Vinylogue mono- and bimetallic cationic sesquifulvalene and monohydro sesquifulvalene complexes for second harmonic generation

The donor-acceptor complexes with a vinylogue monohydro sesquifulvalene and sesquifulvalene backbone of the type [eta(5)-C5H5)Ru{mu-(eta(5)-C5H4)C2H2(eta(6)-C7H7)}ML](PF6)(n) [n = 0: ML = none (1), Cr(CO)(3) (2); n = 1: ML = Ru(eta(5)-C5H5) (3a), Ru(eta(5)-C5Me5) (3b)] and [(eta(5)-C5H5)Ru{mu-(eta(5)-C5H4)C2H2(eta(7)- C7H6)}ML](PF6)(n) [n = 1: ML = none (4), Cr(CO)3 (5); n = 2: NIL = Ru(eta(5)-C5H5) (6a), Ru(eta(5)-C5Me5) (6b)], respectively, have been synthesised, and spectroscopically and structurally characterised. A charge-shift correlation was carried out by means of H-1 NMR spectroscopic studies and an increased ground-state donor-acceptor interaction in the order 5 < 6b < 4 < 6a was found. The corresponding donor-acceptor interaction in 3a and 3b varies by an insignificant amount. Hyper-Rayleigh scattering (HRS) was applied to determine the first hyperpolarisability beta of the mono- and dicationic complexes 3a-6b. The beta values obtained for the cationic sesquifulvalene complexes 4-6b are among the largest ever measured for ruthenocenyl containing complexes due to a strong resonance enhancement: the sesquifulvalene complexes 4-6a, 6b show first hyperpolarisabilities which range between 360 and 700 x 10(-30) esu, whereas beta for the monohydrosesquifulvalene complexes are considerably lower (75 and 162 x 10(-30) esu). For the latter complexes the first hyperpolarisability doubles on going from Ru(eta(5)-C5Me5) (3b) to Ru(eta(5)-C5H5) (3a) in the acceptor unit.