Effect of substituent on dimensionality and properties in divalent metal isophthalate coordination polymers with a conformationally flexible dipyridylamide coligand

• Nickel or cadmium coordination polymers with isophthalate-type ligands.
• Inclusion of conformationally flexible 3-pyridylmethylnicotinamide (3-pmna).
• 1-D ribbons for both nickel isophthalate and 5-nitroisophthalate derivatives.
• 1-D ribbon for cadmium isophthalate but 2-D layer for 5-nitroisophthalate derivative.
• Increase in dimensionality on nitro group substitution counter to previous trends.

Hydrothermal reaction of divalent metal nitrates and 3-pyridylmethylnicotinamide (3-pmna) with either isophthalic acid (H2iph) or 5-nitroisophthalic acid (H2nip) has afforded a series of four coordination polymer solids that were structurally characterized via single-crystal X-ray crystallography. [Ni(iph)(3-pmna)]n (1) and [Cd(iph)(3-pmna)]n (2) both exhibit a {M2(OCO)2} dimer-based 1-D ribbon topology with metal–metal contacts bridged by both ip and 3-pmna ligands. [Ni(nip)(3-pmna)]n (3) has the same topology as its unsubstituted congener 1, showing a null effect on the part of the nip nitro group. On the other hand [Cd(nip)(3-pmna)]n (4) exhibits a {Cd2O2} dimer-based 2-D (4,4) layer topology, a rare example of the nitro group imposing a higher dimensionality in the resulting coordination polymer. While 2 showed strong blue–violet luminescence, quenching mechanisms due to the nitro group rendered 4 non-luminescent. Thermal properties of these new materials are also investigated.

[Cd(iph)(3-pmna)]n (iph = isophthalate, 3-pmna = 3-pyridylmethylnicotinamide) exhibits dimer-based 1-D ribbon motifs. Nitro group substitution in [Cd(nip)(3-pmna)]n (nip = 5-nitroisophthalate) shows in an increase in dimensionality to a dimer-based layer topology, counter to previously reported structure-directing trends.Figure optionsDownload as PowerPoint slide