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External control over the mechanical function of materials is paramount in the development of nanoscale machines. Yet, exploiting changes in atomic behaviour to produce controlled scalable motion is a formidable challenge. Here, we present an ultra-flexible coordination framework material in which a cooperative electronic transition induces an extreme abrupt change in the crystal lattice conformation. This arises due to a change in the preferred coordination character of Fe(II) sites at different spin states, generating scissor-type flexing of the crystal lattice. Diluting the framework with transition-inactive Ni(II) sites disrupts longrange communication of spin state through the lattice, producing a more gradual transition and continuous lattice movement, thus generating colossal positive and negative linear thermal expansion behaviour, with coefficients of thermal expansion an order of magnitude greater than previously reported. This study has wider implications in the development of advanced responsive structures, demonstrating electronic control over mechanical motion. [ABSTRACT FROM AUTHOR]

The properties of atmospheric CO2 fixation, metamagnetism, reversible guest adsorption and zero thermal expansion have been combined in a single robust MOF, [Cu3(bpac)3(CO3)2](ClO4)2·H2O (1·H2O). This compound is a ditopically-bridged copper carbonate kagome lattice where desolvation of the MOF allows subtle tuning of the metamagnetic and uniaxial ZTE behaviour. [ABSTRACT FROM AUTHOR]

Metal-organic framework materials (MOFs) have recently been shown in some cases to exhibit strong negative thermal expansion (NTE) behavior, while framework interpenetration has been found to reduce NTE in many materials. Using powder and single-crystal diffraction methods we investigate the thermal expansion behavior of interpenetrated Cu3(btb)2 (MOF-14) and find that it exhibits an anomalously large NTE effect. Temperature-dependent structural analysis shows that, contrary to other interpenetrated materials, in MOF-14 the large positive thermal expansion of weak interactions that hold the interpenetrating networks together results in a low-energy contractive distortion of the overall framework structure, demonstrating a new mechanism for NTE. [ABSTRACT FROM AUTHOR]

Cyanidometallate complexes are highly versatile building units for the generation of functional porous materials. Here we report five new pillared Hofmann layer compounds incorporating the tetracyanidometallates [MoO(CN)4]2−and [MnN(CN)4]2−. These metalloligands, which are new to this class of materials, have been combined with divalent 1st-row transition metals to produce Hofmann layers that are linked into three-dimensional frameworks by ditopic bridging dipyridyls. We report the structures and anomalous thermal expansion properties of five new materials: [Mn(H2O)(bpy)½{MoO(CN)4(bpy)½}]·2H2O (1), [Mn(H2O)(bpy)½{MnN(CN)4(bpy)½}]·2H2O (2), [Fe(H2O)(bpy)½{MnN(CN)4(bpy)½}]·2H2O (3), [Co(H2O)(bpy)½{MnN(CN)4(bpy)½}]·2H2O (4) and [{Mn(H2O)2}½{Mn(bpa)2}½{MoO(CN)4(bpa)½}]·MeOH (5), (where bpy = 4,4′-bipyridine and bpa = 4,4′-bipyridylacetylene). [ABSTRACT FROM AUTHOR]

Powder diffraction is used to study thermal expansion properties of MOF-5 at moderate helium gas pressures: 1.7 bar (100–500 K) and 5–150 bar (150–300 K). The framework shows negative thermal expansion (NTE) at all pressures, but vibrational motions causing NTE are damped with increasing pressures, leading to decreased NTE. [ABSTRACT FROM AUTHOR]

The effect of MII substitution on the magnitude of the negative thermal expansion (NTE) behavior within a series of Prussian Blue analogues, MIIPtIV(CN)6 for MII = Mn, Fe, Co, Ni, Cu, Zn, Cd, has been investigated using variable-temperature powder X-ray diffraction (100–400 K). The NTE behavior varies widely with MII substitution, from near zero thermal expansion in NiPt(CN)6 (α = dI/I dT = -1.02(11) × 10-8 K-1) up to a maximum in CdPt(CN)6 (α = -10.02(11) × 10-6 K-1). The trend in the magnitude of the NTE behavior, with increasing atomic number (Z) of the MII ion, follows the order MnII > FeII > CoII > NiII < CuII < ZnII < CdII, which correlates with the trends for MII cation size, the lattice parameter, and structural flexibility as indicated by the temperature-dependent structural refinements and Raman spectroscopy. Analysis of the temperature dependence of the average structures suggests that the differences in the thermal expansion are due principally to the different strengths of the metal-cyanide binding interaction and, accordingly, the different energies of transverse vibration of the cyanide bridge, with enhanced NTE behavior for more flexible lattices. [ABSTRACT FROM AUTHOR]

The instantaneous structure of the cyanide-bridged negative thermal expansion (NTE) material Zn(CN)2 has been probed using atomic pair distribution function (PDF) analysis of high energy X-ray scattering data (100-400 K). The temperature dependence of the atomic separations extracted from the PDFs indicates an increase of the average transverse displacement of the cyanide bridge from the line connecting the Zn... centers with increasing temperature. This allows the contraction of non-nearest-neighbor Zn…Zn' and Zn…C/N distances despite the observed expansion of the individual direct Zn—C/N and C—N bonds. Thus, this analysis provides definitive structural confirmation that an increase in the average displacement of bridging atoms is the origin of the NTE behavior. The lattice parameters reveal a slight reduction in the NTE behavior at high temperature from a minimum coefficient of thermal expansion (α = dl/ldT) of -19.8 × 10-6 K-1 below 180 K, which is attributed to interaction between the doubly interpenetrated frameworks that comprise the structure. [ABSTRACT FROM AUTHOR]

The article discusses the negative thermal expansion (NTE) in nanoporous Prussian Blue analogues. The guest-dependent thermal expansion behavior and structure of the Prussian Blue analogues has been examined using variable temperature single-crystal X-ray diffraction. Thermally induced transverse vibrational motion of bridging oxide or cyanide ions draws the metal-atom anchors closer. The NTE effect can be reduced by direct comparison of the thermal expansion of the vacant and guest-loaded frameworks.

The article presents a study which investigates the isostructural tetramethylammonium copper(I) zinc(II) cyanide framework in determining the cancellation of the negative thermal expansion (NTE). The study has used the synchrotron powder and laboratory single-crystal X-ray diffraction supported by discrete Fourier transform (DFT) modeling. Results show that NTE in cristobalite-type cyanide frameworks can be converted to zero thermal expansion by the inclusion of ionic guests.