Coordination polymers incorporating copper(II) and manganese(II) centers bridged by pyridinedicarboxylate ligands: Structure and magnetism

Two heterobimetallic coordination polymers, [Cu(2,4-pydc)₂Mn(H₂O)₄]_x (1) and [Cu(2,5-pydc)₂Mn(H₂O)₂]_x · 4xH₂O (2), have been synthesized and structurally characterized by single crystal X-ray diffraction. Both compounds have extended 2-D sheet structures. In 1 the copper centers are linked in chains by double ligand bridges and these chains are cross-linked through the manganese coordination spheres and O–C–O bridges to form polymeric sheets. In 2 separate O–C–O bridged Cu and Mn chains are connected in an alternating array by additional ligand bridging to generate the overall 2-D structure. Analysis of magnetic data of 1 reveals that ferromagnetic exchange between the O–C–O bridged copper and manganese centers dominates the magnetic properties of this system. The magnetic data for 2 fit well to a model incorporating antiferromagnetic exchange in independent S = 1/2 and S = 5/2 linear chains with J(Cu) = −0.073 cm⁻¹ and J(Mn) = −0.32 cm⁻¹. Unlike the situation in 1, there is no evidence for heterometallic exchange. In both 1 and 2 the significant exchange occurs via O–C–O bridges. To study the effect of thermal dehydration on the magnetic properties of these systems, the compounds Cu(2,4-pydc)₂Mn · H₂O (1d) and Cu(2,5-pydc)₂Mn · H₂O (2d) were synthesized and studied.     

Thermodynamic properties of metal amides determined by ammonia pressure-composition isotherms

Thermodynamic properties of Mg(NH₂)₂ and LiNH₂ were investigated by measurements of NH₃ pressure-composition isotherms (PCI). Van’t Hoff plot of plateau pressures of PCI for decomposition of Mg(NH₂)₂ indicated the standard enthalpy and entropy change of the reactions were ΔH° = (120 ± 11) kJ · mol^?1 (per unit amount of NH₃) and ΔS° = (182 ± 19) J · mol^?1 · K^?1 for the reaction: Mg(NH₂)₂ → MgNH + NH₃, and ΔH° = 112 kJ · mol^?1 and ΔS^o = 157 J · mol^?1 · K^?1 for the reaction: MgNH → (1/3)Mg₃N₂ + (1/3)NH₃. PCI measurements for formation of LiNH₂ were carried out, and temperature dependence of plateau pressures indicated ΔH° = (?108 ± 15) kJ · mol^?1 and ΔS° = (?143 ± 25) J · mol^?1 · K^?1 for the reaction: Li₂NH + NH₃ → 2LiNH₂.     

Magnetic properties of hybrid organo-inorganic copper(II) oxovanadate(V) phosphate and phosphonate bridged systems

The hybrid organo-inorganic compounds [Cu₄(bipy)₄V₄O₁₁(PO₄)₂]nH₂O (n ∼ 5) (1), [Cu₂(phen)₂(PO₄)(H₂PO₄)₂(VO₂) · 2H₂O] (2) and [Cu₂(phen)₂(O₃PCH₂PO₃)(V₂O₅) (H₂O)]H₂O (3) which present different bridging forms of the phosphate/phosphonate group, show different bulk magnetic properties. We herein analyze the magnetic behaviour of these compounds in terms of their structural parameters. We also report a theoretical study for compound (1) assuming four different magnetic exchange pathways between the copper centres present in the tetranuclear unit. For compound (1) the following J values were obtained J₁ = +3.29; J₂ = −0.63; J₃ = −2.23; J₄ = −46.14 cm⁻¹. Compound (2) presents a Curie–Weiss behaviour in the whole range of temperature (3–300 K), and compound (3) shows a maximum for the magnetic susceptibility at 64 K, typical for antiferromagnetic interactions. These data where fitted using a model previously reported in the literature, assuming two different magnetic exchange pathways between the four copper(II) centres, with J₁ = −30.0 and J₂ = −8.5 cm⁻¹.     

Ferromagnetic interaction between [Ni(bdt)2]− anions in [Mn2(Saloph)2(μ-OH)][Ni(bdt)2](CH3CN)2

A new molecule-based magnetic material [Mn₂(Saloph)₂(μ-OH)][Ni(bdt)₂](CH₃CN)₂ was prepared by the metathesis of [Mn(Saloph)(H₂O)(ClO₄)] (S = 2) and TBA[Ni(bdt)₂] (S = 1/2). In the crystal, [Ni(bdt)₂]^? anions form square lattices which are separated from each other by the layers of antiferromagnetically coupled binuclear cations [Mn₂(Saloph)₂(μ-OH)]⁺. The magnetic susceptibility of the material coincides with the sum of the S = 2 van Vleck dimer model and S = 1/2 Heisenberg ferromagnetic square lattice model with 2J = ?92.4 and +4.5 K, respectively. The origin of the ferromagnetic interaction can be explained by the T-shaped intermolecular overlap mode of SOMOs which spreads to the ends of [Ni(bdt)₂]^? molecules.     

Synthesis,crystal structure,spectroscopy and magnetism of a trinuclear nickel(II) complex with 3,5-pyrazoledicarboxylic acid as bridge ligands

A new complex of [Ni₃(dcp)₂(H₂O)₁₀] (1) (H₃dcp = 3,5-pyrazoledicarboxylic acid) has been synthesized from H₃dcp and Ni(NO₃)₂·6H₂O by hydrothermal reaction. Complex 1 has the discrete trinuclear structure. Three Ni(II) ions are bridged by two dcp³⁻ ligands, with 10 coordinated water molecules as terminal ligands. The molecules of [Ni₃(dcp)₂(H₂O)₁₀] extend into three-dimensional supramolecular architectures by intermolecular O–H···O hydrogen bonds as well as π-π stacking interactions. Magnetic susceptibility measurement shows that a weak antiferromagnetic interaction is operative between nickel(II) ions and an excellent simulation of the experimental data gives D = 5.27 cm⁻¹, J = −2.19 cm⁻¹ and g = 2.05.     

A calorimetric and thermodynamic investigation of A2[(UO2)2(MoO4)O2] compounds with A = K and Rb and calculated phase relations in the system (K2MoO4 + UO3 + H2O)

A calorimetric and thermodynamic investigation of two alkali-metal uranyl molybdates with general composition A₂[(UO₂)₂(MoO₄)O₂], where A = K and Rb, was performed. Both phases were synthesized by solid-state sintering of a mixture of potassium or rubidium nitrate, molybdenum (VI) oxide and gamma-uranium (VI) oxide at high temperatures. The synthetic products were characterised by X-ray powder diffraction and X-ray fluorescence methods. The enthalpy of formation of K₂[(UO₂)₂(MoO₄)O₂] was determined using HF-solution calorimetry giving Δ_fH° (T = 298 K, K₂[(UO₂)₂(MoO₄)O₂], cr) = −(4018 ± 8) kJ · mol⁻¹. The low-temperature heat capacity, С_р°, was measured using adiabatic calorimetry from T = (7 to 335) K for K₂[(UO₂)₂(MoO₄)O₂] and from T = (7 to 326) K for Rb₂[(UO₂)₂(MoO₄)O₂]. Using these С_р° values, the third law entropy at T = 298.15 K, S°, is calculated as (374 ± 1) J · K⁻¹ · mol⁻¹ for K₂[(UO₂)₂(MoO₄)O₂] and (390 ± 1) J · K⁻¹ · mol⁻¹ for Rb₂[(UO₂)₂(MoO₄)O₂]. These new experimental results, together with literature data, are used to calculate the Gibbs energy of formation, Δ_fG°, for both phases giving: Δ_fG° (T = 298 K, K₂[(UO₂)₂(MoO₄)O₂], cr) = (−3747 ± 8) kJ · mol⁻¹ and Δ_fG° (T = 298 K, Rb₂[(UO₂)₂(MoO₄)], cr) = −3736 ± 5 kJ · mol⁻¹. Smoothed С_р°(Т) values between 0 K and 320 K are presented, along with values for S° and the functions [H°(T) − H°(0)] and [G°(T) − H°(0)], for both phases. The stability behaviour of various solid phases and solution complexes in the (K₂MoO₄ + UO₃ + H₂O) system with and without CO₂ at T = 298 K was investigated by thermodynamic model calculations using the Gibbs energy minimisation approach.     

Synthesis,molecular and supramolecular structures,electrochemistry and magnetic properties of two macrocyclic dicopper(II) complexes: Microporous supramolecular assembly

Synthesis, molecular and supramolecular structures, electrochemistry and magnetic properties of two diphenoxo-bridged dicopper(II) compounds [Cu^II₂L(H₂O)(ClO₄)]·ClO₄·2H₂O (1) and [Cu^II₂L(N₃)₂]·2H₂O (2) derived from a tetraimino diphenolate macrocyclic ligand H₂L, obtained on [2+2] condensation of 4-methyl-2,6-diformylphenol and 2,2′-dimethyl-1,3-diaminopropane, are presented. Supramolecular structure of both 1 and 2 are three-dimensional resulting from hydrogen bonding interactions. Interestingly, the 3-D self-assembly of 2 contains micropores having the dimension of 0.35 nm. Electrochemical analyses reveal that both of these compounds exhibit two-step couples in the reduction window. Variable-temperature (2–300 K) magnetic susceptibilities measurements of the two compounds reveal that the metal centers in both of the complexes are coupled by strong antiferromagnetic interactions with J values (H = ?JS₁·S₂) ?776 and ?836 cm^?1 for 1 and 2, respectively.     

Spin-crossover in dimeric hydrogen-bonded iron(II) 2-(pyrazolyl)-pyridine and 2-(imidazolyl)-pyridine complexes

Five new hydrogen-bonded solvated iron(II) complexes of pyrazolyl- and imidazolyl-based N,N-chelating ligands have been synthesised. Water to ligand-NH hydrogen-bonded bridges occur in the pseudo-dimeric complexes {cis-[Fe(pypzH)₂(NCX)₂]₂(μ-OH₂)(H₂O)₂} · H₂O · MeOH (where X = S or Se), and in the chain complex {cis-[Fe(pypzH)₂(NCS)₂](μ-OH₂)}_n. A “half” spin-crossover (T_c = 125 K) was observed in the dimeric X = Se complex by means of magnetic measurements and no thermal hysteresis occurred between 4 and 300 K. The crystal structure at 123 K showed Fe–N distances consistent with the magnetism. Each Fe in the dimeric unit was structurally equivalent in the HS–LS state. Removal of the solvate molecules led to HS–HS behaviour over the temperature range 4–300 K. The pseudo-dimer with X = S also showed HS–HS behaviour as did the monomeric analogue cis-[Fe(pypzH)₂(NCS)₂]H₂O and a structurally different methanol-bridged dimer {cis-[Fe(pyimH)₂(NCS)₂]₂(μ-MeOH)₂} · 2MeOH (pypzH = 2-(1H-pyrazol-3-yl)-pyridine; pyimH = 2-(1H-imidazol-2-yl)-pyridine).     

Double cyclometallation of bridging 3,6-bis(2-thienyl)-1,2,4,5-tetrazine in a dinuclear mesityl(dimethylsulfoxide)platinum(II) complex: Structure and properties

3,6-Bis(2-thienyl)-1,2,4,5-tetrazine (bttz) reacts with trans-Pt(dmso)₂(mes)₂, mes = mesityl = 2,4,6-trimethylphenyl, under twofold cyclometallation to yield structurally characterized (μ-bttz-2H⁺)[Pt(dmso)(mes)]₂ with uncoordinated thiophene sulfur atoms and bttz deprotonated in the 3,3′ positions. The structural features include cis-positioned carbanionic ligands, twisted mesityl substituents, S-coordinated dmso ligands with the SO bonds lying in the molecular plane, shortened inter-ring bonds, and rather short Pt–C bonds at 1.998(9)/2.00(1) Å (Pt–C_mes) and 1.985(9)/1.99(1) Å (Pt–C_bttz-2H+). Reversible reduction to {(μ-bttz-2H⁺)[Pt(dmso)(mes)]₂}^? causes a high-energy shift of the charge transfer bands and the appearance of an unresolved EPR signal at g = 1.9905.     

Ab initio crystal structure of nickel(II) hydroxy-terephthalate by synchrotron powder diffraction and magnetic study

The structure of the new hybrid compound [Ni₃(OH)₂(tp)₂(H₂O)₄]·2H₂O (tp = C₈H₄O₄²⁻) has been determined ab initio from synchrotron powder diffraction data and refined with the Rietveld method: space group P-1, a = 10.2077(6) Å, b = 8.0135(5) Å, c = 6.3337(4) Å, α = 97.70 (1)°, β = 97.21(1)°, γ = 108.77(1)°, D_x = 2.124 g/cm³, Rp = 0.045, R_B = 0.095 (757 independent reflections). H atoms were placed geometrically and their position optimized by DFT calculation. The repeating structural unit is the chain [Ni(1)O₆]₂Ni(2)O₆, consisting of two edges sharing octahedrons related by the symmetry center and linked via μ3-OH to a vertex of Ni(2) octahedron. The Ni(1) coordination is ensured by two oxygen atoms from two water molecules, two OH and two oxygen atoms from carboxylate groups. The linkage of the chains by the tp anions forms infinite layers parallel to the (010) planes. Interchain hydrogen bonds between the water molecules coordinating the metal ensure the cohesion of the 2D structure. The structural and magnetic properties are compared with that of the 3D fumarate-based compound [Ni₃(OH)₂(fum)₂(H₂O)₄]·2H₂O (fum = C₄H₂O₄²⁻).     

Copper(II)-methylmalonate complexes with unidentate N-donor ligands: Syntheses,structural characterization and magnetic properties

Two new methylmalonate-bridged copper(II) complexes with the formulas [Cu(3-Ipy)(Memal)(H₂O)] (1) and [Cu(2,4′-bpy)(Memal)(H₂O)] · 3H₂O (2) [Memal = methylmalonate dianion, 3-Ipy = 3-iodopyridine, 2,4′-bpy = 2,4′-bipyridine] have been synthesized and characterized by X-ray diffraction. Both compounds crystallize in the monoclinic space group P2₁/n and Z = 4, with unit cell parameters a = 8.5874(13) Å, b = 7.1738(14) Å, c = 19.093(5) Å, β = 99.509(15)° in 1 and a = 17.375(4) Å, b = 7.3305(14) Å, c = 14.247(3) Å, β = 111.409(15)° in 2. The structures of 1 and 2 consist of zigzag chains of anti-syn carboxylate-bridged copper(II) ions running along the b direction. The pyridine-like ligands occupy one equatorial position of the copper environment avoiding the formation of the sheet-like arrangement observed in previously reported Memal complexes. The chains are grouped together in hydrophilic layers through hydrogen bonds and the layers are pillared through the 3-Ipy (1) and 2,4′-bpy (2) ligands which are stacked through π–π interactions involving alternatively aromatic ligands from two adjacent chains. Magnetic susceptibility measurements of both compounds in the temperature range 2–290 K show the occurrence of intrachain ferromagnetic interactions between the copper(II) ions [J = +2.66(2) cm^?1 (1) and J = +2.62(2) cm^?1 (2)].     

The removal of uranium (VI) from aqueous solutions onto natural sepiolite

The adsorption of uranium (VI) from aqueous solutions onto natural sepiolite has been studied using a batch adsorber. The parameters that affect the uranium (VI) sorption, such as contact time, solution pH, initial uranium(VI) concentration, and temperature, have been investigated and optimized conditions determined. Equilibrium isotherm studies were used to evaluate the maximum sorption capacity of sepiolite and experimental results showed this to be 34.61 mg · g^?1. The experimental results were correlated reasonably well by the Langmuir adsorption isotherm and the isotherm parameters (Q_o and b) were calculated. Thermodynamic parameters (ΔH° = ?126.64 kJ · mol^?1, ΔS° = ?353.84 J · mol^?1 · K^?1, ΔG° = ?21.14 kJ · mol^?1) showed the exothermic heat of adsorption and the feasibility of the process. The results suggested that sepiolite was suitable as sorbent material for recovery and adsorption of uranium (VI) ions from aqueous solutions.     

Synthesis and characterization of three Cu(II), Zn(II), Cd(II) supramolecular complexes bridged by biphenyl 2,2′-dicarboxylate

Three complexes, M₂(bpy)₂(bpdc)₂·xH₂O [M = Cu, x = 0; M = Zn or Cd, x = 2], have been hydrothermally synthesized by 1,1′-biphenyl-2,2′-dicarboxylic acid (H₂bpdc) with 2,2′-bipyridine (bpy) to form binuclear molecules. In each, the two bpdc groups align the two opposing planar [M(bpy)]²⁺ cations. The molecules are connected by C–H⋯O hydrogen bonds, π–π stacking, and C–H⋯π interactions to form three dimensional supramolecular networks. Furthermore, at room temperature, complex 3 exhibits strong photoluminescence.     

Synthesis,crystal structure and standard molar enthalpy of formation of bis(trans-bis(N,N-dimethyl-(1-(R)-phenyl-2-(S)-methyl-2-aminoethoxy-N,O))-copper(II)) heptahydrate

A novel complex, bis(trans-bis(N,N-dimethyl-(1-(R)-phenyl-2-(S)-methyl-2-aminoethoxy-N,O))-copper(II)) heptahydrate (abbreviated as Cu₂(C₁₁H₁₆NO)₄·7H₂O(cr)), was synthesized by the method of liquid phase reflux. The composition and structure of the complex were characterized by chemical analysis, elemental analysis, FTIR, and X-ray crystallography. A reasonable thermochemical cycle was designed based on the preparation reaction of the coordination compound, and standard molar enthalpies of dissolution of reactants and products were measured by an isoperibol solution-reaction calorimeter. Finally, the standard molar enthalpy of formation of the complex Cu₂(C₁₁H₁₆NO)₄·7H₂O(cr) was determined to be ?(4525.22 ± 13.71) kJ · mol^?1 in accordance with Hess’s law.     

Two coordination polymers of manganese(II) isophthalate and their preparation,structures, and magnetic properties

Two manganese coordination polymers, [Mn₂(ip)₂(dmf)]·dmf (1) and [Mn₄(ip)₄(dmf)₆]·2dmf (2) (ip=isophthalate; dmf=N,N-dimethylformamide), have been synthesized and characterized. X-ray crystal structural data reveal that compound 1 crystallizes in triclinic space group P?1, a=9.716(3) Å, b=12.193(3) Å, c=12.576(3) Å, α=62.19(2)°, β=66.423(17)°, γ=72.72(2)°, Z=2, while compound 2 crystallizes in monoclinic space group Cc, a=19.80(3) Å, b=20.20(2) Å, c=18.01(3) Å, β=108.40(4)°, Z=4. Variable-temperature magnetic susceptibilities of compounds 1 and 2 exhibit overall weak antiferromagnetic coupling between the adjacent Mn(II) ions.     

Synthesis,crystal structure,and magnetic properties of K4Mn3(HPO4)4(H2PO4)2

A new layered compound, K₄Mn₃(HPO₄)₄(H₂PO₄)₂ (1), has been synthesized under hydrothermal conditions. It crystallizes in the monoclinic space group P2₁/n with a = 8.874(2) Å, b = 6.554(1) Å, c = 18.075(4) Å, and β = 93.39(3)°. The structure consists of zigzag [Mn₃O₁₄]_n chains of edge-sharing MnO₆ octahedrons and MnO₇ pentagonal bi-pyramids, which form layers of formula [Mn₃(HPO₄)₄(H₂PO₄)₂]^4? in the ab plane via H₂PO₄ and HPO₄ units with vertex-sharing. Potassium ions lie between these layers. Magnetic measurements indicate Curie–Weiss behavior above 6 K for 1. A Heisenberg model, with alternating exchange interactions J₁J₁J₂… within the chain and exchange interactions J₃J₃… between the chains, is proposed to describe the magnetic behavior.     

Thermal reactivity of cis- and trans-bis(triphenylgermyl)bis(tertiary phosphine)platinum(II)

The complex cis-Pt(Ph₃Ge)₂(PMe₂Ph)₂ underwent smooth isomerization to give the trans-isomer at room temperature via an associative five-coordinated intermediate. Thermodynamic parameters and activation energy for the cis to trans isomerization were obtained, ΔH^# = 105 kJ mol⁻¹, ΔS^# = 12.5 J mol⁻¹ K⁻¹, and Ea = 107 kJ mol⁻¹, respectively. Heating of trans-Pt(Ph₃Ge)₂(PMe₂Ph)₂ at 50 °C for 36 days produced trans-PtPh(Ph₃Ge)(PMe₂Ph)₂ followed by the formation of trans-PtPh₂(PMe₂Ph)₂, Pt(PMe₂Ph)₄, and Ph₄Ge finally via elimination of the phenyl group from Ph₃Ge ligand with liberation of the Ph₂Ge unit and subsequent reductive elimination of the remaining Ph₃Ge ligand at 80 °C for 1 month.     

Isothermal titration calorimetric and spectroscopic studies on (alcohol + salt) induced partially folded state of α-lactalbumin and its binding with 8-anilino-1-naphthalenesulfonic acid

Interaction of 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) and isopropanol in the presence of equimolar quantities of guanidine thiocyanate (GndSCN) with bovine α-lactalbumin (α-LA) has been investigated by using a combination of isothermal titration calorimetry, circular dichroism, fluorescence, and ultra-violet spectroscopies at in 20 · 10^?3 mol · dm^?3 phosphate buffer pH 7.0. All the thermal unfolding transitions, in the presence of both the (alcohol + salt) mixtures were found to be reversible as judged by the same values of absorbance observed at different temperatures during cooling after the completion of thermal unfolding. In the presence of the 0.25 mol · dm^?3 (HFIP + GndSCN) equimolar mixture and 0.85 mol · dm^?3 (isopropanol + GndSCN) equimolar mixture, α-lactalbumin was observed to be in the partially folded state with significant loss of native tertiary structure. Intrinsic fluorescence results, acrylamide and potassium iodide quenching, 8-anilino-1-naphthalenesulfonic acid (ANS) binding, and energy transfer results also corroborate the presence of partially folded states of α-lactalbumin. Apart from the generation of the partially folded states, it was also observed that destabilizing action of GndSCN is reduced in the presence of isopropanol compared to that in HFIP. Isothermal titration calorimetry has been used to characterize the energetics of ANS binding to the partially folded states of the protein. ITC results indicate that ANS binds to these partially folded states at pH 7.0 due to the presence of two sequentially binding sites on the protein under the solvent conditions employed. For example, ANS binds to the 0.25 mol · dm^?3 (HFIP + GndSCN) induced partially folded state with affinity constants K₁ = (858 ± 220), K₂ = (1.12 ± 0.25) · 10³; enthalpies of binding ΔH₁ = (4.4 ± 1.0) kJ · mol^?1, ΔH₂ = (2.1 ± 0.2) kJ · mol^?1; and entropies of binding ΔS₁ = 70 J · K^?1 · mol^?1 and ΔS₂ = 65 J · K^?1 · mol^?1, respectively at these two sequential binding sites. In light of the fluorescence results, possible binding sites where ANS can bind to the protein have also been suggested.