Abstract
Triclinic crystals of BaC 4O 4·3H 2O were grown in an aqueous silica gel. Lattice constants were a = 660.38(9) pm, b = 859.83(8) pm, c = 878.26(9) pm, α = 61.281(8)°, β = 63.827(9)°, γ = 70.53(1)°; Z = 2, space group P 1 . Anisotropic refinement of neutron diffraction data led to R w = 0.0234 including anharmonic thermal parameters for H atoms. Ba 2+ has CN 8 + 1. It is surrounded by five water molecules and four O squarate atoms (BaO 271.3–323.1 pm). The squarate dianion is almost planar and shows CC and CO bond lengths indicating the existence of undisturbed resonance stabilization, although one O squarate atom is not connected to Ba 2+ (CO 124.4–125.5 pm, CC 145.6–147.7 pm). Asymmetric hydrogen bonds between H 2O and O squarate play an important part in this structure. Obviously the bonding between O squarate and its noncarbon neighbors is dominated by electrostatic and ionic interactions.
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