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

The use of antimony and bismuth in supramolecular chemistry has been largely overlooked in comparison to the lighter elements of Group 15, and the coordination chemistry of the tripodal ligands [Sb(3-py)3] and [Bi(3-py)3] (L) containing the heaviest p-block element bridgehead atoms has been unexplored. We show that these ligands form a common hybrid metal–organic framework (MOF) structure with Cu(I) and Ag(I) (M) salts of weakly coordinating anions (PF6–, SbF6–, and OTf–), composed of a cationic substructure of rhombic cage (M)4(L)4 units linked by Sb/Bi–M bonding. The greater Lewis acidity of Bi compared to Sb can, however, allows anion···Bi interactions to overcome Bi–metal bonding in the case of BF4–, leading to collapse of the MOF structure (which is also seen where harder metals like Li+ are employed). This study therefore provides insight into the way in which the electronic effects of the bridgehead atom in these ligand systems can impact their supramolecular chemistry.


S9
The study of the extended supramolecular complexes by mass spectrometry proved challenging and not very informative. An illustrative example is given below only for the case of 1•AgBF 4 , for which the fragment [1+Ag] + was identified.  The identification of the formation of 3,3´-bipyridine in the reaction mixture was also done by 1 H NMR (see Fig S9). S10

X-ray Crystallographic Studies
Crystallization conditions to obtain quality crystals for single-crystal X-ray diffraction studies As a general procedure, X-ray quality crystals were obtained by slow diffusion of a solution of the corresponding metal precursor (1 equivalent in 5 mL MeCN) into a DCM solution of 1 or 2 (typically 25-50 mg). In order to increase the quality of the crystals, the process can be slowed by placing an intermediate layer of MeCN (ca. 3 mL) between the other two to obtain a more controlled diffusion (Fig. S15). This leads to better quality crystals. Figure S15. Three-layer synthesis method to obtain high-quality crystals for single-crystal X-ray diffraction studies.
Details of the data collections and structural refinements are given in Table S2. Further details of the methods of refinement of the structures are as follows.

1•CuBF 4 and 1•AgBF 4 :
The BF 4anions were disordered and very poorly resolved (disordered by symmetry, on special positions) and they were treated as a rigid body with their site occupancies in the asymmetric unit constrained to 1/4 (for the BF 4in the void) and 1/12 (for the BF 4in the cage), to produce a total of 8 BF 4anions in the unit cell (2 in the cage and 6 in the exo voids, as in the related structures with PF 6and SbF 6anions discussed in the main text). The structure is charge balanced, with 8 Cu + and 8 BF4 -in the unit cell. Restraints were applied to maintain sensible bond distances and geometry, and the BF 4anions were treated as a rigid body for the final refinement cycles. Rigu restraints were applied to keep the ADPS of the disordered BF 4anions to a reasonable value. The presence of BF 4in the crystal was also assigned on the basis of the additional characterization information, as described in the main text, including 19 F NMR and elemental analysis.

1•AgOTf:
The framework structure is clear; however, the OTfanions are not clearly resolved and therefore SQUEEZE 1 was applied (i.e., removing the disordered OTF anions). SQUEEZE was applied accounting for 566 electrons in a total solvent accessible volume of 1054 cubic angstroms per unit cell. This is consistent with the presence of 8 triflates (CF 3 SO 3 -) per unit cell (i.e., 1 CF 3 SO 3 per formula unit), located in 8 voids (2 cages and 6 exo voids), which account for 592 electrons per unit cell. This is also consistent with the expected stoichiometry (i.e., one CF 3 SO 3per Ag + cation), as well as with the elemental analysis. The presence of OTfin the crystal was also determined by 19 F NMR.   Analysing the X-ray structures of the MOFs, we found that in those containing the Sb ligand, the pyramidalization of the metal atom (Cu or Ag) was much greater than that in those containing the Bi ligand. The N-M-Sb (M = Cu, Ag) angle varies between 108.3 and 112.6° (Fig. S19 left), while the N-M-Bi (M = Cu, Ag) angle takes the values 93.7 and 96.0° (Fig. S19 right). The rather unusual, almost planar coordination of the pyridyl-N atoms of the Bi-ligand to the Cu(I) and Ag(I) centers can be seen from the sums of the N-M-N bond angles (ΣMα, M = Cu, Ag), which are very close to 360 (Fig S20, right).

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Powder X-ray studies Figure S23. Comparison of the experimental (above, red) and the predicted (below, blue) XRPD patterns for compound 1•CuBF 4 . Figure S24. Comparison of the experimental (above, red) and the predicted (below, blue) XRPD patterns for compound 1•CuPF 6 .

Computational details
All computations were carried out using the Gaussian16 package, 2 in which the hybrid method of Austin, Petersson and Frisch with spherical atom dispersion terms (APFD) was applied. 3 The triple zeta cc-pVTZ-PP basis set with effective core potentials was used for the heavy atoms (Sb, Bi, Cu, Ag), 4-7 as found in the basis set exchange library, 8 and 6-31G(d') was used for the rest of the atoms. Geometry optimizations were performed without symmetry restrictions using the initial coordinates derived from X-ray data when available, and frequency analyses were performed to ensure that a minimum structure with no imaginary frequencies was achieved in each case. Energy Decomposition Analysis (EDA) was performed on the geometry optimized models and on the X-ray geometry models with the AOMix program. 9,10 NBO analysis was performed with the NBO 7.0 program. 11 The visualization of the calculation results was performed with GaussView 6.1. 12

Optimization of the model structure
The X-ray derived model structure of the compound 2•AgSbF 6 was optimized without symmetry restrictions using various functionals, and, in all cases, the Bi-Ag distance was found to be shorter than in the X-ray structure.

Study of the E  M interaction
The energy of the E-M interaction was calculated using an Energy Decomposition Analysis (EDA) that was carried out on both the optimized structures and the X-ray derived structures. The composition of the orbitals involved in the interaction was studied using a NBO analysis.