Unusual Magnetism of an Unsymmetrical Trinickel Chain
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abstract
An extended metal atom chain (EMAC) compound with an unsymmetrical trinickel core and the formula [Ni3(dpa)4-(CH 3CN)](PF6)22CH2Cl 2 (12CH2Cl2, dpa is the anion of 2,2-dipyridylamine) has the central Ni atom in an essentially square-planar configuration. Besides having four equatorial nitrogen atoms, the two terminal metal centers have axial interactions that are notably different with one having a strongly bound acetonitrile molecule with a Ni(3)-N(3) distance of 2.108(5) while the other unit has a very weak interaction with an axial PF6 anion [Ni(1)-F(1) separation of 2.690 ]. In these outer units, the Ni(3) atom is pulled out of the idealized plane of the four equatorial nitrogen atoms by 0.239 , while in the one with an axial PF6 anion the metal atom is pulled from the plane of the equatorial nitrogen atoms by only 0.097 . In 1 there are two unpaired electrons and an S = 1 state prevails from ca. 25 to 300 K. This magnetic behavior differs considerably from that of symmetrical trinickel EMACs with two strongly pyramidal terminal nickel atoms. A discussion of the effect of various axial ligands on the geometry of the terminal nickel atoms is provided. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.