Organometallic complexes for nonlinear optics Part 21. Syntheses and quadratic hyperpolarizabilities of alkynyl complexes containing optically active 1,2-bis(methylphenylphosphino)benzene ligands

The preparation of the chloro complex trans-[FeCl₂{(R,R)-diph}₂] (1) and the alkynyl complexes trans-[M(4-C≡CC₆H₄R)Cl{(R,R)-diph}₂] [M = Fe, R = NO₂ (2); M = Ru, R = H (4), NO₂ (5), (E)-CH=CH-4-C₆H₄NO₂ (6); M = Os, R = NO₂ (7)], incorporating the optically active diphosphine 1,2-bis(methylphenylphosphino)benzene (diph), are described. Oxidation potentials, as determined by cyclic voltammetry, increase as 2 < 7 < 5. Molecular quadratic nonlinearities by hyper-Rayleigh scattering at 1064 nm increase upon introduction of an acceptor group (4 < 5), chain-lengthening of bridging group (5 < 6), and proceeding from 3d to 4d and 5d metal (2 ≤ 5 ≤ 7). Two-level-corrected nonlinearities reproduce the first two trends, but metal variation follows the sequence 2 < 7 < 5. The experimental and two-level-corrected nonlinearities for 6 (2795 × 10^-30 and 406 × 10^-30 esu, respectively), are amongst the largest observed thus far for organometallic complexes. Crystals of complexes 2 and 7 exhibit second-harmonic generation (assessed using the Kurtz powder technique), with an efficiency for the former of twice that of urea.