The geometry of calcium carboxylate interactions in crystalline complexes

Abstract

The geometries of some 170 examples of calciumcarboxylate interactions from crystal structures of calcium complexes are reviewed. Calcium-carboxylate interactions fall into three main categories: a unidentate mode in which the Ca ion binds to only one of the carboxylate O atoms; a bidentate mode in which the carboxylate ion uses both O atoms to chelate the Ca ion; and an additional chelation mode, the a mode, that is observed when a suitable ligand for the Ca ion is attached at the a position and in which chelation of the Ca ion is achieved by use of the ct substituent together with one of the carboxylate O atoms. The three modes show distinct geometrical preferences, but in each there is a strong tendency for the Ca ion to lie near the plane of the carboxylate group. In general, there is little tendency for a Ca ion to be collinear with the C-O bond. The unidentate examples cluster on both sides of the C-O bond, with most Ca ions lying at Ca--O-C angles of about 150-170 ° on the side away from the second O atom of the carboxylate group, or 110-140 ° on the side toward the second O atom.

Isomorphous Polymeric Complexes of Ca2+ and Pb2+ with 9,10-Dihydro-9-oxo-10-acridineacetate (CMA−) Ligands: [M(CMA)2(H2O)2]

“…Furthermore, a polymeric structure is commonly observed for Ca 2÷ and Pb 2+ carboxylates. The bond lengths and bond angles for the metal coordination in [Ca(CMA)2(H20)2] are in agreement with the average values found for a series of calcium bidendate carboxylates (Einspahr & Bugg, 1980). The distances found in the PbOs polyhedron are characteristic for lead(II) carboxylates (Bensch & Gunter, 1987;Blake, Gould, Grant, Milne, Reed & Winpenny, 1994;Bryant, Chacko & Etter, 1984;Chandler, Hampden-Smith & Duesler, 1992;Glowiak, Koztowski, Erre, Micera & Gulianti, 1992;Jones, Schelbach, Shwarzmann, Thone & Vielmader, 1988;Lis, 1984;Mak, Yip, O'Reilly, Smith & Kennard, 1985).…”

Metal Ion Interactions with Crude Oil Components: Specificity of Ca2+ Binding to Naphthenic Acid at an Oil/Water Interface

“…Thus, specifically for Ca 2+ , monodentate coordination with one carboxylate O atom and hydrogen bonded water, bidentate coordination, with both carboxylate O atoms, or bridging (see Figure 6a-c) are notable [82]. On the other hand, a major difference in bonding mode with carboxylic acids in the case of magnesium is the formation of uncoordinated ionic species of the form shown in Figure 6d [87].…”

“…The structures of metal carboxylate complexes have been extensively studied over the years and have allowed the detailed examination of X-ray crystallographic data by Einspahr and Bugg [82] and Carrell et al [83], which, together with other investigations [47,[84][85][86] has culminated in the principal binding modes shown in Figure 6 being identified. Thus, specifically for Ca 2+ , monodentate coordination with one carboxylate O atom and hydrogen bonded water, bidentate coordination, with both carboxylate O atoms, or bridging (see Figure 6a-c) are notable [82]. On the other hand, a major difference in bonding mode with carboxylic acids in the case of magnesium is the formation of uncoordinated ionic species of the form shown in Figure 6d [87].…”

Refined structure of concanavalin A complexed with methyl α-D-mannopyranoside at 2.0 Å resolution and comparison with the saccharide-free structure

“…Using an upper limit of 2.8 A for a calciumoxygen bond for a bidentate carboxylic group (Einspahr & Bugg, 1981) the calcium ion is seven coordinate in the A, B, and D subunits but six coordinate in the C subunit. The individual ligand bond distances are shown in Table 8 and the temperature factors are shown in Table 9.…”