(1-Ferrocenyl-η⁶-borabenzene)(η⁵-cyclopentadienyl)cobalt(1+):  A New Heterobimetallic Basic NLO Chromophore^,

Abstract

The heterobimetallic cationic NLO chromophore (1-ferrocenyl-η6-borabenzene)(η5-cyclopentadienyl)cobalt(1+) ([{1-((η5-C5H5)Fe(η5-C5H4))-η6-BC5H5}Co(η5-C5H5)]+, 1 +) has been synthesized by reaction of FcBBr2 and cobaltocene and subsequent oxidation with FeCl3. The neutral bimetallic compound 1 is paramagnetic and exhibits an ESR spectrum similar to that of the mononuclear 19-valence-electron complex Co(1-Ph-η6-borabenzene)2. Complex 1-PF6 crystallizes in monoclinic space group P21/c with a = 10.541(3) Å, b = 17.647(5) Å, c = 10.965(3) Å, β = 96.38(2)°, Z = 4, and V = 2027.0(10) Å3. NMR data for the oxidized diamagnetic cation 1 + indicate that the positive charge is predominantly localized on the (borabenzene)cobalt moiety. The X-ray structure determination of 1-PF6 shows the two sandwich units in mutually trans positions. The structural data denote an increased electronic interaction between the donating ferrocenyl group and the borabenzene unit. A cyclic voltammetric study of 1-PF6 or 1 reveals three reversible redox couples (−1/0, 0/+1, +1/+2), resembling those of the mononuclear parent compounds, although the redox potentials are slightly shifted due to the mutual influence of the electron-donating and -accepting properties of the different sandwich units. The UV−vis spectrum of 1 + confirms the enhanced donor−acceptor interaction by a strong, negative solvatochromic absorption about λ = 600 nm which is assigned to a charge-transfer transition. The determination of the first hyperpolarizability β by means of hyper Rayleigh scattering yields (90 ± 30) × 10-30 esu, which is unexpectedly high in the face of the directly coupled donor−acceptor pair.

Second Harmonic Generation and Two-Photon Fluorescence as Nonlinear Optical Properties of Dipolar Mononuclear Sesquifulvalene Complexes

“…Concomitantly the CϪC bond linking the five-and seven-membered rings is somewhat shorter than expected for a sp 2 -sp 2 carboncarbon bond. Additionally, it is worth mentioning that the vector of the connecting bond between the two π-termini in 4a and 4b is slightly tilted towards the metal centre indicating the electron-withdrawing property of the tropylium part [36] (Table 1).…”

Electronic and optical properties of conjugated group 8 metallocene derivatives

“…A wide variety of metallocene-donor-acceptor compounds have been synthesised; in addition to traditional organic acceptors, main group moieties, 20 transition-metal coordination complexes, 6,[21][22][23] and organometallic groups [24][25][26][27][28] have been used as acceptors. The second-order NLO properties of a selection of these compounds are summarised in Table 1, along with absorption maxima.…”

Donor−Acceptor Interaction in Cationic Archetype Mono- and Dinuclear Sesquifulvalene Complexes [(η5-C5H5)Fe{µ-(η5-C5H4)(η7-C7H6)}M′L′]n+ (n = 1, 2)

“…Schematic presentation of the molecular structure of the sesquifulvalene complexes including the notations of special geometric parameters found in Table 3 which are known from corresponding mononuclear complexes and their uncoordinated monocyclic organic species. [18] Electronic Excitation UV/Vis spectroscopic studies were performed with solutions of different solvent polarity such as dichloromethane and nitromethane, to elucidate solvatochromism which gives an indication of the dipole change ∆µ between the ground and the excited state, [19] and is thus relevant for the first hyperpolarizability β according to the two-level approximation. In accordance to it, the CϪC distances between the bridge-head carbon atom C8 and the proximal carbon atoms C9 and C12 of the five-membered ring are distinctly longer than the CϪC distances within the endocyclic buta- Figure 5) of the cationic sesquifulvalene complexes [(η 5 -C 5 H 5 )Fe{µ-(η 5 -C 5 H 4 )(η 7 -C 7 H 6 )}MЈLЈ] ϩ [MЈLЈ ϭ Cr(CO) 3 (3), none (4), Ru(η 5 -C 5 H 5 ) ϩ (5), Ru(η 5 -C 5 Me 5 ) ϩ (6)] and the corresponding structural parameters of the fulvene complex [(η 5 -C 5 H 5 )Fe{η 6 -C 5 H 4 C(C 6 H 5 ) 2 diene unit C9...C12.…”

“…The static first hyperpolarizability β 0 has been calculated by means of the two-level model, [21] taking into account the low-energy DϪA CT transition. [18] Their values are difficult to discuss with respect to increasing DϪA interaction due to (i) the margin of error in the determination of the first hyperpolarizability by HRS, (ii) the fact that the SHG signal occurs in the region of considerable DϪA CT absorption, and (iii) the contribution of both the LϪA CT and DϪA CT transition to the SHG. The experimentally obtained first hyperpolarizability β and the calculated static hyperpolarizability β 0 for 5 and 6 ( Table 4) are comparable although slightly larger for 5 with MЈLЈ ϭ Ru(η 5 -C 5 H 5 ) ϩ which has been shown to be the stronger electron-accepting moiety by means of NMR spectroscopy and cyclic voltammetry studies.…”