Determination of ZFS parameters from the EPR spectra of mono-, di- and trinuclear MnII complexes: impact of magnetic coupling

A family of new Mn^II compounds, consisting of seven dinuclear, three mononuclear, and four trinuclear ones, were synthesised using benzoic acid derivatives n-RC₆H₄COOH, where n-R = 2-MeO, 3-MeO, 4-MeO, or 4-^tBu, and 2,2'-bipyridine (bpy) or 1,10-phenantroline (phen) as blocking ligands. The crystal structures of nine of these compounds and the magnetic studies of all of them are reported here. Each type of compound was formed depending on the presence or absence of ClO₄^- ions, the solvent used, and/or the presence of a small amount of water in the reaction medium. The use of the tert-buthylbenzoate ligand gave unexpected results, very likely due to the steric hindrance caused by the voluminous ^tBu groups. The EPR spectra of each type of compound give some peculiar features that allow its identification. Attempts to fit these spectra have been made in order to determine the ZFS parameters, D and E, of the Mn^II ion (for mononuclear and dinuclear systems) or of the ground state (for trinuclear systems). For trinuclear systems, the single-ion ZFS parameters estimated from those of the ground state provided a good simulation of the EPR spectra of these compounds. The EPR signals observed in each case have been rationalised according to the energy level distribution and the plausible population in the excited states. In some particular situations, the sign of D_Mn could be determined from the fit of the EPR spectra of the antiferromagnetic dinuclear compounds, the source of the difference between the spectra lying in the second excited state.

Syntheses, structures, and chiroptical and magnetic properties of chiral clusters built from Schiff bases: a novel [MnIIMnIII6NaI2] core

Enantiomeric pairs of clusters with Mn^IIMnIII3Na^I and the unprecedented Mn^IIMnIII6NaI2 cores have been synthesized employing enantiomerically pure Schiff bases.

Singlet ground states in compounds with a [MnIII4O2]8+ core due to broken degeneration

Energy distribution of spin states depending on the distinction between the magnetic interactions. Singlet ground states due to broken degeneration of S_T ≠ 0 states. Attempt to assign spin states to a particular spin configuration.

New insights into the comprehension of the magnetic properties of dinuclear Mn(III) compounds with the general formula [{MnL(NN)}2(μ-O)(μ-n-RC6H4COO)2]X2

Five new dinuclear Mn(iii) compounds with benzoato derivative bridges [{Mn(bpy)L}2(μ-O)(μ-n-RC6H4COO)2]X2 (n-R = 3-MeO, 4-MeO and 4-tBu, X = NO3(-) and ClO4(-)) were synthesised and characterised. According to X-ray diffraction, the X anions tend to be coordinated to the Mn ions and may occupy the place of the monodentate ligand L. Two structural isomers that only differ in one of their monodentate ligands have been obtained with the 3-MeOC6H4COO(-) bridges. For all compounds, the Mn(iii) ions display elongated octahedra with a pronounced rhombic distortion. To quantify these distortions separately, the elongation and rhombicity parameters Δ and ρ have been defined. The magnetic study shows a good relationship between the distortion of the coordination polyhedra and the zero field splitting parameters (DMn and EMn). From the magnetic data of a powder sample, it is possible to determine the sign and magnitude of DMn for ferromagnetic systems or weak antiferromagnetic systems with DMn < 0. For this kind of dinuclear compound, the R group at the meta position, the rhombic distortion of the octahedra, and large torsion angles between the Jahn-Teller axes lead to ferromagnetic interactions.

A Ferromagnetic Salicylaldoximate/Azide Mn(II)2Mn(III)6 Cluster with an S = 17 Ground State and a Single-Molecule-Magnet Response

One new Mn(II)2Mn(III)6 cluster exhibiting an S = 17 spin ground state and single-molecule-magnet properties has been designed linking Mn(III)3-salicylaldoximate triangles and tetracoordinated Mn(II) cations by means of end-on azido bridges. The ferromagnetic coupling has been rationalized as a function of their structural parameters.

Neutral and ionic platinum compounds containing a cyclometallated chiral primary amine: synthesis, antitumor activity, DNA interaction and topoisomerase I-cathepsin B inhibition

The synthesis and preliminary biological evaluation of neutral and cationic platinum derivatives of chiral 1-(1-naphthyl)ethylamine are reported, namely cycloplatinated neutral complexes [PtCl{(R or S)-NH(2)CH(CH(3))C(10)H(6)}(L)] [L = SOMe(2) ( 1-R or 1-S ), L = PPh(3) (2-R or 2-S), L = P(4-FC(6)H(4))(3) (3-R), L = P(CH(2))(3)N(3)(CH(2))(3) (4-R)], cycloplatinated cationic complexes [Pt{(R)-NH(2)CH(CH(3))C(10)H(6)}{L}]Cl [L = Ph(2)PCH(2)CH(2)PPh(2) (5-R), L = (C(6)F(5))(2)PCH(2)CH(2)P(C(6)F(5))(2) (6-R)] and the Pt(ii) coordination compound trans-[PtCl(2){(R)-NH(2)CH(CH(3))C(10)H(6)}(2)] (7-R). The X-ray molecular structure of 7-R is reported. The cytotoxic activity against a panel of human adenocarcinoma cell lines (A-549 lung, MDA-MB-231 and MCF-7 breast, and HCT-116 colon), cell cycle arrest and apoptosis, DNA interaction, topoisomerase I and cathepsin B inhibition, and Pt cell uptake of the studied compounds are presented. Remarkable cytotoxicity was observed for most of the synthesized Pt(ii) compounds regardless of (i) the absolute configuration R or S, and (ii) the coordinated/cyclometallated (neutral or cationic) nature of the complexes. The most potent compound 2-R (IC(50) = 270 nM) showed a 148-fold increase in potency with regard to cisplatin in HCT-116 colon cancer cells. Preliminary biological results point out to different biomolecular targets for the investigated compounds. Neutral cyclometallated complexes 1-R and 2-R, modify the DNA migration as cisplatin, cationic platinacycle 5-R was able to inhibit topoisomerase I-promoted DNA supercoiling, and Pt(ii) coordination compound 7-R turned out to be the most potent inhibitor of cathepsin B. Induction of G-1 phase ( 2-R and 5-R ), and S and G-2 phases (6-R) arrests are related to the antiproliferative activity of some representative compounds upon A-549 cells. Induction of apoptosis is also observed for 2-R and 6-R.

Kinetico-mechanistic studies on the formation of seven-membered [C,N]-platinacycles: the effect of methyl or fluoro substituents on the aryl ancillary ligands

The reactions of dinuclear [Pt2(4-RC6H4)4(μ-SEt2)2] (R = Me or F), or mononuclear [Pt(4-RC6H4)2(SMe2)2] (R = Me or H), platinum(ii) compounds with imines of the general formula 2-X,6-YC6H3CH[double bond, length as m-dash]NCH2Ph (X = Br, Y = F; X = Cl, Y = F; X = Br, Y = H) produced seven-membered [C,N]-platinacycles. The reaction consists of the initial formation of cyclometallated platinum(iv) compounds followed by a three step process: reductive elimination, isomerisation of the resulting non-cyclometallated intermediate and a final cycloplatination process. Combined (1)H NMR and UV-Vis kinetico-mechanistic studies indicated that the rate determining step of the process depends on the nature of the aryl-Pt ligand (phenyl, p-tolyl or p-fluorophenyl).

Copper(ii) cubanes with a {Cu4O} core and well defined S = 1 ground state

Three copper cubanes with the unusual S = 1 ground state have been characterized and their magnetic properties rationalized as a function of the asymmetry of the {Cu₄O₄} cage and correlated with the Cu–O–Cu bond angles.

Ruthenium complexes of P-stereogenic phosphines with a heterocyclic substituent

Optically pure P-stereogenic monophosphorus ligands containing a heterocyclic substituent have been prepared. They have been coordinated to Ru-η⁶-arene moieties in which the ligands act as mono- or bidentate. The complexes catalyse asymmetric transfer hydrogenation reactions with up to 70% ee.

Magnetic Behavior of Heterometallic Wheels Having a [Mn(IV)6M2O9](10+) Core with M = Ca(2+) and Sr(2+)

Two new heterometallic Mn(IV)-M(2+) compounds with formula [Mn6M2O9(4-(t)BuC6H4COO)10(4-(t)BuC6H4COOH)5] (M = Ca(2+) (1), Sr(2+) (2)) have been crystallized. The core of both compounds consists of a planar Mn6 ring, where the Mn(IV) ions are alternatively bridged by (μ3-O)2(μ-RCOO) and (μ4-O)(μ-RCOO)2 ligands, and the two alkaline earth ions are located to both sides of the wheel, linked to the oxo bridges, generating three fused [Mn2M2O4](4+) cuboids. These compounds show a net antiferromagnetic behavior, more important for 2 (Sr(2+)) than for 1 (Ca(2+)). The fitting of the experimental data was performed with the support of DFT calculations, considering four different exchange pathways: two between adjacent Mn(IV) ions (J1 and J2) and two between nonadjacent Mn(IV) ions (J3 and J4). The results of the analysis show that J1 and J2 are of the opposite sign, the ferromagnetic contribution corresponding to the [Mn2(μ4-O)(μ-RCOO)2](4+) unit (J2). The influence of the M(2+) ions in the magnetic behavior is analyzed for 1 and 2 and for three hypothetical models with the structural parameters of 1 containing Mg(2+), Sr(2+) or without the M(2+) ions. In spite of the diamagnetic character of the alkaline earth ions, their influence on the magnetic behavior has been evidenced and correlated with their polarizing effect. Moreover, the magnetic interactions between nonadjacent ions are non-negligible.

Kinetico-mechanistic studies of substitution reactions on cross-bridged cyclen Co(III) complexes with nucleosides and nucleotides

Kinetico-mechanistic studies on the substitution reactivity of the [Co{(μ-ET)cyclen}(H2O)2](3+) complex cation at pH values within the 6.0-7.0 range with biologically significant ligands have been carried out. The substitution processes have been found to occur exclusively on the mono-hydroxobridged [(Co{(μ-ET)cyclen}(H2O))2(μ-OH)](5+) species formed after equilibration of the cobalt complex in the relevant medium. The studies conducted on the substitution of the aqua/hydroxo ligands of this dinuclear species are indicative of a dominant role of outer-sphere complexation, involving hydrogen-bonding interactions. The values of the outer-sphere complex formation equilibrium constant are in line with the intervention of both the exiting aqua ligands and the NH groups at the encapsulating {(μ-ET)cyclen} ligand. These complexes result in the preferential formation of O- or N-bonded nucleotides depending on the structure of the base moiety of the ligand. Even the entry of the different donor bonded nucleotides is hampered by the hydrogen-bonding interaction with the dangling moiety of an already coordinated ligand. In general the overall substitution processes occur at a faster rate than those published for the fully alkylated encapsulating {(Me)2(μ-ET)cyclen} ligand derivative, as expected for the still available base-catalysing NH groups in the {(μ-ET)cyclen} ligand.

Short Access to Belt Compounds with Spatially Close C=C Bonds and Their Transannular Reactions

Two domino Diels-Alder adducts were obtained from 3,7-bis(cyclopenta-2,4-dien-1-ylidene)-cis-bicyclo[3.3.0]octane and dimethyl acetylenedicarboxylate or N-methylmaleimide under microwave irradiation. From the first adduct, a C20H24 diene with C2v symmetry was obtained by Zn/AcOH reduction, hydrolysis, oxidative decarboxylation, and selective hydrogenation. Photochemical [2+2] cycloaddition of this diene gave a thermally unstable cyclobutane derivative, which reverts to the diene. However, both the diene and the cyclobutane derivatives could be identified by X-ray diffraction analysis upon irradiation of the diene crystal. New six-membered rings are formed upon the transannular addition of bromine or iodine to the diene. The N-type selectivity of the addition was examined by theoretical calculations, which revealed the distinct susceptibility of the doubly bonded carbon atoms to the bromine attack.

Optimization of xanthatin extraction from Xanthium spinosum L. and its cytotoxic, anti-angiogenesis and antiviral properties

The aqueous extraction of the sesquiterpene lactone xanthatin from Xanthium spinosum L. favours the conversion of xanthinin (1) to xanthatin (2) via the loss of acetic acid. The cytotoxic (Hep-G2 and L1210 human cell lines) and antiviral activities of isolated xanthatin are established. This natural compound shows significant cytotoxicity against the Hep-G2 cell line and our experimental results reveal its strong anti-angiogenesis capacity in vitro. The structure of xanthatin is determined by spectroscopic methods and for the first time confirmed by X-ray diffraction.