Uncovering the Hidden Landscape of Tris(4‐pyridyl) Ligands: Topological Complexity Derived from the Bridgehead

Abstract

Supramolecular main group chemistry is a developing field which parallels the conventional domain of metallo‐organic chemistry. Little explored building blocks in this area are main group metal‐based ligands which have the appropriate donor symmetry to build desired molecular or extended arrangements. Tris(pyridyl) main group ligands (E(py)3, E=main group metal) are potentially highly versatile building blocks since shifting the N‐donor arms from the 2‐ to the 3‐positions and 4‐positions provides a very simple way of changing the ligand character from mononuclear/chelating to multidentate/metal‐bridging. Here, the coordination behaviour of the first main group metal tris(4‐pyridyl) ligands, E(4‐py)3 (E=Sb, Bi, Ph−Sn) is explored, as well as their ability to build metal‐organic frameworks (MOFs). The complicated topology of these MOFs shows a marked influence on the counter anion and on the ability of the E(4‐py)3 ligands to switch coordination mode, depending on the steric and donor character of the bridgehead. This structure‐directing influence of the bridgehead provides a potential building strategy for future molecular and MOF design in this area.

Cation- and Anion-Mediated Supramolecular Assembly of Bismuth and Antimony Tris(3-pyridyl) Complexes

“…However, the Bi···N interactions in 2 [3.374(4) Å] are significantly longer than those recently observed in the structure of Bi(4-py) 3 [range 3.071(5)–3.306(5) Å], which also forms a polymeric arrangement in the solid state through Bi···N interactions. 25 …”

“…This feature has also recently been highlighted in a study of the formation of 2D or 3D networks using Group 15 tris(4-pyridyl) ligands. 25 …”

“…No hydrolysis was observed for 1 week after the addition of either ca. 10 equiv of H 2 O in CDCl 3 or deuterated dimethyl sulfoxide (DMSO- 25 Coordination Chemistry. With ligands 1 and 2 in hand, we moved to explore their coordination chemistry and evaluate the impact of the bridgehead on building supramolecular arrangements.…”

“…This feature has also recently been highlighted in a study of the formation of 2D or 3D networks using Group 15 tris(4-pyridyl) ligands. 25 Preliminary studies indicate that the bridgehead−metal interaction also has a large impact on the luminescence properties of the 3D MOFs. For instance, when excited with UV light (λ ex = 375 nm) at room temperature, the Bi(III)/ Cu(I) MOF 2•CuPF 6 exhibits bright-green luminescence (λ max,em = 530 nm), while its Sb analogue 1•CuPF 6 shows red-shifted luminescence in the orange region (λ max,em = 570 nm; see the SI).…”

“…Most recently, attention has been directed to the effects of moving the donor N atoms from the 2 position to the 3 and 4 positions of the pyridyl ring units. − The expected result is that the ligand character switches from the intramolecular N,N,N-chelation mode normally observed for the tris­(2-pyridyl) ligands (Figure c) to the separate use of the donor N atoms in intermolecular bonding (Figure d,e). This modification can therefore be employed as a strategy for the formation of cages and metal–organic frameworks (MOFs).…”