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 [(η5-C5H4COOH)2Fe] (FeACH2) 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 [(η5-C5H5)2Co] and [(η6-C6H6)2Cr] and consequent reduction of O2 to the strongly basic anion O2−; (ii) deprotonation of FeACH2 to yield the anion FeACH− (or FeAC2−); (iii) precipitation of the insoluble organometallic salts formed between the organometallic acidate and the diamagnetic cation [(η5-C5H5)2Co]+ or the paramagnetic cation [(η6-C6H6)2Cr]+. The novel materials [(η5-C5H5)2Co]+[(η5-C5H4COOH)(η5-C5H4COO)Fe]− (1), [(η5-C5H5)2Co]+[(η5-C5H4COOH)(η5-C5H4COO)Fe]−·H2O (2), {[(η6-C6H6)2Cr]+}2{[(η5-C5H4COOH)(η5-C5H4COO)Fe]2[(η5-C5H4COOH)2Fe]}2− (3) and [(η6-C6H6)2Cr]+{[(η5-C5H4COOH)(η5-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 FeII and CoIII are present in 1 and 2 whereas FeII and paramagnetic 17 electrons CrI 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–Hδ+⋯Oδ− bonds between cations and anions. The structure of the ‘heavily hydrated’ species {[(η5-C5H5)2Co]+}2[(η5-C5H4COO)2Fe]2−·7.75H2O (5), in which the acid is completely deprotonated, will also be discussed.