Metal Chains of Cobalt

A powder diffraction pattern from a typical preparation of Co3(dpa)4Cl2 shows that both tetragonal and orthorhombic forms are present, with the former making up 10 20%. Both forms when dissolved in CH2CI2 give the same 

NMR spectrum. The two forms of the molecule, being energetically similar, crystallize out simultaneously from CH2CI2 solution.  

Compounds Co5(tpda)5X2 show two reversible redox couples at about -I-0.35 and -1-0.85 V (vs. Ag/AgCl). The first oxidation is metal centered, and the product has been structurally characterized. The second oxidation product is stable on the timescale of spectroelectrochemistry but undergoes reduction to form the corresponding one electron oxidation product under crystallization conditions. 

Magnetic measurements revealed anomalous magnetic behavior with intermediate magnetic moment values between quartet and doublet states. From MO theory, the larger a molecule is and more metal atoms it contains and the lower the energy gap between the HOMO and LUMO. Consequently, the higher spin state is more accessible. The C07 chain has spin admixed state from S = 1/2 to S = 7/2. 

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