Stepwise Crystallization: Illustrative Examples of the Use of Metalloligands [Cu₆(mna)₆]^6– and [Ag₆(Hmna)₂(mna)₄]^4– (H₂mna = 2-Mercapto Nicotinic Acid) in the Formation of Heterometallic Two- and Three-Dimensional Assemblies with brucite, pcu, and sql Topologies

Abstract

Three new inorganic coordination polymers, {[Mn(H 2 O) 6 ]-[Mn 2 (H 2 O) 6 ][(Cu 6 (mna) 6 ]•6H 2 O}, 1, {[Mn 4 (OH) 2 (H 2 O) 10 ][(Cu 6 (mna) 6 ]• 8H 2 O}, 2, and {[Mn 2 (H 2 O) 5 ][Ag 6 (Hmna) 2 (mna) 4 ]•20H 2 O}, 3, have been synthesized at room temperature through a sequential crystallization route. In addition, we have also prepared and characterized the molecular precursor [Cu 6 (Hmna) 6 ]. Compounds 1 and 3 have a two-dimensional structure, whereas 2 has a three-dimensional structure. The formation of 2 has been achieved by minor modification in the synthetic composition, suggesting the subtle relationship between the reactant composition and the structure. The hexanuclear copper and silver cluster cores have Cu•••Cu and Ag•••Ag distances close to the sum of the van der Waals radii of Cu 1+ and Ag 1+ , respectively. The connectivity between [Cu 6 (mna) 6 ] 6− cluster units and Mn 2+ ions gives rise to a brucite related layer in 1 and a pcu-net in 2. The [Ag 6 (Hmna) 2 (mna) 4 ] 4− cluster in 3, on the other hand, forms a sql-net with Mn 2+ . Compound 1 exhibits an interesting and reversible hydrochromic behavior, changing from pale yellow to red, on heating at 70 °C or treatment under a vacuum. Electron paramagnetic resonance studies indicate no change in the valence states, suggesting the color change could be due to changes in the coordination environment only. The magnetic studies indicate weak antiferromagnetic behavior. Proton conductivity studies indicate moderate proton migrations in 1 and 3. The present study clearly establishes sequential crystallization as an important pathway for the synthesis of heterometallic coordination polymers.

Piezochromism and hydrochromism through electron transfer: new stories for viologen materials

“…Reversible solid-state hydrochromism related to dehydration–hydration has long been known in transition metal compounds, 26 among the best known examples being copper sulfate pentahydrate and cobalt nitrate hexahydrate. The phenomenon has also been observed in organic species.…”

Effect of three bis-pyridyl-bis-amide ligands with various spacers on the structural diversity of new multifunctional cobalt(II) coordination polymers

“…The dihedral angle between the two pyridine rings of 3-bpcb ligand is 6.841. Topologically, if the dinuclear {Co 2 } SBU is considered as a 6-connected node and the two types of bridging ligands (1,4-NDC and 3-bpcb) are considered as linkers, the 3D framework of complex 3 represents a 6-connected pcu network with {4 12 .6 3 } topology [38,39] (Fig. 3d).…”

A Two-Dimensional Metal-Organic-Framework Formed From a Cobalt(II) Ion and a Bifunctional Ligand Exhibiting Thermochromic Behavior

“…Depending on the external stimuli, which causes the color change in these materials, such as, light, temperature, pressure, and solvent molecules, they are categorized as photochromic (Pardo et al, 2011;Tandekar et al, 2018), thermochromic (Lim et al, 2018;Liu and Li, 2019), piezochromic , and solvatochromic materials (Lu et al, 2011;Mehlana et al, 2013), respectively. The investigation of the underlying mechanism for such sort of chromic behavior reveals that the color change is associated to the one of the following reasons: (i) charge transfer (CT)/electron transfer between the organic ligands [such as, 4,4-bipyridinium (Toma et al, 2015;Zhang et al, 2016), vialogen based ligands (Wan et al, 2015;Hu et al, 2017)] and the metal which changes their absorption properties, (ii) disruption of the interaction between the solvent molecules and the compounds which leads to the alterations in the crystal packing/supramolecular interactions (such as, hydrogen bonding, and π···π interactions), and (iii) coordination geometry transformations (Kundu et al, 2014;Burneo et al, 2015;Thapa et al, 2018) due to the loss of metal bound solvent molecules/rearrangement of the coordinating atoms around the metal centers.…”