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) containing 1,1-dithiolate ligands have been synthesized and characterized. The 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-C6H4Br)) (3) Complex 1 exhibits a solvatochromic charge-transfer absorption in the 430-488 nm region of the spectrum and a luminescence around 635 nm in ambient temperature CH2Cl2 solution. These observations are consistent with what has been seen previously in related Pt diimine 1,1-dithiolate complexes. The nature of the emissive state is assigned as a 3(mixed metal/dithiolate-to-diimine) charge transfer, while the solvatochromic absorption band corresponds to the singlet transition of similar orbital character. The other complexes also exhibit a low-energy solvatochromic absorption. The crystal structures of two of the complexes have been determined, representing the first time that Pt(diimine)(1,1-dithiolate) complexes have been crystallographically studied. The structures confirm the expected square planar coordination geometry with distortions in bond angles dictated by the constraints 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; 75.01(8)degrees and 75.40(8)degrees; 79.2(2)degrees and 79.0(2)degrees, respectively). 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) Angstrom, 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: monoclinic, 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.