A [Zn₄O(fcCO₂)₆] oxocarboxylate cluster: synthesis, chemical and physical properties

Abstract The reaction of the ferrocene derivative Fe( ƞ 5 -C 5 H 4 CO 2 H)( ƞ 5 -C 5 H 4 CH=CH 2 ) (=fcCO 2 H) ( 1 ) with the zinc reagents [Zn(OAc) 2 ]· x H 2 O (OAc = acetate; 2a , x = 0; 2b , x = 2) or ZnEt 2 ( 3 ) in non-aqueous solvents toluene or tetrahydrofuran resulted in the formation of the cluster [Zn 4 O(fcCO 2 ) 6 ] ( 4 ). The structure of 4 in the solid state has been determined by single-crystal X-ray diffraction analysis. Cluster 4 crystallizes in the triclinic space group P <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <m:mrow> <m:mover accent="true"> <m:mn>1</m:mn> <m:mo>‾</m:mo> </m:mover> </m:mrow> </m:math> $\overline{1}$ . In 4 , the cluster core is set-up by four zinc(II) ions which are forming the vertices of a tetrahedron with a μ 4 -oxygen atom in its center. Six μ -fcCO 2 units bridge the edges of the tetrahedron. IR spectroscopy confirms with ∆ ν CO2 = 91 cm −1 (∆ ν CO2 = ν CO2,asym − ν CO2,sym ) the μ -bridging character of the fcCO 2 entities. Cyclic voltammetry studies showed a reversible redox event at E° ′ = 245 mV versus FcH/FcH + (FcH = Fe( ƞ 5 -C 5 H 5 ) 2 ) for 4 with the six fcCO 2 redox events superimposed. High-resolution ESI-TOF measurements verified the identity of 4 .