A systematic investigation of structural transformation in a copper pyrazolato system: a case study

Dissolution-recrystallization structural transformation (DRST) is a powerful tool to unravel unequivocally the mechanism of dynamic conversion processes, based on the structures of the initial reactants, final products and sometimes intermediates isolated from the reaction mixture. Herein, we illustrate the details of the conversion processes of (CuIpz)3 into [CuII(OH)pz]6 (pzH = 4-chloro-3,5-diphenylpyrazole) through DRSTs. Based on crystal structure determination and spectroscopic methods, the most encountered species, (CuIpz)3, is in equilibrium with (CuIpz)4 in solution with the tetramer becoming dominant at low temperature, indicating an entropy-controlled conversion between these two structural isomers. The CuI trimer/tetramer in solution further experiences an oxidation if exposed to the open air, resulting in the formation of a pentanuclear mixed-valence intermediate CuI3CuII2(OMe)2pz5 which can be isolated as single crystals at -20 °C and has been structurally characterized for the first time. The final product isolated from the solution is the fully oxidized hexanuclear [CuII(OMe)pz]6, which is easily transformed into [CuII(OH)pz]6 in the presence of humidity.

Crystal structures, and magnetic and thermal properties of basic copper formates with two-dimensional triangular-lattice magnetic networks

Basic copper formate, [Cu₃(OH)₄(HCOO)₂], was selectively prepared by hydrolysis of formate ions in concentrated aqueous solutions of copper formate. This material exhibits a two-dimensional distorted triangular-lattice magnetic network of Cu(ii) ions where S = 1/2. The dominance of antiferromagnetic interactions with J/k_B = 35.7(2) K and a magnetic anomaly at approximately 2.3 K that corresponds to a paramagnetic-to-antiferromagnetic ordering transition were revealed by magnetic measurements. The field dependence of the magnetisation at 2 K corresponds to the 1/3-magnetisation plateau that is commonly observed in a two-dimensional triangular-lattice system. Moreover, heat-capacity measurements found a λ-type anomaly at 2.15 K, which is the magnetic transition temperature. This material may be a good candidate for a geometrical frustration system with novel magnetic phenomena such as spin-liquid states.

Basic copper formate, [Cu₃(OH)₄(HCOO)₂], has a distorted two-dimensional triangular lattice magnetic network and showed antiferromagnetic ordering at 2.15 K.

On the Border between Low-Nuclearity and One-Dimensional Solids: A Unique Interplay of 1,2,4-Triazolyl-Based {CuII5(OH)2} Clusters and MoVI-Oxide Matrix

A pentanuclear Cu^II₅-hydroxo cluster possessing an unusual linear-shaped configuration was formed and crystallized under hydrothermal conditions as a result of the unique cooperation of bridging 1,2,4-triazole ligand ( trans-1,4-cyclohexanediyl-4,4'-bi(1,2,4-triazole) ( tr₂ cy)), Mo^VI-oxide, and CuSO₄. This structural motif can be rationalized by assuming in situ generation of {Cu₂Mo₆O₂₂}^4- anions, which represent heteroleptic derivatives of γ-type [Mo₈O₂₆]^4- further interlinked by [Cu₃(OH)₂]⁴⁺ cations through [ N- N] bridges. The framework structure of the resulting compound [Cu₅(OH)₂( tr₂ cy)₂Mo₆O₂₂]·6H₂O (1) is thus built up from neutral heterometallic {Cu₅(OH)₂Mo₆O₂₂} _n layers pillared with tetradentate tr₂ cy. Quantum-chemical calculations demonstrate that the exclusive site of the parent γ-[Mo₈O₂₆]^4- cluster into which Cu^II inserts corresponds with the site that has the lowest defect ("MoO₂ vacancy") formation energy, demonstrating how the local metal-polyoxomolybdate chemistry can express itself in the final crystal structure. Magnetic susceptibility measurements of 1 show strong antiferromagnetic coupling within the Cu₅ chain with exchange parameters J₁ = -500(40) K (-348(28) cm^-1), J₂ = -350(10) K (-243(7) cm^-1) and g = 2.32(2), χ² = 6.5 × 10^-4. Periodic quantum-chemical calculations reproduce the antiferromagnetic character of 1 and connect it with an effective ligand-mediated spin coupling mechanism that comes about from the favorable structural arrangement between the Cu centers and the OH^-, O^2-, and tr₂ cy bridging ligands.

NICS values scan in three-dimensional space of the hoop-shaped π-conjugated molecules [6]8cyclacene and [16]trannulene

In this work, [6]₈cyclacene and [16]trannulene are used as representative molecules to further study the aromaticity from a new research perspective by using the NICS values scan in three-dimensional space methodology. A huge difference of aromaticity has been observed in three-dimensional space through the method.

Bonding and optical properties of spirocyclic-phosphazene derivatives. A DFT approach

The bonding properties of phosphazenes and spirocyclophosphazenes containing tris-2,2′-dioxybiphenyl groups and their derivatives were investigated by means of different computational techniques.