Synthesis, Crystal Structures, Raman and EPR Studies of Mixed Trihalides in Association with Transition Metal (Co II –Zn II ) Tris-chelates

Four new isostructural salts, [M(phen) 3 ](I 2 Br) 2 ·3CH 2 Cl 2 where, M=Co ( 1 ), Ni ( 2 ), Cu ( 3 ), or Zn ( 4 ) have been synthesized by reacting the metal nitrates with 1,10–phenanthroline (phen) in presence of potassium bromide and iodine in a two phase procedure. The [Cu(phen) 3 ] 2+ coordination corresponds to tetragonally elongated octahedron while the other three are much more symmetrical. The pure Cu 2+ complex as well as other salts doped with Cu 2+ give hyperfine resolved EPR spectra in a wide temperature range showing dynamic Jahn–Teller distortion. The trihalide ion is nearly linear with bond distances in the range, I–I (2.786–2.833 Å) and I–Br (2.759–2.794 Å). Geometry optimization (DFT and MP2 methods) predicts a much more unsymmetrical “gas phase” structure for I 2 Br − ion. Calculated Raman frequencies are in reasonable agreement with observed values. Electronic spectral results show that the integrity of the trihalide ion is retained in solution. Graphical Abstract Three new isostructural compounds having the general formula [M(phen) 3 ](I 2 Br) 2 having nearly symmetrical I 2 Br − ion are synthesized and characterized.