Synthesis, crystal structure and magnetic properties of the chiral iron(II) chain [Fe(bpym)(NCS) 2] n (bpym = 2,2′-bipyrimidine)

Abstract

The iron(II) compound of formula [Fe(bpym)(NCS) 2] n (bpym = 2,2′-bipyrimidine) has been synthesized and its crystal structure determined by X-ray diffraction methods. It crystallizes in the tetragonal P4 1 (No. 76) and P4 3 space groups, a = 8.849(2), c=16.486(3) A ̊ , V=1290.9(5) A ̊ 3, Z=4, D c=1.699 g cm −3, M r =330.2, F(000)=664, λ( Mo Kα)=0.71073 A ̊ , μ( Mo Kα)=14.8 cm −1 and T=295 K. A total of 2449 reflections was collected over the range 3≤2 ϑ≤55°; of these, 1657 were unique and 1321 were considered as observed (13 σ( I)) and used in the structural analysis. The final R and R w residuals were 0.027 and 0.026, respectively. The structure is made up of chiral (Δ and Λ enantiomers crystallize in the same crop) chains of iron(II) atoms bridged by bis-chelating bpym, the electroneutrality being achieved by N-bonded thiocyanato groups in cis position. Each metal atom is in a distorted FeN 6 octahedral environment, the FeN bonds ranging from 2.265(3) to 2.028(4) A . The intrachain metal-metal separation is 5.960(1) Å. Variable-temperature magnetic susceptibility data in the temperatyre range 290–4.2 K show that the iron(II) is high-spin and interacts in an antiferromagnetic fashion, the relevant parameters being J=−3.5 cm −1 and g=2.12 ( H=−JΣ i=1 n S i· S i+1 with S i= S i+1=2) . The magnitude of the exchange coupling compares well with that reported for other structurally characterized bpym-bridged iron(II) complexes.