Synthesis, characterization, and magnetic properties of new binuclear CuCu bis(oxamato) complexes

Two new neutral, binuclear Cu^IICu^II bis(oxamato) complexes with the formula [Cu₂(opba)(pmdta)(MeOH)] · 1/2MeOH · dmf (3) and [Cu₂(nabo)(pmdta)(MeOH)] (4), with opba = o-phenylene-bis(oxamato), nabo = 2,3-naphthalene-bis(oxamato), pmdta = N,N,N′,N″,N″-pentamethyldiethylenetriamine and dmf = dimethylformamide have been synthesized and their crystal structures have been determined. The structure of 3 consists of dimeric [Cu₂(opba)(pmdta)(MeOH)] entities, joined together by mutual intermolecular Cu?O contacts of the Cu²⁺ ion of one [Cu(opba)]²⁻ complex fragment and one carboxylate atom of the oxamato group of a second [Cu(opba)]²⁻ complex fragment. The structure of 4 consists of neutral binuclear complexes joined together by hydrogen bonds and π-π interactions, giving rise to an unique supramolecular 1D-chain. The magnetic properties of 3 and 4 were studied by susceptibility measurements versus temperature. For the intramolecular J parameter, identical values of (−114 ± 2) cm⁻¹ (3) and (−112 ± 2) cm⁻¹ (4) were obtained.     

Structural and equilibrium studies on mixed ligand complexes of Co(II), Ni(II), Cu(II) and Zn(II) with N-(2-benzimidazolyl)methyliminodiacetic acid and typical N, N donor ligands

Mixed ligand complexes: [Co(L)(bipy)] · 3H₂O (1), [Ni(L)(phen)] · H₂O (2), [Cu(L)(phen)] · 3H₂O (3) and [Zn(L)(bipy)] · 3H₂O (4), where L²⁻ = two -COOH deprotonated dianion of N-(2-benzimidazolyl)methyliminodiacetic acid (H₂bzimida, hereafter, H₂L), bipy = 2,2′ bipyridine and phen = 1,10-phenanthroline have been isolated and characterized by elemental analysis, spectral and magnetic measurements and thermal studies. Single crystal X-ray diffraction studies show octahedral geometry for 1, 2 and 4 and square pyramidal geometry for 3. Equilibrium studies in aqueous solution (ionic strength I = 10⁻¹ mol dm⁻³ (NaNO₃), at 25 ± 1 °C) using different molar proportions of M(II):H₂L:B, where M = Co, Ni, Cu and Zn and B = phen, bipy and en (ethylene diamine), however, provides evidence of formation of mononuclear and binuclear binary and mixed ligand complexes: M(L), M(H₋₁L)⁻, M(B)²⁺, M(L)(B), M(H₋₁L)(B)⁻, M₂(H₋₁L)(OH), (B)M(H₋₁L)M(B)⁺, where H₋₁L³⁻ represents two -COOH and the benzimidazole N₁-H deprotonated quadridentate (O⁻, N, O⁻, N), or, quinquedentate (O⁻, N, O⁻, N, N⁻) function of the coordinated ligand H₂L. Binuclear mixed ligand complex formation equilibria: M(L)(B) + M(B)²⁺ ? (B)M(H₋₁L)M(B)⁺ + H⁺ is favoured with higher π-acidity of the B ligands. For Co(II), Ni(II) and Cu(II), these equilibria are accompanied by blue shift of the electronic absorption maxima of M(II) ions, as a negatively charged bridging benzimidazolate moiety provides stronger ligand field than a neutral one. Solution stability of the mixed ligand complexes are in the expected order: Co(II) < Ni(II) < Cu(II) > Zn(II). The Δ log K_M values are less negetive than their statistical values, indicating favoured formation of the mixed ligand complexes over the binary ones.     

Substituent dependent dimensionalities in cobalt isophthalate supramolecular complexes and coordination polymers containing dipyridylamine ligands

Hydrothermal synthesis has afforded cobalt 5-substituted isophthalate complexes with 4,4′-dipyridylamine (dpa) ligands, showing different dimensionalities depending on the steric bulk and hydrogen-bonding facility of the substituent. [Co(tBuip)(dpa)(H₂O)]_n (1, tBuip = 5-tert-butylisophthalate) is a (4,4) grid two-dimensional coordination polymer featuring 2-fold parallel interpenetration. [Co(MeOip)₂(Hdpa)₂] (2, MeOip = 5-methoxyisophthalate) is organized into 3-fold parallel interpenetrated (4,4) grids through strong N-H⁺?O⁻ hydrogen bonding. {([Co(OHip)(dpa)(H₂O)₃])₃·2H₂O}_n (3, OHip = 5-hydroxyisophthalate) possesses 1-D chain motifs. The 5-methyl derivative {[Co(mip)(dpa)]·3H₂O}_n (4, mip = 5-methylisophthalate) has a 3-D 6⁵8 cds topology. {[Co(H₂O)₄(Hdpa)₂](nip)₂·2H₂O} (5, nip = 5-nitroisophthalate) and {[Co(sip)(Hdpa)(H₂O)₄]·2H₂O} (6, sip = 5-sulfoisophthalate) are coordination complexes. Antiferromagnetic superexchange is observed in 1 and 4, with concomitant zero-field splitting. Thermal decomposition behavior of the higher dimensionality complexes is also discussed.     

Divalent metal 1,3-phenylenediacetate coordination polymers with rigid or flexible dipyridyl tethers: Chains, layers, and interpenetrated networks

Hydrothermal synthesis has afforded four divalent metal 1,3-phenylenediacetate (1,3-phda) coordination polymers containing different dipyridyl-type ligands. {[Cu(1,3-phda)(dpa)(H₂O)]·H₂O}_n (1, dpa = 4,4′-dipyridylamine) exhibits a simple 2-D (4,4) rhomboid grid structure. {[Co(1,3-phda)(bpy)]·1.5H₂O}_n (2, bpy = 4,4′-bipyridine) also possesses a (4,4) layer structure, but with syn-syn bridged {Co₂(OCO)₂} dimeric kernels serving as 4-connected nodes. {[Co(H₂O)₄(3-bpmpH₂)](1,3-phda)₂·8H₂O}_n (3, 3-bpmp = bis(3-pyridylmethyl)piperazine) manifests cationic 1-D [Co(H₂O)₄(3-bpmpH₂)]_n⁴ⁿ⁺ chains linked into higher dimensionality by unligated 1,3-phda anions and curled tetrameric water molecule units. {[Ni(1,3-phda)(4-bpmp)(H₂O)₂]·2H₂O}_n (4, 4-bpmp = bis(4-pyridylmethyl)piperazine) has an underlying twofold interpenetrated 6⁵8 (cds) 3-D network topology. Variable temperature magnetic susceptibility studies revealed the presence of weak antiferromagnetic coupling and zero-field splitting (J = −1.65(4) cm⁻¹ and D = 30.9(7) cm⁻¹ with g = 2.20(1)) within the {Co₂(OCO)₂} dimers in 2.     

Synthesis, crystal structure and action on Escherichia coli by microcalorimetry of copper complexes with 1,10-phenanthroline and amino acid

Copper complexes: [Cu(phen)(L-Ser)(H₂O)Cl] (1), [Cu(phen)(Gly)(H₂O)]Cl·3H₂O (2), [Cu(phen)(L-Ala)(H₂O)]Cl·H₂O (3), [Cu(phen)(L-Phe)(H₂O)]Cl·2.5H₂O (4), Cu(phen)₂Cl₂·6H₂O (5) (phen = 1,10-phenanthroline) were synthesized and characterized. The structure of 1 was characterized by X-ray crystallography and showed in a triclinic system with space group P1, a = 6.8953(15) Å, b = 10.737(2) Å, c = 11.894(3) Å, α = 110.395(3)°, β = 94.183(4)° and γ = 100.540(3)°. The antibacterial activities on Escherichia coli (E. coli) of these five copper complexes and CuCl₂ (6) were investigated by microcalorimetry. By analyzing the obtained metabolic thermogenic data and curves, crucial parameters such as rate constant of bacterial growth (k), half inhibitory concentration (IC₅₀), and generation time (t_G) were determined. All these copper complexes could stimulate the growth of the E. coli at their lower concentration. At their higher concentration they all showed antibacterial action. The inhibition on E. coli was 5 > 1 ≈ 2 ≈ 3 ≈ 4 > 6. And the antibacterial mechanism was discussed preliminarily.     

Pyridyldicarboxamide-based multinuclear complexes: Syntheses, structural characterizations, and magnetic properties

Using the pyridine dicarboxamide derivative N,N′-bis(1,3,4-thiadiazol-2-yl)-2,6-pyridinedi-carboxamide (H₂-btapca) as ligand, two novel polynuclear complexes: dimeric {[Cu₂(μ₂-O₂H)(btapca)₂]·DMF·H₂O} (1) and tetrameric {[Ni₄((μ₂-O₂H)₂(btapca)₄)]·DMF·MeOH·3.5H₂O} (2) were obtained. In complex 1, two center Cu(II) ions are bounded by two btapca ligands and one aqueous molecule acting as a μ₂-H₂O bridge connect them together. Complex 2 is a tetrameric complex, in which the based backbone is an assumed Ni₄ tetrahedron with two μ₂-O₂H bridges existing inside the tetrahedron forming a basic [Ni₂(μ₂-O₂H)]₂ core, which are surrounded by four btapca ligands. The magnetic properties of the two polynuclear complexes were determined, the results show that for both of the two complexes, the overall weak ferromagnetic exchange interactions between central metal ions are evident, the best fitting parameters are: J = 7.47 cm⁻¹ (g = 2.21) for dimeric Cu(II) complex 1, and 2J₁ = 4.8 cm⁻¹, 2J₂ = −0.00204 cm⁻¹(g = 2.14, zJ′ = 0.00077 cm⁻¹) for tetrameric Ni(II) complex 2.     

Synthesis, structures and magnetic properties of oxamido-bridged trinuclear Cu-M-Cu macrocyclic complexes (M = Mn(II) and Co(II))

Two oxamido-bridged trinuclear complexes of formula {[(LCu)(EtOH)]₂Mn(EtOH)₂}(ClO₄)₂ (1) and {[(LCu)(EtOH)]₂Co(EtOH)₂}(ClO₄)₂ · 2H₂O (2) (H₂L = 2,3-dioxo-5,6:13,14-dichlorobenzo-7,12-diphenyl-1,4,8,11-tetraazacyclo-pentadeca-7,11-diene) have been synthesized and structurally characterized. The central ions of complexes 1-2 (Mn(II), Co(II)) are all bridged by macrocyclic oxamido groups. Their magnetic properties were studied by susceptibility versus temperature measurement, the best fitting of the experimental data led to J = −16.91 cm⁻¹ for 1 and J = −27.73 cm⁻¹ for 2.     

New yttrium(III) and copper(II) coordination polymers with partially protonated cyclohexane-1,2,3,4,5,6-hexacarboxylato ligands: Synthesis, crystal structures and properties

Two coordination polymers, [Y(H₂O)₄(H₃chhc)]·6H₂O (1) and [Cu₅(H₂O)₁₀(Hchhc)₂]·4H₂O (2) with H₆chhc = cyclohexane-1,2,3,4,5,6-hexacarboxylic acid) represent rare examples of metal complexes with partially protonated cyclohexane-1,2,3,4,5,6-hexacarboxylato ligands. The [Y(H₂O)₄]³⁺ units in 1 are interlinked by the triprotonated (H₃chhc)³⁻ anions in a η⁵μ₄ bridging mode to form 2D (4³)₂(4⁶·6⁶·8³) topological networks, which are stacked along [0 1 0] direction in ···ABAB··· fashion with the lattice H₂O molecules sandwiched between layers. The pentameric [Cu₅(H₂O)₁₀]¹⁰⁺ units in 2 are bridged by monoprotonated (Hchhc)⁵⁻ anions in a η⁸μ₆ fashion to generate a 3D MOF of an unprecendented (4³)(4⁵·6⁷·8³) topology with the lattice H₂O molecules in channels. The temperature-dependent magnetic susceptibility data of 2 could be modeled to a combination of a linear chain of equally-spaced Cu(II) ions (J₁ = 1.86 cm⁻¹) with an isosceles triangular Cu₃ unit (J₂ = 5.86 cm⁻¹).     

Synthesis and characterization of chromium(III) octaphenylporphyrin complexes with various axial ligands: An insight into porphyrin distortion

Influence of axial ligands, MeCN, H₂O, py, and piperidine (pip), on distortion of (2,3,5,10,12,13,15,20-octaphenylporphinato)chromium(III), [Cr(OPP)]⁺, was investigated by X-ray crystallography and UV-vis and ESR spectroscopies. In crystal structures of [Cr(OPP)(MeCN)(H₂O)]ClO₄ · MeCN and [Cr(OPP)(H₂O)₂]ClO₄ · 3THF, the OPP²⁻ ligand had a planar structure. On the other hand, crystal structures of [Cr(OPP)(pip)₂]ClO₄ · 2CH₂Cl₂ and [Cr(OPP)(py)₂]ClO₄ exhibited a waved structure and a saddle-shaped structure with ruffling, respectively. In the UV-vis spectrum of [Cr(OPP)(py)₂]ClO₄ in CH₂Cl₂, the large red shift of the Soret band was observed. Furthermore, the small D value of 0.10 cm⁻¹ was obtained for [Cr(OPP)(py)₂]ClO₄ from the ESR spectrum in frozen 1,2-dichloroethane solution at 5 K. These results suggest that the OPP²⁻ ligand is distorted both in solid and in solution, and that the axial ligand would exert some effects on the porphyrin distortion.     

Zinc complexes with tricarballylic acid and Lewis bases with zero- and two-dimensional structures

Three ternary zinc complexes of the open chain polycarboxylic acid, tricarballylic (1,2,3-propane-tricarboxylic) acid (PTCH₃) have been isolated and characterized with crystallographic and physicochemical techniques. [Zn(PTCH)(phen)(H₂O)]₂ · 4H₂O (1) (where phen = 1,10-phenanthroline) has a unique dinuclear structure, while [Zn(PTCH)(bpy)]_n · 3nH₂O (2) and [Zn(PTCH)(epy)]_n · 4nH₂O (3) (where bpy = 4,4′-bipyridine and epy = 1,2-bis(4-pyridine)ethane) have 2D polymeric structures. The bis-deprotonated ligand, in all three complexes, uses for coordination only two oxygen atoms, which belong to the same carboxylate in 1, and to two different carboxylates in 2 and 3.     

Synthesis, structure and magnetic property of μ-phenoxo-μ-acetato-bis(η-acetato)dicobalt(II, II) complexes

Dinuclear cobalt(II) complexes Co₂(bpmp)(OAc)₃ (1) and Co₂(bpcp)(OAc)₃ (2) have been synthesized by using acyclic ligands 2,6-bis((4-(pyridin-2-yl)pyrimidin-2-ylthio)methyl)-4-methylphenol [H(bpmp)] and 2,6-bis((4-(pyridin-2-yl)pyrimidin-2-ylthio)methyl)-4-chlorophenol [H(bpcp)] with versatile coordination sites. X-ray analysis uncovered that complex 1 · 3H₂O contains a μ-phenoxo-μ-acetato-bis(η²-acetato) dicobalt(II, II) core. Magnetic susceptibility was measured for 1 over the temperature range 1.8-300 K, and the best theoretical fitting parameters were g = 2.12(6), J = −3.63(9) cm⁻¹ and D = −12(4) cm⁻¹.     

Synthesis and spectral investigation of manganese(II), cadmium(II) and oxovanadium(IV) complexes with 2,6-diacetylpyridine bis(2-aminobenzoylhydrazone): Crystal structure of manganese(II) and cadmium(II) complexes

The chelating behavior of 2,6-diacetylpyridine bis(2-aminobenzoylhydrazone) (H₂dapa) towards manganese(II), cadmium(II) and oxovanadium(IV) ions has been studied by elemental analyses, conductance measurements, magnetic properties and spectral (IR, ¹H NMR, UV-Vis and EPR) studies. The IR spectral studies suggest the pentadentate nature of the ligand with pyridine nitrogen, two azomethine nitrogens and two carbonyl oxygen atoms as the ligating sites. Six coordinate structure for [VO(H₂dapa)]SO₄ · H₂O and seven coordinate structures for [Mn(H₂dapa)(Cl)(H₂O)]Cl · 2H₂O and [Cd(H₂dapa)Cl₂] · H₂O complexes have been proposed. Pentagonal bipyramidal geometry for [Mn(H₂dapa)(Cl)(H₂O)]Cl · 2H₂O and [Cd(H₂dapa)(Cl₂)] · H₂O complexes was confirmed by single crystal analysis. The X-band EPR spectra of the oxovanadium(IV) and manganese(II) complexes in the polycrystalline state at room (300 K) and also at liquid nitrogen temperature (77 K) were recorded and their salient features are reported.     

Synthesis, structure and magnetic properties of a pair of copper dicarboxylate/dipyridylamine coordination polymers with a non-interpenetrated CdSO4 topology

Hydrothermal synthesis has afforded a pair of divalent copper coordination polymers containing the kinked and hydrogen-bonding capable imine 4,4′-dipyridylamine (dpa) and aromatic dicarboxylates, {[Cu(iph)(dpa)]·0.5H₂O}_n (1, iph = isophthalate) and [Cu(tdc)(dpa)]_n (2, tdc = 2,5-thiophenedicarboxylate). Compounds 1 and 2 contain orthogonally disposed parallel sets of 1-D [Cu(iph)]_n and [Cu(tdc)]_n chains, respectively, containing dicarboxylate-bridged dinuclear {CuOCO}₂ units. The chain motifs are joined by tethering dpa ligands to construct uncommon non-interpenetrated 3-D CdSO₄ lattices (6⁵8 topology) in both cases. Variable temperature magnetic studies show the presence of weak antiferromagnetic coupling within the {CuOCO}₂ dimers in both complexes, with J = −2.66(3) and −1.68(5) cm⁻¹ for 1 and 2, respectively.     

Aqueous acid-base chemistry involving dioxovanadium(V) complexes of 2,6-pyridinedimethanol, and the X-ray structures of Na[VO2{2,6-(OCH2)2NC5H3}] · 4H2O and [1-H-2,6-(HOCH2)2NC5H3]Cl

Reaction of NH₄VO₃ with 2,6-pyridinedimethanol in water at 85 °C followed by the room temperature addition of HCl (aq) yields [HVO₂(pydim)]_x (pydim = 2,6-pyridinedimethanolato dianion), as a sparingly soluble off-white solid. This acid may be deprotonated by titration with NaOH (aq), yielding Na[VO₂(pydim)] · 4H₂O, which has been structurally characterized by single-crystal X-ray diffraction. Treating Na[VO₂(pydim)] · 4H₂O with HCl (aq) regenerates [HVO₂(pydim)]_x, but reaction with additional NaOH (aq) displaces the pyridinedimethanolato ligand from the vanadium center. Similarly, treating [HVO₂(pydim)]_x with excess HCl (aq) strips the pyridinedimethanolato ligand from the vanadium center and yields the adduct [H₃(pydim)]⁺Cl⁻ as one component in a mixture of products. This adduct has been structurally characterized by single-crystal X-ray diffraction. The optimum pH range for stable dioxovanadium(V) complexes stabilized by the 2,6-pyridinedimethanolato ligand is at least 1.5-9.4.     

Equilibrium and structural studies on Co(II), Ni(II), Cu(II) and Zn(II) complexes with N-(2-benzimidazolyl)methyliminodiacetic acid: crystal structures of Ni(II) and Cu(II) complexes

Combined pH-metric, UV-Vis, ¹H NMR and EPR spectral investigations on the complex formation of M(II) ions (M=Co, Ni, Cu and Zn) with N-(2-benzimidazolyl)methyliminodiacetic acid (H₂bzimida, hereafter H₂L) in aqueous solution at a fixed ionic strength, I=10⁻¹ mol dm⁻³, at 25 ± 1 °C indicate the formation of M(L), M(H₋₁L)⁻ and M₂(H₋₁L)⁺ complexes. Proton-ligand and metal-ligand constants and the complex formation equilibria have been elucidated. Solid complexes, [M(L)(H₂O)₂] · nH₂O (n=1 for M = Co and Zn, n=2 for M = Ni) and {Cu (μ-L) · 4H₂O}_n, have been isolated and characterized by elemental analysis, spectral, conductance and magnetic measurements and thermal studies. Structures of [Ni(L)(H₂O)₂] · 2H₂O and {Cu(μ-L) · 4H₂O}_n have been determined by single crystal X-ray diffraction. The nickel(II) complex exists in a distorted octahedral environment in which the metal ion is coordinated by the two carboxylate O atoms, the amino-N atom of the iminodiacetate moiety and the pyridine type N-atom of the benzimidazole moiety. Two aqua O atoms function as fifth and sixth donor atoms. The copper(II) complex is made up of interpenetrating polymeric chains of antiferromagnetically coupled Cu(II) ions linked by carboxylato bridges in syn-anti (apical-equatorial) bonding mode and stabilized via interchain hydrogen bonds and π-π stacking interactions.     

Synthesis, structures and magnetic properties of oxamido-bridged trinuclear Cu(II)-Mn(II)-Cu(II) complexes

Based on self-assembly of the dissymmetrical mononuclear entity CuL(CH₃OH) [H₂L = (E)-N¹-(2-((2-aminocyclohexydiimino)(phenyl)methyl)-4-chlorophenyl)-N²-(2-benzyl-4-chlorophenyl)oxalamide] with Mn(II), two trinuclear complexes were prepared. They are of the formula [(LCuN₃)₂Mn(CH₃OH)₂] · 2CH₃OH · 2H₂O (1) and [(LCuSCN)₂Mn(H₂O)₂] · 4CH₃OH (2). Their magnetic properties were studied by susceptibility versus temperature measurement, the best fitting of the experimental data led to J = −14.40 cm⁻¹ for 1 and J = −15.48 cm⁻¹ for 2. Hydrogen bonds help complex 1 to produce a novel S type one-dimensional chain-like supramolecular structure. In complex 2, Cl?Cl interaction also results in the formation of a one-dimensional structure.     

Aqua bridge cleavage and metal ion extrusion by thiocyanate anions in a dicopper complex

Reaction of the imidazolidinyl phenolate-based ligand, H₃L [(2-(2′-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine)] with Cu(ClO₄)₂·6H₂O produces an aqua-bridged cationic reactant complex [Cu₂(μ-H₂O)(μ-L)][ClO₄]·1.5H₂O (1·1.5H₂O). Solution phase interaction of 1·1.5H₂O with SCN⁻ anions in 1:1 molar ratio leads to [Cu₂(μ-L)(NCS)]·2H₂O (2·2H₂O) that does not possess anymore the reactive aqua bridge but instead a terminal SCN⁻ anion coordinated only to one Cu^II ion. Whereas in 1:2 molar ratio, partial extrusion of the Cu^II ions takes place to generate in situ [Cu(NCS)₃(OH₂)]⁻ anions. These complex anions then quantitatively replace anions in 1·1.5H₂O via ‘anion metathesis’ and concurrently remove the aqua bridge by coordination of linear MeCN to one of the Cu^II ions to give [Cu₂(μ-L)(CH₃CN)][Cu(NCS)₃(OH₂)] (3). The literature unknown [Cu(NCS)₃(OH₂)]⁻ anion forms an intimate H-bonded assembly with the cationic part of 3 to yield a novel [Cu₃] isosceles triangle. The precursor complex is known as antiferromagnetic whereas in 2·2H₂O, the Cu^II (S = 1/2) ions in a dinuclear entity exhibit ferromagnetic interactions (J/k_B = +15.0 K and g = 2.22) to yield an S_T = 1 spin ground state in good agreement with the M versus H data below 8 K.     

New examples of low-dimensional metal-pydco complexes: Syntheses, structures and magnetic properties

This work presents a systematic investigation on coordination chemistry of a novel pyridine-2,6-dicarboxylic acid N-oxide (pydco), and also reveals the significant function of supramolecular interactions in dominating the resultant crystalline nets. Assemblies of pydco with transition-metal ions under similar conditions yield a series of polymers in the absence/presence of the organonitrogen ligands {[Cu(pydco)(L)_0.5(H₂O)] · 2H₂O}_n (L = bipy (1), bpa (2) and bpe (3)), {[M(pydco)(bpp)(H₂O)] · 2H₂O}_n (M = Cu (4) and Ni (5)), [Ag₂(pydco)]_n (6) and [Ag₂Cu(pydco)₂]_n (7) (bipy = 4,4′-bipyridine, bpa = 1,2-bis(4-pyridyl)ethane, bpe = 1,2-bis(4-pyridyl)ethene, bpp = 1,3-bis(4-pyridyl)propane). 1-5 feature different structural characteristics, although they exhibit analogous chain networks. Remarkably, extended architectures are further constructed with the aid of weak interactions. Reaction of pydco with AgAc yields a 2-D polymer 6, which was reported in our recent Communication. A mixed-metal coordination polymer 7 was obtained by the self-assembly of AgAc, Cu(Ac)₂ · H₂O and pydco.In 7, two left- and right-hand helical chains are constructed by carboxylic groups of pydco and Cu centers, which are further connected by [AgCO₂]₂ cores into a 2-D network. Structural evolution under the co-ligand intervention in this series of compounds, as well as the general coordination rule of pydco, has been further discussed. Furthermore, variable temperature magnetic properties of 1, 3 and 7 are also studied. The magnetic measurements of 1 and 3 reveal the existence of weak antiferromagnetic interactions with J₁ = −4.59 cm⁻¹ and J₂ = −4.63 cm⁻¹, respectively. Whereas 7 displays weak ferromagnetic interactions with J₃ = 1.81 cm⁻¹.     

Reactions of cyanooxo-molybdates and -tungstates with picolinic acid, 2-pyridinecarboxaldehyde and 2,2′-pyridil: X-ray crystal structure of (PPh4)2[Mo(CN)4O(pic)] · 2.5H2O

The syntheses of (PPh₄)₂[M(CN)₃O(pic)] · nH₂O (M = Mo, W; n = 2.5, 4; pic = picolinate anion) as well as (PPh₄)₂[Mo(CN)₄O(apic)] · 3H₂O (apic = 2-pyridinecarboxaldehyde) are presented. The salts have been characterised by elemental analysis, IR and UV-Vis spectroscopy, cyclic voltammetry and X-ray crystal structure determination of (PPh₄)₂[Mo(CN)₃O(pic)] · 2.5H₂O. The anion in the latter salt is approximately octahedral with O and N donor atoms of pic situated in the trans and cis position to the MoO bond, respectively. The picolinate complexes have the characteristic MLCT bands in the visible spectra with the absorption maxima linearly dependent on the Reichardt’s E_T solvent parameter. These complexes are shown to exhibit the strongest solvatochromic effect of all studied tricyanooxo and hexacyano complexes of Mo(IV) and W(IV). The obtained values of E_1/2 in these salts [0.333 V (Mo) and 0.018 V (W) in 1,2-C₂H₄Cl₂] were found to be the highest of all [M(CN)₃O(LL)]²⁻ type complexes making these salts show reversibility in a remarkable variety of solvents. The oxidation of coordinated apic to pic has been demonstrated by means of electronic spectroscopy. The isolated salts were used to monitor the reaction of [M(CN)₄O(H₂O)]²⁻ with 2,2′-pyridil in water-ethanol solution. It was found that 2,2′-pyridil disproportionate to Hpic and apic in the first step and the other decomposition products of 2,2′-pyridil postulated in the literature were not observed.     

Topological diversity in copper aromatic meta-dicarboxylate coordination polymers with bis(pyridylformyl)piperazine coligands

Hydrothermal synthesis has afforded divalent copper coordination polymers containing bis(4-pyridylformyl)piperazine (4-bpfp) tethers and aromatic meta-dicarboxylate ligands. {[Cu(ip)(4-bpfp)]·2H₂O}_n (1, ip = isophthalate) possesses a (4, 4) rectangular grid structure with an unusual ABCD stacking pattern along a 4₁ screw axis. Sterically bulky substituents in the 5-position of the isophthalate ligands reduced the coordination polymer dimensionality, with [Cu₂(tBuip)₂(4-bpfp)(H₂O)₂]_n (2, tBuip = 5-tert-butylisophthalate) and {[Cu(MeOip)(HMeOip)₂(4-bpfp)]·3H₂O}_n (3, MeOip = 5-methoxyisophthalate) displaying 1D polymeric ladder and chain motifs, respectively. Compound 3 possesses a rare twofold interpenetrated binodal supramolecular hms net with (6³)(6⁹8) topology. Longer meta-disposed acetate pendant arms induced a doubly interpenetrated 3D primitive cubic topology in {[Cu₂(1,3-phda)₂(H₂O)₂(4-bpfp)]}_n (4, 1,3-phda = 1,3-phenylenediacetate), which possesses antiferromagnetically coupled {Cu₂O₂} kernels (J = −6.14(8) cm⁻¹).