The first complex of the ligand NSe (selenonitrosyl), TpOs(NSe)Cl2 [Tp = hydrotris (1- p...

The first complex of the ligand NSe (selenonitrosyl), TpOs(NSe)Cl₂ [Tp = hydrotris (1- pyrazolyl)borate], is shown. The osmium–nitrogen distances are:

Os–N(1): 210.1(7) pm

Os–N(3): 206.6(8) pm

Os–N(5): 206.9(7) pm

a. Which ligand, Cl or NSe, has the larger trans influence? Explain briefly.

b. The nitrogen–selenium distance in this compound is among the shortest N – Se distances known. Why is this distance so short? (See T. J. Crevier, S. Lovell, J. M. Mayer, A. L. Rheingold, I. A. Guzei, J. Am. Chem. Soc ., 1998 , 120 , 6607.)