Assembly of a New Cyano‐bridged 4f‐3d Dimer Sm(DMSO)4‐ (H2O)3Cr(CN)6 and Crystal Structure of [K3(18‐crown‐6)3‐(H2O)4]Cr(CN)6·3H2O

A new cyano‐bridged binuclear 4f‐3d complex Sm(DMSO)₄‐(H₂O)₃Cr(CN)₆ was synthesized and characterized by single crystal structure analysis. It crystallizes in monoclinic, space group P2₁ with a=0.9367(2) nm, b = 1.3917(3) nm, c = 1.1212(2) run, β = 99.88(3)° and Z = 2. In this binuclear complex, Sm atom is eight coordinated and linked to the Cr atom by a cyano bridge. The molecules packs to form 3D structure due to the hydrogen bonds among them. [K₃(18‐C‐6)₃(H₂O)₄]Cr(CN)₆·3H₂O (18‐C‐6 represents 18‐crown‐6‐ether) that was synthesized as a byproduct in the preparation of a Gd—Cr complex is also structurally characterized. Crystal data: triclinic, space group P‐l with a = 1.0496(7) nm, b= 1.1567(14) nm, c = 1.3530(13) nm, a = 94.15(9)°, β = 96.04(8)°, γ = 95.25(9)° and Z = l. [K₃(18‐C‐6)₃(H₂O)₄]‐Cr(CN)₆·3H₂O consists of ionic [K₃(18‐C‐6)₃(H₂O)₄]³⁺ and [Cr(CN)₆]^3‐ pairs, of which the [K₃(18‐C‐6)₃(H₂O)₄]³⁺ ion is a trinuclear duster connected by water, and K atoms are eight coordinated by eight oxygen atoms of one 18‐C‐6 and two water molecules.     

Syntheses,Structures, and Properties of Mono‐ and Tetranuclear Nickel(II) Complexes Derived from a Tridentate Schiff Base Ligand

Three new nickel(II) complexes constructed with N‐(2‐hydroxybenzyl)‐β‐alanine (H₂L), namely [NiL(phen)H₂O]·H₂O ( 1 ) (phen = 1.10‐phenanthroline), [Ni₄L₄(H₂O)₄]·5H₂O ( 2 ) and K[Ni₄L₄(NCS)(H₂O)₅]·5.42H₂O ( 3 ) have been synthesized and characterized by single‐crystal X‐ray diffraction analysis. Complex 1 exhibits a discrete structure, and the structures are bound together through hydrogen bonding to a one‐dimensional chain in ladder‐like fashion. Complexes 2 and 3 contain similar [Ni₄(μ₂‐O)₆] cores with “zig‐zig” arrangement. In complex 3 , the tetranuclear nickel units [Ni₄L₄(H₂O)₄] and [Ni₄L₄(NCS)(H₂O)] are alternately bridged by potassium atoms to a one‐dimensional chain. The neighboring chains are further linked up by {K₂O₂} units to a two‐dimensional layer structure. Moreover, the IR, XRD, TGA and the temperature‐dependent magnetic susceptibility for 2 and 3 have also been studied.     

Mono‐ and Di‐Potassium Derivatives of Benzenepentacarboxylic Acid

The synthesis and structure of the hydrated mono‐ and di‐potassium salts of benzenepentacarboxylic acid are reported – [K(H₄BPC)(H₂O)₂]·(H₂O) 1 and [K₂(H₃BPC)(H₂O)₃]·(H₂O) 2 (BPC = benzenepentacarboxylate). In both instances the structures are complex coordination networks, predominantly containing η¹ binding modes of the carboxylate and carboxylic acid groups, although bridging (O,O) and (O,O′) carboxylates and μ₂‐H₂O ligands also feature. Extensive hydrogen bonding is present through the carboxylic acid groups and both coordinated and interstitial water molecules.     

Syntheses,Crystal Structures,and Magnetic Properties of Three 1D Chain Metal–Nitroxide Complexes Bridged by ­Flexible Dicarboxylate Anions

Three new one‐dimensional (1D) chain metal–nitroxide complexes {[Cu(NIT4Py)₂(suc)(H₂O)] · 3H₂O}_n ( 1 ), {[Cd(NIT4Py)₂(suc)(H₂O)] · [Cd(NIT4Py)₂(suc)(H₂O)₂] · 3H₂O}_n ( 2 ), and {[Zn(NIT4Py)(glu)(H₂O)] · H₂O}_n ( 3 ) [NIT4Py = 2‐(4′‐pyridyl)‐4, 4, 5, 5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide, suc = succinate anion and glu = glutarate anion] were synthesized and structurally characterized. Single‐crystal X‐ray analyses indicate that the three complexes crystallize in neutral 1D chains in which the metal‐nitroxide units are linked by flexible dicarboxylate anions. The succinate anions only adopt trans configuration in complexes 1 and 2 , whereas the glutarate anion has gauche/anti conformation in complex 3 . Magnetic measurements show that complex 1 exhibits weak antiferromagnetic interactions between the copper ions and the nitroxides.     

Synthesis,Structures, and Properties of Four Novel Coordination Compounds based on a Flexible Tetrakis(imidazol‐1‐ylmethyl)methane Ligand

Four coordination polymers, namely, [Zn₂(TIYM)(2,6‐PYDC)₂]_n · n(CH₃OH) · 3n(H₂O) ( 1 ), [Cu(TIYM)(2,6‐PYDC)]_n · 3n(H₂O) ( 2 ), [Co(TIYM)(2,6‐PYDC)]_n · n(CH₃OH) · 3n(H₂O) ( 3 ), and [Cd₂(TIYM)(2,6‐PYDC)₂(H₂O)]_n · n(H₂O) ( 4 ) with the flexible N‐containing ligand [tetrakis(imidazol‐1‐ylmethyl)methane (TIYM)] and the N‐containing dicarboxylic acid [2,6‐pyridinedicarboxylic acid (2,6‐PYDC)] were prepared. Compounds 1 – 4 show various structures because of different N–C_center–N angles (θ) of TIYM ligands and changing coordination modes of 2,6‐PYDC. Compounds 1 , 2 , and 3 display a similar 1D ladder‐like chain, whereas 4 gives a 1D quad‐core lifting platform shaped belt. The structural diversities in 1 – 4 suggest that the multiple coordination modes or the different freely twist angles of ligands and the presence of different metal atoms play important roles in the resulting structures of the coordination polymers. Furthermore, the solid‐state luminescence properties of 1 and 4 , and the magnetic properties of 3 were investigated.     

Syntheses,Structures, and Luminescence of Metal(II) Coordination Polymers based on Flexible 1,1′‐(1,4‐Butanediyl)bis(imidazole) and Tetrachlorobenzene‐1,4‐dicarboxylate Ligands

The coordination polymers, {[Co(bbim)₂(H₂O)₂](tcbdc) · 2H₂O}_n ( 1 ), {[Ni(tcbdc)(bbim)(H₂O)₂] · 2DMF}_n ( 2 ), and {[Cu₂(tcbdc)₂(bbim)₄] · 4H₂O}_n ( 3 ) [bbim = 1,1′‐(1,4‐butanediyl)bis(imidazole) and tcbdc^2– = tetrachlorobenzene‐1,4‐dicarboxylate] were synthesized and characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis, luminescence, and single‐crystal X‐ray diffraction analysis. Complex 1 has a double‐stranded chain structure through doubly bridged [Co(bbim)₂] units. Complex 2 exhibits two‐dimensional square grid, whereas complex 3 has a three‐dimensional porous network structure with an unprecedented 4⁴ · 6¹¹ topological structure through interpenetrating square grid. The water molecules in complex 3 occupy the vacancy through three kinds of hydrogen bond interactions. Upon excitation at 370 nm, complexes 1 – 3 present solid‐state luminescence at room temperature.     

Gadolinium(III)‐Hydroxy Ladders Trapped in Succinate Frameworks with Optimized Magnetocaloric Effect

Two kinds of inorganic gadolinium(III)‐hydroxy “ladders”, [2×n] and [3×n], were successfully trapped in succinate (suc) coordination polymers, [Gd₂(OH)₂(suc)₂(H₂O)]_n ? 2n H₂O ( 1 ) and [Gd₆(OH)₈(suc)₅(H₂O)₂]_n ? 4n H₂O ( 2 ), respectively. Such coordination polymers could be regarded as alternating inorganic–organic hybrid materials with relatively high density. Magnetic and heat capacity studies reveal a large cryogenic magnetocaloric effect (MCE) in both compounds, namely (ΔH=70 kG) 42.8 J kg^?1 K^?1 for complex 1 and 48.0 J kg^?1 K^?1 for complex 2 . The effect of the high density is evident, which gives very large volumetric MCEs up to 120 and 144 mJ cm^?3 K^?1 for complexes 1 and 2 , respectively.     

Synthesis,Structures, and Luminescent Properties of Three Alkaline Earth Metal‐based MOFs Assembled from 3‐(3‐Carboxyphenoxy) Phthalic Acid Ligand

Three two‐dimensional (2D) coordination complexes, namely [Ca₂(HL)₂(H₂O)₅]_n · 2nH₂O ( 1 ), [Sr(HL)(H₂O)₃]_n · nH₂O ( 2 ), and [Ba(HL)(H₂O)₃]_n · nH₂O ( 3 ) [H₃L = 3‐(3‐carboxy‐phenoxy) phthalic acid], were synthesized by using the ligand H₃L and alkaline earth metals. Structural analysis reveals that the structures of complexes 1 – 3 can be described as 2D networks with the point (Schälfli) symbol for net: {3¹² · 4¹⁴ · 5²} topology. Additionally, the thermal stability and solid‐state luminescent properties of compounds 1 – 3 were investigated at room temperature. The quantum yield (QY) of compound 2 is 10.75 %, which is much higher than the QY of the free H₃L ligand (QY_H3L < 1 %).     

Assembled synthesis of luminescent mono/double‐layered 2D and 3D Zn (II)‐based coordination polymers tuned by flexible bis (pyridyl)propane‐1,2‐diamines and diverse organic dicarboxylates

Six mono/double‐layered 2D and three 3D coordination polymers were synthesized by a self‐assembly reaction of Zn (II) salts, organic dicarboxylic acids and L1/L2 ligands. These polymeric formulas are named as [Zn(L1)(C₄H₂O₄)_0.5 (H₂O)]_n·0.5n(C₄H₂O₄)·2nH₂O ( 1 ), [Zn₂(L2)(C₄H₂O₄)₂]_n·2nH₂O ( 2 ), [Zn(L1)(m‐BDC)]_n ( 3 ), [Zn₂(L2)(m‐BDC)₂]_n·2nH₂O ( 4 ), [Zn₃(L1)₂(p‐BDC)₃(H₂O)₄]_n·2nH₂O ( 5 ), [Zn₂(OH)(L2) (p‐BDC)_1.5]_n ( 6 ), [Zn₂(L1)(p‐BDC)₂]_n·5nH₂O ( 7 ), [Zn₂(L2)(p‐BDC)₂]_n·3nH₂O ( 8 ) and [Zn₂(L1)(C₄H₄O₄)_1.5(H₂O)]_n·n(ClO₄)·nH₂O ( 9 ) [L1 = N,N′‐bis (pyridin‐4‐ylmethyl)propane‐1,2‐diamine, L2 = N,N′‐bis (pyridin‐3‐ylmethyl)propane‐1,2‐ diamine, m‐BDC^2? = m‐benzene dicarboxylate, p‐BDC^2? = p‐benzene dicarboxylate]. Meanwhile, these polymers have been characterized by elemental analysis, infrared, thermogravimetry (TG), photoluminescence, powder and single‐crystal X‐ray diffraction. Polymers 1–6 present mono‐ and double (4,4)‐layer motifs accomplished by L1/L2 ligands with diverse conformations and organic dicarboxylates, and the layer thickness locates in the range of 5.8–15.0 Å. In three 3D polymers, the L1 and L2 molecules adopt the same cis‐conformations and join adjacent Zn (II) cations together with p‐BDC^2? or succinate, giving rise to different binodal (4,4)‐c nets with (4.5².8³)(4.5³.7²) ( 7 ), pts ( 8 ) topology and twofold interpenetrated binodal (5,5)‐c nets with (3².4⁴.5².6²)(3.4³.5².6⁴) ( 9 ). Therefore, the diverse conformations of the two bis (pyridyl)‐propane‐1,2‐diamines and the feature of different organic dicarboxylate can effectively influence the architectures of these polymers. Powder X‐ray diffraction patterns demonstrate that these bulk solid polymers are pure phase. TG analyses indicate that these polymers have certain thermal stability. Luminescent investigation reveals that the emission maximum of these polymers varies from 402 to 449 nm in the solid state at room temperature. Moreover, 1 , 3 and 5–8 show average luminescence lifetimes from 8.81 to 16.30 ns.     

Synthesis,Structure, and Fluorescent Properties of Lanthanide Complexes Based on 8‐Hydroxyquinoline‐7‐carboxylic Acid

The lanthanide complex [Eu₃(8‐HQCA)₃(COOH)(OH)₂(H₂O)₃]_n · nH₂O (8‐HQCA = 8‐hydroxyquinoline‐7‐carboxylic acid) was synthesized and characterized. Single‐crystal X‐ray diffraction shows that the trinuclear structures are linked by ligands to form 2D layers. The results of DFT calculation shows that energy can be transferred effectively from the ligand to Eu^III ions. A series of heteronuclear complexes {[(Eu_1–xY_x)₃(8‐HQCA)₃(COOH) (OH)₂(H₂O)₃]_n · nH₂O (x = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8)} were synthesized and their luminescent properties were studied. The results showed that the doping of Y^III ions could change the fluorescent intensity of the Eu^III complex, but could not change their positions.     

Synthesis, Spectral and Thermal Analyses of Novel Bi- and Polyhomonuclear Complexes of Pyrimidine Bisazo-dianil Derivatives

Seven new bi‐ and polyhomonuclear transition metal complexes with three polyhydroxlated bisazodianil ligands were synthesized and characterized. The ligands were derived from condensation of 6‐(5‐formyl‐2‐hydroxyphenylazo)‐2,4‐dihydroxypyrimidine with aliphatic diamines (H₈L¹, H₈L² and H₆L³). The data of elemental and thermal analyses, molar conductance measurement, IR, electronic and ESR spectra as well as magnetic moment measurements support the formation of [L¹Co₇Cl₆(H₂O)₁₀]·22H₂O ( 1 ), [H₂L²Mn₆Cl₆(H₂O)₈]·3H₂O·2EtOH ( 3 ), [L²Co₈Cl₈(H₂O)₁₂]·24H₂O ( 4 ), [H₄L³Co₂Cl₂(H₂O)₂]·8H₂O·2EtOH ( 6 ) with a tetrahedral geometry and [H₂L¹Ni₅Cl₄(H₂O)₁₆]·19H₂O·EtOH ( 2 ), [L²Ni₈Cl₈(H₂O)₂₈]·8H₂O·EtOH ( 5 ) with an octahedral geometry while [H₆L³Cu₃(H₂O)₇]Cl₃·10H₂O ( 7 ) has a distorted tetrahedral arrangement. The mode of bonding between the metal ions and the ligand molecules is determined and the metal‐metal interaction was studied. The activation thermo‐kinetic parameters for the thermal decomposition steps of the complexes E*, ΔH*, ΔS*, and ΔG* were calculated.     

Preparation,Structure, Spectral,and Magnetic Properties of Copper(II) Halogenonicotinates: Crystal and Molecular Structure of Tetrakis(μ‐2‐chloronicotinato‐O,O′)‐diaquadicopper(II)

The characterization of the complexes [Cu₂(2‐Clnic)₄(H₂O)₂] ( 1 ), [Cu(2,6‐Cl₂nic)₂(H₂O)₂] ( 2 ) and [Cu(5‐Brnic)₂(H₂O)₂]_n ( 3 ) (where 2‐Clnic = 2‐chloronicotinate, 2,6‐Cl₂nic = 2,6‐dichloronicotinate or 5‐Brnic = 5‐bromonicotinate) was based on elemental analysis, IR, electronic and EPR spectra, and magnetic susceptibility. Complex 1 was also studied by X‐ray analysis at 298 1a and 80 K 1b . The complex 1 contains a dinuclear Cu‐acetate molecular structure in which the carboxyl groups of the 2‐chloronicotinate ligands act as bridges and water molecules are at apical positions. The stereochemistry about Cu atom at both temperatures is typical for square pyramidal geometry with CuO₄O chromophore. The Cu‐Cu distance is 2.6513(8) and 2.6382(6) Å for 1a and 1b , respectively. The Cu atoms are displaced by 0.2069(9) and 0.1973(7) Å, respectively, from the plane containing four oxygen atoms bonded to the Cu atom toward the apical water molecules. Strong and weak hydrogen bonds as well as C–Cl···π interactions in the crystal structure are discussed as well. Both complexes, monomeric [Cu(2,6‐Cl₂nic)₂(H₂O)₂] ( 2 ) and polymeric [Cu(5‐Brnic)₂(H₂O)₂]_n ( 3 ), possess octahedral copper(II) stereochemistry with differing tetragonal distortions.     

Pb(II) and Mn(II) Coordination Compounds Involving 5,5′‐(1,4‐Phenylene)bis(1H‐tetrazole):Synthesis,Characterization, and Effect on Thermal Decomposition of Ammonium Perchlorate

Two coordination compounds [Pb₄(BDT)₃(OH)₂(H₂O)₄]·H₂O ( 1 ) and [Mn(H₂O)₆]·(HBDT)₂·2H₂O ( 2 ) [H₂BDT?5,5′‐(1,4‐phenylene)bis(1H‐tetrazole)] had been hydrothermally synthesized. 1 and 2 had been characterized by single‐crystal X‐ray diffraction, IR, elemental and thermal analyses. Structural analysis reveals that 1 exhibits 2D layer structure extended through BDT with two different coordination modes rings in transverse and vertical. 2 consists of [Mn(H₂O)₆]²⁺, free HBDT and water. In addition, 1 and 2 were explored as luminescent materials and additives to promote the thermal decomposition of ammonium perchlorate by differential scanning calorimetry.     

Synthesis,Crystal Structure and Magnetic Behaviour of {[Co(dimb)2(H2O)2]·(NO3)2·(H2O)2}n

The title complex {[Co(dimb)₂(H₂O)₂]·(NO₃)₂·(H₂O)₂}_n ( 1 ) (dimb = 1,3‐di(imidazol‐1‐ylmethyl)‐5‐methylbenzene) has been hydrothermally synthesized by the reaction of dimb with Co(NO₃)₂·6H₂O in aqueous solution. The cobalt(II) atoms are linked by bridging dimb ligands to form 2D corrugated and wavy networks containing Co₄(dimb)₄ macrocyclic motifs. Two neighboring independent layers interlinked each other in a parallel fashion to construct three‐dimensional structure by O–H···O, N–H···O and C–H···O hydrogen bonds. Magnetic measurement shows the weak antiferromagnetic interaction with a one‐dimensional chain model in the range of 5–300 K, with J of –0.68 cm⁻¹.     

Syntheses,Crystal Structures,and Magnetic Properties of Three Metal‐Nitroxide Complexes with the V‐shaped 4, 4′‐Oxybis(benzoate)

Three new metal–nitroxide complexes {[Ni(NIT4Py)₂(obb)(H₂O)₂] · 1.5H₂O}_n ( 1 ), {[Co(NIT4Py)₂(obb)(H₂O)₂] · 2H₂O}_n ( 2 ), and [Co(IM4Py)₂(obb)₂(H₂O)₂][Co(IM4Py)₂(H₂O)₄] · 10H₂O ( 3 ) with the V‐shaped 4,4′‐oxybis(benzoate) [NIT4Py = 2‐(4′‐pyridyl)‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide, IM4Py = 2‐(4′‐pyridyl)‐4,4,5,5‐tetramethylimidazoline‐1‐oxide, and obb = 4, 4′‐oxybis(benzoate) anion] were synthesized and structurally characterized. Single‐crystal X‐ray analyses indicate that complexes 1 and 2 crystallize in neutral one‐dimensional (1D) zigzag chains, in which the nitroxide–metal–nitroxide units are linked by the V‐shaped 4,4′‐oxybis(benzoate) anions, whereas complex 3 consists of isolated mononuclear [Co(IM4Py)₂(obb)₂(H₂O)₂]^2– anions and [Co(IM4Py)₂(H₂O)₄]²⁺ ions. Magnetic measurements show that complexes 1 and 2 both exhibit weak antiferromagnetic interactions between the metal ions and the nitroxides.     

Structural variation from trinuclears to 1D chains: Syntheses,structures and properties

Five complexes [Co₃(Hpmad)₆]·(4‐sb)₂·(CH₃COO)₂·(H₂O)₂ ( 1 ), [Co₃(Hpmad)₆]·(3‐sb)₂·(CH₃COO)₂·(H₂O)_0.5 ( 2 ), [Co(Hpmad)₂(4‐sb)]_n ( 3 ), [Co(Hpmad)₂(3‐sb)]_n ( 4 ) and {[Co(Hpmad)(SO₄)(H₂O)₂]·H₂O}_n ( 5 ) [Hpmad is 2‐pyrimidineamidoxime, H₂(4‐sb) is 4‐sulfobenzoic acid and H₂(3‐sb) is 3‐sulfobenzoic acid], were prepared at room temperature. Complexes 1 – 5 were characterized by elemental analyses, single crystal X‐ray diffractions, powder X‐ray diffractions, infrared spectra, thermogravimetric analyses, fluorescence spectra and magnetic susceptibility measurements. Complexes 1 and 2 possess the linear trinuclear Co²⁺ structures. Complexes 3 and 4 exhibit similar one‐dimensional (1D) chains. Complex 5 comprises the 1D helical chain. The change of anion in cobalt salt from CH₃COO^? to Cl^? to SO₄^2? leads to the structural evolution from the linear trinuclear Co²⁺ structure to the 1D chain to the 1D helical chain. Complexes 1 – 5 exhibit the Hpmad‐based emissions. The magnetic properties of 1–5 were also investigated.     

Syntheses,Structures, and Properties of the 3D Lanthanide Organic Frameworks with N‐Heterocyclic Polycarboxylic Acids

Four 3D lanthanide organic frameworks from potassium pyrazine‐2, 3, 5, 6‐tetracarboxylate (K₄pztc) or potassium pyridine‐2, 3, 5, 6‐tetracarboxylate (K₄pdtc), namely, {[KEu(pztc)(H₂O)₂] · H₂O}_n ( 1 ), {[KTb(pztc)(H₂O)₂] · 1.25H₂O}_n ( 2 ), {[KLn(pdtc)(H₂O)] · H₂O}_n [Ln = Gd ( 3 ), Ho ( 4 )], were synthesized by reaction of the corresponding lanthanide oxides with K₄pztc or K₄pdtc in presence of HCl under hydrothermal conditions, and characterized by elemental analysis, TGA, IR and fluorescence spectroscopy as well as X‐ray diffraction. In complexes 1 and 2 , the dodecadentate chelator pztc^4– links four Ln^III ions and four K^I ions. The coordination mode of the pztc^4– ligand is reported for the first time herein. Complexes 3 and 4 are isostructural with earlier reported Nd, Dy, Er complexes. Moreover, the Eu^III and Tb^III complexes exhibit the characteristic luminescence.     

Synergistic Catalytic Effect of a Series of Energetic Coordination Compounds based on Tetrazole‐1‐acetic Acid on Thermal Decomposition of HMX

A series of energetic coordination compounds [Co(tza)₂}_n ( 1 ), [Bi(tza)₃]_n ( 2 ), {[Cu₄(tza)₆(OH)₂] · 4H₂O}_n ( 3 ), [Mn(tza)₂]_n ( 4 ), {[Bi(tza)(C₂O₄)(H₂O)] · H₂O}_n ( 5 ) and [Fe₃O(tza)₆(H₂O)₃]NO₃ ( 6 ) based on tetrazole‐1‐acetic acid (Htza) were synthesized though environmentally friendly methods. The coordination compounds were characterized by elemental analyses, IR spectroscopy, single‐crystal and powder X‐ray diffraction (PXRD), thermogravimetric analyses (TG), and differential scanning calorimetry (DSC). Their catalytic performances and the synergetic catalytic effects between 1 and 2 , 3 and 4 , 5 and 6 on the thermal decomposition of octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine (HMX) were all investigated by DSC. The results revealed that compounds 1 – 6 are thermally stable energetic compounds and they all exhibit high catalytic action for HMX thermal decomposition. The catalytic effects of the compounds on HMX thermal decomposition are closely related to the oxides, which come from the decomposition of the compounds, but have no positive relationships with the heat releases of the compounds themselves. Moreover, the synergetic catalytic effects between 1 and 2 , 3 and 4 , 5 and 6 were observed. Their mixtures at different mass ratio have different synergetic catalytic effects, and the sequence of the biggest synergetic index (SI) in each system is copper‐manganese system (compounds 3 and 4 ) > iron‐bismuth system (compounds 5 and 6 ) > cobalt‐bismuth system (compounds 1 and 2 ), indicating that the synergistic catalytic effects are mainly related to the combination and the proportion of the compounds.     

Poly[[di‐μ2‐aqua‐di‐μ5‐croconato(2–)‐nickel(II)dipotassium(I)] tetra­hydrate]

In the title compound, {[K₂Ni(C₅O₅)₂(H₂O)₂]·4H₂O}_n, the Ni atom lies on an inversion centre. Two inversion‐related croconate [4,5‐dihydroxy‐4‐cyclo­pentene‐1,2,3‐trionate(2−)] ligands and an Ni^II ion form a near‐planar symmetrical [Ni(C₅O₅)₂]²⁻ moiety. The near‐square coordination centre of the moiety is then extended to an octa­hedral core by vertically bonding two water mol­ecules in the [Ni(C₅O₅)₂(H₂O)₂]²⁻ coordination anion. The crystal structure is characterized by a three‐dimensional network, involving strong K⋯O⋯K binding, K⋯O—Ni binding and hydrogen bonding.