A family of three-dimensional 3d–4f and 4d–4f heterometallic coordination polymers based on mixed isonicotinate and 2-sulfobenzoate ligands: syntheses, structures and photoluminescent properties

Abstract

Hydrothermal reactions of isonicotinic acid (Hina), 2-sulfobenzoic acid (H(2)sba), d-block metal salts and lanthanide oxides/hydroxides yielded 17 three-dimensional (3D) 3d-4f and 4d-4f heterometallic coordination polymers (HCPs). They are formulated as [LaAg(sba)(ina)(2)](n) (1), [Ln(2)Ag(2)(sba)(2)(ina)(4)(H(2)O)(2)](n) [Ln = Pr (2), Nd (3), Sm (4), Eu (5), Gd (6), Tb (7), Dy (8), Ho (9), Er (10)] and [Ln(2)Cu(2)(sba)(2)(ina)(4)(H(2)O)(2)](n) [Ln = La (11), Pr (12), Nd (13), Sm (14), Eu (15), Gd (16), Tb (17)]. Their structures were characterized by single crystal X-ray diffraction, powder X-ray diffraction (XRD), infrared (IR) spectroscopy, elemental analysis (EA), and thermogravimetric analysis (TGA). It reveals that they represent two structural types of 3D HCPs. Furthermore, the investigations of their solid-state photoluminescent (PL) property demonstrate the extraordinary emission behaviors. HCP 1(La-Ag) exhibits tunable blue-to-green PL emissions by variation of excitation light. HCPs 6(Gd-Ag), 11(La-Cu), 12(Pr-Cu) and 16(Gd-Cu) show d(10)-metal-based ligand-to-metal charge transfer (LMCT) or metal-to-ligand charge transfer (MLCT) emissions. HCPs 3(Nd-Ag), 4(Sm-Ag), 5(Eu-Ag), 7(Tb-Ag), 8(Dy-Ag), 13(Nd-Cu), 14(Sm-Cu), 15(Eu-Cu) and 17(Tb-Cu) display characteristic PL emissions of the corresponding Ln(III) ions, while both d(10)-metal-based and 4f-metal-centered emissions are observed in the emission spectra of 4(Sm-Ag), 8(Dy-Ag), 14(Sm-Cu) and 17(Tb-Cu).

Three-dimensional Yb(III)–Ag(I) heterometallic coordination polymer showing dual photoluminescent emissions in the visible and near-infrared regions

“…However, these two kinds of coordination modes are commonly encountered for ina ligand in 4d-4f HCPs [25]. Interestingly, two sba ligands exhibit two unique coordination modes, which differ from those observed in the former two structural types of 4d-4f HCPs [20]. It confirms once again the viewpoint that the difference of ionic radii of the lanthanide series sometimes results in different coordination modes of ligands, and thus different crystal structures.…”

“…Therefore, the emission peak at 477 nm can be assigned to ligand-to-ligand charge transfer (LLCT). However, a bathochromic shift (about 42 nm as compared with the free ligands and 23 nm as compared with a related La-Ag HCP [20]) is observed due to the different coordination environment of ligands exhibited in HCP 1.…”

“…Besides, the emissions of [Ag-pyridyl coordination units]-based ligand-to-metal or metal-to-ligand charge transfer (LMCT or MLCT) are generally located at about 500 nm or higher [26,27]. Third, the free Hina and H 2 sba ligands display PL emissions centered at 436 nm (excitation at 265 nm) [28] and 434 nm (excitation at 272 nm) [20], respectively. Therefore, the emission peak at 477 nm can be assigned to ligand-to-ligand charge transfer (LLCT).…”

“…This is the so-called "antenna effect" or sensitization process. Recently, we have reported a series of Ln(III)-Ag(I) [from La to Er except Ce and Pm] heterometallic coordination polymers (HCPs) based on mixed isonicotinate and 2-sulfobenzoate ligands [20]. PL studies revealed that sensitization of lanthanide luminescence by d 10 -metal-based coordination units was achieved in some of the HCPs.…”

“…In this research, we used Yb(NO 3 ) 3 ·5H 2 O and AgNO 3 as metal sources and a Yb(III)-Ag(I) HCP, formulated as [Yb 2 Ag 2 (sba) 2 (ina) 4 (H 2 O) 3 ] n · nH 2 O (1), was obtained by hydrothermal reaction [21]. Single-crystal X-ray diffraction indicates that it has a completely different crystal structure from the former two types of Ln(III)-Ag(I) HCPs [20]. HCP 1 exhibits both ligand-to-ligand charge transfer (LLCT) emission in the visible region and Yb(III)-centered 2 F 5/2 → 2 F 7/2 emission in the NIR region, although sensitization of Yb(III) luminescence by Ag(I) is not realized as we expect.…”