Dramatic variation of magnetic exchange through double end-on azide bridges in a series of ladder-like copper(II) coordination polymers

Three ladder-like coordination polymers, [CU2(phprpy)(2)-mu-(N-3)(2)(N-3)(2)], 1; [CU2(terpy)(2)-mu-(N-3)(4)Cu-2-mu-(N-3)(2)(N-3)(2)], 2; and[CU2(terpy)(2)-mu-(N-3)(2)(N-3)(2)Cu-3-mu-(N-3)(4)(N-3)(2)], 3, consisting of CU2+ ions with double end-on azide bridges were synthesized, their crystal structures and magnetic properties were determined, and spin dimer analysis was performed to explain the signs and strengths of their strong spin exchange interactions [phprpy is 4-(3-phenylpropyl)pyridine and terpy is 2,2':6,2-terpyridine]. Although these compounds have ladder-like arrangements Of CU2+ ions, their magnetic structures are described as isolated dimers for 1 and 2 and as isolated trimers for 3. The predominant spin exchange paths in 1-3 have double end-on azide bridges linking adjacent CU2+ ions, and the geometrical parameters of these bridging structures are similar. However, the spin dimer of 1 exhibits a strong ferromagnetic coupling; that of 2, a strong antiferromagnetic coupling; and that of 3, a weak ferromagnetic coupling. These findings are well explained by the present spin dimer analysis and show that the nature and geometry of the nonbridging ligands can have a strong influence on the sign and strength of the spin exchange interaction between CU2+ ions connected by double end-on azide bridges.