Four new high-spin cobalt(II) complexes of formula [Co(H₂O)₆](H₂bta)·dpo·4H₂O (1), [{Co(H₂O)₄(dpo)}₂(bta)]·4H₂O·(2), [Co(H₂O)₂)(dpo)₂(H₂bta)]_n (3) and [Co(H₂O)₃(dpo)(bta)_1/2]_n (4) (H₄bta = 1,2,4,5-benzenetetracarboxylic acid and dpo = 4,4′-bipyridine-N,N′-dioxide) have been synthesized and their structures solved by single crystal X-ray diffraction methods. Compound 1 is an ionic salt whose structure is made up of [Co(H₂O)₆]²⁺ cations, H₂bta²⁻ anions, uncoordinated dpo groups and crystallization water molecules, which are linked by extensive hydrogen bonds to afford a three-dimensional network. The structure of 2 consists of bta-bridged dinuclear cobalt(II) complexes where four coordinated water molecules and a terminally bound dpo ligand complete the six coordination around each cobalt atom. The bta ligand in 2 adopts the bis-monodentate bridging mode through two trans carboxylate-oxygen atoms, the intramolecular cobalt–cobalt distance being 11.46(2) Å. The structure of 3 is constituted by uniform chains of cobalt(II) ions bridged by the dideprotonated H₂bta²⁻ species through two trans carboxylate-oxygen atoms. Two coordinated water molecules and two terminally bound dpo ligands achieve the six coordination around each cobalt atom. The intrachain cobalt–cobalt separation is 11.387(1) Å. The structure of 4 consists of corrugated layers of cobalt(II) ions bridged by bis-monodentate dpo and bta⁴⁻ ligands, (through two trans carboxylate-oxygen atoms), three coordinated water molecules in a fac arrangement achieving the six-coordination around each cobalt atom. The investigation of the magnetic behaviour of 2–4 in the temperature range 1.9–300 K shows the occurrence of very weak antiferromagnetic interactions between the high-spin cobalt(II) ions, the strong decrease of χ_MT upon cooling which is observed for this family of complexes ligands being mainly due to the depopulation of the higher energy Kramers doublets of the high-spin octahedral cobalt(II) centers.

TAMOF-1 is a robust, highly porous metal–organic framework built from Cu²⁺ centers linked by a L-histidine derivative. Thanks to its high porosity and homochirality, TAMOF-1 has shown interesting molecular recognition properties, being able to resolve racemic mixtures of small organic molecules in gas and liquid phases. Now, we have discovered that TAMOF-1 also offers a competitive performance as solid adsorbent for CO₂ physisorption, offering promising CO₂ adsorption capacity ( > 3.8 mmol g^–1) and CO₂/CH₄ Ideal Adsorbed Solution Theory (IAST) selectivity ( > 40) at ambient conditions. Moreover, the material exhibits favorable adsorption kinetics under dynamic conditions, demonstrating good stability in high-humidity environments and minimal degradation in strongly acidic media. We have identified the key interactions of CO₂ within the TAMOF-1 framework by a combination of structural (neutron diffraction), spectroscopic and theoretical analyses which conclude a dual-site adsorption mechanism with the majority of adsorbed CO₂ molecules occupying the empty voids in the TAMOF-1 channels without strong, directional supramolecular interactions. This very weak dominant binding opens the possibility of a low energy regeneration process for convenient CO₂ purification. These features identify TAMOF-1 as a viable solid-state adsorbent for the realization of affordable biogas upgrading.

Infinite network involving two hydrogen-bonded tetrameric water rings (S₄ and D_2h) in a (4,4)-square grid crystal host