The structure of the Ir(I) complex [Ir2(mu-OPy)2(CO)4] (Opy = 2-pyridonate) has been fully characterized in its head-to-head (A) configuration as a "dimer of dimers" AA in which two binuclear complexes are connected by means of a weak, but unsupported, iridium-iridium interaction (Ir(2)...Ir(2A) 2.9808(6) A). The head-to-tail isomer, referred to as B, was found in equilibrium with A in solution. It has been shown that this complex can be oxidized by diiodine to give iridium chains with highly selective configurations and general formula I-[Ir2(mu-OPy)2(CO)4]n-I (n = 1-3). The synthesis of IAI (1), of the isomers IAAI (2AA) and IABI (2AB), and of IABAI (3) is reported. DFT calculations have been carried out on A and B and on the known isomers of 1-3, as well as on two isomers of the hypothetic chain of eight Ir(1.25) atoms corresponding to n = 4. The stability of the metal chain is assigned to a 2-electron/2n-center sigma bond delocalized along the metal backbone and supplemented with a weak attractive interaction of the metallophilic type. Calculations confirm that further oxidation of the Ir chains corresponding to n > 1 by iodine, yielding the cleavage of one or two unsupported bond(s), is a highly exothermic process. The formation of the I-[Ir2(mu-OPy)2(CO)4]n-I chains is also computed to be exothermic, either highly for n = 1 or still significantly for n = 2 and 3. At variance with these results, the formation of an octanuclear chain is predicted to be no more than marginally exothermic (DeltaG = 1.7 kcal.mol(-1)), mainly because of interligand strain induced by the steric bulk of the amidate rings.

CommunicationsThe array of metal atoms (yellow) in the first hexanuclear Ir-chain compound is almost linear. This 1D oligomer is a molecular piece of a ™metal wire∫ related to the infinite mixedvalence metal chains, such as the Krogmann salts. Crystalline samples of the Ir complex have a copper-like appearance. For more information see the Communication by Oro, Ciriano, and co-workers on the following pagesº.Compounds containing discrete chains of metal-bonded atoms are interesting not only from a theoretical point of view but also because of their potential applications, particularly as nanoscale electronic devices. Reproducible and welldefined syntheses for these compounds include ligand-assisted reactions with conjugated polyenes [1] and polydentate ligands, such as oligo-a-pyridylamino ligands. [2] In these cases, the number of available coordination sites of the ligand determines the length of the metallic chain. Another interesting approach involves the formation of metallic chains by oxidation of dinuclear complexes containing d 8 square-planar metal centers or by reduction of d 7 metal compounds. With this methodology there are, in principle, no limitations to the chain length other than the thermodynamic stability of the compound, provided that the steric encumbrance between the links is kept at minimum. To date, this method has allowed the isolation of only two rare 1D rhodium-chain compounds [3] and the platinum, [4] rhodium, [5] and iridium [6] blues, which typically consist of tetrametallic chains. [7] Between both situations only a remarkable octanuclear platinum chain, reported by Matsumoto and co-workers, is known. [8] Moreover, while several fractional oxidation states of the metal centers have been found for the platinum blues, only the averaged oxidation state of þ 1.5 has been reported for the tetranuclear rhodium and iridium blues. Herein we describe the novel iridium compound HH,HT,HH-[Ir 6 (m-OPy) 6 (I) 2 (CO) 12 ] containing an unprecedented linear metal chain made up of six iridium atoms in a formal oxidation state of þ 1.33.Oxidation of a toluene solution of the dinuclear complex [Ir 2 (m-OPy) 2 (CO) 4 ] [6a] (1; Opy ¼ 2-pyridonate) with diiodine (in a 3:1 molar ratio) at 0 8C immediately gave an EPR-silent, dark-blue solution from which a crystalline solid having a copper-like aspect (2) was isolated in good yield (75 %) on

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