Turning a "useless" ligand into a "useful" ligand: a magneto-structural study of an unusual family of Cu(II) wheels derived from functionalised phenolic oximes

While the phenolic oximes (R-saoH2) are well known for producing monometallic complexes of the type [M(II)(R-saoH)2] with Cu(II) ions in near quantitative yield, their derivatisation opens the door to much more varied and interesting coordination chemistry. Here we show that combining the complimentary diethanolamine and phenolic oxime moieties into one organic framework (H4L1 and H4L2) allows for the preparation and isolation of an unusual family of [Cu(II)]n wheels, including saddle-shaped, single-stranded [Cu(II)8] wheels of general formula [Cu8(HL1)4(X)4](n)[Y] (when n = 0, X = Cl(-), NO3(-), AcO(-), N3(-); when n = 2+ X = (OAc)2/(2,2'-bpy)2 and Y = [BF4]2) and [Cu8(HL2)4(X)4] (X = Cl(-), Br(-)), a rectangular [Cu6(HL1)4] wheel, and a heterometallic [Cu4Na2(HL1)2(H2L1)2] hexagon. Magnetic studies show very strong antiferromagnetic exchange between neighbouring metal ions, leading to diamagnetic ground states in all cases. DFT studies reveal that the magnitude of the exchange constants are correlated to the Cu-N-O-Cu dihedral angles, which in turn are correlated to the planarity/puckering of the [Cu(II)]n rings.

A family of polynuclear cobalt complexes upon employment of an indeno-quinoxaline based oxime ligand

The employment of an indeno-quinoxaline based oxime ligand in cobalt chemistry afforded a new family of polynuclear cobalt clusters.

pH dependent facile synthesis of di- and trinuclear oxime based Cu(ii) complexes: antiferromagnetic coupling in the dinuclear cores and spin frustration in the triangular core

Two antiferromagnetic dinuclear and one spin frustrated trinuclear cores of oxime based Cu(ii) compounds have been synthesized by changing the pH of the reaction mixtures.

New rare-topology [Cu4] cluster coordination polymer employing 2-(oxyimino)propionate as a ligand

The reported compound, {Na2[Cu4(HCOO)2(pa)4(CH3OH)] · CH3OH} n (1, H2pa = 2-(hydroxyimino)propionic acid), is a sodium salt of an anionic coordination polymer, comprising rare-topology tetranuclear cluster units, linked through Cu–O bonds to form a polymeric chain. Each cluster unit comprises four Cu2+ cations, chelating 2-(oxyimino)propionate ligands, two formate ligands and one terminal methanol ligand. The neighbouring polymeric chains contact through O–H…O hydrogen bonds and are interconnected by Na–O coordination bonds to form a three-dimensional network.

Novel oximato-bridged platinum(II) di- and trimer(s): synthetic, structural, and in vitro anticancer activity studies

Novel platinum complexes of trans geometry [PtCl(2){(Z)-R(H)C═NOH}(2)] [R = Me (1), Et (3)] and [PtCl(2){(E)-R(H)C═NOH}{(Z)-R(H)C═NOH}] [R = Me (2), Et (4)] as well as the classic trans-[PtCl(2)(R(2)C═NOH)(2)] [R = Me, Et] were reacted with an equivalent amount of silver acetate in acetone solution at ambient temperature, resulting in formation of unprecedented head-to-tail-oriented oximato-bridged dimers [PtCl{μ-(Z)-R(H)C═NO}{(Z)-R(H)C═NOH}](2) [R = Me (5), Et (7)], [PtCl{μ-(Z)-R(H)C═NO}{(E)-R(H)C═NOH}](2) [R = Me (6), Et (8)], and [PtCl(μ-R(2)C═NO)(R(2)C═NOH)](2) [R = Me (9), Et (10)], correspondingly. The dimeric species feature a unique six-membered diplatinacycle and represent the first example of oxime ligands coordinated to platinum via the oxygen atom. All complexes were characterized by elemental analyses, electrospray ionization mass spectrometry, IR and multinuclear ((1)H, (13)C, and (195)Pt) NMR spectroscopy, as well as X-ray diffraction in the cases of dimers 6 and 9. Furthermore, the crystal and molecular structures of a trimeric oximato-bridged complex 11 comprising three platinum units connected in a chain way were established. The cytotoxicity of both dimers and the respective monomers was comparatively evaluated in three human cancer cell lines: cisplatin-sensitive CH1 cells as well as cisplatin-resistant SW480 and A549 cells, whereupon structure-activity relationships were drawn. Thus, it was found that dimerization results in a substantial (up to 7-fold) improvement of IC(50) values of (aldoxime)Pt(II) compounds, whereas for the analogous complexes featuring ketoxime ligands the reverse trend was observed. Remarkably, the novel dimers yielded no cross-resistance with cisplatin in SW480 cells, exhibiting up to 2-fold enhanced cytotoxicity in comparison with the CH1 cell line and thereby possessing a promising potential to overcome resistance toward platinum anticancer drugs. The latter point was also confirmed by investigating the potency of apoptosis induction in the case of one monomer as well as one dimer; the investigated complexes proved to be strong apoptotic agents which could induce cell death even in the cisplatin-resistant SW480 cell line.

Investigation of the zinc(II)-benzoate-2-pyridinealdoxime reaction system

The employment of pyridine-2-carbaldehyde oxime (paoH) in zinc(II) benzoate chemistry, in the absence or presence of azide ions, is described. The syntheses, crystal structures and spectroscopic characterization are reported for the complexes [Zn(O(2)CPh)(2)(paoH)(2)] (1), [Zn(12)(OH)(4)(O(2)CPh)(16)(pao)(4)] (2) and [Zn(4)(OH)(2)(pao)(4)(N(3))(2)] (3). The Zn(II) centre in octahedral 1 is coordinated by two monodentate PhCO(2)(-) groups and two N,N'-chelating paoH ligands. The metallic skeleton of 2 describes a tetrahedron encapsulated in a distorted cube. The {Zn(12)(μ-OH)(4)(μ(3)-ΟR)(4)}(16+) core of the cluster can be conveniently described as consisting of a central {Zn(4)(μ(3)-ΟR)(4)}(4+) cubane subunit (RO(-) = pao(-)) linked to four {Zn(2)(μ-OH)}(3+) subunits via the OH(-) group of each of the latter, which becomes μ(3). The molecule of 3 has an inverse 12-metallacrown-4 topology. Two triply bridging hydroxido groups are accommodated into the metallacrown ring. Each pao(-) ligand adopts the η(1) : η(1) : η(1) : μ coordination mode, chelating one Zn(II) atom and bridging a Zn(II)(2) pair. Complexes 1 and 2 display photoluminescence with maxima at ∼355 nm and ∼375 nm, upon maximum excitation at 314 nm; the origin of the photoluminescence is discussed.