High Intensity Trip‐Multiplet Transitions, a Reality! Synthesis, Properties, and Crystal Structure of l‐Bis(triphenylphosphine)iminium trans‐Dibromophthalocyaninato(2–)molybdate(III)

Abstract

AbstractOxophthalocyaninato(2–)molybdenum(IV), activated by bromine oxidation prior to use, reacts with fused triphenylphosphine in the presence of bis(triphenylphosphine)iminium bromide to yield linear‐bis(triphenylphosphine)iminium trans‐dibromophthalocyaninato(2–)molybdate(III), l(PNP)trans[Mo(Br)2pc2−]. It crystallizes triclinic with crystal data: a = 10.506(1) Å, b = 12.436(2) Å, c = 12.918(2) Å, α = 76.186(1)°, β = 67.890(1)°, γ = 68.689(1)°; space group P1 (No. 2); Z = 1. MoIII is in a pseudo‐octahedral coordination geometry with the bromo ligands in trans‐arrangement. The MoNp and MoBr distance is 2.043(10) and 2.588(1) Å, respectively. The PNP cation adopts a linear conformation. In the IR spectrum vas(MoBr) is observed at 218 cm−1 and vas(PN) of the linear (PNP) core at 1406 cm−1. Cyclic and differential‐pulse voltammetry show two quasi‐reversible cathodic processes at −1.15 and −0.53 V vs. Ag/AgCl. The first is assigned to a phthalocyaninate directed reduction (pc2−/pc3−), while the latter arises from a Mo directed reduction (MoIII/MoII). Spectral monitoring confirms the reversible MoIII/MoII reduction. Two quasi‐reversible anodic processes at 0.60 and 1.27 V are assigned to the successive Mo directed oxidation with redox couples MoIII/MoIV and MoIV/MoV. For the first time, three very intense spin‐allowed trip‐quartet transitions are observed in the electronic absorption spectra at 7140 (TQI), 16890 (TQ2) and 18700 cm−1 (TQ3) together with a sing‐quartet transition at 15850 cm−1 and characteristic „Q”︁ region with maximum at 28500 cm−1 and „N”︁ region at 37400 cm−1. All electronic excitations are of comparable intensity. A prominent low temperature emission at 6690 cm−1 is assigned to a spin‐forbidden trip‐sextet.