Polymeric end-to-end bibridged cadmium(II)thiocyanates containing monodentate and bidentate N-donor organic blockers: Supramolecular synthons based on π-π and/or C-H⋯π interactions

Treatment of Cd(NO₃)₂·4H₂O with two equivalents of NH₄NCS in combination with two equivalents of imH [imH=imidazole] or one equivalent of pfan [pfan=((pyridin-2-yl)formylidene) aniline] results neutral 1D polymers of the type [Cd(imH)₂(NCS)(SCN)] _n (1) or [Cd(pfan)(NCS)(SCN)]_n (2). X-ray structure determinations show that in both polynuclear 1 and 2, octahedral Cd^II ions occupy centre of symmetry with a CdN₄S₂ chromophore. The metal ions are linked through N and S atoms of NCS^- alternately in doubly bridged end-to-end fashion; two mutually trans N atoms of monodentate imH units complete hexacoordination of each metal centre in 1. Similar NCS-bibridging chain is present in 2 with one bidentate (N,N) Schiff base chelator (pfan) in cis orientation. The 1D chains in 1 are further engaged in intermolecular hydrogen bonding (N-H⋯S) between N of imH and coordinated S of NCS^- along with aromatic π-π stacking of imH moieties that constrain the 1D chains to lie in bc-plane, which are further linked via C-H⋯π interactions. In 2, 1D chains participate in two kinds of π-π interactions. Supramers 1 and 2 display intraligand ¹(π-π^*) fluorescence and intraligand ³(π-π^*) phosphorescence in glassy solutions (MeOH at 77 K).