Contrasting low-dimensional magnetism in the 3D metal-organic frameworks [Cu(VF6)(pyz)2]4H2O and [Cu(HF2)(pyz)2]SbF6 (pyz = pyrazine)

[Cu(VF₆)(pyz)₂]4H₂O (1) and [Cu(HF₂)(pyz)₂]SbF₆ (2) form tetragonal frameworks that consist of 2D [Cu(pyz)₂]^2+ square lattices that are linked in 3D by bridging VF₆^2- (1) or HF₂^- (2) anions. Magnetic susceptibility data shows apparent paramagnetism, although not simple Curie-Weiss behavior, in 1. For 2, a broad maximum in χ(T) at 12.5 K and a sharp kink at 4.3 K indicate short- (SRO) and long-range (LRO) magnetic ordering, respectively. Additional experimental data for 1 (e.g., heat capacity and μ^+SR) however, indicate that a LRO state occurs below 3.6 K whereas pulsed-field magnetization data suggest a superposition of AFM Cu^2+ layers and fluctuating V^4+ moments. The structural and magnetic behavior of 1 and 2 will be described as well as possible new directions.