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

Rational combination of pyridazine, hydroxo and carboxylate bridging ligands led to the assembly of three types of mixed-ligand polynuclear Cu(II) clusters (A: [Cu2(μ-OH)(μ-pdz)(μ-COO)]; B: [Cu4(μ3OH)2(μ-pdz)2]; C: [Cu5(μ-OH)2(μ-pdz)4(μ-COO)2(μ-H2O)2]) and their integration into 3D framework structures. Mixed-ligand complexes [Cu2(μ-OH){TMA}(L)(H2O)] (1), [Cu4(μ3-OH)2{ATC}2(L)2(H2O)2]·H2O (2) [Cu4(μ3-OH)2{TDC}3(L)2(H2O)2]·7H2O (3) (L = 1,3-bis(pyridazin-4-yl)adamantane; TMA = benzene1,3,5-tricarboxylate, ATC = adamantane-1,3,5-tricarboxylate, TDC = 2,5-thiophenedicarboxylate) and [Cu5(μ-OH)2{X}4(L)2(H2O)2]·nH2O (X = benzene-1,3-dicarboxylate, BDC, n = 5 (4) and 5-hydroxybenzene-1,3-dicarboxylate, HO-BDC, n = 6 (5)) are prepared under hydrothermal conditions. Trigonal bridges TMA and ATC 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) Å. The framework in 3 is a primitive cubic net (pcu) with multiple bispyridazine and TDC links between the tetranuclear nodes of type B. Compounds 4 and 5 adopt uninodal ten-coordinated framework topologies (bct) embedding unprecedented centrosymmetric openchain pentanuclear clusters of type C with two kinds of multiple bridges, Cu(μ-OH)(μ-pdz)2Cu and Cu(μ-COO)(μ-H2O)Cu (Cu⋯Cu distances are 3.175 and 3.324 Å, 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; g = 2.1). Strong antiferromagnetic coupling is relevant also for type B, which consequently results in a diamagnetic ground state (J1 = −110 cm; J2 = −228 cm, g = 2.07). For pentanuclear clusters of type C in 4, the exchange model is based on a strongly antiferromagnetically coupled central linear trinuclear Cu3 group (J1 = −125 cm) and two outer Cu centers weakly antiferromagnetically coupled to the terminal Cu ions of the triad (J2 = −12.5 cm).