Organometallic crystals engineering - Part 7. Construction of mixed-metal crystalline systems via electrostatic interactions and cooperative strong and weak hydrogen bonds

The dicarboxylic organometallic acid [(eta(5)-C5H4COOH)(2)Fe] (FeACH(2)) has been used to produce a series of novel mixed-metal mixed-valent crystalline materials by the sequence of reaction steps: (i) oxidation in the air of THF solutions of [(eta(5)-C5H5)(2)Co] and [(eta(6)-C6H6)(2)Cr] and consequent reduction of O-2 to the strongly basic anion O-2(-); (ii) deprotonation of FeACH(2) to yield the anion FeACH(-) (or FeAC(2)(-)); (iii) precipitation of the insoluble organometallic salts formed between the organometallic acidate and the diamagnetic cation [(eta(5)-C5H5)(2)Co](+) or the paramagnetic cation [(eta(6)-C6H6)(2)Cr](+). The novel materials [(eta(5)-C5H5)(2)Co](+)[(eta(5)-C5H4COOH)(eta(5)-C5H4COO)Fe](-) (1), [(eta(5)-C5H5)(2)Co](+)[(eta(5)-C5H4COOH)(eta(5)-C5H4COO)Fe](-). H2O {[(eta(6)-C6H6)(2)Cr](+)}(2)-{[(eta(5)-C5H4COOH)(eta(5)-C5H4COO)Fe](2)[(eta(5)-C5H4COOH)(2)Fe]}(2-) (3) and [(eta(6)-C6H6)(2)Cr](+){[(eta(5)-C5H4COOH)(eta(5)-C5H4COO)Fe}(-). H2O (4) have been prepared and structurally characterised by low temperature single-crystal X-ray diffraction. The four species contain different electronic and spin metal centres: 18 electrons Fe-II and Co-III are present in 1 and 2 whereas Fe-II and paramagnetic 17 electrons Cr-I are present in 3 and 4. The crystalline edifices are held together by the complementary contribution of neutral O-H ... O and/or negatively charged O-H ... O(-) hydrogen bonding interactions between the acid moieties and of charge assisted C-Hdelta+... Odelta- bonds between cations and anions. The structure of the 'heavily hydrated' species {[(eta(5)-C5H5)(2)Co](+)}(2)[(eta(5)-C5H4COO)(2)Fe](2-). 7.75H(2)O (5), in which the acid is completely deprotonated, will also be discussed. (C) 2000 Elsevier Science S.A. All rights reserved.