Syntheses, structures and luminescence behaviours of Group 12 metal(II) thiocyanate complexes with a tetradentate Schiff base: Variation in molecular and crystalline architectures with the change of congeneric metal ions

One pentacoordinated mononuclear complex [Zn(L)(NCS)]PF6 (1), one hexacoordinated 2D coordination polymer {[Cd2(L)(NCS)4]·0.24(CH3OH)}n (2) and one pentacoordinated 1D polymeric chain [Hg2(L)(SCN)4]n (3) [L = N,N′-(bis(pyridine-2-yl)benzylidene)-1,4-butanediamine] have been synthesized and X-ray crystallographically characterized. Structural analyses revealed interesting variations in the coordination behaviour of the Schiff base (L) from tetradentate chelation to binucleating bis(bidentate) congregation on going from 1 to 2/3. The pseudohalide exhibits terminal N-coordination in 1, both μ1,3 and μ1,1 bridges in 2 and terminal S-coordination along with μ1,1 linkages in 3. In 1/3, each pentacoordinated zinc(II)/mercury(II) centre adopts a distorted trigonal bipyramidal/square pyramidal geometry with a ZnN5/HgN2S3 chromophore, whereas both Cd1 and Cd2 centres in 2 adopt a distorted octahedral geometry with CdN3S3 and CdN6 chromophores, respectively. Weak intermolecular S···S and S···π interactions with multiple C–H···N hydrogen bonds promote the dimensionalities in 1–3. The complexes display intraligand 1(π–π∗) fluorescence in the solid state and in DMF solutions at room temperature.

Graphical abstractThe syntheses, crystal structures and luminescence behaviours of three congeneric Group 12 metal(II) thiocyanate complexes with a tetradentate Schiff base ligand (L) are described. The interesting change in the ligational motifs of L and pseudohalide with the change of metal ion template is highlighted.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Three Group 12 metal(II) thiocyanate compounds of a tetradentate Schiff base are isolated. ► X-ray structures reveal interesting changes in the coordination modes of the Schiff base and pseudohalide. ► Thermal studies show different thermal decomposition patterns of the compounds. ► The compounds exhibit 1(π–π∗) fluorescence in the solid and solution states at room temperature.