In recent years the phenomenon of negative thermal expansion (NTE; that is, contraction upon warming) over a broad temperature range has been detected in a select group of materials [1] and attributed to mechanisms that include electronic and magnetic transitions [2] and transverse atomic and molecular vibrations. [1,[3][4][5][6][7][8] Among the vibrational systems, materials that have received particular attention include AM 2 O 8 , AM 2 O 7 , A 2 M 3 O 12 , and a number of zeolites, [3] which contain MÀOÀM' bridges that undergo transverse vibration to cause contraction of the M-M' distance, and a diverse family of metal cyanides, [4][5][6][7][8] which contain MÀCNÀM' bridges that show an analogous effect but with increased vibrational flexibility. The presence of a highly flexible diatomic linker in the cyanide phases leads to pronounced thermal expansion behavior, examples of which include the largest isotropic [4] and anisotropic [5] NTE reported to date. A common NTE mechanism proposed for both the oxide and cyanide systems is the coupling of these transverse vibrations into concerted low-energy lattice modes that involve the rotation and/or translation of undistorted metal-coordination polyhedra, known as rigid unit modes (RUMs). [9] With thermal population, these modes counteract the higherenergy longitudinal modes that cause bond-length expansion, thereby leading to bulk NTE behavior.Recently, NTE has also been proposed in a series of isoreticular metal-organic framework (IRMOF) materials following the detected thermal contraction of gas-sorbed samples of IRMOF-1. [10] Theoretical simulations [11] of these materials have suggested an NTE mechanism closely analogous to that of the metal cyanide phases, [6,7] involving the transverse vibration of linear organic linkers. Following a more general investigation of such materials, herein we present the NTE properties of [Cu 3 (btc) 2 ] (btc = 1,3,5-benzenetricarboxylate), a metal-organic framework that consists of dicopper tetracarboxylate "paddlewheels" and aromatic ring motifs. [12] Through crystallographic characterization we elucidate a structural mechanism that involves two unique components: transverse vibration of planar, rather than linear, linkers, and local molecular vibrations within the framework.The highly symmetric structure of [Cu 3 (btc) 2 ] can be conveniently considered as consisting of octahedral supramolecular cages that link through their vertices to form a three-dimensional cubic framework (Figure 1 inset). As the material readily binds atmospheric water and gases at the coordinatively unsaturated Cu sites, [13] samples for powder and single-crystal X-ray diffraction measurement were sealed under vacuum in glass capillaries following their thorough Figure 1. Temperature-dependent variation in the lattice parameter of [Cu 3 (btc) 2 ] by PXRD (filled circles) and SC-XRD (open squares). Error bars show one estimated standard deviation (esd). A representation of the unit cell of [Cu 3 (btc) 2 ] is depicted in the inset.

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A 1-D chain CP with both SCO and redox activity has been successfully prepared by the combination of a bis-pyridyl functionalised TTF core and a Schiff base-like N2O2 ligand.

IV (CN)6 (M: Mn, Fe, Co, Ni, Cu, Zn, Cd). -The title compounds are characterized by variable-temperature powder XRD (100-400 K) and Raman spectroscopy. The trend in the magnitude of the negative thermal expansion behavior of the compounds follows the order Mn II > Fe II > Co II > Ni II < Cu II < Zn II < Cd II , which correlates with the trends for M II cation size, the lattice parameter, and structural flexibility. -(CHAPMAN, K. W.; CHUPAS, P. J.; KEPERT*, C.