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.
The effects of moving the donor N-atom from the 2-position in lithium (2-pyridyl)- and (2-quinolyl)aluminates to the more remote position in (8-quinolyl)aluminates have been investigated by solid-state structural and DFT...
The substitution of heavier, more metallic atoms into
classical
organic ligand frameworks provides an important strategy for tuning
ligand properties, such as ligand bite and donor character, and is
the basis for the emerging area of main-group supramolecular chemistry.
In this paper, we explore two new ligands [E(2-Me-8-qy)3] [E = Sb (1), Bi (2); qy = quinolyl],
allowing a fundamental comparison of their coordination behavior with
classical tris(2-pyridyl) ligands of the type [E′(2-py)3] (E = a range of bridgehead atoms and groups, py = pyridyl).
A range of new coordination modes to Cu+, Ag+, and Au+ is seen for 1 and 2, in the absence of steric constraints at the bridgehead and with
their more remote N-donor atoms. A particular feature is the adaptive
nature of these new ligands, with the ability to adjust coordination
mode in response to the hard–soft character of coordinated
metal ions, influenced also by the character of the bridgehead atom
(Sb or Bi). These features can be seen in a comparison between [Cu2{Sb(2-Me-8-qy)3}2](PF6)2 (1·CuPF6) and [Cu{Bi(2-Me-8-qy)3}](PF6) (2·CuPF6),
the first containing a dimeric cation in which 1 adopts
an unprecedented intramolecular N,N,Sb-coordination mode while in the second, 2 adopts
an unusual N,N,(π-)C coordination mode. In contrast, the previously
reported analogous ligands [E(6-Me-2-py)3] (E = Sb, Bi;
2-py = 2-pyridyl) show a tris-chelating mode in their
complexes with CuPF6, which is typical for the extensive tris(2-pyridyl) family with a range of metals. The greater
polarity of the Bi–C bond in 2 results in ligand
transfer reactions with Au(I). Although this reactivity is not in
itself unusual, the characterization of several products by single-crystal
X-ray diffraction provides snapshots of the ligand transfer reaction
involved, with one of the products (the bimetallic complex [(BiCl){ClAu2(2-Me-8-qy)3}] (8)) containing a Au2Bi core in which the shortest Au → Bi donor–acceptor
bond to date is observed.
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