Substituent Effects of Isophthalate Derivatives on the Construction of Zinc(II) Coordination Polymers Incorporating Flexible Bis(imidazolyl) Ligands

Eight Zn(II) coordination polymers, [Zn(EtO-ip)(bimb)](n)(DMF)(n) (1), [Zn(PrO-ip)(bimb)(0.5)](n) (2), [Zn-2(NO2-ip)(2)(bimb)(2)](n)(H2O)(n) (3), [Zn-2(NO2-ip)(2)(bimb)(1.5)](n)(H2O)(n) (4), [Zn(MeO-ip)(bmib)(0.5)](n)(H2O)(0.5n) (5), [Zn(EtO-ip)(bmib)(0.5)](n) (6), [Zn(PrO-ip)(bmib)](n) (7), and [Zn (NO2-ip)(bmib)](n) (8) (EtO-ip = 5-ethoxyisophthalate, PrO-ip = 5-propoxyisophthalate, NO2-ip = 5-nitroisophthalate, MeO-ip = 5-methoxyisophthalate, bimb = 1,4-bis(imidazol-1'-yl)butane, bmib = 1,4-bis(2-methylimidazol-1'-yl)butane), have been prepared and characterized by single-crystal X-ray diffraction analyses. In 1, bis-monodentate EtO-ip and exo-bidentate bimb connect four-coordinated Zn(II) into a corrugated 2-D layer. In 2, mu(2),eta(2)-carboxylate and monodentate carboxylate in PrO-ip bridge dinuclear Zn(II) units to generate a [Zn-2(PrO-ip)(4)]n layer, which is further extended by bimb into a 3-D network. Interestingly, bis-monodentate NO2-ip and bimb in 3 connect four-coordinated Zn(II) into two independent 2-D layers, which are stabilized by pi center dot center dot center dot pi stacking interactions from phenyl rings of NO2-ip in different layers. In 4, mu(3)-bridged NO2-ip alternately links single Zn(II) ions and dinuclear Zn(II) units into a 1-D chain containing square-shaped cavities, which is further extended by bimb into a 2-fold interpenetrating 3-D framework. However, mu(3)-bridged MeO-ip and EtO-ip together with bmib in 5 and 6 link dinuclear Zn(II) units into a 2-D layer. In 7, bis-monodentate PrO-ip and bmib connect four-coordinated Zn(II) ions into a 2-D corrugated layer, while four-coordinated Zn(II) ions in 8 are linked by bis-monodentate NO2-ip and bmib into a 3-fold interpenetrating framework consisting of left- and right-handed helical chains. The thermal stability and luminescent properties of 1-8 in the solid state were investigated in detail.