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A series of bifunctional hexagonal MOFs have been successfully constructed by the introduction of various amine functional groups within the unsaturated Cu-based MOF, HKUST, to access amino-modified frameworks. The prepared compounds are cost-effective and display high chemical and thermal stability. They were effectually exploited as efficacious and superb heterogeneous catalysts in rapid and facile Knoevenagel condensation reactions for a variety of substrates containing different electron-donating and electron-withdrawing substituents with very high conversion, good reusability under mild conditions, and very short reaction time. The contaminant presence of Lewis acid and basic sites resulted in efficient condensation reactions by the prepared catalysts. [ABSTRACT FROM AUTHOR]

A series of bifunctional hexagonal MOFs have been successfully constructed by the introduction of various amine functional groups within the unsaturated Cu-based MOF, HKUST, to access amino-modified frameworks. The prepared compounds are cost-effective and display high chemical and thermal stability. They were effectually exploited as efficacious and superb heterogeneous catalysts in rapid and facile Knoevenagel condensation reactions for a variety of substrates containing different electron-donating and electron-withdrawing substituents with very high conversion, good reusability under mild conditions, and very short reaction time. The contaminant presence of Lewis acid and basic sites resulted in efficient condensation reactions by the prepared catalysts. [ABSTRACT FROM AUTHOR]

Herein, we have employed a convenient method to study kinetic and thermodynamic parameters of the adsorption of molybdenum from wastewater by using modified Zr‐based metal–organic frameworks, UIO‐66‐NH2‐X, as adsorbents. The frameworks were fabricated with a simple and fast method from terephthalic acids and Zirconium metal ions and modified via introduction of aldehyde groups using imine condensation. This is the first report in which MOFs have been utilized as adsorbents in molybdenum adsorption. The prepared adsorbents show high adsorption efficiency, which is representative of an improvement compared to other literature. The adsorption capacity and molybdenum removal for the modified framework are 667 mg/g and 93%, respectively which is a significant and remarkable value among other previously reported articles. The experimental adsorption data could be well interpreted with the pseudo‐second‐order kinetics and the Langmuir isotherm model. Thermodynamic studies illustrated a spontaneous exothermic mechanism for the adsorption process. [ABSTRACT FROM AUTHOR]

In this work, three bifunctional metal‐organic frameworks (MOFs) were constructed through the introduction of various linear amine functional groups within MIL‐101(Cr). The unsaturated chromium metal center was incorporated with three various ligands including ethylene diamine, diethylene triamine, and diamino butane. The resultant prepared MOFs contain unsaturated chromium centers as Lewis acidic centers and amine groups as basic sites. The contemporary existence of basic and acidic centers allowed prepared bifunctional compounds to be highly effectual heterogeneous catalysts for chemical fixation of CO2 with epoxides, affording cyclic carbonates, under relatively mild conditions and in the absence of either solvent or cocatalyst. High tendency of prepared structures toward CO2 adsorption followed by speeding up the nucleophilic attack resulted in gaining excellent conversion, selectivity, and activity for large epoxide as well as bulky ones. The synthesized catalyst outperforms other reported heterogeneous catalysts. High conversion, TON, recyclability, and mild reaction conditions are some distinctive characteristics of the bifunctional synergetic catalysts. [ABSTRACT FROM AUTHOR]

Metal-organic frameworks (MOFs) as acid catalysts provide active sites with particularly appropriate for glycerol conversion. In this study, Mil-118-SnO2 was synthesized by doping SnO2 quantum dots with Mil-118. The SnO2 quantum dots were formed through the epoxide-assisted precipitation route as a proton scavenger and following ring-opening that drives hydrolysis and, ultimately, condensation of the hydrated metal. The Mil-118-SnO2 was used as a catalyst for the production of five-member (2, 2-dimethyl-1, 3-dioxolane-4-methanol) and six-member (2,2-dimethyl-dioxane-5-ol, (II)) cycles. The results revealed a higher conversion rate and selectivity for Mil-118-SnO2 than for Mil-118. An increase was observed in conversion and selectivity, which was related to the improvement of the acidic properties of Mil-118 after doping SnO2 quantum dots. The experiments were conducted under mild conditions, producing a 40% increase in conversion and selectivity. This catalyst could be reused up to five times with 97% selectivity during a cycle. Glycerol is produced as the key byproduct in the transesterification process. The as-synthesized Mil-118-SnO2 then was used as a heterogeneous catalyst for the glycerol conversion to solketal. The experiments were carried out under mild conditions, which produced a 40% increase in conversion and selectivity. [ABSTRACT FROM AUTHOR]

Metal–organic frameworks (MOFs) have proved to be particularly appropriate for CO2 conversion. In the present work, we report metalloporphyrin‐based MOFs, PCN‐222(M) (M = Fe, Co, Ni, and Cu), which promote photocatalytic CO2 conversion to valuable chemicals. These ultra‐highly stable frameworks are constructed from Zr6 clusters and metalloporphyrin linkers. Metalloporphyrinic MOF has been synthesized and employed as a visible‐light photocatalyst for carbon dioxide to form formate. The effect of metalloporphyrinic PCN‐222(M) on CO2 reduction has been studied. Remarkably, PCN‐222(M) is highly efficient in visible light‐driven CO2 reduction into formate ion compared with the nonmetal porphyrinic PCN‐222. Metal ions of porphyrinic linkers play a great role in CO2 sorption, light harvesting, bandgap, photoluminescence (pL) intensity, and charge transfer, which influence CO2 reduction. CO2 adsorption and activation over metal ions of porphyrinic linkers play a significant part in the improvement of the conversion efficiency; the product obtained was characterized by gas chromatography/mass spectrometry (GC/MS) and ion mobility spectrometry (IMS) analyses. The reaction mechanism has been discussed in detail. [ABSTRACT FROM AUTHOR]

A porphyrinic mesoporous metal–organic framework (PCN-222(M) (M = Mn, Fe, Cu)) has been synthesized by a simple sonochemical preparation method without high temperature in a short period of time. The ultrasonic method for the preparation of PCN-222(M) was found to be an efficient procedure with a good quantitative yield (PCN-222(M)-U). Harmful cationic and anionic dyes have been removed from wastewater using PCN-222(M). The comparative study of the influences of metalloporphyrin and non-metal porphyrin frameworks (PCN-222) on the adsorption process has been performed. Remarkably high adsorption capacity over PCN-222(M) for the anionic dyes is reported. The porphyrinic metal center of frameworks and pH values affected dye adsorption capacity, indicating the effective role of electrostatic interactions on dye adsorption. Due to the aggregation of MB and MO, a significant increase in the adsorption capacity was observed in a mixture of MB-MO solution at pH 7. High adsorption capacity over PCN-222(M) has been estimated using Langmuir and Freundlich equations. The adsorption kinetics, thermodynamic parameters, stability and reusability of adsorbents have also been reported. The stability of PCN-222(M) in water over three months was investigated (PCN-222(M)-3). [ABSTRACT FROM AUTHOR]

Metal–organic frameworks with diverse structures and unique properties have demonstrated that can be an ideal substitute for natural enzymes in colorimetric sensing platform for analyte detection in various fields such as environmental chemistry, biotechnology and clinical diagnostics, which have attracted the scientist's attention, recently. In this study, a porous coordination network (denoted as PCN-222) was synthesized as a new biomimetic material from an iron linked tetrakis (4-carboxyphenyl) porphyrin (named as Fe-TCPP) as a heme-like ligand and Zr6 linker as a node. This catalyst shows the peroxidase and catalase activities clearly. The mechanism of peroxidase activity for PCN-222 was investigated using the spectrophotometric methods and its activity was compared with the other nanoparticles which, the results showed a higher activity than the other catalysts. Also, the hydrogen peroxide was detected by PCN-222(Fe) based on the peroxidase-like activity. For detection of hydrogen peroxide a linear range of 3–200 µM and detection of limit (LOD) 1 µM (3σ/slope), under optimal conditions were obtained. Moreover, based on the high tendency of PCN-222(Fe) to combine with the TMB as a chromogenic substrate in the peroxidase-like activity, we developed the sensitive and selective colorimetric assay for glucose detection that was found a detection limit (LOD) of 2.2 µM in the linear range from 12 to 75 µM. Finally due to the good catalytic activity of PCN-222(Fe), it was used to detection of glucose and hydrogen peroxide in real samples. [ABSTRACT FROM AUTHOR]

In contrast to early transition metal complexes of d0 electron configuration, their main group metal analogues are usually poor catalysts for ethylene polymerisation due to their diminished tendency to insert ethylene into an M–R bond. Interestingly, we found that ring strain in the transition structure of the insertion reaction is most likely responsible to set the ease of the process. Ethylene insertion into an M–R bond requires a four-membered ring transition structure. Strain in a four-membered ring was shown to be dependent on the metal identity (transition or main group/d or p block). For early transition metals, due to the presence of empty valence d orbitals, the strain is negligible but, for main group metals, the strain is significant and so destabilizes the corresponding transition structure. Our claim gains support from investigation of ethylene insertion into an M–allyl bond. In this case, the relevant insertion preferentially passes through a six-membered ring transition structure with an accessibly low activation barrier. In contrast to four-membered ring transition structures, six-membered ones do not suffer significantly from ring strain, causing the insertion activation barrier to become independent of the metal identity. It becomes obvious from our study that this previously undisclosed factor should play the pivotal role in determining the reactivity of many catalysts. [ABSTRACT FROM AUTHOR]

In this paper, regarding outstanding electrocatalytic properties of metal organic frame works for fuel cell applications, we have synthesised and investigated comprehensively the elecrocatalytic stability of PCN-222 (PCN = porous coordination network) for the oxygen reduction reaction (ORR) in acidic media. ORR is a main reaction that take parts in cathodic part of a fuel cell and preparation of a stable and efficient electrocatalyst for this reaction will effectively improve the fuel cell output. The 3D heme-like metal organic framework (MOF) was constructed from Fe(III) porphyrin linkers and Zr6 clusters. The catalyst stability tests manifested that the PCN-222 is much more stable than the other metal macrocycles. The assembled PCN-222 catalyst possesses ultra stability, high activity and excellent tolerance to the crossover effect of methanol, which could be used as a unique alternative to common ORR catalysts in an acidic direct methanol fuel cell.Graphical Abstract: [ABSTRACT FROM AUTHOR]

We report the synthesis of a composite from cobalt porphyrin-based metal organic framework (MOF) and multi-walled carbon nanotube (MWCNT), possessing good catalytic activity toward oxygen reduction (OR) and oxygen evolution (OE) processes. A 3-D porous coordination network (PCN) with 3-D nanochannels was synthesized using ultrastable Zr clusters and tetrakis(4-carboxyphenyl)porphyrin cobalt(II). Located in the backbone of MOF, cobalt porphyrins as the active centers are easily accessible to the reactants. The composite exhibits smaller overpotentials and higher current for OR and OE reactions compared to the commercial Pt/C catalyst. A proton-coupled electron transfer mechanism has been suggested due to the pH dependence of water oxidation on the electrocatalyst. Furthermore, the stability of the catalyst has been verified by various techniques. Our designed heterogeneous, inexpensive, and stable electrocatalyst is a proper candidate for acidic fuel cells and water splitting devices under near neutral condition without requirement of pyrolysis process. [ABSTRACT FROM AUTHOR]

Two post-synthetic strategies have been used to prepare oxovanadium(IV) complexes covalently anchored to the organic linkers of UiO-66(NH) (UiO = University of Oslo) metal-organic framework. In the first method, the available amino groups of UiO-66(NH) were treated with salicylaldehyde to form the modified UiO-66 (UiO-66-SI). The synthesized UiO-66-SI was then treated with [VO(acac)] to produce UiO-66-SI/VO(acac). In the second method, UiO-66(NH) was directly treated with [VO(acac)] to form UiO-66-N/VO(acac). The synthesized compounds were characterized by FTIR, XRD, N sorption, FE-SEM, TEM, EDX, ICP-AES, TGA and UV-Vis spectroscopy. The catalytic performances of UiO-66-SI/VO(acac) and UiO-66-N/VO(acac) were assessed in the epoxidation of geraniol with tert-butyl hydroperoxide. The results indicated 100% conversion with 100% selectivity towards 2,3-epoxygeraniol after 60 and 120 min of reaction time. These excellent catalytic activities can be attributed to the high dispersion of the catalytic sites on MOF and the proper pore size of UiO-66(NH). Moreover, the structure of both catalysts remains intact during the catalytic reaction and the catalysts can be successfully recycled three times. High yields and excellent selectivity towards the 2,3-epoxygeraniol product, short reaction time, mild reaction conditions and recyclability of the solid catalysts are some of the advantages of these catalytic systems. [ABSTRACT FROM AUTHOR]

We report on the design of a bio-inspired composite as a noble-metal-free electrocatalyst for the oxygen reduction reaction (ORR). The composite is made from the assembly of pyridine-functionalized graphene (G-py) and a 3 D metal-organic framework (MOF) deposited onto a glassy carbon electrode (GCE). The 3 D heme-like MOF was synthesized from tetrakis(4-carboxyphenyl)porphyrin iron(III) chloride and Zr6 clusters for the assembly of the stable porous coordination network. G-py, which possesses an axial ligand to anchor to the centers of porphyrin in the MOF, results in a significant change in the electronic and geometric structure of centers, which enhances the rate of ORR and durability during cycling in acidic media. The occurrence potential of the ORR by the composite is shifted to the positive potential near 100 mV. Our results introduce a new strategy for the rational design of inexpensive and highly stable oxygen reduction electrocatalysts for fuel cells without the requirement of pyrolysis. [ABSTRACT FROM AUTHOR]

5-(4-Chlorobenzyl)-1H-tetrazole ligand (HL) was synthesized by Sharpless method. Furthermore, a tetrazole based Zn(II) metal organic framework, [Zn(L)2]n (1), (L = 5-(4-Chlorobenzyl)tetrazolate), was synthesized by in situ reaction of 4-chlorobenzeneacetonitrile, NaN3 and ZnCl2 under hydrothermal conditions. Both compounds are structurally characterized by elemental analysis, IR, and single crystal X-ray diffraction. Compound 1 displays undulated 2D layers, sql/Shubnikov tetragonal plane net with (44.62) point symbol. Fluorescence measurements and thermogravimetric analysis of 1 were also performed. In addition, we describe here a complex precursor, hydrothermal route to prepare ZnO nano and micro structures. The effects of reaction temperature and pH on the growth process and morphology of ZnO nano and micro structures were investigated. Finally, a possible growth mechanism is proposed. The obtained samples have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). [ABSTRACT FROM AUTHOR]

The main goal of this research is to investigate the structural and thermochemical aspects of complexation between La with tetrapropyl malonamide (TPMA) and tetrapropyl diglycolamide (TPDGA) ligands via density functional theory (DFT) methods. In this respect, the structural parameters of [La-TPMA] and [La-TPDGA] complexes have been calculated and compared with the available X-ray crystallographic data. These comparisons revealed that both calculated structural values using B3LYP and M06 are in a reliable agreement with X-ray crystal structure with a near accuracy. In the next step, the more efficiency of diglycolamides in comparison with malonamides in the extraction of La have been analyzed by calculating thermochemical properties of the complexation. It should be stated that this issue has been observed in many experimental elucidations. In the next step, the inclusion of solvent effects on thermodynamical properties of complexation has been evaluated via polarized continuum model (PCM) calculations. In this context, enthalpy and Gibbs free energy changes have been determined in the presence of three solvents, chloroform, toluene and n-hexane. Our obtained results demonstrate that using n-hexane as solvent is more favorable thermodynamically than chloroform and toluene that confirms the previously observed experiments. Finally, the bond orders of some selected key bonds in TPMA and TPDGA ligands and their corresponded La complexes have been evaluated comparatively to analyze the electronic features of coordination in [La-TPMA] and [La-TPDGA] complexes. [ABSTRACT FROM AUTHOR]

Abstract. The metal organic framework, [Cu5(C5H2N2O3)4(H2O)4(NO3)2 ·10H2O] n ( 1), was synthesized by a hydrothermal reaction via copper nitrate and in situ generated 3-hydroxopyrazine-2-carboxylate from 3-aminopyrazine-2-carboxylic acid. Compound 1 was characterized by elemental analysis, infrared spectroscopy, TG analysis, and single-crystal X-ray diffraction. It has a 3D structure constructed from Cu2+ cations, bridging NO3- anions, and 3-hydroxopyrazine-2-carboxylate units. The NO3- anions act as μ2-bridging ligand and the 3-hydroxopyrazine-2-carboxylate units coordinate pentadentately through the two oxygen atoms of their carboxylate group, the oxygen atom of the hydroxyl group and two nitrogen atoms. The ligands link the CuII ions to form trinuclear units. These are further connected to form a novel 3D MOF, with a novel 4-nodal 3,3,3,4-connected net topology of an unprecedented point (Schläfli) symbol (6.7.9)(64.8.9)(7.102)(72.10). [ABSTRACT FROM AUTHOR]

Four rhenium(I) complexes, [Re(CO)3Br(Ln)] (n = 1–4), [Ln = (4-fluorophenyl)pyridin-2-ylmethyleneamine (L1), (4-chlorophe nyl)pyridin-2-ylmethyleneamine (L2), (4-bromophenyl)pyridin-2- ylmethyleneamine (L3), and (4-iodophenyl)pyridin-2-ylmethylenea mine, (L4)] have been synthesized and characterized by CHN analyses, 1H, 13C-NMR, IR, and UV-vis spectroscopy. The molecular structure of [Re(CO)3Br(L1)] is a distorted octahedron around rhenium with one Br, facial arrangement of three COs, and one diimine. UV-vis absorption and emission properties of the complexes have been studied at room temperature and the redox potentials are approximately insensitive to the substituent on the phenyl ring of ligands. [ABSTRACT FROM PUBLISHER]

This article describes a fast and reproducible approach to synthesize silver nanoparticles with an average size of 12 and 17 nm. The first step in this process involves the formation of an Ag complex by reaction of AgNO3 with diimine ligand. In the second step, oleylamine bonds to Ag complex, reduces Ag+ to Ag°, and subsequently caps the silver nanoparticles. In this process, OLA undergoes metal-ion-induced oxidation to nitriles. FT-IR and UV-vis spectroscopy, TEM, XRD, and EDAX were used to characterize these silver nanoparticles. The concentration of OLA was critical to the formation of silver nanoparticles with various sizes. [ABSTRACT FROM AUTHOR]

Two rhenium(I) complexes, [Re(CO)3Br(Ln)] (n = 1, 2), (L1= N,N'-bis[1-(4-chlorophenyl)ethylidene]ethane-1,2-diamine and L2 = N,N'-bis[1-(4-nitrophenyl)ethylidene]ethane-1,2-diamine) have been synthesized and characterized by CHN analyses, 1H NMR, IR, and UV-Vis spectroscopy. The molecular structure of [Re(CO)3Br(L1)] is a distorted octahedron around rhenium with one Br, facial arrangement of three CO's, and one diimine. The UV-Vis spectra of the complexes have metal-to-ligand charge transfer bands increasing in wavelength when the L2 ligand is replaced by L1, in agreement with the oxidation potential of the complexes. [ABSTRACT FROM AUTHOR]

Two ligands, N,N'-bis[1-(4-chlorophenyl)ethylidene]ethane-1,2-diamine (L1) and N,N'-bis- [1-(4-nitrophenyl)ethylidene]ethane-1,2-diamine (L2) and their corresponding copper(I) complexes, [Cu(L1)2]ClO4 (1) and [Cu(L2)2]ClO4 (2), have been synthesized and characterized by CHN analyses, 1H-NMR, IR, and UV-Vis spectroscopy. The crystal structures of L1 and [Cu(L1)2]ClO4 (1) were determined from single crystal X-ray diffraction. L1 lies across a crystallographic inversion center and the C=N is approximately coplanar with the benzene ring and adopts E configuration. The coordination polyhedron about copper(I) in 1 is best described as a distorted tetrahedron. Quasireversible redox behavior is observed for the complexes. [ABSTRACT FROM AUTHOR]

Two new ligands, N1, N2-Bis(3-phenylallylidene)propane1,2-diamine, ca2men and 1, 2-diphenyl-N, N'-bis(3-phenylallylidene) ethane1, 2-diamine, phca2dpen, and their corresponding copper(I) complexes, [Cu(ca2men)2]BPh4 1 and [Cu(phca2dpen)2]ClO4 2, were synthesized and characterized by C,H,N analyses, IR, and UV/VIS spectroscopy. The crystal and molecular structures of 1 and 2 were determined by X-ray crystallography from single-crystal data. The coordination polyhedron about the CuI center in the two complexes is best described as a distorted tetrahedron. The spectral analysis of the complexes identifies an increasing in wavelength of the first metal to ligand charge transfer band with increasing of the substituents in the ligands. A quasireversible redox behavior is observed for complex 1 and 2 (E1/2= 0.71 and 0.83 V). [ABSTRACT FROM AUTHOR]

The ligand, morpholin-4-yl-pyridin-2-ylmethylene-amine 4-ampc, and its corresponding copper(I) complexes, [Cu(4-ampc)2]BPh4 1, and [Cu(4-ampc)(PPh3)2]BPh4 2, have been synthesized and characterized by CHN analyses, 1H-NMR, IR, and UV-Vis spectroscopies. The crystal and molecular structures of [Cu(4-ampc)2]BPh4 1 were determined by X-ray crystallography from a single-crystal. The coordination polyhedron about copper(I) is best described as a distorted tetrahedron. Quasireversible and irriversible redox behaviors were observed for 1 and 2, respectively. [ABSTRACT FROM AUTHOR]

The ligand, N,N'-bis-(4-methoxy-benzylidene)-ethane-1,2-diamine (mb2en), and its corresponding copper(I) complexes, [Cu(mb2en)2]ClO4 (1), and [Cu(mb2en)(PPh3)2]BPh4 (2), have been synthesized and characterized by CHN analyses, 1H and 13C-NMR, IR, and UV-Vis spectroscopies. The crystal and molecular structure of [Cu(mb2en)2]ClO4 (1), were determined by X-ray crystallography from a single-crystal. The coordination polyhedron about copper(I) is best described as a distorted tetrahedron. Quasi-irreversible redox behavior was observed for 1 and 2 (E1/2 = 0.55 and 0.95 V, respectively). [ABSTRACT FROM AUTHOR]

Four copper(I) complexes, [Cu(diimine)2]ClO4 (1 - 4, Diimine[dbnd](4-fluorophenyl)pyridin-2-ylmethylene-amine, (1) (4-chlorophenyl)pyridin-2-ylmethyleneamine, (2), (4-bromophenyl)pyridin-2-ylmethyleneamine, (3), and (4-iodophenyl)pyridin-2-ylmethyleneamine, (4)) have been synthesized and characterized by CHN analyses, 1H NMR, IR, and UV - vis spectroscopy. The crystal structure of [Cu(B)2]ClO4 (2) was determined from single crystal X-ray diffraction. The coordination polyhedron about the copper(I) center in 2 is best described as a distorted tetrahedron. A quasi-reversible redox behavior is observed for the complexes. The spectral, structural, and redox data of these complexes are compared with similar iminopyridine copper(I) complexes. The variation of substituent on the phenyl ring of iminopyridine ligands did not show significant change in the absorption and redox properties of these types of complexes. [ABSTRACT FROM AUTHOR]

A series of complexes of the type M(nca2en)X2, where nca2en=/N,N'-bis(2-nitrocinnamaldehyde)-1,2-diiminoethane, M(II) =Co, Ni or Zn and X=Cl, Br, I have been synthesized and characterized. The crystal and molecular structure of Zn(nca2en)Br2 8 was determined by X-ray crystallography from single-crystal data. The complex 8 crystallizes in monoclinic system, having Zn ion in distorted tetrahedral geometry, Br(1)-Zn(1)- Br(2), 117.37(4)°; N(3)-Zn(1)-N(2), 82.57(18)°. This structure consists of intermolecular hydrogen bond of the type C-H-X. The formation of the C-H-M weak intramolecular hydrogen bonds due to the trapping of C-H bonds in the vicinity of the metal atoms is reported for 8. The 1H NMR study of Zn complexes gives further evidence for the presence of such interactions. The spectral properties of the above complexes are also discussed. [ABSTRACT FROM AUTHOR]

A series of new complexes of the Schiff base obtained from trans- cinnamaldehyde and 1,2-diaminoethane (en) with the general formula of M(ca 2 en)X 2 (M = Co(II), Ni(II), Zn(II); X = Cl, Br, I, NCS, N 3 ; (ca 2 en) = N,N ′-bis( trans- cinnamaldehyde)-1,2-diiminoethane) have been synthesized and characterized. The crystal structures of three pseudo -tetrahedral complexes, Co(ca 2 en)Cl 2 ( 1 ), Co(ca 2 en)Br 2 ( 2 ), and Ni(ca 2 en)Br 2 ( 5 ), were determined by X-ray diffraction. Crystal data for 1 , Co(ca 2 en)Cl 2 : monoclinic; space group P 2 1 / c ; a = 7.1925(14) Å, b = 20.327(4) Å, c = 14.029(3) Å; β =95.06(3)°; V = 2043.1(7) Å 3 ; Z = 4; and final R 1 = 0.0381 ( wR 2 = 0.0718) for 4653 independent reflections with I > 2σ( I ) and 226 parameters; 2 , Co(ca 2 en)Br 2 ; monoclinic, space group P 2 1 / c ; a = 7.3780(6) Å, b = 20.4372(17) Å, c = 14.1649(12) Å; β = 94.902(2)°; V = 2128.1(3) Å 3 ; Z = 4; and final R 1 = 0.0491 ( wR 2 = 0.1052) for 5858 independent reflections with I > 2σ( I ) and 227 parameters; 5 , Ni(ca 2 en)Br 2 : monoclinic, space group P 2 1 / c ; a = 7.2388(6) Å, b = 20.4651(16) Å, c = 14.2782(12) Å; β = 94.160(2)°; V = 2109.6(3) Å 3 ; Z = 4; R 1 = 0.0481 ( wR 2 = 0.0907) for 5914 independent reflections with I > 2σ( I ) and 227 parameters. The structures consist of discrete molecules in which the coordination polyhedra about the central metal ion are highly distorted tetrahedra with Cl(1)-Co-Cl(2), 115.51(3)°; N(1)-Co-N(2), 83.71(7)°; Br(1)-Co-Br(2), 114.58(4)°; N(1)-Co-N(2), 84.92(19)°; and Br(1)-Ni-Br(2), 125.23(3)°; N(1)-Ni-N(2), 85.11(15)° in 1 , 2 , and 5 , respectively. The stiryl groups are cis -endo with respect to the metal atom and the chelate ring is puckered. Utilization is made of electronic and vibrational spectra in structural diagnosis of other complexes. [ABSTRACT FROM AUTHOR]