A comparative study on structures and theoretical models of Rh azido complexes

Abstract

The syntheses of PF 6 − salt of six-coordinate Rh(III) azido complexes containing polypyridyl ligands have been accomplished by treatment of the corresponding Rh(III) chloride with NaN 3 in EtOH–H 2 O followed by the addition of NH 4 PF 6 . The complexes have been characterized by UV–vis, FTIR, 1 H and 14 N-NMR spectroscopy along with elemental analysis. The X-ray crystal structures of compounds [Rh(tpy)(phen)(N 3 )](PF 6 ) 2 ( 1 ·(PF 6 ) 2 , tpy: 2,2′:6′,2″-terpyridine, phen: 1,10-phenanthroline) and [Rh(tpy)(bpy)(N 3 )](PF 6 ) 2 ( 2 ·(PF 6 ) 2 , bpy: 2,2′-bipyridine) confirm that a rhodium atom is six-coordinate and the tpy and bpy or phen ligands are orthogonal and the RhN 3 distances are 2.038(7) and 2.048(6) A, respectively. The two NN distances for the coordinated azide in complex 1 ·(PF 6 ) 2 are identical with distances of 1.17 (1) and 1.17 (1) A. However, the two NN distances for the azido group in the complex 2 may or may not be inequivalent with 1.170(8) and 1.15(1) A. The bond angles formed by the azide group, Rh, and the axially-positioned nitrogen atom are 172.1(3) and 173.5(8)°. In order to answer the question as to whether the two NN distances in 2 would be expected to be different, calculations were carried out at HF/LANL2DZ and HF/SDD levels of theory. The results indeed predict the NN distances in 2 to be different.