This
study represents the first explorative investigation on the
supramolecular structural diversity in Hg(II) coordination chemistry
with triazole-thiourea ligands leading to a variety of mononuclear,
binuclear, and coordination polymers: {[Hg(L1)2(L1
–
)2]} (1), {[Hg2(L1)2(μ2-I)2I2]·DMSO} (2), {[Hg(L2)(μ2-I)I]·MeOH}∝ (3), {[Hg2(μ-L3
–)4]}∝ (4), {[HgCl(L4
–)L4]·MeOH}
(5), {[Hg2(L4)2(μ2-I)2(I)2]·2MeOH} (6), {[Hg2(μ2-L5
–
)4]}∝ (7), {[Hg2(μ2-Cl)2(L6
–
)2(L6)2]} (8), {[Hg2(μ2-Br)2(L6
–
)2(L6)2]} (9), and
{[Hg2(μ2-I)2(L6
–)2(L6)2]} (10). A reaction mechanism was suggested for the unexpected
ligand rearrangement occurring in {[Hg2I3(μ3-L5′)]}∝ (11). The ligands were fully characterized including by X-ray crystallography
and computational means. This includes six new triazole-thiourea based
ligands, namely, 1-R-3-(4H-1,2,4-triazol-4-yl)thiourea
(where R = methyl (L1), ethyl (L2), propyl
(L3), isopropyl (L4), and its polymorph
(L4-poly), allyl (L5), ethyl acetate (L6), and its solvate (L6_MeOH)). Under UV light
excitation, 7, 10, and 11 exhibit
visible photoluminescence of wide origin, ranging from ligand-centered
(LC) fluorescence combined with organic-ligand-to-metal charge transfer
(LMCT) emissive states in 7 and 10, up to
halide-to-metal charge transfer (XMCT) combined with halide-to-ligand
charge transfer (XLCT) emissive states in 11. The variable
emission mechanisms in the obtained coordination polymers were elucidated
by experimental proofs confronted with theoretical calculations of
the electronic densities of states, proving that Hg(II) halide coordination
polymers involving flexible 1,2,4-triazole-based ligands form a promising
class of luminescent molecular materials.