N,C,N -Pincers in Platinum Bimetallic Complexes: Influence of the Pincer and Bridging Ligands on the Metal-Metal Bond and the Photophysical Properties.

Precursors PtCl{κ 3 - N,C,N -[py-C 6 HMe 2 -py]} ( 1 ), PtCl{κ 3 - N,C,N -[py-O-C 6 H 3 -O-py]} ( 2 ), Pt(OH){κ 3 - N,C,N -[py-C 6 HMe 2 -py]} ( 3 ), and Pt(OH){κ 3 - N,C,N -[py-O-C 6 H 3 -O-py]} ( 4 ) were used to prepare d 8 -platinum bimetallic complexes. Precursors 1 and 2 react with AgBF 4 and 7-azaindole (H az ) to give [Pt{κ 3 - N,C,N -[py-C 6 HMe 2 -py]}{κ 1 - N -[H az ]}]BF 4 ( 5 ) and [Pt{κ 3 - N,C,N -[py-O-C 6 H 3 -O-py]}{κ 1 - N -[H az ]}]BF 4 ( 6 ) and 3 and 4 with indolo[2,3- b ]indole (H 2 ii ) to generate Pt{κ 1 - N -[H ii ]}{κ 3 - N,C,N -[py-C 6 HMe 2 -py]} ( 7 ) and Pt{κ 1 - N -[H ii ]}{κ 3 - N,C,N -[py-O-C 6 H 3 -O-py]} ( 8 ). Subsequent addition of 3 and 4 to 5 - 7 affords bimetallic derivatives [{Pt[κ 3 - N,C,N -(py-C 6 HMe 2 -py)]} 2 {μ- N,N -[ az ]}]BF 4 ( 9 ), [{Pt[κ 3 - N,C,N -(py-O-C 6 H 3 -O-py)]} 2 {μ- N,N -[ az ]}]BF 4 ( 10 ), and {Pt[κ 3 - N,C,N -(py-C 6 HMe 2 -py)]} 2 {μ- N,N -[ ii ]} ( 11 ). X-ray structures of 9 - 11 reveal separations between the metals in sequence 9 (3.0515(4) Å) < 10 (3.2689(9) Å) < 11 (3.2949(2) Å). DFT calculations support σ overlap of the dz 2 orbitals of platinum atoms, for 9 and 10 . Accordingly, their absorption spectra show a MMLCT transition. Complex 9 is a red emitter. The excited state has 3 MMLCT characteristics and a Pt-Pt separation of 2.763 Å. Complex 11 is a dual emitter in the red and NIR regions, in solid. Both excited states have a 3 LC/LMCT characteristic and platinum-platinum separations of 3.290 and 3.202 Å. Intermediate 5 is a green emitter that achieves quantum yields close to unity, when diluted in PMMA and 1,2-dichloroethane at low concentrations.