The reaction of a methanolic solution containing M(ClO₄)₂·nH₂O (M = Cu, Ni, Zn or Cd) or CoCl₂·6H₂O with bis(2-(3,5-dimethyl-1H-pyrazol-1-yl)ethyl)amine (bedmpza) in the presence of NaN₃ afforded the complexes [Cu(bedmpza)(μ_1,1-N₃)]₂(ClO₄)₂ (1), [Ni(bedmpza)(N₃)(μ_1,1-N₃)]₂·1.5H₂O (2), [Co(bedmpza)(N₃)₂] (3), [Zn(bedmpza)(N₃)]ClO₄ (4) and [Cd(bedmpza)(N₃)(μ_1,1-N₃)]₂·1.5H₂O (5). The five complexes were characterized by spectroscopic techniques and their molecular structures were determined by single crystal X-ray crystallography. The two mononuclear complexes 3 and 4 display distorted TBP and tetrahedral geometry, respectively with the azide ions acting as monodentate ligands. Doubly bridged end-on-azido dinuclear complexes were obtained in the remaining compounds. Compounds 2 and 5 are isomorphic with distorted octahedral geometry, whereas distorted square pyramidal geometry was determined in the Cu(II) complex 1. The magnetic properties for complexes 1 and 2 were investigated by measuring the magnetic susceptibilities at variable temperatures (300–2 K). The Ni(II) complex exhibits moderate ferromagnetic coupling, whereas [Cu(bedmpza)(μ_1,1-N₃)]₂(ClO₄)₂ (1) which contains two crystallographic independent dinuclear subunits in the unit cell, with different Cu–N(N3)–Cu bond angles, reveals different signs in the magnetic coupling. The complex represents the first example in the literature that has simultaneously two moieties with ferro- (J = 15.4 cm⁻¹) and antiferromagnetic (J = −18.9 cm⁻¹) interactions.

Four new cobalt(II) complexes [Co(6-MeTPA)Cl]ClO₄/PF₆ (2/2a), [Co(6-Me₂TPA)Cl]ClO₄/PF₆ (3/3a), [Co(BPQA)Cl]ClO₄/PF₆ (4/4a) and [Co(BQPA)Cl]ClO₄/PF₆ (5/5a) as well as [Co(TPA)Cl]ClO₄ (1) where TPA = tris(2-pyridylmethyl)amine, 6-MeTPA = ((6-methyl-2-pyridyl)methyl)bis(2-pyridylmethyl)amine, 6-Me₂TPA = bis(6-methyl-2-pyridyl)methyl)-(2-pyridylmethyl)amine, BPQA = bis(2-pyridylmethyl)-(2-quinolylmethyl)-amine and BQPA = bis(2-quinolylmethyl)-(2-pyridylmethyl)amine were synthesized and structurally characterized. Single crystal X-ray crystallography confirmed the distorted trigonal bipyramidal geometries of complexes 2a–5a. Spectrophotometric titrations and conductivity measurements of the complexes in the CH₃CN–H₂O mixture showed that the chloro complexes exist in equilibrium with the corresponding hydrolyzed aqua species, [Co(L)(H₂O)]²⁺. The pK_a values of the coordinated H₂O in aqua complexes vary from 8.4 to 8.7 (37 °C). The interactions of the complexes (1–5) with DNA have been investigated at pH = 7.0 and 9.0 (10 mM Tris-HCl buffer) and 37 °C where very high catalytic cleavage was observed. Under pseudo Michaelis–Menten kinetic conditions, the catalytic rate constants, k_cat, decrease in the order 4>2>5>1>3. At pH 7.0 (10 mM Tris-HCl buffer) and 37 °C, the k_cat value for complex 4 (6.02 h⁻¹), where [Co(BPQA)(H₂O)]²⁺ is the major species, corresponds to 170 million rate enhancement over the non-catalyzed DNA. Electrophoretic experiments conducted in the presence and absence of radical scavengers (DMSO, KI, NaN₃) ruled out the oxidative mechanistic pathway of the reaction and suggested that the hydrolytic mechanism is the preferred one. This finding was in agreement with the observed increase in the k_cat values at pH 9.0 compared to the corresponding values at pH 7.0 as a result of the increased concentration of the reactive hydroxo species, [Co(L)(OH)]⁺. The reactivity of the synthesized complexes in catalyzing the DNA cleavage is discussed in relation to the steric effect imposed by the coordinated pyridyl ligand around the central cobalt(II) center.

A series of dinuclear metal(II)-acetato complexes: [Ni₂(μ-L^ClO)(μ₂-OAc)₂](PF₆)·3H₂O (1), [Ni₂(μ-L^ClO)(μ₂-OAc)₂](ClO₄)·CH₃COCH₃ (2), [Cu₂(μ-L^ClO)(μ₂-OAc)(ClO₄)](ClO₄) (3), [Cu₂(μ-L^ClO)(OAc)₂](PF₆)·H₂O (4), [Zn₂(μ-L^ClO)(μ₂-OAc)₂](PF₆) (5) and [Mn₂(L^Cl-O)(μ₂-OAc)₂](ClO₄)·H₂O (6), where L^ClO⁻ = 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-chlorophenolate, were synthesized. The complexes were structurally characterized by spectroscopic techniques and single crystal X-ray crystallography. Six-coordinate geometries with doubly bridged acetato ligands were found in Ni(II), Zn(II) and Mn(II) complexes 1, 2, 5 and 6, whereas with Cu(II) complexes a five-coordinate species was obtained with 4, and mixed five- and six-coordinate geometries with a doubly bridged dimetal core were observed in 3. The magnetic properties of complexes 1–4 and 6 were studied at variable temperatures and revealed weak to very weak antiferromagnetic interactions in 1, 2, 4 and 6 (J = −0.55 to −9.4 cm⁻¹) and ferromagnetic coupling in 3 (J = 15.4 cm⁻¹). These results are consistent with DFT calculations performed at the B3LYP/def2-TZVP(-f) level of theory. Under physiological conditions, the interaction of the dinculear complexes 1–5 with supercoiled plasmid ds-DNA did not show any pronounced nuclease activity, but Ni(II) complexes 1 and 2 revealed a strong ability to unwind the supercoiled conformation of ds-DNA. The mechanistic studies performed on the interaction of the Ni(II) complexes with DNA demonstrated the important impact of the nickel(II) ion in the unwinding process. In combination with the DNA study, the phosphatase activity of complexes 1, 3, and 5 was examined by the phosphodiester hydrolysis of bis(2,4-dinitrophenol)phosphate (BDNPP) in the pH range of 5.5–10.5 at 25 °C. The Michaelis–Menten kinetics performed at pH 7 and 10.7 showed that catalytic efficiencies k_cat/K_M (k_cat = catalytic rate constant, K_M = substrate binding constant) decrease in the order: Ni(II), 1 > Zn(II), 5 > Cu(II), 3. A similar trend was also observed with the turnover numbers at pH = 7. The results are discussed in relation to the coordination geometry and nature of the metal center as well as the steric environment imposed by the compartmental phenoxido ligand.

Five new dinuclear bridged-phenoxido dichlorido-metal( ii ) complexes [M ₂ (μ-L ^Cl O)(X) ₂ Cl ₂ ]PF ₆ /ClO ₄ complexes, where M( ii ) = Co, Ni, Cu ( 1–4 ) and Zn ( 5 ); X = CH ₃ OH, H ₂ O or 0 were synthesized and structurally characterized. Complexes 1–4 revealed weak to moderate antiferromagnetic coupling.