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The capability of bis(dioxolene) ligands to access multiple redox states makes them ideal candidates to tune the electronic properties of metal complexes, for example to achieve valence tautomerism (VT). In this study, a family of dinuclear cobalt complexes have been isolated with the bridging bis(dioxolene) thean− ligand in the cat2−‐cat2−, cat2−‐SQ⋅− and SQ⋅−‐SQ⋅− states (cat2−=catecholate, SQ⋅−=semiquinonate): [{CoIII(tpa)}2(theacat−cat)](PF6)2 (1), [{CoIII(tpa)}2(theacat−SQ)](PF6)3 (2), and [{CoIII(tpa)}2(theaSQ−SQ)](PF6)4 (3) (theaH4=2,3,6,7‐tetrahydroxy‐9,10‐dimethyl‐9,10‐dihydro‐9,10‐ethanoanthracene, tpa=tris(2‐pyridylmethyl)amine). Multi‐technique analysis confirms that 1, 2 and 3 adopt low spin‐CoIII containing {CoIII‐cat‐cat‐CoIII}, {CoIII‐cat‐SQ‐CoIII} and {CoIII‐SQ‐SQ‐CoIII} states, respectively. Compound 1 undergoes thermally‐induced {CoIII‐cat‐cat‐CoIII} ⇌ {CoIII‐cat‐SQ‐CoII} VT in the solid‐ and solution‐states above 300 K, involving high spin‐CoII. This interconversion is contrary to expectations, as tpa typically stabilizes low spin‐CoIII‐catecholate. Compound 2 is mixed‐valence class II/II–III, indicating a localized electronic structure, with electron transfer faster than the EPR and solvent rearrangement timescales, but slower than the infrared timescale. Compound 3 exhibits strong antiferromagnetic exchange. The overlap between the dioxolene π‐orbitals in thean− increases the accessibility of the cat2−‐SQ⋅− state, resulting in VT for 1. This study demonstrates that thean− can be isolated in multiple oxidation states in metal complexes, which is promising for applications in magnetic materials. [ABSTRACT FROM AUTHOR]

The oxidation of Tp*WIII(NCMe)(CO) [Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate] by iodine in refluxing acetonitrile produces paramagnetic Tp*WIIII2(CO), with μeff = 1.70 μB and ν(CO) = 1881 cm−1. The analogous bromo complex, Tp*WIIIBr2(CO) (μeff = 1.72 μB, ν(CO) = 1905 cm−1), is produced by the oxidative decarbonylation of Tp*WI(CO)3 with bromoacetonitrile in refluxing tetrahydrofuran. The crystal structures of both complexes reveal mononuclear, six-coordinate, distorted octahedral metal complexes bearing facial Tp* and mutually cis halide and carbonyl ligands. The structures, magnetic moments and spectroscopic data (including isotropically shifted NMR spectra) are consistent with a low-spin, doublet ground state in these, the first reported, 15-electron, d3 dihalo(carbonyl)–W(III) complexes. [ABSTRACT FROM AUTHOR]

We describe the reaction of anion [RhCl6]3− with a series of hydantoin ligands (HL1, HL2 and HL3 = 5-methyl-5-(2-, 3- and 4-pyridyl)-2,4-imidazolidenedione, respectively). Based on spectroscopic, cyclic voltammetric, elemental and MS analyses, the complexes have the general formula K[RhCl2(L1)2] ( 1), cis- and trans-K[RhCl4(HL2)2] ( 2a and 2b) and cis- and trans-K[RhCl4(HL3)2] ( 3a and 3b). Complexes 2a, 2b, 3a and 3b were characterized successfully using infrared, 1H NMR and 13C NMR spectral analyses. Dissolution of complex 1 in dimethylsulfoxide (DMSO) led to elimination of one KL1 ligand and coordination of two DMSO molecules as ligands and transformation of this complex to cis- and trans-[RhCl2L1(DMSO)2] ( 1a and 1b). Recrystallization led to separation and isolation of crystals of 1a from the initial mixture. X-ray analysis results showed that this complex was crystallized as solvated complex cis-[RhCl2L1(DMSO)2]DMSO. The catalytic activity of these complexes was then evaluated for the hydrogenation of various ketones. [ABSTRACT FROM AUTHOR]

Remarkable electronic lability is evident from a preliminary study of a dinuclear cobalt complex with a bis(dioxolene) bridging ligand and tetraazamacrocylic ancillary ligands. Structural, magnetic, spectroscopic, and electrochemical data indicate coinciding metal- and ligand-based mixed-valence involving cobalt(II)/cobalt(III) and catecholate/semiquinonate couples. A thermally stimulated spin-crossover or valence-tautomeric transition is also observed above 200 K. [ABSTRACT FROM AUTHOR]

Exploration of the reactivity of the versatile polyoxometalate precursor [As2W19O67(H2O)]14− with yttrium salts and organic proligands derived from 2-picolinic acid: 2,5-pyridinedicarboxylic acid (pdcH2) and 5-(methoxycarbonyl)-2-pyridinecarboxylic acid (mcpcH), has afforded the three new hybrid complexes [Y{AsW8O30}2(AsO)2{WO2(pdc)}2]13− (1) and [{Y(H2O)3}2{As2W19O68}{WO2(L)}2]8− (L− =pdcH− (2) or mcpc− (3)). The structurally-related and organic ligand free species [{Y(H2O)3}4{Y(H2O)6}2{As2W19O68}2{WO3(H2O)}4(AsO)2]20− (4) was also obtained. Structural characterization of the mixed salts of the four complexes, K8H5[1]·9H2O, K2.5H5.5[2]·37H2O, K2.5H5.5[3]·34H2O and K6Na2H4[4]·30H2O, has revealed that five membered N,O-chelated {WO2(L)} units play a key structural role in complexes 1–3. With no picolinate-based ligand present in 4, additional arsenite fragments bind to the analogous tungsten coordination sites. [ABSTRACT FROM AUTHOR]

The reaction of α‐keto‐stabilized diphosphine ylides [Ph2P(CH2)nPPh2═C(H)C(O)C6H4‐p‐CN] (n = 1 (Y1); n = 2 (Y2)) with dibromo(1,5‐cyclooctadiene) palladium(II)/platinum(II) complexes, [Pd/PtBr2(cod)], in equimolar ratio gave the new cyclometalated Pd(II) and Pt(II) complexes [Br2Pd(κ2‐Y1)] (1), [Br2Pt(κ2‐Y1)] (2), [Br2Pd(κ2‐Y2)] (3) and [Br2Pt(κ2‐Y2)] (4). These compounds were screened in a search for novel antibacterial agents and characterized successfully using Fourier transfer infrared and NMR (1H, 13C and 31P) spectroscopic methods. Also, the structures of complexes 1 and 2 were characterized using X‐ray crystallography. The results showed that the P,C‐chelated complexes 1 and 2 have structures consisting of five‐membered rings, while 3 and 4 have six‐membered rings, formed by coordination of the ligand through the phosphine group and the ylidic carbon atom to the metal centre. Also, a theoretical study of the structures of complexes 1–4 was conducted at the BP86/def2‐SVP level of theory. The nature of metal–ligand bonds in the complexes was investigated using energy decomposition analyses (EDA) and extended transition state combined with natural orbitals for chemical valence analyses. The results of EDA confirmed that the main portions of ΔEint, about 57–58%, in the complexes are allocated to ΔEelstat. New Pd/Pt complexes, P,C‐coordinated, were characterized using Fourier transform infrared and NMR (1H, 13C and 31P) spectroscopic methods and X‐ray crystallography. The results of energy decomposition analysis confirm that the main portions of ΔEint, about 57–58%, in the complexes are allocated to ΔEelstat. [ABSTRACT FROM AUTHOR]

The reaction of new phosphonium-phosphine oxide salt [P(O)Ph 2 (CH 2 ) 2 PPh 2 CH 2 C(O)C 6 H 4 NO 2 ]Br ( 1 ) with mercury(II) iodide in a methanolic solution yielded [P(O)Ph 2 (CH 2 ) 2 PPh 2 CH 2 C(O)C 6 H 4 NO 2 ] 2 [Hg 2 I 5 Br]( 2 ). These two compounds were fully characterized by elemental analysis, IR, 1 H, 31 P, and 13 C NMR spectra. Crystal and molecular structure of 2 has been determined by means of X-ray diffraction. In mercury compound, the phosphine oxide salt is found as a counter ion letting the mercury(II) ion to bound halides to all four coordination sites and to give dimermercurate(II) ions as the structure-constructing species. The neighboring [P(O)Ph 2 (CH 2 ) 2 PPh 2 CH 2 C(O)C 6 H 4 NO 2 ] 2+ cations are joined together by intramolecular C H⋯O hydrogen bonds to give a 1-D chain structure along the crystallographic b -axis. The [Hg 2 I 5 Br] 2− anions act as cross-linkers between neighbouring strands extending the supramolecular structure into 2D layers in (110) planes as well as balances the charge of the complex. The significant effects of C H⋯X (X O, Br and I) and π⋯π aromatic interactions play a major role in the crystal packing of compound 2 . [ABSTRACT FROM AUTHOR]

Five members of a new family of polyoxometalate (POM)-ligated tetranuclear rare earth metal complexes have been synthesized and characterized. These compounds have the general formula (HDABCO)8H5Li8[Ln4As5W40O144(H2O)10(gly)2]·25H2O [Ln = Gd (1), Tb (2), Dy (3), Ho (4) and Y = (5), HDABCO = monoprotonated 1,4-diazabicyclooctane, gly = glycine] and were synthesized from the preformed POM precursor [As2W19O67(H2O)]14-. The structure is comprised of two {As2W19O68} building blocks linked by a unit containing four rare earth ions and two additional tungsten centers, with the two glycine ligands playing a key bridging role. Two crystallographically distinct rare earth ions are present in each complex, both of which possess axially compressed, approximate square antiprismatic coordination geometry. The variable-temperature magnetic susceptibility profiles for 2-4 are dominated by population/depopulation of the MJ sublevels of the relevant ground terms, and fitting of the data has afforded the ligand field parameters in each case, from which the energies of the MJ sublevels can be calculated. Alternating current magnetic susceptibility data have revealed the onset of slow magnetic relaxation for 3, with the energy barrier to magnetization reversal determined to be 3.9(1) K. As for other lanthanoid complexes that display slow magnetic relaxation, this energy barrier is due to the splitting of the MJ sublevels of the Dy3+ ions such that the ground sublevel has a relatively large ∣MJ∣ value, thereby affording Ising-type magnetic anisotropy. This complex is thus the first POM-supported polynuclear lanthanoid-based SMM. Simulation of the W-band EPR spectrum of 1 has afforded the spin Hamiltonian parameters for this species, while the X-band EPR spectrum of 3 indicates the presence of a non-negligible fourth-order transverse component of the anisotropy, which is responsible for the small effective energy barrier observed for 3 and the absence of slow magnetic relaxation for 4. [ABSTRACT FROM AUTHOR]

Abstract: A trinuclear copper(II) complex and a tetranuclear copper(II) complex that each incorporate a 9-tungstoarsenate(III) polyoxoanion ligand and several 2,2′-bipyridine (2,2′-bpy) ligands co-crystallize as the acid form: H4[{Cu(2,2′-bpy)}3(α-AsW9O33)]·[{Cu(2,2′-bpy)2}{Cu(2,2′-bpy)}3(α-AsW9O33)]·38H2O (1). Compound 1 was obtained from a hydrothermal reaction employing the trivacant lacunary polyoxometalate [α-AsW9O33]9− as a precursor. The α-isomeric form of the parent ion is retained in both product anions. Four different coordination modes are observed for the seven copper centers, with unusual structural distortions imposed by the steric bulk of the polyanion. Intra- and intermolecular π-stacking of the 2,2′-bpy ligands are both evident. Variable temperature magnetic susceptibility, magnetization and EPR data are consistent with very weak antiferromagnetic interactions between the copper centers that are likely mediated by the π-stacking of the 2,2′-bpy ligands. [Copyright &y& Elsevier]

Graphical abstract Two mononuclear Pd/Pt complexes with new bidentate carbon donor ligand have been synthesized. All newly synthesized compounds were characterized by X-ray analysis and physicochemical and spectroscopic data. Theoretical study on the structure of all complexes was investigated. Cytotoxic activity of all complexes has been performed. Abstract The new phosphonium salt, the C,C-chelating phosphorus ylide ligand, (MeOC 6 H 5 C(O)CH PPh 2 (CH 2) 2 PPh 2 CHC(O)C 6 H 5 OMe), and its Pd(II) and Pt(II) complexes have been synthesized and the cytotoxic activity of the synthesized complexes against three human cancer cell lines, including HeLa (Human cervix cancer cell line), KB (human oral cancer cell line) and U87 MG (human glioblastoma cell line) were evaluated using an MTT assay. The new compounds were identified and characterized using multinuclear (1H, 13C and 31P) NMR, infrared (IR) spectroscopy, elemental analysis, and through UV absorption and fluorescence emission spectra. Also, the crystal structure of the phosphorus ylide ligand was determined by single-crystal X-ray diffraction analysis. According to the obtained results from the MTT assay, the Pd(II) and Pt(II) complexes demonstrated a higher cytotoxic activity against KB human oral cancer cells in comparison with other cell lines, rendering these compounds into suitable candidates for further anti-oral cancer studies. Furthermore, a theoretical study on structure and nature of the M C bonding between the Y ligand (ylide) and MCl 2 fragment in the [YMCl 2 ] (M = Pd, Pt and Y = (MeOC 6 H 5 C(O)CH PPh 2 (CH 2) 2 PPh 2 CHC(O)C 6 H 5 OMe)) complexes have been reported via NBO and energy-decomposition analysis (EDA). [ABSTRACT FROM AUTHOR]