Double Carboxylate Bridges Research Articles

Enhanced catalytic performance for CO2 cycloaddition and Knoevenagel condensation reactions via stable Eu3+ modified Mn-MOF

The construction of MOF-based catalysts containing simultaneous Lewis acid and Lewis base sites has been considered as an efficient approach to enhance chemical fixation of CO2 into value-added products and Knoevenagel condensation reaction. Herein, one novel Eu3+-modified Mn-MOF (Eu3+@Mn-MOF-1) was successfully synthesized by solvothermal synthesis and post-synthesis modification. In Mn-MOF-1, the alternating chains with single and double carboxylate bridges are connected by H2L4− ligands to form a three-dimensional framework with 1D channels along a axis. Interestingly, the activated state of Eu3+@Mn-MOF-1 (noted as Eu3+@Mn-MOF-1a) with the removal of coordinated and lattice H2O molecules displayed excellent thermal stability. Furthermore, it is worth emphasizing that the inner surfaces of Eu3+@Mn-MOF-1a are functionalized by pentiful Lewis acid sites (tri- and penta-coordinated Mn2+ ions and modified Eu3+ ions) and Lewis base sites (uncoordinated Ocarboxylate and Npyridine). By virtue of the abundant co-existing Lewis acid-base sites, Eu3+@Mn-MOF-1a exhibited high catalytic performance for the cycloaddition of CO2 with epoxides and Knoevenagel condensation of aldehydes and malononitrile with preferable repeatability under mild conditions without the requirement of any solvent. Moreover, Eu3+@Mn-MOF-1a performed much higher activity for the cycloaddition of CO2 with epoxides than Mn-MOF-1a under the same conditions. In addition, Eu3+@Mn-MOF-1a also shows the yield of benzylidenemalononitrile can reach 99.9 % at room temperature within 1 h, representing about 1.3-fold increase compared to that of Mn-MOF-1a (76.0 %). The improvement of catalytic performance suggested the contribution of Eu3+ ions to the reaction. Hence, this work provides an efficient approach for the construction of MOFs with Lewis base sites by elaborately designing organic ligands and Lewis acid sites by post-synthetic modification to expose and/or introduce more unsaturated metal sites.

Coordination polymers incorporating Bi(III) and 2,4,6-pyridine tricarboxylic acid and its derivatives: Synthesis, structure and topology

Bi(III) as its oxide combined with 2,4,6-pyridine tricarboxylic acid, H2pdc-COOH, and various pyridine-derived additives in dimethylformamide (dmf) under solvothermal conditions produced three novel bismuth coordination polymers, {[Bi(μ-pdc-COO)2][NH2Me2]3}n, 1, {[Bi(μ-pdc-COO)2][C5H7N2]3·C5H6N2}n, 2, and {[Bi2(μ-pdc-COO)2(μ-pdc-COOH)(pdc-COOH)][NH2Me2]4·2dmf·NHMe2}n, 3. The anionic coordination network topologies are two-dimensional, chains-of-loops and ladders, respectively, but the local 8-coordinate environments about the bismuth(III) centres are in each case between that of a square antiprism and that of a hexagonal bipyramid. When the 4-carboxy substituent in H2pdc-COOH is replaced by another potentially coordinating substituent to give 4-R-2,6-pyridine dicarboxylic acid, H2pdc-R (R = OH, NH2, Cl), the salts obtained contain discrete centrosymmetric dinuclear 8-coordinate bismuth anions with either double O-bridges between the metal centres, [Bi2(μ-pdc-R)2(pdc-R)2(dmf)2][NH2Me2]2 (R = OH, NH2), 4 and 5, or double carboxylate bridges with one long Bi–O bond, [Bi2(μ-pdc-NMe2)2(pdc-NMe2)2(dmf)2][NH2Me2]2, 6 (R = Cl, but replaced by dimethylamine during the reaction). The structures and supramolecular networks of 1–6 are described and compared as an exploration of alternatives to the conventional carboxylate-based organic linking units.

Manganese(II) and cobalt(II) coordination polymers with m-phenylenediacrylate: Synthesis, structures, and magnetic properties

Three coordination polymers based on m-phenylenediacrylic acid (H2mpda) with manganese(II) and cobalt(II), [Mn(Hmpda)2(H2O)2]n (1), Co(Hmpda)2(H2O)2]n (2), [Co(mpda)(H2O)2] (3) were synthesized by the hydrothermal methods and their structures and magnetic properties were fully characterized. Compounds 1 and 2 are isomorphous coordination compounds in which carboxylate-bridged square-grid 2D sheets are separated by bilayers of Hmpda−. While compound 3 is composed of 1D coordination chains based on binuclear units with double carboxylate bridges. Magnetic investigations on the compounds have been carried out and revealed weak antiferromagnetic exchange mediated through the carboxylate bridges.

Crystal structure of di-μ-isobutyrato-κ(4) O:O'-bis-[cis-di-chlorido-(dimethyl sulfoxide-κS)rhenium(III)

The title compound, [Re2(C3H7COO)2Cl4{(CH3)2SO}2], comprises binuclear complex mol-ecules [Re-Re = 2.24502 (13) Å] involving cis-oriented double carboxyl-ate bridges, four equatorial chloride ions and two weakly bonded O atoms from dimethyl sulfoxide ligands in the axial positions at the Re(III) atoms. In the crystal, mol-ecules are linked into corrugated layers parallel to (101) by very weak C-H⋯Cl and C-H⋯O hydrogen-bonding inter-actions. C-H⋯Cl hydrogen bonding provides the links between layers to consolidate a three-dimensional framework.

Solvothermal synthesis, structures, and magnetic properties of NiII compounds directed by N,N′-bridging auxiliary ligands

Three NiII-based metal–organic frameworks (MOFs) were synthesized from the nitro-functionalized dicarboxylate ligand 2,2′-dinitro-biphenyl-4,4′-dicarboxylate (H2dnpdc) and different N-donor bridging ligands. X-ray analyses revealed that all compounds exhibit 3D architectures. Compound 1, {Ni(dnpdc)(bipy)}n, exhibits 3D framework in which the 2D Ni(dnpdc) sheets are pillared by bipy, with a new (4,6)-connected self-penetrated net topology. In compound 2, {[Ni3(dnpdc)3(bipy)3(H2O)2]·(H2O)2}n, the binuclear Ni2(COO)2 units and mononuclear units are interlinked by the dnpdc and bipy ligands into 3D framework, which displays a rare 3-fold interpenetrated (4,6)-connected net topology. Compound 3, {Ni(dnpdc)(bpee)·H2O}n, displays a 6-fold interpenetrated diamond net based on the mononuclear NiII unit. The magnetic studies of 1 reveal that the double carboxylate bridges in the nonplanar syn-skew conformation mediate ferromagnetic interactions between the NiII ions.

Crystal structure of cis-bis-(μ-β-alanine-κ(2) O:O')bis[tri-chlorido-rhenium(III)](Re-Re) sesquihydrate.

The structure of the title compound, [Re2Cl6(C3H7NO2)2]·1.5H2O, comprises a dinuclear complex cation [Re-Re = 2.2494 (3) Å] involving cis-oriented double carboxyl-ate bridges, four equatorial chloride ions and two weakly bonded chloride ligands in the axial positions at the two rhenium(III) atoms. In the crystal, two complex mol-ecules and two water mol-ecules constitute hydrogen-bonded dimers, while an extensive hydrogen-bonding network involving the groups of the zwitterionic ligand is important for generation of the framework. An additional partially occupied water molecule is disordered over two sets of sites about a symmetry centre with a site-occupancy ratio of 0.3:0.2.

Supramolecular assemblies built from lanthanide ammoniocarboxylates and cucurbit[6]uril

The reaction of lanthanide nitrates with different aminocarboxylic acids in the presence of cucurbit[6]uril (CB6) in water at room temperature yielded five novel complexes which were crystallographically characterized. The cerium complex involving the zwitterionic form of β-alanine (β-Ala), [Ce(β-Ala)(CB6)(NO3)(H2O)3]·2NO3·5H2O (1), is a molecular species in which the metal cation is bound to three carbonyl groups of CB6 and one monodentate carboxylate; the ammonium-bearing chain is encapsulated in the CB6 cavity, with the ammonium group hydrogen bonded to the uncomplexed portal. With a longer alkyl chain, 6-aminohexanoic acid (6-ah) leads to a different, dimeric structure in [Ce(6-ah)(CB6)(H2O)3]2·6NO3·17H2O (2), in which two metal ions connect two CB6 molecules and are further bridged by two carboxylate groups. The alkyl chains are included in the CB6 cavities and the ammonium groups are hydrogen bonded to the uncomplexed portals. Neighbouring, perpendicular dimers are associated through ammonium-water, water-carbonyl and CH⋯O(carbonyl) hydrogen bonds. Three complexes were obtained with the enantiopure α-amino acid L-methionine (L-Met), all of which are chiral. In [Yb(L-Met)(H2O)7]·CB6·3NO3·7H2O (3) and [Dy(L-Met)(H2O)7]4[Dy(NO3)2(H2O)5]·4CB6·13NO3·29H2O (4), the metal ions are bound to one monodentate carboxylate and seven water molecules. The ammonium group is involved in hydrogen bonding with two CB6 molecules and the thioether-containing chain is included in the cavity of one CB6, with the sulphur atom shortest contact being with a ureido carbon atom. The supramolecular arrangement is columnar, the neighbouring chains being connected by hydrogen bonds formed by the ammonium groups. The neodymium complex [Nd(L-Met)(CB6)(NO3)(H2O)3]2[Nd(L-Met)(L-Met – H)(H2O)5]2·8NO3·30H2O (5) displays two dinuclear units held by double carboxylate bridges. In one of them, the metal atoms are bound to CB6 and the L-Met molecules are excluded from the CB6 cavities while, in the other, the metal atoms are not bound to CB6, but two L-Met ligands are hydrogen bonded to CB6 portals and encapsulated. Together with previous results involving other aminocarboxylic acids, these complexes illustrate the different association modes between lanthanide ions, CB6 molecules and ammoniocarboxylates, which depend on the nature and geometry of the latter, and on a balance between CB6 complexation to the lanthanide ion and ammoniocarboxylate/CB6 association through weak interactions. Short contacts between the sulphur atoms of L-Met and ureido carbon atoms in 3–5 are likely indicative of the presence of weak dipole–dipole interactions.

Synthesis, structures, and magnetic properties of transition metal compounds with 2,2′-dinitrobiphenyl-4,4′-dicarboxylate and N,N′-chelating ligands

Solvothermal reactions of Co(II), Ni(II), Zn(II) salts with 2,2'-dinitrobiphenyl-4,4'-dicarboxylate (dnpdc) and 2,2'-bipyridyl-like chelating ligands yielded five compounds formulated as [Co(dnpdc)(bipy)](n)·nH(2)O (1), [M(dnpdc)(phen)](n) (2, M = Co; 3, M = Ni; 4, M = Zn) and [Co(dnpdc)(biql)](n)·2nH(2)O (5) (bipy = 2,2'-bipyridine, phen = 1,10-phenanthroline and biql = 2,2'-biquinoline). With bipy or phen as coligands, compounds 1-4 exhibit isomorphous 3D M(dnpdc) metal-organic frameworks in which double carboxylate bridged chains are interlinked by the backbones of the dicarboxylate ligands. The bipy or phen ligands are involved in interchain hydrogen bonding or π-π interactions to form 1D zipper-like arrays in the rhombic channels of the frameworks, playing a templating role and determining the channel dimensions. The biql coligand is too bulky for the 1D double carboxylate bridged chain and the rhombic channel. Instead, in compound 5, the dnpdc ligands link metal ions into 1D zigzag metal-organic chains and the biql ligands are arranged into 2D (6,3) arrays through extensive π-π stacking interactions. In compounds 1-3, the double carboxylate bridges in the nonplanar syn-skew conformation mediate ferromagnetic interactions along the chains, while the chelating ligands provide supramolecular pathways for interchain antiferromagnetic interactions. The π-π interactions in 5 also evoke weak antiferromagnetic interactions.

Organic acid effect on the structures of Cd(II) metal-organic complexes based on 2-(3-pyridyl)imidazo[4,5-f]-1,10-phenanthroline

Three new Cd(II) complexes consisting of phenanthroline derivative and organic acid ligands, formulated as [Cd3(3-PIP)2(L1)6] (I), [Cd(3-PIP)(L2)] · H2O (II), and [Cd(3-PIP)(L3)] (III) (3-PIP = 2-(3-pyridyl)imidazo[4,5-f]-1,10-phenanthroline, HL1 = 3,5-dinitrobenzoic acid, H2L2 = oxalic acid, H2L3 = benzene-1,3-dicarboxylic acid), have been synthesized via the hydrothermal reaction and characterized by single-crystal X-ray diffraction, elemental analyses and FT-IR spectra. Complex I is a trinuclear structure. Complex II features a 1D zigzag chain. Complex III shows a twisted double chain of binuclear units sustained by double carboxylate bridges. Three complexes are further extended into 3D supramolecular frameworks by hydrogen bonding and π-π-stacking interactions. The structural differences among I–III show that the organic carboxylates have important effects on the structures. Furthermore, the supramolecular interactions are the critical factors in determining the final structures of the complexes. In addition, the thermal stabilities and luminescent properties of complexes I and II are also investigated.

Diverse Manganese(II) Coordination Polymers with Mixed Azide and Zwitterionic Dicarboxylate Ligands: Structure and Magnetic Properties

The reactions of manganese(II) acetate or perchlorate, sodium azide, and the inner-salt-type dicarboxylate ligand 1,3-bis(4-carboxylato-1-pyridinium)propane (L) under different conditions yielded four different Mn(II) coordination polymers with mixed azide and carboxylate bridges: {[Mn(L)(N(3))]ClO(4).0.5H(2)O}(n) (1), {[Mn(2)(L)(2)(N(3))(2)][Mn(N(3))(4)(H(2)O)(2)].2H(2)O}(n) (2), {[Mn(2)(L)(2)(N(3))(2)(H(2)O)(2)]Br(N(3)).2H(2)O}(n) (3), and [Mn(4) (L)(2)(N(3))(8)](n) (4). The compounds exhibit great diversity in their structures and magnetic properties. Both 1 and 2 contain anionic chains featuring a mixed (OCO)(2)(EO-N(3)) triple bridge (EO = end-on) between adjacent Mn(II) ions. In 1, two independent sets of triple bridges with apparently different structural parameters alternate in the AABB sequence, and the resulting alternating chains are cross-linked into a cationic 3D framework by the cationic dipyridinium spacers. Differently, the chains in 2 have uniform bridges and are interlinked into a 2D coordination layer. An expression of the magnetic susceptibility for 1D systems with alternating J(1)J(1)J(2)J(2) interactions has been deduced and applied to 1. Magnetic studies on 1 and 2 reveal that the (OCO)(2)(EO-N(3)) triple bridges induce antiferromagnetic coupling between Mn(II) ions, and magnetostructural analyses suggest that the magnitude of the coupling can be correlated to the Mn-N and Mn-N-Mn parameters. Compound 3 contains 2D coordination layers in which the chains with alternating double EO-azide and double carboxylate bridges are interlinked by the dipyridinium spacers, and magnetic studies suggest alternating ferro- and antiferromagnetic interactions through the alternating bridges. The 3D framework of compound 4 is formed by the organic ligands interlinking the unique manganese-azide-carboxylate layers in which the [Mn(4)(mu(3)-N(3))(2)(mu(2)-N(3))(2)(mu(2)-COO)(4)] clusters are interlinked through EE-azide bridges (EE = end-to-end). The structure represents a novel type of self-catenated 8-connected 3D net. Magnetostructural analyses suggest that all of the short bridging moieties in 4, including (mu(3)-EO-N(3))(2), (OCO)(EO-N(3)), (OCO)(EO-N(3))(2), and single EE-N(3), propagate antiferromagnetic coupling.

Self-Assembly of Metal-Organic Coordination Polymers Constructed from a Bent Dicarboxylate Ligand: Diversity of Coordination Modes, Structures, and Gas Adsorption

We have synthesized five new metal-organic coordination polymers incorporating the bent ligand H(2)hfipbb [4,4'-(hexafluoroisopropylidene)bis(benzoic acid)] with different transition metal ions and co-ligands via solvothermal reactions to give [Zn(2)(hfipbb)(2)(py)(2)] x DMF (1), [Zn(2)(hfipbb)(2)(4,4'-bipy)(H(2)O)] (2), [Zn(2)(hfipbb)(2)(bpdab)].2DMF (3), [Cd(2)(hfipbb)(2)(DMF)(2)] x 2 DMF (4), and [Co(hfipbb)(dpp)] x MeOH (5) (py = pyridine, 4,4'-bipy = 4,4'-bipyridine, bpdab = 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene, dpp = 1,3-di(4-pyridyl)propane). Compound 1 displays a 2-fold 2D-->2D parallel interpenetrated layer network with one-dimensional (1D) helical channels, while 3 exhibits a three-dimensional pillared helical-layer open framework of alpha-Po topology based upon binuclear paddlewheel units. In compounds 2 and 5, binuclear motifs with double carboxylate bridges are linked by hfipbb(2-) ligands into a 1D ribbon, which are further assembled into two-dimensional non-interpenetrated (4,4) layers via bipyridyl co-ligands. However, the different bridging modes of hfipbb(2-) ligands and the different disposition of the coordinated co-ligands around metal ions result in subtle differences in the final architecture. Thus, 2 is based on a binuclear cluster node, double-stranded hfipbb(2-) linkers, and single-stranded 4,4'-bipy linkers, while 5 is based on a binuclear cluster node and hfipbb(2-) and dpp linkers which are both double-stranded. Among these compounds, the Cd(II) complex 4 is possibly the most interesting because it represents a rare example in which metal centers are linked by carboxylate groups into infinite chains further joined together by hfipbb(2-) spacers to form a 2D network with tubular helical channels. All these coordination polymers exhibit low solvent-accessible volumes. Both 3 and 4 retain structural integrity and permanent microporosity upon evacuation of guest molecules, with hydrogen uptakes of 0.57 and 0.78 wt %, respectively, at 20 bar and 77 K.

Novel cobalt(II) coordination polymers based on 1,2,4,5-benzenetetracarboxylic acid and extended bis-monodentate ligands

Four new high-spin cobalt(II) complexes of formulae [Co2(bta)(4,4′-bpy)2(H2O)2]n (1), {Hbpe[Co(Hbta)(bpe)(H2O)2]}n (2), {[Co(H2bta)(azpy)(H2O)2]·azpy}n (3) and {[Co2(bta)(bpa)2(H2O)4]·8H2O}n (4) with H4bta = 1,2,4,5-benzenetetracarboxylic acid, 4,4′-bpy = 4,4′-bipyridine, bpe = trans-1,2-bis(4-pyridyl)ethene, azpy = 4,4′-azobispyridine and bpa = trans-1,2-bis(4-pyridyl)ethane, have been prepared and characterized by single crystal X-ray diffraction. Compounds 1–4 exhibit two-dimensional networks where the fully (1 and 4) or partially (2 and 3) deprotonated tetracarboxylic ligand connects two (2 and 3) or four (1 and 4) cobalt(II) ions through two trans-carboxylate (1–3) or all the carboxylate groups (4) whereas the co-ligands 4,4′-bpy (1), bpe (2), azpy (3) and bpa (4) act as two-fold connectors in trans- (bpe and azpy) and gauche- (bpa) conformations. The cobalt(II) ions in 1 are five-coordinated with two nitrogen atoms from two 4,4′-bpy ligands in the axial positions and a water molecule and two carboxylate-oxygens building the trigonal plane. Six-coordinated cobalt(II) ions occur in 2–4 with two pyridyl-nitrogen atoms, two carboxylate-oxygens and two trans-coordinated water molecules in a somewhat distorted octahedral surrounding. The magnetic properties of 1–4 have been investigated in the temperature range 1.9–300 K. Compound 1 shows a weak antiferromagnetic interaction between the five-coordinated cobalt(II) ions (0.13 ≤ |J| ≤ 0.28 cm−1, Ĥ = −JŜ1·Ŝ2), the exchange pathway involved being the double carboxylate bridges in the syn–syn conformation [cobalt–cobalt separation] of 3.6465(9) A. As the magnetic interactions between the cobalt(II) ions through the phenyl ring of the bta group in 2–4 and those across the extended bpe (2), azpy (3) and bpa (4) bridges are negligible, the strong decrease of χMT upon cooling observed for 2–4 is mainly due to the depopulation of the higher Kramer doublets of the six-coordinated cobalt(II) ions.

Synthesis, characterization, in vivo antitumor properties of the cluster rhenium compound with GABA ligands and its synergism with cisplatin

A new dirhenium(III) complex cis-[Re2(GABA)2Cl5(H2O)]Cl.2H2O with zwitterionic gamma-aminobutyrate ligands was prepared and characterized by spectral methods and crystallography. The structure of the compound is comprised of dinuclear complex cations (Re-Re 2.2437(3) A) involving cis-oriented double carboxylate bridges, four equatorial chloride ions and two weakly bonded aqua and chloride ligands in the axial positions at two rhenium centers (Re-O 2.363(3), Re-Cl 2.6735(12) A). Antitumor properties of the complex were studied in the model of tumor growth with the use of Wistar rats inoculated by tumor carcinoma Guerink cells. The introduction of the compound in dosage according to the scheme of antioxidant therapy, inhibited the tumor growth by ca. 60% and led to stabilization of red blood cells in the tumor-bearing organisms. The combined introduction of the compound and cisplatin had a significant impact on the tumor growth and the disappearance of the tumors in most of the animals.

New coordination polymers based on the triangular [Cu3(μ3-OH)(μ-pz)3]2+ unit and unsaturated carboxylates

By reacting copper(II) acrylate with pyrazole (Hpz), two trinuclear copper derivatives [Cu3(mu3-OH)(mu-pz)3(CH2CHCOO)2(H2O)2(Hpz)], 1, and [Cu3(mu3-OH)(mu-pz)3(CH2CHCOO)2(CH3OH)], 2, are obtained, in water and methanol respectively, while copper(II) methacrylate affords [Cu3(mu3-OH)(mu-pz)3(CH2C(CH3)COO)2], 3, independently from the solvent used. In 1 and 2 two triangular trinuclear units are connected through acrylate bridges forming hexanuclear clusters that, in the case of 2 are further connected through double syn-syn carboxylate bridges, generating a 1-D coordination polymer. In the case of 3 a different 1-D coordination polymer is obtained by alternating syn-syn and syn-anti double carboxylate bridges connecting the trinuclear clusters. In all cases H-bonds contribute both to the stabilization of these arrangements and to the formation of more extended supramolecular networks. Compounds 1-3 are valuable catalysts in the peroxidative oxidation with aqueous H2O2, in MeCN at 25 degrees C, of cycloalkanes (i.e. cyclohexane and cyclopentane) to the corresponding ketones and alcohols (overall yield up to 36%, TON = 36), following a radical mechanism as shown by radical trap experiments, and the effects of various factors are studied. Electrochemical experiments show that the copper(II) centres are reduced to copper(I) and copper(0).

One-, Two-, and Three-Dimensional Coordination Polymers of Stilbenedicarboxylate with Different Metal Ions

Using trans-stilbene-4,4′-dicarboxylic acid (H2STDC) as bridging ligand, we have prepared four new coordination polymers with different transition metal ions, [Cu(STDC)(H2O)(py)2]·2py (1), [Cd(STDC)(py)2]·0.5py (2), [Co(STDC)(py)2]·0.5py (3), and [Ni2(STDC)2(py)4(H2O)]·py·0.5H2O (4), by hydrothermal reactions in the presence of pyridine (py). In compound 1, single metal ions are linked into quasi-linear coordination chains by the organic ligand, and the chains are further assembled into 3D supermolecular architectures through strong O−H (coordinate water)···O (carboxylate) and weak C−H (py)···π (benzene) hydrogen bonds. In compounds 2 and 3, which are isomorphous, binuclear motifs with double carboxylate bridges are linked into two-dimensional (4,4) coordination layers exhibiting 2-fold inclined interpenetration. The last compound exhibits an abnormal 5-fold interpenetration of diamond networks, in which the tetrahedral building unit is defined by a binuclear motif with triple (two carboxylates and a wate...

Synthesis, crystal structure and magnetic properties of an isophthalate-bridged manganese(II) chain complex

An isophthalate-bridged manganese(II) chain complex of [Mn 2(phen) 4( m-phth)] n [ClO 4] 2 n ·2 nH 2O, where phen is 1,10- phenanthroline and m-phth is isophthalate (dianion of benzene-1,3-dicarboxylic acid), has been prepared and characterized by X-ray crystallography and magnetic measurements. It crystallizes in the triclinic system, space group P 1 ̄ , with a=14.651(1), b=16.679(7), c=13.561(4) Å, α=101.46(3), β=113.91(2), δ=65.52(3)° and Z=2. The structure consists of cationic isophthalate-bridged [Mn 2(phen) 4( m-phth)] 2+ chains, non-coordinated perchlorate anions and crystallized water molecules. Each isophthalate is bound to four manganese atoms through carboxylate oxygens with the syn–syn bridging mode, affording manganese(II) pairs which are linked by the isophthalate group to yield a one-dimensional chain running along the a axis. The intrachain Mn⋯Mn separations are 4.86 and 4.66 Å (through the double carboxylate bridges) and 7.16 Å (the shortest distance through the bridging isophthalate), respectively. The manganese(II) ion displays a distorted octahedral coordination being linked to four nitrogen atoms of two phen ligands and two oxygen atoms of two carboxylate groups from two isophthalate ligands. The variable temperature magnetic susceptibility of the title complex in the temperature range 1.5–300 K has been interpreted in terms of an Mn(II) dimer with a molecular field approximation, the values obtained for J, g(fixed) and z J′ being 3.23 cm −1, 2.00 and −0.35 cm −1, respectively, indicating a weakly ferromagnetic exchange coupling within the Mn(II) dimer with double carboxylates in syn–syn conformation.

Solid-state carbon-13 nuclear magnetic resonance investigations of bismuth citrate complexes and crystal structure of Na2[Bi2(cit)2]·7H2O

The complex Na2[Bi2(cit)2]·7H2O (H4cit = 3-carboxy-3-hydroxypentane-1,5-dioic acid) crystallized during reactions of the antiulcer drug ranitidine bismuth citrate with the tripeptide glutathione (γ-L-Glu-L-Cys-Gly) at low pH. X-Ray analysis showed one [Bi(cit)]– fragment per asymmetric unit with Bi3+ chelated to a terminal carboxylate group; citrate also binds, in tridentate mode, to the bismuth of an equivalent [Bi(cit)]– unit (related to the first by a C2 axis)via one oxygen donor from each of the remaining two carboxylate groups and the alkoxy group. Both ends of the resultant dimeric anion {Bi(µ-cit)2Bi}2– bind to adjacent dimers, related by n-glide plane symmetry, via double carboxylate bridges, to form a continuous polymeric anionic chain [{Bi(µ-cit)2Bi}n]2n– running throughout the crystal. In this way each bismuth atom achieves six-co-ordination [Bi–O 2.210(10)–2.505(10)A] with a nido-pentagonal-bipyramidal geometry, the vacant axial site providing evidence for a stereochemically active lone pair and the second axial site being occupied by the alkoxy donor. The parallel polyanionic chains are linked by anion–cation interactions [Na ⋯ O (cit) 2.37–2.50 A] and by bonds of largely ionic character (Bi ⋯ O 3.003–3.095 A) to give the overall three-dimensional solid-state structure which incorporates seven water molecules per dianionic subunit. The solid-state cross-polarization magic angle spinning 13C NMR spectrum of this complex is assigned with the aid of dipolar-dephasing and inversion-recovery cross-polarization experiments, and compared to those of ranitidine bismuth citrate and bismuth citrate Bi(Hcit). The IR and solid-state 13C NMR data suggested that the alkoxy group is protonated in Bi(Hcit) but deprotonated in ranitidine bismuth citrate, and that the latter contains similar dimeric units to Na2[Bi2(cit)2]·7H2O. The general modes of aggregration of dimeric [{Bi(µ-cit)2Bi}n]2n– units and the relevance to antiulcer activity are discussed.

Significant antiferromagnetic coupling in a terephthalate (ta)-bridged manganese(II) compound: preparation, crystal structure and magnetic properties of the chain [Mn2(bipy)4(ta)][ClO4]2(bipy = 2,2′-bipyridine)

A new manganese(II) compound [Mn2(bipy)4(ta)][ClO4]21(bipy = 2,2′-bipyridme, ta = terephthalate dianion) has been synthesised and its crystal structure determined by single-crystal X-ray diffraction. It crystallizes in the triclinic system, space group P, with a= 9.516(2), b= 11.613(3), c= 11.615(3)A, α= 70.92(2), β= 80.16(2), γ= 76.64(2)° and Z= 1. The structure consists of canonic terephthalate-bridged [Mn2(bipy)4(ta)]2+ chains and non-co-ordinated perchlorate anions. Each terephthalate is bound to four manganese atoms through carboxylate oxygens with the sym-sym bridging mode, affording manganese(II) pairs which are linked by the terephthalate group to yield a one-dimensional chain running along the a axis. The intrachain Mn ⋯ Mn separations through the double carboxylate and terephthalate bridges are 4.643(1) and 9.637(2)A, respectively The manganese(II) ion displays a severely distorted octahedral co-ordination being linked to four nitrogen atoms of two bipy ligands and to two oxygen atoms of two carboxylate groups from two terephthalate ligands. The magnetic susceptibility of 1 as a function of temperature (4.2–290 K) exhibits a sharp maximum at 6.0 K which is consistent with a significant antiferromagnetic coupling between the metal centres. This magnetic behaviour has been interpreted in terms of a dimer with a molecular field approximation, the values obtained for J, g and zJ′ being –1.35 cm–1,1.97 and –0.04cm–1, respectively. In the light of the structural data, it can be concluded that the double-carboxylate bridge between the manganese(II) pairs provides a more efficient exchange pathway than that of terephthalate and most likely is responsible for the observed J value.

Chlorotin carboxylates by direct substitution on tin tetrachloride

Substitution reactions have been carried out on tin tetrachloride with carboxylic acids RCOOH ( R  H, CH 3, C(CH 3) 3, CF 3) and with salts of the same acids. In the first three cases only disubstituted products were isolated. With silver trifluoroacetate disubstituted and tetrasubstituted products were obtained. The compounds were examined by spectroscopic and other methods. Polymeric structures with double carboxylate bridges are proposed for the formate and the acetate. The trimethylacetate is assumed to be dimeric. The fluoroacetate probably contains rings with bridging carboxylate groups.