Synthesis, crystal structure and surface photo-electric property of a series of Co(II) coordination polymers and supramolecules

Four new Co(II) coordination complexes, [Co(o-phta)(pz)₂]_n1, [Co(PTA)₂(Imh)₂]·(HPTA)·H₂O 2, {[Co(pdc)₂(H₂O)]·(ppz)·2H₂O}_n3, [K₂Co₂(ox)(btec)(CH₃OH)₂]_n4, (H₂phta = o-phthalic acid, pz = pyrazole, HPTA = p-toluic acid, ppz = piperazine, Imh = imidazole, H₂pdc = pyridine-2,5-dicarboxylic acid, H₂(ox) = oxalic acid, H₄btec = 1,2,4,5-benzenetetracarboxylic acid), were hydrothermally synthesized and characterized by X-ray single crystal diffraction, IR, UV–Vis absorption spectrum, TG analysis and elemental analysis. The surface photovoltage properties of the four Co(II) complexes were investigated by the surface photovoltage spectroscopy (SPS). The structural analyses indicate that complexes 1 and 3 are 1D coordination polymers and complex 2 is a mononuclear molecular complex. Complexes 1, 2 and 3 are connected into 2D supramolecules by hydrogen bonds, respectively. Complex 4 is a coordination polymer with 3D structure, exhibiting a 4-nodal(4,5,6,12)-connected topology with a Schläfli symbol of (4¹⁰)₂(4²⁴·6³²·8¹⁰)(4⁵·6)₂(4⁹·6⁵·8). The results of SPS show the four complexes exhibit obvious photovoltaic responses in 300–800 nm, which indicates they all possess photo-electric conversion properties. By the comparative analysis of the SPS, it is found that structure of the complex, species of ligand and coordination micro-environment of the Co(II) ion affect the SPS. The relationships between SPS and UV–Vis absorption spectra are discussed.     

Synthesis, structures, and magnetic properties of one-dimensional Fe-M (M = Ni, Cu) coordination polymers bridged by nitroprusside

Self-assembling [Fe(CN)₅(NO)]²⁻ and [M(L)]²⁺ (M = Ni, Cu; L = macrocycles) led to one-dimensional coordination polymers, [Ni(L1)][Fe(CN)₅(NO)] · 2H₂O (1) with parallel chains and [Cu(L2)][Fe(CN)₅(NO)] · 3H₂O (2) exhibiting a slanted chain structure. Compound 1 contains a planar macrocycle L1 coordinated to a slightly distorted octahedral Ni(II) ion in which the planarity of L1 gives rise to piling up chains in parallel. In contrast, a more flexible macrocyclic ligand L2 in 2 that surrounds a Cu center with a tetragonal elongation has bulky cyclohexyl groups together with pendant methyl side groups. The presence of the methyl groups on L2 in a chain makes the cyclohexyl groups in an adjacent chain tilted against the CuN₄ basal plane with the methyl groups, eventually resulting in the slanted chain structure. Magnetic data demonstrate that antiferromagnetic interactions (J ≈ −0.13 cm⁻¹) are operating although the paramagnetic centers are linked by the long diamagnetic [Fe(CN)₅(NO)]²⁻ anion.     

Self assembly of a Fe(L) complex with octacyano metallates [M(CN)8] (L = pentadentate macrocyclic ligand, M = Mo, W): Crystal structure and magnetic properties

The self assembly of [Fe^III(L)]Cl₂ClO₄ (L = pentadentate macrocyclic ligand) with octacyano metallates [M^IV(CN)₈]⁴⁻ (M = Mo, W) leads to bimetallic cyano-bridged 2-D coordination polymers of formula [{Fe(L)}₃{M(CN)₈}₂]Cl·xH₂O with M = Mo (2), or W (3). The structure of the tungsten analogue has been established by single crystal X-ray diffraction. The magnetic properties for both Mo and W derivative are reported.     

A series of d transition metal coordination complexes: Structures and comparative study of surface electron behaviors (n = 9, 8, 7, 6, 5)

Ten transition metal coordination complexes [Cu₂(phen)(p-tpha)(μ-O)]_n1, [Cu(m-tpha)(imH)₂]_n2, [Ni(5-Haipa)₂(H₂O)₂]_n3, [Ni(phen)₂(H₂O)₂]·btc·[Ni(H₂O)₆]_0.5·9H₂O 4, [Co(2,5-pdc)(H₂O)₂]_n·nH₂O 5, [Co₂(2,5-pdc)₂(H₂O)₆]_n·2nH₂O 6, [Fe(2,5-Hpdc)₂(H₂O)₂]·H₂O 7, [Co(C₆H₄NO₂)₃]·H₂O 8, [Fe₂(μ₂-btec)(μ₂-H₂btec)(bipy)₂(H₂O)₂]_n9, [Mn(phen)(2,5-pdc)(H₂O)₂]·H₂O 10 (H₄btec = 1,2,4,5-benzenetetracarboxylic acid, phen = 1,10-phenanthroline, 2,5-H₂pdc = 2,5-pyridine-dicarboxylic acid, p-tpha = p-phthalic acid, m-tpha = m-phthalic acid, bipy = 2,2′-bipyridine, 5-H₂aipa = 5-aminoisophthalic acid, imH = imidazole, H₃btc = 1,3,5-benzenetricarboxylic acid) were synthesized through hydrothermal method. They were characterized by UV-Vis absorption spectra, single-crystal X-ray diffraction and surface photovoltage spectra (SPS). Structural analysis indicated that the complexes 1, 2, 3, 5, 6 and 9 were linked into infinite structures bridged by organic acid ligands. The other four complexes were molecular complexes and further connected to 2D or 3D structures by the hydrogen bonds. The SPS of complexes 1-10 indicate that there are positive response bands in the range of 300-800 nm showing different levels of photo-electric conversion properties. The intensity, position, shape and the number of the response bands in SPS are obviously different since the structure, species, valence, dⁿ electrons configuration and coordinated environment of the center metals are different. There are good relationships between SPS and UV-Vis spectra.     

Investigation of the MSO4 · xH2O (M = Zn, x = 7; M = Cd, x = 8/3)/methyl 2-pyridyl ketone oxime reaction system: A novel Cd(II) coordination polymer versus mononuclear and dinuclear Zn(II) complexes

The reactions of methyl 2-pyridyl ketone oxime, (py)C(Me)NOH, with MSO₄ · xH₂O (M = Zn, x = 7; M = Cd, x = 8/3), in the absence of an external base, have been investigated. The synthetic study has led to the two new complexes [Zn(SO₄){(py)C(Me)NOH}(H₂O)₃] · H₂O (1 · H₂O) and [Zn₂(SO₄)₂{(py)C(Me)NOH}₄] · (py)C(Me)NOH [2 · (py)C(Me)NOH], and the coordination polymer [Cd(SO₄){(py)C(Me)NOH}(H₂O)]_n · [Cd(SO₄){(py)C(Me)NOH}(H₂O)₂]_n (3). In the three complexes the organic ligand chelates through its nitrogen atoms. The sulfate anion in 1 · H₂O is monodentate; the complex molecule is the mer isomer considering the positions of the aqua ligands. The Zn^II centers in 2 · (py)C(Me)NOH are bridged by two syn, anti η¹:η¹:μ₂ ligands; each metal ion has the cis-cis-trans disposition of the coordinated sulfate oxygen, pyridyl nitrogen and oxime nitrogens, respectively. The molecular structure of 3 is unique consisting of two different linear and ladder - type chains. π-π stacking interactions and/or hydrogen bonds lead to the formation of interesting supramolecular architectures in the three complexes. The thermal decomposition of complex 3 has been studied. Characteristic vibrational (IR, Raman) bands are discussed in terms of the nature of bonding and the structures of the three complexes.     

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

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

Construction of crystal structures of metal(II)-benzoates (M = Mn, Ni, Co, Cu, Zn, and Cd) and 1,2-bis(4-pyridyl)ethane: Effects of metal coordination modes and their catalytic activities

Five polymeric metal(II)-benzoate complexes of formula [Mn(O₂CPh)₂(CH₃OH)₂(bpa)]_n (1-Mn), [Co(O₂CPh)₂(H₂O)(bpa)_1.5]_n (2-Co), [Ni(O₂CPh)₂(H₂O)(bpa)_1.5]_n (3-Ni), [Cu(O₂CPh)₂(CH₃OH)₂(bpa)]_n (4-Cu), and [Cd(O₂CPh)₂(bpa)_1.5]_n (6-Cd) have been synthesized and characterized (bpa = 1,2-bis(4-pyridyl)ethane). They showed two kinds of structures: parallelogram-like two-dimensional sheets for Co, Ni, and Cd, and one-dimensional chains for Mn, Cu, and Zn. Since similar structures provide similar coordination geometries, the structures depend on the coordination geometries of metal ions. The compounds 1-Mn, 2-Co, 4-Cu, 5-Zn, and 6-Cd have catalyzed efficiently the transesterification of a variety of esters, while 3-Ni has displayed a very slow conversion. The reactivity of catalyst 6-Cd containing Cd ion, well known as an inert metal ion for the ligand substitution, was found to be comparable to that of 5-Zn. The reactivities of the compounds used in this study are in the order of 5-Zn > 6-Cd > 1-Mn > 4-Cu > 2-Co ? 3-Ni, indicating that the non-redox metal-containing compounds (5-Zn and 6-Cd) show better activity than the redox-active metal-containing compounds (1-Mn, 4-Cu, 2-Co, and 3-Ni).     

Four novel Co(II) and Mn(II) coordination polymers with triazolyl derivate: Syntheses, crystal structures and magnetic properties

Four novel coordination polymers, one-dimensional chains [M(PTE)₂(N₃)₂]_n (M = Mn for 1 and Co for 2), and two-dimensional layers [M(PTE)₂(dca)₂]_n (M = Mn for 3 and Co for 4) (PTE = 1-(2,4-difluorophenyl-2-(1H-1,2,4-triazol-1-yl)ethanone, dca = dicyanamide anion, N(CN)₂⁻), have been synthesized under mild ambient conditions and structurally characterized by single crystal X-ray diffraction. In all four crystal structures, the metal atoms adopt octahedral coordination geometry with six nitrogen atoms from two monodentate PTE ligands and four azido (or dca) bridging ligands. The crystal structures of 1 and 2 are isostructural 1-D polymeric chains, alternatively linked by double end-on and double end-to-end azido bridges. However, the bent dca ligands as bidentate μ₂-1,5 bridging ligands interlink the octahedral metal units to lead to 2-D (4,4) grid networks in 3 and 4. Temperature-dependent magnetic measurements in 2-300 K have been performed for these four polymers, and suggest alternative ferro- and antiferromagnetic couplings for end-on and end-to-end azido bridges in 1, and the dominant ferromagnetic coupling in 2, respectively. Both polymers 3 and 4 show weak antiferromagnetic exchanges through the μ₂-1,5-dca bridges. The effects of auxiliary coligands on the structure and the nature of these magnetic exchanges are discussed in the light of the crystal structures in detail.     

Heterodimetallic Pd-based carboxylate-bridged complexes: Synthesis and structure of single-crystalline Pd-M (M = Mn, Co, Ni, Cu, Zn, Nd, Eu, Ce) acetates

A series of crystalline Pd^II-based heterodimetallic acetate-bridged complexes containing the transition (Mn^II, Co^II, Ni^II, Cu^II), post-transition (Zn^II) and rare-earth (Ce^IV, Nd^III, Eu^III) metals were synthesized starting from Pd₃(OOCMe)₆ and the complementary metal(II, III) acetates. The crystal and molecular structures of the binuclear Pd^IIM^II(μ-OOCMe)₄L (M = Mn, Co, Ni, Zn; L = H₂O, MeCN), trinuclear and tetranuclear (M = Nd, Eu) and complexes were established by X-ray diffraction.     

Two-dimensional oxides constructed from octamolybdate clusters and M/tetrapyridylpyrazine subunits (M = Co, Ni: n = 2; M = Cu: n = 1)

The hydrothermal reactions of MoO₃, tetra-2-pyridylpyrazine (tpyprz) and M(CH₃CO₂)₂ · 2H₂O (M = Co, Ni) yielded the two-dimensional oxides [M₂(tpyprz)(H₂O)₂Mo₈O₂₆] · xH₂O [M = Co, x = 1.8 (1); M = Ni, x = 0.6 (2)]. However, the reaction of (NH₄)₆Mo₇O₂₄ · 4H₂O, tpyprz and Cu(CH₃CO₂)₂ · H₂O produced [{Cu₂(tpyprz)}₂Mo₈O₂₆] · 2H₂O (3 · 2H₂O). The isomorphous structures of 1 and 2 are constructed from clusters linked through {M₂(tpyprz)(H₂O)₂}⁴⁺ subunits into two-dimensional networks. While the structure of 3 is also two-dimensional, the molybdate building block is present as the δ-isomer and the secondary-metal/ligand component consists of a one-dimensional chain. The structure of 3 is compared to that of the previously reported three-dimensional material [{Cu₂(tpyprz)}₂Mo₈O₂₆] · 7H₂O which contains clusters and structurally distinct chains.     

Syntheses and structure of heterobimetallic helical polymeric Mo-M(II) (M = Mn, Co, Zn, Cd or Ni) complexes using a flexidentate metalloligand

A series of heterobimetallic polymeric complexes of manganese, cobalt, zinc, cadmium and nickel, [M(Mo₂O₅L₂)(MeOH)₂(H₂O)₂]_n·nH₂O {M = Mn (2), n = 1, Co (3), n = 0, Zn (4), n = 1 and Cd (5), n = 1} and [Ni(Mo₂O₅L₂)(MeOH)(H₂O)₃]_n·2H₂O·MeOH (6) have been synthesized form the reaction of [{Na₄(H₂O)₄(μ-H₂O)₂} ⊂ (Mo₂O₅L₂)₂] (1) {LH₂ = 2-(3,5-di-tert-butyl-2-hydroxybenzylamino)acetic acid} with the corresponding metal salts. The complexes have been structurally characterized. The Complexes, 3 and 6 undergo thermal decomposition to afford mixed oxides of the type, MMoO₄·MoO₃ {M = Co or Ni}.     

One-dimensional Zn(II) oligo(phenyleneethynylene)dicarboxylate coordination polymers: Synthesis, crystal structures, thermal and photoluminescent properties

The rigid, π-conjugated dicarboxylic acid 1,4-bis-[2-(4-carboxyphenyl)ethynyl]-2,5-dihexylbenzene {HO₂C[PEP(hexyl)₂EP]CO₂H} has been used to synthesise the new crystalline coordination polymers {Zn(O₂C[PEP(hexyl)₂EP]CO₂)(DMF)₂} (1) and {Zn(O₂C[PEP(hexyl)₂EP]CO₂)(DEF)₂} (2) in N,N-dimethylformamide (DMF) and N,N-diethylformamide (DEF), respectively, under mild conditions. Single-crystal X-ray crystallography revealed that 1 and 2 are isostructural and consist of uncharged zigzag coordination chains in which [Zn(formamide)₂]²⁺ fragments are bridged by (O₂C[PEP(hexyl)₂EP]CO₂)²⁻ ligands. The zigzag chains possess different intra-chain Zn?Zn?Zn angles due to the different volumes of the coordinating formamide molecules and subtle differences in the hydrophobic inter-chain interactions. Upon heating 1 and 2 to 200 °C, removal of the coordinating formamide molecules occurs, yielding the formamide-free compounds 1-DMF and 2-DEF of composition {Zn(O₂C[PEP(hexyl)₂EP]CO₂)}. According to powder X-ray diffraction and FT-IR spectroscopy studies, these materials are not crystalline but still possess partial ordering of intact, yet modified coordination chains in a structural arrangement which appears to be related to the respective parent compounds. Compounds 1, 2, 1-DMF and 2-DEF exhibit blue photoluminescence. The emission maxima of 1-DMF and 2-DEF are red-shifted by ca. 25 nm with respect to λ_max of 1 and 2, respectively.     

Three trinuclear Cu-M-Cu (M = Co, Ni and Zn) complexes including macrocyclic oxamido bridge: Synthesis, structures and magnetic properties

Based on the complex ligand (CuL H2L = 2,3-dioxo-5,6:15,16-dibenzo-1,4,8,13-tetraazacyclotetradeca-7,13-diene), which includes macrocyclic oxamido bridge, three trinuclear complexes were prepared. They are of the formula [(CuL)₂M(ClO₄)₂] (M = Co(1), Ni(2)) and [(CuL)₂Zn(CH₃OH)₂] · (ClO₄)₂ (3). The crystal structures of the three complexes have been determined and the M(II) of the three complexes all exist on the mirror plane. Complex 1 is the first Cu-Co complex bridged by oxamido. Their magnetic properties were studied by susceptibility versus temperature measurement, the best fitting of the experimental data led to J = −28.12 cm⁻¹ for 1, J = −42.88 cm⁻¹ for 2, and J = −2.13 cm⁻¹ for 3.     

Syntheses of PbO nano-powders using new nano-structured lead(II) coordination polymers

Nano-structures of two new Pb(II) coordination polymers, [Pb(DPAcO)₂]_n (1) and [Pb(MPAcO)₂]_n (2), HDPAcO = diphenyl acetic acid and HMPAcO = monophenyl acetic acid} were synthesized by a sonochemical method. The new nano-structures were characterized by scanning electron microscopy, X-ray powder diffraction, IR spectroscopy and elemental analyses. Compound 2 was structurally characterized by single crystal X-ray diffraction. The crystal structure of the compound 2 consists of one-dimensional polymeric units of [Pb(MPAcO)₂] and shows the coordination number in the Pb^II ions is six. The thermal stability of compounds 1 and 2 were studied by thermal gravimetric and differential thermal analyses and shows that nanostructures of compounds 1-2 are somewhat less stable then their bulk materials. PbO nano-powders were obtained by calcinations of the nano-structures of compounds 1 and 2 at 400 °C.     

Ligand-directed metal(II) coordination polymers: Unusual disorder, and photoluminescence

2,6-Dimethyl-4-phenylpyridine-3,5-dicarboxylic acid (H₂mppdc, H₂L) is firstly employed in coordination chemistry. Two metal-organic coordination polymers with a general formula of M₂L₂(4,4′-bpy)_x(H₂O)_4−2x (M = Zn or Co, x = 1 or 2) are assembled from H₂L, 4,4′-bipyridine, zinc and cobalt salt under hydrothermal conditions, and characterized by single-crystal X-ray diffraction analyses. Of the crystal structures of title compounds, L ligands, limited in the environment from 4,4′-bipyridine, array in head-to-head and head-to-tail modes which are corresponding to the 1D (1) and 3D (2) polymeric structures, respectively. Interesting disorders occur in the crystal lattice of compound 1. And compound 2 has a 3D 4² · 6¹⁰ · 8³ topology. Solid-state H₂L and 1 have expected photoluminescence at room temperature.     

Assembly of metal coordination framework, [M(C5O5)(dpe)], with a 2D bi-layer architecture: Thermal stability and magnetic properties (M = Mn, Fe, Cd and Co; dpe = 1,2-bis(4-pyridyl)ethane)

A series of coordination polymers, [M(C₅O₅)(dpe)] (M = Mn 1, Fe 2, Cd 3 and Co 4; dpe = 1,2-bis(4-pyridyl)ethane) with a 2D metal-organic framework (MOF) has been synthesized and characterized by single-crystal X-ray diffraction studies. Structural determination reveals that compounds 1-4 are isostructural and possess a 2D brick-wall-like layered framework with a rectangle grid as the basic building unit through the connectivity of metal ions with μ₃-, μ₄-croconates and anti-dpe ligands. Two 2D layers are then cross-linkaged by gauche-dpe ligands to complete a 2D bi-layered MOF and then extended to a 3D supramolecular architecture through π-π and C-H?O interactions between the croconate and pyridyl rings of dpe, which exhibit high thermo-stability and keep their crystalline forms up to 350 °C. The magnetic exchange coupling between the metal centers for compounds 1, 2 and 4 was analyzed and based on the Curie-Weiss expression and a binuclear magnetic model. The negative values of the Weiss constant and the magnetic exchange coupling constant indicate the antiferromagnetic nature between the metal ions via the bridges of bis-bidentate adjacent μ₃-croconate ligands.     

Synthesis, structures and DNA binding of ternary transition metal complexes M(II)L with the 2,2-bipyridylamine (L = p-HB, M = Co, Ni, Cu and Zn)

New ternary transition metal complexes of formulations [Co(bpa)(p-HB)₂](bpa = 2,2′-bipyridylamine, p-HB = p-hydroxybenzenecarboxylic acid) (1), [Ni(bpa)(p-HB)(H₂O)₂]⁺(NO₃)⁻ · H₂O (2), , [Cu(bpa)(p-HB)Cl] (4) and [Zn(bpa)(p-HB)₂]₂ · 0.5H₂O (5) are prepared, their structural features are characterized by crystal structural studies, and their DNA binding propensity has been evaluated by fluorescence method. The molecular structure of complex 1 shows the six coordinate octahedral geometry with one bpa and two p-HB ligands, complex 2 is the cationic complex and has the six coordinate octahedral structure with one bpa, one p-HB and two aqua ligands, complex 3 is also the cationic complex of octahedral coordination with two bpa and one p-HB ligands, complex 4 is five coordinate distorted square pyramidal with one bpa, one p-HB and chloride ligands and complex 5 has the distorted octahedral coordination with two p-HB and one bpa ligands. In all of the complexes, both bpa and p-HB act as the bidentate N and O-donor ligands, respectively. The intermolecular H-bond networks, together with π-π interaction in their solid state are also described. The complexes show the competitive inhibition of ethidium binding to DNA, and the DNA binding propensity can be reflected as the relative order: 3 > 2 > 1 > 5 > 4, in which the cationic charged Ni(II) complexes 2 and 3 show the most effective inhibition ability.     

Synthesis, structure and properties of copper(II) and manganese(II) coordination polymers with 1,5-dinitronaphthalene-3,7-dicarboxylate

Two new metal-organic coordination polymers with 1,5-dinitronaphthalene-3,7-dicarboxylate (NNDC), [Cu₂(NNDC)₂(DMF)_1.8(DMSO)_2.2(H₂O)₂]·H₂O (1) and [Mn₃(NNDC)₃(DMSO)₄]·2DMSO (2) have been synthesized under solvothermal conditions and characterized by single crystal X-ray diffraction and Thermogravimetric Analysis (TGA). The structure of compound 1 consists of one-dimensional chains with copper ions being linked by the dicarboxylate ligands. The coordination chains are associated into ladder-like double chains through O-H?O hydrogen bonds and π-π interactions, and the ladders are packed in a cross fashion through further π-π interactions to give the three-dimensional structure. The Mn(II) compound exhibits a 3D framework with the pcu topology, in which [Mn₃(COO)₆] clusters as octahedral secondary building blocks are linked by the naphthalene spacers. Magnetic analyses were carried out based on both temperature- and field-dependent data, consistently suggesting relatively weak antiferromagnetic interactions within the carboxylate bridged [Mn₃(COO)₆] cluster.     

Structural diversity and optical properties in the M-X-isonicotinic (M = Zn, Cd; X = Cl, Br, I) system: New zero-, one-, two- and three-dimensional inorganic-organic hybrids

Assembly of isonicotinic acid ligand (HL) with metal halide, five new hybrid complexes [CdI₂(C₅H₄NCOOH)(C₅H₄NHCOO)] · H₂O (1), Na_n[ZnCl₂(C₅H₄NCOO)]_n · 2nH₂O (2), [CdX(C₅H₄NCOO)]_n (X = Br (3), I (4)) and [Cd₃Cl₂(OH)₂(C₅H₄NCOO)₂]_n (5) were obtained, which display a variety of structural motifs, ranging from zero-dimensional to complicated three-dimensional networks. Complex 1 possesses an isolated unit MX₂ that is further connected into 3D networks through hydrogen bonding and π-π stacking interactions. Complex 2 is characterized by an infinite one-dimensional chain of zinc atoms bridged by L⁻ ligands. While complexes 3 and 4 possess X-bridging ^∞₁[CdX_2/2] inorganic chains connected by L⁻ ligands to form a 2D hybrid network structure. In the case of 5, the cadmium(II) cation is bridged by μ₃-Cl atom and μ₃-OH⁻ group to form a 2-D ^∞₂[Cd_6/2Cl_6/3(μ₃-OH)₂] inorganic layer which is further extended into 3-D framework by bridging L⁻ ligand via Cd-N and Cd-O bonds. The optical properties of 1, 4, and 5 in the solid state are investigated at room temperature and time-dependent DFT (TDDFT) calculation using the B3LYP functional has been performed on 1. The result indicated that the emission band of 1 is attributed to an admixture of MLCT (metal-to-ligand charge-transfer) and LLCT (ligand-to-ligand charge-transfer).     

Two-dimensional coordination polymers of Zn(II) and Cd(II) derived from 3,3′,5,5′-azobenzenetetracarboxylic acid exhibiting solvent facilitated structure reversibility

Two Cd(II) and Zn(II) coordination polymers based on 3,3′,5,5′-azobenzenetetracarboxylic acid (H₄abtc): [Cd₂(abtc)(H₂O)₆]·DMF·0.5H₂O (1) and [Zn₂(abtc)(bpy)(H₂O)₂]·DMF·H₂O (2) are synthesized and structurally characterized. Both 1 and 2 are 2D polymers but interconnected by solvent molecules to generate 3D suprastructures. Solvent expulsion leads to rupture of both structures, but upon re-exposure to the solvent mixture they exhibit remarkable ability to regain the original structure reversibly from the almost amorphous solvent-expelled form. Compounds with such structural flexibility and reversibility are expected to have some useful functionality.