Syntheses, structures and luminescence behaviors of mono- and dinuclear complexes of type [M(L)(NCS)₂]_n [M=Zn/Hg, n=1; M=Cd, n=2; L=(N,N-diethyl,N′-(pyridin-2-yl)benzylidene)ethane-1,2-diamine]: Variation of coordination matrices and nuclearities with the change of congeneric metal ions

Abstract

One-pot reaction of zinc(II)/cadmium(II)/mercury(II) acetate, a tridentate Schiff base (L) and ammonium thiocyanate in a 1:1:2 molar ratio in MeOH solution at room temperature results in neutral mono-/dinuclear compound of the type [Zn(L)(NCS)₂] (1)/[Cd(L)(NCS)(SCN)]₂ (2)/[Hg(L)(SCN)₂] (3) [L = (N,N-diethyl,N′-(pyridin-2-yl)benzylidene)ethane-1,2-diamine]. X-ray crystallographic study reveals an interesting variation in ligational motifs of thiocyanate from terminal N-coordination (in 1) to both terminal N-coordination and symmetrical double end-to-end bridging (in 2) and terminal S-coordination (in 3). In mononuclear 1/3, each metal(II) center adopts a distorted square pyramidal geometry with ZnN₅ (for 1)/HgN₃S₂ (for 3) chromophore, whereas each cadmium(II) center in centrosymmetric dinuclear 2 has distorted octahedral environment with a CdN₅S chromophore. Interesting variations in coordination matrices, nuclearities, and molecular and crystalline architectures are observed in these congeneric Group 12 metal ion complexes. Compounds 1–3 display high energy intraligand 1(Π–Π*) fluorescence in the solid state and in DMF solutions at room temperature.