Synthesis, molecular structure, and physical properties of [tetrakis((methylthio)methyl)borate](2)M (M=Fe,Co,Ni)

The synthesis and characterization of a series of [RTt](2)M (RTt(-) = tetrakis((methylthio)methyl)borate; M = Fe, Co, Ni) complexes are reported. Isostructural derivatives of the ne wry synthesized phenyltris((methylthio)methyl)-borate (PhTt(-)) also have been prepared and characterized. In each case, the ligand provides tridentate, face-capping coordination to the divalent metal ion. The Fe(II) complexes exhibit spin-crossover behavior both in solution and in the solid state. For [PhTt]Fe-2, the temperature dependence of mu(eff) has been mapped between 5 K (1.3 mu(B)) and 400 K (3.2 mu(B)). The low-spin Co(II) derivatives exhibit characteristic axial EPR spectra; for [PhTt]Co-2, g(perpendicular to) = 2.185, g(parallel to) = 2.035, A(perpendicular to) = 55 G, and A(parallel to) = 42 G. Using O-h Fe(II) and Co(II) derivatives as benchmarks, the ligand field strength imparted by these anions is significant and falls just below that of the neutral macrocycle 1,4,7-trithiacyclononane (ttcn). All complexes have been characterized by X-ray diffraction. X-ray data: [PhTt]Fe-2 . 0.6Et(2)O, monoclinic space group C2/c, with a = 22.293(4) Angstrom, b = 12.842(8) Angstrom, c = 15.326(2) Angstrom, beta = 130.28(6)degrees, V = 3347.4(5) Angstrom(3), and Z = 4; [RTt]Co-2, triclinic space group <P(1)over bar>, with a = 8.396(6) Angstrom, b = 8.850(2) Angstrom, c = 9.124(4) Angstrom, alpha = 107.43(2)degrees, beta = 92.20(4)degrees, gamma = 94.50(4)degrees, V = 643.0(3) Angstrom(3), and Z = 1; [PhTt]Co-2, monoclinic space group P2(1)/c, with a = 8.821(1) Angstrom, b = 14.127(8) Angstrom, c = 12.055(3) Angstrom, beta = 103.93(2)degrees, V = 1458.0(5) Angstrom(3), and Z = 2; [RTt]Ni-2, triclinic space group <P(1)over bar>, with a = 8.607(3) Angstrom, b = 8.876(3) Angstrom, c = 9.173(3) Angstrom, alpha = 107.44(2)degrees, beta = 92.92(2)degrees, gamma = 93.38(2)degrees, V = 665.70(3) Angstrom(3), and Z = 1; [PhTt]Ni-2: triclinic space group <P(1)over bar>, with a = 8.627(7) Angstrom, b = 8.862(4) Angstrom, c = 10.559(6) Angstrom, alpha = 75.08(4)degrees, beta = 76.64(5)degrees, gamma = 72.71(5)degrees, V = 734.3(8) Angstrom(3), and Z = 1.