The synthesis and reactivity of a new technetium(III) precursor. The crystal structures of [TcCl3(MeCN){P(C6H4Me-3)3}2] and [Tc(bipy)3]2+ (bipy=2,2'-bipyridine)

The reduction of [TcCl4(PPh3)2] with zinc metal in acetonitrile in the presence of triphenylphosphine gives the orange crystalline technetium(III) complex [TcCl3(MeCN)(PPh3)2]1 in good yield. Suitable crystals of 1 were grown, but the crystal structure could not be determined satisfactorily due to pseudo-symmetry in the crystal lattice. To overcome this problem the crystal and molecular structure of the tri-m-tolylphosphine analogue [TcCl3(MeCN){P(C6H4Me-3)3}2]1a was determined. Crystals of 1a are triclinic, space group P with Z= 2 in a unit cell of dimensions a= 10.157(2), b= 10.302(2), c= 22.073(2)A, α= 87.27(2), β= 86.66(1) and γ= 66.87(1)°. The structure was refined based on 5636 reflections converging to R= 0.039. Complex 1a exhibits a distorted pseudo-octahedral geometry with two trans P(C6H4Me-3)3 groups, three meridionally disposed chloride groups, and a linear terminally N-bound acetonitrile ligand. The reaction of 1 with the aromatic imines 2,2′-bipyridine (bipy), 1,10-phenanthroline (phen), and 2,2′:6′2″-terpyridine (terpy) gives the blue-black technetium(II) dicationic complexes [Tc(bipy)3]2+, [Tc(phen)3]2+ and [Tc(terpy)2]2+ isolated as their [BPh4]– or [PF6]– salts. The crystal and molecular structure of one of these novel technetium(II) complexes, [Tc(bipy)3][PF6]22a, has been determined. Crystals of 2a are trigonal, space group Pc1 (no. 165) with Z= 2 in a unit cell of dimensions a= 10.847(2) and c= 16.299(3)A. The structure was refined based on 414 unique reflections converging to R= 0.0525. The monomeric complex 2a exhibits exact D3 symmetry with the Tc–N bonds [2.077(10)A] equivalent by symmetry. The electrochemical behaviour of complexes 1, 2 and 3 has been investigated.