Cyclophosphazenes as Nodal Ligands in Coordination Polymers

Herein, we show that cyclotriphosphazenes carrying organo amino side chains, (RNH)6P3N3 {R = n-propyl (1),
cyclohexyl (2), benzyl (3)}, and (C4H8N)6P3N3 (4) produce supramolecular coordination compounds in conjunction
with silver salts by formation of linear N−Ag−N connections via nitrogen centers of the phosphazene ring. Crystalline
materials were obtained by layering methanol solutions containing phosphazene ligands with methanol solutions of
AgClO4 and AgNO3. The donor ability of the anion and the steric demand of the lipophilic ligand sphere R control
the topology of the coordination network:  (1)2(AgClO4)3 forms a graphite-type (6,3) network. All three N(ring) atoms
of the phosphazene ligand coordinate to silver ions, which, in return, linearly bridge two phosphazene ligands. The
phosphazene−Ag(I) arrangement in 1(AgNO3)2 exists of zigzag chains featuring one bridging silver ion and one
terminally coordinated silver ion per ligand molecule. The terminally located Ag(I) ions of neighboring chains are
bridged by nitrate ions, resulting in a 2D network. Both 2(AgClO4) and 4(AgClO4) contain only one bridging silver
ion per phosphazene ligand, which leaves one N(ring) site vacant and gives 1D zigzag chain arrangements. The
crystal structures of 3(AgClO4)2 and 3(AgNO3)2 resemble that of 1(AgNO3)2, but show additional Ag−π(aryl) interactions
between the terminally arranged silver ions and benzyl groups. Treatment of 3 with a methanol solution containing
both AgNO3 and AgClO4 leads to the heteroanion derivative 3(AgNO3)(AgClO4). Phosphazene ligands 1−3 have
the ability to undergo hydrogen bonding to anions via the six NH groups, and the coordination polymers containing
these ligands feature dense networks of NH···O bonds.