Selective metal substitution for the preparation of heterobimetallic microporous coordination polymers

The designed synthesis of heterobimetallic microporous coordination polymers (MCPs) is reported by a strategy employing the selective replacement of a single metal in homometallic MCPs with two unique metal coordination environments: octahedral and tetrahedral. This strategy is successful in the preparation of six mixed-metal MCPs, where Co/Zn and Ni/Zn versions of MOF-4, MOF-39, and a Zn-BTEC MCP are reported.     

Ferromagnetic interactions in heterobimetallic chains formed through the secondary coordination of dithiolene complexes

A novel paramagnetic ( S = 1/2) copper dithiolene complex based on the tfadt ligand (tfadt: 3-trifluoromethyl-acrylonitrile-2,3-dithiolate) is prepared as its n-Bu 4N (+) salt and crystallized with [Ni(cyclam)] (2+) into infinite, one-dimensional chains through CN...Ni interactions, avoiding any direct (antiferromagnetic) overlap between the dithiolene complexes. An unprecedented ferromagnetic interaction within the heterobimetallic chains between the S = 1/2 [Cu(tfadt) 2] (2-) and the S = 1 [Ni(cyclam)] (2+) tectons is observed, despite the fact that the SOMOs of both [Cu(tfadt) 2] (2-) (with d x (2) - y (2) symmetry) and [Ni(cyclam)] (2+) (with d x (2) - y (2) and d z (2) symmetry) have the same e g symmetry. The experimental exchange interaction deduced from the fit of the magnetic susceptibility ( J exp/ k B = +5.0 K) was confirmed by theoretical calculations ( J calc/ k B = +7.3 K), and a rationale is given for the presence of an intrachain ferromagnetic interaction.     

Synthesis, characterization, and coordination chemistry of two new tartaric acid-derived bis(phosphite) ligands

The syntheses of two chiral bis(phosphite) ligands with tartaric acid-derived backbones: 1 (from dimethyl tartrate) and 2 (from dipyrollidene tartramide), three complexes of 1: cis-Mo(CO)₄(1), cis-PtCl₂(1), and cis-PdCl₂(1) and two complexes of 2: cis-Mo(CO)₄(2) and cis-PdCl₂(2) are described. Each ligand and complex has been fully characterized by ¹H, ¹³C, and ³¹P NMR spectroscopy, and the coordination ³¹P NMR chemical shifts have been compared to those observed for complexes of related ligands. The X-ray crystal structures of each of the metal complexes have also been determined. The X-ray crystal structures indicate that the conformation of the seven-membered chelate ring varies depending on the substituents on the tartrate backbone. However, the conformations of the seven-membered rings do not change when the metal center is changed or when the coordination environment around the metal center is changed.     

Synthesis and characterization of a complex salt and heterobimetallic coordination polymers of 1-benzoyl-1-cyanoethylene-2,2-dithiolate

The complex salt (NBu₄ⁿ)₂ [Cu(bcd)₂] and heterobimetallic coordination polymers MM′(bcd)₂ [M=2Ag^I, Cd^II, Hg^II or Pb^II; M′=Ni^II or Cu^II; bcd²⁻=1-benzoyl-1-cyanoethylene-2,2-dithiolate] have been synthesized from the reaction of Na₂[M′(bcd)₂] generated in situ with NBu₄ⁿBr or metal salts MX₂ [X=MeCO₂⁻, NO₃⁻, Cl⁻ or SO₄²⁻]. The complexes were characterized by elemental analyses, molar conductance, magnetic susceptibility, i.r., n.m.r., electronic and e.s.r. spectra and solid-state conductivity measurements. The MCu(bcd)₂ polymers are diamagnetic, suggesting strongly antiferromagnetically coupled Cu^II ions. The conductivities of the pressed pellets of the compounds are very small and they do not show semiconducting behaviour in the considered temperature range.*Presented at the 10th Symposium on Modern Trends in Inorganic Chemistry (MTIC-X), December 15–17, 2003, Indian Institute of Technology, Mumbai, India.     

Conformation and barrier to inversion of a 12-membered heterocycle containing two disulfide bonds

Raman and ¹H NMR spectroscopic data obtained for a dimeric product 4c formed on iodine oxidation of N-pnenyl-N-thiomethyl-thioglycolic acid amide (3c) indicate that this product is 4,11-diphenyl-4,11-diaza-1,2,7,8-tetrathia-cyclododecane-5,10-dione. The barrier to interconversion between the conformers of 4c has been determined by DNMR. The height of the barrier (ΔG^≠ = 17.3 ±0.1 $\text{kcal}\text{mol}$) is in agreement with the proposed structure. This investigation thus gives a support to the previously proposed mechanism of regiospecific dimeric oxidations of unsymmetrical dithols of type 3c.     

Aromaticity of benzene in the facial coordination mode: a structural and theoretical study

The effects of facial coordination of benzene to a trinuclear transition-metal cluster have been studied by structure correlation and DFT calculational methods. Data taken from the X-ray crystal structures of twelve complexes [(eta-C(5)H(4)R")Co(3)(micro(3)-eta(2):eta(2):eta(2)-C(6)H(4)RR')] 1 b-1 m were analyzed by using standard statistical methods. The prototypal facial arene ligand is considerably expanded with respect to free benzene and shows a small but highly significant Kekulè distortion (d(CC)=1.42, 1.45 A). DFT MO calculations were carried out on the model complexes [(eta-C(5)H(5))M(3)(micro-eta(2):eta(2):eta(2)-C(6)H(6))] 1 a (M=Co), 2 (M=Rh), and 3 (M=Ir). Ring currents in the facial benzene and apical cyclopentadienyl ligands have been assessed by nucleus independent chemical shift (NICS) calculations. Compared to the free ligand (with the optimized D(6h) structure as well as with D(3h) and a C(3v) geometries similar to that in the prototypal facial arene), facial benzene exhibits somewhat reduced but still substantial cyclic electron delocalization (CED). The calculated order of CED is benzene approximately [(CO)(3)Cr(eta-C(6)H(6))] 4 > 1 > 2 > 3.     

A semiempirical study of heterocycle oligomers and polymers in different dielectric media

Four common five-membered heterocycles—pyrrole, phosphole, thiophene, and furan—and their oligomers with the chain length of 2, 4, 6, and 10 units have been studied quantum chemically using the semiempirical PM 3 parameterization. The oligomers of pyrrole and phosphole with the homolytically dissociated N? H bond and P? H bond, respectively, and oligomers of thiophene and furan with one electron removed per monomer unit (4n + 2 π-electron bipolaron systems) have also been studied. The electronic properties of the respective polymers were extrapolated from the oligomer data. Bulk polymer effects on the electronic structure were modeled using the self-consistent reaction field theory in the multicavity approximation (MC a SCRF ). © 1995 John Wiley & Sons, Inc.     

Solid state synthesis and characterization of a triple chain calcium(II) coordination polymer showing two different bridging 4-nitrobenzoate coordination modes

The solid state reaction of [Ca(H₂O)₄(η¹-4-nba)(η²-4-nba)] 1 (4-nba = 4-nitrobenzoate) with 2-methylimidazole (L²) at 100 °C results in the formation of a Ca(II) coordination polymer [Ca(H₂O)(L²)(4-nba)₂]_n2. Compound 2 was characterized by elemental analysis, spectral and thermal methods, and its structure determined. The coordination polymer 2 crystallizes in the centrosymmetric monoclinic space group P2₁/n with all atoms situated in general positions and its structure consists of a central Ca(II), a monodentate 2-methylimidazole, a bridging water ligand (μ₂-H₂O), a bidentate bridging (μ₂-η¹:η¹) 4-nba ligand and a monoatomic bridging (μ₂-η²) 4-nba ligand. Each seven-fold coordinated Ca(II) in the title compound is bonded to a nitrogen atom of a terminal 2-methylimidazole (L²) ligand, two symmetry related water molecules and four symmetry related 4-nba ligands, resulting in a distorted pentagonal bipyramidal {CaO₆N} polyhedron. Due to the bridging nature of the aqua and 4-nba ligands [(2-methylimidazole)calcium(II)] units in 2 are linked into a one-dimensional coordination polymer consisting of three chains, all of which propagate along b-axis. In the triple chain coordination polymer a Ca···Ca separation of 3.8432(3) Å is observed between neighbouring Ca(II) ions. The oxygen atoms of the carboxylate and nitro functionalities of the 4-nba ligand and the coordinated water are involved in O–H···O, N–H···O and C–H···O interactions. A comparative study of nine alkaline-earth 4-nitrobenzoate compounds is described.     

Synthesis, structure, and fluorescence of two cadmium(II)-citrate coordination polymers with different coordination architectures

Two novel Cd(II)-citrate complexes were obtained with different metal/ligand ratios through hydrothermal method. Their structures were determined by single-crystal X-ray diffraction analysis. Although their topological structures are both 2-D layer network assemblies, both central Cd(II) ions and Hcit³⁻ ligands display completely different coordination modes. In polymeric complex 1, Hcit³⁻ serves as a μ₁₀-bridged and central Cd(II) ions adopt 6- and 8-coordinated configurations. In contrast, a μ₉-bridged and 6- and 7-coordinated environments between Cd(II) and Hcit³⁻ are established in the polymeric complex 2. Two Complexes remain stable up to approximately 300 °C. The complex 1 exhibits strong fluorescent emission band at 450 nm (λ=346 nm) as well as complex 2 exhibits strong fluorescent emission band at 430 (λ=346 nm).     

An unusual oxo-bridged rhenium complex with the Re centers in different coordination environments

The reaction of the complex [ReOBr₃(PPh₃)₂] with 3,5-dimethylpyrazole (3,5-Me₂pzH) in acidified acetone at room temperature has been examined and a novel dinuclear oxocompound, [{ReOBr₄}(μ-O){ReO(3,5-Me₂pzH)₄}], has been obtained. It has been studied by IR, UV–Vis spectroscopy, magnetization measurements and X-ray crystallography. The electronic structure of [{ReOBr₄}(μ-O){ReO(3,5-Me₂pzH)₄}] has been calculated with the density functional theory (DFT) method. The spin-allowed singlet–singlet electronic transitions of [{ReOBr₄}(μ-O){ReO(3,5-Me₂pzH)₄}] have been calculated with the time-dependent DFT method, and the UV–Vis spectrum of the title compound has been discussed on this basis.     

31P NMR study of the hydrolytic activity of ethriol phosphite and triphenyl phosphite in a two-phase system

The hydrolytic activity of ethriol phosphite and triphenyl phosphite in the p-xylene/water two-phase system was studied by the³¹P NMR method. It was shown that the rate of hydrolysis can be controlled by varying the pH of the aqueous phase. Hydrolysis of triphenyl phosphite is much slower than that of ethriol phosphite in the tested pH range. Coordination of ethriol phosphite with a rhodium carbonyl complex completely suppresses its hydrolysis.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1026–1030, May, 1991.     

Unprecedented eta3-M3 coordination mode in a terpyridine ligand

The gold(I) complex [Au3(C6F5)3(eta3-Fcterpy)](Fcterpy = 4'-ferrocenyl-2,2'ratio6',2'-terpyridine) represents the first example of a terpyridine ligand bonded to three different metals. The aurophilic interactions present in the molecule may contribute to the overall stability of the system, as was shown by DFT calculations. The positive Mayer indices (0.152 and 0.138), as well as the magnitude of the binding interaction between terpy and the Au(I)L fragments, support this interpretation.     

Synthesis, Structure and Photoluminescence of Two Zinc Carboxyl－ate Polymers with Different Coordination Architectures

The hydrothermal reaction of ZnO with benzene‐1,4‐dicarboxylic add gave Zn·BDC·2H₂O (1) and Zn‐BDC·H₂O (2) (BDC = benzene‐1, 4‐dicarboxylate), respectively. Polymer 1 (C₄H₄O₃ZH_0.5) shows a one‐dimensional zigzag chain structure built up from the alternate connection of tetrahedral ZnO₄ and BDC units. Polymer 2 (C₄H₃O_2.5Zn_0.5) possesses a three‐dimensional framework containing infinite zigzag Zn·Zn·Zn pseudochains generated by five‐coordinate zinc centers and a rectangular channel system including three groups of different straight channels along the [001], [010] and [60–1] directions. The two metal‐organic polymeric compounds exhibit strong photoluminescent emission bands at 402 nm (λ_ex = 260 nm) (for 1) and at 344 nm and 385 nm (λ_ex = 279 nm) (for 2) in the solid state at room temperature.     

Synthesis and structural characterization of a new heterobimetallic coordination complex of barium and cobalt for use as a precursor for chemical vapor deposition

Ba(dmae)2 (dmaeH=N,N-dimethylaminoethanol, C4H11NO) reacts with Co(acac)2 (acac=2,4-pentanedionate) to produce the trinuclear coordination complex [Ba2Co(acac)4(dmae)3(dmaeH)] in an 85% yield. Spectroscopic and single-crystal X-ray diffraction experiments indicate that the complex possesses a structure in which two barium atoms and a cobalt atom are bridged by acac and dmae groups. The barium centers are eight and nine coordinate with BaO7N and BaO7N2 coordination spheres while the cobalt is a more regular CoO5N octahedron. This 2:1 heterobimetallic molecular complex was investigated as precursor for the deposition of thin film by AACVD. The film was characterized by SEM and XRD. TGA shows that the complex starts thermal decomposition upon heating in nitrogen atmosphere at 105 degrees C to produce barium cobalt oxide material of a Ba2CoO3 composition with an orthorhombic structure. The synthetic approach detailed here represents a unique route to the formation of a heterobimetallic barium cobalt coordination complex.     

An unsymmetrical coordination environment leading to two slow relaxation modes in a Dy2 single-molecule magnet

A Dy(2) single-molecule magnet was isolated using a mixed ligand strategy in which the Dy(III) ions adopt distinct coordination environments. This leads to two unique relaxation modes due to a single-ion type relaxation mechanism. Energy barriers were obtained from individually fitting the overlapping peaks.     

Supramolecular framework with two different kinds of channels via self-assembly of 1D coordination polymers in a prismatic manner

Slow diffusion of Cu(ClO4)2 with p-C6H4(SiMe2(4-Py))2 yields a supramolecular framework consisting of two kinds of channels via self-assembly of a 1D double-stranded chain in a prismatic fashion. The channel has a 11 x 11 A2 cross section (Cu...C = 11.13 A) with a 6 x 6 A2 square pore. The channels are infinitely arranged, resulting in another kind of channel with similar pores. Thus, two different kinds of channels with different solvate molecules coexist in a 1:2 ratio. Weak C-H...pi interaction may be one of the driving forces in the assembly of the prismatic channel structure.     

Hydrothermal synthesis, characterization and fluorescence property of a novel layered fluorinated gallium phosphite with heptameric building unit

A new fluorinated gallium phosphite, Ga₃F₂(2,2′-bipy)₂(HPO₃)₂(H_1.5PO₃)₂1, which is the first layered gallium phosphite with neutral framework, has been hydrothermally synthesized in the presence of 2,2′-bipyridine (2,2′-bipy) acting as a ligand. The as-synthesized product was characterized by single-crystal X-ray diffraction, powder X-ray diffraction, IR spectroscopy, thermogravimetric analysis (TGA), ICP-AES and elemental analyses and fluorescent spectrum. Single-crystal X-ray diffraction analysis reveals that compound 1 crystallizes in the monoclinic space group C2/c (No. 15) with cell parameters a=17.633(3) Å, b=9.883(2) Å, c=16.793(3) Å, β=109.88(3)°, V=2752.1(9) Å³ and Z=4. The construction of two-dimensional (2D)-layered structure in compound 1 may be viewed as the assembly of heptameric building unit, which is the first to be found in gallium phosphate/phosphite. The heptameric building unit exists in two types of configuration, which alternately connect through oxygen atoms from HPO₃ pseudo-pyramids to form a layer with 10-membered ring windows viewed along the a-axis. The adjacent layers are stably packed together and exhibit interesting three-dimensional (3D) supramolecular array via π-π interactions of the 2,2′-bipy groups. Additionally, compound 1 shows strong fluorescent property in solid state at room temperature.     

Metal-organic coordination architectures of azole heterocycle ligands bearing acetic acid groups: Synthesis, structure and magnetic properties

Four new coordination complexes with azole heterocycle ligands bearing acetic acid groups, [Co(L¹)₂]_n (1), [CuL¹N₃]_n (2), [Cu(L²)₂·0.5C₂H₅OH·H₂O]_n (3) and [Co(L²)₂]_n (4) (here, HL¹=1H-imidazole-1-yl-acetic acid, HL²=1H-benzimidazole-1-yl-acetic acid) have been synthesized and structurally characterized. Single-crystal structure analysis shows that 3 and 4 are 2D complexes with 4⁴-sql topologies, while another 2D complex 1 has a (4³)₂(4⁶)-kgd topology. And 2 is a 3D complex composed dinuclear μ_1,1-bridging azido Cu^II entities with distorted rutile topology. The magnetic properties of 1 and 2 have been studied.     

2[Mn(acacen)]+ + 1[Fe(CN)5NO]- polynuclear heterobimetallic coordination compounds of different dimensionality in the solid state

Depending on the synthetic conditions, five heterometallic Mn(III)Fe(II) polynuclear compounds with the same ratio of constituents, 2[Mn(acacen)](+)/[Fe(CN)(5)NO](2-), of different nuclearity and dimensionality (0D, 1D, 2D) were isolated. A [Mn(acacen)MeOH](2)[Fe(CN)(5)NO]·1.5MeOH, 1 complex has been prepared by reaction of Mn(III)/Schiff base (SB) complex, [Mn(acacen)Cl] (H(2)acacen is N,N'-ethylenebis(acetylacetoneimine)) with sodium nitroprusside (NP). Single crystal X-ray diffraction analyses reveal that crystallization of 1 from coordinating or non-coordinating solvents results in different coordination polynuclear materials: from C(2)H(5)OH [{Mn(acacen)H(2)O}(2)Fe(CN)(5)NO]·C(2)H(5)OH, 2, a trinuclear complex is formed; from CH(3)CN [{Mn(acacen)H(2)O}(4)Fe(CN)(5)NO][Fe(CN)(5)NO]·4CH(3)CN, an ionic compound with a pentanuclear bimetallic cation is formed 3; from i-C(3)H(7)OH [{Mn(acacen)}(2)(i-PrOH)Fe(CN)(5)NO](n), a coordination chain polymer 4 is formed; from toluene [{Mn(acacen)}(2)Fe(CN)(5)NO](n), a layered network 5 is formed. As the magnetic measurements show, for all compounds the weak interaction between Mn(III)S = 2 spins through the NP bridge is antiferromagnetic and exhibits no significant photoactivity.