Syntheses and solid-state structures of tris(pyrazolyl)methane complexes of iron(II) with unique spin-crossover behaviors and group 1 and 2 metals

The complexes {lcub}Fe[HC(3,5-Me₂pz)₃]₂{rcub}(BF ₄)₂ (1), {lcub}Fe[HC(pz)₃]₂{rcub}(BF ₄)₂ (2), and {lcub}Fe[PhC(pz)₂(py)] ₂{rcub}(BF₄)₂ (3) (pz = 1-pyrazolyl ring, py = pyridyl ring) have been synthesized any characterized crystallographically. Complex 1 is high-spin in the solid state and undergoes a decrease in magnetic moment at lower temperatures, changing to a 50:50 mixture of high-spin and low-spin forms. Both of these forms have been characterized crystallographically. Complex 2 changes over to the high-spin state upon heating above 295 K and is completely high-spin at ca. 470 K in the solid phase. Complex 3 is low-spin at all temperatures studied. The complexes {lcub}Co[HC(3,5-Me ₂pz)₃]₂{rcub}(BF₄)₂ (4 ) and {lcub}Cu[HC(3,5-Me₂pz)₃]₂{rcub}(BF ₄)₂ (5) have also been synthesized and characterized in the solid-state at 220 K and 125 K. Below 155 K these complexes were found to undergo a phase change that is similar to that observed in 1. This phase change occurs with no change in spin-state for the cobalt(II) complex and is responsible for the unusual spin-crossover behavior of 1.; The reaction of NaI with two equivalents of HC(pz)₃ or HC(3,5-Me ₂pz)₃ (pz = pyrazolyl ring) leads to the formation of {lcub}[HC(pz) ₃]₂Na{rcub}(I) (6) and {lcub}[HC(3,5-Me₂pz) ₃]₂Na{rcub}(I) (7), respectively. Both compounds have trigonally distorted octahedral arrangements about the sodium(I). The complex {lcub}[HC(pz)₃]₂Sr{rcub}(BF₄)₂ ( 8) forms in the reaction of Sr(acac)₂ (acac = acetylacetonate) with HBF₄•Et₂O followed by two equivalents of HC(pz) ₃. The structure is highly distorted, showing κ₃-bonding of both tris(pyrazolyl)methane ligands as well as interactions with the metal from three fluorine atoms from the BF₄− counterions. The symmetrical structure of 6 and this nine-coordinate structure of 8 are both very different from the distorted, 6-coordinate structure {lcub}[HC(pz)₃]₂Pb)(BF₄)₂, indicating that for this compound the lone pair on lead(II) is influencing the structure. In order to facilitate this chemistry, the synthesis of Na{lcub}B[3,5-(CF ₃)₂C₆H₃]₄), needed to prepare HBAr_f, has been dramatically improved. The main change is to add NaBF₄ to the reaction mixture before forming the Grignard from the reaction of magnesium and 3,5-(CF₃)₂C ₆H₃Br. The Grignard reacts with the NaBF₄ as it forms, reducing the danger of explosion and leading to a higher isolated yield of the product.