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) (.) 4H(2)O 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 ID 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 I 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 I D chains in I are further engaged in intermolecular hydrogen bonding (N-(HS)-S-...) between N of imH and coordinated S of NCS- along with aromatic pi-pi stacking of imH moieties that constrain the I D chains to lie in be-plane, which are further linked via C-H(...)pi interactions. In 2, ID chains participate in two kinds of pi-pi interactions. Supramers I and 2 display intraligand(1) (pi-pi*) fluorescence and intraligand phosphorescence in glassy solutions (MeOH at 77 K). (C) 2004 Elsevier Ltd. All rights reserved.