Diverse structures and dimensionalities in hybrid frameworks of strontium and lanthanum with isomeric dihydroxybenzoates

Abstract

Investigations of Sr and La derivatives of 2,3-, 2,4-, 3,5-, and 2,6-dihydroxybenzoic acids have revealed that it is possible to obtain chain and layered structures of these materials. [Sr₂(2,3-DHB)₄(H₂O)₄]·3H₂O, I, and [Sr(2,4-DHB)₂(H₂O)₄]·H₂O, II, are both one-dimensional coordination polymers based on dimers; both the carboxylate and phenolic oxygens bond to the metal in I and only the carboxylate oxygens bond to the metal in II. [Sr(3,5-DHB)₂(H₂O)₂]·4H₂O, III, has a one-dimensional chain structure with large channels and involves extended Sr-O-Sr connectivity. [Sr(CH₃CO₂)(2,4-DHB)(H₂O)₃]·H₂O, IV, also has a chain structure with extended Sr-O-Sr connectivity, but the chain structure is formed by bridging acetate units, unlike in III where the Dihydroxybenzoate (DHB) is the bridging unit. [Sr(2,6-DHB)₂(H₂O)₂]·0.5H₂O, V, is a two-dimensional coordination polymer where both carboxylate and phenolic oxygens coordinate to the metal. A lanthanum compound with the composition [La(CH₃CO₂)₂(2,4-DHB)H₂O]·0.18H₂O, VI, with a one-dimensional chain structure with extended La-O-La connectivity, has been prepared. Besides these chain and layered structures, zero-dimensional dimers of rare-earth DHBs with the general formula [La(CH₃CO₂)₂(DHB)(H₂O)₂], with 3,5- (VII), 2,6- (VIII), and 2,3-dihydroxybenzoic acids (IX) have been synthesized. The diverse structures of the strontium and lanthanum DHBs are described. The study demonstrates that it is possible to obtain interesting structures of metal DHBs with different dimensionalities. The structures appear to be controlled largely by geometrical rather than electronic factors.