The cluster [Ni6(H2L)2(HL1)2(N3)8].2C2H5OH.2H2O [1.2C2H5OH.2H2O], featuring four fused defective cubanes, has been obtained via azido-bridge-driven dimerization of two phenolate-centered trinuclear Ni3 fragments.
Three different types of copper(II) complexes have been studied of the hexadentate Schiff base ligand N,N'-bis[2-{(salicylidenimine)amino}ethyl] piperazine (H2L) having the piperazine backbone in the chair form and axial-axial (a,a) N-atom lone pairs in the free state. The structure of the products is influenced by the reaction conditions and by the exogenous ligands, affecting the conformation of the piperazine moiety (primary structure) and the topology and nuclearity of the resulting complexes (secondary structure). In [Cu2L(DMF)2]X2 (X = ClO4-, la; NO3-, 1b), the lone-pairs of chair-piperazine adopt the equatorial-equatorial (e,e) conformation. In the presence of NEt3 and NaN3, two types of [CuII4] complexes [Cu4(L)2(OH)2(H2O)2]X2 x nH2O (X = ClO4-, n = 1, 2a; X = NO3-, n = 4, 2b) and [Cu4(L)2(N3)2(H2O)2]X2 x H2O (X = ClO4-, 3a; NO3-, 3b) are obtained where four copper(II) ions are bridged by two hexadentate micro3-piperazine ligands, this time in chair-e,a conformation, and by two OH and N3 groups. In CH3CN, reactions of 1, 2 or 3 with NaN3 always produce the double end-to-end azido bridged 1D polymer [Cu2L(N3)2], (4) having a chair-e,e piperazine backbone. All studied conformations of the piperazine bridge mediate antiferromagnetic interactions between the Cu(II) ions, as revealed by bulk magnetization measurements. The striking difference in intensity of the coupling through trans-e,e piperazine observed for complexes la and 4 might be due to complementarily effects between the ligands involved.
The heteronuclear [Na(2)Cu(4)(bemp)(2)(OH)(2)(NO(3))(2)(OH(2))(4)] x 5 H(2)O (1 x 5H(2)O; H(3)bemp: 2,6-bis-[(2-hydroxyethylimino)-methyl]-4-methyl-phenol) cluster has been synthesized in aqueous-methanol at room temperature and structurally characterized. The water soluble complex is obtained from the template assembly of two [Cu(2)(bemp)(OH)] neutral fragments through their weak oxophillic interactions with two interconnected NaNO(3) units as core. Four [Na(2)Cu(4)] units form a metal-organic cage arrangement in the crystal lattice that traps a (H(2)O)(7) cluster. Variable-temperature magnetic susceptibility measurements (2-300 K) reveals a strong antiferromagnetic coupling between the Cu(II) ions within the dimers with J = -124.1 cm(-1) (in the H = -2JS(1)S(2) convention). The interaction of complex 1 x 3H(2)O with calf thymus DNA (binding constant K(b), 4.6 x 10(4) M(-1)) in Tris buffer was studied by UV-visible and emission titration, and cyclic voltammetry. The hexanuclear Na(2)Cu(4) complex also binds double-stranded supercoiled plasmid pBR322 DNA and displays efficient hydrolytic cleavage. The hydrolytic mechanism is supported by evidence from DNA relegation employing T4 ligase assay and reactive oxygen species (ROS) quenching cleavage experiments.
The Ni(4) inverse metallacrown (NHEt(3)) [Ni(4)(bmo)4(Hael)2(ael)2](ClO(4))3 [(NHEt(3)).1.(ClO(4))3], with the inverse 12-MC-4 motif, has been assembled via simultaneous chelation and bridging of butan-2,3-dionemonoxime (Hbmo) and 2-amino ethanol (Hael).
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