High spinndash;low spin crossover and antiferromagnetic interactions in tris(1hyphen;pyrrolidinecarbodithioato)iron (III) and the 4hyphen;morpholine (FeM) and dibutyl analogs, effect of recrystallization solvent, and crystal structure of FeMsdot;nitrobenzene

摘要

High sensitivity magnetic susceptibility determinations, especially in the range 1.2ndash;4.2 K on pure and dilute tris(pyrrolidinecarbodithioato)iron(III) (FeP) in its high spin form, show that a maximum at about 2 K is caused by antiferromagnetic interactions. The analogous chromium(III) complex does not exhibit significant antiferromagnetism compared to that of the iron complex, and it is likely that the uppereelectrons possessed by the iron and not by the chromium are responsible for the bulk of the antiferromagnetism. As the iron atoms are about 9 Aring; apart in discrete molecules, the antiferromagnetic interactions presumably occur between unpaired spins delocalized on to the ligands of adjacent molecules. This is in keeping with NMR evidence that spin delocalization is greater in the iron(III) than in the chromium(III) complex. When diluted with large amounts of the cobalt(III) analog (CoP), FeP exhibits a spin state equilibrium. Thus, the structure of the FeP molecule is modified slightly (presumably with shortening of the Fendash;S bond) to approach that of the CoP host lattice, which has a shorter metalndash;sulfur bond. The previous history of the samples of ferric dithiocarbamate complexes is shown to be far more important than had previously been suspected: When crystallized from benzene, FeP exhibits a high spinndash;low spin equilibrium, in constrast with the pure high spin behavior of the complex when not crystallized from benzene. The effect of adding 7percnt; of benzene to the lattice is much greater than that of adding 50percnt; of CoP. The dibutyl analog shows similar effects. The tris(4hyphen;morpholinecarbodithioatohyphen;S,Srsquo;)iron(III) complex FeM is shown, by single crystal xhyphen;ray data, to contain short Fendash;S bond lengths (average 2.353 Aring;) when recrystallized from nitrobenzene. This indicates that the complex is principally low spin, in keeping with the observed magnetism and with the general strong solvent effect on the spin state. It is now proposed that the difference in Fendash;S bond lengths between FeP crystallized from chloroform and FeP from benzene (the reverse of the expected differences) is due to experimental error. Crystal data for FeMsdot;nitrobenzene: space groupP21/c,Z=4,a=9.713(3) Aring;,b=31.419(8) Aring;,c=9.718(2) Aring;, bgr;=105.04(2) deg;,V=2864 Aring;3,R=3.3percnt;, 2712 reflections.