Electronic Spectra of the Tetraphenylcyclobutadienecyclopentadienylnickel(II) Cation and Radical.

Properties of the tetraphenylcyclobutadienecyclopentadienylnickel(II) cation 1 and its tetra-o-fluoro derivative 1a have been measured and calculated. The B3LYP/TZP optimized geometry of the free cation 1 agrees with a single-crystal X-ray diffraction structure except that in the crystal one of the phenyl substituents is strongly twisted to permit a close-packing interaction of two of its hydrogens with a nearby BF4(-) anion. The low-energy parts of the solution electronic absorption and magnetic circular dichroism (MCD) spectra of 1 and 1a have been interpreted by comparison with TD-DFT (B3LYP/TZP) results. Reduction or pulse radiolysis lead to a neutral 19-electron radical, whose visible absorption and MCD spectra have been recorded and interpreted as well. The reduction is facilitated by ∼0.1 V upon going from 1 to 1a. Unsuccessful attempts to prepare several other aryl substituted derivatives of 1 by the classical synthetic route are described in the Supporting Information .

Characterization and in vitro cytotoxicity testing of ethanolamine-derived cadmium chelating agents.

We have synthesized and characterized the new cadmium chelating agent potassium bis(2-hydroxyethyl)aminoethyldithiocarbonate hemihydrate, K[bhexan] x 0.5H2O (2), that is structurally related to the known effective in vivo cadmium chelating agent potassium bis(2-hydroxyethyl)dithiocarbamate, K[bhedtc] (1). The corresponding cadmium complex of 2 differs from di(bis(2-hydroxyethyl)dithiocarbamato)cadmium(II), Cd(bhedtc)2 (3), in that the insoluble compound exhibits an elemental composition consistent with a cadmium:ligand ratio of 2:1. The cytotoxicity of the 1-3 was investigated using the human osteoblast-like cell line, Saos-2. Compounds 1 or 2 did not affect cell adherence or cell viability in the 100-500 microM concentration range studied, whereas 3 resulted in a concentration-dependent increase in loss of cell adherence and decrease in cell viability. Overall, the results of the loss of cell adherence, trypan blue exclusion and MTT assays showed that administration of 3 (cadmium complex of 1) resulted in cytotoxicity lower than that of cadmium chloride, but higher than that of the chelator 1 alone. The effect of simultaneous addition of cadmium chloride and 1 or 2 on cell viability was also assessed using the MTT assay. For the 100 microM cadmium chloride experiments, cell viability comparable to control cells was achieved for both 1 and 2 in the 100-500 microM concentration range studied. Cell viability comparable to control cells was achieved for 1 but not 2 in the 100-500 microM concentration range studied for the 200 microM cadmium chloride experiments. Thus 1 appears more effective than 2 in the ability to mediate the cytotoxic effects of cadmium in vitro upon concomitant administration.

Oligomers of "extended viologen", p-phenylene-bis-4,4'-(1-aryl-2,6-diphenylpyridinium), as candidates for electron-dopable molecular wires.

We report the synthesis and spectral characterization of the first five members of an oligomeric series built from alternating p-connected 1,4-benzene and 1,4-pyridinium rings, 1[n]-4[n], n=1-5, with p-phenylene-bis-4,4'-(1-aryl-2,6-diphenylpyridinium) ("extended viologen") as the repeating unit. The lengths of these rodlike molecules range from 2 to 9 nm. The monomer was obtained from p-phenylene-bis-4,4'-(2,6-diphenylpyrylium) (5) and p-phenylenediamine (6) or p-aminoacetanilide (9). Higher oligomers were synthesized by stepwise elaboration of the monomer by reactions with the appropriate bis-pyrylium (5) or pyrylium-phenylene-pyridinium (8) salts. Eight different counterions were used, and dodecamethylcarba-closo-dodecaborate was found to offer particularly favorable solubility characteristics. Ultraviolet absorption spectra of the oligomers suggest that the individual extended viologen segments interact only weakly, as a result of the strongly twisted orientation of the benzene rings that separate them. The UV spectrum of the monomer was interpreted by comparison with semiempirical INDO/S calculations performed at a DFT optimized geometry.

Anionic carbonato and oxalato cobalt(III) nitrogen mustard complexes.

Synthetic approaches to cobalt(III) complexes [Co(L)(L')2] containing the bidentate dialkylating nitrogen mustard N,N-bis(2-chloroethyl)-1,2-ethanediamine (L = dce) together with anionic ancilliary ligands (L') which are either carbonato (CO3(2-)), oxalato (ox2-), bis(2-hydroxyethyl)dithiocarbamato (bhedtc-), 2-pyridine carboxylato (pico-) or 2-pyrazine carboxylato (pyzc-) were investigated. Synthetic routes were developed using the related amines N,N-diethyl-1,2-ethanediamine (dee) and 1,2-ethanediamine (en). The complexes [Co(CO3)2(L)]- (L = dee 1, dce 2), [Co(ox)2(L)]- (L = dee 3, dce 4), [Co(bhedtc)2(dee)]+ 5, [Co(bhedtc)2(en)]+ 6, mer-[Co(pico)3], mer-[Co(pyzc)]3 7 and [Co(pico)2(dee)]+ 8 were prepared and were characterised by IR, UV-Vis, 1H and 13C[1H] NMR spectroscopy, mass spectrometry and cyclic voltammetry. [Co(bhedtc)2(en)]BPh4 6b and trans(O)-[Co(pico)2(dee)]ClO4 8 were characterised by X-ray crystallography. In vitro biological tests were carried out on complexes 1-4 in order to assess the degree to which coordination of the mustard to cobalt attenuated its cytotoxicity, and the differential toxicity in air vs. nitrogen.