Windmill Co₄{Co₄(μ₄‐O)} with 16 Divergent Branches Forming a Family of Metal–Organic Frameworks: Organic Metrics Control Topology, Gas Sorption, and Magnetism

Abstract

A series of highly connected metal-organic frameworks (MOFs), [Co8 (O)(OH)4 (H2 O)4 (ina)8 ](NO3 )2 ⋅2 C2 H5 OH⋅4 H2 O (1), [Co8 (O)(OH)4 (H2 O)4 (pba)8 ](NO3 )2 ⋅8 C2 H5 OH⋅28 H2 O (2), and [Co8 (O)(OH)4 (H2 O)4 (pbba)8 ](NO3 )2 ⋅guest (3), in which ina=isonicotinate, pba=4-pyridylbenzoate, and pbba=4-(pyridine-4-yl)phenylbenzoate, is reported. These MOFs contain a new secondary building unit (SBU), with a square Co4 (μ4 -O) central unit having the rare μ4 -O(2-) motif, which is decorated by the other four peripheral cobalt atoms through μ3 -OH in a windmill-like shape. This SBU holds 16 divergent connecting organic ligands, pyridyl-carboxylates, to form three different frameworks. The high porosity of desolvated 2 is shown by the efficient gas absorption of N2 , CO2 , CH4 , and H2 . In addition, 1 and 2 exhibit unusual canted antiferromagnetic behavior with spin-glass-like relaxation, with blocking temperatures that are fairly high, 20 K (1) and 10 K (2), for cobalt materials. The relationship between the metal clusters and linkers has been studied, in which the size and rotational degrees of freedom of the ligands are found to control the topology, gas sorption, and magnetic properties.

A Microporous Co(II)‐Based 3‐D Metal Organic Framework Built from Magnetic Infinite Rod‐Shaped Secondary Building Units

“…All dc and ac data reveal that Co 5 ‐INA displays unusual magnetic phenomena that can be attributed to a spin‐canted antiferromagnet with spin‐glass‐like relaxation , …”

“…Paramagnetic 3d metal ions have been widely employed for this purpose due to their interesting magnetic properties. Their use has afforded MOFs displaying various interesting magnetic phenomena such as single‐molecule magnetism (SMM),, , single‐chain magnetism (SCM),, spin canting,, metamagnetic transitions, spin glass relaxation, etc. Most of the magnetic MOFs are based on Co 2+ mainly because of the presence of three unpaired electrons in the high‐spin octahedral Co 2+ ion and its significant single‐ion magnetic anisotropy , …”

“…One quite inexpensive commercially available polytopic ligand that combines several of the above‐mentioned characteristics and has been proven powerful for the construction of multidimensional metal–organic coordination networks is isonicotinic acid (HINA). In fact, several of the INA – MOFs are based on Co 2+ ions with some of them displaying or even combining interesting sorption, magnetic and SCSC transformation properties …”

Octanuclear Cobalt(II) Cluster-Based Metal–Organic Framework with Caged Structure Exhibiting the Selective Adsorption of Ethane over Ethylene

“…Additionally, almost all of the reported octanuclear cobalt oxide clusters exist in the discrete molecules. Only two polymeric structures constructed from the octanuclear cobalt oxide clusters as the basic units have been documented. , …”

Three novel topologically different metal–organic frameworks built from 3-nitro-4-(pyridin-4-yl)benzoic acid

“…On the other hand, as a branch of rigid ligands, 4-(pyridin-4yl)benzoic acid (pba) has been widely adopted to build MOFs (Mehlana et al, 2015). Because of the simultaneous existence of the hard-base carboxylate group and the soft-base N-atom donor of the pyridyl ring, many pba-based MOFs with different topologies, like dia (Mehlana et al, 2012;Zhou et al, 2012;Elsaidi et al, 2014;Zeng et al, 2013;Zhang et al, 2017;Wang et al, 2017), pcu (Das et al, 2011;Zhang et al, 2011;, rtl (Zhou et al, 2014), tsi (Chen et al, 2016), hxl (Fang et al, 2013), bcu (Zeng, Zhou et al, 2010;Zhou et al, 2015), fsc (Elsaidi et al, 2016), ncb (Zhang et al, 2009(Zhang et al, , 2012Zhao, Mao et al, 2016), bnn (Fang, Zhang et al, 2015), tfz-d (Liu, Luo et al, 2014), mdf (Wang, Fang et al, 2010), sql , pts and qtz (Mehlana et al, 2013), have been reported. Moreover, a few novel topological pba-based MOFs with the Schlä fli symbols (3 6 Á4 18 Á5 3 Á6) (Ding et al, 2017), (8 4 Á12 2 )(8) 2 (Wang et al, 2018), and (3 3 Á4 12 Á5 3 Á6 3 )(3 6 Á4 12 Á5 9 Á6) (Fang, Cheng et al, 2014) have been known.…”