Dithiolene dimetallic molybdenum(v) complexes displaying intraligand charge transfer (ILCT) emission

Abstract

Bifunctional dithiolene ligands have been coordinated to the Mo^V(O)(μ-S₂)Mo^V(O) unit to afford [Mo₂O₂(μ-S)₂(BPyDTS₂)₂]²2⁻ (1²⁻) (BPyDTS₂ (2-bis-(2-pyridyl)methylene-1,3-dithiolene) dianions. Reaction of the 1²⁻ molybdenum dimer with pentacarbonylchlorothenium(I) affords a tetrametallic complex of formula [Mo₂O₂(μ-S)₂(BPyDTS₂)₂{Re(CO)₃Cl}₂]²⁻ (2²⁻). The monomeric (CH₃)₂Sn(BPyDTS₂) (3) tin complex has also been prepared for comparative purposes. In the structure of (Et₄N)₂[1], the two metal atoms are in a square pyramidal coordination environment defined by two bridging sulfur atoms, one terminal oxygen atom and the two sulfur atoms of the bifunctional dithiolene ligand. This arrangement leaves two nitrogen atoms on each side which coordinate to two Re atoms in the 2²⁻ tetrametallic complex. Compound 3 has a distorted tetrahedral structure defined by two carbon atoms of the methyl groups and two sulfur atoms of the dithiolene ligand. The luminescence properties of all three complexes in acetonitrile have been investigated. Detailed studies supported on quantum mechanical calculations revealed that complex 1²⁻ shows photoluminescence in the 600–800 nm region with a maximum wavelength of 628 nm and an emission quantum yield of 0.092, associated with an intraligand charge transfer (ILCT) transition. Coordination of two Re(CO)₃Cl fragments to 1²⁻ to afford 2²⁻ does not affect the emission spectrum and shape although it decreases the quantum yield, approximately by a factor of 4.6. Compound 3 exhibits a similar emission spectrum to those of the complexes 1²⁻ and 2²⁻ in good agreement with the ILCT assignment. The quantum yield of 3 lies between that of the 1²⁻ and 2²⁻ complexes.