Icosane

Abstract: The temperature dependence of the magnetic susceptibility (4.2-300 K) is reported for a series of crystalline salts of first-row transition-metal ions encapsulated by hexaamine ligands of the sar type where sar =3,6,10,13,16,19-hexaazabicyclo [6.6.6] icosane

Abstract: The copper(II) complex of the N4S2 encapsulating ligand 1-methyl-8-ammonio-3,13-dithia-6,10,16,19-tetraazabicyclo-[6.6.6]icosane,[Cu(AMN4S2sarH)]3+, is reported. Crystals of the complex are monoclinic, of space group P21/a (Z = 4, a = 16.463(3) A, b = 11.073(3) A, c = 17.138(3) A, β = 106.20(1)°, R = 0.053 (3449 F)). The coordination about the copper(II) atom is a distorted version of a 4 + 2 elongated octahedron with the pronounced tetragonal distortion arising from long Cu—N and Cu—S axial bonds of 2.447(5) and 2.600(2) A, respectively. The presence of longer Cu—S bonds (2.436(2), 2.600(2) A) cis to shorter Cu—N bonds (2.012(5), 2.029(5) A) results in a tilting of the capping groups in relation to the pseudo-3-fold axis of the metal complex, the two caps being eclipsed with respect to one another. The randomly orientated frozen solution EPR spectrum and lowtemperature (~10 K) absorption spectrum are indicative of an orthorhombically distorted complex with a pronounced tetragonal elongation, consistent with the crystal structure determination and room-temperature magnetic moment of 1.75 μB. Computer simulation of the randomly orientated frozen solution X-band EPR spectrum yielded gz = 2.189, gx = 2.048, gy = 2.074, and Az = 160.5 × 10−4 cm−1. Ligand nitrogen hyperfine coupling was not resolved on the MI = −/2 parallel resonance at S-band microwave frequencies, presumably a consequence of the low symmetry around the Cu(II) ion. From the analysis of the absorption spectrum, angular-overlap-model ligandfield parameters of eσ (N) = 6000, eσ(S) = 6100 cm−1 (for the shortest Cu—N and Cu—S bonds), ζ= 600 cm−1, and k = 0.69 were obtained, resulting in calculated g values in very good agreement with those found from EPR measurements.

Abstract: Syntheses based on the reaction of Pt(en)/sub 3//sup 4 +/ with formaldehyde, and ammonia or nitromethane, yielded the macrobicyclic complexes (1,3,6,8,10,13,16,19-octaazabicyclo(6.6.6)icosane)platinum(IV), Pt(sep)/sup 4 +/, and (1,8-dinitro-3,6,10,13,16,19-hexaazabicyclo(6.6.6)icosane)platinum(IV), Pt(diamsar)/sup 4 +/, respectively. Reduction of the latter complex with SnCl/sub 2/ in acid yielded (1,8-diamino-3,6,10,13,16,19-hexaazabicyclo(6.6.6)icosane)platinum(IV), Pt(diamsar)/sup 4 +/. These complexes are substitution-inert, diamagnetic octahedral ions and were characterized by X-ray crystallographic analysis of the Pt(sep)/sup 4 +/ by absorption and NMR spectroscopy. Addition of an electron to the Pt(IV) complexes, radiolytically or electrochemically, yielded transient monomeric macrobicyclic Pt(III) ions. ..gamma..-Radiolysis of crystalline samples yielded a Pt(III) complex stabilized in the crystalline lattice, detected by ESR spectroscopy. Polarography of Pt(diamsar)/sup 4 +/ in aprotic solvent showed essentially irreversible one-electron reductions at +0.17 and -1.00 V and two-electron irreversble reduction at -2.20 V (in acetone, vs Ag/AgCl). The Pt(III) transient of the first reduction decayed (t/sub 1///sub 2/ < 10/sup -3/ s) to yield the monodeprotonated Pt(IV) complex and 0.5 mol of hydrogen/mol of complex. The liftime of the related Pt(sep)/sup 3 +/ transient was longer, though still in the millisecond range. This intramolecular redox process in aprotic solvents was not observed in water, however. In aqueous solution, the Pt(diamsar)/sup 3 +/ transient decayed withmore » a first-order rate constant of 6 X 10/sup -3/ s/sup -1/ (pH 6.8 or 10.0) in pulse radiolysis experiments.« less

Abstract: The oxidation of 4,4′-dimethyl-2,2′-bipyridine with potassium permanganate in water gives 2,2′-bipyridine-4,4′-dicarboxylic acid and 4′-methyl-2,2?-bipyridine-4-carboxylic acid. The latter acid is oxidized to the diacid by boiling nitric acid. Complexes of the type Ru ( bpy )2L2+ have been prepared where L is 2,2′-bipyridine-4,4′- dicarboxylic acid, diethyl 2,2′-bipyridine-4,4′-dicarboxylate, 4′- methyl-2,2′-bipyridine-4-carboxylic acid and ethyl 4′-methyl-2,2′- bipyridine-4-carboxylate. These complexes have been compared with [ Ru ( bpy )3]2+ as sensitizers for the photoreduction of water. Stern- Volmer analysis has been applied to the quenching of their luminescence by methylviologen (mv2+), [Co(sep)]3+ (sep is 1,3,6,8,10,13,16,19- octaazabicyclo [6.6.6] icosane ) and [Co( CLsar )]3+ ( CLsar is 1-chloro- 3,6,10,13,16,19-hexaazabicyclo[6.6.6] icosane ). Changes in the Stern-Volmer constants have been related to the free energy changes associated with the oxidative quenching and the overall charges of the ruthenium complexes. The rates of formation of hydrogen compared favourably in sacrificial cycles with the ruthenium complexes as sensitizers, mv2+, Co(sep)3+ as electron-transfer agents, platinum/poly(vinyl alcohol) as catalyst, and ethylenediaminetetraacetic acid as electron donor. The results obtained have been discussed in terms of variations in the efficiencies of cage escape in the oxidative quenching and competition between electron transfer and energy transfer.