Manganese(II) and zinc(II) compounds via amino acid derivatives: Effects of temperature and solvents

To investigate the influence of temperature and the ratios of solvents on the design and synthesis of metal-organic frameworks (MOFs), we have synthesized and structurally characterized a series of supramolecular assemblies based on different amino acid derivatives and nitrogen-containing heterocyclic ligands, namely [Mn(phen)₂(phth)(H₂O)]·4H₂O (1), [Mn(phen)₂(HL1)₂]·3.5H₂O (2), [Zn(bpp)₂(L-Me)₂] (3), and [Zn(bpp)(L-Me)₂] (4) (H₂phth = phthalic acid, H₂L¹ = phthalyl-l-valine, H₂L = (+)-N-tosyl-l-glutamic acid, phen = 1,10-phenanthroline, bpp = 1,3-bis(4-pyridyl)propane, and L-Me = C₁₂H₁₃NO₆S-CH₃). Compounds 1 and 2, which are assembled through noncovalent interactions, were obtained by controlling the temperature. In 1, π-π stacking and hydrogen-bonding interactions lead to stacking in a 3D supramolecular network, while in 2, π-π stacking interactions form 1D chains that extend along the c-axis. Depending on the solvents employed, compounds 3 and 4 could be generated, with a 1D bpp-connected Zn-bpp-Zn double chain that is further hydrogen-bonded into a 2D network that extends parallel to the ac plane in 3, and a single chain in 4.     

Synthesis and characterization of nickel(II) complexes bearing 2-(imidazol-2-yl)pyridines or 2-(pyridin-2-yl)phenanthroimidazoles/oxazoles and their polymerization of norbornene

Series of 2-R₁-6-(1-R₂-4,5-diphenyl-1H-imidazol-2-yl)pyridine (R₁ = R₂ = H, L1; R₁ = Me, R₂ = H, L2; R₁ = H, R₂ = Me, L3; R₁ = R₂ = Me, L4), 2-(6-R₁-pyridin-2-yl)-1H-phenanthro[9,10-d]imidazole (R₁ = H, L5; R₁ = Me, L6) and 2-(pyridin-2-yl)phenanthro[9,10-d]oxazole (L7) were synthesized and used to prepare their corresponding dihalonickel complexes (C1-C9). All organic compounds and nickel complexes were characterized by elemental and spectroscopic analyses. Molecular structures of C1, C4, C5 and C8 were confirmed by the single-crystal X-ray diffraction analysis. The single-crystal X-ray analysis revealed complex C1 as a distorted octahedral geometry, complex C4 as a distorted square pyramidal geometry, complex C5 as a distorted trigonal bipyramidal configuration, and complex C8 as a tetrahedral geometry. Upon activation with methylaluminoxane (MAO), the nickel complexes showed good activity towards norbornene polymerization through main additional and minor ring-opening metathesis. The reaction parameters such as norbornene concentration, reaction temperature and different coordinate environments caused by the ligands affected their catalytic performances.     

Construction of three low dimensional Zn(II) complexes based on different organic-carboxylic acids

Three new Zn(II) complexes based on different organic-carboxylic acids, [Zn(mba)₂(2,2′-bipy)] (1), [Zn(mpdaH)₂(H₂O)₄] · 4H₂O (2) and [Zn(cda)₂(H₂O)₂]_n (3) (Hmba = 4-methylbenzoic acid, H₂mpda = 2,6-dimethylpyridine-3,5-dicarboxylic acid and H₂cda = chelidonic acid) have been synthesized successfully under hydrothermal conditions. X-ray single crystal diffractions show that compounds 1 and 2 are the mononuclear and 3 is one-dimensional chain, in which the Zn(II) centers have different coordination geometries with octahedron for 1 and 2 and tetrahedron for 3. Through π-π stacking and/or hydrogen bonding (O-H?O and O-H?N) interactions, different supramolecular structures are assembled, namely, 2D supramolecular layer for 1 and 3D supramolecular networks for 2 and 3. Furthermore, the IR, TGA and luminescent properties are also investigated in this work.     

Synthesis, crystal structures and characterization of three novel complexes with N-[2-(2-hydroxybenzylideneamino)ethyl]-4-methyl-benzene-sulfonamide as ligand

Reaction of the N-tosyl-ethylenediamine and salicylaldehyde forms a new sulfonamide Schiff base N-[2-(2-hydroxybenzylideneamino)ethyl]-4-methyl-benzene-sulfonamide (H₂L). Three novel complexes constructed from H₂L, namely, [M(HL)₂] · xH₂O (M = Cu, x = 0 for 1, M = Ni, x = 0 for 2 and M = Zn, x = 1 for 3) have been prepared and characterized via X-ray single-crystal diffraction, elemental analysis, X-ray powder diffraction (XRPD), FT-IR, UV-Vis, TGA and photoluminescence measurements. Complex hydrogen bonds, C-H···π and π-π stacking interactions lead 1-3 to present 1-D, 2-D and 3-D supramolecular architectures, respectively.     

Mononuclear and unsymmetric dinuclear complexes of the tripodal ligand 2-hydroxyethyl-bis(2-{pyrid-2-yl}ethyl)amine

Reaction of bis(2-{pyrid-2-yl}ethyl)amine with 2-bromoethanol in the presence of Na₂CO₃ yields the title ligand, LH. Treatment of LH with the CuBr₂ or Zn(O₂CMe)₂ · 2H₂O yields pure crystalline [CuBr(LH)]Br · H₂O (1 · H₂O) and [Zn₂(O₂CMe)₂(μ-O₂CMe)(μ-L)] (2). Reaction of LH with Cu(O₂CMe)₂ · H₂O affords a low yield of [Cu₂Cl₂(μ-O₂CMe)(μ-L)] (3), the Cl⁻ ligands apparently originating from the CH₂Cl₂ crystallization solvent. Compound 1 · H₂O is a near-regular square-pyramidal complex with a neutral, protonated LH ligand. In contrast, 2 and 3 are both unusual unsymmetric dinuclear complexes, with a five-coordinate [ML(O₂CMe)] (M = Zn or Cu) unit linked to a second metal ion through the deprotonated ligand alkoxide donor and O,O′-bridging acetate ligand.     

Supramolecular isomers of lanthanides(III): Synthesis, crystal structures and luminescent properties

Six lanthanide coordination polymers La₂(1,4-BDOA)₂(OX)(H₂O) (1), Ln₂(1,4-BDOA)₂(OX)(H₂O) [Ln = La (2); Ln = Pr (3); Ln = Sm (4); Ln = Eu (5); Ln = Tb (6)], [BDOA = benzene-1,4-dioxydiacetate; OX = oxalate] had been prepared under hydrothermal conditions, which were characterized by elemental analysis, infrared spectroscopy, thermogravimetric analysis, and single-crystal X-ray diffraction. Compounds 1-6 crystallize in a triclinic system, space group ; compounds 1 and 2 are true structural supramolecular isomers based on BDOA ligands constructed from different acid effects; compounds 2-5 are isostructural and exhibit new 3D 12-connected topological networks, which are the same as the topological structure of 6, while 1 shows another 3D 11-connected topological architecture. Furthermore, the luminescent properties of 5 and 6 were studied.     

Imidazole derivatives of binuclear copper (II) and nickel (II) complexes incorporating bis(1,4,7-triazacyclononan-1-yl) ligands

A series of new binuclear copper (II) and nickel (II) complexes of the macrocyclic ligands bis(1,4,7-triazacyclononan-1-yl)butane (L^but) and bis(1,4,7-triazacyclononan-1-yl)-m-xylene (L^mx) have been synthesized: [Cu₂L^butBr₄] (1), [Cu₂L^but(imidazole)₂Br₂](ClO₄)₂ (2), [Cu₂L^mx(μ-OH)(imidazole)₂](ClO₄)₃ (3), [Cu₂L^but(imidazole)₄](ClO₄)₄ · H₂O (4), [Cu₂L^mx(imidazole)₄](ClO₄)₄ (5), [Ni₂ L^but(H₂O)₆](ClO₄)₄ · 2H₂O (6), [Ni₂L^but(imidazole)₆](ClO₄)₄ · 2H₂O (7) and [Ni₂L^mx (imidazole)₄(H₂O)₂](ClO₄)₄ · 3H₂O (8). Complexes 1, 2, 7 and 8 have been characterized by single crystal X-ray studies. In each of the complexes, the two tridentate 1,4,7-triazacyclononane rings of the ligand facially coordinate to separate metal centres. The distorted square-pyramidal coordination sphere of the copper (II) centres is completed by bromide anions in the case of 1 and/or monodentate imidazole ligands in complexes 2, 4 and 5. Complex 3 has been formulated as a monohydroxo-bridged complex featuring two terminal imidazole ligands. Complexes 6-8 feature distorted octahedral nickel (II) centres with water and/or monodentate imidazole ligands occupying the remaining coordination sites. Within the crystal structures, the ligands adopt trans conformations, with the two metal binding compartments widely separated, perhaps as a consequence of electrostatic repulsion between the cationic metal centres. The imidazole-bearing complexes may be viewed as simple models for the coordinative interaction of the binuclear complexes of bis (tacn) ligands with protein molecules bearing multiple surface-exposed histidine residues.     

Conversion of 2-(aminomethyl) substituted pyridine and quinoline to their dicarbonyldiimides using copper(II) acetate

In air, hydrated ethanolic (95%) solution of 2-(aminomethyl) substituted pyridine and quinoline, on stirring with half equivalent of Cu(OAc)₂·H₂O, respectively afforded [Cu(bpca)(OAc)(H₂O)]·H₂O (1) and [Cu(bqca)(OAc)(H₂O)] (2) {bpca = bis(2-pyridylcarbonyl)diimide ion and bqca = bis(2-quinolylcarbonyl)diimide ion} in good yields. These reactions involve oxidation of the methylene group and formation of the bond between nitrogen and carbon in N-C(O) through coupling. The complex [Cu(pqca)(OAc)(H₂O)]₃[Cu₂(OAc)₄(EtOH)₂]_1.5 (3) {pqca = (2-pyridylcarbonyl)(2-quinolylcarbonyl)diimide ion} was synthesized by stirring an ethanolic solution of the Schiff base [(2-pyridyl)-N-((2-quinolyl)methylene)methanamine] (L1) and with one equivalent of Cu(OAc)₂·H₂O. A plausible mechanism for the conversion has been proposed. The free ligands were isolated as crystalline solids from compounds 1-3, by extrusion of Cu²⁺ ion using EDTA²⁻. The molecular structures of 1-3 and bqcaH were established by X-ray crystallography and compounds having quinolyl group have π-stacking interactions.     

Cobalt(II) coordination polymers assembled from polycarboxylate and benzotriazole: Syntheses, structures and physical properties

Hydrothermal reactions of cobalt(II) salt with H₂CAM or H₂SDBA and HBTA in the presence of NaOH afford two interesting coordination polymers, Co₃(CAM)₂(BTA)₂ (1) and Co₃(SDBA)₂(BTA)₂ (2) (H₂CAM = camphoric acid, H₂SDBA = 4,4′-dicarboxybiphenyl sulfone, HBTA = benzotriazole), both of which have been structurally characterized by single-crystal X-ray, elemental analysis, infrared spectroscopy, and thermogravimetric analysis. Complexes 1 and 2 are isostructural and possess two-dimensional covalent network, comprising an unusual linear Co(II) chains of mixed T_d-O_h-T_d geometries. Temperature-dependent magnetic measurements indicate the existence of antiferromagnetic interactions in both 1 and 2.     

Effect of anions on cadmium(II) complexes with ligand 2-(pyrazin-2-yl)-1H-benzimidazole

Three new supramolecular complexes based on a 2-(pyrazin-2-yl)-1H-benzimidazole (Hpbi) and a series of Cd(II) salts have been solvothermally synthesized and structurally characterized by single-crystal X-ray diffraction analysis. Reaction of CdCl₂·2.5H₂O with Hpbi afforded a one-dimensional chain [Cd(Hpbi)Cl₂] (1), which exhibits a three-dimensional (3-D) supramolecular architecture through intermolecular X-H···Cl (X = N and C) hydrogen bonds and π-π stacking interactions. When using CdBr₂·4H₂O instead of CdCl₂·2.5H₂O under similar reaction conditions, a bisnuclear complex [Cd(Hpbi)₂Br₂] (2) is obtained, which obviously exhibits intermolecular X-H···Br (X = N and C) hydrogen bonds and π-π stacking interactions. When CdI₂ take place of CdCl₂·2.5H₂O, a mononuclear complex, [Cd(Hpbi)₂I₂] (3), is isolated, which shows a 3D supramolecule framework formed by intermolecule hydrogen bonds and π-π packing interactions. Interestingly, the Hpbi ligand exhibits the same coordination modes in complexes 1-3. It is noteworthy that the radius of anions plays an important role in affecting the structures and luminescent intensity of the final products. The TGA for 1-3 have been investigated and discussed in detail.     

A series of 1-D to 3-D metal-organic coordination architectures assembled with V-shaped bis(pyridyl)thiadiazole under co-ligand intervention

Six new coordination polymers based on V-shaped linkage 2,5-bis(4-pyridyl)-1,3,4-thiadiazole (bpt) and transition metal ions, [Co(bpt)(pm)_0.5(H₂O)]_n · 3nH₂O (1), [Cu₂(bpt)(pm)(H₂O)₄]_n (2), [Co(bpt)(pydc)]_n · 2nCHCl₃ · nH₂O (3), [Cu₂(bpt)(pydc)₂(H₂O)₂]_n (4), [Cu₂(bpt)(pydco)₂(H₂O)₂]_n · nH₂O (5) and [Cd(bpt)(pydco)]_n (6) (H₄pm = pyromellitic acid, H₂pydc = pyridine-2,6-dicarboxylic acid, H₂pydco = pyridine-2,6-dicarboxylic acid N-oxide), have been synthesized under the intervention of various polycarboxylate ligands. Complex 1 exhibits a 3-D 4-connected structure with 1-D nanosized open channels encapsulated lots of water molecules. Complex 2 represents a 2-D grid containing two types of rectangular windows. When pydc and pydco instead of pm, complexes 3 and 6 were obtained with highly undulated 2-D layers. The interlayers of 3 are filled with two kinds of solvent molecules, whereas 6 is a double-layered framework without free molecules. Complexes 4 and 5 consist of two distinct 1-D infinite chains held together to form different 2-D supramolecular networks. Importantly, bpt spacer shows changeful conformational geometries and generates complicated crystalline architectures with the introduction of polycarboxylate ligands. Additionally, thermal stability of complexes 1, 3 and 5, fluorescent properties of 6 and X-ray powder diffraction of 1 have also been investigated.     

Syntheses, crystal structures and properties of Cd(II) and Co(II) complexes with 4,4′-dipyridylsulfide ligand

Two new coordination polymers [Cd(dps)₂Cl₂] (1) and [Co(dps)₂(H₂O)₂]·(abs)₂(H₂O)₂ (2) (dps = 4, 4′-dipyridylsulfide, Habs = 4-amino benzenesulfonic acid) have been synthesized under similar conditions and characterized by elemental analysis, fluorescence spectra and single crystal X-ray diffraction. Compound 1 displays a dps-bridged 2D puckered, grid-like layer, which is further linked by C-H?Cl hydrogen bonds to form a 3D supramolecular architecture. Compound 2 shows a dps-bridged double-stranded chain structure, which is extended by N-H?O and O-H?O hydrogen bonds generating a 3D network. Solid-state fluorescence results reveal that both complexes can emit strong emission bands, at 467 nm and 518 nm for 1 and 344 nm for 2, respectively. Magnetic measurements show that there are weak antiferromagnetic interactions between the adjacent Co(II) ions in 2.     

Construction of a series of 0D, 2D and 3D inorganic-organic hybrid coordination polymers based on octamolybdate and 2-(2-pyridyl)imidazole and its derivative

Four octamolybdate-based compounds, that is, Cu^II₂(L¹)₄(Mo₈O₂₆) (1), Cu^II₂(HL²)₄(Mo₈O₂₆)₂ (2), [Cu^IIL²(H₂O)(Mo₈O₂₆)_0.5]·2H₂O (3) and [Cu^IIL²(H₂O)(Mo₈O₂₆)_0.5]·2H₂O (4) (L¹ = 2-(2-pyridyl)imidazole, L² = 2-(1-(pyridine-3-ylmethyl)-1H-imidazol-2-yl)pyridine), have been hydrothermally synthesized via changing the reaction conditions and structurally characterized by single-crystal X-ray diffraction. With L¹ ligand, we obtained compound 1, which is a 0D molecule and extends to a 3D supramolecular structure via hydrogen-bonding interactions. By using L² instead of L¹ ligand, compound 2 comes into being which is as well a discrete molecule and further extended to a 3D supramolecular structure by hydrogen bonds. Intriguingly, compounds 3 and 4 are supramolecular isomers: the former is a 2D 4-connected network and the latter is a 3D (3,4)-connected framework. The measurements of diffuse reflectance for compounds 1-4 indicate that they are potential wide gap semiconductors.     

Crystal structures and luminescent properties of zinc(II) and cadmium(II) compounds constructed from 5-sulfoisophthalic acid and flexible bis-triazole ligands

Four new cadmium(II) and zinc(II) coordination polymers {[Zn(btrp)(SIP)][Zn_0.5(H₂O)₃]}_n (1), {[Cd_1.5(btrp)(SIP)(H₂O)₂]·2H₂O}_n (2), {[Cd_1.5(btrb)(SIP)(H₂O)₃]·2H₂O}_n (3), {[Zn_1.5(btrb)_1.5(SIP)(H₂O)₂]·2H₂O}_n (4) (btrp = 1,3-bis(1,2,4-triazol-1-yl)propane, btrb = 1,3-bis(1,2,4-triazol-1-yl)butane, NaH₂SIP = 5-sulfoisophthalic acid monosodium salt) have been synthesized under hydrothermal conditions and structurally characterized. Compound 1 possesses an infinite 1D ladder-like chain structure with [Zn(H₂O)₆]²⁺ trapped in the pores, which is further interconnected by π?π interactions to lead to a 2D supramolecular architecture. Compounds 2 and 3 features two similar 2D layer structures, and the resulting 2D structures are interconnected by hydrogen-bond interactions to lead to 3D supramolecular architectures. Compound 4 is a 2D parallel ladder structure, and through the interpenetrating btrb ligand, it constructs into 3D architectures. Luminescence analyses were performed on all the four compounds, which show strong fluorescent emissions in the solid state at room temperature.     

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.     

Alteration of molecular conformations and spectral properties for nickel(II), zinc(II) and copper(II) complexes having 3,8-di(thiophen-2′,2′′-yl)-1,10-phenanthroline ligands

Four transition metal complexes of 3,8-di(thiophen-2′,2″-yl)-1,10-phenanthroline (dtphen), formulated as [Ni(dtphen)₂(H₂O)₂]·(ClO₄)₂ (1), [Zn(dtphen)₂(H₂O)]·(ClO₄)₂ (2) [Cu(dtphen)₂(H₂O)]·(ClO₄)₂ (3), [Cu(dtphen)(phen)₂]·(ClO₄)₂ (4) (phen = 1,10-phenanthroline) with different metal-to-ligand ratios, were synthesized and characterized herein. The X-ray single-crystal diffraction studies of 1-4 exhibit that different molecular configurations for the dtphen ligand can be observed where the side thiophene rings adopt the trans/trans, trans/cis, trans/disorder and cis/cis conformations relative to the central 1,10-phenanthroline unit in different compounds. Fluorescence emission spectra of 1-4 in methanol show that the fluorescence emission of 2 is much stronger than the other three metal complexes, which is mainly due to its full d¹⁰ electronic configuration of Zn(II) ion.     

Hydrogen-bonded copper(II) and nickel(II) complexes and coordination polymeric structures containing reduced Schiff base ligands

Complexes [Cu(HSas)(H₂O)] · 2H₂O (H₃Sas = N-(2-hydroxybenzyl)-l-aspartic acid) (1), [Cu(HMeSglu)(H₂O)] · 2H₂O (H₃MeSglu = (N-(2-hydroxy-5-methylbenzyl)-l-glutamic acid) (2), [Cu₂(Smet)₂] (H₂Smet = (N-(2-hydroxybenzyl)-l-methionine) (3), [Ni(HSas)(H₂O)] (4), [Ni₂(Smet)₂(H₂O)₂] (5), and [Ni(HSapg)₂] (H₂Sapg = (N-(2-hydroxybenzyl)-l-aspargine) (6) have been synthesized and characterized by chemical and spectroscopic methods. Structural determination by single crystal X-ray diffraction studies revealed 1D coordination polymeric structures in 2 and 4, and hydrogen-bonded network structure in 5 and 6. In contrast to previously reported coordination compounds with similar ligands, the phenol remains protonated and bonded to the metal ions in 2 and 4, and also probably in 1. However, the phenolic group is non-bonded in 6.     

Hydrothermal synthesis, structural determination, and thermal properties of 2-D cobalt- and nickel-based coordination polymers incorporating pendant-arm 3-pyridinecarboxylate ligands

Hydrothermal synthesis has afforded a family of four coordination polymers containing divalent nickel or cobalt and pendant-arm pyridylcarboxylate ligands. Utilizing 3-pyridylacetic acid and appropriate metal precursors produced [M(3-pyrac)₂(H₂O)₂] phases (M = Co (1); M = Ni (2)), while 3-pyridylpropionic acid generated [M(3-pyrprop)₂(H₂O)₂] coordination polymers (M = Co (3); M = Ni (4)). Single crystal X-ray diffraction revealed that 1-4 all display discrete 2-D layers with (4,4)-topology, anchored via bridging 3-pyridylcarboxylate ligands bearing monodentate carboxylate termini. Intralamellar hydrogen bonding between the aquo ligands and unligated carboxylate oxygen atoms is observed within 1-4. The pseudo 3-D structures of 1-4 are further assembled via stacking of individual neutral layers by interlayer hydrogen bonding. Thermal properties are also discussed.     

Syntheses, structures, luminescent and magnetic properties of a novel class of metal complexes constructed from 2-(2-pyridyl)benzimidazole and 5-hydroxy-1,3-benzenedicarboxylic acid

Four novel metal coordination polymers, [Zn(2-PBIM)(OH-BDC)]_n (1), [Cd(2-PBIM)(OH-BDC)]_n (2), [Mn(2-PBIM)(OH-BDC)]_n·1.5nH₂O (3), [Cu(2-PBIM)(OH-BDC)]_n·nH₂O (4) [2-PBIM = 2-(2-pyridyl)benzimidazole; OH-H₂BDC = 5-hydroxy-1,3-benzenedicarboxylic acid], have been synthesized under hydrothermal conditions and structurally characterized by single crystal X-ray diffraction analysis, elemental analysis, IR spectroscopy, and thermogravimetric analysis. Compound 1 possesses left-handed screw (M-helix) and right-handed screw (P-helix) chains that are further connected though intermolecular hydrogen bonds and π-π stacking interactions resulting in a three-dimensional (3D) network. Compound 2 has a two-dimensional metal-organic framework which is connected into a 3D network by intermolecular hydrogen bonds and π-π stacking interactions. Compounds 3 and 4 are isostructural and possess one-dimensional (1D) channels. Free 2-PBIM and OH-H₂BDC ligands and complexes 1, 2 show fluorescent emissions in the visible and near-infrared region. Magnetic susceptibility measurements indicate that both 3 and 4 exhibit antiferromagnetic coupling between adjacent center atoms.     

Protonation and Zn(II) complexation with versatile valine and glycylglycine N-pyrimidines derivatives: crystal structures of layered {[Zn(HL1)2] · 2H2O}n and [Zn(HL2)2(H2O)4]

Protonation and Zn(II) complexation of N-substituted amino acids, valine (H₂L1) and glycylglycine (H₂L2), with 4-amino-1,6-dihydro-1-methyl-5-nitroso-6-oxopyrimidin-2-yl as substituent, were studied by potentiometric and UV-Vis measurements. Bianions L1 and L2 suffer three protonation steps in aqueous medium corresponding to the amide and carboxylate groups of the amino acidic moiety, and the nitrogen atom of the nitroso group of the pyrimidine fragment. Both ligands form mononuclear Zn(II) complexes in aqueous solutions. The binding donor groups are the nitroso and/or the oxo groups of the pyrimidinic moiety or the carboxylate group, depending on whether the ligands are neutral or anionic, respectively. Weak metal-to-ligand interactions were observed independently of the functionality used by the corresponding ligand on bonding to Zn(II). The reaction of ZnCl₂ with the monodeprotonated ligands (1:1) yields a polynuclear 2D {[Zn(HL1)₂] · 2H₂O}_n and a mononuclear [Zn(HL2)₂(H₂O)₄] complexes, showing the influence of the susbtituent on the amino acids fragment as well as the versatility of this class of compounds when acting as ligands.