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)CI (1), Pt(Bab)CI (2), Pd(Br-Bab)CI (3), Pt(Br-Bab)CI (4), and Pd3Cl4(Tab)(2) (5) have been synthesized and fully characterized. The molecular structures of I 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 pi to pi* transitions with significant contributions from d(pi) lone pairs of the Pt(II) center in the pi level, and the electronic transitions in the Pd(II) complexes are either d(z(2)) to pi* charge-transfer transitions or pi to pi* transitions similar to the Pt(II) complexes.