New μ4-Oxido-Bridged Copper Benzoate Quasi-Tetrahedron and Bis-μ3-Hydroxido-Bridged Copper Azide and Copper Thiocyanate Stepped Cubanes: Core Conversion, Structural Diversity, and Magnetic Properties

[Cu2(μ4-O)Cu2] and [Cu2(μ3-OH)2Cu2] geometrical arrangements are found in a new family of tetranuclear complexes: [Cu4(μ4-O)(μ-bip)2(μ-O2CPh)4] .0.5CH2Cl2 (1.0.5CH2Cl2), [Cu4(μ3-OH)2(μ-bip)2(N3)4](2), and [Cu4- (μ3-OH)2(μ-bip)2(NCS)4(DMF)2](3.2DMF)[Hbip = 2,6-bis(benzyliminomethyl)-4-methylphenol; DMF = dimethyl- formamide]. These complexes have been characterized by X-ray crystallography, and their magnetic properties have been studied. Complex 1 reacts with azide and thiocyanate anions, leading to 2 and 3 with a change of the [Cu4(μ4-O)] core into [Cu4(μ3-OH)2] units. These compounds are new examples of [Cu4] complexes where CuII ions are connected by two types of water-derived ligands: oxide and hydroxide. Formation of these [Cu4] complexes can be controlled by changing the bridging ligands, which allows an effective tuning of the self-assembly. The study of the magnetic properties reveals that these complexes exhibit strong intramolecular antiferromagnetic interactions to yield a ST = 0 ground state. For the three complexes, the temperature dependence of the magnetic susceptibility was fitted using a model with two isolated S = 1/2 dimers based on the H = -2J{SCu,1.SCu,2} spin Hamiltonian with J/kB =-289 K for 1; J/kB =-464 and -405 K for 2 and 3, respectively (where J is the exchange constant through the oxido-phenoxido or hydroxido-phenoxido bridges, respectively)