Polymorphism and polytypism in zinc aliphatic carboxylate: The complex case of Zn(C11H21O2)2

Crystallographic study was performed on the zinc undecanoate Zn(C11H21O2)2 by X-ray diffraction. Three polymorphs A, B and C were identified. The structures of A and B were solved from X-ray diffraction on platelets like single crystals obtained by crystallization in methanol. Polymorph A: SG = P21/c, a = 54.411(4) Å, b = 4.666(4) Å, c = 9.2231(8) Å, β = 92.54(7)°, V = 2341(2) Å3, Z = 4; polymorph B: SG = Cc, a = 53.451(2) Å, b = 4.707(1) Å, c = 9.178(1) Å, β = 91.53(7)°, V = 2308(2) Å3, Z = 4. Polymorph C has been detected in powder samples obtained by precipitation in aqueous solution. Its structure was solved from X-ray synchrotron diffraction data: SG = Pna21, a = 9.3386(6) Å, b = 4.7393(3) Å, c = 54.646(5) Å, V = 2418.5(3) Å3 and Z = 4. The three polymorphs have the usual layered structures encountered in zinc linear carboxylates series with Zn atoms in tetrahedral O-coordination. The forms A and C have the same building blocks but differ by their stacking. Two adjacent layers are 180° rotated around the short and the long axis in A and C respectively. The form B presents conformational disorder leading to modification of the preceding layers. In these form, the layers maintain the same orientation along the stacking direction.