A Fused Poly(truncated rhombic dodecahedron)-Containing 3D Coordination Polymer: A Multifunctional Material with Exceptional Properties

Abstract

The design of new and inexpensive metal-containing functional materials is of great interest. Herein is reported a unique thermochromic near-IR emitting coordination polymer, 3D-[Cu8I8(L1)2] n , CP2, which is formed when ArS­(CH2)4SAr (L1, Ar = 4-C6H4OMe) reacts with 2 equiv of CuI in EtCN. In MeCN, CP1 ([Cu4I4(L1)­(MeCN)2] n , consisting of an alternating [-Cu4I4-L1-Cu4I4-L1-] n chain where the Cu4I4 cubane units bear two metal-bound MeCN molecules, is formed. Heat-driven elimination of these MeCN’s in solid CP1 also leads to CP2 through a predisposed organization of the Cu4I4 units prone to fusion after MeCN eliminations (i.e., a rare case of template effect). The CP2 structure exhibits parallel 1D-(Cu8I8) n chains, (z-axis; designated 1D-[CuI] n ) as secondary building units (SBU) held together by parallel thioether ligands (x,y-axes), forming a nonporous 3D network. The structure of this 1D-[CuI] n SBU is unprecedented and consists of a series of fused and twisted open Cu4I4 cubanes forming a fused poly­(truncated rhombic dodecahedron). Unexpectedly, the compact 3D CP2 exhibits a solid-to-solid phase transition at 100 °C and a hysteresis of ∼20 °C. CP1 emits intensively (298 K: λemi = 564 nm; Φe = 0.35), whereas CP2 presents a strongly red-shifted weaker emission (298 K: λemi ∼ 740 nm, Φe < 0.0001). Moreover, CP2, which is stable over long periods of time, exhibits thermochromism where the emission intensity of the near-IR band decreases significantly at the benefit of a ligand-centered phosphorescence at 415 nm. Altogether, these properties listed above make CP2 exceptional. The low-energy singlet and triplet excited states have been assigned to ligand/metal-to-ligand charge transfer based on DFT and TD-DFT computations.

2,2′-Ethylenebis(1,3-dithiane) as a polydentate μ2-, μ4- and μ5-assembling ligand for the construction of sulphur-rich Cu(i), Hg(ii) and heterometallic Cu(i)/Hg(ii) coordination polymers featuring uncommon network architectures

“…Metal-bound MeCN ligands are often coordinated in a quite labile manner on a given metal center. 62,63 However, in the case of CP13, no degradation of the yellow crystals by the dissociation of volatile MeCN was observed, even upon exposure to air for prolonged periods.…”

Chain Length Effect on the Structural and Emission Properties of the CuI/Bis((4-methoxyphenyl)thio)alkane Coordination Polymers

“…36 The other 3D-CP in this series is CP4, [(Cu 8 I 8 )- (L4) 2 ] n , where L4 bears a (CH 2 ) 4 chain. 38 The link between CP4 and CP8 is noteworthy since both share similarities. Both CPs are 3D, use a globular SBU, and the (CH 2 ) m chains exhibit m = 8 in CP8 and m = 4 in CP4, stressing the fact that one is a factor of the other.…”

“…We have also recently demonstrated that outcome of the reaction of CuI with L4 depends crucially on the choice of acetonitrile vs propionitrile. 38 Therefore, we also performed the reaction with EtCN instead of MeCN as the solvent. However, in the case of L8, no impact on the architecture was observed; in both cases the material crystallizes in the tetragonal space group I41̅ a.…”

“…49−53 Except for the previously reported CP4, no emission thermochromism was detected in this series. 38 The emission quantum yield (Φ e ) measurements (at 298 K) allow for the division into two categories: strong yellow emission, CP1, CP3, CP5, and CP7 (Φ e > 0.23), and weak blueish luminescence, CP2, CP4, CP6, and CP8 (Φ e < 0.11), with the latter group being less intense (note that this latter 0.11 value is associated with a Cu 4 I 4 chromophore, which is usually strongly emissive). The quantum yield of CP1 is not known but it is reported to be strongly emissive.…”

“…36 One exception was recently reported for a 3D-CP [(Cu 8 I 8 )(L4) 2 ] n (CP4) formed when CuI was reacted with para-MeOC 6 H 4 S(CH 2 ) 4 SC 6 H 4 OMe (L4) in which a very rare 1D-SBU (Cu 8 I 8 ) n as a poly(truncated rhombic dodecahedron) formed. 38 Concurrently, when m = 1, a strongly emissive 1D-CP of the formula [Cu 4 I 4 (ligand) 2 ] n (CP1) formed instead, where the SBU is a closed cubane. 39,40 This observation suggests that the CP structure and SBU motif, and consequently, the network's properties, appear to be chain length dependent.…”