Gd4B4O11F2: Synthesis and crystal structure of a rare-earth fluoride borate exhibiting a new “fundamental building block” in borate chemistry

A new gadolinium fluoride borate Gd4B4O11F2 was yielded in a Walker-type multianvil apparatus at 7.5 GPa and 1100 °C. Gd4B4O11F2 crystallizes monoclinically in the space group C2/c with the lattice parameters a=1361.3(3) pm, b=464.2(2) pm, c=1374.1(3) pm, and β=91.32(3)° (Z=4). The crystal structure exhibits a structural motif not yet reported from borate chemistry: two BO4-tetrahedra (□) and two BO3-groups (▵) are connected via common corners, leading to the fundamental building block 2▵2□:▵□□▵. In the two crystallographically identical BO4-tetrahedra, a distortion resulting in a very long B–O-bond is found.