Isomerism in coordination complexes and polymers derived from bispyridylurea ligands: Effect of solvents, conformational flexibility, and positional isomerism of the ligands

Reactions between Cd(NO3)(2)center dot 6H(2)O and N,N'-bis(3-pyridyl)urea (3bpu)/N,N'-bis(4-pyr-idyl)urea (4bpu) with a 1:2 metal:ligand ratio under various solvent systems (polar/nonpolar) afforded four discrete coordination complexes, namely, [{(H2O)(2)-Cd(3bpu)(4)}-(NO3)(2)-2H(2)O center dot X] 1, [{(H2O)(2)Cd(3bpu)(4)}-(NO3)(2)] 3, [{(H2O)(2)Cd(3bpu)(4)}center dot(NO3)(2 center dot)2H(2)O center dot p-xylene] 4, [{(H2O)(2) (NO3)(2)Cd(mu-4bpu)(2)}] 8, and four coordination polymers, namely, [{(H2O)(3)(NO3)Cd(mu-3bpu)}center dot(NO3)center dot H2O-1/2o-xylene](n) 2, [{(H2O)(3)(NO3)Cd(mu-3bpu)}center dot(NO3)-X](n) 5, [{(NO3)(2)Cd(mu-3bpu)(2)}](n) 6, [{(H2O)(NO3)Cd(mu-4bpu)(2)}center dot(NO3)-EtOH center dot nitrobenzene](n) 7, which were mainly characterized by single-crystal X-ray diffractometry. The effect of solvents, conformational flexibility, and positional isomerism of the ligands on the various isomerisms (supramolecular isomerism and polymorphism) is discussed.