Polymeric end-to-end bibridged cadmium(II)thiocyanates containing monodentate and bidentate N-donor organic blockers: supramolecular synthons based on <f>π–π</f> and/or C–H<f>⋯</f>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 CdII 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<f>⋯</f>S) between N of imH and coordinated S of NCS- along with aromatic <f>π–π</f> stacking of imH moieties that constrain the 1D chains to lie in bc-plane, which are further linked via C–H<f>⋯</f>π interactions. In 2, 1D chains participate in two kinds of <f>π–π</f> interactions. Supramers 1 and 2 display intraligand <f>1(π–π*)</f> fluorescence and intraligand <f>3(π–π*)</f> phosphorescence in glassy solutions (MeOH at 77 K). [Copyright &y& Elsevier]