ISSN:
0947-6539
Keywords:
bimetallic complexes
;
NLO materials
;
sandwich complexes
;
sesquifulvalenes
;
solvatochromism
;
Chemistry
;
General Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
In order to construct bimetallic organometallic donor-acceptor complexes with nonlinear optical (NLO) properties, the bimetallic sesquifulvalene complexes [{CpFe(η5-C5H4)}Z{η7-C7H6)Cr-(CO)3}]BF4 (2BF4) have been synthesized with different bridging functions Z (2a: Z = - 2b: Z = C2; 2c: Z = (E)-C2H2). X-ray structure determinations show that 2a BF4 and 2c BF4 crystallize in acentric space groups (P41, P212121), whereas crystalline 2b BF4 has the centric space group P21/c. The organometallic fragments in 2a adopt a transoid conformation, those in 2b and 2c are cisoid. The cyclo-C5 and cyclo-C7 rings of the sesquifulvalene ligands are almost coplanar; this allows an optimum electronic interaction between the ferrocenyl donor and the [η7-C7H6)Cr(CO)3]+ acceptor moiety in the crystalline state. Cyclovoltammetric studies show an electrochemically reversible one-electron oxidation ( 〉 0 mV vs. FeH/FcH+, FcH = ferrocene) and an irreversible one-electron reduction (≤-900 mV), which are assigned to the ferrocenyl and [(η7-C7H6)Cr(CO)3]+ units, respectively. UV/vis spectra reveal low-energy absorptions for 2a-c at about λ=600 nm, showing strong negative solvatochromism. These absorption maxima are related to a charge-transfer excitation between the ferrocenyl and the [(η7-C7H6)Cr(CO)3]+ groups, indicating considerable nonlinear optical properties. Determination of the first hyperpolarizability β by means of hyper Rayleigh scattering yields exceptionally large β values: β(2b) = 570 × 10-30 esu and β(2c) = 320 × 10-30 esu. These unexpectedly large β values are explained by resonance enhancement.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/chem.19960020117
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