL²]₂(2) (L¹ = the dianionic (N¹-salicylidene)(N⁴-(hydroxy(pyridin-2-yl)methyl) S-methyl-isothiosemicarbazide) ligand and L² = the doubly deprotonated (N¹-salicylidene)(N⁴-(picolinoyl) S-methyl-isothiosemicarbazide) ligand). In the complex 1, the formed L¹ ligand appears as result of an addition reaction of the precursors, while for 2 a redox mechanism is implicated in the formation of L². Despite the fact that the initial organic precursors are the same, the resulting ligands obtained in the template reaction are different. In 1, the Ni(II) metal ion adopts a square-planar geometry and the [NiL¹] units are forming dimerized chains through weak Ni···Ni interactions (3.336 and 3.632 Å). In 2, the Cu(II) metal ions adopt a square-pyramidal geometry and form dinuclear species through weak Cu···O (phenoxo) interactions. The magnetic susceptibility measurements of the complexes reveal the diamagnetic nature of 1 as expected for a square planar Ni(II) complex and a paramagnetic behavior for 2 with weak intra-dimer antiferromagnetic interaction (J/k_B = −2.1(1) K).     

Synthesis and characterization of new oligomeric and polymeric complexes based on the [Cu(bpca)] unit [Hbpca = bis(2-pyridylcarbonyl)amine]

Five novel bpca-based Cu(II) polynuclear coordination compounds [Hbpca = bis(2-pyridylcarbonyl)amine] were prepared using the [Cu(bpca)(H₂O)₂](NO₃)·2H₂O (1) building block and characterized by single crystal X-ray diffraction. We have also isolated and characterized two new crystal forms of the starting species, with lower water contents. Three of the new products are dinuclear complexes obtained by reacting 1 with different rigid or flexible spacer ligands: [Cu₂(bpca)₂(H₂O)₂(bipy)](NO₃)₂·6H₂O (2) (bipy = 4,4′-bipyridine) and [Cu₂(bpca)₂(H₂O)₂(bpete)](NO₃)₂·xH₂O (3) [bpete = (E)-1,2-di(pyridin-4-yl)ethane] are linear dumbbell-like species with Cu?Cu separations of 11.075 and 13.275 Å, respectively. The third dinuclear compound, [Cu₂(bpca)₂(H₂O)₂(bpx)](NO₃)₂·8H₂O (4) [bpx = 1,4-bis((1H-pyrazol-1-yl)methyl)benzene], with the flexible bpx ligand, assumes an unusual S-shaped conformation and shows a quite shorter Cu?Cu contact of 6.869 Å only. We have also obtained a chiral 1D neutral polymeric complex, [Cu₃(bpca)₂(bipy)₃(NO₃)₄]·6H₂O (5), that shows a central linear -Cu-bipy-Cu- chain, with all these Cu atoms connected to two lateral [Cu(bpca)(NO₃)₂]⁻ groups on two opposite sides by means of bipy spacers. An unprecedented type of Cu(II) neutral trinuclear complex, [Cu₃(bpca)₂(H₂O)₂(NO₃)₂] (6), was obtained which has a centrosymmetric structure with two external [Cu(bpca)(NO₃)₂]⁻ units chelating on a central copper atom via the two pairs of carbonyl groups of the bpca ligands. The central metal is octahedral with two axial water molecules, while the two lateral Cu atoms are in square pyramidal geometry; the Cu?Cu separation is 5.205 Å. The magnetic properties of 6 have been rationalized through a ferromagnetic coupling between the central metal ion and the peripheral ones which are coupled by a smaller antiferromagnetic interaction. DFT calculations have been also performed in order to give a better insight into magnetic interactions.     

Synthesis and magnetic properties of the copper(II) complex derived from dimethyl aminomethylphosphine oxide ligand. X-ray crystal structure of DMAO and [Cu(NO3)2(POC3H10N)2]

The synthesis and properties of the copper(II) complex with dimethylaminomethylphosphine oxide as a ligand will be presented. The complex, with the formula [Cu(NO₃)₂(POC₃H₁₀N)₂] 1, has been characterized by elemental analysis, IR spectroscopy, SQUID and X-ray measurements. The X-ray structure was determined for the complex 1 and for the ligand dimethylaminomethylphosphine oxide (DMAO) 2. The single crystal X-ray structure of 1 shows that in the crystal the copper ions form distorted octahedral environment, consisting of two oxygen and two nitrogen atoms from the DMAO ligand. Additionally, one oxygen atom of each anion is semi-coordinated to the copper ion. The solid state magnetic measurements show that the complex 1 is paramagnetic with weak antiferromagnetic interactions in low temperatures.     

Polynuclear nickel (II) and copper (II) complexes of hexaazamacrocycles incorporating pairs of diethylenetriamine subunits separated by aromatic spacers

A series of Ni(II) and Cu(II) complexes of the hexaaza macrocycles, 3,6,9,17,20,23-hexaazatricyclo[23.3.1.1^11,15]triaconta-1(29),11(30),12,14,25,27-hexaene (L¹) and 3,6,9,16,19,22-hexaazatricyclo[22.2.2.2^11,14]triaconta-1(26),11(29),12,14(30),24(28),25-hexaene (L²), have been prepared and the crystal structures determined for [Ni₂L¹(O₂CCH₃)₂(H₂O)₂](ClO₄)₂ (1), [Ni₂L²(DMF)₆](ClO₄)₄ · 2H₂O (2), {[Cu₂L²Br(O₂CCH₃)](ClO₄)₂}_n (3), [Cu₂L²(μ-CO₃)(H₂O)₂]₂(ClO₄)₄ · 8H₂O (4), [Cu₂L²(O₂CCH₃)₂](BF₄)₂ (5), and [Cu₂L¹(μ-imidazolate)Br]₂Br₄ · 6H₂O (6). In these complexes, two metal centers are bound per ligand; in 1 and 3-6, the N₃ subunits of L¹ or L² coordinate meridionally to the metal centers, whilst in 2, each N₃ subunit in L² adopts a facial mode of coordination. The binuclear cations in 1 and 2 have chair-like conformations, with the distorted octahedral Ni(II) coordination spheres completed by terminal water and a bidentate acetate ligand in 1 and three DMF ligands in 2. The Cu(II) centers in 3-6 generally reside in square planar environments, although a weakly binding ligand enters the coordination sphere in some cases, generating a distorted square pyramidal geometry. The binuclear [Cu₂L²]⁴⁺ units in 3, 4 and 5 adopt similar bowl-shaped conformations, stabilized by H-bonding interactions between pairs of amine groups from L² and a perchlorate or tetrafluoroborate anion. In 3, the binuclear units are linked through acetate groups, bridging in a syn-anti fashion, to produce a zig-zag polymeric chain structure, whilst 4 incorporates a tetrameric cation consisting of two binuclear units linked via a pair of carbonate bridges. Compound 6 features an imidazolate bridge between the two Cu(II) centers bound by L¹. Pairs of [Cu₂L¹(μ-imidazolate)]³⁺ units are then weakly linked through a pair of bromide anions.     

Interaction of copper(II) complexes with bis(p-nitrophenyl)phosphate: Structural and spectral studies

When the complexes [Cu(L1)(H₂O)](ClO₄)₂1, where L1 = 4-methyl-1-(pyrid-2-ylmethyl)-1,4-diazacycloheptane, and [Cu(L2)Cl₂] 2, where L2 = 4-methyl-1-(quinol-2-ylmethyl)-1,4-diazacycloheptane are interacted with one/two equivalents of bis(p-nitrophenylphosphate, (p-NO₂Ph)₂PO₂, BNP), no hydrolysis of BNP is observed. From the solution the adducts of copper(II) complexes [Cu₂(L1)₂((p-NO₂Ph)₂PO₂)₂]-(ClO₄)₂3 and [Cu(L2)((p-NO₂Ph)₂PO₂)₂]·H₂O 4 have been isolated and structurally characterised. The X-ray crystal structure of 3 contains two Cu(L1) units bridged by two BNP molecules. The Cu···Cu distance (5.1 Å) reveals no Cu-Cu interaction. On the other hand, the complex 4 is mononuclear with Cu(II) coordinated to the 3N ligand as well as BNP molecules through phosphate oxygen. The trigonality index (τ, 0.37) observed for 4 is high suggesting the presence of significant trigonal distortion in the coordination geometry around copper(II). The complexes are further characterized by spectral and electrochemical studies.     

Mono- and dinuclear manganese(II) complexes derived from the cis/trans isomers of 2,4,5-tris(2-pyridyl)-4,5-dihydroimidazole

Two new manganese(II) complexes, [Mn(L1)(L1H)(ClO₄)(H₂O)][ClO₄]₂·0.5CH₃CN·H₂O (1) [L1 = trans-(±)2-(2,5-di(pyridin-2-yl)-4,5-dihydro-1H-imidazol-4-yl)pyridine)] and [Mn₂(μ-L2)₂(H₂O)₃(CH₃CN)₃][ClO₄]₄·2CH₃CN (2) [L2 = cis-(±)2-(2,5-di(pyridin-2-yl)-4,5-dihydro-1H-imidazol-4-yl)pyridine)], have been prepared and examined by single-crystal X-ray diffraction analysis, showing that complex 1 is a mononuclear compound, whereas complex 2 is a dinuclear species. The cis/trans isomers L1 and L2 have similar coordination properties, but behave as bidentate and tridentate chelating ligands, respectively, giving distorted octahedral metal coordination geometries. X-ray diffraction studies revealed that the molecular and crystal structures are stabilized by a series of intra- and intermolecular interactions. In both cases extended supramolecular networks are generated, in compound 1 through O-H···O, O-H···N, N-H···O, N-H···N, C-H···O, C-H···N, C-H···π and π···π interactions, and in compound 2 through O-H···O, O-H···N, C-H···O and π···π interactions. The observed structural differences between the two metal complexes might be a consequence of these stabilizing effects.     

The syntheses, characterizations, X-ray crystal structures and properties of Cu(I) complexes of a bis-bidentate schiff base ligand

Bis-bidentate Schiff base ligand L and its two mononuclear complexes [CuL(CH₃CN)₂]ClO₄ (1) and [CuL(PPh₃)₂]ClO₄ (2) have been prepared and thoroughly characterized by elemental analyses, IR, UV-Vis, NMR spectroscopy and X-ray diffraction analysis. In both the complexes the metal ion auxiliaries adopt tetrahedral coordination environment. Their reactivity, electrochemical and photophysical behavior have been studied. Complex 1 shows reversible Cu^II/I couple with potential 0.74 V versus Ag/AgCl in CH₂Cl₂. At room temperature L is weakly fluorescent in CH₂Cl₂, however in Cu(I) complexes 1 and 2 the emission in quenched.     

Construction of one-, two- and three-dimensional Cu(I) polymeric architectures containing bis(diphenylphosphino)acetylene and 4,4′-bipyridine linking ligands

One-dimensional {[Cu₂(dppa)₂(4,4′-bipy)(CH₃CN)₂](BF₄)₂ · 2CH₃CN}_n (1), two-dimensional {[Cu₂(dppa)(4,4′-bipy)₂(CH₃CN)₂](BF₄)₂ · 4CH₂Cl₂ · 4H₂O}_n (2) and three-dimensional {[Cu₂(dppa)(4,4′-bipy)₃](BF₄)₂ · 2CH₂Cl₂ · 3CH₃CN · 3H₂O}_n (3) polymeric complexes have been prepared by self-assembly of [Cu(MeCN)₄]BF₄, Ph₂PCCPPh₂ (dppa) and 4,4′-bipyridine (4,4′-bipy) in a 2:2:1, 1:1:1 and 2:2:3 molar ratio, respectively. The structures of 1-3, determined by an X-ray diffraction study, reveal a linear spring-like architecture for 1, a planar honeycomb grid for 2 and an interlocked adamantoid network for 3.     

Synthesis and characterization of Cu(II) and Ni(II) complexes of a tripodal ligand containing imidazoles

Two complexes of the formula [MH₃L](ClO₄)₂ [M = Cu(II) (1), Ni(II) (2)] have been prepared by the reaction of M(ClO₄)₂ · 6H₂O with the ligand (H₃L) formed by the Schiff base condensation of tris(2-aminoethyl)amine (tren) with three molar equivalents of 4-methyl-5-imidazolecarboxaldehyde and structurally and magnetically characterized. The structures of 1 and 2 are isomorphous with each other and with the iron(II) complex of H₃L which has been reported previously. The ligand, while potentially heptadentate, forms six coordinate complexes with both metal centers forming three M-N_imine and three M-N_imidazole bonds. The tren central N atom is at a nonbonded distance from M of 3.261 Å for 1 and 3.329 Å for 2. The neutral complex CuHL 3 was prepared by reaction of H₃L with Cu(OCH₃)₂ and the ionic complex Na[NiL] 4 was prepared by deprotonation of 2 with aqueous sodium hydroxide. Magnetic measurements of 1-3 are consistent with the spin-only values expected for S = 1/2 (d⁹, Cu(II)) and S = 1 (d⁸, Ni (II)) systems.