Germanium(II) dicationic complexes
[2][3] Much more weakly coordinated Germanium (II) dications have been isolated as complexes with polyether ligands, such as crown ethers and [2.2.2]cryptand.
Since these reports, similar cationic Ge(II) complexes have been prepared employing crown ethers, azamacrocycles, and bulky isocyanide ligands.
[3][4][5][8][9] In the preparation of Ge(II) cationic complexes, triflate is often chosen as a counter anion as it is relatively weakly coordinating.
The germanium cryptand salt precipitated from solution as a white powder, and the identity was established using proton NMR and crystal X-ray diffraction.
[6] The carbene stabilized germanium chloride side products (structures given below) were identified in solution after the reaction.
Rupar et al. reported the synthesis of various germanium crown ethers employing GeCl2•dioxane as the source of Ge(II).
VSEPR theory is used to predict geometric distortions about atoms with nonbonding electrons (lone pairs), but in some cases heavier main group elements can violate VSEPR theory, displaying a stereochemically inactive or "spherically symmetric" lone pair, deemed the inert-pair effect.
[11] Ge(II) complexes can possess stereochemically active or inactive lone pairs, depending on the ligand.
[13] The crystal structure of the Ge(II) cryptand[2.2.2] complex reveals a much longer Ge-O distance of 2.49 Å,[6] similarly the Ge-O distances range from 2.38-2.49 Å in the Ge(II) ([12]crown-4)2 sandwich complex.
Due to this weak coordination, such Ge(II) crown ether complexes could be useful for the preparation of other germanium compounds.
Bandyopadhyay et al. have investigated the reactivity of a GeOTf+ [15]crown-5 complex, and found that the weakly coordinating triflate could be exchanged for H2O or NH3.
The empty p orbitals of Ge(II) dications make them potential π-acceptors for transition metal complexes.
Intriguingly, dicationic Ge(II) complexes have been shown to act as ligands for Au(I) and Ag(I).
[14] Raut and Majumdar report the use of a bis(α-iminopyridine) ligand to prepare a Ge(II) dicationic complex that coordinates to the electron rich Au(I) or Ag(I) metal centers.
