Copper(I) Halides (X = Br, I) Coordinated to Bis(arylthio)methane Ligands: Aryl Substitution and Halide Effects on the Dimensionality, Cluster Size, and Luminescence Properties of the Coordination Polymers

Bis­(phenylthio)­methane (L1) reacts with CuI to yield
the 1D-coordination polymer [{Cu4(μ3-I)4}­(μ-L1)2]n (1) bearing cubane Cu4I4 clusters as connecting nodes. The crystal structures at 115, 155,
195, and 235 K provided evidence for a phase transition changing from
the monoclinic space group C2/c to P21/c. The self-assembly process
of CuI with bis­(p-tolylthio)­methane (L2), bis­(4-methoxyphenylthio)­methane (L3), and bis­(4-bromo-phenylthio)­methane
(L4) affords the 1D-coordination polymers [{Cu4(μ3-I)4}­(μ-Lx)2]n (x = 2, 3, or 4). Compounds 2 and 4 are isostructural
with C2/c low temperature polymorph
of 1, whereas the inversion centers and 2-fold axes are
lost in 3 (space group Cc). The use
of bis­(m-tolylthio)­methane (L5) has
no impact on the composition and overall topology of the resulting
1D ribbon of [{Cu4(μ3-I)4}­(μ-L5)2]n (5). Even the coordination of the sterically crowded dithioether bis­(5-tert-butyl-2-methylphenylthio)­methane (L8)
does not alter the network topology generating the 1D polymer [{Cu4(μ3-I)4}­(μ-L8)2]n (8). The
1D polymer [{Cu­(μ2-Br)2Cu}­(L1)2] (9) results from the coordination of L1 with CuBr in a 1:1 metal-to-ligand ratio. In contrast to
the mean Cu···Cu distances, which are <2.8 Å
noted for the Cu4(μ3-I)4 clusters
in the 1D polymers 1–8, the Cu···Cu
contact within the Cu­(μ2-Br)2Cu rhomboids
of 9 [2.9194(8) Å] is above the sum of the van der
Waals radii of two Cu atoms. The structural arrangement of 1D polymer
[{Cu­(μ2-Br)2Cu}­(L3)2]n (11) is quite similar
to that of 9. While the reaction of CuBr with L5 results in a similar 1D polymer [{Cu­(μ2-Br)2Cu}­(L5)2]n (12), the reaction of CuBr with L2 leads
to the dinuclear complex [{Cu­(μ2-Br)2Cu}­(η1-L2)4] (10) ligated by
four pendent bis­(p-tolylthio)­methane ligands. The
ligation of bis­(o-tolylthio)­methane, L6, on CuBr also yields a discrete complex [{Cu­(μ2-Br)2Cu}­(MeCN)2(η1-L6)2] (13) bearing MeCN and dangling dithioether
ligands. A strong luminescence is detected for all CuI polymers, all
exhibiting emission lifetimes in the microsecond time scale (i.e.,
phosphorescence). The polymers containing the Cu4I4 core (1–8) exhibit the typically
observed low-energy band and sometimes a weaker high-energy band.
The nature of the low-energy band was proposed based on literature
DFT and TDDFT computations and is predicted to be a mixture of cluster-centered
(CC*) and metal/halide-to-ligand charger transfer (M/XLCT). An approximate
relationship between the Cu···Cu distance and the emission
maxima corroborates the CC* contribution to the nature of the excited
states. The emission of the rhomboid-containing materials is assigned
to M/XLCT based on literature works on similar motifs.