Conformationally Rigid Chelate Rings in Metal Complexes of Pyridyloxy-Substituted 2,2‘-Dioxybiphenyl-Cyclotetra- and Cyclotriphosphazene Platforms

Divalent metal halides react with pyridyloxy-substituted 2,2‘-dioxybiphenyl-cyclotri- and cyclotetraphosphazene ligands
to form the complexes, [MLX2] [M = Co or Cu; L = (2,2‘-dioxybiphenyl)tetrakis(2-pyridyloxy)cyclotriphosphazene
(L1) or (2,2‘-dioxybiphenyl)tetrakis(4-methyl-2-pyridyloxy)cyclotriphosphazene (L2); X = Cl or Br], [ZnLCl2] [L =
bis(2,2‘-dioxybiphenyl)bis(2-pyridyloxy)cyclotriphosphazene (L3) or bis(2,2‘-dioxybiphenyl)bis(4-methyl-2-pyridyloxy)cyclotriphosphazene (L4)], [MLCl2] [M = Cu or Hg; L = tris(2,2‘-dioxybiphenyl)bis(2-pyridyloxy)cyclotetraphosphazene
(L5)] and [Cu2LCl4] (L = trans-bis(2,2‘-dioxybiphenyl)tetrakis(2-pyridyloxy)cyclotetraphosphazene (L6)]. Single-crystal
X-ray structures show the L2 ligand complexes to have a N3Cl2 five-coordinate, trigonal-bipyramidal donor set with
the phosphazene ring and pendant pyridyloxy nitrogens binding to the metal ions. The coordinated L2 ligand in the
complex, [CoL2Cl2], slowly hydrolyses in acetonitrile with the loss of a pyridine pendant arm to form a dimetallic
species, which has been characterized by crystallography as [{CoL2aCl}]2·4MeCN (L2a = [N3P3(biph)(OPy)3(O)]-,
biph = 2,2‘-dioxybiphenyl, OPy = 2-oxopyridine). The ligands, L3, L4, L5, and L6, bind to the metal halides via
gem-substituted pyridyloxy nitrogens only. The resulting rigid eight-membered chelate rings all have distorted boat
conformations, which force distorted-tetrahedral N2Cl2 coordination environments onto the metal ions. The
spectroscopic (ESR and electronic) and magnetic properties of the complexes are reported.