High-temperature, high-pressure hydrothermal synthesis, crystal structure, and infrared and NMR spectroscopy of a barium lead borate with a 2D layer structure: [BaPb(HO)][BO(OH)]

With a high-temperature, high-pressure hydrothermal technique, a new barium lead borate, [Ba 3 Pb(H 2 O)][B 11 O 19 (OH) 3 ] ( 1 ), has been synthesized and characterized by single-crystal X-ray diffraction, and infrared and solid-state NMR spectroscopy. The structure of 1 contains planar thick layers of borates with the Ba 2+ cations at sites in the inter- and intralayer space. Each layer consists of three single sheets. The central sheet is very corrugated and is built up from the fundamental building block (FBB) 2Δ3 :〈Δ2 〉-〈Δ2 〉. On both sides of the central sheet there are borate single chains formed of the very rare FBB 2Δ4 :〈Δ2 〉-〈3 〉Δ via corner-sharing. This FBB was first observed in a high-pressure polymorph of CaB 2 O 4 . These chains are linked into a sheet by PbO 5 (H 2 O) polyhedra, which are further linked to the central sheet by sharing vertices between triangles and tetrahedra to form a thick layer. The IR spectrum shows the presence of hydroxyl groups of HBO 4 , water molecules, BO 3 triangles, and BO 4 tetrahedra. The presence of BO 3 and BO 4 polyhedra was also confirmed by 11 B MAS NMR spectroscopy. The structure of the hydrothermally synthesized barium lead borate contains an unusual fundamental building block, 2Δ4 :〈Δ2 〉-〈3 〉Δ, which was also found in the high-pressure form of CaB 2 O 4 synthesized at 900 °C under a pressure of 15-25 kbar.