Structural, solvatochromism and magnetic properties of two halogen bridged dinuclear copper (II) complexes: A density functional study

Magneto-structural maps and bridged-ligand effect for dichloro-bridged dinuclear copper(ii) complexes: a theoretical perspective

Theoretical understanding of magneto-structural correlations in dichloro-bridged dicopper(ii) complexes can guide the design of magnetic materials having broad-scale applications. However, previous reports suggest these correlations are complicated and unclear. To clarify possible correlations, magnetic coupling constants (J _calc) of variants of a representative {Cu-(μ-Cl)₂-Cu} complex A were calculated through BS-DFT. The variation of the Cu-(μ-Cl)-Cu angle (α), Cu⋯Cu distance (R ₀), and Cu-Cl-Cu-Cl dihedral angle (τ) followed by structural optimization and calculation of the magnetic coupling constant (J _calc) revealed several trends. J _calc increased linearly with R ₀ and τ, and initially increased and then decreased with α. Further, bridging ligand effects on J _calc for dicopper(ii) complexes were evaluated through BS-DFT; the results revealed that J _calc increased with increasing ligand field strength (I^- < Br^- < Cl^- < N₃ ^- < F^-). Furthermore, a linear relationship was found between the spin density of the bridging ligand and J _calc.

The effect of anions in the synthesis and structure of pyrazolylamidino copper(II) complexes

Six new pyrazolylamidino Cu(II) complexes are synthesized directly from the reactions of Cu(X)₂ salts (X = ClO₄^-, BF₄^-, or Cl^-) and pyrazole (pzH) in nitrile solution (RCN, R = Me or Et) at 298 K via the metal-mediated coupling of RCN with pzH: [Cu(HNC(R)pz)₂(X)₂] (X = ClO₄^- or BF₄^-, R = Me, 1 or 7 and Et, 2 or 8, respectively) and dichloro Cu(II) complexes [Cu₂Cl₂(μ-Cl)₂(HNC(Me)pz)₂] (3) and [CuCl₂(HNC(Et)pz)] (4). Four more new complexes, [Cu₂(μ-Cl)₂(HNC(Me)pz)₂(pzH)₂][X]₂ (X = ClO₄^-, 5 and BF₄^-, 9) and [Cu₂(μ-Cl)₂(HNC(Et)pz)₂(pzH)₂(X)₂] (X = ClO₄^-, 6 and BF₄^-, 10), are obtained indirectly from the anion substitution reaction with Cl^- ions in 1 and 7, and 2 and 8, respectively. All complexes are characterized by EA, FTIR, UV-vis and EPR spectroscopy and X-ray crystallographic analyses. HNC(Et)pz or pzH is unobserved in both the nitrile-exchange reaction of 2 to d₆-1 and the anion-substitution reaction of 2 to d₆-5 in the CD₃CN solution. The ¹H NMR results reveal that the pzH-RCN coupling is intramolecular and reversible on a Cu(II) center. The crystal structures of these complexes show diverse supramolecular assemblies through imino NH⋯anion hydrogen bonds and pyrazolylamidino pz-pz (π⋯π) and pz-Cu(II) (π⋯metal) interactions. EPR results suggest weak magnetic couplings between Cu(II) centers in the polynuclear Cu(II) complexes. The yield and rate of the formation of 1 are higher in the reaction of Cu(ClO₄)₂ with a 4-fold molar excess of pzH compared with a 2-fold excess, indicating that [Cu(pzH)₄]²⁺ is the more active species for pzH-RCN coupling. The highest rate for the formation of 1 is achieved when [Cu(pzH)₄(ClO₄)₂] is used in MeCN solution. Thus, a plausible synthetic path for synthesizing pyrazolylamidino Cu(II) complexes is established. An intermediate species, [Cu(HNC(Me)pz)₂(pzH)₂][ClO₄]₂ (1a), is proposed for the synthetic process based on spectroscopic studies and DFT calculations. The reaction of [Cu(pzH)₄X₂] (X = ClO₄^-, Cl^-, NO₃^-, or BF₄^-) in MeCN solution suggests that the lability of coordinated anions upon nitrile substitution affects the rate of the formation of bis-pyrazolylamidino Cu(II) complexes.

Structural, Electrical, and Magnetic Versatility of the Oxalate-Based [CuFe] Compounds Containing 2,2':6',2″-Terpyridine: Anion-Directed Synthesis

The heterodimetallic [CuFe] compounds [Cu^II₄(terpy)₄Cl₅][Fe^III(C₂O₄)₃]·10H₂O (1;terpy = 2,2':6',2''-terpyridine), [Cu^II₂(H₂O)₂(terpy)₂(C₂O₄)][Cu^IIFe^III(CH₃OH)(terpy)(C₂O₄)₃]₂ (2), and {[Cu₂^IIFe^III(H₂O)(terpy)₂(C₂O₄)_7/2]·6H₂O}_n (3) were obtained using building block approach, from reaction of aqueous solution of [Fe(C₂O₄)₃]^3- and a methanol solution containing Cu²⁺ ions and terpy by the layering technique. Interestingly, by changing only the anion of the starting salt of copper(II), Cu(NO₃)₂·3H₂O instead of CuCl₂·2H₂O, an unexpected change in the type of bridge, oxalate (2 and 3) versus chloride (1), was achieved, thus affecting the overall structural architecture. Two polymorphs of 3D coordination polymer [Cu^IIFe^II₂(H₂O)(terpy)(C₂O₄)₃]_n (4), crystallizing in the triclinic (a) and monoclinic (b) space groups, were formed hydrothermally, depending on whether CuCl₂·2H₂O or Cu(NO₃)₂·3H₂O was added to the water, besides K₃[Fe(C₂O₄)₃]·3H₂O and terpy, respectively. Under hydrothermal conditions iron(III) from initial building block is reduced to the divalent state, creating 2D honeycomb [Fe^II₂(C₂O₄)₃]_n^2n- layers, which are bridged by [Cu(H₂O)(terpy)]²⁺ cations. Compounds were investigated by single-crystal X-ray diffraction, IR, and impedance spectroscopies, magnetization measurements, and density functional theory (DFT) calculations. In compounds 1 and 2, 0D magnetism is observed, with 1 having a ground-state spin of 1 due to different interactions through chloride bridges of Cu²⁺ ions in tetramer [Cu^II₄(terpy)₄Cl₅]³⁺ and 2 showing strong antiferromagnetic coupling of Cu²⁺ ions mediated by oxalate ligand in [Cu^II₂(H₂O)₂(terpy)₂(C₂O₄)]²⁺ and weak ones between Cu²⁺ and Fe³⁺ ions through oxalate bridge in [Cu^IIFe^III(CH₃OH)(terpy)(C₂O₄)₃]^-. Polymer 4 exhibits antiferromagnetic phase transition at 25 K: The [Fe^II₂(C₂O₄)₃]_n^2n- layers are antiferromagnetically ordered, and a small amount of interlayer interaction is transferred through [Cu(H₂O)(terpy)]²⁺ cations via O_ox-Cu-O_ox bridges. Additionally, compounds 1 and 2 are electrical insulators, while 4a and 4b show proton conductivity.

Ultrasound-assisted synthesis of two novel [CuBr(diamine)2·H2O]Br complexes: Solvatochromism, crystal structure, physicochemical, Hirshfeld surface thermal, DNA/binding, antitumor and antibacterial activities

Two new hydrated monocationic Cu(II) complexes with 1,3-propylenediamine and 1,2-ethylenediamine of general formula [CuBr(N-N)₂·H₂O]Br were prepared. The complexes were identified by means of several spectroscopic tools (Uv-visible, IR and MS), thermally (TG/DTA) and CHN-elemental analysis. The three dimensional structure for complex A and B was provide by X-ray diffraction studies and showed the Cu(II) ion as 4 + 1 + 1 coordinated, four nitrogen atoms of the diamine ligands, one bromide ion and one H₂O semi-coordinated to the Cu(II) center, a typical trans effect is clearly observed in the two complexes. The molecular crystal structures are linked via several H-bonds like N_H…Br and N_H…O. Additionally, intra-molecular H-bonds of kind C_H…Br is observed; these interactions lead to crystal structure three dimensional architecture packing. Hirshfeld surfaces (HSA) analysis was served to figure out the inter-contacts and fingerprints atoms percentage. DNA-binding, antitumor and antibacterial effectiveness of the desired complexes were evaluated.