Structure and magnetic properties of chains of diamonds of four spins formed by metal(II) hexafluoroacetylacetonates (metal = cobalt, nickel) and the nitronyl nitroxide radical 4,4,5,5-tetramethyl-2-ethyl-4,5-dihydro-1H-imidazolyl-1-oxyl 3-oxide

Metal hexafluoroacetylacetonates, M(hfac), (M = Co, Ni), react with the nitronyl nitroxide radical 4,4,5,5-tetramethyl-2- ethyl-4,5-dihydro- IH-imidazolyl- 1-oxy1 3-oxide, NITEt, yielding adducts of formula [M(hfac),NITEt],. The X-ray crystal structure of the cobalt derivative has shown that the compound crystallizes in the monoclinic system, space group Pi, with a = 10.996 (3) A, b = 11.479 (4) A, c = 13.311 A, a = 60.97 (2)O. 0 = 65.28 (2)O, y = 81.67 (2)O, and Z = 1. The structure consists of dinuclear [Co(hfac),NITEt], centrosymmetric units, with the nitronyl nitrcxide radical bridging two different metal ions through one of its oxygen atoms. Weak interactions between different [M(hfa~)~N1TEtg]r,o ups cause the magnetic properties to be those of chains rather than of discrete clusters. The intermolecular coupling constant of [Ni(hfac),NITEt], has been calculated from the low-temperature magnetic data as J’= 2 cm-’ by applying the equation for S = 1 chains, while the intramolecular coupling constant has been estimated to be 300 cm-’ from the high-temperature data.