A porous three-dimensional copper(II) metal-organic framework (MOF) {[Cu 2 (tci)(OH)(pip) 0.5 (H 2 O)]·6H 2 O} n (1) [tci = tris (2-carboxyethyl)isocyanurate, pip = piperazine] has been generated under hydrothermal conditions at 120 °C. Single crystal X-ray diffraction reveals that the polymer exhibits a novel three-dimensional framework based on planar tetranuclear copper(II) cluster units. The variable temperature magnetic susceptibility data in the range 2-280 K show antiferromagnetic spin-spin coupling in the tetranuclear unit in complex 1. A theoretical fitting of the magnetic data gives J values of 31.3 cm 1 , 30.8 cm 1 , and 13.5 cm 1 . metal-organic framework, tetranuclear copper cluster unit, topology, magnetism