Molecular and crystal structure of (2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl)-(1 → 3)-[2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl-(1 → 6)]-(2,4-di-O-acetyl-β-d-glucopyranosyl)-(1 → 3)-1,2,4,6-tetra-O-acetyl-β-d-glucopyranose