Structure, Dynamics, and Photophysics in the Copper(I) Iodide–Tetrahydrothiophene System

Combination
of CuI and tetrahydrothiophene (THT) in MeCN or neat
THT produces various phases, depending upon experimental conditions.
Green luminescent product (CuI)4(THT)2 (1) consists of Cu4I4 cubane units knit
into a 3-D network by μ2-THT ligands. Dull yellow
luminescent (CuI)10(THT)7(MeCN) (2) contains {[Cu4I4(THT)]­(μ2-THT)2(Cu2I2)­(μ2-THT)2[Cu4I4(NCMe)]} “rungs”
linked into 1-D ladders by pairs of μ2-THT ligands.
Two molecular (CuI)4(THT)4 phases were found:
orange luminescent 3a and yellow luminescent 3b. Triclinic 3b is the more stable phase at 25 °C,
but it undergoes endothermic transformation to monoclinic 3a at 38 °C. Compound 3a transforms to a triclinic
phase (3a′) that retains orange emission at −60
°C. Nonemissive (CuI)3(THT)3·MeCN
(4) is a 2-D sheet structure in which Cu3(THT)3 rings are linked in trigonal directions by rhomboid Cu2I2 dimer units. The previously reported (CuI)2(THT)4 (5) is a molecular dimer. Temperature
and mixing ratio domains for the formation of the CuI–THT phases
from MeCN are presented. Luminescence in 1, 2, 3a, and 3b is rationalized on the basis
of varying degrees of halide-to-metal charge transfer (XMCT) and metal-centered
(MC) behavior. Low-temperature spectra reveal reversible changes,
including modest red shifts for 1 and 2,
and splitting into two excitation/emission band pairs for 3a and 3b.