Syntheses, molecular and crystalline architectures, and luminescence behaviours of two dinuclear cadmium(II) compounds containing a tetradentate N-donor di-Schiff base

Two dinuclear cadmium(II) compounds of the types [Cd(L)(μ-Cl)]2(PF6)2 (1) and [Cd(L)(μ1,5-dca)]2(ClO4)2.0.66MeOH (2) [L = N,N′-(bis(pyridin-2-yl)benzylidene)-1,3-propanediamine; dca = dicyanamide] have been synthesized and characterized on the basis of microanalytical, spectroscopic and other physicochemical results. X-ray structural studies show that in 1 and 2 each hexacoordinated cadmium(II) adopts a distorted octahedral geometry with CdN4Cl2 (1)/CdN6 (2) chromophore ligated through four N atoms of L along with two chlorides in 1 forming a four-membered Cd–(Cl)2–Cd rhombohedral bridging loop and two nitrile N atoms of two μ1,5 dicyanamides in 2 affording a larger 12-membered Cd–(NCNCN)2–Cd ring with boat conformation. In the crystalline state, individual units in 1 are packed through multiple weak CH⋯F hydrogen bonds and CH⋯π and π ⋯π interactions affording a 2D sheet structure. The dinuclear units in 2 are engaged in weak intermolecular CH⋯O and CH⋯N hydrogen bondings to give a 2D continuum, which is further stabilized by π⋯π interactions through pyridine rings of L. In DMF solutions, 1 and 2 show high-energy intraligand 1(π–π*) fluorescence at room temperature.