A family of q5-monocyclopentadienylruthenium(~~) derivatives possessing coordinated p-substituted benzonitriles has been studied by optical third-harmonic ...
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1861
J. MATER. CHEM., 1995, 5(11), 1861-1865
Downloaded by Universidade da Madeira (UMA) on 13 March 2013 Published on 01 January 1995 on http://pubs.rsc.org | doi:10.1039/JM9950501861
Third-harmonic Generation in Organometallic Ruthenium(ii) Derivatives containing Coordinated p-Substituted Benzonitriles Albert0 R. Dias," M.-Helena Garcia,"9bJ O ~C. O Rodrigues,@Jan C. Petersen,' Thomas Bjsrnholmd and Tommy Geisler" a Centro de Quimica Estrutural, lnstituto Superior Tecnico, Av. Rovisco Pais, 7096 Lisboa Codex, Portugal Faculdade de Ciencias da Universidade de Lisboa, Ed C7, R. Ernest0 de Vasconcelos, 7 700 Lisboa, Portugal Danish Institute of Fundamental Metrology, Anker Engelunds Vej 7, Bldg. 307, 2800 Lyngby, Denmark d Center for Interdisciplinary Studies of Molecular Interactions, Department of Chemistry, Symbion Science Park, University of Copenhagen, Fruebjergvej 3, 2 700 Copenhagen 0, Denmark Institute of Physics, Aalborg University, Pontoppidanstrsde 703, 9220 Aalborg 0st, Denmark
A family of q5-monocyclopentadienylruthenium(~~) derivatives possessing coordinated p-substituted benzonitriles has been studied by optical third-harmonic generation (THG) at the fundamental wavelength of A= 1064 nm. Thin films of the compounds in a polymer matrix of poly(methy1methacrylate)(PMMA) were studied using the Maker fringe technique. For the compound possessing the p-NCC,H,CGH,N02 coordinated nitrile the second hyperpolarizability,y( - 30;0,0,0), was determined to be 2.3 x 10-33esu. Spectroscopic results show evidence of 7t back-donation resulting in an extension of the electronic n-system. We propose that this n back-donation is the origin of this significant value of y.
The current interest in organic materials with large non-linear optical properties is due to their potential as optical devices in photonics and integrated optics applications.'p2 Promising new results in the synthesis of many new organic and organometallic compounds have been ~ b t a i n e d ,thus ~ , ~stimulating this area of research. In these compounds, the magnitudes of the second- and third-order non-linear optical (NLO) effects have been associated with the n-conjugation present in organic and organometallic molecular and polymeric materials. In addition, electron-donor and/or electron-acceptor groups attached to finite-sized conjugated structures seem to play a major We have recently studied chiral organometallic compounds with respect to second-order non-linearities by secondharmonic g e n e r a t i ~ n(SHG) ~ . ~ at the fundamental wavelength of 1064nm. These studies showed that coordination of nsubstituted benzonitriles to y5-monocyclopentadienyliron(~~)/ ruthenium(I1) organometallic fragments lead to an enhancement of n delocalization on the coordinated nitrile. These compounds show significant efficiencies in SHG relative to that of urea. Although the organometallic fragment had been identified as a n donor group via back-donation to the nitrile functional group, the largest SHG efficiencies were obtained for compounds where the nitrile partner had the p-substituting group playing the role of n acceptor, which is the case in compounds such as [Fe(q5-C5H,)((+)-DIOP)( pNCC,H,NO,)][ PF,] and the similar Ru" CF,SO,- salt. In these compounds, SHG efficiencies were 38 and 10 times higher, respectively, than that of urea. In the present work an analogous new series of Ru" compounds was synthesized and studied with respect to their third-order non-linear efficiencies. The technique of thirdharmonic generation (THG) was used in these studies. While non-centrosymmetric materials are required to show secondorder effects, this is not the case for third-order effects. Therefore, the bidentate phosphine DPPE [ lJ-bis(dipheny1phosphino)ethane] was introduced in most of these cases instead of the expensive chiral ligand (+)-DIOP [(+)-2,3O-isopropylidene-2,3-dihydroxy1,4-bis(diphenylphosphino)butane] used in the related compounds cited above for SHG. It is shown that n back-donation is an important factor governing the hyperpolarizability of these compounds.
Experimental Synthesis and Characterization The general route of preparation of these new y5-monocyclopen tadien yl (p-nitro benzoni trile)ruthenium (11) derivatives of the general formulae [Ru(q5-C5H5)(PP)(p-NCR)][X] [PP = DPPE, R = C6H4N02, X = B(C6H5)4- (I), PF6- (2), CF3SO3- (3), p-CH3C6H4SO3 - (4), BF4 - ( 5 ) ; PP = DPPE, X = PF6-, R = C6H,N02 (9), C6H4N(CH3)2(lo), C6H4C6H5 ( l l ) , C(H)=C(H)C6H4N02(12), C6H4C6H4N02(13)] was by halide abstraction of the parent neutral complex [Ru(q5-C5H5)(PP)Cl] with a salt of the appropriate counterion and a slight excess of the appropriate nitrile in absolute methanol or acetone. The molecular structure of compound 13 is shown in Fig. 1. The synthesis and characterization of the analogous compounds containing the chiral phosphine (+)-DIOP and p-nitrobenzonitrile as coordinated chromophores and the following counter-ions PF6- (6), CF,SO,(7), p-CH3C6H$03 - (8) were reported in our previous work concerned with SHG properties of this generic family.7 All studied compounds were fairly stable in air and moisture in the solid state and were obtained with yields in the range 50-96%. The values found for elemental analysis after recrystallization of the compounds were in good agreement with the proposed chemical formulae. Elemental analyses were performed using a Fisons Instruments EA1108 system. Data acquisitions, integration and handling were performed using a PC with the software package Eager-200 (Carlo Erba Instruments). Melting point values obtained using a Reishert
r
7+
Fig. 1 Molecular structure of the [Ru($-C,H,)(DPPE) ( p-NCC6H,C6H4N02)][ PF,] (13) compound
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Downloaded by Universidade da Madeira (UMA) on 13 March 2013 Published on 01 January 1995 on http://pubs.rsc.org | doi:10.1039/JM9950501861
1862
J. MATER. CHEM., 1995, VOL . 5
Table 2 'H NMR data for [Ru(q'-C,H,)(DPPE)( p-NCR)[X] Thermovar are given below for each compound together with complexes elemental percentages and other relevant experimental information. IR spectra (KBr pellets) were recorded using a Perkin2 3 Elmer 457 spectrophotometer. The spectra showed the expected peaks and only frequencies of significant bands are listed. The molar conductivities of mol 1-' solutions of the complexes in nitromethane were recorded with a Schott 6 5 CGB55 Konduktometer and values in the range of 72counter-ion 6, multiplicity, relative integral, 96 i 2 - I cm2 mol-' were found, in agreement with values reXassignment' ported for 1 : 1 electrolytes.8 'H, I3C and 31P NMR spectra were recorded using a Varian Unity 300 spectrometer. The 'H NMR data reported in parts per million (ppm) downfield from internal Me& obtained from C2H6]acetone solutions are presented in Tables 1 and 2, while data from I3C NMR studies referred to the chloroform triplet chemical shift are presented in Tables 3 and 4. DPPE 'H (C2H2] dichloromethane) and I3C NMR (['HI chloroform) data were very similar for all the complexes: 'H: 2.62 (m, 2 H, CH2), 2.67 (m, 2 H, CH,), 7.30 (m, 4 H, C ~ H S )7.48 , (m, 6 H, C~HS), 7.53 (m, 6 H, C ~ H S )7.80 , (m, 4 H, C6H-j). l3c:27.80 [t, CH2, 'J(CP) 23.381, 137.09 [C-ipso, J(CP) 11.311. The C-meta, C-para and C-ortho were obscured. BF4The 31PNMR spectra ([2H]chloroform) reported in ppm downfield from the external standard (85% H,PO,) showed an equivalent deshielding for coordinated DPPE for all com" In [2H6]acetone with TMS as internal standard. pounds, the corresponding singlet being placed in the narrow 79.7-80.2 ppm range. Under the same experimental conditions uncoordinated DPPE showed signals at ca. 12.1 ppm.
Table 1 'H NMR data for [Ru(q'-C,H,)(DPPE)( p-NCR)][PF6] comp1exes R in [Ru(Y/'-C,H,)DPPE( p-NCR)]
+
6, multiplicity, relative integral, assignment"
Table 3 I3C NMR data for [Ru($-C,H,)(DPPE)(p-NCR)][PF6] complexes R in [Ru($-C,H,)DPPE( p-NCR)]
2 2
+
82.75 (C,H,), 116.67 [C( 123.65 [C(3), C(5)], 124.16 (CN), 133.37 [C(2), C(6)], 149.40 ~ 4 ) i
3
3 U
6 6
5
5 2.98 [s, 6 H, N(CH,),], 4.97 (s, 5 H, q5-C5H5),6.40 [d, 2 H, H(3), H(5)1, 6.59 Ed, 2 H, H(2), H(6)I 5.05 (s, 5 H, q5-C5H5),6.77 Cd, 2 H, H(6), H(10)1, 7.46-7.64b [m, 27 H, H(2), H(3), H(7), H(8), H(9), H ( l l ) , H(12)+Ph] 5.01 (s, 5 H, q5-C,H,), 6.01 rd, 1 H. H(8L 'J(H, H ) 16.51, 6.51 'Id, 1 H, H(7), 'J(H, H) 16.51, 7.63 [d, ' 2 H, H(2), H"" L
,
' In [2H6]acetone with TMS as internal standard. Obscured by the protons of the phosphines.
