Komplexe mit aromatischen Carbonsäuren, IV. Ca2[C6H2(COO)4]·6H2O - Eine neue Schichtstruktur/ Complexes with Aromatic Carboxylic Acids, IV. Ca2[C6H2(COO)4]·6H2O - A Novel Layer Structure
Single crystals of Ca2[C6H2(COO)4]·6H2O were grown in aqueous silica gel. Ca2+ has CN 6+2. The coordination polyhedron is formed by three water molecules and five oxygen atoms of carboxylate groups. Six oxygen atoms are closely bound (235,9-243,9 pm), the two remaining coordination partners are considerably more remote from Ca2+ (268,2 and 273,8 pm). COO- groups chelate Ca2+ in an asymmetric manner, but the C -O bond lengths do not differ markedly (125,2-126,3 pm). The connection of Ca2+ with [C6H2(COO)4]4- leads to rigid layers. Adjacent layers are interlinked by hydrogen bonds. Those oxygen atoms which are weakly bound to Ca2+ are favoured as proton acceptors in hydrogen bonds. The COO groups are tilted differently against the C6-ring plane. One is approximately coplanar, but the other is oriented almost perpendicularly.