S K-edge X-ray absorption studies of tetranuclear iron-sulfur clusters: mu-sulfide bonding and its contribution to electron delocalization.

X-ray absorption spectroscopy (XAS) at the sulfur ( approximately 2470 eV) and chlorine ( approximately 2822 eV) K-edges has been applied to a series of 4Fe-4S model complexes. These are compared to 2Fe-2S model complexes to obtain insight into the localized ground state in the mixed-valence dimer versus the delocalized ground state in the mixed-valence tetramer. The preedges of hypothetical delocalized mixed-valence dimers [Fe(2)S(2)](+) are estimated using trends from experimental data and density functional calculations, for comparison to the delocalized mixed-valence tetramer [Fe(4)S(4)](2+). The differences between these two mixed-valence sites are due to the change of the sulfide-bridging mode from micro(2) to micro(3). The terminal chloride and thiolate ligands are used as spectator ligands for the electron density of the iron center. From the intensity of the preedge, the covalency of the terminal ligands is found to increase in the tetramer as compared to the dimer. This is associated with a higher effective nuclear charge on the iron in the tetramer (derived from the energies of the preedge). The micro(3)-bridging sulfide in the tetramer has a reduced covalency per bond (39%) as compared to the micro(2)-bridging sulfide in the dimer (51%). A simple perturbation model is used to derive a quadratic dependence of the superexchange coupling constant J on the covalency of the metal ions with the bridging ligands. This relationship is used to estimate the superexchange contribution in the tetramer (J = -156 cm(-)(1)) as compared to the mixed-valence dimer (J = -360 cm(-)(1)). These results, combined with estimates for the double exchange and the vibronic coupling contributions of the dimer sub-site of the tetramer, lead to a delocalized S(t) = (9)/(2) spin ground state for the mixed-valence dimer in the tetramer. Thus, the decrease in the covalency, hence the superexchange pathway associated with changing the bridging mode of the sulfides from micro(2) to micro(3) on going from the dimer to the tetramer, significantly contributes to the delocalization of the excess electron over the dimer sub-site in the tetramer.     

Design and synthesis of multidentate ligands via metal promoted C-N bond formation processes and their coordination chemistry

This presentation reports some novel examples of organic ring amination reactions via metal mediation. The organic transformations are highly regioselective and can be controlled by the proper selection of the mediator complex. The two isomeric organic ligands viz. HL¹ and HL² were isolated in their pure states by the removal of the metal ions. These were fully characterized. The ligand HL¹ has lowpKa, 8.5. Upon deprotonation, it behaves as a potentialbis chelating N,N,N-donors. The coordination chemistry of the HL¹ ligand involving some 3d-metal ions is described. Two unusual low-spin complexes of manganese(II) and iron(III) are reported. The ferric complex displayed a rhombic EPR while, the corresponding manganese compound showed a complex pattern due to hyperfine coupling. All the complexes displayed large number of redox responses. A brief mention about the future projection of this work is noted.     

Hydrothermal synthesis and structural characterization of a new 3D chiral coordination polymer [Cd2(C4H4O6)2]n

A new chiral coordination polymer [Cd₂(C₄H₄O₆)₂] _n (I) has been synthesized and characterized by elemental analysis, IR, and X-ray single-crystal diffraction. The X-ray diffraction analysis reveals that I crystallizes in the orthorhombic system, space group P2₁2₁2₁. The adjacent Cd(1) and Cd(2) centers are linked by one tartrate ligand through tridentate coordination to form a dimer. The dimer is further connected to the other dimer via tartrate ligands to construct an infinite three-dimensional (3D) coordination polymer. The unit cell parameters for I: a = 7.4984(17), b = 7.9106(18), c = 19.560(4) ?, V = 1160.2(5) ?³, Z = 4.     

Supramolecular assemblies tailored by dipyridyl-1,2-4-thiadiazoles: influence of the building blocks in the predictability of the final network

ABSTRACT

Coordinatively unsaturated dithiophosphato complex [Cd((MeO)₂PS₂)₂] (1) was reacted with the bifunctional ligands 3,5-di-(4-pyridyl)-1,2,4-thiadiazole (L1) and 3,5-di-(3-pyridyl)-1,2,4-thiadiazole (L2) to give the helicoidal coordination polymer (1·L1)_∞ and the paddle-wheel dimer (1·L2)₂, both characterised by single-crystal X-ray diffraction. A comparison of the structures with the different supramolecular constructs obtained by reacting L1 and L2 with differently P-substituted dithiophosphoric Ni^II complexes allowed to evaluate the role of the metal ion for the predictable assembly of this class of coordination polymers.     

New photoluminescent coordination polymers constructed from dicarboxylate and 1,2-bis(imidazol-1-ylmethyl)benzene

Two new metal-organic frameworks, namely, Cd(Pda)(Bix)_0.5(H₂O) (I) and Cd₂(Glut)₂(Bix)(H₂O) (II) (H₂Pda is 1,3-phenylenediacetic acid, H₂Glut is glutaric acid, and Bix is 1,4-bis(imidazol-1-ylmethyl)benzene), have been synthesized under hydrothermal conditions by employing mixed ligands with Cd(II) nitrate. In complex I, the adjacent Cd(II) atoms are bridged by two Pda ligands to result in 1D Cd(II)-Pda double chains, which are further linked by Bix ligands to generate a SQL with the node defined by a Cd(II) dimer, whereas II represents a three-dimensional coordination polymer with an unprecedented (4².5)₂(4⁴.5⁹.6⁸.7⁵.8²) topology, in which infinite cadmium-carboxylate chains are linked by the ligands to form a metal-organic coordination network. Moreover, the luminescence properties of two complexes have also been investigated.     

Synthesis and characterization of dinuclear late transition-metal (copper(I), silver(I), rhenium(I)) complexes with a bis-pyridylimine ligand linked by S–S bonding

Two dinuclear complexes with novel coordination type, [Cu₂(DPDIDT)₂](PF₆)₂ (1) and [Ag₂(DPDIDT)₂](BF₄)₂ (2), plus a dinuclear complex of the usual coordination type, {Re(Cl)(CO)₃}₂(DPDIDT) (3) as a comparative complex were prepared from bis-(4-(2-pyridylmethyleneiminophenyl))disulfide (DPDIDT) and the relevant metal sources. Complexes (1) and (2) exist in solution as dimer structures of the square-pole type according to the interpretation of the ESI mass and ¹H NMR spectra. The density functional theory calculations for the monomer and dimer models of the Cu(I) complex cations, [Cu_n(DPDIDT)_n]ⁿ⁺ (n = 1, 2), demonstrated that the dimer form is structurally more stable than the monomer form. The UV–Vis absorption spectra of complexes (1) and (3) both exhibit a typical MLCT absorption band in the 400–700 nm region. The Re(I) complex (3) was revealed to possess a facial configuration with respect to the three carbonyl ligands by ¹H NMR and IR data.     

Synthesis and characterization of the [Cu(Cin2bda)2]ClO4 and [Cu(Ncin2bda)2]ClO4 complexes: Crystal structure of [Cu(Ncin2bda)2]ClO4

Two copper(I) complexes [Cu(Cin₂bda)₂]ClO₄ (I) and [Cu(Ncin₂bda)₂]ClO₄ (II) have been prepared by the reaction of the ligands N²,N²′-bis(3-phenylallylidene)biphenyl-2,2′-diamine (L¹) and N²,N²′-bis[3-(2-nitrophenyl)allylidene]biphenyl-2,2′-diamine (L²) and copper(I) salt. These compounds were characterized by CHN analyses, ¹H NMR, IR, and UV-Vis spectroscopy. The C=N stretching frequency in the copper(I) complexes shows a shift to a lower frequency relative to the free ligand due to the coordination of the nitrogen atoms. The crystal and molecular structure of II was determined by X-ray single-crystal crystallography. The coordination polyhedron about the copper(I) center in the complex is best described as a distorted tetrahedron. A quasireversible redox behavior was observed for complexes I and II. The article is published in the original.     

Bis‐copper(II) Complex of Triply‐linked Corrole Dimer and Its Dication

Copper complexes of corroles have recently been a subject of keen interest due to their ligand non‐innocent character and unique redox properties. Here we investigated bis‐copper complex of a triply‐linked corrole dimer that serves as a pair of divalent metal ligands but can be reduced to a pair of trivalent metal ligands. Reaction of triply‐linked corrole dimer 2 with Cu(acac)₂ (acac=acetylacetonate) gave bis‐copper(II) complex 2Cu as a highly planar molecule with a mean‐plane deviation value of 0.020 Å, where the two copper ions were revealed to be divalent by ESR, SQUID, and XPS methods. Oxidation of 2Cu with two equivalents of AgBF₄ gave complex 3Cu , which was characterized as a bis‐copper(II) complex of a dicationic triply‐linked corrole dimer not as the corresponding bis‐copper(III) complex. In accord with this assignment, the structural parameters around the copper ions were revealed to be quite similar for 2Cu and 3Cu . Importantly, the magnetic spin–spin interaction differs depending on the redox‐state of the ligand, being weak ferromagnetic in 2Cu and antiferromagnetic in 3Cu .     

Auxiliary ligand-directed structural variation of the Zn(II)–1,4-bis(imidazol-1-yl)benzene net: synthesis,characterization, and luminescence

In this article, two different anionic ligands, 3,4-oxybis(benzoate) (bopH₂) and sulfate, have been employed as co-ligands to perform a comparison on the structures of coordination polymers based on the Zn(II)–rigid 1,4-bis(imidazol-1-yl)benzene (bib) net. Two new coordination polymers, {Zn(bib)(bop)}_∞ (1) and {Zn(bib)(SO₄)}_∞ (2), were synthesized from hydrothermal reactions and characterized by elemental analyses, IR and single-crystal X-ray diffraction. Complex 1 contains two unique 2-D layers, which are further interpenetrated to form a two-fold 2-D?→?2-D framework. However, 2 consists of a 3-D structure with pcu topology constructed by sulfates as pillars. The structural difference of 1 and 2 indicates that size of the ancillary ligands play important roles in formation of such coordination architectures. Thermal and fluorescence properties of 1 and 2 are also investigated in the solid state.     

Different coordination patterns for two related unsymmetrical compartmental ligands: crystal structures and IR analysis of [Cu(C21H21O2N3)(OH2)(ClO4)]ClO4·2H2O and [Zn2(C22H21O3N2)(C22H20O3N2)]ClO4

The crystal structures of the new complexes [Cu(HL1)(OH₂)(ClO₄)]ClO₄·2H₂O (1) and [Zn₂(HL2)(L2)]ClO₄ (2), derived from two related, phenol-based compartmental ligands, are described. Compound 2 constitutes the first report of a complex obtained from H₂L2. The metal compounds are structurally different; 2 is a dimer in which all the heteroatoms of the ligand take part in coordination, while 1 is mononuclear containing a pair of cis-oriented ligands that complete an “open” coordination sphere, in which the aldehyde group of HL1 is not involved. The protonation status of the central phenol groups of HL1 and H₂L2 are also dissimilar between the complexes. Infrared vibrational analyses of both complexes, as well as their respective ligands, were performed to connect the observed spectral features with the structural properties of the solids. While some distinctive bands shifted upon complexation, it was not possible to confirm involvement of the aromatic aldehyde group in coordination by this technique. ¹H NMR experiments involving 2 suggest that its particular protonation status is maintained upon dissolution in d₆-DMSO.     

Synthesis,crystal structure,redox behavior and DNA-binding properties of a series of copper(II) complexes with two new carboxamide derivatives

Four mononuclear copper(II) complexes of two new carboxamide derivatives formulated as [Cu(L¹)₂](ClO₄)₂ (1a), [Cu(L¹)₂](NO₃)₂ (1b), [Cu(L²)₂(H₂O)₂](ClO₄)₂ (2a), and [Cu(L²)₂(H₂O)](NO₃)₂ (2b) have been isolated in pure form from the reaction of L¹ and L² [where L¹ = N-(furan-2-ylmethyl)-2-pyridinecarboxamide and L² = N-(thiophen-2-ylmethyl)-2-pyridinecarboxamide] with copper(II) salts of perchlorate and nitrate. All the complexes were characterized by physicochemical and spectroscopic tools along with single-crystal X-ray diffraction studies. The structural analyses showed that 1 is monomeric of square planar geometry with copper(II) chelated by two L¹ ligands. Complex 2 differs in coordination geometry, being octahedral and distorted square pyramidal. Two L² ligands occupy the equatorial positions of the octahedral 2a and the basal sites of the pyramidal 2b, with water molecules that complete the coordination sphere in each case. Electrochemical studies using cyclic voltammetry showed a reversible redox behavior of the copper(II) in 1 and 2. The electronic spectroscopic behavior and the trend of one electron equivalent redox potential corresponding to a Cu^II/Cu^I couple have also been confirmed by density functional theory calculations. The spectroscopic and viscosity measurement study in tris–HCl buffer suggested an intercalative interaction of 1a and 2 with calf thymus DNA likely due to the stacking between the non-coordinated furan and thiophene chromophore with the base pairs of DNA.     

Investigation of cobalt (1,10-phenanthroline)-bis-(3,6-di-<Emphasis Type="Italic">tert</Emphasis>-butyl-<Emphasis Type="Italic">o</Emphasis>-benzosemiquinolate) by X-ray diffraction,IR and ESR spectroscopy,magnetochemistry, and precision calorimetry

The bistable cobalt complex containing two symmetrical 3,6-di-tert-butyl-o-benzoquinone and one 1,10-phenanthroline moieties as ligands (1) was synthesized. Complex 1 was isolated in the individual state and characterized by IR and ESR spectroscopy, X-ray diffraction, magnetochemical studies, and precision calorimetry. A change in temperature causes the reversible metal-ligand electron transfer and spin crossover (redox isomerism) in complex 1 in the crystalline state. The redox-isomeric transformation at ∼250 K is accompanied by the phase transition. The structural study at two temperatures confirmed the changes in the molecular and crystal structure associated with the redox-isomeric transformation.     

Note: Synthesis,Characterization and Crystal Structures of the Coordination Polymers [Cu(II)(NO3)2(BBMB) and [Mn(II)Cl2(BBMB)2] [BBMB = 1,4-Bis(1-Benzimidazolylmethyl) Benzene]

Two novel coordination polymers, [Cu(II)(NO₃)₂(bbmb)] _n (1) and [Mn(II)(Cl₂)(BBMB)₂] (2) [bbmb = 1,4-bis(1-benzimidazolylmethyl)benzene], were synthesized and characterized by IR and thermal analyses. Single-crystal X-ray diffraction analysis shows that Polymer 1 exhibits a distorted metal tetrahedron in its structure, involving two nitrogen atoms from bbmb ligands and two oxygen atoms from NO₃ groups. Each Cu(II)(NO₃)₂ unit is bridged by bbmb to form a zigzag chain structure. Polymer 2 possesses a two-dimensional network. The coordination environment around Mn(II) is a distorted octahedron and its solid-state structure exhibits a layered packing mode. In the polymers the two coordinating nitrogen atoms on bridging bbmb ligands are trans to the central benzene plane.     

Supramolecular Influences on Metal Ion Coordination: Lead(II) under Eight-coordination

Crystal structure determinations on the “acid salt” of Pb(II) and dipicolinic acid (pyridine-2,6-dicarboxylic acid, dipicH²), regarded as composed of dimer entities, [Pb²(dipic)²(dipicH²)²(OH²)⁶], 1, infinitely cross-linked, and on the complex of 2,4-dinitrophenol (2,4-DNPH), a simpler coordination polymer, [Pb(2,4-DNP)²]n, 2, show both solid state structures to be influenced by π-stacking of the ligands. Although the Pb(II) coordination environment in 1 can be regarded as “hemidirected” and that in 2 as “holodirected”, it is argued that inter-dimer stacking interactions, rather than lone pair effects, are responsible for the distorted 9-coordination of Pb in 1. In 2, Pb adopts close-to-cubic 8-coordination.     

Estimation of coordination bond energies of NH3, H2O and Et2NH ligands in the Ni(II) and Cu(II) complexes

Tridentate ligands 2-hydroxyphenylsalicylaldimine (SAPH₂), 2-hydroxyphenyl-2-hydroxy-1-naphtalaldimine (NAPH₂) and Ni(II) complexes with multidentate ligand Bis-N·N′-(salicylidene)-1,3-propanediamine (LH₂) as well as mononuclear complex of Cu(II) were prepared using the same multidentate ligand. Diethylamine (Et₂NH), NH₃ and H₂O monodentate ligands were bound to these complexes coordinatively. The heat absorbed at the temperatures where these ligands thermally dissociated from the complexes were measured using the TG and DSC methods. It is assumed that the states both of the complexes with and without the monodentate ligands are solid and coordination bond energy for the monodentate ligand is calculated. It is seen that these calculated coordination bond energies are comparable with hydrogen bond energies.     

Coordination of 2-phosphorylalkyl-substituted 1,8-naphthyridines in complexes with lanthanide nitrates

The reaction of 2-phosphorylalkyl-substituted 1,8-naphthyridines, viz., 2-[2-(diphenylphosphoryl)propan-2-yl]-1,8-naphthyridine (L ¹ ) and 2-[2-(diphenylphosphoryl)ethyl]-1,8-naph-thyridine (L ² ), with lanthanide nitrates (Nd, Eu, or Lu) afforded complexes with the metal-to-ligand molar ratio of 1: 1 and 1: 2. Based on the IR and Raman spectroscopic data, it was found that the coordination of the ligands L ¹ and L ² in all complexes occurs through the P=O group and the nitrogen atoms of the naphthyridine moiety.     

Crystal structures,electrochemical properties,antioxidant screening and in vitro cytotoxic studies on four novel Cu(II) complexes of bidentate Schiff base ligands derived from 2-methoxyethylamine

Four novel Schiff base ligands and their copper(II) complexes, [Cu(L¹)₂] (1), [Cu(L²)₂] (2), [Cu(L³)₂] (3), and [Cu(L⁴)₂] (4), were synthesized and characterized by elemental analyses, FT-IR, and UV–Vis spectroscopy. The ligands were synthesized from the condensation of 2-methoxyethylamine with various salicylaldehyde derivatives (x-salicylaldehyde for HLⁿ, x = H (n = 1), 5-Br (n = 2), 3-OMe (n = 3), and 4-OMe (n = 4)). The molecular structures of 1, 2, and 3 were determined by the single crystal X-ray diffraction technique. The redox behavior studies of the complexes in acetonitrile display the electronic effects of the groups on the redox potential. The antioxidant activity of the Schiff base ligands and their Cu(II) complexes was evaluated using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging method and FRAP assay. Furthermore, the in vitro anticancer activity of compounds was screened, including MTT and migration assays against gastric cancer cell line (MKN-45). The results show that all ligands and complexes have antioxidant and anticancer activity in a concentration-dependent way.     

以D-樟脑酸与1，4-二（咪唑-1-基）丁烷为配体构筑的两个配位聚合物的结构与磁性

水热合成了2个以D-樟脑酸（D-H₂cam）与1,4-二（咪唑-1-基）丁烷（1,4-bimb）为配体的配位聚合物：[Co（D-cam）（1,4-bimb）]_n·4nH₂O（1）和[Ni（D-cam）（1,4-bimb）]_n（2）。通过X-射线单晶衍射,元素分析,红外光谱,XRD分析,热重,和磁性分析对其结构进行了表征。测定了这两个聚合物的磁性。结构分析表明,1为P2空间群,其链状结构由氢键作用连接形成二维结构;2为Pna2₁空间群,呈四重穿插的dia网络结构。     

A novel interdigitating metal-organic architecture showing the double edge-containing (4,4)topology based on the eight-connected Mn4 tetramer

This article presents the structure of a tight stacking coordination polymer, {Mn₄(bpy)₂(H₂O)₂(HBT C)₄}_n, 1, (bpy=4,4′-dipyridine, H₃BTC=1,3,5-benzenetricarboxylic acid), which is self-assembled from the combination of MnCl₂, H₃BTC and bpy ligands via hydrothermal synthesis, and which has been further characterized by IR, element analysis, TG-DTA, variable-temperature magnetic susceptibility measurements. The overall structure of polymer 1 is the 3D interdigitating arrangement, constructed from the eight-connected Mn₄ tetramer. Further, the magnetic measurements reveal that polymer 1 displays a weak antiferromagnetic behavior with θ?=??3.36?K between Mn(II) ions in the electronic configuration of d⁵ high spin (S?=?5/2).     

Synthesis,characterization and antimicrobial activities of triorganotin(IV) complexes with azo-azomethine carboxylate ligands: crystal structure of a tributyltin(IV) and a trimethyltin(IV) complex

Triorganotin(IV) complexes with polyaromatic azo-azomethine carboxylate ligands viz. 2-{4-hydroxy-3-[(2/4-hydroxyphenylimino)methyl]phenylazo}benzoic acids [H₃L¹/H₃L²] were synthesized by reacting the ligands with either bis-tri-n-butyltin(IV) oxide (for 1 and 4) or trimethyltin(IV) chloride in presence of triethylamine (for 2 and 5) or triphenyltin(IV) hydroxide (for 3 and 6). The complexes were characterized by elemental analysis, UV, IR, NMR, and mass spectrometry. NMR spectroscopic studies of the compounds suggested that the complexes adopt four-coordinate tetrahedral geometry around tin in solution. Molecular structures of 1 and 2 were determined by single-crystal X-ray diffraction. Both complexes have distorted trigonal bipyramidal geometry around tin in the solid state. Compound 1 is a one-dimensional (1-D) double chain coordination polymer which can be described as two different 24- and 30-membered non-porous macrocyclic rings constructed from two tributyltin units and two ligand moieties. The structure of 2 comprises a discrete cyclic centrosymmetric dimer with two lattice water molecules per formula unit. In the dimer, two trimethyltin entities are bridged by two ligand moieties. The dimers are further interconnected with lattice water molecules by multiple O–H?O hydrogen bonds to form a 1-D H-bonded network. The complexes were also screened for their antimicrobial activities.