The design, synthesis, and structure determination of a pentacoordinate square-pyramidal molybdenum(VI) complex

Five new anionic aqueous dioxidovanadium­(V) complexes, [{VO2L1,2}­A­(H2O) n ]α (1–5), with the aroylhydrazone ligands pyridine-4-carboxylic acid (3-ethoxy-2-hydroxybenzylidene)­hydrazide (H2L1) and furan-2-carboxylic acid (3-ethoxy-2-hydroxybenzylidene)­hydrazide (H2L2) incorporating different alkali metals (A = Na+, K+, Cs+) as countercation were synthesized and characterized by various physicochemical techniques. The solution-phase stabilities of 1–5 were determined by time-dependent NMR and UV–vis, and also the octanol/water partition coefficients were obtained by spectroscopic techniques. X-ray crystallography of 2–4 confirmed the presence of vanadium­(V) centers coordinated by two cis-oxido-O atoms and the O, N, and O atoms of a dianionic tridentate ligand. To evaluate the biological behavior, all complexes were screened for their DNA/protein binding propensity through spectroscopic experiments. Finally, a cytotoxicity study of 1–5 was performed against colon (HT-29), breast (MCF-7), and cervical (HeLa) cancer cell lines and a noncancerous NIH-3T3 cell line. The cytotoxicity was cell-selective, being more active against HT-29 than against other cells. In addition, the role of hydrophobicity in the cytotoxicity was explained in that an optimal hydrophobicity is essential for high cytotoxicity. Moreover, the results of wound-healing assays indicated antimigration in case of HT-29 cells. Remarkably, 1 with an IC50 value of 5.42 ± 0.15 μM showed greater activity in comparison to cisplatin against the HT-29 cell line.

A new complex containing the {OVv(μ-O)VvO}4+ unit has been synthesized and structurally characterized. Cyclic voltammogram of this complex showed that the two VV centers of the V2O3 4+ core are found to undergo electrochemical reduction in two distinctly separate steps not observed previously in similar systems. A rare mixed-oxidation state species [L(O)VIVOVV(O)L]- has been electrogenerated from the structurally characterized parent divanadium (V) species in solution state and characterized by IR, EPR, and electronic spectroscopy.

4-(p-X-phenyl)thiosemicarbazone of napthaldehyde {where X = Cl (HL¹) and X = Br (HL²)}, thiosemicarbazone of quinoline-2-carbaldehyde (HL³) and 4-(p-fluorophenyl)thiosemicarbazone of salicylaldehyde (H₂L⁴) and their copper(I) {[Cu(HL¹)(PPh₃)₂Br]·CH₃CN (1) and [Cu(HL²)(PPh₃)₂Cl]·DMSO (2)} and copper(II) {[(Cu₂L³₂Cl)₂(μ-Cl)₂]·2H₂O (3) and [Cu(L⁴)(Py)] (4)} complexes are reported herein. The synthesized ligands and their copper complexes were successfully characterized by elemental analysis, cyclic voltammetry, NMR, ESI-MS, IR and UV-Vis spectroscopy. Molecular structures of all the Cu(I) and Cu(II) complexes have been determined by X-ray crystallography. All the complexes (1-4) were tested for their ability to exhibit DNA-binding and -cleavage activity. The complexes effectively interact with CT-DNA possibly by groove binding mode, with binding constants ranging from 10⁴ to 10⁵ M⁻¹. Among the complexes, 3 shows the highest chemical (60%) as well as photo-induced (80%) DNA cleavage activity against pUC19 DNA. Finally, the in vitro antiproliferative activity of all the complexes was assayed against the HeLa cell line. Some of the complexes have proved to be as active as the clinical referred drugs, and the greater potency of 3 may be correlated with its aqueous solubility and the presence of the quinonoidal group in the thiosemicarbazone ligand coordinated to the metal.

A series of mononuclear non-oxido vanadium(IV) [V(IV)(L(1-4))2] (1-4), oxidoethoxido vanadium(V) [V(V)O(L(1-4))(OEt)] (5-8), and dinuclear μ-oxidodioxidodivanadium(V) [V(V)2O3(L(1))2] (9) complexes with tridentate aroylazine ligands are reported [H2L(1) = 2-furoylazine of 2-hydroxy-1-acetonaphthone, H2L(2) = 2-thiophenoylazine of 2-hydroxy-1-acetonaphthone, H2L(3) = 1-naphthoylazine of 2-hydroxy-1-acetonaphthone, H2L(4) = 3-hydroxy-2-naphthoylazine of 2-hydroxy-1-acetonaphthone]. The complexes are characterized by elemental analysis, by various spectroscopic techniques, and by single-crystal X-ray diffraction (for 2, 3, 5, 6, 8, and 9). The non-oxido V(IV) complexes (1-4) are quite stable in open air as well as in solution, and DFT calculations allow predicting EPR and UV-vis spectra and the electronic structure. The solution behavior of the [V(V)O(L(1-4))(OEt)] compounds (5-8) is studied confirming the formation of at least two different types of V(V) species in solution, monomeric corresponding to 5-8, and μ-oxidodioxidodivanadium [V(V)2O3(L(1-4))2] compounds. The μ-oxidodioxidodivanadium compound [V(V)2O3(L(1))2] (9), generated from the corresponding mononuclear complex [V(V)O(L(1))(OEt)] (5), is characterized in solution and in the solid state. The single-crystal X-ray diffraction analyses of the non-oxido vanadium(IV) compounds (2 and 3) show a N2O4 binding set and a trigonal prismatic geometry, and those of the V(V)O complexes 5, 6, and 8 and the μ-oxidodioxidodivanadium(V) (9) reveal that the metal center is in a distorted square pyramidal geometry with O4N binding sets. For the μ-oxidodioxidodivanadium species in equilibrium with 5-8 in CH2Cl2, no mixed-valence complexes are detected by chronocoulometric and EPR studies. However, upon progressive transfer of two electrons, two distinct monomeric V(IV)O species are detected and characterized by EPR spectroscopy and DFT calculations.

A number of boronium ions with the general formula [R 2 BL 2 ] + (where L is a donor, such as an amine), some borenium [R 2 BL] + , and even borinium [R 2 B] + ions have been synthesized and structurally characterized. [1] In all these compounds, boron has a formal oxidation state of + III. In addition to the academic interest in the bonding properties in these species, some of them have found application as catalysts in polymerization [2] or Diels-Alder reactions.[3]Boronium cations are also efficient initiators for the dehydrogenation of ammonia-borane. [4] The boron atom of the boronium ions is more or less tetrahedrally coordinated by the two substituents R (for example, amido groups) and two donor ligands L (such as pyridine). In contrast, uncoordinated borinium species, such as the (dimethylamido)(2,2,6,6-tetramethylpiperidino)boron cation, [5] feature an almost linear NÀ BÀN unit.Herein we report the synthesis of the dication2+ (1; hpp = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidate), the first representative of a new class of boron dications with the general formula2+ (R being an amido group) having two boron atoms in the formal oxidation state + II. The surprisingly simple synthesis of 1 involves treating diborane(4) B 2 Cl 2 (NMe 2 ) 2 , prepared from B 2 (NMe 2 ) 4 , [6] with two equivalents of the free base hppH [see Eq. (1)]. Presumably, the diborane(4) species [{Me 2 NB(hpp)} 2 ] forms initially, which then reacts with the released HCl to form the salt [{Me 2 (H)NB(hpp)} 2 ](Cl) 2 . The hpp ligands stabilize the dinuclear species and protect it from oxidation or disproportionation.The chloride salt of 1 can be crystallized as a dichloromethane solvate from a mixture of dichloromethane/hexane. The structure of 1 as determined by X-ray diffraction measurements is given in Figure 1. The B À B bond (174.6 pm) lies well within the range of typical BÀB single bonds. For example, gas-phase electron diffraction measurements of B 2 (NMe 2 ) 4 and B 2 (OMe) 4 gave B À B bond lengths of 176.2(1.1) and 172.0(6) pm, respectively. [7] Recently we reported the synthesis of [{HB(hpp)} 2 ][8] containing a slightly longer BÀB single bond (177.2(3) pm). The BÀN bonds to the hpp ligands in 1 are 153.9-155.2 pm long, and the bonds to the two NMe 2 H ligands have lengths of 160.1 and 160.6 pm. For comparison, the B À N bonds to the hpp ligands in [{HB-(hpp)} 2 ] fall within the range 156.3(3)-158.2(3) pm.[8] The B À NHMe 2 bond lengths are similar to those reported for amine adducts of BH 3 . In H 3 BNH 3 , [9] H 3 BNMe 3 [10] and H 3 B(quinuclidine), [11] BÀN bonds of 156.4, 161.6, and 160.8 pm, respectively, were measured in the solid state. The

Three highly stable, hexacoordinated nonoxidovanadium(IV), V(IV)(L)2, complexes (1-3) have been isolated and structurally characterized with tridentate aroylhydrazonates containing ONO donor atoms. All the complexes are stable in the open air in the solid state as well as in solution, a phenomenon rarely observed in nonoxidovanadium(IV) complexes. The complexes have good solubility in organic solvents, permitting electrochemical and various spectroscopic investigations. The existence of nonoxidovanadium(IV) complexes was confirmed by elemental analysis, ESI mass spectroscopy, cyclic voltammetry, EPR, and magnetic susceptibility measurements. X-ray crystallography showed the N3O3 donor set to define a trigonal prismatic geometry in each case. All the complexes show in vitro insulin mimetic activity against insulin responsive L6 myoblast cells, with complex 3 being the most potent, which is comparable to insulin at the complex concentration of 4 μM, while the others have moderate insulin mimetic activity. In addition, the in vitro antiproliferative activity of complexes 1-3 against the HeLa cell line was assayed. The cytotoxicity of the complexes is affected by the various functional groups attached to the bezoylhydrazone derivative and 2 showed considerable antiproliferative activity compared to the most commonly used chemotherapeutic drugs.

Eight alkali metal ion-mediated dioxidovanadium(v), [{V(V)O2L(1-6)}A(H2O)n]∝, complexes for A = Li(+), Na(+), K(+) and Cs(+), containing tridentate aroylhydrazonate ligands coordinating via ONO donor atoms, are described. All the synthesised ligands and the metal complexes were successfully characterised by elemental analysis, IR, UV-Vis and NMR spectroscopy. X-ray crystallographic investigation of 3, 5-7 shows the presence of distorted NO4 coordination geometries for LVO2(-) in each case, and varying μ-oxido and/or μ-aqua bridging with interesting variations correlated with the size of the alkali metal ions: with small Li(+), no bridging-O is found but four ion aggregates are found with Na(+), chains for K(+) and finally, layers for Cs(+). Two (5) or three-dimensional (3, 6 and 7) architectures are consolidated by hydrogen bonding. The dioxidovanadium(v) complexes were found to exhibit DNA binding activity due to their interaction with CT-DNA by the groove binding mode, with binding constants ranging from 10(3) to 10(4) M(-1). Complexes 1-8 were also tested for DNA nuclease activity against pUC19 plasmid DNA which showed that 6 and 7 had the best DNA binding and photonuclease activity; these results support their good protein binding and cleavage activity with binding constants ranging from 10(4) to 10(5) M(-1). Finally, the in vitro antiproliferative activity of all complexes was assayed against the HeLa cell line. Some of the complexes (2, 5, 6 and 7) show considerable activity compared to commonly used chemotherapeutic drugs. The variation in cytotoxicity of the complexes is influenced by the various functional groups attached to the aroylhydrazone derivative.