Rational Self-Assembly of a Tricobalt Extended Metal Atom Chain and Hexafluoridometallate Building-Blocks into One-Dimensional Coordination Polymers

Following our recent work on the first crystallographically characterized coordination polymers based on tricobalt Extended Metal Atom Chains (EMACs), [Co₃(dpa)₄)MF₆]∙2DMF (M = Zr(IV) (1), Sn(IV) (2) and Re(IV) (3)), we have generalized our synthetic approach based on robust fluoride complexes to prepare new self-assembled one-dimensional (1D) polymers formed by [Co₃(dpa)₄]²+ and 5d [MF₆]²- (M = Ir(IV) (4), and Os(IV) (5)) building blocks. These 1D complexes are isostructural, crystallizing in the P4/ncc space group such that the four-fold axis is coincident with the metal axes of the rigorously linear chains. Magnetic studies reveal ferromagnetic coupling between the S = 1/2 {Co₃} and [MF₆]²- units for the complexes 3 and 4, while non-magnetic [MF₆]²- linkers of 1 and 5 mediate antiferromagnetic coupling between the {Co₃} spins. In the case of 2, no significant exchange coupling was observed. Spin-crossover behavior, which was observed in the parent [Co₃(dpa)₄Cl₂] complex, was not detected in 1-5 up to 300 K. This work demonstrates that EMAC and [MF₆]²- complexes should be considered as appealing building-blocks to design new functional coordination networks.

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