SYNTHESIS, CRYSTAL-STRUCTURE AND MAGNETIC-PROPERTIES OF THE CHIRAL IRON(II) CHAIN [FE(BPYM)(NCS)(2)](N) (BPYM=2,2'-BIPYRIMIDINE)

The iron(II) compound of formula [Fe(bpym)(NCS)(2)](n) (bpym = 2,2'-bi pyrimidine) 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) Angstrom, V = 1290.9(5) Angstrom(3),Z = 4,D-c = 1.699 g cm(-3), M(r) = 330.2, F (000) = 664, lambda(Mo K alpha) = 0.71073 Angstrom, mu(MoK alpha) = 14 .8 cm(-1) and T = 295 K. A total of 2449 reflections was collected ove r the range 3 less than or equal to 2 theta less than or equal to 55 d egrees; of these, 1657 were unique and 1321 were considered as observe d (1>3 sigma(l)) and used in the structural analysis. The final R and R(w) residuals were 0.027 and 0.026, respectively. The structure is ma de up of chiral (Delta and Lambda enantiomers crystallize in the same crop) chains of iron(II) atoms bridged by bis-chelating bpym, the elec troneutrality being achieved by N-bonded thiocyanato groups in cis pos ition. Each metal atom is in a distorted FeN6 octahedral environment, the Fe-N bonds ranging from 2.265(3) to 2.028(4) Angstrom. The intrach ain metal-metal separation is 5.960(1) A. Variable-temperature magneti c susceptibility data in the temperature 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) over ca p = -J Sigma(i=1)(n)(S) over cap(i) (S) over cap(i+1) with S-i = S-i+1 = 2). The magnitude of the exchange coupling compares well with that r eported for other structurally characterized bpym-bridged iron(II) com plexes.