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In nature, C-H bond oxidation of CH

Cytostatic metallo-drugs mostly bind to the nucleobases of DNA. A new family of dinuclear transition metal complexes was rationally designed to selectively target the phosphate diesters of the DNA backbone by covalent bonding. The synthesis and characterization of the first dinuclear NiII2 complex of this family are presented, and its DNA binding and interference with DNA synthesis in polymerase chain reaction (PCR) are investigated and compared to those of the analogous CuII2 complex. The NiII2 complex also binds to DNA but forms fewer intermolecular DNA cross-links, while it interferes with DNA synthesis in PCR at lower concentrations than CuII2. To simulate possible competing phosphate-based ligands in vivo, these effects have been studied for both complexes with 100-200-fold excesses of phosphate and ATP, which provided no disturbance. The cytotoxicity of both complexes has been studied for human cancer cells and human stem cells with similar rates of proliferation. CuII2 shows the lowest IC50 values and a remarkable preference for killing the cancer cells. Three different assays show that the CuII2 complex induces apoptosis in cancer cells. These results are discussed to gain insight into the mechanisms of action and demonstrate the potential of this family of dinuclear complexes as anticancer drugs acting by a new binding target.

Single-molecule magnets (SMMs) retain a magnetization without applied magnetic field for a decent time due to an energy barrier U for spin-reversal. Despite the success to increase U, the difficult to control magnetic quantum tunneling often leads to a decreased effective barrier U-eff and a fast relaxation. Here, we demonstrate the influence of the exchange coupling on the tunneling probability in two heptanuclear SMMs hosting the same spin-system with the same high spin ground state S-t = 21/2. A chirality-induced symmetry reduction leads to a switch of the Mn-III-Mn-III exchange from antiferromagnetic in the achiral SMM [(Mn6CrIII)-Cr-III](3+) to ferromagnetic in the new chiral SMM (RR)[(Mn6CrIII)-Cr-III](3+). Multispin Hamiltonian analysis by full-matrix i diagonalization demonstrates that the ferromagnetic interactions in (RR)[(Mn6CrIII)-Cr-III](3+) enforce a well-defined S, = 21/2 ground state with substantially less mixing of Ms substates in contrast to [(Mn6CrIII)-Cr-III](3+)and no tunneling pathways below the top of the energy barrier. This is experimentally verified as U-eff is smaller than the calculated energy barrier U in [114.n1116Cr1193 due to tunneling pathways, whereas U-eff equals U in (RR)[(Mn6CrIII)-Cr-III](3+) demonstrating the absence of quantum tunneling.

The reaction of the new dinucleating ligand susan(6-Me) with Fe(BF4)(2)6H(2)O results in formation of the homovalent (FeFeII)-Fe-II complex [(susan(6-Me)){Fe-II(-F)(2)Fe-II}](2+) and the mixed-valence (FeFeIII)-Fe-II complex [(susan(6-Me)){(FeF)-F-II(-F)(FeF)-F-III}](2+) depending on the absence or presence of dioxygen, respectively. Complex [(susan(6-Me)){(FeF)-F-II(-F)(FeF)-F-III}](2+) is the first molecular mixed-valence complex with a fluorido bridge. The short Fe-III-F bond of 1.87 a causes a large reorganization energy, resulting in a localized class II system with an intervalence charge-transfer band of high energy at 10000 cm(1).

A reversible carboxylate shift has been observed in a mu-oxo diferric complex in solution by UV-vis-NIR and FTIR spectroscopy triggered by the addition of a base or an acid. A terminal acetate decoordinates upon the addition of a proton, resulting in a shift of the remaining terminal acetato to a mu-eta(1) :eta(1) bridge. The addition of a base restores the original structure containing only terminal acetates. The implications for metalloenzymes with carboxylate-bridged nonheme diiron active sites are discussed.

The reaction of the new dinucleating ligand susan

The results are reported of an ab initio study of bromine dioxide BrO2, 1, and of the T-shaped trans- and cis-dihydroxides 2 and 3 of dihydrogen bromate (HO)2BrO. The thermochemistry has been explored of potential synthetic routes to (HO)2BrO involving water addition to BrO2, hydroxyl addition to bromous acid HOBrO, 4, protonation/reduction of bromic acid HOBrO2, 5, via tautomers 6-8 of protonated bromic acid, and by reduction/protonation of bromic acid via radical anion [HOBrO2](-), 9. The potential energy surface analyses were performed at the MP2(full)/6-311G* level (or better) and with the consideration of aqueous solvation at the SMD(MP2(full)/6-311G*) level (or better), and higher-level energies were computed at levels up to QCISD(full,T)/6-311++G(2df,2pd)//MP2. The addition of RO radical to bromous acid or bromite esters and the reduction of protonated bromic acid or protonated bromate esters are promising leads for possible synthetic exploration. Spin density distributions and molecular electrostatic potentials were computed at the QCISD(full)/6-311G*//MP2(full)/6-311G* level to characterize the electronic structures of 1-3. Both radicals employ maximally occupied (pseudo) π-systems to transfer electron density from bromine to the periphery. While the formation of the (3c-5e) π-system suffices to avoid hypervalency in 1, the formation of the (4c-7e) π-system in 2 or 3 still leaves the bromine formally hypervalent and (HO)2BrO requires delocalization of bromine density into σ*-SMOs over the trans O-Br-O moiety. Molecular orbital theory is employed to describe the mechanisms for the avoidance of hypervalency and for spin delocalization and spin polarization. The (4c-7e) π-system in 2 is truly remarkable in that it contains five π-symmetric spin molecular orbitals (SMO) with unique shapes.

The structural, spectroscopic, and magnetic properties of a series of [(Mn6CrIII)-Cr-III](3+) (= [{(talen(t-Bu2))-Mn-3(III)}(2){Cr-III(CN)(6)}](3+)) compounds have been investigated by single-crystal X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and electronic absorption spectroscopy, elemental analysis, electro spray ionization-mass spectrometry (ESI-MS) and matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS), cyclic voltammetry, AC and DC magnetic measurements, as well as theoretical analysis. The crystal structures obtained with [Cr-III(CN)(6)](3-) as a counterion exhibit (quasi-)one-dimensional (1D) chains formed by hydrogen-bonded (1) or covalently linked (2) trications and trianions. The rod-shaped anion lactate enforces a rod packing of the [(Mn6CrIII)-Cr-III](3+) complexes in the highly symmetric space group R (3) over bar (3) with a collinear arrangement of the molecular S-6 axes. Incorporation of the spherical anion BPh4- leads to less-symmetric crystal structures (4-6) with noncollinear orientations of the [(Mn6CrIII)-Cr-III](3+) complexes, as evidenced by the angle between the approximate molecular C-3 axes taking no specific values in the range of 2 degrees-69 degrees. AC magnetic measurements on freshly isolated crystals (1a and 3a-6a), air-dried crystals (3b-6b), and vacuum-dried powder samples (3c-6c) indicate single-molecule magnet (SMM) behavior for all samples with U-eff values up to 28 K. The DC magnetic data are analyzed by a full-matrix diagonalization of the appropriate spin-Hamiltonian including isotropic exchange, zero-field splitting, and Zeeman interaction, taking into account the relative orientation of the D-tensors. Simulations for 3a-6a and 3c-6c indicate a weak antiferromagnetic exchange between the Mn-III ions in the trinuclear subunits (J(Mn-Mn) = -0.70 to -0.85 cm(-1), (H) over cap (ex) = -2 Sigma(i(j),(S) over cap (j)) that is overcome by the stronger antiferromagnetic interaction via the Cr-C N-Mn pathway (J(Cr-Mn) = -3.00 to -5.00 cm(-1)), leading to an overall ferrimagnetic coupling scheme with an S-t = 21/2 spin ground state. The differences in U-eff, J(Mn-Mn), and J(Cr-Mn) for the investigated samples are rationalized in terms of subtle variations in the molecular and crystal structures. In particular, a magnetostructural correlation between the Mn-N-C N bond length and the J(Cr-Mn) exchange coupling is inferred from the magnetic measurements and corroborated by DFT calculations. The results of this detailed study on [(Mn6CrIII)-Cr-III](3+) allow the formulation of some key recipes for a rational improvement of the SMM behavior.

The new europium fluoride carbodiimide Eu(4)F(5)(CN(2))(2) was synthesized by solid state reaction from mixtures of EuF(3) and Li(2)(CN(2)) at 700 °C. The crystal structure as refined by single crystal X-ray diffraction (P ̅42(1)c, no. 114, a = 16.053(1) Å, c = 6.5150(6) Å, Z = 8) reveals three crystallographically distinct [N═C═N](2-) ions in the structure of mixed-valent Eu(4)F(5)(CN(2))(2). The presence of one Eu(3+) and three Eu(2+) per formula unit Eu(4)F(5)(CN(2))(2) is confirmed by magnetic measurements and (151)Eu-Mössbauer spectroscopy. The arrangement of Eu ions and gravity centers of [NCN](2-) ions in the structure of Eu(4)F(5)(CN(2))(2) follow the motif formed by atoms in the CuAl(2)-type structure. A possible high-symmetry structure of Eu(4)F(5)(CN(2))(2) is discussed on the basis of a group-subgroup scheme.

Tetracyanamidosilicates of the type ARE[Si(CN(2))(4)] with A = K, Rb, and Cs and RE = Y and La-Lu have been prepared by a solid-state metathesis reaction. The potassium compounds with RE = La-Gd crystallize orthorhombically in the space group P2(1)2(1)2. Rubidium as well as cesium compounds crystallize tetragonally in the space group I4. The luminescent properties of ARE[Si(CN(2))(4)]:Ln compounds with RE = Y, La, and Gd doped with 5 mol % Ln = Ce, Eu, or Tb were investigated. Temperature-dependent magnetic susceptibilities were measured for KGd[Si(CN(2))(4)]. The value of the magnetic moment is 7.3 mu(B)/Gd(3+) ion, which is in line with the expected value for the [Xe]4f(7) configuration of Gd(3+).