Hydrotris(1,2,4‐triazolyl)borato Complexes with the Main Group Elements Ca, Sr, and Pb – Unexpectedly Bent ML 2 Structures and a Stereochemically Inactive Lone Pair at Lead(II)

The coordination of the modified poly(azolyl)borato ligand hydrotris(1,2,4‐triazolyl)borato (L) with main group metals leads to complexes with coordination numbers of eight and the formula [CaL 2 (H 2 O) 2 ], [SrL 2 (H 2 O) 2 ], and [PbL 2 (H 2 O) 2 ]. The two L ligands coordinate in a “bent” arrangement to allow for the coordination of the two aqua ligands. This is in sharp contrast to six‐coordinated, pseudo‐octahedral CaTp 2 and PbTp 2 complexes [Tp = hydrotris(pyrazolyl)borato]. The calcium, strontium, and lead complexes are isostructural. No stereochemical lone pair activity is evident in [PbL 2 (H 2 O) 2 ]. Two additional water molecules of crystallization complete the crystal structure of [CaL 2 (H 2 O) 2 ] · 2 H 2 O and [PbL 2 (H 2 O) 2 ] · 2 H 2 O. In the synthesis of [PbL 2 (H 2 O) 2 ] an intermediate of the form $^2_\infty$ [Pb(μ 3 ‐L)(NO 3 )H 2 O] could isolated and structurally characterized. There, the lead(II) center is seven coordinated with a presumably stereochemically active lone pair. Long M–L bonds argue for a more ionic bonding to the modified tris(triazolyl)borato ligand when compared to analogous M–Tp complexes.