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This study reports on the multiresponsive behavior of Co(II) bis(tolylterpyridine) nitrate crystals. Each crystal contains a single Co(II) complex and can accommodate up to 4 H2O molecules per asymmetric unit. In its fully hydrated form, the crystal contains planar hexameric hydrogen-bonded H2O clusters. The adsorption and desorption of H2O occur reversibly with changes in humidity, despite the absence of extended H2O channels. Furthermore, the crystals exhibit a crystal-to-crystal thermal phase transition. The structural studies reveal the dynamic nature of these crystals, which contribute to their multiresponsive behavior.Graphical Abstract

We obtained two types of crystals of a complex under different crystallization conditions, each exhibiting distinct molecular arrangements and magnetic interactions: one type consists of isolated complexes, while the other forms one-dimensional chains without extra bridging ligands. This approach provides a new avenue for tuning the magnetic properties of metal-complex-based materials.The same trinuclear copper complex crystalizes in two different arrangements: one with isolated complexes and the other forming one-dimensional chains. This approach provides a new avenue for tuning the magnetic properties of metal-complex-based materials.

Ordered arrays of copper nanostructures were fabricated and modified with porphyrin molecules in order to evaluate fluorescence enhancement due to the localized surface plasmon resonance. The nanostructures were prepared by thermally depositing copper on the upper hemispheres of two-dimensional silica colloidal crystals. The wavelength at which the surface plasmon resonance of the nanostructures was generated was tuned to a longer wavelength than the interband transition region of copper (>590 nm) by controlling the diameter of the underlying silica particles. Immobilization of porphyrin monolayers onto the nanostructures was achieved viaself-assembly of 16-mercaptohexadecanoic acid, which also suppressed the oxidation of the copper surface. The maximum fluorescence enhancement of porphyrin by a factor of 89.2 was achieved as compared with that on a planar Cu plate (CuP) due to the generation of the surface plasmon resonance. Furthermore, it was found that while the fluorescence from the porphyrin was quenched within the interband transition region, it was efficiently enhanced at longer wavelengths. It was demonstrated that the enhancement induced by the proximity of the fluorophore to the nanostructures was enough to overcome the highly efficient quenching effects of the metal. From these results, it is speculated that the surface plasmon resonance of copper has tremendous potential for practical use as high functional plasmonic sensor and devices.