Unprecedented Pt-Pt Bonded Trimer {[Pt 2 Cu 4 (CtCPh) 8 ]} 3 Showing Unusual Near-Infrared Luminescence Jonathan P. H. Charmant, † Juan Fornie ´s,* ,‡ Julio Go ´mez, †,§ Elena Lalinde,* ,§ Rosa I. Merino, ‡ M. Teresa Moreno, § and A. Guy Orpen † School of Chemistry, University of Bristol, Bristol, BS8 1TS, U.K., Instituto de Ciencia de Materiales de Arago ´ n, Universidad de Zaragoza-Consejo Superior de Investigaciones Cientı ´ficas, 50009 Zaragoza, Spain, and Departamento de Quı ´mica, Universidad de La Rioja, 26001, Logron ˜ o, Spain Received March 23, 1999 The homoleptic high-nuclearity platinum-copper acetylide complex of stoichiometry [PtCu 2 - (CtCPh) 4 ] crystallizes in at least three different polymorphic forms. Dark violet-green crystals with metallic reflectance have been shown by an X-ray diffraction study to be formed by discrete trimers of an hexanuclear octahedral cluster unit {[Pt 2 Cu 4 (CtCPh) 8 ]} 3 stabilized by two unsupported Pt-Pt interactions [2.995(1) Å]. The photoluminescence behavior of this complex which is dramatically influenced by strong axial Pt‚‚‚Pt interactions either in solid state or in solution (CH 2 Cl 2 298, 77 K) has been studied. For several decades there has been considerable interest in the study of the very unusual and highly anisotropic ground- and excited-state properties of complexes in which metal(d 8 )-metal(d 8 ) interactions are present. 1 Predominant are square-planar d 8 platinum complexes which often form stacked linear chain ma- terials with short Pt‚‚‚Pt contacts (<3.5 Å). 1e-h,2 In these complexes spectroscopic investigations have revealed that such stacking results in the appearance of a low- energy absorption band, often accompanied by visible luminescence, which displays a strong dependence on the interchain metal-metal separation. 1g,2j Consider- able experimental work 2 and recent theoretical calcula- tions 3 seem to indicate that the structural aspects of the stacking are governed not only by Pt‚‚‚Pt interactions but also by interligand steric repulsions and interligand charge-transfer bonding. 2m In fact, often the relatively weak Pt‚‚‚Pt bonding interactions may be offset by other favorable interactions, as is illustrated by the very rich polymorphism exhibited by Pt(II) diimine compounds 2m [e.g., Pt‚‚‚Pt in [Pt(bipy)Cl 2 ] red (3.45 Å), 4a yellow (4.44 Å) 4b ]. In other cases, these metal-metal or ligand- ligand (π-π) interactions are so enhanced that com- plexes oligomerize in solution, leading to supramolec- ular architectures with characteristic photophysical properties. 4c However, it has been noted that the electronic properties of the ligands have a primary effect on the strength of Pt‚‚‚Pt bonding, with stronger-field and π-acidic ligands enhancing the interactions of stacked complexes. 2m,3 In fact the shortest M-M dis- tances are found in complexes with ligands such as diimine, 2l CO, 2h,3,5 CN - , 1g or CNR. 3 The alkynyl ligand (CtCR) bears some similarity (it is a potent σ-donor, but the π-acceptor bonding component is not very important) to the isoelectronic CN - , CO, or CNR ligands; however related stacked complexes with this ligand were until now unknown. We report here a new class of aggregates which are based on discrete trimers of a hexanuclear octahedral platinum-copper alkynyl cluster {[Pt 2 Cu 4 (CtCPh) 8 ]} 3 , † University of Bristol. ‡ Universidad de Zaragoza-Consejo Superior de Investigaciones Cientı ´ficas. § Universidad de La Rioja. (1) (a) For example see: Extended Linear Chain Compounds; Miller, J. S., Ed.; Plenum Press: New York, 1982; Vols. 1-3. (b) Miller, J. S.; Epstein, A. J. Prog. Inorg. Chem. 1976, 20, 1. (c) Mann, K. R.; Lewis, N. S.; Williams, R. M.; Gray, H. B.; Gordon, J. G. Inorg. Chem. 1978, 17, 828. (d) Finnis, G. M.; Canadell, E.; Campana, Ch.; Dumbar, K. R. Angew. Chem., Int., Ed. Engl. 1996, 35, 2772, and references therein. (e) Zipp, A. P. Coord. Chem. Rev. 1988, 84, 47. (f) Krogmann, K. Angew. Chem., Int. Ed. Engl. 1969, 8, 35. (g) Gliemann, G.; Yersin, H. Struct. Bonding 1985, 62, 87. (h) Houlding, V. H.; Miskowski, V. M. Coord. Chem. Rev. 1991, 111. (i) Crosby, G. A.; Kendrick, K. R. Coord. Chem. 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Acta 1995, 240, 41. 3353 Organometallics 1999, 18, 3353-3358 10.1021/om9902030 CCC: $18.00 © 1999 American Chemical Society Publication on Web 07/24/1999