Organometallic crystal engineering with multidentate building blocks and template guest size effect. Supra-anionic organic frameworks obtained from cyclobutane-1,2,3,4-tetracarboxylic and trans-acotinic acids †

Abstract

The organic acids cyclobutane-1,2,3,4-tetracarboxylic C4H4(CO2H)4, and trans-acotinic acid C3H3(CO2H)3, have been treated in thf with the organometallic hydroxides [Co(η5-C5H5)2]+[OH]–, [Co(η5-C5Me5)2]+[OH]–, and [Cr(η6-C6H6)2]+[OH]– prepared in situ from the oxidation of the corresponding neutral complexes, to yield the novel organic–organometallic crystalline materials [Co(η5-C5H5)2]+[C4H4(CO2H)3COO]– 1, [Cr(η6-C6H6)2]+[C4H4(CO2H)3CO2]–·H2O 2, and [Co(η5-C5Me5)2]+[C3H3(CO2H)2CO2(H)·C3H3(CO2H)2CO2]–·H2O 3. Self-assembly of the monodeprotonated organic acid C4H4(CO2H)4 generates supra-anionic framework structures held together by O–H· · ·O and O–H· · ·O– hydrogen bonds which accommodate the diamagnetic [Co(η5-C5H5)2]+ and paramagnetic [Cr(η6-C6H6)2]+ cations, respectively. Crystalline 1 does not form single crystals with defined shapes but rather an “enamel” like material which grows parallel to the crystallographic bc plane. The same reaction between trans-acotinic acid and [Co(η5-C5Me5)2]+[OH]–generates a large honeycomb-type structure in [Co(η5-C5Me5)2]+[C3H3(CO2H)2CO2(H)·C3H3(CO2H)2CO2]–·H2O 3. The effect of the size of the templating units [Co(η5-C5H5)2]+ and [Co(η5-C5Me5)2]+ is discussed. The previously unknown structure of the starting material [Co(η5-C5Me5)2]+[PF6]– 4, used for the preparation of [Co(η5-C5Me5)2]+[OH]–, has also been determined.