One-dimensional complexes with metal-containing backbones have been attractive to physicists and chemists for several decades, [1] and their interest has been further increased in the last ten years by potential applications in nanoelectronics.[2] Apart from the family of platinum and iridium blues, most chains of metal atoms were constrained to be aligned by means of purposely designed ligands. [3,4] The polypyridylamido ligands have produced to date the widest variety of metal chains with controlled lengths, as far as the nature and the number of metal atoms are concerned. [3] Strings with three to nine metal atoms were obtained with Cr and Ni. Chains containing three or five metal atoms, characterized for Co, Cu, Ru, and Rh, have unprecedented structural versatility and magnetic behavior that is hard to predict.[3] Even though heterometallic chain complexes are not uncommon [5] and often exhibit similarity to platinum blues [6] or involve weak noncovalent interactions between heavy atoms, [7] all linear complexes with polypyridylamido or closely related ligands characterized to date incorporate a single type of metal atoms. We report here the synthesis, Xray structure, and magnetic properties of [Co 2 PdCl 2 (dpa) 4 ] (1; dpa = bis(2-pyridyl)amide), the first trinuclear complex of dpa with a heteronuclear backbone. The magnetic behavior of 1 was investigated and found to be consistent with a complex interaction involving zero-field splitting superimposed on strong exchange coupling between two high-spin Co II ions separated by a diamagnetic Pd center. The ground-state electronic structure of 1 was interpreted by means of DFT calculations.Complex 1 was synthesized by a variant of the protocol currently used to obtain trinuclear dipyridylamide complexes.[8] Single-crystal X-ray analysis of 1·(C 2 H 5 ) 2 O resulted in the structure displayed in Figure 1. The heterometallic chain is helically wrapped by four syn-syn-type ligands, and the complex exhibits approximate D 4 symmetry. The average CoÀN (2.16 ) and CoÀCl (2.34 ) distances are quite similar to those observed at room temperature for the isolated, highspin Co II ion in the unsymmetrical form of [Co 3 Cl 2 (dpa) 4 ].[9]The average Pd À N (2.01 ) is much shorter than the average Co À N distance and suggests that the Pd atom is essentially low-spin (S = 0) in square-planar coordination. The relatively short PdÀCo distance (2.52 ) is consistent with a weak metal-metal interaction, as confirmed by DFT calculations.

One-dimensional complexes with metal-containing backbones have been attractive to physicists and chemists for several decades, [1] and their interest has been further increased in the last ten years by potential applications in nanoelectronics.[2] Apart from the family of platinum and iridium blues, most chains of metal atoms were constrained to be aligned by means of purposely designed ligands. [3,4] The polypyridylamido ligands have produced to date the widest variety of metal chains with controlled lengths, as far as the nature and the number of metal atoms are concerned. [3] Strings with three to nine metal atoms were obtained with Cr and Ni. Chains containing three or five metal atoms, characterized for Co, Cu, Ru, and Rh, have unprecedented structural versatility and magnetic behavior that is hard to predict.[3] Even though heterometallic chain complexes are not uncommon [5] and often exhibit similarity to platinum blues [6] or involve weak noncovalent interactions between heavy atoms, [7] all linear complexes with polypyridylamido or closely related ligands characterized to date incorporate a single type of metal atoms. We report here the synthesis, Xray structure, and magnetic properties of [Co 2 PdCl 2 (dpa) 4 ] (1; dpa = bis(2-pyridyl)amide), the first trinuclear complex of dpa with a heteronuclear backbone. The magnetic behavior of 1 was investigated and found to be consistent with a complex interaction involving zero-field splitting superimposed on strong exchange coupling between two high-spin Co II ions separated by a diamagnetic Pd center. The ground-state electronic structure of 1 was interpreted by means of DFT calculations.Complex 1 was synthesized by a variant of the protocol currently used to obtain trinuclear dipyridylamide complexes.[8] Single-crystal X-ray analysis of 1·(C 2 H 5 ) 2 O resulted in the structure displayed in Figure 1. The heterometallic chain is helically wrapped by four syn-syn-type ligands, and the complex exhibits approximate D 4 symmetry. The average CoÀN (2.16 ) and CoÀCl (2.34 ) distances are quite similar to those observed at room temperature for the isolated, highspin Co II ion in the unsymmetrical form of [Co 3 Cl 2 (dpa) 4 ].[9]The average Pd À N (2.01 ) is much shorter than the average Co À N distance and suggests that the Pd atom is essentially low-spin (S = 0) in square-planar coordination. The relatively short PdÀCo distance (2.52 ) is consistent with a weak metal-metal interaction, as confirmed by DFT calculations.

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