Dihydrogen Catalysis of the Reversible Formation and Cleavage of CH and NH Bonds of Aminopyridinate Ligands Bound to (η5‐C5Me5)IrIII

This study focuses on a series of cationic complexes of iridium that contain aminopyridinate (Ap) ligands bound to an (η⁵‐C₅Me₅)Ir^III fragment. The new complexes have the chemical composition [Ir(Ap)(η⁵‐C₅Me₅)]⁺, exist in the form of two isomers ( 1⁺ and 2⁺ ) and were isolated as salts of the BAr_F^? anion (BAr_F=B[3,5‐(CF₃)₂C₆H₃]₄). Four Ap ligands that differ in the nature of their bulky aryl substituents at the amido nitrogen atom and pyridinic ring were employed. In the presence of H₂, the electrophilicity of the Ir^III centre of these complexes allows for a reversible prototropic rearrangement that changes the nature and coordination mode of the aminopyridinate ligand between the well‐known κ²‐N,N′‐bidentate binding in 1⁺ and the unprecedented κ‐N,η³‐pseudo‐allyl‐coordination mode in isomers 2⁺ through activation of a benzylic C?H bond and formal proton transfer to the amido nitrogen atom. Experimental and computational studies evidence that the overall rearrangement, which entails reversible formation and cleavage of H?H, C?H and N?H bonds, is catalysed by dihydrogen under homogeneous conditions.     

Synthesis and Diverse Transformations of a Dinitrogen Dititanium Hydride Complex Bearing Rigid Acridane‐Based PNP‐Pincer Ligands

Studies on N₂ activation and transformation by transition metal hydride complexes are of particular interest and importance. The synthesis and diverse transformations of a dinitrogen dititanium hydride complex bearing the rigid acridane‐based ^acriPNP‐pincer ligands {[(^acriPNP)Ti]₂(μ₂‐η¹:η²‐N₂)(μ₂‐H)₂} are presented. This complex enabled N₂ cleavage and hydrogenation even without additional H₂ or other reducing agents. Furthermore, diverse transformations of the N₂ unit with a variety of organometallic compounds such as ZnMe₂, MgMe₂, AlMe₃, B(C₆F₅)₃, PinBH, and PhSiH₃ have been well established at the rigid ^acriPNP‐ligated dititanium framework, such as reversible bonding‐mode change between the end‐on and side‐on/end‐on fashions, diborylative N=N bond cleavage, the formal insertion of two dimethylaluminum species into the N=N bond, and the formal insertion of two silylene units into the N=N bond. This work has revealed many unprecedented aspects of dinitrogen reaction chemistry.     

Phenakite‐Type BeP2N4—A Possible Precursor for a New Hard Spinel‐Type Material

BeP₂N₄ was synthesized in a multi‐anvil apparatus starting from Be₃N₂ and P₃N₅ at 5 GPa and 1500 °C. The compound crystallizes in the phenakite structure type (space group R$\bar 3$ , no. 148) with a=1269.45(2) pm, c=834.86(2) pm, V=1165.13(4)×10⁶ pm³ and Z=18. As isostructural and isovalence‐electronic α‐Si₃N₄ transforms into β‐Si₃N₄ at high pressure and temperature, we studied the phase transition of BeP₂N₄ into the spinel structure type by using density functional theory calculations. The predicted transition pressure of 24 GPa is within the reach of today’s state of the art high‐pressure experimental setups. Calculations of inverse spinel‐type BeP₂N₄ revealed this polymorph to be always higher in enthalpy than either phenakite‐type or spinel‐type BeP₂N₄. The predicted bulk modulus of spinel‐type BeP₂N₄ is in the range of corundum and γ‐Si₃N₄ and about 40 GPa higher than that of phenakite‐type BeP₂N₄. This finding implies an increase in hardness in analogy to that occurring for the β‐ to γ‐Si₃N₄ transition. In hypothetical spinel‐type BeP₂N₄ the coordination number of phosphorus is increased from 4 to 6. So far only coordination numbers up to 5 have been experimentally realized (γ‐P₃N₅), though a sixfold coordination for P has been predicted for hypothetic δ‐P₃N₅. We believe, our findings provide a strong incentive for further high‐pressure experiments in the quest for novel hard materials with yet unprecedented structural motives.     

Synthesis,structural characterization and thermal properties of a new copper(II) one‐dimensional coordination polymer based on bridging N,N′‐bis(2‐hydroxybenzylidene)‐2,2‐dimethylpropane‐1,3‐diamine and dicyanamide ligands

The design and synthesis of polymeric coordination compounds of 3d transition metals are of great interest in the search for functional materials. The coordination chemistry of the copper(II) ion is of interest currently due to potential applications in the areas of molecular biology and magnetochemistry. A novel coordination polymer of Cu^II with bridging N,N′‐bis(2‐hydroxyphenyl)‐2,2‐dimethylpropane‐1,3‐diamine (H₂L‐DM) and dicyanamide (dca) ligands, catena‐poly[[[μ₂‐2,2‐dimethyl‐N,N′‐bis(2‐oxidobenzylidene)propane‐1,3‐diamine‐1:2κ⁶O,N,N′,O′:O,O′]dicopper(II)]‐di‐μ‐dicyanamido‐1:2′κ²N¹:N⁵;2:1′κ²N¹:N⁵], [Cu₂(C₁₉H₂₀N₂O₂)(C₂N₃)₂]_n, has been synthesized and characterized by CHN elemental analysis, IR spectroscopy, thermal analysis and X‐ray single‐crystal diffraction analysis. Structural studies show that the Cu^II centres in the dimeric asymmetric unit adopt distorted square‐pyramidal geometries, as confirmed by the Addison parameter (τ) values. The chelating characteristics of the L‐DM²⁻ ligand results in the formation of a Cu^II dimer with a double phenolate bridge in the asymmetric unit. In the crystal, the dimeric units are further linked to adjacent dimeric units through μ_1,5‐dca bridges to produce one‐dimensional polymeric chains.     

Rare‐Earth‐Metal Nitridophosphates through High‐Pressure Metathesis

Developing a synthetic method to target an broad spectrum of unknown phases can lead to fascinating discoveries. The preparation of the first rare‐earth‐metal nitridophosphate LiNdP₄N₈ is reported. High‐pressure solid‐state metathesis between LiPN₂ and NdF₃ was employed to yield a highly crystalline product. The in situ formed LiF is believed to act both as the thermodynamic driving force and as a flux to aiding single‐crystal formation in dimensions suitable for crystal structure analysis. Magnetic properties stemming from Nd³⁺ ions were measured by SQUID magnetometry. LiNdP₄N₈ serves as a model system for the exploration of rare‐earth‐metal nitridophosphates that may even be expanded to transition metals. High‐pressure metathesis enables the systematic study of these uncharted regions of nitride‐based materials with unprecedented properties.     

A fourfold interpenetrating cadmium(II) metal–organic framework based on 2,4,6‐tris(pyridin‐4‐yl)‐1,3,5‐triazine with reversible photochromic properties

2,4,6‐Tris(pyridin‐4‐yl)‐1,3,5‐triazine (tpt), as an organic molecule with an electron‐deficient nature, has attracted considerable interest because of its photoinduced electron transfer from neutral organic molecules to form stable anionic radicals. This makes it an excellent candidate as an organic linker in the construction of photochromic complexes. Such a photochromic three‐dimensional (3D) metal–organic framework (MOF) has been prepared using this ligand. Crystallization of tpt with Cd(NO₃)₂·4H₂O in an N,N‐dimethylacetamide–methanol mixed‐solvent system under solvothermal conditions afforded the 3D MOF poly[[bis(nitrato‐κ²O,O′)cadmium(II)]‐μ₃‐2,4,6‐tris(pyridin‐4‐yl)‐1,3,5‐triazine‐κ³N²:N⁴:N⁶], [Cd(NO₃)₂(C₁₈H₁₂N₆)]_n, which was characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis and single‐crystal X‐ray diffraction. The X‐ray diffraction crystal structure analysis reveals that the asymmetric unit contains one independent Cd^II cation, one tpt ligand and two coordinated NO₃^? anions. The Cd^II cations are connected by tpt ligands to generate a 3D framework. The single framework leaves voids that are filled by mutual interpenetration of three independent equivalent frameworks in a fourfold interpenetrating architecture. The compound shows a good thermal stability and exhibits a reversible photochromic behaviour, which may originate from the photoinduced electron‐transfer generation of radicals in the tpt ligand.     

Double thermoresponsive block–random copolymers with adjustable phase transition temperatures: From block‐like to gradient‐like behavior

Stimuli‐responsive block–random copolymers are very useful “smart” materials as their switching behavior can be tuned by simply adjusting the composition of the random copolymer block. Because of that, we synthesized double thermoresponsive poly(N‐acryloylpyrrolidine)‐block‐poly(N‐acryloylpiperidine‐co‐N‐acryloylpyrrolidine) (PAPy‐b‐P(APi‐co‐APy)) copolymers via reversible addition fragmentation chain transfer (RAFT) polymerization and investigated their temperature‐induced self‐assembly in aqueous solution. By varying the APi/APy ratio in the random copolymer block, its phase transition temperature (PTT₁) can indeed be precisely adjusted while the temperature‐induced collapse upon heating leads to a fully reversible well‐defined micellization. By making the two blocks compositionally similar to more than 60%, the polymers' mechanistic thermoresponsiveness can furthermore be changed from block‐like to rather gradient‐like behavior. This means the micellization onset at PTT₁ and the corona collapse at the PTT of the more hydrophilic pure PAPy block (PTT₂) overlap resulting in one single broad transition. This work thus contributes to the detailed understanding of design, synthesis and mechanistic behavior of tailored “on‐demand” switchable materials. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 399–411     

Molecular Ruby under Pressure

The intensely luminescent chromium(III) complexes [Cr(ddpd)₂]³⁺ and [Cr(H₂tpda)₂]³⁺ show surprising pressure‐induced red shifts of up to ?15 cm^?1 kbar^?1 for their sharp spin‐flip emission bands (ddpd=N,N′‐dimethyl‐N,N′‐dipyridine‐2‐yl‐pyridine‐2,6‐diamine; H₂tpda=2,6‐bis(2‐pyridylamino)pyridine). These shifts surpass that of the established standard, ruby Al₂O₃:Cr³⁺, by a factor of 20. Beyond the common application in the crystalline state, the very high quantum yield of [Cr(ddpd)₂]³⁺ enables optical pressure sensing in aqueous and methanolic solution. These unique features of the molecular rubies [Cr(ddpd)₂]³⁺ and [Cr(H₂tpda)₂]³⁺ pave the way for highly sensitive optical pressure determination and unprecedented molecule‐based pressure sensing with a single type of emitter.     

3‐Cyano‐6‐hydroxy‐4‐methyl‐2‐pyridone: two new pseudopolymorphs and two cocrystals with products of an in situ nucleophilic aromatic substitution

Four crystal structures of 3‐cyano‐6‐hydroxy‐4‐methyl‐2‐pyridone (CMP), viz. the dimethyl sulfoxide monosolvate, C₇H₆N₂O₂·C₂H₆OS, (1), the N,N‐dimethylacetamide monosolvate, C₇H₆N₂O₂·C₄H₉NO, (2), a cocrystal with 2‐amino‐4‐dimethylamino‐6‐methylpyrimidine (as the salt 2‐amino‐4‐dimethylamino‐6‐methylpyrimidin‐1‐ium 5‐cyano‐4‐methyl‐6‐oxo‐1,6‐dihydropyridin‐2‐olate), C₇H₁₃N₄⁺·C₇H₅N₂O₂⁻, (3), and a cocrystal with N,N‐dimethylacetamide and 4,6‐diamino‐2‐dimethylamino‐1,3,5‐triazine [as the solvated salt 2,6‐diamino‐4‐dimethylamino‐1,3,5‐triazin‐1‐ium 5‐cyano‐4‐methyl‐6‐oxo‐1,6‐dihydropyridin‐2‐olate–N,N‐dimethylacetamide (1/1)], C₅H₁₁N₆⁺·C₇H₅N₂O₂⁻·C₄H₉NO, (4), are reported. Solvates (1) and (2) both contain the hydroxy group in a para position with respect to the cyano group of CMP, acting as a hydrogen‐bond donor and leading to rather similar packing motifs. In cocrystals (3) and (4), hydrolysis of the solvent molecules occurs and an in situ nucleophilic aromatic substitution of a Cl atom with a dimethylamino group has taken place. Within all four structures, an R₂²(8) N—H...O hydrogen‐bonding pattern is observed, connecting the CMP molecules, but the pattern differs depending on which O atom participates in the motif, either the ortho or para O atom with respect to the cyano group. Solvents and coformers are attached to these arrangements via single‐point O—H...O interactions in (1) and (2) or by additional R₄⁴(16) hydrogen‐bonding patterns in (3) and (4). Since the in situ nucleophilic aromatic substitution of the coformers occurs, the possible Watson–Crick C–G base‐pair‐like arrangement is inhibited, yet the cyano group of the CMP molecules participates in hydrogen bonds with their coformers, influencing the crystal packing to form chains.     

Synthesis of transition‐metal‐ion‐selective poly(N‐isopropylacrylamide) hydrogels by the incorporation of an Aza crown ether

A functionalized cyclam was synthesized by the attachment of a polymerizable acryloyl group to one of the four nitrogens on the cyclam molecule. The polymerization of the functionalized cyclam was performed with N‐isopropylacrylamide and N,N′‐methylene bisacrylamide, and the gels obtained were studied in the presence of different transition‐metal‐ion solutions. There was a drastic difference in the phase‐transition temperature (T_c) of the poly(N‐isopropylacrylamide) (PNIPAAm)/cyclam gel in comparison with the pure PNIPAAm gel. For the described system, a T_c shift of 15 °C was obtained. The presence of functionalized cyclam increased the hydrophilicity and T_c of the aforementioned polymer gels in deionized water (at pH 6) because of the presence of protonated amino moieties. The PNIPAAm/cyclam gels showed a dependence of the swelling behavior on pH. T_c of the pure PNIPAAm gel was weakly influenced by the presence of any transition‐metal ions, such as Cu²⁺, Ni²⁺, Zn²⁺, and Mn²⁺. The addition of Cu²⁺ or Ni²⁺ to the PNIPAAm/cyclam gel reduced T_c of the polymer gel, and a shift of approximately 12 °C was observed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1594–1602, 2003     

A two‐dimensional copper(II) coordination polymer based on 2‐propyl‐1H‐imidazole‐4,5‐dicarboxylic acid

Single‐crystal X‐ray diffraction analysis of poly[bis(μ₂‐5‐carboxy‐2‐propyl‐1H‐imidazole‐4‐carboxylato‐κ³N³,O⁴:O⁵)copper(II)], [Cu(C₈H₉N₂O₄)₂)]_n, indicates that one carboxylic acid group of the 2‐propyl‐1H‐imidazole‐4,5‐dicarboxylic acid (H₃PDI) ligand is deprotonated. The resulting H₂PDI⁻ anion, acting as a bridge, connects the Cu^II cations to form a two‐dimensional (4,4)‐connected layer. Adjacent layers are further linked through interlayer hydrogen‐bond interactions, resulting in a three‐dimensional supramolecular structure.     

Energetic propane‐1,3‐diaminium and butane‐1,4‐diaminium salts of N,N′‐dinitroethylenediazanide: syntheses,crystal structures and thermal properties

The acidity of the amine H atoms and the consequent salt formation ability of ethylenedinitramine (EDNA) were analyzed in an attempt to improve the thermal stability of EDNA. Two short‐chain alkanediamine bases, namely propane‐1,3‐diamine and butane‐1,4‐diamine, were chosen for this purpose. The resulting salts, namely propane‐1,3‐diaminium N,N′‐dinitroethylenediazanide, C₃H₁₂N₂²⁺·C₂H₄N₄O₄^2?, and butane‐1,4‐diaminium N,N′‐dinitroethylenediazanide, C₄H₁₄N₂²⁺·C₂H₄N₄O₄^2?, crystallize in the orthorhombic space group Pbca and the monoclinic space group P2₁/n, respectively. The resulting salts display extensive hydrogen‐bonding networks because of the presence of ammonium and diazenide ions in the crystal lattice. This results in an enhanced thermal stability and raises the thermal decomposition temperatures to 202 and 221 °C compared to 180 °C for EDNA. The extensive hydrogen bonding present also plays a crucial role in lowering the sensitivity to impact of these energetic salts.     

Poly[[chlorido(1,10‐phenanthroline‐κ2N,N′)copper(II)]‐μ3‐1,1,3,3‐tetracyano‐2‐ethoxypropenido‐κ3N:N′:N′′]: coordination polymer sheets linked into bilayers by hydrogen bonds

In the title compound, [Cu(C₉H₅N₄O)Cl(C₁₂H₈N₂)]_n or [Cu(tcnoet)Cl(phen)]_n, where phen is 1,10‐phenanthroline and tcnoet is 1,1,3,3‐tetracyano‐2‐ethoxypropenide, the axially elongated (4 + 2) coordination polyhedron around the Cu^II centre contains N atoms from three different tcnoet ligands. The resulting coordination polymer takes the form of sheets which are linked in pairs by a single C—H...N hydrogen bond to form bilayers. The bond lengths provide evidence for significant bond fixation in the phen ligand and extensive electronic delocalization in the tcnoet ligand, where the two –C(CN)₂ units are rotated, in conrotatory fashion, out of the plane of the central C₃O fragment.     

Tunable Trimers: Using Temperature and Pressure to Control Luminescent Emission in Gold(I) Pyrazolate‐Based Trimers

A systematic investigation into the relationship between the solid‐state luminescence and the intermolecular Au???Au interactions in a series of pyrazolate‐based gold(I) trimers; tris(μ₂‐pyrazolato‐N,N′)‐tri‐gold(I) ( 1 ), tris(μ₂‐3,4,5‐ trimethylpyrazolato‐N,N′)‐tri‐gold(I) ( 2 ), tris(μ₂‐3‐methyl‐5‐phenylpyrazolato‐N,N′)‐tri‐gold(I) ( 3 ) and tris(μ₂‐3,5‐diphenylpyrazolato‐N,N′)‐tri‐gold(I) ( 4 ) has been carried out using variable temperature and high pressure X‐ray crystallography, solid‐state emission spectroscopy, Raman spectroscopy and computational techniques. Single‐crystal X‐ray studies show that there is a significant reduction in the intertrimer Au???Au distances both with decreasing temperature and increasing pressure. In the four complexes, the reduction in temperature from 293 to 100 K is accompanied by a reduction in the shortest intermolecular Au???Au contacts of between 0.04 and 0.08 Å. The solid‐state luminescent emission spectra of 1 and 2 display a red shift with decreasing temperature or increasing pressure. Compound 3 does not emit under ambient conditions but displays increasingly red‐shifted luminescence upon cooling or compression. Compound 4 remains emissionless, consistent with the absence of intermolecular Au???Au interactions. The largest pressure induced shift in emission is observed in 2 with a red shift of approximately 630 cm^?1 per GPa between ambient and 3.80 GPa. The shifts in all the complexes can be correlated with changes in Au???Au distance observed by diffraction.     

Reactivity of TpMe2‐Supported Yttrium Alkyl Complexes toward Aromatic N‐Heterocycles: Ring‐Opening or CC Bond Formation Directed by CH Activation

Unusual chemical transformations such as three‐component combination and ring‐opening of N‐heterocycles or formation of a carbon–carbon double bond through multiple C–H activation were observed in the reactions of Tp^Me2‐supported yttrium alkyl complexes with aromatic N‐heterocycles. The scorpionate‐anchored yttrium dialkyl complex [Tp^Me2Y(CH₂Ph)₂(THF)] reacted with 1‐methylimidazole in 1:2 molar ratio to give a rare hexanuclear 24‐membered rare‐earth metallomacrocyclic compound [Tp^Me2Y(μ‐N,C‐Im)(η²‐N,C‐Im)]₆ ( 1 ; Im=1‐methylimidazolyl) through two kinds of C–H activations at the C2‐ and C5‐positions of the imidazole ring. However, [Tp^Me2Y(CH₂Ph)₂(THF)] reacted with two equivalents of 1‐methylbenzimidazole to afford a C–C coupling/ring‐opening/C–C coupling product [Tp^Me2Y{η³‐(N,N,N)‐N(CH₃)C₆H₄NHCH?C(Ph)CN(CH₃)C₆H₄NH}] ( 2 ). Further investigations indicated that [Tp^Me2Y(CH₂Ph)₂(THF)] reacted with benzothiazole in 1:1 or 1:2 molar ratio to produce a C–C coupling/ring‐opening product {(Tp^Me2)Y[μ‐η²:η¹‐SC₆H₄N(CH?CHPh)](THF)}₂ ( 3 ). Moreover, the mixed Tp^Me2/Cp yttrium monoalkyl complex [(Tp^Me2)CpYCH₂Ph(THF)] reacted with two equivalents of 1‐methylimidazole in THF at room temperature to afford a trinuclear yttrium complex [Tp^Me2CpY(μ‐N,C‐Im)]₃ ( 5 ), whereas when the above reaction was carried out at 55 °C for two days, two structurally characterized metal complexes [Tp^Me2Y(Im‐Tp^Me2)] ( 7 ; Im‐Tp^Me2=1‐methyl‐imidazolyl‐Tp^Me2) and [Cp₃Y(HIm)] ( 8 ; HIm=1‐methylimidazole) were obtained in 26 and 17 % isolated yields, respectively, accompanied by some unidentified materials. The formation of 7 reveals an uncommon example of construction of a C?C bond through multiple C–H activations.     

Facile P−C/C−H Bond‐Cleavage Reactivity of Nickel Bis(diphosphine) Complexes

Unusual cleavage of P?C and C?H bonds of the P₂N₂ ligand, in heteroleptic [Ni(P₂N₂)(diphosphine)]²⁺ complexes under mild conditions, results in the formation of an iminium formyl nickelate featuring a C,P,P‐tridentate coordination mode. The structures of both the heteroleptic [Ni(P₂N₂)(diphosphine)]²⁺ complexes and the resulting iminium formyl nickelate have been characterized by NMR spectroscopy and single‐crystal X‐ray diffraction analysis. Density functional theory (DFT) calculations were employed to investigate the mechanism of the P?C/C?H bond cleavage, which involves C?H bond cleavage, hydride rotation, Ni?C/P?H bond formation, and P?C bond cleavage.     

Synthesis and Rearrangement of Stable NHC→Silylene Adducts and Their Unique Reactivity towards Cyclohexylisocyanide

The syntheses and reactivity of the two N‐heterocyclic carbene (NHC)→ silylene complexes 2 and 4 have been investigated. The latter are easily accessible by reaction of the zwitterionic, N‐heterocyclic silylene LSi: 1 [L=Ar‐N‐C(=CH₂)CH?C(Me)‐N‐Ar, Ar=2,6‐iPr₂C₆H₃] with 1,3,4,5‐tetramethylimidazol‐2‐ylidene and 1,3‐diisopropyl‐4,5‐dimethylimidazol‐2‐ylidene, respectively. While compound 2 undergoes facile rearrangement above ?20 °C to give the unsymmetrical N‐heterocyclic silylcarbene 3 , the derivative 4 remains unchanged even after boiling in benzene. The remarkable reactivity of 3 and 4 towards cyclohexylisocyanide has been examined which leads in a unique series of C? H, Si? H, and C? N bond activations to the new triaminosilanes 5 and 6 , respectively. The novel compounds 3 , 4 , 5 , and 6 were fully characterized by ¹H, ¹³C, and ²⁹Si NMR spectroscopy, EI‐MS, elemental analysis, and single‐crystal X‐ray diffraction.     

A five‐coordinate iron(III) porphyrin complex including a neutral axial pyridine N‐oxide ligand

While six‐coordinate iron(III) porphyrin complexes with pyridine N‐oxides as axial ligands have been studied as they exhibit rare spin‐crossover behavior, studies of five‐coordinate iron(III) porphyrin complexes including neutral axial ligands are rare. A five‐coordinate pyridine N‐oxide–5,10,15,20‐tetraphenylporphyrinate–iron(III) complex, namely (pyridine N‐oxide‐κO)(5,10,15,20‐tetraphenylporphinato‐κ⁴N,N′,N′′,N′′′)iron(III) hexafluoroantimonate(V) dichloromethane disolvate, [Fe(C₄₄H₂₈N₄)(C₅H₅NO)][SbF₆]·2CH₂Cl₂, was isolated and its crystal structure determined in the space group P. The porphyrin core is moderately saddled and the Fe—O—N bond angle is 122.08 (13)°. The average Fe—N bond length is 2.03 Å and the Fe—ONC₅H₅ bond length is 1.9500 (14) Å. This complex provides a rare example of a five‐coordinate iron(III) porphyrin complex that is coordinated to a neutral organic ligand through an O‐monodentate binding mode.     

A two‐dimensional mixed‐valence CuII/CuI coordination polymer constructed from 2‐(pyridin‐3‐yl)‐1H‐imidazole‐4,5‐dicarboxylate

Coordination polymers are a thriving class of functional solid‐state materials and there have been noticeable efforts and progress toward designing periodic functional structures with desired geometrical attributes and chemical properties for targeted applications. Self‐assembly of metal ions and organic ligands is one of the most efficient and widely utilized methods for the construction of CPs under hydro(solvo)thermal conditions. 2‐(Pyridin‐3‐yl)‐1H‐imidazole‐4,5‐dicarboxylate (HPIDC²⁻) has been proven to be an excellent multidentate ligand due to its multiple deprotonation and coordination modes. Crystals of poly[aquabis[μ₃‐5‐carboxy‐2‐(pyridin‐3‐yl)‐1H‐imidazole‐4‐carboxylato‐κ⁵N¹,O⁵:N³,O⁴:N²]copper(II)dicopper(I)], [Cu^IICu^I₂(C₁₀H₅N₃O₄)₂(H₂O)]_n, (I), were obtained from 2‐(pyridin‐3‐yl)‐1H‐imidazole‐4,5‐dicarboxylic acid (H₃PIDC) and copper(II) chloride under hydrothermal conditions. The asymmetric unit consists of one independent Cu^II ion, two Cu^I ions, two HPIDC²⁻ ligands and one coordinated water molecule. The Cu^II centre displays a square‐pyramidal geometry (CuN₂O₃), with two N,O‐chelating HPIDC²⁻ ligands occupying the basal plane in a trans geometry and one O atom from a coordinated water molecule in the axial position. The Cu^I atoms adopt three‐coordinated Y‐shaped coordinations. In each [CuN₂O] unit, deprotonated HPIDC²⁻ acts as an N,O‐chelating ligand, and a symmetry‐equivalent HPIDC²⁻ ligand acts as an N‐atom donor via the pyridine group. The HPIDC²⁻ ligands in the polymer serve as T‐shaped 3‐connectors and adopt a μ₃‐κ²N,O:κ²N′,O′:κN′′‐coordination mode, linking one Cu^II and two Cu^I cations. The Cu cations are arranged in one‐dimensional –Cu1–Cu2–Cu3– chains along the [001] direction. Further crosslinking of these chains by HPIDC²⁻ ligands along the b axis in a –Cu2–HPIDC²⁻–Cu3–HPIDC²⁻–Cu1– sequence results in a two‐dimensional polymer in the (100) plane. The resulting (2,3)‐connected net has a (12³)₂(12)₃ topology. Powder X‐ray diffraction confirmed the phase purity for (I), and susceptibilty measurements indicated a very weak ferromagnetic behaviour. A thermogravimetric analysis shows the loss of the apical aqua ligand before decomposition of the title compound.     

Two ZnII mononuclear coordination compounds with pyridinedicarboxylate and auxiliary N‐(pyridin‐4‐ylmethylidene)hydroxylamine ligands

Two new mononuclear coordination compounds, bis{4‐[(hydroxyimino)methyl]pyridinium} diaquabis(pyridine‐2,5‐dicarboxylato‐κ²N,O²)zincate(II), (C₆H₇N₂O)₂[Zn(C₇H₃NO₄)₂(H₂O)₂], (1), and (pyridine‐2,6‐dicarboxylato‐κ³O²,N,O⁶)bis[N‐(pyridin‐4‐ylmethylidene‐κN)hydroxylamine]zinc(II), [Zn(C₇H₃NO₄)(C₆H₆N₂O)₂], (2), have been synthesized and characterized by single‐crystal X‐ray diffractometry. The centrosymmetric Zn^II cation in (1) is octahedrally coordinated by two chelating pyridine‐2,5‐dicarboxylate ligands and by two water molecules in a distorted octahedral geometry. In (2), the Zn^II cation is coordinated by a tridentate pyridine‐2,6‐dicarboxylate dianion and by two N‐(pyridin‐4‐ylmethylidene)hydroxylamine molecules in a distorted C₂‐symmetric trigonal bipyramidal coordination geometry.