Structural Transformation from a Discrete Cu4II Cluster to Two Extended Cu4II + Cu1II Chain-Based Three-Dimensional Frameworks by Changing the Spacer Functionality: Synthesis, Crystal Structures, and Magnetic Properties

Three unique [Cu-4(mu(3)-OH)(2)](6+) core-based magnetic complexes, [Cu-4(amtrz)(2)(mu(3)-OH)(2)(nb)(6)]center dot 2H(2)O (1), {[Cu-5(H2O)(6)(trz)(2)(mu(3)-OH)(2)(btc)(2)]center dot 0.6H(2)O}(n) (2), and {[Cu-5(H2O)(2)(Htrz)(2)(mu(3)-OH)(2)(btec)(2)]center dot 0.125H(2)O}(n), (3) (amtrz = 4-amino-1,2,4-triazole, Htrz = 1,2,4-triazole, Hnb = 4-nitrobenzoic acid, H(3)btc = 1,2,3-benzenetricarboxylic acid, and H(4)btec = 1,2,4,5-benzenetetracarboxylic acid), were synthesized by varying the spacer functionality of the mixed ligands. Significantly resulting from the cooperative cocoordination of the metal ions with polytopic triazolyl and carboxylate groups, a structural transformation from a discrete Cu-4(II), cluster for 1 to two alternate Cu-4(II), + Cu-1(II) chain-based three-dimensional frameworks for 2 and 3 was achieved. Moreover, the connectivity manner of the structural subunits in 2 and 3 depends strongly on the number and position of the carboxylate group attached on the phenyl backbone. The nearest-neighbor interactions within the Cu-4(II) cluster and between Cu-4(II) cluster and Cu-1(II) core mediated by the mixed short bridges were quantitatively calculated and compared based on the established magneto-structural relationships. Strong antiferromagnetic coupling interactions up to -206(4) cm(-1) were observed in the isolated Cu-4(II) cluster due to the favorable spatial orientation of the mixed multiple heterobridges toward the spin carriers.