The arrangement of first- and second-shell water molecules in trivalent aluminum complexes: results from density functional theory and structural crystallography

The structural and energetic features of a variety of gas-phase aluminum ion hydrates containing up to 18 water molecules have been studied computationally using density functional theory. Comparisons are made with experimental data from neutron diffraction studies of aluminum-containing crystal structures listed in the Cambridge Structural Database. Computational studies indicate that the hexahydrated structure Al[H(2)O](6)(3+) (with symmetry T(h)()), in which all six water molecules are located in the innermost coordination shell, is lower in energy than that of Al[H(2)O](5)(3+).[H(2)O], where only five water molecules are in the inner shell and one water molecule is in the second shell. The analogous complex with four water molecules in the inner shell and two in the outer shell undergoes spontaneous proton transfer during the optimization to give [Al[H(2)O](2)[OH](2)](+).[H(3)O(+)](2), which is lower in energy than Al[H(2)O](6)(3+); this finding of H(3)O(+) is consistent with the acidity of concentrated Al(3+) solutions. Since, however, Al[H(2)O](6)(3+) is detected in solutions of Al(3+), additional water molecules are presumed to stabilize the hexa-aquo Al(3+) cation. Three models of a trivalent aluminum ion complex surrounded by a total of 18 water molecules arranged in a first shell containing 6 water molecules and a second shell of 12 water molecules are discussed. We find that a model with S(6) symmetry for which the Al[H(2)O](6)(3+) unit remains essentially octahedral and participates in an integrated hydrogen bonded network with the 12 outer-shell water molecules is lowest in energy. Interactions between the 12 second-shell water molecules and the trivalent aluminum ion in Al[H(2)O](6)(3+) do not appear to be sufficiently strong to orient the dipole moments of these second-shell water molecules toward the Al(3+) ion.     

C-H activation by a mononuclear manganese(III) hydroxide complex: synthesis and characterization of a manganese-lipoxygenase mimic?

Lipoxygenases are mononuclear non-heme metalloenzymes that regio- and stereospecifically convert 1,4-pentadiene subunit-containing fatty acids into alkyl peroxides. The rate-determining step is generally accepted to be hydrogen atom abstraction from the pentadiene subunit of the substrate by an active metal(III)-hydroxide species to give a metal(II)-water species and an organic radical. All known plant and animal lipoxygenases contain iron as the active metal; recently, however, manganese was found to be the active metal in a fungal lipoxygenase. Reported here are the synthesis and characterization of a mononuclear Mn(III) complex, [Mn(III)(PY5)(OH)](CF(3)SO(3))(2) (PY5 = 2,6-bis(bis(2-pyridyl)methoxymethane)pyridine), that reacts with hydrocarbon substrates in a manner most consistent with hydrogen atom abstraction and provides chemical precedence for the proposed reaction mechanism. The neutral penta-pyridyl ligation of PY5 endows a strong Lewis acidic character to the metal center allowing the Mn(III) compound to perform this oxidation chemistry. Thermodynamic analysis of [Mn(III)(PY5)(OH)](2+) and the reduced product, [Mn(II)(PY5)(H(2)O)](2+), estimates the strength of the O-H bond in the metal-bound water in the Mn(II) complex to be 82 (+/-2) kcal mol(-)(1), slightly less than that of the O-H bond in the related reduced iron complex, [Fe(II)(PY5)(MeOH)](2+). [Mn(III)(PY5)(OH)](2+) reacts with hydrocarbon substrates at rates comparable to those of the analogous [Fe(III)(PY5)(OMe)](2+) at 323 K. The crystal structure of [Mn(III)(PY5)(OH)](2+) displays Jahn-Teller distortions that are absent in [Mn(II)(PY5)(H(2)O)](2+), notably a compression along the Mn(III)-OH axis. Consequently, a large internal structural reorganization is anticipated for hydrogen atom transfer, which may be correlated to the lessened dependence of the rate of substrate oxidation on the substrate bond dissociation energy as compared to other metal complexes. The results presented here suggest that manganese is a viable metal for lipoxygenase activity and that, with similar coordination spheres, iron and manganese can oxidize substrates through a similar mechanism.     

Modeling water exchange on an aluminum polyoxocation

For the first time, water exchange on a polymeric complex has been modeled using a combination of gas-phase ab initio calculations and molecular dynamics (MD) simulations. The GaO4Al12(OH)24(H2O)12(7+)aq ion (GaAl12) was chosen because high-quality experimental data exist, including an activation enthalpy (+63 +/- 7 kJ/mol) and an activation volume (+3 +/- 1 cm3/mol). We took a two-step approach. First, the local solvent structure and the initial states for reaction were inferred from the molecular dynamics simulations. Second, we used this information to evaluate initial-state structures in the ab initio calculations. The energy differences between the initial and transition states from the ab initio calculations varied from +59 kJ/mol to +53 kJ/mol depending upon details, closely approximating the activation enthalpy.     

Theoretical study of adsorption of sarin and soman on tetrahedral edge clay mineral fragments

This study provides details of the structure and interactions of Sarin and Soman with edge tetrahedral fragments of clay minerals. The adsorption mechanism of Sarin and Soman on these mineral fragments containing the Si(4+) and Al(3+) central cations was investigated. The calculations were performed using the B3LYP and MP2 levels of theory in conjunction with the 6-31G(d) basis set. The studied systems were fully optimized. Optimized geometries, adsorption energies, and Gibbs free energies of Sarin and Soman adsorption complexes were computed. The number and strength of formed intermolecular interactions have been analyzed using the AIM theory. The charge of the systems and a termination of the mineral fragment are the main contributing factors on the formation of intermolecular interactions in the studied systems. In the neutral complexes, Sarin and Soman is physisorbed on these mineral fragments due to the formation of C-H...O, and O-H...O hydrogen bonds. The chemical bond is formed between a phosphorus atom of Sarin and Soman and an oxygen atom of the -2 charged clusters containing an Al(3+) central cation and -1 charged complex containing a Si(4+) central cation (chemisorption). Sarin and Soman interact mostly in the same way with the same terminated edge mineral fragments containing different central cations. However, the interaction energies of the complexes with an Al(3+) central cation are larger than these values for the Si(4+) complexes. The interaction enthalpies of all studied systems corrected for the basis set superposition error were found to be negative. However, on the basis of the Gibbs free energy values, only strongly interacting complexes containing a charged edge mineral fragment with an Al(3+) central cation are stable at room temperature. We can conclude that Sarin and Soman will be adsorbed preferably on this type of edge mineral surfaces. Moreover, on the basis of the character of these edge surfaces, a tetrahedral edge mineral fragment can provide effective centers for the dissociation.     

Computational and experimental study of the mechanism of hydrogen generation from water by a molecular molybdenum-oxo electrocatalyst

We investigate the mechanism for the electrocatalytic generation of hydrogen from water by the molecular molybdenum-oxo complex, [(PY5Me(2))MoO](2+) (PY5Me(2) = 2,6-bis(1,1-bis(2-pyridyl)ethyl)pyridine). Computational and experimental evidence suggests that the electrocatalysis consists of three distinct electrochemical reductions, which precede the onset of catalysis. Cyclic voltammetry studies indicate that the first two reductions are accompanied by protonations to afford the Mo-aqua complex, [(PY5Me(2))Mo(OH(2))](+). Calculations support hydrogen evolution from this complex upon the third reduction, via the oxidative addition of a proton from the bound water to the metal center and finally an α-H abstraction to release hydrogen. Calculations further suggest that introducing electron-withdrawing substituents such as fluorides in the para positions of the pyridine rings can reduce the potential associated with the reductive steps, without substantially affecting the kinetics. After the third reduction, there are kinetic bottlenecks to the formation of the Mo-hydride and subsequent hydrogen release. Computational evidence also suggests an alternative to direct α-H abstraction as a mechanism for H(2) release which exhibits a lower barrier. The new mechanism is one in which a water acts as an intramolecular proton relay between the protons of the hydroxide and the hydride ligands. The calculated kinetics are in reasonable agreement with experimental measurements. Additionally, we propose a mechanism for the stoichiometric reaction of [(PY5Me(2))Mo(CF(3)SO(3))](+) with water to yield hydrogen and [(PY(5)Me(2))MoO](2+) along with the implications for the viability of an alternate catalytic cycle involving just two reductions to generate the active catalyst.     

Studies on metallochromic indicators-III Hematoxylin and hematein

The use of hematoxylin and hematein as metallochromic indicators in direct EDTA titration of Zr(4+), Th(4+), Bi(3+), VO(+), Ga(3+), In(3+), Al(3+), Pb(+), Zn(2+), Mn(2+), Cd(2+), Cu(2+), Ni(2+), Co(2+), Mg(2+), and a few rare earths is described. Aluminium is titrated directly in presence of acetate buffer, lactic or glycoliic acid being used as auxiliary complexing agent. Mixtures of two metal ions can be titrated if one is Bi(3+) and the other Al(3+), Pb(2+), Zn(2+), Cu(2+), Cd(2+), La(3+), Ce(3+), Pr(3+), Nd(3+), Sm(3+), Gd(3+) or Er(3+). Aluminium alloys can be analysed via EDTA titrations, with these indicators.     

Single ion and dimerization studies of the Al(III) ion in aqueous solution

Aqueous trivalent aluminum (Al) ions and their oligomers play important roles in diverse areas, such as environmental sciences and medicine. The geometries of octahedral Al(H(2)O)(6)(3+) and tetrahedral Al(OH)(4)(-) species have been studied extensively. However, structures of intermediate hydrolysis products of the Al(III) ion, such as the penta-coordinated Al(OH)(2+) species, which exists at pH values ranging from 3.0 to 4.3, and their mode of formation have been poorly understood. Here, we present that a trigonal bipyramidal Al(OH)(H(2)O)(4)(2+) structure is formed in aqueous solution and how this monomeric species dimerizes to a dinuclear [(H(2)O)(4)Al(OH)(2)Al(H(2)O)(4)](4+) complex in aqueous solution. The Gibbs free energy change calculations indicate that the formation of the dinuclear complex is preferred over the existence of two single trigonal bipyramidal Al(OH)(H(2)O)(4)(2+) species in aqueous solution. This study captures the solution dynamics and proton transfer in the oligomerization reactions of penta-coordinated Al(OH)(2+) species in aqueous solution.     

Europium complexation by an aquatic fulvic acid - effects of competing ions

Effects of competing ions, Fe (2+)Fe (3+) and Al(3+), on Eu(3+) complexation with an aquatic fulvic acid (FA), have been investigated using an ion exchange technique. The influence of different concentrations (10(-6), 10(-4) M) of the competing ions on the distribution coefficient for Eu was measured, and the overall complex formation function, beta(ov), was resolved for the Eu systems with Fe and Al. All systems showed pH-dependent beta(ov)-functions. The presence of 10(-4) M concentration of competing ion reduced the resolved complex formation function (logbeta(ov)) for Eu complexation with fulvic acid by 0.6 and 0.4 log units at pH 5 for Fe and Al, respectively. this indicates that Fe has a more perturbing effect on Eu-FA complexation than Al. In similar competition studies Sr and Eu were found not to perturb each others complexation with fulvic acid, suggesting therefore that the two metals probably bind to different sites on the fulvic acid molecule.     

First-row transition metal complexes of the strongly donating pentadentate ligand PY4Im

The new ligand PY4Im, which incorporates an axial N-heterocyclic carbene and four equatorial pyridine donors, is readily prepared on a multigram scale. Six-coordinate first row transition metal complexes of the general formula [(PY4Im)M(MeCN)](2+) (M = Fe, Co, Ni, Cu), where the PY4Im ligand coordinates in a square pyramidal pentadentate fashion, have been prepared. Structural, spectroscopic, and electrochemical characterization of these compounds provides evidence that PY4Im is a strongly donating ligand that favors the formation of low-spin complexes. Chemical oxidation of the iron(II) complex provides a low spin iron(III) complex, which has also been structurally and spectroscopically characterized. In the case of manganese(II), the PY4Im ligand is unable to either enforce a low-spin state or fully accommodate the metal ion. Rather, the ligand binds in a tridentate, face-capping mode.     

A potentiometeric study of protonation and complex formation of xylenol orange with alkaline earth and aluminum ions

Xylenol orange (XO) is one of the complexometric indicators, that can bind to metal cations at both their amino and acidic groups. In this study the protonation constants and distribution diagrams of XO were studied pH-metrically, and the corresponding six protonation constants were calculated. The complex formation between XO (L) and alkaline earth ions (M) was investigated and the formation constants of the resulting complexes ML, MHL, M(2)L and M(2)HL were determined. The stabilities of both ML and M(2)L complexes were found to vary in the order Mg(2+)> Ca(2+)> Sr(2+)> Ba(2+). Studying the complex formation between Al(3+) ion (M) and XO (L), it was observed that four complexed species with stoichiometries ML, ML(2), MHL and MH(2)L could be formed in solution. It was also found that the Al L(2) complex can act as a chelating agent for further complexation with two cations other than Al(3+) ion (i.e. Ba, L, Al, L, Ba, Mg, L, Al, L, Mg, and Mg, L, Al, L, Ba). The formation constants of the resulting mixed complexes were determined and their distribution diagrams were investigated.     

Spectral characterization of a novel near-infrared cyanine dye: a study of its complexation with metal ions

The spectral features of the near-infrared (NIR) dye TG-170 in different solutions and its complexation with several metal ions were investigated. The absorbance maxima of the dye are at λ=819, 805, and 791 nm in dimethyl sulfoxide (DMSO), methanol, and a buffer of pH 5.9, respectively. These values match the output of a commercially available laser diode (780 nm), thus making use of such a source practical for excitation. The emission wavelengths of the dye are at λ_em =822, 812, and 803 nm in DMSO, methanol, and the buffer, respectively. The molar absorptivity and fluorescence quantum yield increase accordingly. The addition of either an Al(III) ion or Be(II) ion resulted in fluorescence quenching of the dye. The Stern–Volmer quenching constant, K_SV, was calculated from the Stern–Volmer plot to be K_SV=3.11×10⁵ M⁻¹ for the Al(III) ion and K_SV=1.17×10⁶ M⁻¹ for the Be(II) ion. The molar ratio of the metal to the dye was established to be 1:1 for both metal ions. The stability constant, K_S, of the metal–dye complex was calculated to be 4.37×10⁴ M⁻¹ for the Al–dye complex and 1.94×10⁶ M⁻¹ for the Be–dye complex.     

Crystal structure of [Al4(OH)6(H2O)12][Al(H2O)6]2Br12: a new polyaluminum compound

A vertex-shared tetrahedral [Al(4)(OH)(6)(H(2)O)(12)](6+) (Al(4)) and a disordered [Al(H(2)O)(6)](3+) (Al(1)) that coexist in a 1:2 ratio within each unit cell were observed in the structure of [Al(4)(OH)(6)(H(2)O)(12)][Al(H(2)O)(6)](2)Br(12), which crystallized in a cubic Fd3m space group from a spontaneously hydrolyzed solution of AlBr(3). The former is composed of four AlO(6) octahedra that are connected to each other by sharing three vertexes of each octahedron and form a large regular tetrahedron with ideal T(d) symmetry. The central Al(3+) ion of the latter is coordinated by 6 disordered OH(2) molecules, that form a core-shell structure with ideal D(3d) symmetry.     

Hybrid Structure of the Type 1 Pilus of Uropathogenic Escherichia coli

Type 1 pili are filamentous protein assemblies on the surface of Gram‐negative bacteria that mediate adhesion to host cells during the infection process. The molecular structure of type 1 pili remains elusive on the atomic scale owing to their insolubility and noncrystallinity. Herein we describe an approach for hybrid‐structure determination that is based on data from solution‐state NMR spectroscopy on the soluble subunit and solid‐state NMR spectroscopy and STEM data on the assembled pilus. Our approach is based on iterative modeling driven by structural information extracted from different sources and provides a general tool to access pseudo atomic structures of protein assemblies with complex subunit folds. By using this methodology, we determined the local conformation of the FimA pilus subunit in the context of the assembled type 1 pilus, determined the exact helical pilus architecture, and elucidated the intermolecular interfaces contributing to pilus assembly and stability with atomic detail.     

Kinetics of metal ion exchange between citric acid and serum transferrin

The exchange of Fe(3+), Tb(3+), In(3+), Ga(3+), and Al(3+) between the C-terminal metal-binding site of the serum iron transport protein transferrin and the low-molecular-mass serum chelating agent citrate has been studied at pH 7.4 and 25 degrees C. The removal of Ga(3+), In(3+), and Al(3+) follows simple saturation kinetics with respect to the citrate concentration. In contrast, removal of both Fe(3+) and Tb(3+) shows a combination of saturation and first-order kinetic behavior with respect to the citrate concentration. The saturation component is consistent with a mechanism for metal release in which access to the bound metal is controlled by a rate-limiting conformational change in the protein. The first-order kinetic pathway is very rapid for Tb(3+), and this is attributed to a direct attack of the citrate on the Tb(3+) ion within the closed protein conformation. It is suggested that this pathway is more readily available for Tb(3+) because of the larger coordination number for this cation and the presence of an aquated coordination site in the Tb(3+)-CO(3)-Tf ternary complex. There is relatively little variation in the k(max) values for the saturation pathway for Tb(3+), Ga(3+), Al(3+), and In(3+), but the k(max) value for Fe(3+) is significantly smaller. It is suggested that protein interactions across the interdomain cleft of transferrin largely control the release of the first group of metal ions, while the breaking of stronger metal-protein bonds slows the rate of iron release. The rates of metal binding to apotransferrin are clearly controlled in large part by the hydrolytic tendencies of the free metal ions. For the more amphoteric metal ions Al(3+) and Ga(3+), there is rapid protein binding, and the addition of citrate actually retards this reaction. In contrast, the nonamphoteric In(3+) ion binds very slowly in the absence of citrate, presumably due to the rapid formation of polymeric In-hydroxo complexes upon addition of the unchelated metal ion to the pH 7.4 protein solution. The addition of citrate to the reaction accelerates the binding of In(3+) to apoTf, presumably by forming soluble, mononuclear In-citrate complexes.     

Al3+, Ca2+, Mg2+, and Li+ in aqueous solution: calculated first-shell anharmonic OH vibrations at 300 K

The anharmonic OH stretching vibrational frequencies, ν(OH), for the first-shell water molecules around the Li(+), Ca(2+), Mg(2+), and Al(3+) ions in dilute aqueous solutions have been calculated based on classical molecular dynamics (MD) simulations and quantum-mechanical (QM) calculations. For Li(+)(aq), Ca(2+)(aq), Mg(2+)(aq), and Al(3+)(aq), our calculated IR frequency shifts, Δν(OH), with respect to the gas-phase water frequency, are about -300, -350, -450, and -750?cm(-1), compared to -290, -290, -420, and -830?cm(-1) from experimental infrared (IR) studies. The agreement is thus quite good, except for the order between Li(+) and Ca(2+). Given that the polarizing field from the Ca(2+) ion ought to be larger than that from Li(+)(aq), our calculated result seems reasonable. Also the absolute OH frequencies agree well with experiment. The method we used is a sequential four-step procedure: QM(electronic) to make a force field+MD simulation+QM(electronic) for point-charge-embedded M(n+) (H(2)O)(y) (second?shell) (H(2)O)(z) (third?shell) clusters+QM(vibrational) to yield the OH spectrum. The many-body Ca(2+)-water force-field presented in this paper is new. IR intensity-weighting of the density-of-states frequency distributions was carried out by means of the squared dipole moment derivatives.     

Aqueous divalent metal-nitrate interactions: hydration versus ion pairing

Nitrate aqueous solutions, Mg(NO(3))(2), Ca(NO(3))(2), Sr(NO(3))(2), and Pb(NO(3))(2), are investigated using Raman spectroscopy and free energy profiles from molecular dynamics (MD) simulations. Analysis of the in-plane deformation, symmetric stretch, and asymmetric stretch vibrational modes of the nitrate ions reveal perturbation caused by the metal cations and hydrating water molecules. Results show that Pb(2+) has a strong tendency to form contact ion pairs with nitrate relative to Sr(2+), Ca(2+), and Mg(2+), and contact ion pair formation decreases with decreasing cation size and increasing cation charge density: Pb(2+) > Sr(2+) > Ca(2+) > Mg(2+). In the case of Mg(2+), the Mg(2+)-OH(2) intermolecular modes indicate strong hydration by water molecules and no contact ion pairing with nitrate. Free energy profiles provide evidence for the experimentally observed trend and clarification between solvent-separated, solvent-shared, and contact ion pairs, particularly for Mg(2+) relative to other cations.     

Elucidation of codoping effects on the solubility enhancement of Er3+ in SiO2 glass: striking difference between Al and P codoping

The codoping effect mechanism of Al and P on the solubility enhancement of Er(3+) ion in SiO(2) glass was clarified by electron spin-echo envelope modulation spectroscopy. It turned out that doped P ions preferentially coordinate to the Er(3+) ion to form a "solvation shell structure", and the environment is similar to that in phosphate glass, while doped Al ions do not form such a selective solvation structure, taking octahedral coordination. This striking difference indicates that the primary roles of the P-doping and the Al-doping are attributed to "enthalpy of mixing" and to "entropy of mixing", respectively.     

Interatomic potentials of cadmium-argon B1(3sigma+) and X0+(1sigma+) states based on near-dissociation expansion and 'hot' bands observed in the B1 <-- X0+ excitation spectrum

B1(3sigma+) <-- X0+(1sigma+) excitation spectrum of the cadmium-argon van der Waals molecule has been recorded in the experiment of a continuous supersonic molecular beam crossed with a pulsed dye laser beam. The B1-state dissociation energy was directly observed and a long-range behavior of the B1-state intermolecular potential was derived using a near-dissociation expansion procedure of LeRoy and Bernstein. A first-time direct determination of the X0+ ground state characteristics based on 'hot' bands observed is presented as well. The new result is compared with other experimental and theoretical reports available in the literature.     

Hydrogen atom abstraction by a mononuclear ferric hydroxide complex: insights into the reactivity of lipoxygenase

The lipoxygenase mimic [Fe(III)(PY5)(OH)](CF3SO3)2 is synthesized from the reaction of [Fe(II)(PY5)(MeCN)](CF3SO3)2 with iodosobenzene, with low-temperature studies suggesting the possible intermediacy of an Fe(IV) oxo species. The Fe(III)-OH complex is isolated and identified by a combination of solution and solid-state methods, including EPR and IR spectroscopy. [Fe(III)(PY5)(OH)](2+) reacts with weak X-H bonds in a manner consistent with hydrogen-atom abstraction. The composition of this complex allows meaningful comparisons to be made with previously reported Mn(III)-OH and Fe(III)-OMe lipoxygenase mimics. The bond dissociation energy (BDE) of the O-H bond formed upon reduction to [Fe(II)(PY5)(H2O)]2+ is estimated to be 80 kcal mol(-1), 2 kcal mol(-1) lower than that in the structurally analogous [Mn(II)(PY5)(H2O)]2+ complex, supporting the generally accepted idea that Mn(III) is the thermodynamically superior oxidant at parity of coordination sphere. The identity of the metal has a large influence on the entropy of activation for the reaction with 9,10-dihydroanthracene; [Mn(III)(PY5)(OH)]2+ has a 10 eu more negative DeltaS++ value than either [Fe(III)(PY5)(OH)]2+ or [Fe(III)(PY5)(OMe)]2+, presumably because of the increased structural reorganization that occurs upon reduction to [Mn(II)(PY5)(H2O)]2+. The greater enthalpic driving force for the reduction of Mn(III) correlates with [Mn(III)(PY5)(OH)]2+ reacting more quickly than [Fe(III)(PY5)(OH)]2+. Curiously, [Fe(III)(PY5)(OMe)]2+ reacts with substrates only about twice as fast as [Fe(III)(PY5)(OH)]2+, despite a 4 kcal mol(-1) greater enthalpic driving force for the methoxide complex.     

Isomorphic coordination polymers of cobalt(II), zinc(II) with a flexible ligand of cis,cis,cis-1,2,3,4-cyclopentanetetracarboxylic acid and their molecular alloys: crystal structures, thermal decomposition mechanisms and magnetic properties

Three new isomorphic coordination polymers of Co(2+), Zn(2+) ions with flexible multicarboxylic acid ligand of the cis,cis,cis-1,2,3,4-cyclopentanetetracarboxylic acid (H(4)L), [Co(4)L(2)(H(2)O)(8)]·3H(2)O (1), [Zn(4)L(2)(H(2)O)(8)]·3H(2)O (2) and [Co(0.8)Zn(3.2)L(2)(H(2)O)(8)]·3H(2)O (3), have been synthesized under hydrothermal conditions and by means of controlling the pH of the reaction mixtures (with an initial pH of 6.0 for 1, 4.0 for 2, and 5.0 for 3, respectively). In the crystal of 1, two crystallographically different Co(2+) ions (Co1 and Co2) form a negatively-charged coordination polymeric chain, which contains a centrosymmetric, linear, trinuclear Co(2+) cluster (Co(3)L(2)) subunit; another crystallographically independent Co(2+) ion (Co3) coordinated to six water molecules acts as a counter ions to link the neighboring coordination polymeric chains via intermolecular H-bond interactions. The Co(2+) ions in 1 were completely and partially replaced by Zn(2+) ions to give 2 and 3, respectively. Complex 3 shows a novel molecular alloy nature, due to the random distributions of the Co(2+) and Zn(2+) ions. Three isomorphic complexes exhibit distinct thermal decomposition mechanisms. The deprotonated cis,cis,cis-1,2,3,4-cyclopentanetetracarboxylic acid ligands decompose at 420-750 °C to give the residue CoO in 1, ZnO + C in 2 and CoO + ZnO in 3. Complex 1 shows a complicated magnetic behavior with co-existence of antiferromagnetic exchange interactions between neighboring Co(2+) ions as well as strong spin-orbital coupling interactions for each Co(2+) ion; complex 3 exhibits a magnetically isolated high-spin Co(2+) ion behavior with strong spin-orbital coupling interactions.