Extended metal atom chains (EMACs) of five chromium or cobalt atoms: Symmetrical or unsymmetrical?
Abstract
Structural studies of pentachromium and pentacobalt extended metal atom chain (EMAC) systems are presented in which the metal chains are helically wrapped by either the pentadentate dianion tripyridyldiamide (tpda) or its diethyl-substituted analogue bis(4-ethyl-2-pyridylamido)pyridine (etpda). The compound Cr5(tpda)4(NCS)2, (1) has alternating long and short Cr–Cr distances, contrary to recent reports that describe it as symmetrical with essentially equally spaced chromium atoms (Eur. J. Inorg. Chem., 1999, 1243; J. Phys. Chem. B, 2004, 108, 959). The linear Cr510+ chain is composed of two Cr24+ quadruply bonded units and an isolated high spin CrII unit. The new compounds Cr5(etpda)4Cl2
(2), [Cr5(etpda)4FCl]PF6
(3), and Co5(etpda)4(NCS)2
(4) employ the etpda