Syntheses, crystal structures and luminescent properties of two novel lanthanide/4-pya complexes: [Ln(4-pya)3(H2O)2]2 (Ln = Eu, La; 4-pya = trans-4-pyridylacrylate)

Reactions of Ln₂O₃ and trans-4-pyridylacrylic acid (4-Hpya) in EtOH/H₂O or MeOH/H₂O produced two new lanthanide/4-pya complexes [Ln(4-pya)₃(H₂O)₂]₂ (1: Ln = Eu; 2: Ln = La) in low yields. However, reactions of LnCl₃ · 6H₂O with 4-Hpya/aqueous ammonia in EtOH/H₂O or MeOH/H₂O gave rise to 1 or 2 in higher yields. Both compounds were structurally characterized by elemental analysis, IR spectroscopy and X-ray analysis. Compounds 1 · 2EtOH · 2H₂O and 2 · 2MeOH · 2H₂O were confirmed to possess one-dimensional polymeric chain structures. In the structure of 1, each Eu(III) adopts a monocapped square-antiprism coordination geometry and each dimer [Eu(4-pya)₃(H₂O)₂]₂ within the chain is interconnected by two pairs of different bridging 4-pya ligands. On the other hand, each La(III) of 2 takes a bicapped square-antiprism coordination geometry and each dimer [La(4-pya)₃(H₂O)₂]₂ within the chain is linked by two pairs of tridentate bridging 4-pya ligands. The luminescent properties of 1 and 2 in the solid state were investigated.     

New 4,5-dichlorophthalhydrazidate-bridged chained coordination polymers

The hydrothermal self-assemblies of Pb²⁺/Cd²⁺ salt, 4,5-dichlorophthalic acid (dcpha), N₂H₄·H₂O together with 1,10-phenanthroline·H₂O (phen) or 2,2′-bipyridine (bpy) generated two new monoacylhydrazidate-bridged 1-D chained coordination polymers [Pb₂(DCPTH)₄(phen)₂] 1 and [Cd₃(DCPTH)₂(dcph)₂(bpy)₂] 2 (DCPTH=4,5-dichlorophthalhydrazidate, dcph=4,5-dichlorophthalate). The monoacylhydrazidate ligand DCPTH originated from the hydrothermal in situ acylation reaction between dcpha and N₂H₄·H₂O. In compound 1, two types of coordination modes for DCPTH are found, which link alternately the Pb(II) centers into a 1-D chain structure of compound 1 with ancillary phen molecules. In compound 2, DCPTH and dcph as the mixed bridges extend the Cd(II) centers into a 1-D chain structure of compound 2 with auxiliary bpy molecules. DCPTH in compound 2 shows a different coordination mode from those observed in compound 1.     

In situ benzene-1,4-disulfonate ligand synthesis and electric conductivities of four silver 4-sulfobenzoate or benzene-1,4-disulfonate complexes

The reaction of 4,4′-bipyridine (bipy), AgNO₃ and 4-sulfobenzoate (4-sb) led to an unprecedented complex, {[Ag₂(4,4′-bipy)₂(H₂O)₂]·(1,4-bds)·(2H₂O)}_n (1), in which benzene-1,4-disulfonate (1,4-bds) was synthesized in situ. This does not happen in the similar 1,2-bis(4-pyridyl)ethylene (bpe) system, where the complex {[Ag₂(bpe)₂(H₂O)₂]·(4-sb)·3H₂O}_n (2) is formed. The same in situ reaction occurred when triphenylphosphine (PPh₃) was added into the bipy and silver reaction solution, resulting in the complex [Ag₂(PPh3)₄(1,4-bds)]. 2DMF (3). Complex 4, {[Ag₂(Ph₃P)₂(4-sb)(H₂O)]·(H₂O)}_n, was synthesized similar to the synthesis of complex 3, without the presence of 4,4′-bipyridine. Complexes 1-4 were characterized by single-crystal X-ray analyses, elemental analyses, IR spectra, TG analyses, fluorescence studies and electric conductivity. Complexes 1 and 2 are cation-anion species. Complexes 3 and 4 are silver triphenylphosphine complexes, where the phenyl embrace interactions play important roles. In 3, the six-fold phenyl embrace (6PEs) connect the molecules into a 1-d hybrid zig-zag infinite chain. Complex 4 is a one-dimensional branch-like polymer containing a 1-d necklace-like backbone made up of an [Ag₂(4-sb)(H₂O)] unit and PPh₃ ‘‘leaves”. Two new coordination modes for the 1,4-bds ligands and one for the 4-sb ligand are observed. Complexes 1-3 are semi-conductors, while complex 4 is an insulator.     

The tunable coordination architectures of a flexible multicarboxylate N-(4-carboxyphenyl)iminodiacetic acid via different metal ions, pH values and auxiliary ligand

{[Pb₃(CPIDA)₂(H₂O)₃]·H₂O}_n1, {[Cd₃(CPIDA)₂(H₂O)₄]·5H₂O}_n2, [Cd(HCPIDA)(bpy)(H₂O)]_n3 (bpy=4,4′-bipyridine) and {[Co₃(CPIDA)₂(bpy)₃(H₂O)₄]·2H₂O}_n4 were synthesized with N-(4-carboxyphenyl) iminodiacetic acid (H₃CPIDA). In 1, the CPIDA³⁻ ligands adopt chelating and bridging modes with Pb(II) to possess a 3D porous framework. In 2D-layer 2, the CPIDA³⁻ ligands display a simple bridging mode with Cd(II). The 2D layers have parallelogram-shaped channels along a axis. With bpy ligands, the HCPIDA²⁻ ligands in 3 show more abundant modes, but 3 still displays a 2D sheet on bc plane for the unidentate bpy molecules. However, in 3D-framework 4, the bpy ligands adopt bridging bidentate at a higher pH value and the CPIDA³⁻ ligands show bis-bidentate modes with Co(II). Additionally, 2D correlation analysis of FTIR was introduced to ascertain the characteristic adsorptions location of the carboxylate groups with different coordination modes in 4 with thermal and magnetic perturbation. Compounds 1, 2 and 4 exhibit the fluorescent emissions at room temperature.     

A series of 2D lanthanide (III) coordination polymers constructed from 2-(pyridin-3-yl)-1H-imidazole-4,5-dicarboxylate

Reactions of 2-(pyridine-3-yl)-1H-4,5-imidazoledicarboxylic acid (H₃PyIDC) with a series of Ln(III) ions affords ten coordination polymers, namely, {[Ln(H₂PyIDC)(HPyIDC)(H₂O)₂]·H₂O}_n [Ln=Nd (1), Sm (2), Eu (3) and Gd (4)], {[Ln(HPyIDC)(H₂O)₃]·(H₂PyIDC)·H₂O}_n [Ln=Gd (5), Tb (6), Dy (7), Ho (8) and Er (9)], and {[Y₂(HPyIDC)₂(H₂O)₅]·(bpy)·(NO₃)₂·3H₂O}_n (10) (bpy=4,4′-bipyridine). They exhibit three types of networks: complexes 1-4 are isomorphous coordination networks containing neutral 2D metal-organic layers, while complexes 5-9 are isomorphous, which consist of cationic metal-organic layers and anionic organic layers, and complex 10 is a 2D network built up from 4-connected HPyIDC²⁻ anion and 4-connected Y(III) ions. In addition, thermogravimetric analyses and solid-state luminescent properties of the selected complexes are investigated. They exhibit intense, characteristic emissions in the visible region at room temperature.     

Complexes derived from the copper(II)/succinamic acid/N,N′,N″-chelate tertiary reaction systems: Synthesis,structural and spectroscopic studies

The use of succinamic acid (H₂sucm) in Cu^II/N,N′,N″-donor [2,2′:6′,2″-terpyridine (terpy), 2,6-bis(3,5-dimethylpyrazol-1-yl)pyridine (dmbppy)] reaction mixtures yielded compounds [Cu(Hsucm)(terpy)]_n(ClO₄)_n (1), [Cu(Hsucm)(terpy)(MeOH)](ClO₄) (2), [Cu₂(Hsucm)₂(terpy)₂](ClO₄)₂ (3), [Cu(ClO₄)₂(terpy)(MeOH)] (4), [Cu(Hsucm)(dmbppy)]_n(NO₃)_n·3nH₂O (5^.3nH₂O), and [CuCl₂(dmbppy)]·H₂O (6·H₂O). The succinamate(−1) ligand exists in four different coordination modes in the structures of 1–3 and 5, i.e., the μ₂-κO:κO′:κO″ in 1 and 5 which involves asymmetric chelating coordination of the carboxylato group and ligation of the amide O-atom leading to 1D coordination polymers, the μ₂-κ²O:κO′ in 3 which involves asymmetric chelating and bridging coordination of the carboxylato group, and the asymmetric chelating mode in 2. The primary amide group, either coordinated in 1 and 5, or uncoordinated in 2 and 3, participate in hydrogen bonding interactions, leading to interesting crystal structures. Characteristic IR bands of the complexes are discussed in terms of the known structures and the coordination modes of the Hsucm⁻ ligands. The thermal decomposition of complex 5·3nH₂O was monitored by TG/DTG and DTA measurements.     

Synthesis, crystal structure, and property of one- and two-dimensional complexes based on paradodecatungstate-B cluster

Three polyoxotungstates, Na₈[Cu(H₂O)₂(H₂W₁₂O₄₂)]·30H₂O (1), Na₈[Cd(H₂O)₂(H₂W₁₂O₄₂)]·20H₂O (2), and Na_7.4[Cd_1.3(H₂O)₂(H₂W₁₂O₄₂)]·24H₂O (3), were synthesized and characterized by elemental and thermogravimetric (TG)analysis, infrared spectroscopy and X-ray single-crystal analysis. Both complexes 1 and 2 exhibit one-dimensional structure with two neighboring paradodecatungstate-B clusters, [H₂W₁₂O₄₂]¹⁰⁻, linked by [Cu(H₂O)₂]²⁺ or [Cd(H₂O)₂]²⁺ units, while complex 3 displays a two-dimensional network structure. The electrochemical behaviors of complexes 1 and 3 were investigated in the buffer solution of pH 4.8. The results of electrocatalysis reveal that the reduced species of complexes 1 and 3 are electrocatalytically active for the reduction of nitrite. Complex 1 exhibits the electrocatalytic activity for the reduction of nitrate as well. The surface photovoltage spectroscopy (SPS) and electric field-induced SPS (EFISPS) measurements show that the surface photovoltage behavior of complex 1 is complicated while complex 3 bears the property of n-type semiconductor.     

Synthesis and properties of novel 5-(cyclohepta-2′,4′,6′-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-triones: methodology for synthesizing cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates

Novel condensation reaction of tropone with N-substituted and N,N′-disubstitued barbituric acids in Ac₂O afforded 5-(cyclohepta-2′,4′,6′-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (8a-f) in moderate to good yields. The ¹³C NMR spectral study of 8a-f revealed that the contribution of zwitterionic resonance structures is less important as compared with that of 8,8-dicyanoheptafulvene. The rotational barriers (ΔG^‡) around the exocyclic double bond of mono-substituted derivatives 8a-c were obtained to be 14.51-15.03 kcal mol⁻¹ by the variable temperature ¹H NMR measurements. The electrochemical properties of 8a-f were also studied by CV measurement. Upon treatment with DDQ, 8a-c underwent oxidative cyclization to give two products, 7 and 9-substituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates (11a-c·BF₄⁻ and 12a-c·BF₄⁻) in various ratios, while that of disubstituted derivatives 8d-f afforded 7,9-disubstituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborate (11d-f·BF₄⁻) in good yields. Similarly, preparation of known 5-(1′-oxocycloheptatrien-2′-yl)-pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (14a-d) and novel derivatives 14e,f was carried out. Treatment of 14a-c with aq. HBF₄/Ac₂O afforded two kinds of novel products 11a-c·BF₄⁻ and 12a,c·BF₄⁻ in various ratios, respectively, while that of 14d-f afforded 11d-f. The product ratios of 11a-c·BF₄⁻ and 12a-c·BF₄⁻ observed in two kinds of cyclization reactions were rationalized on the basis of MO calculations of model compounds 20a and 21a. The spectroscopic and electrochemical properties of 11a-f·BF₄⁻ and 12a-c·BF₄⁻ were studied, and structural characterization of 11c·BF₄⁻ based on the X-ray crystal analysis and MO calculation was also performed.     

Preparation of three terbium complexes with p-aminobenzoic acid and investigation of crystal structure influence on luminescence property

Three new rare earth p-aminobenzoic acid complexes, [Tb₂L₆(H₂O)₂]_n (1), [Tb₂L₆(H₂O)₄]·2H₂O (2) and [Tb(phen)₂L₂(H₂O)₂](phen)L·4H₂O (3) (HL: p-aminobenzoic acid; phen: 1, 10-phenanthroline), with different structural forms are reported in this paper. Complex 1 is a polymolecule with a two-dimensional plane structure. Compound 2 is a binuclear molecule, and 3 appears to be a mononuclear complex. The fluorescence intensity, the fluorescence life-time and emission quantum yield of 2, which has two coordination water molecules, is better than those of 1, which has only one coordination water molecule. This is an unusual phenomenon for general fluorescent rare earth complexes. The fluorescence performance of 3 is the most unsatisfactory among the three complexes. Their crystal structures show that the coordination mode of the ligand is an important factor influencing the luminescence properties of a fluorescent rare earth complex.     

Exploring the reactivity of an N-pyrazole, P-phosphine hybrid ligand with Cu(I), Ag(I) and Au(I) precursors

The reactivity of (3,5-dimethyl-1H-pyrazol-1-yl)ethyldiphenylphosphine (L) hybrid ligand against Cu(I), Ag(I) and Au(I) has been assayed and compounds [Cu(L)₂](PF₆) (1), [Ag(L)]₂(PF₆)₂·2C₂H₄Cl₂·2C₄H₁₀O (2) and [AuCl(L)]₂ (3) have been isolated and fully characterised. A fully characterisation by analytical and spectroscopic methods of 1-3 are presented and X-ray crystal structures of 1 and 2 are also reported. The similar data obtained between 2 and 3 permits to do a serious purpose of the structure of 3 in solid and solution.     

Syntheses,crystal structures,and magnetic and luminescent properties of a series of lanthanide coordination polymers with chelidamic acid ligand

A series of lanthanide(III) complexes with chelidamic acid ligand, [Ln(C₇H₂NO₅)·3H₂O]_n·nH₂O (Ln = La (1), Y (2), Sm (3), and Nd (4)), [Gd₂(C₇H₂NO₅)₃·4H₂O]_n·2nH₂O (5) and [Ce(C₇H₂NO₅)·1.5H₂O]_n (6), have been synthesized by hydrothermal method and structurally characterized by single-crystal X-ray diffraction. Complexes 1–4 are isostructural and possess 2D framework. Complex 5 contains two different Gd(III) ions linked through carboxylate group to form a 2D framework. Complex 6 exhibits a (4⁴) topology 2D network. The variable-temperature magnetic properties of 3 and 5 have been investigated. Furthermore, the photoluminescent properties of 1, 2, 3, and 5 at room temperature were also studied.     

Assembly of silver(I) coordination polymers incorporating pyromellitic acid and N-heterocyclic ligands

Five mixed ligands coordination polymers [Ag₄(apym)₂(pma)·(H₂O)₂]_n (1), {[Ag₄(dmapym)₄(pma)·(H₂O)₂]·(H₂O)₆}_n (2), [Ag₂(apyz)₂(H₂pma)·(H₂O)₄]_n (3), {[Ag₄(apyz)₂(pma)·(H₂O)₂]·(H₂O)₂}_n (4) and [Ag₄(NH₃)₈(pma)·(H₂O)₆]_n (5) (apym = 2-aminopyrimidine, dmapym = 4, 6-dimethyl-2-aminopyrimidine, apyz = 2-aminopyrazine, H₄pma = pyromellitic acid) were synthesized and characterized. For 1 and 2, as the substituents change from H to methyl, the dimensions of 1–2 decrease from three-dimension (3D) to one-dimension (1D) due to the steric effect of methyl groups. For 3 and 4, as the ratios of Ag₂O/apyz/pma vary from 1:1:1 to 2:1:1, the structure of 3 is a 1D ladder structure built from Ag-apyz double chains and pma anions, while the structure of 4 is a two-dimension (2D) grid. As excess ammonia is added to above four reaction systems, the structure of 5 contains unprecedented {[Ag(NH₃)₂]⁺}_n chains and pma anions. The substituent on the pyrimidyl ring, ratios of reactants, solvent systems and ligand isomers intensively influence the coordination environments of metal ion and the coordination modes of the carboxyl group, and thus determine the structures of the coordination polymers. The photoluminescent properties of 1–5 were also investigated.     

Syntheses, structures and photoluminescence of a series of coordination frameworks based on dicarboxylate anion and bis(imidazole) ligand

In this article, ten new coordination frameworks, namely, [Ni(H₂O)₆]·(L3) (1), [Zn(L3)(H₂O)₃] (2), [Cd(L3)(H₂O)₃]·5.25H₂O (3), [Ag(L1)(H₂O)]·0.5(L3) (4), [Ni(L3)(L1)] (5), [Zn(L3)(L1)_0.5]·H₂O (6), [Cd(L3)(L1)_0.5(H₂O)] (7), [CoCl(L3)_0.5(L1)_0.5] (8), [ZnCl(L3)_0.5(L2)_0.5] (9), and [CoCl(L3)_0.5(L2)_0.5] (10), where L1 = 1,1′-(1,4)-butanediyl)bis(imidazole), L2 = 1,1′-(1,4-butanediyl)bis(2-ethylbenzimidazole) and H₂L3 = 3,3′-(p-xylylenediamino)bis(benzoic acid), have been synthesized by varying the metal centers and nitrogen-containing secondary ligands. These structures have been determined by single-crystal X-ray diffraction analyses, elemental analyses and IR spectra. In 1, the L3 anion is not coordinated to the Ni(II) center as a free ligand. The Ni(II) ion is coordinated by water molecules to form the cationic [Ni(H₂O)₆]²⁺ complex. The hydrogen bonds between L3 anions and [Ni(H₂O)₆]²⁺ cations result in a three-dimensional (3D) supramolecular structure of 1. In compounds 2 and 3, the metal centers are linked by the organic L3 anions to generate 1D infinite chain structures, respectively. The hydrogen bonds between carboxylate oxygen atoms and water molecules lead the structures of 2 and 3 to form 3D supramolecular structures. In 4, the L3 anion is not coordinated to the Ag(I) center, while the L1 ligands bridge adjacent Ag(I) centers to give 1D Ag-L1 chains. The hydrogen bonds among neighboring L3 anions form infinite 2D honeycomb-like layers, in the middle of which there exist large windows. Then, 1D Ag-L1 chains thread in the large windows of the 2D layer network, giving a 3D polythreaded structure. Considering the hydrogen bonds between the water molecules and L3 anions, the structure is further linked into a 3D supramolecular structure. Compounds 5 and 7 were synthesized through their parent compounds 1 and 3, respectively, while 6 and 9 were obtained by their parent compound 2. In 5, the L3 anions and L1 ligands connect the Ni(II) atoms to give a 3D 3-fold interpenetrating dimondoid topology. Compound 6 exhibits a 3D three-fold interpenetrating α-Po network structure formed by L1 ligands connecting Zn-L3 sheets, while compound 7 shows a 2D (4,4) network topology with the L1 ligands connecting the Cd-L3 double chains. In compound 8, the L1 ligands linked Co-L3 chains into a 2D layer structure. Two mutual 2D layers interpenetrated in an inclined mode to generate a unique 3D architecture of 8. Compounds 9 and 10 display the same 2D layer structures with (4,4) network topologies. The effects of the N-containing ligands and the metal ions on the structures of the complexes 1-10 were discussed. In addition, the luminescent properties of compounds 2-4, 6, 7 and 9 were also investigated.     

Anion effect on the construction of copper(II) coordination polymers with the twisted ligand bis(4-pyridylthio)methane

The reaction of CuSO₄ · H₂O with 4-bpytm [4-bpytm = bis(4-pyridylthio)methane] in EtOH afforded the complex [Cu(SO₄)(4-bpytm)(H₂O)₃] · H₂O (1 · H₂O) while the reaction of 4-bpytm with Cu(NO₃)₂ · 3H₂O in EtOH afforded the complex [Cu(NO₃)₂(4-bpytm)₂] · H₂O (2 · H₂O). The reaction of 4-bpytm with Cu(NO₃)₂ · 3H₂O in EtOH/dmf under microwave irradiation afforded the pseudo-polymorph [Cu(NO₃)₂(4-bpytm)₂] · Solv (2 · Solv). Compound 1 · H₂O forms helical chains while compounds 2 · H₂O and 2 · Solv are 2D coordination polymers with a (4,4) topology based on rhombic grids in 2 · H₂O and on a parquet motif in 2 · Solv. The 3D supramolecular organization through hydrogen bonding is analyzed for the three compounds and their thermal behaviour was also investigated.     

Architecture of zero-, one-, two- and three-dimensional structures based on metal ions and pyrazine-2,6-dicarboxylic acid

Six new complexes: [Ln₂(pzda)₃(H₂O)₂] · 2.5H₂O (Ln = Nd, (1); Eu, (2)), [Co(pzda) (bpe)] · 0.125(bpe) · 1.75H₂O (3), [Mn(pzda)(H₂O)_1.5] (4), [Co₂(pzda)₂(bpe)(H₂O)₄] · 0.5(CH₃OH) · H₂O (5) and [Co(pzda)(2,2′-bpy)(H₂O)] · 0.5H₂O (6) (H₂pzda = pyrazine-2,6-dicarboxylic acid, bpe = 1,2-bis(4-pyridyl)ethane, 2,2′-bpy = 2,2′-bipyridine) were obtained from metal salts and H₂pzda under hydro(solvo)thermal conditions. The single crystal X-ray structural analysis reveals that the title complexes have different structures, ranging from zero- to three- dimensions, which are mainly due to the different metal ions, and especially the coordination modes of the pzda ligands. Complexes 1 and 2 have 3D metal-organic frameworks containing a 1D tri-strand array, in which the pzda ligand adopts a pentadentate mode to link lanthanide ions. Complex 3 has a 2D metal-organic framework, in which the pzda ligand acts in a tetradentate mode to connect Co(II) ions into 1D chains, which are further connected by bpe spacers into a 2D framework. While in 4, both of the two carboxylate groups of the pzda ligand adopt μ₂-O bridging modes to link Mn(II) ions into a 1D coordination polymer, which is further assembled into a 2D supramolecular network containing double-stranded hydrogen-bonded helical chains. In both 5 and 6, the pzda ligand binds metal ions as a tridentate ligand (ONO mode) to form zero dimensional structures. Complex 5 is a binuclear molecule, while 6 is a mononuclear complex, which can be attributed to the bridging ligand bpe for 5 and the terminal auxiliary ligand 2,2′-bpy for 6.     

Syntheses and characterizations of nine coordination polymers of transition metals with carboxylate anions and bis(imidazole) ligands

Nine new compounds, namely [CuL1(biim-6)] · H₂O (1), [ZnL1(biim-6)] · H₂O (2), [MnL1(biim-6)] · H₂O (3), [MnL1(biim-4)] (4), [Co₂(L2)₂(biim-5)₃ · 6H₂O] · 8H₂O (5), [ZnL3(biim-6)] (6), [ZnL3(biim-5)] (7), [CdL3(biim-5) · 1.5H₂O] · 0.5H₂O (8) and [CdL4(biim-6) · 2H₂O] (9) [where L1 = oxalate anion, L2 = fumarate anion, L3 = phthalate anion, L4 = p-phthalate anion, biim-4 = 1,1′-(1,4-butanediyl)bis(imidazole), biim-5 = 1,1′-(1,5-pentanedidyl)bis(imidazole) and biim-6 = 1,1′-(1,6-hexanedidyl)bis(imidazole)] were successfully synthesized. Compounds 1–3 are isostructural, and display 2D polymeric structures. Compound 4 shows a threefold interpenetrating diamondoid framework. In compound 5, the anions act as counterions, and the metal cations are bridged by bis(imidazole) ligands to form 1D polymeric chains. Compounds 6–9 show 2D polymeric structures. The magnetic properties for 1, 3 and 4 and luminescent properties for 2 and 6–9 are discussed. Thermogravimetric analyses (TGA) for these compounds are also discussed.     

Modelling the use of lanthanides(III) as probes at calcium(II) binding sites in biological systems: Preparation and characterization of neodymium(III) and calcium(II) malonamato(-1) complexes

A bioinorganic approach into the problem of the isomorphous substitution of calcium(II) by lanthanide(III) ions in biological systems is discussed. Reactions of malonamic acid (H₂malm) with Ca^II and Nd^III sources under similar conditions yielded the compounds [Ca(Hmalm)₂]_n (1), [Nd(Hmalm)₂(H₂O)₂]_n(NO₃)_n (2) and [Nd(Hmalm)₂(H₂O)₂]_nCl_n·2nH₂O (3·2nH₂O). Their X-ray crystal structure data show that the malonamate(-1) ligand presents two different ligation modes and coordinates through the two carboxylate and the amide-O atoms, thus bridging three Ca^II ions in 1 and two Nd^III ions in 2 and 3·2nH₂O. Complex 1 is a 3D coordination polymer based on neutral repeating units, whereas 2 and 3·2nH₂O are 1D coordination polymers based on the same cationic repeating unit. Hydrogen bonding interactions further stabilize the 3D framework structure of 1 and assemble the 1D chains of 2 and 3·2nH₂O into 3D networks. The three complexes were characterized spectroscopically (IR, far-IR, and Raman) and the thermal decomposition of 2 and 3·2nH₂O was monitored by TG/DTA and TG/DTG measurements. Variable-temperature magnetic susceptibility data for 2 are also reported. The bioinorganic chemistry relevance of our results is discussed.     

A series of Cd(II) complexes with π-π stacking and hydrogen bonding interactions: Structural diversities by varying the ligands

Seven new Cd(II) complexes consisting of different phenanthroline derivatives and organic acid ligands, formulated as [Cd(PIP)₂(dnba)₂] (1), [Cd(PIP)(ox)]·H₂O (2), [Cd(PIP)(1,4-bdc)(H₂O)]·4H₂O (3), [Cd(3-PIP)₂(H₂O)₂]·4H₂O (4), [Cd₂(3-PIP)₄(4,4′-bpdc)(H₂O)₂]·5H₂O (5), [Cd(3-PIP)(nip)(H₂O)]·H₂O (6), [Cd₂(TIP)₄(4,4′-bpdc)(H₂O)₂]·3H₂O (7) (PIP=2-phenylimidazo[4,5-f]1,10-phenanthroline, 3-PIP=2-(3-pyridyl)imidazo[4,5-f]1,10-phenanthroline, TIP=2-(2-thienyl)imidazo[4,5-f]1,10-phenanthroline, Hdnba=3,5-dinitrobenzoic acid, H₂ox=oxalic acid, 1,4-H₂bdc=benzene-1,4-dicarboxylic acid, 4,4′-H₂bpdc=biphenyl-4,4′-dicarboxylic acid, H₂nip=5-nitroisophthalic acid) have been synthesized under hydrothermal conditions. Complexes 1 and 4 possess mononuclear structures; complexes 5 and 7 are isostructural and have dinuclear structures; complexes 2 and 3 feature 1D chain structures; complex 6 contains 1D double chain, which are further extended to a 3D supramolecular structure by π-π stacking and hydrogen bonding interactions. The N-donor ligands with extended π-system and organic acid ligands play a crucial role in the formation of the final supramolecular frameworks. Moreover, thermal properties and fluorescence of 1-7 are also investigated.     

Solid chemistry of the Zn/1,2,4-triazolate/anion system: Separation of 2D isoreticular layers tuned by the terminal counteranions X (X=Cl, Br, I, SCN)

An array of 2D isoreticular layers, viz. [Zn(atrz)X]_∞ (1·X; X=Cl⁻, Br⁻, I⁻; atrz=3-amino-1,2,4-triazole anion), [Zn₄(atrz)₄(SCN)₄·H₂O]_∞ (1·SCN·H₂O) and [Zn(trz)X]_∞ (2·X; X=Cl⁻, Br⁻, I⁻; trz=1,2,4-triazole anion), have been hydrothermally synthesized and structurally characterized. Compounds 1·X and 1·SCN·H₂O are constructed from binuclear planar Zn₂(atrz)₂ subunits and exhibit (4,4) topological network when the subunits are simplified as four-connected nodes. Based on changing the terminal counteranions X (X=Cl⁻, Br⁻, I⁻, SCN⁻), the average interlayer separations of 1·X and 1·SCN·H₂O are enlarged, which equal to 5.851, 6.153, 6.651 and 8.292 Å, respectively. As a result, H₂O molecules reside in the spaces between two adjacent layers of 1·SCN·H₂O. 2 and 1 are the isomorphous structures. In common with 1, the interlayer separations of 2·X are widened with increasing the ion radius. Solid-state luminescence properties and thermogravimetric analyses of 1 and 2 were investigated, respectively.     

Piperazinediium,Zr(IV) and Ce(IV) pyridine-2,6-dicarboxylates: Syntheses,characterizations, crystal structures, ab initio HF,DFT calculations and solution studies

The novel title compounds, (pipzH₂)_1.5(pydcH)₃·3.7H₂O, 1, (pipzH₂)[Zr(pydc)₃]·8H₂O, 2 and (pipzH₂)[Ce(pydc)₃]·8H₂O, 3 in which pydcH₂ is pyridine-2,6-dicarboxylic acid and pipz is piperazine were obtained in aqueous solution. The compounds were characterized by IR, ¹H NMR and ¹³C NMR spectroscopy, elemental analyses, and X-ray crystallography. Compound 1 is resulted from proton transfer between pydcH₂ and pipz. However, compounds 2 and 3 are resulted from complexation of 1 and corresponding metallic salts. Both compounds 2 and 3 contain three pyridine-2,6-dicarboxylate species as tridentate ligands, one piperazinediium as counter ion, and eight-uncoordinated water molecules in the asymmetric unit. In both structures each M(IV) is coordinated in a distorted tricapped trigonal prism geometry by three nitrogen and six oxygen atoms of carboxylate groups of three (pydc)²⁻ fragments. In the crystal structures of 1, 2 and 3, extensive O–H···O, N–H···O and C–H···O hydrogen bonds as well as electrostatic forces, C–H···π, C–O···π and π–π stacking play important roles in stabilizing structures. The geometrical parameters of the [M(pydc)₃]²⁻ anionic complexes, where M = Ce(IV), Zr(IV) have been optimized with the B3LYP method of density functional theory (DFT) and ab initio Hartree–Fock (HF) methods for comparison. In addition, we have studied the structures of (pydc)²⁻ anion and its mono and doubly protonated forms, (pydcH)⁻ and pydcH₂. The electronic properties of the anionic complexes and ligands have been investigated based on the natural bond orbital (NBO) analysis at the B3LYP method which verifies that the synergistic effect has been occurred in the title complexes. In solution study of 2, the stoichiometry and stability constant of complexation of pipz, pydc, pydc–pipz proton transfer system and Zr(IV) ion in aqueous solution were investigated by potentiometric method.