Syntheses, spectroscopic and molecular quadratic nonlinear optical properties of dipolar ruthenium(II) complexes of the ligand 1,2-phenylenebis(dimethylarsine)

摘要

Six new complex salts trans-[(RuCl)-Cl-II(pdma)(2)L][PF6](n) [pdma=1,2-phenylenebis(dimethylarsine); L=(E,E,E)-1,6-bis(4-pyridyl) hexa-1,3,5-triene (bph), n=1, 5; L=N-methyl-4-[(E)-2-(4-pyridyl) ethenyl]pyridinium (Mebpe(+)), n=2, 7; L=N-methyl-4-[(E,E)-4-(4-pyridyl)buta-1,3-dienyl]pyridinium (Mebpb(+)), n=2, 8; L=N-methyl-4-{(E,E,E)-6-(4-pyridyl)hexa-1,3,5-trienyl} pyridinium (Mebph(+)), n=2, 9; L=bis(4-pyridyl) acetylene (bpa), n=1, 10; L=N-methyl-4-[2-(4-pyridyl)ethynyl] pyridinium (Mebpa(+)), n=2, 11] have been prepared. The electronic absorption spectra of 5 and 7-11 display intense, visible metal-to-ligand charge-transfer (MLCT) bands, with lambda(max) values in the range 434-492 nm in acetonitrile. Cyclic voltammetric studies reveal reversible Ru-III/II waves with E-1/2 values in the range 1.06-1.15 V vs. Ag-AgCl, together with irreversible L-based reduction processes. Along with a number of previously reported related compounds (B. J. Coe et al., J. Chem. Soc., Dalton Trans., 1996, 3917; 1997, 591; 2000, 797), salts 5 and 7-11 have been investigated by using Stark (electroabsorption) spectroscopy in butyronitrile glasses at 77 K. These studies have afforded dipole moment changes Deltamu(12) for the MLCT transitions which have been used to calculate molecular static first hyperpolarizabilities beta(0) according to the two-state equation beta(0)=3Deltamu(12)(mu(12))(2)/(E-max)(2) (mu(12)=transition dipole moment, E-max=MLCT energy). MLCT absorption and electrochemical data show that a trans-{(RuCl)-Cl-II(pdma)(2)}(+) centre is considerably less electron-rich than a {Ru-II(NH3)(5)}(2+) unit. Although the beta(0) responses of the pdma complexes are only a little smaller than those of their {Ru-II(NH3)(5)}(2+) analogues, this result is partly attributable to unexpected changes in the relative mu(12) values on freezing. Thus, substantial increases in mu(12) for the arsine compounds act to partially offset the beta(0)-decreasing influence of their higher E-max values when compared with the analogous pentaammine species. Single crystal X-ray structures have been obtained for the salts 1.2.5MeCN, 4.2MeCN, 7 and 11, but only 1.2.5MeCN adopts a non-centrosymmetric space group (Fdd2) such as may show bulk NLO effects.