We provide definitive experimental proof that the archetypal string-like compound [Cr5(tpda)4(NCS)2] has alternating long and short Cr–Cr separations in the solid state, as conjectured by F. A. Cotton, rather than essentially equally spaced Cr atoms, as initially claimed (H2tpda = N2,N6-di(pyridin-2-yl)pyridine-2,6-diamine). Single-crystal X-ray data collected from 292 to 3 K revealed that the misinterpretation is caused by pseudo-merohedral twinning and that bond length alternation is enhanced at low temperature.
The structure of a pentachromium(II) extended metal atom chain at 3 K: Cotton's conjecture proven / Cornia, Andrea; Nicolini, Alessio; Mcmonagle, Charles J.; Probert, Michael R.. - In: DALTON TRANSACTIONS. - ISSN 1477-9226. - 51:(2022), pp. 16790-16794. [10.1039/D2DT03103E]