Formation of Zn(ii) and Pb(ii) coordination polymers of tetrakis(4-pyridyl)cyclobutane controlled by benzene and toluene

Abstract

Reactions of Zn(NO3)2·6H2O with tetrakis(4-pyridyl)cyclobutane (tpcb) in MeOH followed by addition of benzene or toluene gave rise to two two-dimensional (2D) coordination polymers {[Zn(tpcb)(NO3)2]·2S}n (1: S = benzene; 2: S = toluene). The analogue reactions of Pb(NO3)2 with tpcb in similar solvent systems resulted in the formation of {[Pb(tpcb)0.5(NO3)2(MeOH)]·benzene}n (3) and [Pb(tpcb)(NO3)2(MeOH)]n (4), respectively. Slow evaporation of the MeOH solution containing Pb(NO3)2 and tpcb generated [Pb(tpcb)(NO3)2(H2O)]n (5). Compounds 1 and 2 show similar 2D networks but differ in their packing modes, namely “overlapping” and “crisscross” modes. Compound 3 exhibits a 3D porous framework in which its 1D channels are occupied by benzene molecules. Compound 4 consists of 1D [Pb(tpcb)(NO3)2(MeOH)]n chains which are linked by weak Pb⋯N secondary interactions to form a 2D gridlike network. Compound 5 has a 3D structure constructed by dinuclear [Pb2(tpcb)6(NO3)4(H2O)2] units and tpcb bridges with a Schlafli symbol of (4·62)·(42·610·82). The solvent effects may be ascribed to the formation of the five 2D and 3D coordination polymers 1–5. The inclusion of benzene and toluene molecules in the frameworks of 1 and 2 along with the time lengths of their crystal growth may provide an interesting approach to the selective separation of benzene and toluene.