Low-temperature modification of Ba(BF 4 ) 2 (H 2 O) 3 .

The crystal structure of the low-temperature modification of Ba(BF 4 ) 2 (H 2 O) 3 , barium bis(tetra-fluorido-borate) trihydrate, was determined at 150 K. In contrast to the room-temperature modification, which crystallizes in the space group C 222 1 [ a = 7.1763 (6), b = 18.052 (2), c = 7.1631 (6) Å, V = 927.93 (15) Å 3 at 300 K, Z = 4; Charkin et al. (2023 ▸). J. Struct. Chem . 64 , 253-261], the low-temperature phase is monoclinic, space group P 2 1 [ a = 7.0550 (4), b = 7.1706 (3), c = 9.4182 (6) Å, β = 109.295 (7) o , V = 449.68 (5) Å 3 , Z = 2]. The structure of the low-temperature modification of Ba(BF 4 ) 2 (H 2 O) 3 features O-H⋯F and O-H⋯O hydrogen bonding between water mol-ecules and BF 4 - anions. One of the coordinating water mol-ecules in the low-temperature modification is disordered over two sets of sites.