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

Symmetric trans-[Pt(PPh3)(2)(C drop CR)(2)] and unsymmetrical trans-[Pt(PPh 3)(2)Cl(C drop CR)], (R = C6H4-pNO(2), C6H4-pOCH(3)), Pt(II) acetylides wer e prepared and characterised, as well as unsymmetrical Pt(II) bis-acetylide s, 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-a cetylides, trans-[Pd(PPh3)(2)(C drop CR)(2)] (R = C6H4-pNO(2), C6H5) were s ynthesised and characterised by IR, NMR, and UV-vis spectroscopies. The opt ical properties of the new complexes were compared within a series of known Pt(II) complexes containing different phosphines and cis-tuans configurati on. 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-acetylid es dispersed in polymethylmethacrylate (PMMA) show that the second-order no nlinear optical (NLO) properties depend on the strength of the donor-accept or substituent of the acetylide ligand. Third-order NLO properties (in part icular 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 t he NLO properties. The single crystal X-ray structure of trans-[Pt(PPh3)(2) (C dropC-C6H5)(C dropC-C6H4NO2)] shows that the unsymmetrical molecule crys tallised in the Pbca centric space groups. (C) 2001 Elsevier Science B.V. A ll rights reserved.