Syntheses and structural characterization of luminescent platinum(II) complexes containing di-tert-butylbipyridine and new 1,1-dithiolate ligands

Three new di-tert-butylbipyridine (dbbpy) complexes of platinum(II) (1-3) c ontaining 1,1-dithiolate ligands have been synthesized and characterized. T he 1,1-dithiolates are 2,2-diacetylethylene-1,1-dithiolate (S2C=C(C(O)Me)(2 )) (1), 2-cyano-2-p-bromophenylethylene-1,1-dithiolate (S2C=C(CN)(p-C6H4Br) ) (2), and p-bromophenyl-2-cyano-3,3-dithiolatoacrylate (S2C=C(CN)(COO-p-C6 H4Br)) (3) Complex 1 exhibits a solvatochromic charge-transfer absorption i n the 430-488 nm region of the spectrum and a luminescence around 635 nm in ambient temperature CH2Cl2 solution. These observations are consistent wit h what has been seen previously in related Pt diimine 1,1-dithiolate comple xes. The nature of the emissive state is assigned as a 3(mixed metal/dithio late-to-diimine) charge transfer, while the solvatochromic absorption band corresponds to the singlet transition of similar orbital character. The oth er complexes also exhibit a low-energy solvatochromic absorption. The cryst al structures of two of the complexes have been determined, representing th e first time that Pt(diimine)(1,1-dithiolate) complexes have been crystallo graphically studied. The structures confirm the expected square planar coor dination geometry with distortions in bond angles dictated by the constrain ts of the chelating ligands. The Pt-S and Pt-N bond lengths and S-Pt-S and N-R-N bond angles for the two structures are identical within experimental error (2.283(2) and 2.278(2) Angstrom; 2.053(6) and 2.050(8) Angstrom; 75.0 1(8)degrees and 75.40(8)degrees; 79.2(2)degrees and 79.0(2)degrees, respect ively). Crystal data for 1: monoclinic, space group P2(1)/n (No. 14), with a = 7.20480(10) Angstrom, b = 20.53880(10) Angstrom, c = 19.1072(2) Angstro m, a = 93.830, V = Angstrom (3), Z = 4, R1 = 3.34% (I > 2 sigma (I)), wR2 = 9.88% (I > 2 sigma (I)) for 3922 unique reflections. Crystal data for 2: m onoclinic, space group P2(1)/n (No. 14), with a = 15.0940(5) Angstrom, b = 9.5182(3) Angstrom, c = 20.4772(7) Angstrom, beta = 111.151(1)degrees, V = Angstrom (3), Z = 4, R1 = 4.07% (I > 2 sigma (I)), wR2 = 8.64% (I > 2 sigma (I) for 3859 unique reflections.