Theoretical Study on the Structures and Magnetic Properties of Metal String Complexes Containing Rigid Equatorial Ligands [Ni3(L)4(NCS)2] (L = dzp-, mpmpa-, mppda-, mptpa-)

Density functional theory at the BP86 level was used to investigate the influence of equatorial ligands on the Ni–Ni interactions and magnetic coupling properties of metal string complexes [Ni3（L）4（NCS）2] （L represents the rigid equatorial ligands; L = dzp- （1）, mpmpa- （2）, mppda- （3）, mptpa- （4））. The following conclusions can be drawn. （1） With increasing the radius of the connecting atom in the cental ring in equatorial ligands, the two pyridine rings bend down, resulting in the decreasing distance between the two pyridine-nitrogen atoms and the Ni–Ni distance. Therefore, the strength order of the Ni–Ni interaction is 4 〉 2 〉 3 〉 1. The Ni–Ni interactions in 2 and 4 are stronger than those in Ni3（dpa）4（NCS）2 containing no-rigid equatorial ligands. （2） The calculated -Jab is 4 〉 2 〉 3 〉 1. There are two types of magnetic exchange pathways in these complexes： the σ-type pathway through the Ni36＋ chains and the δ-type pathway through the equatorial ligands. The magnetic coupling through the metals is the dominant part. Hence, the magnetic coupling strength increases with increasing the Ni–Ni interaction. Modifying the radius of the connecting atom may be one of the means to fine tuning of magnetic coupling strength of this kind of metal string complexes.

A Defective Linear Pentachromium Complex for the Enhanced Catalysis of the Cycloaddition of CO2 with Propylene Oxide

Based on the ligand（2,7-bis（α-pyrimidylamino）-1,8-naphthyridine（H2 bpmany））, a linear pentachromium complex [Cr5（μ5-bpmany）4Cl2]PF6（1, μ5-bpmany = 2,7-bis（a-pyrimidylamino）-1,8-naphthyridine） was synthesized. The crystal structure of compound 1 has been characterized by X-ray crystallography. Interestingly, one metal atom in the center is missing in this linear chain, leading to the defective pentachromium metal string structure which is similar with the reported complex [Cr5（μ5-dpznda）4Cl2]（2, dpznda = N^2,N^7-di（pyrazin-2-yl）-1,8-naphthyridine-2,7-diamine）. The central Cr（Ⅲ） ion of 1 is eight-coordinated and is also rare in the chromium complex. The reaction of carbon dioxide with propylene oxide that generates propylene carbonate（PC） when catalyzed by [Cr5（μ5-bpmany）4Cl2]PF6 was investigated. Different reaction conditions including temperature and pressure were studied to optimize the reaction conditions.