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 ligand as “insulation” around a central pentametal-atom “wire.” Compound 3, like all other oxidized pentachromium compounds, has very disparate alternating short–long–short–long Cr–Cr distances, 2.032(3)
 				Å, 2.560(6)
 				Å, 1.873(5)
 				Å, and 2.509(4)
 				Å. Compound 4 shows a nearly uniform spacing of the Co atoms, although the outer Co–Co distances (2.279[4]
 				Å) are slightly longer than the inner ones (2.239[4]
 				Å).
                                    本文介绍了五
铬和五
钴扩展
金属原子链(
EMAC)系统的结构研究,在这些系统中,
金属链被五价二元离子三
吡啶二酰胺(tpda)或其
二乙基取代类似物双(4-乙基-2-
吡啶氨基)
吡啶(etpda)螺旋包裹。化合物 Cr5(tpda)4(
NCS)2,(1)具有交替的长短
铬-
铬距离,这与最近关于
铬原子间距基本相等的对称性的报道相反(《欧洲物理
化学杂志》,1999 年,1243 期;《物理
化学 B》,2004 年,108 期,959 页)。线性 Cr510+ 链由两个 Cr24+ 四键单元和一个孤立的高自旋 CrII 单元组成。新化合物 Cr5(etpda)4Cl2 (2)、[Cr5(etpda)4FCl]PF6 (3) 和 Co5(etpda)4(
NCS)2 (4) 采用 etpda 
配体作为中心五
金属原子 "线 "周围的 "绝缘体"。化合物 3 与所有其他氧化五
铬化合物一样,具有非常不同的短-长-短-长交替的
铬-
铬距离,分别为 2.032(3)埃、2.560(6)埃、1.873(5)埃和 2.509(4)埃。化合物 4 显示出几乎均匀的 Co 原子间距,尽管外层 Co-Co 间距(2.279[4] Å)略长于内层(2.239[4] Å)。