Synthesis, characterisation and optical properties of symmetrical and unsymmetrical Pt(II) and Pd(II) bis-acetylides.: Crystal structure of trans-[Pt(PPh3)2(CC-C6H5)(CC-C6H4NO2)]

Symmetric trans-[Pt(PPh3)(2)(C drop CR)(2)] and unsymmetrical trans-[Pt(PPh3)(2)Cl(C drop CR)], (R = C6H4-pNO(2), C6H4-pOCH(3)), Pt(II) acetylides were prepared and characterised, as well as unsymmetrical Pt(II) bis-acetylides, trans-[Pt(PPh3)(2)(C drop CR)(C drop CR')], (R = C6H4-pNO(2), R' = C6H5; R = C6H4-pOCH(3), R' = C6H5; R = C6H4-pOCH(3), R' = C6H4-pNO(2); R = C6H4-pNO(2), R' = [(eta (5)-C5H4)Fe(eta (5)-C5H5)]). Also symmetric Pd(II) bis-acetylides, trans-[Pd(PPh3)(2)(C drop CR)(2)] (R = C6H4-pNO(2), C6H5) were synthesised and characterised by IR, NMR, and UV-vis spectroscopies. The optical properties of the new complexes were compared within a series of known Pt(II) complexes containing different phosphines and cis-tuans configuration. The absorption and photoluminescence spectra indicate that the emission is found in the range 355-600 nm, depending on the nature of the acetylide ligand bound to Pt. Measurements of SHG for the unsymmetrical bis-acetylides dispersed in polymethylmethacrylate (PMMA) show that the second-order nonlinear optical (NLO) properties depend on the strength of the donor-acceptor substituent of the acetylide ligand. Third-order NLO properties (in particular the nonlinear absorption coefficient alpha (2)) were measured by the Z-scan technique; strong push-push and pull-pull substituents on the Pt(II) symmetric bis-acetylides induce electronic delocalisation and tuning of the NLO properties. The single crystal X-ray structure of trans-[Pt(PPh3)(2)(C dropC-C6H5)(C dropC-C6H4NO2)] shows that the unsymmetrical molecule crystallised in the Pbca centric space groups. (C) 2001 Elsevier Science B.V. All rights reserved.