Syn-syn Bridging Research Articles

Mixed N,O-donor Directed Blue Emissive Nano-dispersed Mesoporous Mn(II)-MOF: Dual Sensing Probe for Recyclable and Ultrasensitive ppb-Level Recognition of TNP and Cr(VI)-Oxoanions.

A new mesoporous Mn(II)-MOF [Mn2(phen)2(nia)2]∞ with 4-c uninodal net topology and reiterating rectangular channels in its cargo-net like extension was synthesized using π-conjugated phenanthroline (phen) and syn-syn bridging 5-nitroisopthalic acid (nia) linkers. The MOF (1) exhibited phase purity, uniform morphology, photo and thermal stability, and robustness; duly triggered by the exceptional framework rigidity via intermolecular H-bonding and interlayer π-π stacking interactions. The bright-blue luminescence of the MOF nano-dispersion was explored for sensitive, specific and ultrafast detection of trinitrophenol (TNP) with extremely low LOD (90.62 nM), high KSV (18.27×104 M-1) and Kq (4×1014 M-1s-1). The vapor-phase TNP sensing was also accomplished. Additionally, 1 served towards discriminatory, aqueous-phase monitoring of Cr(VI)-oxoanions, depicting LODs: 36.08 and 35.70 ppb; KSV: 3.46×104 and 4.87×104 M-1; Kq: 3.26×1013 M-1s-1 and 4.31×1013 M-1s-1; and response time: 32 and 40s for CrO4 2- and Cr2O7 2- respectively. The quenching mechanisms (i. e., RET, PET, IFE, weak interactions, collisional quenching and π⋅⋅⋅π stacking) was explained from several experimental investigations and theoretical DFT calculations. The recyclable sensing events and quantification from complex environmental matrices with admirable recovery rates and high KSV (13.02-22.44×104; ~6.31-10.98×104 and ~6.60-11.42×104 M-1 for TNP, CrO4 2- and Cr2O7 2-) undoubtedly advocated the consistency of the probe.

Trinuclear heterometallic CuII–MII (M = Mn and Co) complexes of N,O donor ligands with o-nitro benzoate anion: Structures, magnetic properties and catalytic oxidase activities

Three new heterometallic complexes [(CuL1)2Mn(o-(NO2)C6H4CO2)2] (1), and{[(CuL2)2Mn(o-(NO2)C6H4CO2)2]·2CH3CN} (2) and {[(CuL2)2Co(o-(NO2)C6H4CO2)2]·2H2O} (3) have been synthesized using [CuL1]/[CuL2] as metalloligands (where H2L1 = N,N′-bis(2-hydroxynaphthyl-methylidene)-1,3-propanediamine, H2L2 = N,Ń-bis(methyl2-hydroxynaphthyl-methylidene)-1,3-propanediamine). Structural characterization of complexes (1–3) show that contains linear trinuclear architecture, where the terminal [CuL1]/[CuL2] units are coordinated to the central MnII (for 1 and 2)/CoII (for 3) through double phenoxido bridge along with a syn-syn bridging carboxylate anion. Complexes 1 and 2 exhibit biomimetic catecholase-like activity with the turn over numbers (kcat) of 164 and 140 h−1, respectively. The mass spectral study suggest the most probable mechanism of this biomimetic oxidase reaction whereas, cyclic voltammetry measurements indicate that CuII is reducible to CuI during catalysis. Variable temperature (2–300 K) magnetic susceptibility measurements reveal that all complexes (1–3) possess an overall antiferromagnetic coupling between CuII and the hetero metal ions with J values of –7.027(2), –7.076(1) and –2.2(1) cm−1, respectively.

Fluorite-like hydrolyzed hexanuclear coordination clusters of Zr(IV) and Hf(IV) with syn-syn bridging N,N,N-trimethylglycine in soft crystal structures exhibiting cold-crystallization

Tetravalent metal ions are hydrolyzed under presence of N,N,N-trimethylglycine hydrochloride (betaine hydrochloride, [Hbet]Cl) in aqueous solutions to afford [M6(μ3-O)4(μ3-OH)4(μ-bet)8(κ-bet)4(H2O)4]12+ (M4+ = Zr4+ (1), Hf4+ (2)) as hydrated perchlorate salts. These compounds were characterized by single crystal X-ray diffraction, elemental analysis and IR spectroscopy. As a result, we have found that fluorite-like [M6O8] coordination clusters are formed through octahedral arrangement of six M4+ linked by μ3-O atoms. Additionally, each pair of neighboring M4+ are connected by the μ-bet ligand through a syn-syn bridging coordination of its carboxylate moiety. This interaction seems to prevent further growth of the fluorite structure leading to formation of MO2. It was difficult to directly distinguish each μ3-O atom to be μ3-OH− or μ3-O2− due to its strongly anisotropic thermal displacement in the obtained structures. Bond valence sum analysis suggested that four μ3-OH− and four μ3-O2− are alternately arranged in the [M6O8] core motifs. Indeed, such a symmetric structure of [M6(μ3-O)4(μ3-OH)4] was confirmed in another phase of 1 at 296 K, where 1 transforms to a monoclinic structure (1′). The number of ClO4− counteranions found in the structure determination is not enough to compensate + 12 charge of [M6(μ3-O)4(μ3-OH)4(μ-bet)8(κ-bet)4(H2O)4]12+ in any unit cells of 1, 1′ and 2. Instead, large solvent/ion accessible voids have been actually observed in their crystal structures, indicating that the missing ClO4− are located therein and are significantly disordered to make them invisible in the crystallography. DSC analysis revealed that ClO4− and H2O/H3O+ in the crystal lattice of 1 undergo unique structure relaxation and rearrangements pronounced by cold-crystallization to induce the phase transition from 1 to 1′ with elevating temperature.

Tri- and pentanuclear CuII–CdII complexes of N2O2 donor ligands with the variation of carboxylate coligands: Structural elucidation and theoretical study

Three new heterometallic copper(II)-cadmium(II) complexes [(CuL1)2Cd3(C6H5CO2)6] (1), {[(CuL2)2Cd(o-(NO2)C6H4CO2)2]·2NCMe} (2), and [{CuL2(H2O)0.65(NCMe)0.35}2Cd3(m-(NO2)C6H4CO2)6] (3) have been synthesized using [CuL1]/[CuL2] as metalloligand (where H2L1 = N,N′-bis(2-hydroxynaphthyl-methylidene)-1,3-propanediamine, H2L2 = N,Ń-bis(methyl2-hydroxynaphthyl-methylidene)-1,3-propanediamine). Single crystal structure analyses reveal that complexes 1 and 3 exist as pentanuclear entities in which the [CuL1]/[CuL2] units are bonded to the terminal CdII centres of the benzoate (for 1)/m-nitro benzoate (for 3) bridged linear [Cd3(C6H5CO2)6] (for 1)/[Cd3(m-(NO2)C6H4CO2)6] (for 3) unit through double phenoxido oxygen atoms. On the other hand, complex 2 contains a linear, trinuclear structure in which the square pyramidal [CuL2] units are connected with the central octahedral CdII ion via double phenoxido bridges and also additionally through a syn-syn bridging o-nitro benzoate group. A theoretical investigation on the geometries and energies of the complexes reveals that in the presence of the naphthalene group in H2L1 the pentanuclear geometry of complex 1 is favored over the trinuclear ones, usually formed with the salen type ligands. In addition, substitution of benzoate ion at meta position by nitro group stabilizes pentanuclear structure more than ortho-substitution, corroborating the formation of pentanuclear complex 3 and trinuclear complex 2.

Modulation of Nuclearity in CuII -MnII Complexes of a N2 O2 Donor Ligand Depending upon Carboxylate Anions: Structures, Magnetic Properties and Catalytic Oxidase Activities.

Three new hetero-metallic copper(II)-manganese(II) complexes, [(CuL)2 Mn3 (C6 H5 CO2 )6 ] (1), [(CuL)2 Mn(CH3 CO2 )2 ] (2), and {[(CuL)2 Mn(C6 H5 CH2 CO2 )2 ] ⋅ 2CH3 CN} (3), have been synthesized using [CuL] as ''metalloligand'' (where H2 L=N,N'-bis(2-hydroxynaphthyl-methylidene)-1,3-propanediamine). Single-crystal structural analyses show an almost linear penta-nuclear structure for complex 1 where a square planar [CuL] unit is connected to each of the two terminal MnII ions of a linear, centrosymmetric [Mn3 (benzoate)6 ] unit through the double phenoxido bridges. Both complexes 2 and 3 possess a linear tri-nuclear structure where two terminal square-pyramidal [CuL] units are bonded to the central MnII ion through double phenoxido oxygen atoms along with a syn-syn bridging acetate (for 2)/phenyl acetate (for 3). All three complexes exhibit catecholase, and phenoxazinone synthase-like activities under aerial conditions. For catecholase like activity, the turnover numbers (kcat ) are 595, 40, and 205 h-1 whereas, for phenoxazinone synthase like activity, the turnover numbers are 25, 4, and 11 h-1 for complexes 1-3, respectively. The mechanism of both catalytic oxidase activities is proposed on the basis of mass spectral evidences. Variable-temperature (2-300 K) dc molar magnetic susceptibility measurements of 1 reveal antiferromagnetic interactions between the Cu-Mn centres (J1 =-29.3 cm-1 ), and also between the Mn-Mn centres of the [Mn3 (benzoate)6 ] unit (J2 =-0.68 cm-1 ). On increasing the magnetic field at 2 K, its ground spin state changes from S=3/2 to S=5/2 at 4 T, attributable to the low value of J2 which makes the excited spin states close in energy with the ground spin state. Complexes 2 and 3 show antiferromagnetic coupling interactions between the Cu-Mn pairs with J values of -9.51, and -5.32 cm-1 , respectively.

Phosphatase-like Activity of Tetranuclear Iron(III) and Zinc(II) Complexes.

Three new tetranuclear iron(III) and zinc(II) complexes, [Fe4(cpdp)2(phth)2(OH)2]·8H2O (1), [Fe4(cpdp)2(terephth)2(OH)2] (2), and [Zn4(Hcpdp)2(suc)]Br2·12H2O (3), have been synthesized as models for the active site of phosphoester hydrolases by utilizing a polydentate ligand, N, N'-bis[2-carboxybenzomethyl]- N, N'-bis[2-pyridylmethyl]-1,3-diaminopropan-2-ol (H3cpdp) in combination with exogeneous phthalate (phth), terephthalate (terephth), and succinate (suc). Single crystal X-ray analyses reveal that the metallic core of complex 1 consists of four distorted octahedral iron(III) ions with average intraligand Fe---Fe separation of 3.656(2) Å, while the structure 3 represents a tetranuclear metallic core containing four distorted trigonal bipyramidal zinc(II) ions with average intraligand Zn---Zn separation of 3.472(2) Å. The molecular structure of complex 2 has been optimized by the DFT method which shows that its core arrangement is similar to that of 1. Complex 1 has a very interesting centrosymmetric structure that includes two crystallographically equivalent [Fe2(cpdp)]3+ dinuclear units, connected together by a pair of syn-syn bridging phthalates and a pair of bridging hydroxides to generate a "dimer of dimers" structural motif. In complex 3, a succinate group connects two crystallographically equivalent [Zn2(Hcpdp)]2+ dinuclear units in a syn-syn bidentate manner forming a "dimer of dimers" structural design. All three complexes show phosphatase-like activity that has been examined in methanol-water (1:1; v/v) using bis( p-nitrophenyl) phosphate (BNPP) as model substrate by applying the UV-vis spectrophotometric technique. In each case, the kinetic data have been analyzed by the Michaelis-Menten approach. The order of catalytic efficiency for the conversion of substrate to product follows the trend 1 > 2 > 3 with turnover rates ( kcat) of (2.73 ± 0.13) × 10-5 for 1, (1.06 ± 0.07) × 10-5 for 2, and (2.33 ± 0.18) × 10-6 s-1 for 3. These kcat values are comparable to, albeit slightly lower than, the values reported for similar iron(III)- and zinc(II)-based model complexes in the literature. DFT calculations have been carried out to support the proposed mechanism for phosphatase-like activity.

Synthesis, characterization and anticancer property of a Dy(III) compound with [Dy4(OH)4]8 + secondary building units

A novel [Dy4(pytza)5(OH)4(H2O)7Cl]Cl2·4H2O compound based on 5-(4-pyridyl)tetrazole-2-acetic acid (Hpytza) has been designed and prepared. This compound is an unprecedented two dimensional network consisting of a tetranuclear cubic [Dy4(OH)4]8+ secondary building unit (SBU) and tridentate pytza via the pyridine-N and the carboxylate group in a μ1,3-COO syn-syn bridging mode. PEG-5000 (poly(ethyleneglycol-5000)) coated [Dy4(pytza)5(OH)4(H2O)7Cl]Cl2·4H2O nanoparticles (NPs) have good dispersity in distilled water. In vitro study on Hela cells shows that such NPs show high toxicity while Hpytza is non-toxic in nature. Furthermore, such NPs can effectively inhibit the migration of Hela cells even at a low concentration, indicating their potential to inhibit the transfer of tumors in vivo.

Bond breakage under pressure in a metal organic framework.

The internal free volume of porous materials diminishes upon mechanical compression, and such volume collapse can have chemical consequences. We report here the endothermic bond breakage in a metal-organic framework (MOF) during compression-induced collapse. Upon bulk compression at 1.9GPa, the effective number for Zr-O bonds between Zr(iv) ions and carboxylate groups in UiO-66 decreased from 4.0 to 1.9, as determined by EXAFS, and the internal free volume was synchronously collapsed. Consistent with the EXAFS data, IR spectra confirmed conversion of syn-syn bridging carboxylates to monodentate ligation, thus establishing mechanochemical reactions induced by external compression of MOFs. Substantial mechanical energy (∼4 kJ g-1) was absorbed by UiO-66 nanocrystals during compression, as demonstrated from nanocompression of single crystals (600 nm) in situ during scanning electron microscopy, which establishes the potential application of MOFs as mechanical energy absorbers for hydrostatic and shock compression.

A novel 3D energetic coordination polymer containing Co(II) atoms in a pentanuclear cluster

A novel coordination polymer [Co5(OH)2(dnbpdc)4(H2O)6]·16H2O (1) (dnbpdc = 6,6′-dinitro-4,4′-biphenyldicarboxylic acid) is obtained from a hydrothermal reaction. The structure of complex 1 is characterized by elemental analysis, IR spectroscopy, and single crystal X-ray diffraction analysis. The title compound (C56H70Co5N8O56, Mr = 2045.85) crystallizes in the triclinic space group P-1 with a = 11.9349(2) A, b = 12.1895(2) A, c = 15.420(2) A, α = 109.390(7)°, β = 94.786(1)°, γ = 108.027(9)°, V = 1968.4(4) A3, Z = 1, Dc = 1.726 g/cm3, F(000) = 1045, μ(MoKα) = 1.154 mm–1, T = 133(2) K, the final R = 0.0316 and wR = 0.0692 for 7032 observed reflections with I > 2σ(I). The coordination polymer is built of a pentanuclear Co(II) cluster, four dnbpdc ligands, two hydroxyl groups, six coordination water and sixteen crystal water molecules. Ligand oxygen atoms exhibit three types of coordination modes (monodentate, syn-syn bridging bidentate and bridging tridentate). Moreover, the infinite three-dimensional supramolecular network is generated by coordination and hydrogen bonds. The thermal stability of complex 1 is evaluated by differential scanning calorimetry and thermogravimetric analysis.

A New Quartz-like Metal–Organic Framework Constructed from a Versatile Pyrazole-Based Spacer

Two new coordination polymers, 1∞[Cu2(L)4(MeOH)]·MeOH (1) and 3∞[Cu(L)2]·5H2O (2), have been obtained exploring the potential of 5-amino-1-phenyl-1H-pyrazole-4-carboxylate (L–) to act as a spacer. The different architectures of these compounds arise from the versatility of this organic ligand. In compound 1, the carboxylato groups (syn-syn bridging mode) and the copper ions generate a binuclear paddle-wheel motif. Each binuclear entity coordinates to another one, through one out of the four pyrazole rings, resulting in double chains. In crystal 2, the organic ligand is coordinated to a copper ion through the carboxylato group (asymmetric chelating) and to another copper ion through the pyrazole nitrogen atom. Compound 2 crystallizes in the hexagonal system with the chiral space group P6122, featuring a quartz-like topology. The magnetic properties of both compounds have been investigated.

Ferro- to antiferromagnetic crossover angle in diphenoxido- and carboxylato-bridged trinuclear Ni(II)₂-Mn(II) complexes: experimental observations and theoretical rationalization.

Three new trinuclear heterometallic Ni(II)-Mn(II) complexes have been synthesized using a [NiL] metalloligand, where H2L = N,N'-bis(salicylidene)-1,3-propanediamine. The complexes [(NiL)2Mn(OCnn)2(CH3OH)2]·CH3OH (1), [(NiL)2Mn(OPh)2(CH3OH)2][(NiL)2Mn(OPh)2]·H2O (2), and [(NiL)2Mn(OSal)2(CH3OH)2]·2[NiL] (3) (where OCnn = cinnamate, OPh = phenylacetate, OSal = salicylate) have been structurally characterized. In all three complexes, in addition to the double phenoxido bridge, the two terminal Ni(II) atoms are linked to the central Mn(II) by means of a syn-syn bridging carboxylate, giving rise to a linear structure. Complexes 1 and 2 with Ni-O-Mn angles of 97.24 and 96.43°, respectively, exhibit ferromagnetic interactions (J(Ni-Mn) = +1.38 and +0.50 cm(-1), respectively), whereas 3 is antiferromagnetic (J(Ni-Mn) = -0.24 cm(-1)), having an Ni-O-Mn angle of 98.51°. DFT calculations indicate that there is a clear magneto-structural correlation between the Ni-O-Mn angle and J(Ni-Mn) values, which is in agreement with the experimental results.

Uncorrelated Dynamical Processes in Tetranuclear Carboxylate Clusters Studied by Variable-Temperature 1H NMR Spectroscopy.

Tetranuclear carboxylate clusters with the general structural formula [M4(L)2(O2CR)4] (M = Cd, Zn; LH2 = 2,6-bis(1-(2-hydroxyphenyl)-iminoethyl)pyridine; R = CH3, C6H5) were studied by variable-temperature (VT) (1)H NMR spectroscopy. The dynamics of these clusters in solution can be described by two uncorrelated dynamical processes. The first dynamical process is the interconversion, both inter- as well as intramolecular, between syn-syn bridging and chelating carboxylate ligands. It is shown that this carboxylate interconversion mechanism is predominantly intramolecular for [Cd4(L)2(O2CCH3)4] (1a), whereas for [Zn4(L)2(O2CCH3)4] (2a) it is predominantly intermolecular. Two models for the second dynamic process, which involves the diiminepyridine ligand, are described. The first model comprises a nondissociative rotation around an internal axis, which changes the chirality of the cluster. The second model is based on the dissociation of the tetranuclear cluster into two dimeric species, which recombine again. This last model is supported by scrambling experiments between [Zn4(L)2(O2CCH3)4] (2a) and [Zn4(L3)2(O2CCH3)4] (5) (L3H2 = 2,6-bis(1-(2-hydroxyphenyl)-iminoethyl)4-chloropyridine).

Hydrogen-Bonding in Two Pyridinium Salts of [Mo2O4Cl4(μ2-dmsH)]3−Complex (dmsH− = a Half-Neutralized Form of 2,2-Dimethylsuccinic Acid)

Reactions of a mononuclear molybdenum(V) starting material, (PyH)5[MoOCl4(H2O)]3Cl2, with 2,2-dimethylsuccinic acid in the presence of base afforded two products, (PyH)3[Mo2O4Cl4(μ2-dmsH)]·1/2CH3CN (1) and (PyH)4[Mo2O4Cl4(μ2-dmsH)]Cl (2). As revealed by the X-ray structure analysis, the half-neutralized form of the dicarboxylic acid, the dmsH− ion, coordinated to the well-known {Mo2O4}2+ core in the syn-syn bidentate bridging manner. In both compounds, the non-ionized terminus of the ligand, the COOH function, participated in hydrogen-bonding interactions. The incorporation of the chloride counteranion in 2, prevented the formation of the common “carboxylic acid dimer” which was observed for 1. Instead, a hydrogen-bonded linkage of the COOH function with the chloride occurred.

Formation of Soluble Hexanuclear Neptunium(IV) Nanoclusters in Aqueous Solution: Growth Termination of Actinide(IV) Hydrous Oxides by Carboxylates

Complexation of Np(IV) with several carboxylates (RCOO(-); R = H, CH(3), or CHR'NH(2); R' = H, CH(3), or CH(2)SH) in moderately acidic aqueous solutions was studied by using UV-vis-NIR and X-ray absorption spectroscopy. As the pH increased, all investigated carboxylates initiated formation of water-soluble hexanuclear complexes, Np(6)(μ-RCOO)(12)(μ(3)-O)(4)(μ(3)-OH)(4), in which the neighboring Np atoms are connected by RCOO(-)syn-syn bridges and the triangular faces of the Np(6) octahedron are capped with μ(3)-O(2-)/μ(3)-OH(-). The structure information of Np(6)(μ-RCOO)(12)(μ(3)-O)(4)(μ(3)-OH)(4) in aqueous solution was extracted from the extended X-ray absorption fine structure data: Np-O(2-) = 2.22-2.23 Å (coordination number N = 1.9-2.2), Np-O(RCOO(-)) and Np-OH(-) = 2.42-2.43 Å (N = 5.6-6.7 in total), Np···C(RCOO(-)) = 3.43 Å (N = 3.3-3.9), Np···Np(neighbor) = 3.80-3.82 Å (N = 3.6-4.0), and Np···Np(terminal) = 5.39-5.41 Å (N = 1.0-1.2). For the simpler carboxylates, the gross stability constants of Np(6)(μ-RCOO)(12)(μ(3)-O)(4)(μ(3)-OH)(4) and related monomers, Np(RCOO)(OH)(2)(+), were determined from the UV-vis-NIR titration data: when R = H, log β(6,12,-12) = 42.7 ± 1.2 and log β(1,1,-2) = 2.51 ± 0.05 at I = 0.62 M and 295 K; when R = CH(3), log β(6,12,-12) = 52.0 ± 0.7 and log β(1,1,-2) = 3.86 ± 0.03 at I = 0.66 M and 295 K.

Crystal and molecular structures of binuclear complexes of salycilic acid {Cu-M} (M = Cu, Sr, Ba)

Heterometallic complexes [CuSr(SalH)4(DMAA)4(H2O)] (II) and [CuBa(SalH)4(DMAA)4 (H2O)] (III) were synthesized by interaction of salicylates of s elements with copper nitrate. A mixture of III and vanadyl sulfate yielded the crystals of a homonuclear complex [CuCu(SalH)4(H2O)2]·2DMAA (I). According to single crystal X-ray data, all of the products are of lantern type and belong to two space groups: I is triclinic, space group P-1, unit cell parameters a = 9.9083(2) A, b = 10.5077(3) A, c = 10.9512(3) A, α = 112.736(2)°, β = 114.0800(10)°, γ = 93.131°; II and III are tetragonal, space group P4/n, lattice parameters a = b = 16.3180(3) A, c = 8.7838(2) A for II and a = b = 16.362(3) A, c = 8.920(1) A III. The copper atoms have a square-pyramidal environment. The coordination number of Sr and Ba is 8, and the coordination polyhedron can be represented as a Thomson cube in both cases. The carboxylic groups are coordinated in a syn-syn bridging mode. The oxygen atom of the hydroxyl group of salicylic acid is not involved in coordination, but forms intramolecular hydrogen bonds to the carboxylic groups. The hydrogen bonds between water and DMAA solvate molecules, as well as — interactions between the aromatic fragments of the dimers, play a particularly important role in the molecular packing in crystal.

Syntheses, X-ray Structures, and Physicochemical Properties of Phenoxo-Bridged Dinuclear Nickel(II) Complexes: Kinetics of Transesterification of 2-Hydroxypropyl-p-nitrophenylphosphate

Four dinuclear nickel(II) complexes [Ni(II)(2)(L(1))(O(2)CMe)(2)(H(2)O)(2)][PF(6)].MeOH.3H(2)O (1), [Ni(II)(2)(L(1))(O(2)CMe)(2)(NCS)] (2), [Ni(II)(2)(L(2))(O(2)CMe)(2)(MeOH)(H(2)O)][ClO(4)] (3), and [Ni(II)(2)(L(2))(O(2)CMe)(2)(MeOH)(H(2)O)][BPh(4)].3MeOH.H(2)O (4) have been synthesized [HL(1): 2,6-bis[N-methyl-N-(2-pyridylethyl)amino]-4-methylphenol; HL(2): 2,6-bis[3-(pyridin-2-yl)pyrazol-1-ylmethyl]-4-methylphenol]. Complexes 1, 3, and 4 are new while complex 2 was reported previously by Fenton and co-workers (the structure of 2 was presented but no physicochemical properties of this complex were reported; in this work such studies have been completed). X-ray crystallographic analyses of 1 and 4 reveal that each nickel(II) center is six-coordinate, terminally coordinated by two nitrogen donors [(pyridin-2-yl)ethylamine unit in 1 and 3-(pyridin-2-yl)pyrazole moiety in 4], and bridged by an endogenous phenolate ion. Each of the acetate ions in 1 adopts a eta(2)-coordination mode (chelating) whereas in 4 each is coordinated in a mu-eta(1):eta(1) syn-syn bridging mode. In 1 each Ni(II) center has water coordination whereas in 4 one Ni(II) center has a methanol and the other has water coordination. The X-ray structure of 3 could not be determined. The physicochemical properties (electronic spectroscopy and cyclic voltammetry) of the cation of 3 are identical to that of 4. Magnetic susceptibility measurements have revealed the occurrence of ferromagnetic coupling of spins of the nickel(II) centers in 2 [J = +9.80 cm(-1)]. The nickel(II) centers in 1 and 3 are antiferromagnetically coupled, but to different extents [J = -48.4 cm(-1) (1); J = -1.24 cm(-1) (3)]. The magnetic properties are correlated with the nature of bridges between the nickel(II) ions. The two coordinated aqua ligands in 1 and the aqua and methanol ligands in 3 have enabled these dinuclear nickel(II) complexes to function as catalysts in the hydrolysis of 2-hydroxypropyl-p-nitrophenylphosphate (HPNP). Complex 1 is more effective in the conversion of substrate to product (p-nitrophenolate ion) than 3, under identical experimental conditions. Pseudo first-order kinetic treatment has been done for complexes 1 and 3. Temperature-dependent measurements were done to evaluate kinetic/thermodynamic parameters for the hydrolysis/transesterification reaction of HPNP and to propose a mechanistic pathway. The activation parameters are DeltaH(++) = 64 kJ mol(-1), DeltaS(++) = -104 J mol(-1) K(-1) for 1 and DeltaH(++) = 68 kJ mol(-1), DeltaS(++) = -109 J mol(-1) K(-1) for 3. A mechanism consistent with the kinetic data is presented.

Synthesis, Structure and Fluorescence Properties of a Trinuclear Zn(II) Complex with N,N,O-donor Schiff Base Ligands and Bridging Acetates

A new centrosymmetric trinuclear Zn(II) complex [Zn3L2(CH3COO)4] (1) has been synthesized by the reaction of Zn(CH3COO)2 · 2H2O with a tridentate N,N,O-donor Schiff base ligand HL [C5H4NC(CH3)=NC6H4(OH)] and systematically characterized by elemental analysis, FT-IR, UV/Vis and thermal methods. Single crystal X-ray structure analysis reveals that three Zn(II) centers are in two different coordination environments. Two terminal Zn(II) centers adopt a distorted squarepyramidal geometry leaving the central Zn(II) in a distorted octahedral environment. Two adjacent metal centers are connected through single μ2-phenolato as well as double μ-acetato-O,O´ syn-syn bridges. Fluorescence properties of the complex as compared to the ligand indicate that the former can serve as a potential photoactive material.

Synthesis and crystal structure of a binuclear copper complex [Cu2( L )2(Cl)2] · 2(C3H7NO), where L = 1H-benzimidazol-2-yl-methanol

The copper(II) compound, (1), [Cu2(L)2(Cl)2] · 2(C3H7NO), C22H28Cl2Cu2N6O4 [where HL = 1H-benzimidazol-2-yl-methanol, C3H7NO = N,N′-dimethylformamide(DMF)], crystallizes in the triclinic space group with a = 8.363(2) Å, b = 8.866(2) Å, c = 9.327(3) Å, α = 91.415(5), β = 93.924(5), γ = 109.318(4)° and Z = 1; R 1 for 2280 observed reflections [I > 2σ(I)] was 0.0356. The centrosymmetric molecule comprises a pair of copper(II) atoms connected by two 1H-benzimidazol-2-yl-methanol ligands in syn-syn bridging mode. Four-coordination of copper(II) is further completed by chloride. The CuII–CuII distance and Cu–OR–Cu bond angle in 1 are 3.043(1) Å and 104.3(1)°, respectively.

Assembling metals (CoIIand MnII) with pyridylcarboxylates in the presence of azide: synthesis, structural aspects and magnetic behavior of three coordination polymers

The reaction between Co(NO3)2.6H2O and substituted pyridylcarboxylic acid [nicotinic acid (Hnic) or trans-3-pyridylacrylic acid (Htpa)] in the presence of NaN3 under hydrothermal conditions yielded [Co(1.5)(nic)2 (Hnic)(N3)]n (1) and [Co(1.5)(tpa)2 (N3)(H2O)]n (2), respectively. Single crystal structure analyses reveal that both complexes are 3D complicated coordination polymers. The basic repeating units in both of the complexes are Co(3) trinuclear clusters containing syn-syn bridging carboxylate and end-on azido linker. A similar reaction using MnCl2.4H2O in presence of equimolar amounts of Htpa and NaN3 yielded a 2D corrugated sheet [Mn(tpa)2]n (3) containing no azide. Complex 3 can also be synthesized under hydrothermal conditions using Natpa in the absence of NaN3. Surprisingly, the same reaction at room temperature yielded a known mononuclear complex [Mn(tpa)2(H2O)4]. Variable temperature magnetic studies down to 2 K revealed the dominant antiferromagnetic nature of the first two complexes with a ferrimagnetic type of behavior despite the facts that they are homometallic and homospin systems. The susceptibility data in both cases were analyzed by a Co3 trinuclear model as well as considering inter-trimer interactions. Complex 3 is weakly antiferromagnetic in nature with an exchange parameter of J = -2 cm(-1) through the syn-anti bridging carboxylate pathway.

Syntheses, Structures, and Characterizations of Four New Lead(II) 5-Sulfosalicylate Complexes with Both Chelating and Bridging Neutral Ligands

Four structurally diverse complexes, {[Pb(Hssal)(2,2'-bipy)](4,4'-bipy)0.5}n (1), [Pb2(Hssal)2(2,2'-bipy)2(4,4'-bipy)(H2O)2] (2), [Pb(Hssal)(phen)(4,4'-bipy)0.5]n (3), and [Pb(Hssal)(2,2'-bipy)(bpe)0.5]n (4), have been synthesized and characterized by elemental analyses, IR, thermogravimetric analyses, fluorescent spectra, and single-crystal X-ray analyses, where Hssal2- is doubly deprotonated 5-sulfosalicylate, 2,2'-bipy is 2,2'-bipyridine, phen is 1,10-phenanthroline, 4,4'-bipy is 4,4'-bipyridine, and bpe is trans-1,2-bis(4-pyridyl)ethylene. The structure of complex 1 possesses a one-dimensional ladderlike chain with guest 4,4'-bipy molecules, while the molecular structure of complex 2 is a dimeric species with a coordinating 4,4'-bipy ligand. Complex 3 consists of a one-dimensional ladderlike chain with monodentate 4,4'-bipyridine but somewhat different from that of complex 1. Complex 4 is a two-dimensional layer structure. In 1-4, all 5-sulfosalicylates are doubly deprotonated, and all carboxylate groups of Hssal2- chelate to PbII ions; however, the coordination modes of sulfonyl groups are different: syn-syn bridging in 1, noncoordinating in 2, syn-skew bridging in 3, and one-atom bridging in 4. The noncoordinating mode of sulfonate in PbII complexes containing 5-sulfosalicylate is first reported in this presentation. The 4,4'-bipy ligands act as guest molecules in 1, dimeric linkers in 2, and monodentates in 3. The pi-pi stacking interactions can be observed in complexes 1-3, whereas there is no such interaction in complex 4. The coordination spheres of PbII ions in 1-4 are controlled by three factors: the activity of a lone pair of electrons, weak Pb-O interactions, and pi-pi stacking interactions. The PbII lone pair in 4 is inactive, whereas in 1-3, they are stereochemically active. The thermal stability and fluorescent property of complexes 1-4 are different from those of PbII complexes only containing chelating ligands, [Pb(Hssal)(2,2'-bipy)(DMF)]n (5), and [Pb(Hssal)(2,2'-bipy)(H2O)]n (6), and [Pb(Hssal)(phen)(DMF)]n (7).