Bismuth as a versatile cation for luminescence in coordination polymers from BiX₃/4,4′-bipy: understanding of photophysics by quantum chemical calculations and structural parallels to lanthanides

Abstract

Coordination polymers (CPs) with bismuth(iii) as a connectivity centre have been prepared from BiX3 (X = Cl-I) and 4,4'-bipyridine (bipy) in order to implement Bi-based luminescence. The products were obtained via different synthetic routes such as solution chemistry, melt syntheses or mechanochemical reactions. Five neutral and anionic 1D-CPs are presented that show a chemical parallel to trivalent lanthanides forming isostructural or closely related 1D-CPs, of which five additional compounds are described. Bi3+ proves to be a versatile cation for luminescence resulting from energy transfer processes between a metal and a ligand in the presented CPs. Quantum chemical calculations were carried out to investigate Bi3+-participation in the luminescence processes. The calculated results allow an assignment of the bright transitions composed of mainly metal-to-ligand-charge transfer (MLCT) character. These results show that Bi3+ can form strongly luminescent coordination compounds with N-donor ligands.

Synthesis and photoluminescence of three bismuth(iii)-organic compounds bearing heterocyclic N-donor ligands

“…14 The origins of these emissive transitions have been attributed to ligand-tometal charge transfer (LMCT), metal-to-ligand charge transfer (MLCT), intraligand transitions (n ← π*)/(π ← π*) that are noticeably shifted from the free ligand emission, and/or intraconfigurational 1 P 1 → 1 S 0 and 3 P 1 → 1 S 0 transitions originating from the 6s 2 closed shell Bi 3+ metal center. [14][15][16][17][18][19]28,30 Intervalence charge transfer has also been recently reported for several Bi systems. 22,29 Additionally, the luminescence behavior of several halobismuthates have been attributed to a combination of metal-centered sp excited states and halogento-metal charge transfer (XMCT).…”

“…Clusters of various sizes were rendered and used for analysis, starting from a single molecular unit to larger systems (dimer, trimer, and pseudo-tetramer). All spectra were computed using a similar approach proposed by Sorg et al, 17 based on single point calculations using a current development version of the ORCA 4.1.2 program package. 48,49 The calculations rely on the use of the CAM-B3LYP functional, a hybrid functional with long-range separation, to compute the density of the compound, 50 associated to def2-SVP basis set for all atoms, 51 and a Relativistic Small Core Effective Pseudopotential for Bi.…”

“…Recently, though, bismuth-based compounds have attracted increasing attention due, in part, to their unique photoluminescence behaviour. [12][13][14][15][16][17][18][19][20][21][22][23] Trivalent bismuth has a [Xe]4f 14 5d 10 6s 2 electron configuration and possesses lone pair electrons (6s 2 ) with variable stereochemical activity. This results in a flexible coordination environment ranging from a hemidirected to holodirected coordination sphere, a range of coordination numbers, and thus, the potential for novel structuretypes.…”

In‐situ Ligand Formation Based Synthesis of a Luminescent Bi‐Nitrile Based Framework: 3∞[Bi2Br6(tcpt)]

“…While the band at higher energy shows approximately one third of the intensity of the band at 417 nm, its intensity increases to two thirds of the intensity of the band at 417 nm for an emission wavelength of 520 nm. Since the excitation spectrum is closely related to the spectra of 1 ∞ [Bi 2 X 6 (4‐bipy)] ( X = Cl, Br; 4‐bipy = 4,4′‐bipyridine), we assume a similar excitation mechanism in 3 ∞ [Bi 2 Br 6 (tcpt)] and thus ascribe both excitation bands to metal‐to‐ligand‐charge‐transfer processes as in other related literature‐known compounds …”

“…Bismuth‐containing coordination compounds and polymers have gained research interest, recently, due to their promising properties in terms of their low toxicity and variable photoluminescence properties . The latter properties include variable processes such as metal‐centered s‐p transitions as well as intra‐ligand and metal‐to‐ligand charge‐transfer (ILCT, MLCT) processes .…”