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b S Supporting Information ' INTRODUCTION ansa-Metallocenes have attracted some interest, due to their versatile electronic and chemical properties. Their characteristics can be altered with the bridge between the Cp rings, resulting in a distorted, bent structure. [1][2][3][4][5][6] In addition, bridged metallocenes of Fe and Co can be used as monomers in ring-opening polymerization (ROP), 3 yielding polymers with interesting electronic, electrochemical, and solubility properties. The nature of the bridge between the two Cp ligands can be modified in a wide range, dominating the physical properties of the resulting polymer. The synthetic approach to an "ansa" function depends on the nature of the metallocene. For the synthesis of ansa-ferrocenes a 1,1 0 -dimetalation and subsequent salt metathesis is a very convenient method, while this transformation is not applicable to the electronically and magnetically highly interesting cobaltocenes. 7,8 The formation of the ansa-metallocenes of Co was successfully performed via a nucleophilic reaction of the corresponding metal salt and two cyclopentadienyl anions, already connected by the bridging function. 9 Here, we report on the synthesis, molecular structure, and electronic and magnetic properties of a new bent ansa-cobaltocene, 1,1 0 -(naphthalene-1,8-diyl)cobaltocene (2).

The paramagnetic dinuclear complexes 1,8-bis(cobaltocenyl)naphthalene (2) and 1,8-bis[(pentamethyl-η(5)-cyclopentadienyl)(η(5)-cyclopentadiendiyl)cobalt(II)]naphthalene (4) were synthesized. The molecular structures were characterized by X-ray structure analysis and consisted of two cobaltocenes linked through a distorted naphthalene clamp. Electronic interactions between the two cobalt atoms were observed by cyclic voltammetric studies. Superconducting quantum interference device (SQUID) measurements of the pure compounds and diluted in their diamagnetic iron derivatives, as well as variable-temperature NMR spectroscopy experiments in solution are presented. Magnetic measurements revealed an antiferromagnetic coupling of the electrons in complexes 2 and 4. From NMR spectroscopy experiments, Curie behavior in the temperature range from -60 to +60 °C can be deduced. The electronic structure and magnetic behavior is supported by results of broken-symmetry DFT and multireference calculations along with UV/Vis spectroscopic data, which revealed an intramolecular through space π-π interaction between the cobaltocene units.