Bpe Ligands Research Articles

Cobalt and Copper Coordination Polymers Containing Acetylacetonato‐Derived Ligands and Bidentate Pyridine Coligands: Synthesis, Crystal Structures and Magnetic Properties

AbstractOne‐dimensional chain derivatives of the general formula [M(acac)2(μ‐bipyridine)] were obtained from (acetylacetonato)cobalt(II) or (trifluoromethylacetylacetonato)copper(II) derivatives and bipyridine‐like bridging ligands: 1,2‐bis(4‐pyridyl)ethane, 4,4′‐bpa (1, Co; 2, Cu), trans‐1,2‐bis(4‐pyridyl)ethylene, 4,4′‐bpe (3, Co; 4, Cu), 1,2‐bis(2‐pyridyl)ethylene, 2,2′‐bpe (5, Co) or pyrazine (7, Cu). The reaction of the copper parent derivative with 2,2′‐bpe gives rise, however, to a dimeric species [{Cu(tfacac)2}2(μ‐2,2′‐bpe)] (6). Derivatives 4–7 were characterized by X‐ray crystallography, which showed linear (4, 7) or zigzag chains (5), depending on the bipyridine ligand shape. In the chain complexes, the metal centre is six‐coordinate; the oxygen donor atoms of the acetylacetonato ligands occupy the equatorial positions and the bridging bipyridine ligands are in trans axial positions. Compound 6 forms a dimer with the two copper atoms in a square pyramidal environment, in which the nitrogen atoms of the bridging 2,2′‐bpe ligand occupy the apical position in each pyramid. Magnetic susceptibility studies of the cobalt compounds are dominated by the spin–orbit coupling characteristic of this metal ion. At low temperatures and in the copper derivatives, weak antiferromagnetic interactions along the chain were observed.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Blue Photoluminescent Dimeric Cu(I) Dithiophosphates Bridged by a Flexible Ligand 1,2-Bis(4-Pyridyl)Ethane

The title compound {Cu[S2P(OC2H5)2](bpe)} n (1) is constructed from flexible ligand bpe (bpe = 1,2-bis(4-pyridyl)ethane) and the Cu[S2P(OC2H5)2], which was characterized by single crystal structure determination, elemental analysis, XRD, and IR spectra. X-ray diffraction studies revealed that polymeric compound 1 consists of dinuclear module to form 1-D chains with the intramolecular Cu···Cu interactions (ca. 2.63 A). This interaction may show a profound influence on the observed blue luminescence emission spectrum for 1. Crystal data for 1 at 293(2) K: Space group P − 1, a = 9.277(3), b = 10.504 (4), c = 31.801(1) A, α = 92.849(3), β = 90.401(2), γ = 114.547(7)°, V = 2813.9(2) A3, Z = 2, R 1 = 0.041.

Influence of nitrogen-containing chelating ligands on the structures of zinc(II) 4,4′-ethylenedibenzoates

The Zn(II) compounds, micro-4,4'-ethylenedibenzoato-bis[acetatoaqua(dipyrido[3,2-a:2',3'-c]phenazine)zinc(II)] dihydrate, [Zn(2)(C(2)H(3)O(2))(2)(C(16)H(10)O(4))(C(18)H(10)N(4))(2)(H(2)O)(2)] x 2H(2)O, (I), and catena-poly[[[aqua(pyrazino[2,3-f][1,10]phenanthroline)zinc(II)]-micro-4,4'-ethylenedibenzoato] N,N-dimethylformamide hemisolvate], {[Zn(C(16)H(10)O(4))(C(14)H(8)N(4))(H(2)O)] x 0.5C(3)H(7)NO}(n), (II), display very different structures because of the influence of the N-donor chelating ligands. In (I), the coordination geometry of each Zn(II) centre is distorted octahedral, involving two N atoms from one dipyrido[3,2-a:2',3'-c]phenazine (L1) ligand, and four O atoms from one bis-chelating acetate anion, one bridging 4,4'-ethylenedibenzoate (bpea) ligand and one water molecule. Adjacent Zn(II) atoms are bridged by one bpea ligand to form a dinuclear complex, and the dinuclear species is centrosymmetric. Two types of pi-pi interactions between neighbouring dinuclear species have been found: one is between the L1 ligands, and the second is between the L1 and bpea ligands. In this way, an interesting two-dimensional supramolecular layer is formed. The layers are further linked by O-H...O and O-H...N hydrogen bonds, generating a three-dimensional supramolecular network. In (II), each Zn(II) atom is square-pyramidally coordinated by two N atoms from one pyrazino[2,3-f][1,10]phenanthroline ligand, three O atoms from two different bpea ligands and one water molecule. The two bpea dianions are situated across inversion centres. The bpea dianions bridge neighbouring Zn(II) centres, giving a one-dimensional chain structure in the ab plane. As in (I), two types of pi-pi interactions between neighbouring chains complete a three-dimensional supramolecular structure. The results indicate that the structures of the N-donor chelating ligands are the dominant factors determining the final supramolecular structures of the two compounds.

New Ruthenium(II) Complexes with Enantiomerically Pure Bis- and Tris(pinene)-Fused Tridentate Ligands. Synthesis, Characterization and Stereoisomeric Analysis

A new set of Ru-Cl complexes containing either the pinene[5,6]bpea ligand (L1) or the C3 symmetric pinene[4,5]tpmOMe (L2) tridentate ligand in combination with the bidentate (B) 2,2'-bipyridine (bpy) or 1,2-diphenylphosphinoethane (dppe) with general formula [RuCl(L1 or L2)(B)](+) have been prepared and thoroughly characterized. In the solid state, X-ray diffraction analysis techniques have been used. In solution, cyclic voltammetry (CV) and 1D and 2D NMR spectroscopy have been employed. DFT calculations have been also performed on these complexes and their achiral analogues previously reported in our group, to interpret and complement experimental results. Whereas isomerically pure complexes ([Ru(II)Cl(L2)(bpy)](BF4), 5 and [Ru(II)Cl(L2)(dppe)](BF4), 6) are obtained when starting from the highly symmetric [Ru(III)Cl3(L2)], 2, isomeric mixtures of cis, fac-[Ru(II)Cl(L1)(bpy)](BF4) (3b/3b'), trans,fac- (3a) and up/down,mer- (3c, 3d) isomers are formed when bpy is added to the less symmetric [Ru(III)Cl3(L1)], 1, in contrast to the case of the bulky dppe ligand that, upon coordination to 1, leads to the trans,fac-[Ru(II)Cl(L1)(dppe)](BF4) (4a) complex as a sole isomer due to steric factors.

Effect of N-Donor Ancillary Ligands on Supramolecular Architectures of a Series of Zinc(II) and Cadmium(II) Complexes with Flexible Tricarboxylate

This work presents a systematic investigation on reactions of a flexible tricarboxylic acid with Zn(II), Cd(II) in the presence of varied N-donor ancillary ligands. Seven new metal−organic frameworks [Zn3(bta)2(bpy)2] (1), [Zn3(bta)2(dpe)2]·2H2O (2), [Zn2(OH)(bta)(bpe)]·2H2O (3), [Zn2(OH)(bta)(bpp)] (4), [Cd2(bta)(bpy)2(H2O)]ClO4·H2O (5), [Cd3(bta)2(bpy)2]·2H2O (6), and [Cd3(bta)2(H2O)2] (7) [bta3− = benzene-1,3,5-triacetate, bpy = 4,4′-bipyridine, dpe = 1,2-di(4-pyridyl)ethylene, bpe = 1,2-bis(4-pyridyl)ethane, and bpp = 1,3-bis(4-pyridyl)propane] have been obtained and characterized by single-crystal X-ray diffraction, IR, thermogravimetric and elemental analyses. Complexes 1−3, 5, and 6 are three-dimensional (3D) architectures containing infinite two-dimensional (2D) networks pillared by N-donor ligands, whereas 4shows 2D network structure. Complex 3 has 2-fold interpenetration of 3D frameworks with 4.82 networks linked by bpe ligands, and 5 features an unusual 3D cationic supramolecular architecture. Complex 7 contains the Kagomé lattice inorganic layers, which are further linked by bta3− ligands to form a 3D supramolecular architecture. The results showed that the structure and flexibility of the N-donor ancillary ligands have great influence on the structure of the complexes. The photoluminescence properties of 1−7 in the solid-state at room temperature have been studied.

Solid‐State Photochemical [2+2] Cycloaddition in a Hydrogen‐Bonded Metal Complex Containing Several Parallel and Crisscross CC bonds

One-dimensional hydrogen-bonded complex [Zn(bpe)(2)(H(2)O)(4)](NO(3))(2).8/3 H(2)O.2/3 bpe (1, bpe=4,4'-bipyridylethylene) containing coordination complex cations [Zn(bpe)(2)(H(2)O)(4)](2+) with parallel and crisscross double bonds undergoes photochemical [2+2] cycloaddition in the solid state and produces tetrakis(4-pyridyl)cyclobutane (tpcb) in up to 100 % yield with rctt-tpcb (2a) as major and rtct-tpcb (2b) as minor product. The bpe ligands with crisscross conformation of C=C bonds appear to undergo pedal-like motion prior to photodimerization. Grinding single crystals to powder accelerates the pedal motion of crisscrossed olefins in the bpe ligands to parallel alignment and provides the rctt-cyclobutane stereoisomer 2a quantitatively. In addition, 100 % photodimerization of ground 1 indicates that the free bpe ligands, which are remote from each other in a pool of water, and NO(3)(-) ions moved toward each other to give a mixture of rctt- and rtct-tpcb isomers.

Hydrogen-bonded Multicomponent Behavior in Tetra-iso-butyl-resorcin[4]arene–1,4-Bis(pyridyl)ethane–Methanol–Water (1/2/0.5/1)

Co-crystallization of the tetra-iso-butyl-resorcin[4]arene (1) with 1,4-bis-(pyridyl)ethane (bpe) obtained from methanol yields a molecular solid of the multicomponent host–guest complex 1 · 2(bpe) · 0.5MeOH · H2O (2) in which 1 assemblies with water molecules to form a hydrogen-bonded dimer. The bpe ligands in both cis- and trans-stereo configurations exist in the complex 2, of which trans-bpe moieties as guests are encapsulated in the capsules constructed by two pairs of opposition bowls of resorcinarenes. The 1,4-bis(pyridyl)ethane (bpe) ligands in both cis- and trans-stereo configurations exist in a multicomponent molecular solid, of which trans-bpe moieties as guests are encapsulated in the capsules constructed by two pairs of opposition bowls of resorcinarenes.

Mechanistic theoretical insight of Ru(II) catalysts with a meridional–facial bpea fashion competition

A novel mechanistic insight for the interconversion between two octahedral ruthenium isomers, trans-mer-[RuIICl2(bpea)(dmso)], 2a, and cis-fac-[RuIICl2(bpea)(dmso)], 2b, (bpea=N,N-bis(2-pyridylmethyl)ethylamine) is reported. The isomer 2a displaying the bpea ligand in a meridional fashion is kinetically favoured with respect to 2b, with the bpea ligand in a facial fashion, which is the thermodynamically favoured one. The dissociative mechanism with the cleavage of a chloro ligand as starting point becomes more feasible with respect to the intramolecular mechanism. However, DFT calculations make competitive the mechanism which dissociates first the dmso ligand. Thus, a further characterisation of all the reaction pathways for the interconversion 2a→2b has been fulfilled.

New alkoxo-bridged mixed-valence cobalt clusters: Synthesis, crystal structures and magnetic properties

Two new Co II/Co III complexes, [{Co IICo III(mea) 3} 2(bpe) 3](ClO 4) 4 · 1.5CH 3OH · 1.5H 2O ( 1) and [ Co 4 II Co 3 III ( dea ) 6 ( CH 3 COO ) 3 ] ( ClO 4 ) 0.75 ( CH 3 COO ) 1.25 · 0.5 H 2 O ( 2) [Hmea = monoethanolamine H 2dea = diethanolamine and bpe = 1,2-bis(4-pyridyl)ethane], have been obtained by reacting cobalt(II) perchlorate ( 1 and 2), Hmea ( 1)/H 2dea ( 2), bpe ( 1) and sodium acetate ( 2). The crystal structures of 1 and 2 have been solved by single crystal X-ray diffraction. Crystal 1 contains “Chinese lantern”-like shaped cations, resulting by connecting two {Co IICo III(mea) 3} moieties with three flexible bpe ligands. The coordination sphere of the outer cobalt(III) ions is built by three amino groups arising from the mea − ligands, and by three bridging alkoxo-oxygen atoms whereas that of the inner cobalt(II) ions is constituted by the three alkoxo oxygen atoms and by three nitrogen atoms from three bpe ligands. The crystallographic analysis of 2 shows the occurrence of heptanuclear [ Co 4 II Co 3 III ] cations, with a central Co II ion and six peripheral cobalt atoms, three of them being divalent and the other three being trivalent. The magnetic properties of 1 and 2 have been investigated in the temperature range 1.9–300 K. A very weak antiferromagnetic interaction [ J = −0.061(2) cm −1] between the high-spin cobalt(II) ions bridged by the bpe ligands occurs in 1 whereas a significant intramolecular ferromagnetic interaction [ J = +2.6(1) cm −1] between the high-spin cobalt(II) ions is present in two leading to a low-lying S = 6 spin state. No out-of-phase ac signal was detected for this anisotropic high-spin molecule down to 1.9 K.

Topological description of a 3D self-catenated nickel hybrid vanadate Ni(bpe)(VO3)2. Thermal stability, spectroscopic and magnetic properties

The three-dimensional Ni(bpe)(VO3)2 hybrid compound, where bpe is 1,2-di(4-pyridyl)ethene, (C12H10N2), has been synthesized using mild hydrothermal conditions under autogeneous pressure at 140 °C during five days, obtaining green emerald prismatic single-crystals suitable for X-ray structure determination. The compound crystallizes in the orthorhombic system, space groupPbcn, with a = 14.9066(5), b = 7.6269(2) and c = 26.9624(10) A, Z = 8, and R1 = 0.0373 for 4149 observed reflections. Single-crystal X-ray diffraction reveals that the crystal structure is composed of a 3D self-catenated 10-connected uninodal net constructed from 36-hxl like {NiV2O6} inorganic sheets linked through bpe ligands. The thermal evolution of the crystal parameters shows three different tendencies during the heating process: (i) initial contraction, (ii) thermal expansion, (iii) structural collapse due to the thermal instability of the organic ligand. The IR spectrum shows the vibrational modes of the bpe organic molecules and those of the (VO4)3− tetrahedral oxoanions. Diffuse reflectance electronic absorption spectroscopy shows the characteristic bands of the Ni(II) d8-high spin cation in slightly distorted octahedral geometry. From the positions of the bands in the electronic spectrum the Dq (940 cm−1) and Racah, B (930 cm−1) and C (3350 cm−1), parameters have been calculated. Magnetic measurements indicate the existence of antiferromagnetic interactions between the Ni(II) centres of the dinuclear units, with a value of the J/k = −59.4, with g = 2.076.

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

Six new complexes: [Ln 2(pzda) 3(H 2O) 2] · 2.5H 2O (Ln = Nd, ( 1); Eu, ( 2)), [Co(pzda) (bpe)] · 0.125(bpe) · 1.75H 2O ( 3), [Mn(pzda)(H 2O) 1.5] ( 4), [Co 2(pzda) 2(bpe)(H 2O) 4] · 0.5(CH 3OH) · H 2O ( 5) and [Co(pzda)(2,2′-bpy)(H 2O)] · 0.5H 2O ( 6) (H 2pzda = pyrazine-2,6-dicarboxylic acid, bpe = 1,2-bis(4-pyridyl)ethane, 2,2′-bpy = 2,2′-bipyridine) were obtained from metal salts and H 2pzda 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 μ 2-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.

Catena-Poly[[[diaquacobalt(II)]-μ-(E)-1,2-bis(4-pyridyl)ethylene-κ2N:N′] bis(4-aminobenzenesulfonate) hexahydrate

In the title compound, {[Co(C12H10N2)(H2O)2](C6H6NO3S)2·6H2O}n, a cobalt coordination polymer, the repeat unit comprises a cobalt complex cation, two 4-amino­benzene­sulfonate anions and six uncoordinated water mol­ecules. In the doubly charged cobalt cation, each Co atom lies on a center of symmetry and is six-coordinated in a distorted octa­hedral geometry formed by four O atoms of four coordinated water mol­ecules, and two N atoms from two (E)-1,2-bis­(4-pyrid­yl)ethyl­ene (bpe) ligands. The bpe ligands bridge the Co atoms, forming a one-dimensional linear chain. Inter­molecular O—H⋯O, O—H⋯N and N—H⋯O hydrogen-bonding inter­actions stabilize this chain structure.

Mechanistic Insights into the Chemistry of Ru(II) Complexes Containing Cl and DMSO Ligands

Two new isomers trans,mer-[RuIICl2(bpea)(DMSO)], 2a, and cis,fac-[RuIICl2(bpea)(DMSO)], 2b, (bpea = N,N-bis(2-pyridylmethyl)ethylamine), as well as the bis-DMSO complex trans,fac-[RuIICl(bpea)(DMSO)2]Cl, 3, have been synthesized and characterized by cyclic voltammetry and UV-vis and 1D and 2D NMR spectroscopy in solution. Their solid-state structure has also been solved by means of single-crystal X-ray diffraction analysis. All the three complexes display a ruthenium metal center possessing a distorted-octahedral type of coordination, where the bpea ligand is coordinated in a meridional fashion in 2a and in a facial fashion in 2b and 3. The isomer 2a is the kinetically favored and thus can be thermally converted into 2b, that is the thermodynamically favored one. A thorough kinetic analysis strongly points toward a dissociative mechanism, where in the first step a chloro ligand is removed from the metal coordination sphere, followed by a geometric rearrangement before the chloro ligand coordinates again, generating the final complex. DFT calculations agree with the experimental data for the proposed mechanism and allow us to further characterize the mechanism of the 2a --> 2b rearrangement by obtaining the intermediates and transition state.

Assemblies of Two Mixed-Ligand Coordination Polymers with Two-Dimensional Metal−Organic Frameworks Constructed from M(II) Ions with Croconate and 1,2-Bis-(4-pyridyl)ethylene (M = Cd and Zn)

Two metal−croconate (C5O52-) complexes, {[Cd2(bpe)(C5O5)2(H2O)]·2H2O}n (1) and {[Zn2(bpe)2(C5O5)2]}·H2O}n (2) (bpe = 1,2-bis(4-pyridyl)ethylene)) with two-dimensional (2-D) metal−organic frameworks (MOFs), have been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction studies. Structural determination reveals that compound 1 possesses a 2-D layered MOF with two rectangular boxes as the basic building units through the connectivity of CdII with μ3-croconates, μ5-croconates, and bpe ligands. In compound 2, a 2-D brick-wall-like layered framework is formed by using a rectangular grid as the basic building unit through the connectivity of ZnII with hybrid μ3-croconates, μ4-croconates, and bpe ligands. Two layers are then cross-linked by the other bpe ligands to complete a 2-D bilayered MOF. Both of the 2-D MOFs are extended to three-dimensional supramolecular architectures through π−π and C−H···O interactions between the croconate and the pyridyl rings of bpe, which exhibit high thermal stability and retain their crystalline forms up to 350 °C.

Poly[[μ2-trans-1,2-di-4-pyridylethylene]hexa-μ2-oxido-nickel(II)divanadate(V)

The structure of the title compound, [NiV2O6(C12H10N2)]n, is composed of corner-sharing [V2O6]2− chains along the c axis, with the [Ni(bpe)]2+ (bpe = trans-1,2-di-4-pyridylethyl­ene) units covalently attached to every V site through O atoms. The Ni atom is octa­hedrally coordinated by two pyridyl N atoms from two different bpe ligands, and four O atoms from four different VO4 tetra­hedra. All the C and H atoms are disordered over two positions each; the site occupancy factors are ca 0.55 and 0.45.

Poly[μ2-trans-1,2-di-4-pyridylethylene-κ2N:N′-μ2-sulfato-κ2O:O′-zinc(II)

The title compound, [Zn(SO(4))(C(12)H(10)N(2))](n), features a layered structure based on [Zn(SO(4))](n) spirals linked by 1,2-di-4-pyridylethylene (bpe) ligands, with the tetrahedral Zn and S atoms lying on twofold axes. The bpe ligands are centrosymmetric. The layers are linked by weak C-H...O interactions.

New Ru Complexes Containing the N-Tridentate bpea and Phosphine Ligands: Consequences of Meridional vs Facial Geometry

The synthesis and isolation of the complex cis,fac-[RuIICl2(bpea)(PPh3)][3; bpea = N,N-bis(2-pyridylmethyl)ethylamine] and three geometrical isomers of the complex [RuIICl(bpea)(dppe)](BF4) [4; dppe = (1,2-diphenylphosphino)ethane], trans,fac (4a), cis,fac (4b), and mer(down) (4c), have been described (see Chart 1 for a drawing of their structures). These complexes have been characterized through analytical, spectroscopic (IR, UV/vis, and 1D and 2D NMR), and electrochemical (cyclic voltammetry) techniques. In addition, complexes 3, 4a, and 4b have been further characterized in the solid state through monocrystal X-ray diffraction analysis. The molecular and electronic structures of isomers 4a, 4b, 4c, and 4d (the mer(up) isomer) have also been studied by means of density functional theory (DFT) calculations. Furthermore, their low-energy electronic transitions have been simulated using time-dependent DFT approaches, which have allowed unraveling of their metal-to-ligand charge-transfer nature. Complexes 3 and 4a-c are capable of catalyzing H-transfer types of reactions between alcohols and aromatic ketones such as acetophenone and 2,2-dimethylpropiophenone (DP). A strong influence of the facial versus meridional geometry in the bpea ligand coordination mode is observed for these catalytic reactions, with the meridional isomer being much more active than the facial one. The meridional isomer is even capable of carrying out the H-transfer reaction of bulky substrates such as DP at room temperature.

Heterogeneization of a new Ru(II) homogeneous asymmetric hydrogenation catalyst containing BINAP and the N-tridentate bpea ligand, through covalent attachment on amorphous AlPO4 support

Following a new methodology to obtain hybrid organic–inorganic solids, the homogeneous complex [RuII(bpea) {(S)(−)(BINAP)}Cl](BF4), (bpea = N,N-bis(2-pyridylmethyl)ethylamine and BINAP = 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl) has been covalently immobilized on an AlPO4 amorphous solid. It was tested in the successive liquid phase enantioselective hydrogenation of several prochiral substrates such us dimethyl itaconate, methyl 2-acetamidoacrylate and methyl 2-acetamidocinnamate, in CH2Cl2 as solvent, ([subs]/[cat] = 0.016/0.000352 = 45.4), hydrogen pressure 6.8 atm and 50–70 °C reaction temperatures. Results obtained indicate that the catalytic activity with a high enantioselectivity (99%) was maintained throughout 10 successive reactions. Furthermore, the immobilized catalyst was easily recovered when repeatedly used and handled for several days, under the same experimental conditions as those in a conventional heterogeneous supported Ru catalyst.

3D supramolecular network assembly and thermal decomposition of new copper(II) complexes with pyrazine-2,6-dicarboxylic acid

Four new Cu(II) complexes [Cu(pzda)(2,2′-bpy)(H 2O)] · 2.5H 2O ( 1), [Cu(pzda)(phen)(H 2O)] · H 2O ( 2), [Cu(pzda)(4,4′-bpy)] · H 2O ( 3) and [Cu(pzda)(bpe) 0.5(H 2O)] ( 4) were synthesized by hydrothermal reactions of copper salt (acetate or sulphate) with pyrazine-2,6-dicarboxylic acid (H 2pzda), and 2,2′-bipyridine (2,2′-bpy), 1,10-phenanthroline (phen), 4,4′-bipyridine (4,4′-bpy) or 1,2-bis(4-pyridyl)-ethane (bpe), respectively. For 1 and 2, they are both monomeric entities which are further assembled into 3D supramolecular networks by hydrogen bonds and π–π stacking interactions. Complex 3 has a 2D metal–organic framework which is connected into 3D supramolecular network by hydrogen bonds. However, for 4, the bpe ligand bridges two Cu(II) ions into binuclear unit, and then the binuclear molecules are assembled into 3D supramolecular network by hydrogen bonds between the coordination water molecule and the carboxylate oxygen atoms. The thermal decomposition mechanism of complexes 1 and 2 cooperated with powder XRD at different temperatures is discussed. The results reveal that once liberation of water molecules takes place the supramolecular network of 1 and 2 collapses.

Self-assembly and structure of three new Zn(II) complexes with pyrazine-2,6-dicarboxylic acid

The reaction of Zn(OAc) 2·2H 2O and pyrazine-2,6-dicarboxylic acid (H 2pzda) with 2,2′-bipyridine (2,2′-bpy), 1,10-phenanthroline (phen) or 1,2-bis(4-pyridyl)-ethane (bpe) gave rise to three new Zn(II) complexes: [Zn(pzda)(2,2′-bpy)(H 2O)]·0.5H 2O ( 1), {[Zn(pzda)(phen)(H 2O)]·H 2O} 2 ( 2) and [Zn 2(pzda) 2(bpe)(H 2O) 4]·1.75H 2O ( 3), respectively. For 1, it is a mononuclear structure which is assembled into 3D supramolecular architecture by strong hydrogen bonds (O–H⋯O, O–H⋯N) as well as π–π stacking interactions. In 2, there are two similar mononuclear units, which are further constructed by the hydrogen bonds and π–π stacking interactions into zipper-like supramolecular structure. However, for 3, the bpe ligand bridges two Zn(II) ions cooperated with blocking ligand pzda into binuclear unit, and then the binuclear molecules are alternatively assembled into 3D supramolecular network by hydrogen bonds between the coordinated water molecules and the carboxylate oxygen atoms. The thermal properties of complexes were also investigated.