Syntheses and structures of the first polynuclear manganese guanidine complexes and of the first manganese complexes containing mono-protonated bis-guanidine ligands

Metallation of two differently alkylated bis-guanidine ligands containing a central pyridine functionality, namely N-2,N-6-bis(1,3-dimethylimidazolidin-2-ylidene)pyridine-2,6-diamine (DMEG(2)py {N7C15H23}, L-1) and N-2,N-6-bis(1,1,3,3-tetramethylguanidine)pyridine-2,6-diamine (TMG(2)py {N7C15H27}, L-2), with manganese(II) bromide and chloride leads to the formation of the novel complexes [MnBr3(TMG(2)pyH)] ([MnBr3(N7C15H28)], (1)), [MnBr2(DMEG(2)pyH)(2)](2+) ([MnBr2(N7C15H24)(2)](2+), (2)), and [Mn2X3(DMEG(2)py)(2)](+) ([Mn2X3(N7C15H23)(2)](+); (3a): X = Cl; (3b): X = Br). 2 and 3 have been isolated as tetrahalomanganate salts. Single crystal X-ray analyses show that all of them contain the manganese atoms in unusual pseudo-tetrahedral coordination environments. 3a center dot 1/2[MnCl4] and 3b center dot 1/2[MnBr4] are isostructural and crystallize in the monoclinic space group C2c. The complex cations 3 exhibit a binuclear structure with two terminal and one bridging halide ion, respectively. The compounds 1 and 2 are mononuclear species crystallizing in the orthorhombic space group P2(1)2(1)2(1) in the case of I and in the triclinic space group P (1) over bar in the case of 2 center dot[MnBr4]. The ability of L-1 and L-2 to bind either two manganese ions naked or only one of them in the mono-protonated stage is the most remarkable property of these ligands. Further striking features are the spatial arrangements of the pyridine-to-manganese bonds which deviate significantly from the situation expected for nitrogen donor functions in sp(2) hybridized stages. Moreover, regarding each chelating ligand portion as a component which occupies one coordination site of the metal atom, a pseudo-tetrahedral metal coordination is identified. To our knowledge, 1 and 2 are the first manganese complexes containing mono-protonated bis-guanidine ligands, whereas 3a and 3b are the first polynuclear manganese-guanidine compounds known so far.