Stereochemically Dependent Synthesis of Two Cu(I) Cluster-Based Coordination Polymers with Thermochromic Luminescence

Two Cu­(I) cluster based coordination polymers, [CuI­(<i>cis</i>-bpype)]·CH₃CN (<b>1</b>) and [Cu₄I₄(<i>cis-</i>bpype)₃(<i>trans</i>-bpype)]·3DMF (<b>2</b>), have been synthesized from <i>cis</i>- and <i>trans</i>-1,2-bis­(4-(pyridin-2-yl)­phenyl)­ethane (<i>cis</i>- and <i>trans-</i>bpype) ligands and {Cu₄I₄(PPh₃)₄} as starting materials. In compound <b>1</b>, adjacent rhomboid-type {Cu₂I₂} units from the decomposition of {Cu₄I₄(PPh₃)₄} starting material connect by <i>cis-</i>bpype ligands to form a 1D framework. Compound <b>2</b> also has a 1D structure, but it has a {M₂L₃}-type coordinated cage constructed by three <i>cis</i>-bpype ligands and two {Cu₄I₄} secondary building units (SBU), and these coordination cages further link by <i>trans</i>-bpype to form the final frameworks. Upon cooling from 300 to 80 K, these Cu­(I) cluster based coordination polymers exhibit interesting thermochromic behavior. In particular, compound <b>2</b> gives a chromic process from green luminescence at room temperature to red luminescence at 80 K and its corresponding CIE coordinates shift from green (0.34, 0.43) at 300 K to red (0.46, 0.42) at 80 K, respectively. This red shift of 124 nm (516 to 640 nm) is large enough to ensure a color change visible to the naked eye, which can be potentially utilized as a temperature sensor with a wide range