Syntheses and Structures of New Luminescent Cyclometalated Palladium(II) and Platinum(II) Complexes:  M(Bab)Cl, M(Br−Bab)Cl (M = Pd(II), Pt(II)), and Pd3Cl4(Tab)2 (Bab = 1,3-bis(7-azaindolyl)phenyl, Br−Bab = 1-Bromo-3,5-bis(7-azaindolyl)phenyl, Tab =1,3,5-tris(7-azaindolyl)phenyl)

The reactions of blue luminescent ligands 1,3-bis(7-azaindolyl)benzene (BabH), 1-bromo-3,5-bis(7-azaindolyl)benzene (Br−BabH), and 1,3,5-tris(7-azaindolyl)benzene (TabH) with K2PdCl4 and K2PtCl4 have been investigated. Five new luminescent cyclometalated palladium(II) and platinum(II) complexes Pd(Bab)Cl (1), Pt(Bab)Cl (2), Pd(Br−Bab)Cl (3), Pt(Br−Bab)Cl (4), and Pd3Cl4(Tab)2 (5) have been synthesized and fully characterized. The molecular structures of 1 and 2, and 3 and 4, are similar. There are however significant variations in the solid-state structures and luminescence of 1 and 2, and 3 and 4. EHMO calculations revealed that it is most likely that the electronic transitions in the Pt(II) complexes are π to π* transitions with significant contributions from d π lone pairs of the Pt(II) center in the π level, and the electronic transitions in the Pd(II) complexes are either d(z 2) to π* charge-transfer transitions or π to π* transitions similar to the Pt(II) complexes.