Pyridinium Ylide-Mediated Diastereoselective Synthesis of Spirocyclopropanyl-pyrazolones via Cascade Michael/Substitution Reaction.

We have devised a highly diastereoselective formal [2 + 1] annulation reaction of arylidene/alkylidine-pyrazolones with in situ-generated supported as well as standard pyridinium ylides to construct spirocyclopropanyl-pyrazolones. The cascade approach exhibits a wide range of functional group tolerance, gram-scale capability, and substrate versatility. A diverse range of spirocyclic cyclopropanes was synthesized extensively with both mediators, and the supported pyridine was reused in subsequent cycles. Density functional theory calculations confirmed the formation of spirocyclopropane as the lower energy pathway.

Recent developments in photodynamic therapy and its application against multidrug resistant cancers.

Recently, photodynamic therapy (PDT) has received a lot of attention for its potential use in cancer treatment. It enables the therapy of a multifocal disease with the least amount of tissue damage. The most widely used prodrug is 5-aminolevulinic acid, which undergoes heme pathway conversion to protoporphyrin IX, which acts as a photosensitizer (PS). Additionally, hematoporphyrin, bacteriochlorin, and phthalocyanine are also studied for their therapeutic potential in cancer. Unfortunately, not every patient who receives PDT experiences a full recovery. Resistance to different anticancer treatments is commonly observed. A few of the resistance mechanisms by which cancer cells escape therapeutics are genetic factors, drug-drug interactions, impaired DNA repair pathways, mutations related to inhibition of apoptosis, epigenetic pathways, etc. Recently, much research has been conducted to develop a new generation of PS based on nanomaterials that could be used to overcome cancer cells' multidrug resistance (MDR). Various metal-based, polymeric, lipidic nanoparticles (NPs), dendrimers, etc, have been utilized in the PDT application against cancer. This article discusses the detailed mechanism by which cancer cells evolve towards MDR as well as recent advances in PDT-based NPs for use against multidrug-resistant cancers.

A reusable polymer anchored pyridine mediated formal [4 + 1] annulation reaction for the diastereoselective synthesis of 2,3-dihydrobenzofurans.

We have developed a highly stereoselective formal [4 + 1] annulation reaction to construct trans-2,3-dihydrobenzofurans utilising in situ generated supported pyridinium ylide. This approach has excellent substrate versatility and gram-scale synthesis capability. Moreover, the polymer-anchored pyridine has been recovered and reused multiple times. The product has been transformed into valuable molecules.

Modulation of iron spin states in highly distorted iron(III) porphyrins: H-bonding interactions and implications in hemoproteins.

A family of five- and six-coordinated Fe-porphyrins which enable us to scrutinize the effects of non-covalent interactions on the out-of-plane displacement of iron and its spin-states and axial ligand orientation in a single distorted macrocyclic environment has been reported. Combined analysis using single-crystal X-ray structure determination and EPR spectral investigation revealed the stabilization of the high-spin state of iron in the five-coordinate complex FeIII(TPPBr8)(OCHMe2), while six-coordinate complexes [FeIII(TPPBr8)(MeOH)2]ClO4, [FeIII(TPPBr8)(H2O)2]ClO4 and [FeIII(TPPBr8)(1-MeIm)2]ClO4 stabilize admixed-high, admixed-intermediate and low-spin states, respectively. The H-bonding interactions between the weak axial H2O/MeOH and perchlorate anion resulted in an elongation of the Fe-O bond which eventually shortened the Fe-N(por) distances leading to the stabilization of the admixed spin state of iron which, otherwise, stabilizes the high-spin (S = 5/2) state only. In addition, the iron atom in [FeIII(TPPBr8)(H2O)2]ClO4 is displaced by 0.02 Å towards one of the water molecules engaged in the H-bonding interactions leading to two different Fe-O (H2O) distances of 2.098(8) and 2.122(9) Å. In contrast, iron in [FeIII(TPPBr8)(MeOH)2]ClO4 sits on the plane of the porphyrin since both the axial methanol units are engaged in similar H-bonding interactions with the ClO4- ion. Moreover, the X-ray structure of low-spin FeII(TPPBr8)(1-MeIm)2 revealed a dihedral angle of 63.0° between two imidazoles which deviates largely from the expected angle of 90° (perpendicular orientations) since the axial imidazole protons are engaged in strong intermolecular C-H⋯π interactions which thereby restrict the axial ligand movement. The complex also displays the shortest Fe-N(1-MeIm) bond along with smallest dihedral angles of 7.8° and 22.4° between the axial imidazole ring and the closest Fe-Np axis due to strong π-interactions between iron and the axial imidazole ligand. Our work highlights the influence of non-covalent interactions on the out-of-plane displacement and spin state of iron and axial ligand orientations which are indeed important steps in the functioning of various hemoproteins.

Reusable Supported Pyridine-Mediated Cascade Synthesis of trans-2,3-Dihydroindoles via In Situ-Generated N-Ylide.

Merrifield resin-anchored pyridines were prepared and applied as reusable mediators for trans-selective cascade synthesis of 2,3-dihydroindoles. The developed approach relied on in situ N-ylide formation followed by Michael substitution reactions. The cascade reaction was also carried out efficiently with simple pyridine. The products were further transformed into synthetically valuable compounds, and supported pyridine was reused for multiple cycles. Density functional theory calculations confirmed the trans-selectivity as the lower-energy pathway.

Graphene quantum dots-hybrid hydrogel as an avant-garde biomimetic scaffold for diabetic wound healing.

In the age of fathoming biomedical predicaments, ardently emerged the field of materiobiology to effectively counter the archetypal and outdated therapies. Correspondingly, the subpar activity of the over-the-counter wound dressing pharmaceuticals have been dominated with the implementation of biocompatible, water-retaining exotic hydrogels to facilitate accelerated diabetic wound healing. Considering a strategy to develop a pragmatic biomimetic scaffold having the ability of dynamic wound healing with diminutive inflammation, we investigated the creation of graphene quantum dot (GQD)-polyacrylic acid (PAA) hybrid hydrogel. We observe appropriate percentage of GQD incorporation in PAA to demonstrate lower pro-inflammatory cytokines, interleukin (IL-6), and tumour necrosis factor (TNF-α) along with higher anti-inflammatory (IL-10) expressions in contrast to natural and standard controls. Likewise, histological examinations corresponding to the in-vitro and in-vivo toxicological analysis of GQD-PAA manifested to be a non-toxic, biocompatible saviour of diabetic wounds. This hybrid hydrogel reports the quickest diabetic wound healing of 13 days. Additionally, the hybrid hydrogel also demonstrates salient antibacterial activity against E. coli. We explore a multifaceted mechanistic approach attributed by the hybrid framework as an avant-garde solution in materiobiology and diabetic wound healing nexus. We believe the GQD-hybrid hydrogel reveals an advancement that could portray a new horizon against diabetic wounds.

Synthesis of fused polycyclic ß-carboline derivatives using Ugi-4CR followed by cascade cyclization.

Ugi-four component reaction (Ugi-4CR) is extremely attractive for diversity-oriented and step economical synthesis as evident from past applications. Here we report the synthesis of fused polycyclic ß-carboline derivatives by sequential Pictet-Spengler's and Ugi-4CR multi-component reaction followed by cascade cyclization. The post cyclisation of Ugi product provides conformationally stable heterocyclic molecule that is expected to be suitable for interaction with different biological targets. The methodology provides a simple and facile access to heterocycles embedded in polycyclic framework which otherwise seems difficult to synthesize by conventional methods. Synthesis of fused Polycyclic ß-Carboline Derivatives Using Ugi-4CR Followed by Cascade Cyclization.

Juxtaposing the quality of compost and vermicompost produced from organic wastes amended with cow dung.

Composting is a propitious technology to change bio-degradable solid waste into organic fertilizers. Considering this, five types of organic waste viz., leaf litter (Tectona grandis), water hyacinth (Eichhornia crassipes), cauliflower waste (Brassica oleracea var. botrytis), coir pith, and mushroom spent waste were composted with and without the use of earthworm (Eisenia fetida). The reaction (pH) and electrical conductivity of compost and vermicompost ranged from 6.98 to 7.45 and 6.97 to 7.36, 0.11 to 0.21 dSm-1, and 0.11 to 0.25 dSm-1, respectively. The chemical oxygen demand both the compost and vermicompost ranged from 687 to 1170 mg l-1 and 633-980 mg l-1 respectively. Cation exchange capacity (CEC) ranged from, 75 to 121 (c mol (p+) kg-1, and 80 to 127 (c mol (p+) kg-1, respectively. The C:N of compost and vermicompost varied from 16:1 to 33:1 and 12:1 to 19:1, respectively. The organic carbon content was decreased (18.3-38.7%), while secondary and micronutrient contents increased over the initial concentration. The NH4+ and NO3- content of compost and vermicompost ranged from 270 to 510 mg kg-1 and 230-430 mg kg-1, 560 to 105 mg kg-1, and 690-1100 mg kg-1, respectively. The nitrification index (NH4+/NO3-) ranged from 0.3 to 0.9 in composts and 0.3 to 0.6 in vermicomposts. The dehydrogenase and urease activity varied from 685 to 1696 µg g-1 hr-1 and 938-2549 µg TPF g-1 day-1 respectively. The bacteria, fungi and actinomycetes population were 2-3, 0.3-0.7 and 3-8 times more in vermicompost over the corresponding compost. This study confirmed that compared to compost, vermicompost showed better nutrients and microbial properties.

Halogen Bond Mediated Self-Assembly of Mononuclear Lanthanide Complexes: Perception of Supramolecular Interactions, Slow Magnetic Relaxation, and Photoluminescence Properties.

Five new mononuclear lanthanide complexes, [LnL2][Et3NH]·THF/H2O (Ln = Nd, Tb, Dy) (H2LCl = 2-bis(2-hydroxy-3,5-dichloro benzyl)aminomethyl]pyridine), Ln = Nd (1), Tb (2), and Dy (3), and (H2LBr = 2-bis(2-hydroxy-3,5-dibromo benzyl)aminomethyl]pyridine), Ln = Nd (4, H2O) and Tb (5), were synthesized and structurally characterized by single-crystal X-ray diffraction analyses. Being isostructural in all the five cases, the metal center is octa-coordinated with a triangular dodecahedron (D2d symmetry) geometry, and it is independent of the halogen substitution (Cl/Br). This close similarity is due to the composite interplay of hydrogen/halogen bond interactions that control the overall crystal packing, yet notable differences in association patterns among the individual ones arise from the subtle stereo-electronic requirement of individual molecules in the three-dimensional (3D) architecture. Hirshfeld surface and density functional theory (DFT) calculations clearly vouch for the importance of the hydrogen bond and halogen bond interactions observed in the structure. Detailed magnetic measurements using direct-current and alternating-current susceptibility measurements show slow magnetic relaxation in 3, a characteristic feature of the single-molecule magnets (SMMs), which is not shown by 1 and 2. Steady-state and time-resolved photoluminescence of Tb(III) complexes shows a strong ligand-to-metal energy transfer that can be modulated by changing the substitution on phenolic ligands. The results from these analyses indicate that it may be advantageous to consider the subtle role of hydrogen bond (HB)/halogen bond (XB) intermolecular interactions judiciously for the design of SMMs and luminescent materials based on halogen-substituted ligands.

Electrochemical, Photophysical, Morphological and DFT Study of Polymorphic Sn(IV)-Porphyrins Containing Fluorinated Axial Ligand.

In this study, we report the polymorphism of six coordinated Sn(IV)- tetrabromophenyl porphyrins axially armed with fluorine-substituted phenolate ligands (structural formula [Sn(TBrPP)2+ (A- )2 ], where A is the axial ligand=3,5-difluoro phenol, compound 1). One form stabilizes in triclinic system (namely, 1α), and the other stabilizes in monoclinic system (namely, 1ß). The two 1α and 1ß polymorphs display distinct photophysical and morphological properties in the solid state. X-ray diffraction study reveals that these polymorphs 1α and 1ß significantly differ in their supramolecular architecture, different axial phenolate conformations, and noncovalent interactions, which are responsible for their distinct solid-state properties. The crystal packing of these polymorphs dominates by intermolecular C-H⋅⋅⋅F, C-H⋅⋅⋅π and C-Br⋅⋅⋅F interhalogen interactions. Furthermore, the solid-state emission spectra of 1α showed red-shifted emission bands with respect to 1ß, in addition the redox behavior of 1α is slightly different in comparison to 1ß. Complementary theoretical studies with Hirshfeld surface analysis show the definite role of Br⋅⋅⋅F interhalogen interactions in the overall stability. Mapping the electrostatic potential isosurfaces with the aid of density functional theory in compound 1 clearly shows the presence of σ-hole, a requisite feature to show halogen interactions in the crystalline state. In addition, lattice energy and single point energy calculation shows that 1α was found to be energetically more favorable and thermodynamically more stable compare to 1ß.

Efficient native strains of rhizobia improved nodulation and productivity of French bean (Phaseolus vulgaris L.) under rainfed condition.

Biological nitrogen fixation is the most important eco-friendly approach to nitrogenous fertilizer management in the rhizosphere. Rhizobium is considered the most important symbiotic N-fixing microorganism. Native strains of Rhizobium perform better than the non-native strains by getting ambient conditions for growth and proliferation. Native strains enhance the soil fertility and productivity of pulses. The study was carried out in three phases, i.e., pot experiment, field experiment, and farmers' field demonstrations. In a pot experiment, two isolated rhizobia were inoculated to seeds of French bean (Phaseolus vulgaris) and applied with and without lime to evaluate crop growth, photosynthetic activity, and nodule characteristics of the target crop. In the field, strains were inoculated to seeds of French bean, which received different combinations of inputs- inorganic fertilizers, lime, and boron- to study the influence of native stains on crop productivity and agronomic efficiency. In comparison to non-limed packaging, the amounts of chlorophyll a, chlorophyll b, total chlorophyll, and chlorophyll a:b were, respectively, 13% to 30%, 1% to 15%, 10% to 27%, and 1% to 20% greater in limed packages. In limed packages compared to non-limed packages, the root length, biomass, density, and growth rate were increased by 16% to 17%, 36% to 52%, 38% to 49%, and 36% to 52%, respectively. In contrast to non-limed packages, limed packages had nodule attributes like the number of nodules per plant and nodular weight, which were 28% to 41% and 33% to 37% greater, respectively. Inoculation of native rhizobia strains with liming to acid soil increased 46% to 72% of leaf nitrogen content over non-limed rhizobia inoculated packages. In a field experiment, the adoption of soil test-based fertilizer application had an advantage of 25% in pod yield over farmers' practice. Acid soil amelioration with lime improved pod yield from 14% to 39% over non-limed packages. Farmers' field demonstration recorded the highest pod yield in the package where seeds were inoculated with S2 (RBHR-21) strain added with soil test-based fertilizers (STD) followed by STD + S1 (RBHR-15) with 98% and 84% increase over farmers' practice. However, experimental evidence favored using both strains for bio-inoculation of the French bean crop.

Computational insight into the halogen bonded self-assembly of hexa-coordinated metalloporphyrins.

We demonstrate herein a computational study probing the influence of metalloporphyrins on intermolecular halogen bonding (XB) during supramolecular self-assembly. The results demonstrate that porphyrin aromatic rings can activate or deactivate halogen bonding interactions, especially those on axial ligands, and further influence the preference type of halogen···halogen bonding during the supramolecular self-assembly. Calculations show that the halogen atom present at the equatorial position has a higher sigma hole potential (VS,max) than that at the axial position. The computational analysis and our observations from the X-ray structure analysis are in good agreement. From structural analysis it is clear that equatorial halogen atoms prefer to participate in Type-II XB interactions whereas the axial halogen atoms either participate in Type-I XB interaction or reluctant to participate in XB interactions due to the decrease of their sigma hole potential. Thus, we demonstrate, herein, for the first time a computational study probing the direct influence of the porphyrin's ring current on the sigma hole potential (VS,max) of the halogen atoms and subsequently the effects of the supramolecular self-assembly.

Synthesis and photophysical properties of pyridyl conjugated triazole appended naphthalenediimide derivatives.

A series of three substituted triazole appended NDI-derivatives, 2,7-bis(3,5-di(pyridin-X-yl)-4H-1,2,4-triazol-4-yl)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone (where X = 2, NDI-PyTz-1; 3, NDI-PyTz-2; and 4, NDI-PyTz-3), were designed, synthesized and well characterized using various analytical and spectroscopic techniques. All the three NDI-PyTz derivatives exhibit decent electronic properties as suggested by DFT, cyclic voltammetry and fluorescence studies. In particular, NDI-PyTz-1 demonstrated the generation of a stable anion radical [NDI-PyTz-1]˙-.

In vitro cartilage construct generation from silk fibroin- chitosan porous scaffold and umbilical cord blood derived human mesenchymal stem cells in dynamic culture condition.

Cartilage construct generation includes a scaffold with appropriate composition to mimic matrix of the damaged tissue on which the stem cells grow and differentiate. In this study, umbilical cord blood (UCB) derived human mesenchymal stem cells (hMSCs) were seeded on freeze dried porous silk-fibroin (SF)/chitosan (CS) scaffolds. Influence of static and dynamic (spinner flask bioreactor) culture conditions on the developing cartilage construct were studied by in-vitro characterization for viability, proliferation, distribution, and chondrogenic differentiation of hMSCs over the scaffold. Constructs developed in spinner flask consisted of 62% live cells, and exhibited 543% more cell density at the core than constructs cultured in static system. Quantification of DNA and glycosaminoglycans accumulation after 21 days showed the progression of chondrogenic differentiation of hMSCs was higher in dynamic culture compared to static one. In constructs generated under dynamic condition, histology staining for proteoglycan matrix, and fluorescence staining for collagen-II and aggrecan showed positive correlation between early and late stage chondrogenic markers, which was further confirmed by quantitative PCR analysis, showing low collagen-I expression and highly expressed Sox9, collagen-II and aggrecan. The present study demonstrated that construct generated by combining 3D SF/CS scaffold with UCB-hMSCs under dynamic condition using spinner flask bioreactor can be used for cartilage tissue regeneration for future medical treatments. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 397-407, 2018.

DFT analysis of the electronic structure of Fe(IV) species active in nitrene transfer catalysis: influence of the coordination sphere.

Nitrene transfer reactions to various hydrocarbon molecules can be efficiently catalyzed by Fe complexes through a mechanism reminiscent of the oxygen transfer function of oxygenase enzymes. Such enzymes exhibit a high-valent iron oxo Fe(IV) = O as the active species, and it has also been proposed that an analogous species, i.e., Fe(IV) = NR (NR being the nitrene group) is responsible for the nitrene transfer activity. We describe here the influence of the Fe(IV) coordination sphere on some key parameters for nitrene transfer efficacy, such as the spin state of the Fe(IV) cation, the electronic affinity, and the bond dissociation energy of the NHR moiety. We explore here the electronic properties of Fe(IV) = NTs (NTs = tolylsulfonylimido group) mononuclear complexes with ligands involving phenolate and nitrogen donor groups, as catalytic properties with such ligands have been found to be quite promising. Six tetradentate ligands were studied, which derive from three different scaffolds: 2-methylenepyridine-N,N-bis(2-methylene-4,6-dichlorophenol) and 2-methylenepyridine-N,N-bis(2-methylene-4,6-dimethylphenol), N,N-dimethyl-N',N'-bis(2-methylene-4,6-dichlorophenol) ethylenediamine, and N,N-dimethyl-N',N'- bis(2-methylene-4,6-dimethylphenol) ethylenediamine, N,N'-bis(2-methylene-4,6-dichlorophenol)-N,N'-dimethyl-1,2-diaminoethane and N,N'-bis(2-methylene-4,6-dimethylphenol)-N,N'-dimethyl-1,2-diaminoethane. Thanks to thorough DFT computations, we present some rationalization of the electronic properties of the resulting Fe(IV) = NTs complexes in relation to their coordination sphere and compare them to other Fe(IV) nitrene active species. We show in particular the important role of the anionic character and strong π-donation of the phenolate groups.

Exploring supramolecular self-assembly of tetraarylporphyrins by halogen bonding: crystal engineering with diversely functionalized six-coordinate tin(L)2-porphyrin tectons.

This study targets the construction of porphyrin assemblies directed by halogen bonds, by utilizing a series of purposely synthesized Sn(axial ligand)2-(5,10,15,20-tetraarylporphyrin) [Sn(L)2-TArP] complexes as building units. The porphyrin moiety and the axial ligands in these compounds contain different combinations of complimentary molecular recognition functions. The former bears p-iodophenyl, p-bromophenyl, 4'-pyridyl, or 3'-pyridyl substituents at the meso positions of the porphyrin ring. The latter comprises either a carboxylate or hydroxy anchor for attachment to the porphyrin-inserted tin ion and a pyridyl-, benzotriazole-, or halophenyl-type aromatic residue as the potential binding site. The various complexes were structurally analyzed by single-crystal X-ray diffraction, accompanied by computational modeling evaluations. Halogen-bonding interactions between the lateral aryl substituents of one unit of the porphyrin complex and the axial ligands of neighboring moieties was successfully expressed in several of the resulting samples. Their occurrence is affected by structural (for example, specific geometry of the six-coordinate complexes) and electronic effects (for example, charge densities and electrostatic potentials). The shortest intermolecular I⋅⋅⋅N halogen-bonding distance of 2.991 Šwas observed between iodophenyl (porphyrin) and benzotriazole (axial ligand) moieties. Manifestation of halogen bonds in these relatively bulky compounds without further activation of the halophenyl donor groups by electron-withdrawing substituents is particularly remarkable.

Intermolecular iodine-iodine interactions in bis(pyridine-3-carboxylato)[tetrakis(4-iodophenyl)porphyrinato]tin(IV) and bis(pyrimidine-5-carboxylato)[tetrakis(4-iodophenyl)porphyrinato]tin(IV).

Crystals of bis(pyridine-3-carboxylato)[tetrakis(4-iodophenyl)porphyrinato]tin(IV) dimethylformamide sesquisolvate, [Sn(C44H24I4N4)(C6H4NO2)2]·1.5C3H7NO, (I), and bis(pyrimidine-5-carboxylato)[tetrakis(4-iodophenyl)porphyrinato]tin(IV) dimethylformamide sesquisolvate, [Sn(C44H24I4N4)(C5H3N2O2)2]·1.5C3H7NO, (II), exhibit interporphyrin iodine-iodine halogen bonds, which direct the supramolecular assembly of the porphyrin entities into halogen-bonded layers. Each molecule interacts with its four nearest neighbours within the layer via eight I···I interactions at approximately 3.8 and 4.0 Å. The two structures are isomorphous and isometric, with the metalloporphyrin complexes located on centres of crystallographic inversion.

A three-dimensional coordination polymer of 3-(3,5-dicarboxybenzyloxy)benzoic acid with zinc.

The synthesis is reported of the tricarboxylic acid 3-(3,5-dicarboxybenzyloxy)benzoic acid (H3L) and the product of its reaction under solvothermal conditions with ZnII cations, namely poly[[µ6-3-(3,5-dicarboxylatobenzyloxy)benzoato](dimethylformamide)-µ3-hydroxido-dizinc(II)], [Zn2(C16H9O7)(OH)(C3H7NO)]n, the formation of which is associated with complete deprotonation of H3L. Its crystal structure consists of a single-framework coordination polymer of the organic L³â» ligand with ZnII cations in a 1:2 ratio, with additional hydroxide and dimethylformamide (DMF) ligands coordinated to the ZnII centres. The ZnII cations are characterized by coordination numbers of 5 and 6, being bridged to each other by hydroxide ligands. In the polymeric framework, the carboxylate- and hydroxy-bridged ZnII cations are arranged in coordination-tessellated columns, which propagate along the a axis of the crystal structure, and each L³â» ligand links to seven different ZnII centres via Zn-O bonds of two different columns. The coordination framework, composed of [Zn2(L)(OH)(DMF)]n units, forms an open architecture, the channel voids within it being filled by the zinc-coordinating DMF ligands. This report provides the first structural evidence for the formation of coordination polymers with H3L via multiple metal-ligand bonds through its carboxylate groups.

A one-dimensional coordination polymer of 5-[(imidazol-1-yl)methyl]benzene-1,3-dicarboxylic acid with Cu(II) cations.

5-[(Imidazol-1-yl)methyl]benzene-1,3-dicarboxylic acid (H2L) was synthesized and the dimethylformamide- and dimethylacetamide-solvated structures of its adducts with Cu(II), namely catena-poly[[copper(II)-bis[µ-3-carboxy-5-[(imidazol-1-yl)methyl]benzoato]] dimethylformamide disolvate], {[Cu(C12H9N2O4)2]·2C3H7NO}n, (I), and catena-poly[[copper(II)-bis[µ-3-carboxy-5-[(imidazol-1-yl)methyl]benzoato]] dimethylacetamide disolvate], {[Cu(C12H9N2O4)2]·2C4H9NO}n, (II), the formation of which are associated with mono-deprotonation of H2L. The two structures are isomorphous and isometric. They consist of one-dimensional coordination polymers of the organic ligand with Cu(II) in a 2:1 ratio, [Cu(µ-HL)2]n, crystallizing as the dimethylformamide (DMF) or dimethylacetamide (DMA) disolvates. The Cu(II) cations are characterized by a coordination number of six, being located on centres of crystallographic inversion. In the polymeric chains, each Cu(II) cation is linked to four neighbouring HL(-) ligands, and the organic ligand is coordinated via Cu-O and Cu-N bonds to two Cu(II) cations. In the corresponding crystal structures of (I) and (II), the coordination chains, aligned parallel to the c axis, are further interlinked by strong hydrogen bonds between the noncoordinated carboxy groups in one array and the coordinated carboxylate groups of neighbouring chains. Molecules of DMF and DMA (disordered) are accommodated at the interface between adjacent polymeric assemblies. This report provides the first structural evidence for the formation of coordination polymers with H2L via multiple metal-ligand bonds through both carboxylate and imidazole groups.

Switching orientation of two axial imidazole ligands between parallel and perpendicular in low-spin Fe(III) and Fe(II) nonplanar porphyrinates.

We have reported here the synthesis, structure, and properties of low-spin bis-imidazole-coordinated Fe(III) and Fe(II) complexes of 5,10,15,20-tetrakis(pentafluorophenyl)-2,3,7,8,12,13,17,18-octachloroporphyrin, [Fe(III)(TFPPCl(8))(L)(2)]ClO(4) and Fe(II)(TFPPCl(8))(L)(2) (L = 1-methylimidazole, 4-methylimidazole, imidazole). The X-ray structure of Fe(II)(TFPPCl(8))(1-MeIm)(2) is reported here, which demonstrated the near-perpendicular axial ligand orientation (dihedral angle between two 1-methylimidazoles is 80.7°) for Fe(II) porphyrins in a highly saddle-distorted macrocyclic environment. Oxidation of Fe(II)(TFPPCl(8))(L)(2) using thianthrenium perchlorate produces [Fe(III)(TFPPCl(8))(L)(2)]ClO(4), which was also isolated in the solid state and characterized spectroscopically. The complex gives rhombic EPR spectra in both solid and solution phases at 77 K and thus represents a rare example of nearly parallel axial ligand orientations for the unhindered imidazoles in a saddle-distorted porphyrin macrocycle. Geometry optimization using DFT also converged to the parallel axial alignment when 1-methylimidazole was used as the axial ligand (the dihedral angle between two axial ligands is 8.6°). The potential energy surface (PES) scan results also show that the relatively parallel axial orientations are energetically preferred for Fe(III), while perpendicular orientations are preferred for the Fe(II) complexes reported here. Bulk oxidation of Fe(II)(TFPPCl(8))(L)(2) in dichloromethane at a constant potential under nitrogen converts it to [Fe(III)(TFPPCl(8))(L)(2)]ClO(4), which gives identical EPR spectra at 77 K and which upon reduction regenerates Fe(II)(TFPPCl(8))(L)(2) again. Thus, we have demonstrated here very rare examples of Fe porphyrins in which the relative axial imidazole orientations switch between parallel and perpendicular just upon changing the oxidation states of iron from +3 to +2, respectively, in a nonplanar porphyrinic environment. These observations could be immensely important for understanding the possible effects of axial histidine orientations on similar macrocyclic deformations observed in various heme proteins.