Mixed-ligand hydroxocopper(II)/pyridazine clusters embedded into 3D framework lattices

Rational combination of pyridazine, hydroxo and carboxylate bridging ligands led to the assembly of three types of mixed-ligand polynuclear Cu(II) clusters (A: [Cu-2(mu-OH)(mu-pdz)(mu-COO)]; B: [Cu-4(mu(3)-OH)(2)(mu-pdz)(2)]; C: [Cu-5(mu-OH)(2)(mu-pdz)(4)(mu-COO)(2)(mu-H2O)(2)]) and their integration into 3D framework structures. Mixed-ligand complexes [Cu-2(mu-OH){TMA}(L)(H2O)] (1), [Cu-4(mu(3)-OH) (2){ATC}(2)(L)(2)(H2O)(2)]center dot H2O (2) [Cu-4(mu(3)-OH)(2){TDC}(3)(L)(2)(H2O)(2)]center dot 7H(2)O (3) (L = 1,3-bis(pyridazin-4- yl)adamantane; TMA(3-) = benzene-1,3,5-tricarboxylate, ATC(3-) = adamantane-1,3,5-tricarboxylate, TDC2- = 2,5-thiophenedicarboxylate) and [Cu-5(mu-OH)(2){X}(4)(L)(2)(H2O)(2)]center dot nH(2)O (X = benzene-1,3-dicarboxylate, BDC2-, n = 5 (4) and 5-hydroxybenzene-1,3-dicarboxylate, HO-BDC2-, n = 6 (5)) are prepared under hydrothermal conditions. Trigonal bridges TMA(3-) and ATC(3-) generate planar Cu(II)/carboxylate subtopologies further pillared into 3D frameworks (1: binodal 3,5-coordinated, doubly interpenetrated tcj-3,5-Ccc2; 2: binodal 3,8-coordinated tfz-d) by bitopic pyridazine ligands. Unprecedented triple bridges in 1 (cluster of type A) support short Cu...Cu separations of 3.0746(6) angstrom. The framework in 3 is a primitive cubic net (pcu) with multiple bis-pyridazine and TDC2- links between the tetranuclear nodes of type B. Compounds 4 and 5 adopt uninodal ten-coordinated framework topologies (bct) embedding unprecedented centrosymmetric open-chain pentanuclear clusters of type C with two kinds of multiple bridges, Cu(mu-OH)(mu-pdz)(2)Cu and Cu(mu-COO)(mu-H2O)Cu (Cu...Cu distances are 3.175 and 3.324 angstrom, respectively). Magnetic coupling phenomena were detected for every type of cluster by susceptibility measurements of 1, 3 and 4. For binuclear clusters A in 1, the intracluster antiferromagnetic exchange interactions lead to a diamagnetic ground state (J = -17.5 cm(-1); g = 2.1). Strong antiferromagnetic coupling is relevant also for type B, which consequently results in a diamagnetic ground state (J(1) = -110 cm(-1); J(2) = -228 cm(-1), g = 2.07). For pentanuclear clusters of type C in 4, the exchange model is based on a strongly antiferromagnetically coupled central linear trinuclear Cu-3 group (J(1) = -125 cm(-1)) and two outer Cu centers weakly antiferromagnetically coupled to the terminal Cu ions of the triad (J(2) = -12.5 cm(-1)).