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Tethering of two biologically active molecules in a single unit is considered as a captivating solution for the extension of existing antibiotics. β-Lactams which display a vast array of biological properties due to various ring substitutions continue to attract the attention of synthetic chemists. The incorporation of the 'isoxazole' nucleus in its appendage is known to enhance the properties of β-lactam compounds. Its inclusion in the compounds offers decreased toxicity, increased efficacy, and improved pharmacokinetics spectrum. In the reported work, we highlight the efficient use of 1,3-dipolar cycloaddition reaction to synthesize novel isoxazole/dihydroisoxazole ring-linked β-lactam hybrids using 3-propargyloxy-β-lactams/3-allyl-β-lactams as synthons. The methodology devised has been found to be highly regioselective and generalized for the selected substrates to provide a variety of novel hybrid compounds under elementary reaction conditions. The synthesized compounds have been well characterized by various spectroscopic techniques and optimized reaction conditions for both types of hybrid compounds have been studied. [ABSTRACT FROM AUTHOR]

The Na+ -mediated assembly of two neutral [Cu(super II)(sub 2)] fragments bridged by a 1,1-N3(super -) group and a dinucleating ligand leads to the new cluster [NaCu4L2(N3)2](CIO4). This composite complex features a combination of both ferro- and anti-ferromagnetic interactions that would not be observed in the absence of Na(super +).

The reaction of Cu(CIO4)2.6H2O and a sterically constrained piperazine imine ligand (H2L), in the presence of NEt3 in methanol, afford a novel tetranuclear copper(II) complex of formula [Cu(super II)(sub 4)(mu3-L)2(mu-OH)2(H2O)2](CIO4)2.H2O. The X-ray structure of this complex reveals an elongated Cu4 quasi-tetradhedron coordinated to two hexadentate chair-(e,a)-mu3-piperazine bridging ligands.

Abstract: The reaction of Cu(ClO4)2·6H2O with dimethylglyoxime (H2dmg) in a 1:1 mole ratio in aqueous methanol at room temperature affords the dinuclear complex [Cu2(μ-Hdmg)4] (1). Reaction of 1 with [Cu(bpy)(H2O)2](ClO4)2 (bpy=2,2′-bipyridine) in a 1:1 mole ratio in aqueous methanol at room temperature yields the tetranuclear complex [Cu4(μ-Hdmg)2(μ-dmg)2(bpy)2(H2O)2](ClO4)2 (2). The direct reaction of Cu(ClO4)2·6H2O with H2dmg and bpy in a 2:2:1 mole ratio in aqueous methanol at room temperature also yields 2 quantitatively. The complexes 1 and 2 were structurally characterized by X-ray crystallography. Unlike the binding in Ni/Co-dmg, two different types of N−O bridging modes during the oxime based metallacycle formation and stacking of square planar units have been identified in these complexes. The neutral dinuclear complex 1 has CuN4O coordination spheres and complex 2 consists of a dicationic [Cu4(μ-Hdmg)2(μ-dmg)2(bpy)2(H2O)2]2+ unit and two uncoordinated ClO4 − anions having CuN4O and CuN2O3 coordination spheres. The two copper(II) ions are at a distance of 3.846(8)Å in 1 for the trans out of plane link and at 3.419(10) and 3.684(10)Å in 2 for the trans out of plane and cis in plane arrangements, respectively. The average Cu–Noxime distances are 1.953 and 1.935Å, respectively. The average basal and apical Cu−Ooxime distances are 1.945, 2.295 and 2.429Å. The UV–Vis spectra of 2 is similar to the spectrum of the reaction mixture of 1 and [Cu(bpy)(H2O)2]2+. Variable temperature magnetic properties measurement shows that the interaction between the paramagnetic copper centers in complex 1 is antiferromagnetic in nature. The EPR spectra of frozen solution of the complexes at 77K consist of axially symmetric fine-structure transitions (ΔM S =1) and half-field signals (ΔM S =2) at ca. 1600G, suggesting the presence of appreciable Cu–Cu interactions. [Copyright &y& Elsevier]

Abstract: The N4O3 coordinating heptadentate imidazolidinyl phenolate ligand, H3L (2-(2′-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) forms with Cu(II) a rare aqua bridged complex [{Cu2(μ-L)(μ-H2O)}2](ClO4)2 ·4.5H2O (1 ·4.5H2O). Complex 1 ·4.5H2O contains two crystallographically different but chemically equivalent dinuclear [Cu2(μ-L)(μ-H2O)]+ cationic units in the asymmetric unit. The copper atoms of each dinuclear unit are in a distorted square-pyramidal environment and are held together by phenolate, imidazolidinyl and aqua bridges with a Cu···Cu separation of av. 3.34Å. The compound exhibits a very weak antiferromagnetic exchange interaction (J =−0.77cm−1, Ĥ = −2 J Ŝ 1 Ŝ 2) between the two copper(II) (S =1/2) ions. The 1H NMR spectrum of the complex shows a total of 17 hyperfine shifted peaks, as expected from the idealized Cs symmetry of the compound, spread over a very large window of chemical shift, spanning about 250ppm. The complex, having an appropriate intermetallic separation for catechol binding, shows catecholase like activity in MeCN at 25°C, with the aerobic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylquinone (3,5-DTBQ). [Copyright &y& Elsevier]

Abstract: Atmospheric CO2 fixation in basic medium (initial pH 8.5) leads to a novel hydrogencarbonate single-oxygen bridged dicopper(II) complex from the dinucleating ligand H3L (2-methyl-2-(2′-hydroxyphenyl)-1,3-bis[4-methyl-4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine). The same reaction in neutral medium (initial pH 6) gives the monocopper(II) complex [CuII(HL1)]·2ClO4 (2) of the zwitterionic ligand (HL1), following 2-(2′-hydroxyphenyl) imidazolidine ring and terminal (2-hydroxyphenyl)methylimine hydrolysis. Both 1 ·4H2O and 2 have been characterized by IR and UV–Vis spectroscopy, conductivity measurements and X-ray crystallography. Variable temperature (2–300K) magnetic measurements show that complex 1 ·4H2O exhibits weak intramolecular antiferromagnetic coupling. [Copyright &y& Elsevier]

Abstract: Reaction of Cu(ClO4)2 ·6H2O with dimethylglyoxime (H2dmg) and triethylamine (pH∼4–5) at room temperature affords oxime bridged dicopper(II/II) complex of formula [Cu2(μ-Hdmg)2(Hdmg)]ClO4 ·H2O (1) (H2dmg=dimethylglyoxime). The complex has been characterized by single-crystal X-ray diffraction analysis. The structure consists of one dinuclear complex cation, [Cu2(μ-Hdmg)2(Hdmg)], and one anion. Two copper(II) ions at a distance of 3.558 Å are bridged by one oxime and one oximate groups in cis arrangement. The geometry around each copper atom is square planar with an overall open-book type arrangement of these planes. The average copper–oxygen distance is (1.953 Å) and the average copper-nitrogen distance is 2.003 Å. The Cu–O(oxime) distance (1.963 Å) is higher than the Cu–O(oximate) distance (1.942 Å) due to different protonation label. The room temperature value of χ M T for the title complex (χ M being the molar magnetic susceptibility for two copper atoms) is low (ca. 0.42 cm3 K mol−1) (μ eff =1.52 μ B). The UV–Vis spectrum of the complex shows a characteristic broad band at 470 nm. [Copyright &y& Elsevier]

The cluster [NaCu4L2(N3)2](CIO4) [1; H3L is 2-(2′-hydroxyphenyl)-1,3-bis[3′-aza-4′-(2″-hydroxyphenyl)prop-4′-en-1′-yl]-1,3-imidazolidine] has been synthesized and structurally characterized. Complex 1 is formed by the template assembly of two [Cu2L(N3)] neutral fragments through their weak oxophilic interactions with a central Na+ cation as observed in metallacrowns. The cluster exhibits a combination of ferro- and antiferromagnetic interactions. End-on N3- bridging of copper ions within the [CuII2] units facilitates stabilization of S = 1 magnetic subunits that mutually cancel via antiferromagnetic coupling as mediated by the O⋯Na+⋯O bridges. [ABSTRACT FROM AUTHOR]

In methanol, the reaction of Cu(ClO4)2·6H2O and a sterically constrained piperazine imine phenol ligand (H2L), in the presence of NEt3, affords a novel tetranuclear copper(II) complex of formula [CuII4(μ3-L)2(μ-OH)2(H2O)2](ClO4)2·H2O (1). The X-ray structure of this complex shows an elongated Cu4 quasi-tetrahedron coordinated to two hexadentate chair-(e,a)-μ3-piperazine bridging ligands. Variable-temperature magnetic studies show an St = 0 spin ground state resulting from antiferromagnetic interactions between CuII ions within the complex. [ABSTRACT FROM AUTHOR]

The new cluster [Cu4L2(N3)]Cl.16H2O has been synthesized and characterized; it features a unique mu4-1,1,3,3 bridging mode for azide, whose capacity to mediate magnetic coupling has been examined through bulk magnetic measurements and numeric fitting procedures.

In methanol, the reaction of Cu(ClO(4))(2).6H(2)O and a sterically constrained piperazine imine phenol ligand (H(2)L), in the presence of NEt(3), affords a novel tetranuclear copper(II) complex of formula [Cu(II)(4)(mu(3)-L)(2)(mu-OH)(2)(H(2)O)(2)](ClO(4))(2).H(2)O (1). The X-ray structure of this complex shows an elongated Cu(4) quasi-tetrahedron coordinated to two hexadentate chair-(e,a)-mu(3)-piperazine bridging ligands. Variable-temperature magnetic studies show an S(t) = 0 spin ground state resulting from antiferromagnetic interactions between Cu(II) ions within the complex.