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

Two Cu(I) cluster based coordination polymers, [CuI(cis-bpype)]·CH3CN (1) and [Cu4I4(cis-bpype)3(trans-bpype)]·3DMF (2), have been synthesized from cis- and trans-1,2-bis(4-(pyridin-2-yl)phenyl)ethane (cis- and trans-bpype) ligands and {Cu4I4(PPh3)4} as starting materials. In compound 1, adjacent rhomboid-type {Cu2I2} units from the decomposition of {Cu4I4(PPh3)4} starting material connect by cis-bpype ligands to form a 1D framework. Compound 2 also has a 1D structure, but it has a {M2L3}-type coordinated cage constructed by three cis-bpype ligands and two {Cu4I4} secondary building units (SBU), and these coordination cages further link by trans-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 2 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.