22 research outputs found
Three-dimensional lanthanide-organic frameworks based on di-, tetra-, and hexameric clusters
Three-dimensional lanthanide-organic frameworks formulated as (CH3)2NH2[Ln(pydc)2] · 1/2H2O [Ln3+ ) Eu3+ (1a)
or Er3+ (1b); pydc2- corresponds to the diprotonated residue of 2,5-pyridinedicarboxylic acid (H2pydc)], [Er4(OH)4(pydc)4(H2O)3] ·H2O
(2), and [PrIII
2PrIV
1.25O(OH)3(pydc)3] (3) have been isolated from typical solvothermal (1a and 1b in N,N-dimethylformamide -
DMF) and hydrothermal (2 and 3) syntheses. Materials were characterized in the solid state using single-crystal X-ray diffraction,
thermogravimetric analysis, vibrational spectroscopy (FT-IR and FT-Raman), electron microscopy, and CHN elemental analysis.
While synthesis in DMF promotes the formation of centrosymmetric dimeric units, which act as building blocks in the construction
of anionic ∞
3{[Ln(pydc)2]-} frameworks having the channels filled by the charge-balancing (CH3)2NH2
+ cations generated in situ by
the solvolysis of DMF, the use of water as the solvent medium promotes clustering of the lanthanide centers: structures of 2 and 3
contain instead tetrameric [Er4(μ3-OH)4]8+ and hexameric |Pr6(μ3-O)2(μ3-OH)6| clusters which act as the building blocks of the networks,
and are bridged by the H2-xpydcx- residues. It is demonstrated that this modular approach is reflected in the topological nature of
the materials inducing 4-, 8-, and 14-connected uninodal networks (the nodes being the centers of gravity of the clusters) with
topologies identical to those of diamond (family 1), and framework types bct (for 2) and bcu-x (for 3), respectively. The
thermogravimetric studies of compound 3 further reveal a significant weight increase between ambient temperature and 450 °C with
this being correlated with the uptake of oxygen from the surrounding environment by the praseodymium oxide inorganic core
Identification of Reaction Conditions That Can Reproducibly Lead to a Particular Vertex Geometry: Quest for a Robust and Reproducible Metal-Carboxylate Noncluster-type SBU
A global assessment of actors and their roles in climate change adaptation
An assessment of the global progress in climate change adaptation is urgently needed. Despite a rising awareness that adaptation should involve diverse societal actors and a shared sense of responsibility, little is known about the types of actors, such as state and non-state, and their roles in different types of adaptation responses as well as in different regions. Based on a large n-structured analysis of case studies, we show that, although individuals or households are the most prominent actors implementing adaptation, they are the least involved in institutional responses, particularly in the global south. Governments are most often involved in planning and civil society in coordinating responses. Adaptation of individuals or households is documented especially in rural areas, and governments in urban areas. Overall, understanding of institutional, multi-actor and transformational adaptation is still limited. These findings contribute to debates around ‘social contracts’ for adaptation, that is, an agreement on the distribution of roles and responsibilities, and inform future adaptation governance