MALONATE INTERCALATION INTO LAYERED CHROMIUM-ZINC DOUBLE HYDROXIDES

Layered double hydroxides of type [Zn2Cr(OH)(6)]X . nH(2)O where X(-) = 1/2 mal(2-), cis-[Cr(mal)(2)(H2O)(2)](-), and 1/3 [Cr(mal)(3)](3-) ( mal = malonate) were synthesized by anion exchange reactions, These co mpounds were characterized by Xray powder diffractometry and IR spectr oscopy and the results were compared with those of the compounds where X(-) = F-, 1/2 CO32-, and NO3-. The IR data allow the significant dis tinction between hydroxide layer OH-groups forming H-bonds with (i) cr ystal water and (ii) intercalated anions. With reference to the forces regarding the second H-bonding interaction the following order became obvious: NO3- < [Cr(mal)(3)](3-) < F- approximate to CO32- < mal(2-) approximate to cis-[Cr(mal)(2)(H2O)(2)](-). Propositions of the malona te arrangements in the interlayer were discussed, The malonate ligands of both anionic complexes are situated with an angle of 54.75 degrees to the plane of OH close packing, The found differences between both are assumed to be caused by spatial reasons. (C) 1995 Academic Press, Inc.