Syntheses, Structures, and Magnetic Properties of Unusual Nonlinear Polynuclear Copper(II) Complexes Containing Derivatives of 1,2,4-Triazole and Pivalate Ligands

Two 3D triazolate-tricarboxylate-bridged Cu(II/I) frameworks by one-pot hydrothermal synthesis exhibiting spin-canted antiferromagnetism and strong antiferromagnetic couplings

Two 3D coordination polymers with the same components but different structures, [Cu(II)(2)Cu(I)(trz)(3)(Hbtc)](n) (1) and [Cu(4)(Htrz)(2)(mu(3)-OH)(2)(btc)(2)](n) (2), were obtained together by a one-pot hydrothermal reaction of Cu(OAc)(2).H(2)O, 1,2,4-triazole (Htrz), and 1,3,5-benzenetricarboxylic acid (H(3)btc). Complex 1 is a mixed-valence Cu(I/II) honeycomb built from wavy Cu(II)-trz-carboxylate layers and Cu(I) nodes with doubly deprotonated Hbtc(2-) ligands covalently filled in the channels. In contrast, 2 is a tetranuclear [Cu(4)(Htrz)(2)(mu(3)-OH)(2)](6+) cluster-based framework extended by a fully deprotonated btc(3-) ligand, displaying a 3,6-connected topological network. More interestingly, spin-canted antiferromagnetism and overall strong antiferromagnetic couplings up to -147.1 cm(-1) are respectively observed for 1 and 2, which are significantly due to the antisymmetric magnetic exchange in the wavy Cu(II)-trz-carboxylate sublayer of 1 and the cooperative 4-fold heterobridges within the tetranuclear cluster of 2.

Two Novel Triazole-Based Metal - Organic Frameworks Consolidated by a Flexible Dicarboxylate Co-ligand: Hydrothermal Synthesis, Crystal Structure, and Luminescence Properties

To explore the effects of a co-ligand on the construction of mixed-ligand metal–organic frameworks (MOFs), two new triazole-based complexes with a flexible dicarboxylate as a co-ligand, {[Zn4(trz)4(gt)2(H2O)2](H2O)2}n 1 and {[Cd2(trz)2(gt)(H2O)2](H2O)4}n 2 (Htrz = 1,2,4-triazole; H2gt = glutaric acid), were synthesized and their structures were fully characterized by elemental analyses, IR spectroscopy, and single-crystal X-ray crystallography. Their thermal stability and luminescence emissions were further investigated to establish their structure–property relationship. Crystal structure determination showed that 1 is a neutral two-dimensional pillared-bilayer network consisting of 14-membered hydrophobic channels, whereas 2 is an infinite three-dimensional framework constructed from tetranuclear [Cd4(trz)4]4+ subunits. Interestingly, the overall structure of both MOFs can be solely supported by ZnII/CdII and trz anions, and were further consolidated by the introduction of a flexible gt co-ligand. In addition, the carboxylate groups in the co-ligand can also serve as a weak O–H···O hydrogen-bond acceptor to capture guest water molecules. The synchronous weight-loss behaviour of trz and gt anions presented by thermogravometric curves suggest their cooperative contributions to the thermal stability of the MOFs. In contrast, the fluorescence emissions of two complexes are significantly dominated by the core trz ligand, rather than the gt co-ligand and metal ions.

Hydrothermal Synthesis, Structural Chemistry, and Magnetic Properties of Materials of the MII/Triazolate/Anion Family, Where MII = Mn, Fe, and Ni

Hydrothermal chemistry has been exploited in the preparation of a series of manganese(II), iron(II), and nickel(II) triazolate frameworks, [Mn7(trz)8(CH3CO2)4(OH)2].2.5H2O (1.2.5H2O), [Mn5(Htrz)2(SO4)4(OH)2] (2), [Fe5(Htrz)2(SO4)4(OH)2] (3), [Fe3(Htrz)3(HSO4)(SO4)2(OH)].H2O (4.H2O), [Ni3(trz)3(OH)3(H2O)4].5H2O (5.5H2O), and [Ni3(trz)5(OH)].2.5H2O (6.2.5H2O). The materials all exhibit three-dimensional structures, reflecting the tendency of triazole/triazolate ligands to bridge multiple metal sites. A prominent characteristic of the structures is the presence of embedded metal clusters as building blocks: heptanuclear MnII units in 1, pentanuclear MII sites in 2 and 3, and trinuclear MII clusters in 4 and 5. The presence of the pentanuclear and trinuclear clusters of magnetic metal cations in 2-5 is reflected in the unusual magnetic characteristics of these materials, all of which exhibit spin frustration. The compound 5.5H2O reversibly desorbs/sorbs solvent. However, the dehydrated phase does not adsorb methanol, N2, O2, or H2, presumably as a consequence of the highly polar void volume and the narrow channels connecting the larger cavities of the void structure.

Hydrothermal and Structural Chemistry of the Zinc(II)- and Cadmium(II)-1,2,4-Triazolate Systems

Hydrothermal reactions of 1,2,4-triazole with zinc and cadmium salts have yielded 10 structurally unique materials of the M(II)/trz/Xn- system, with M(II)=Zn and Cd and Xn-=F-, Cl-, Br-, I-, OH-, NO3-, and SO(4)2- (trz=1,2,4-triazolate). Of the zinc-containing phases, [Zn(trz)2] (1), [Zn2(trz)3(OH)].3H2O (3.3H2O), and [Zn2(trz)(SO4)(OH)] (4) are three-dimensional, while [Zn(trz)Br] (2) is two-dimensional. All six cadmium phases, [Cd3(trz)3F2(H2O)].2.75H2O (5.2.75H2O), [Cd2(trz)2Cl2(H2O)] (6), [Cd3(trz)3Br3] (7), [Cd2(trz)3I] (8), [Cd3(trz)5(NO3)(H2O)].H2O (9.H2O), and [Cd8(trz)4(OH)2(SO4)5(H2O)] (10), are three-dimensional. In all cases, the anionic components Xn- participate in the framework connectivity as bridging ligands. The structural diversity of these materials is reflected in the variety of coordination polyhedra displayed by the metal sites: tetrahedral; trigonal bipyramidal; octahedral. Structures 3, 5, and 7-9 exhibit two distinct polyhedral building blocks. The materials are also characterized by a range of substructural components, including trinuclear and tetranuclear clusters, adamantoid cages, chains, layers, and complex frameworks.

The Rotating Ring-Disk Electrochemistry of the Copper(II) Complex of Thyrotropin-releasing Hormone

Thyrotropin-releasing Hormone (TRH) forms an electroactive Cu(II) complex in aqueous solution. Rotating ring-disk electrochemistry reveals oxidation at the disk electrode and reduction at the ring electrode. The plot of limiting current vs. square root of rotation frequency deviates from the Levich equation, indicating both preceding and following chemical reactions. The reaction following the oxidation is a multiple-electron ECE-type of process that has been seen before in Cu(II)-peptide electrochemistry. The preceding reaction is unusual. The deviation from diffusion-controlled behavior is more pronounced at higher initial concentration of Cu(II) and peptide. We propose that a non-electroactive dimer, Cu(II)(2)-TRH(2), is in a slow equilibrium with the electroactive Cu(II)-TRH. Simulation of the RRDE behavior of the postulated Cu(II)-TRH system has succeeded in matching experimental data. Capillary electrophoresis indicates that there is a negative charge on the dimer. It is suggested that a hydroxo-bridge may link the two Cu(II) centers. Calculations verify that bi-nuclear Cu(II)(2)-TRH(2) complexes are possible.

Tricopper(ii) complexes of unsymmetrical macrocycles incorporating phenol and pyridine moieties: the development of two stepwise routes

Two stepwise approaches to preparing large unsymmetrical macrocycles incorporating diethylenetriamine lateral units are described: the first utilises protecting group chemistry, whereas the second exploits irreversible amide bond formation in the presence of an excess of the amine. In the first approach condensation of two equivalents of N-acetyldiethylenetriamine 1 with 2,6-diformyl-4-methylphenol, followed by a sodium borohydride reduction of the newly formed imine bonds and acidic removal of the protecting groups, yields a phenol-containing "two-armed" precursor as an HCl salt 2. Using the second approach the new pyridine-containing "two-armed" precursor , is prepared from 2,6-dimethylpyridinedicarboxylate and an excess of diethylenetriamine. These two "two-armed" di-primary amine precursors, 2 (after reaction with KOH) and 3, can be condensed with the dicarbonyl head units of choice. The lead templated condensation of 2 with 2,6-diacetylpyridine results in the formation of the macrocyclic dilead(II) complex {[Pb(II)(2)(L1)(Cl)](ClO(4))(2)}(infinity) 4. Transmetallation of 4 with three equivalents of copper(II) perchlorate produces Cu(II)(3)(L1)(OH)(ClO(4))(4) 5. Condensation of 3 with 2,6-diacetylpyridine or 2,6-diformylpyridine in the presence of barium(ii) ions results in the macrocyclic complexes [Ba(II)(H(2)L2)](ClO(4))(2) 6 and [Ba(II)(H(2)L3)](ClO(4))(2) 7, respectively. Copper(II) acetate templates the formation of the crystallographically characterised unsymmetrical macrocyclic complex [Cu(II)(3)(L4)(OH)(NCS)(2)].EtOH, 8.EtOH, from 3, 2,6-diformyl-4-methylphenol and NaNCS.

Solid-State Coordination Chemistry of the Cu/Triazolate/X System (X = F-, Cl-, Br-, I-, OH-, and SO42-)

Hydrothermal reactions of 1,2,4-triazole with the appropriate copper salt have provided eight structurally unique members of the Cu/triazolate/X system, with X = F-, Cl-, Br-, I-, OH-, and SO4(2-). The anionic components X of [Cu3(trz)4(H2O)3]F2 (1) and [Cu6(trz)4Br]Cu4Br4(OH) (4) do not participate in the framework connectivity, acting as isolated charge-compensating counterions. In contrast, the anionic subunits X of [Cu(II)Cu(I)(trz)Cl2] (2), [Cu6(trz)4Br2] (3), [Cu(II)Cu(I)(trz)Br2] (5), [Cu3(trz)I2] (6), [Cu6(II)Cu2(I)(trz)6(SO4)3(OH)2(H2O)] (8), and [Cu4(trz)3]OH.7.5H2O (9.7.5H2O) are intimately involved in the three-dimensional connectivities. The structure of [Cu(II)Cu(I)(trz)2][Cu3(I)I4] (7) is constructed from two independent substructures: a three-dimensional cationic {Cu2(trz)2}n(n+) component and {Cu3I4}n(n-) chains. Curiously, four of the structures are mixed-valence Cu(I)/Cu(II) materials: 2, 5, 7, and 8. The only Cu(II) species is 1, while 3, 4, 6, and 9.7.5H2O exhibit exclusively Cu(I) sites. The magnetic properties of the Cu(II) species 1 and of the mixed-valence materials 5, 7, 8, and the previously reported [Cu3(trz)3OH][Cu2Br4] have been studied. The temperature-dependent magnetic susceptibility of 1 conforms to a simple isotropic model above 13 K, while below this temperature, there is weak ferromagnetic ordering due to spin canting of the antiferromagnetically coupled trimer units. Compounds 5 and 7 exhibit magnetic properties consistent with a one-dimensional chain model. The magnetic data for 8 were fit over the temperature range 2-300 K using the molecular field approximation with J = 204 cm(-1), g = 2.25, and zJ' = -38 cm(-1). The magnetic properties of [Cu3(trz)3OH][Cu2Br4] are similar to those of 8, as anticipated from the presence of similar triangular {Cu3(trz)3(mu3-OH)}(2+) building blocks. The Cu(I) species 3, 4, 6, and 9 as well as the previously reported [Cu(5)(trz)3Cl2] exhibit luminescence thermochromism. The spectra are characterized by broad emissions, long lifetimes, and significant Stokes' shifts, characteristic of phosphorescence.