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), [Zn2(NO2-ip)2­(bimb)2]n­(H2O)n (3), [Zn2(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, μ2,η2-carboxylate and monodentate carboxylate in PrO-ip bridge dinuclear
Zn­(II) units to generate a [Zn2(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 π···π
stacking interactions from phenyl rings of NO2-ip in different
layers. In 4, μ3-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,
μ3-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.