Modulation of S and N Active Sites for Coordination Polymers to Achieve Enhanced Hg²⁺ Sensing Performances

It is challenging and vital to develop coordination polymers (CPs) with an outstanding sensing performance. In this work, CP-based sensors with active S and N sites are first exploited. Three new Cu-CPs [Cu(<b>L</b>)(SCN)₂·2DMF]_n (<b>1</b>), [Cu(<b>L</b>)(SCN)·2DMF]_n (<b>2</b>), and [Cu(<b>L</b>)(CN)·2DMF]_n (<b>3</b>) were successfully synthesized by 9,10-bis(di(pyrimidin-5-yl)methylene)-9,10-dihydroanthracene (<b>L</b>) and SCN^-/CN^- ligands. <b>1</b> demonstrates a 1D wavelike chain, fabricated by <b>L</b> bridges linking with Cu(SCN)₂ units. <b>2</b> exhibits a 2D (3,3)-connected network fabricated by SCN^-, 3-connected <b>L</b>, and Cu units. <b>3</b> exhibits a 3D framework, built by 4-connected Cu centers, CN^-, and <b>L</b> bridges. <b>1</b>-<b>3</b> have good water, pH, and thermal stabilities. <b>1</b> and <b>2</b> have uncoordinated S and N active sites and can detect Hg²⁺ through the fluorescence enhancing ("turn-on") effect. Meanwhile, <b>3</b> only has uncoordinated N active sites and shows a negative Hg²⁺ sensing ability. <b>1</b> and <b>2</b> have ultrahigh Hg²⁺ sensing sensitivity and selectivity. The K_SV and LOD of <b>1</b> toward Hg²⁺ are about 3 and 5 times superior to those of <b>2</b>, separately. <b>1</b> and <b>2</b> represent the first S- and N-rich CP-based sensors and exhibit an excellent "turn-on" Hg²⁺ sensing capacity. Their "turn-on" Hg²⁺ sensing mechanism and difference sensing performances are discussed in detail.