Synthesis and Structure of Redox‐Active Heterotetranuclear Molecular Polygons by Self‐Assembly of Two Ferrocene‐Bridged Bis(pyridines) with Two Transition Metals

The macrocyclic complexes [(η 5 ‐C 5 H 4 C 2 ‐4‐py) 2 Fe] 2 Ni 2 (NO 3 ) 4 ( 2 ), [(η 5 ‐C 5 H 4 C 2 ‐3‐py) 2 Fe] 2 Ag 2 (ClO 4 ) 2 ( 4 ), and [(η 5 ‐C 5 H 4 C 2 ‐3‐py) 2 Fe] 2 Pd 2 Cl 4 ( 5 ) were obtained by reaction of [Ni(H 2 O) 6 ](NO 3 ) 2 , AgClO 4 , and PdCl 2 (COD) with the ligands (η 5 ‐C 5 H 4 C 2 ‐4‐py) 2 Fe ( 1 ) and (η 5 ‐C 5 H 4 C 2 ‐3‐py) 2 Fe ( 3 ), respectively, under high dilution conditions (Scheme 1). The molecular motifs of 2 , 4 , and 5 were studied by single‐crystal X‐ray structural investigations. Elemental analyses and 1 H NMR and IR spectra were also used to confirm the structures. Compound 2 represents an unsymmetric paddlewheel, in which the centers of the four Cp rings define a nearly ideal rectangle with dimensions of 20.2 × 3.3 Å. In principle, macrocycles 4 and 5 can also be described as rectangles, however, due to the 3‐positioned nitrogen donors with deformed edges (17.4 × 3.3 Å for 4 ). In contrast to the offset packing of the molecules in 2 , the macrocycles in the crystal of 4 are aligned, with trapped acetonitrile molecules in between. The intra‐ and intermolecular Ag−Ag distances are 3.50 and 3.79 Å, respectively. Cyclovoltammetric studies reveal chemically reversible ferrocene‐based redox reactions of 1 − 4 . Although no electronic communication was observed between the two identical ferrocene units, a weak through‐bond electronic interaction between ferrocene and nickel, or silver, was established. In 2 a weak antiferromagnetic interaction between the nickel atoms was also found. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)