Solvent-Free Synthesis of Luminescent Copper(I) Coordination Polymers with Thiourea Derivatives

Abstract

This communication reports the solvent-free synthesis of a series of copper(I) cyanide (CuCN) -based coordination polymers showing interesting luminescence properties and specific three-dimensional structures. The new compounds have been achieved by directly grinding CuCN together with thiourea (tu), N-methylthiourea (mtu), N-phenylthiourea (ptu), N,N′-diphenylthiourea (dptu), and 2,4-difluorophenylthiourea (fptu). The resulting compounds are [(CuCN) 2 (tu)] n , [(CuCN) 5 (mtu) 3 ] n , [(CuCN) 3 (mtu) 2 ] n , [CuCN(ptu)] n , [CuCN(dptu)] n , and [(CuCN) 3 (fptu) 2 ] n . "Seeding" crystallization was successful for [(CuCN) 2 (tu)] n , [CuCN(ptu)] n , [CuCN(dptu)] n , and [(CuCN) 3 (fptu) 2 ] n , and their structures have been resolved using Xray single crystal diffraction. Owing to the microcrystalline powdered nature of compounds [(CuCN) 5 (mtu) 3 ] n and [(CuCN) 3 (mtu) 2 ] n , their characterization was mainly based on solid-state NMR, via 13 C cross polarization magic angle spinning for ligand coordination and 1 H magic angle spinning for the weak interactions involving hydrogen atoms. Other solid-state techniques (infrared spectroscopy, X-ray powder diffraction, differential scanning calorimetry, and thermogravimetric analysis) completed the characterization. Finally, the luminescence properties were explored by recording emission and excitation spectra and by evaluating the luminescence quantum yields and lifetimes. Such in-depth study gives promising results for the potential application as luminescent sensors of such compounds. ■ INTRODUCTIONLuminescent coordination polymers have been widely studied in recent decades, and several new materials have been produced and tested. 1 In particular, the chemisorption of small molecules onto these materials has been shown to alter their luminescence properties, 2 prospecting potential applications as molecular sensing systems. In this context, copper(I) coordination polymers have not been as widely explored, if compared to other transition metal or lanthanide analogues. 3−7 In particular, CuCN can provide interesting luminescence properties when reacted with proper ligands. A recent computational study described its particular structure highlighting that, conversely to many inorganic salts forming twoor three-dimensional (2D or 3D) arrays, CuCN is characterized by one-dimensional polymer chains consisting of twocoordinated metal centers and bridging cyano ligands. 8 CuCN itself is characterized by a weak luminescence. 9 However, its photoluminescence emission interestingly shifts from the near UV (392 nm) into the visible region upon the coordination of nucleophiles, while the intensity increases by several orders of magnitude. In some cases, small differences in the ligands, such as the presence of methyl or ethyl groups like in piperazine, methylpiperazine, and ethylpiperazine, can result in remarkable differences in the emission color of the obtained coordination polymers, providing several luminescence tuning possibilities. 10 Despite these promising properties,...

Synthesis and structural characterization of Pd(II) and Cu(I) complexes containing dithiophosphorus ligand and their catalytic activities for Heck reaction

“…The L ligand acts as chelating ligand via its two sulfur atoms in way that the one sulfur atom is bridged between two copper and the other sulfur atom coordinates only to one copper. The Cu2S2 ring shows a particular geometry with alternative long (2.6147(6) Å) and short (2.3085(6) Å) Cu-S distances due to the nature of the orbitals and electrons of the bridging sulfur [50,51]. The Cu-P (Cu-P2, CuA-P2A) and Cuterminal S (Cu-S1, CuA-S1A) lengths are 2.2220(5) and 2.3857 (6), respectively, which fall within the range of copper(I) dithiocomplexes [52,53].…”

Vibrational–Structural Combined Study into Luminescent Mixed Copper(I)/Copper(II) Cyanide Coordination Polymers

“…[31] After the coordination of ligands with N or S atoms as the binding site, the luminescence moves towards the visible region, as the presence of two different transitions leads to two possible emissive paths: metal to CN ligand and metal to S/Nligand; the CC transitions can be discounted if the Cu···Cu distance is longer than 2.8 Å. [33,74] The emission and excitation spectra of the studied compounds are reported in Figure 2, and the corresponding data are listed in Table 2 together with the emission quantum yields. All of the coordination polymers exhibit a broad excitation feature in the λ = 300-375 nm range, which is similar to that displayed by the parent CuCN.…”

“…[31] The compound exhibits weak luminescence, [32] which generally shifts from the near-UV (392 nm) into the visible region and becomes more intense upon the coordination of nucleophiles, such as thioamide ligands. [33] In general, small ligand differences can cause significant differences to the emission colors of coordination polymers, and this enables luminescence tuning. [34] On the other hand, very little attention has been paid to the luminescence of CuCN itself and the variations that occur at different coordination degrees.…”

Complete multinuclear solid‐state NMR of metal‐organic frameworks: The case of α‐Mg‐formate

“…1 H SSNMR can be employed to obtain detailed structural data that is truly complementary to XRD, yet this characterization route is not straightforward due to strong 1 H‐ 1 H homonuclear dipolar coupling that can severely broaden spectra, which arises from the spatial density of hydrogen in MOFs along with the very high 1 H gyromagnetic ratio (γ). Using high‐resolution 1 H SSNMR techniques it is possible to obtain well‐resolved 1 H resonances in MOFs, including those from chemically different species such as phenyl, methyl, amine, and hydroxyl groups. A more challenging situation arises when there are chemically identical but crystallographically non‐equivalent hydrogen atoms; in this situation, the similar 1 H chemical shifts (CSs) and strong 1 H‐ 1 H dipolar coupling result in very complicated lineshapes and overlapping resonances within a narrow CS range that cannot be resolved.…”

“…The use of 13 C SSNMR to investigate MOFs has become fairly common, particularly in recent years . Despite the widespread use of 13 C SSNMR, very challenging situations arise when many crystallographically distinct but otherwise chemically similar carbon centers are present, which gives rise to multiple overlapping 13 C resonances confined within a narrow chemical shift range that cannot be easily simulated or assigned, as in the case of α‐Mg‐formate …”