Two isostructural metal-organic framework (MOF) materials, namely, {[MeSi((3)Py)3]6(Cu6I6)}n (1) and {[ MeSi((3)Qy)3]6(Cu6I6)}n (2), featuring Cu6I6 clusters were synthesized from tridentate arylsilane ligands of the type MeSi((3)Py)3 ((3)Py = 3-pyridyl) and MeSi((3)Qy)3 ((3)Qy = 3-quinolyl), respectively. While the MOF 1 displays the usual thermochromism associated with traditional Cu4I4Py4 clusters, the MOF 2 shows (3)XLCT/(3)MLCT emission due to the Cu6I6 cluster core at both 298 and 77 K, albeit with some marginal variations in its emission wavelengths. Interestingly, an unusual reversal in the mechanochromic luminescent behavior was observed for these isostructural MOFs at 298 K wherein a pronounced blue-shifted high energy emission for 1 (from orange to yellowish-orange) and a red-shifted low-energy emission for 2 (from green to orange) were obtained upon grinding these samples. This is primarily due to the variations in their cuprophilic interactions as 1 displays shorter Cu···Cu distances (2.745(1) Å) in comparison with those present in 2 (3.148(0) Å). As a result, the ground sample of 2 exhibits a prominent red shift in luminescence owing to the reduction of its Cu···Cu distances to an unknown value closer to the sum of van der Waals radii between two Cu(I) atoms (2.80 Å). However, the blue-shifted emission in 1 is presumably attributed to the rise in its lowest unoccupied molecular orbital energy levels caused by changes in the secondary packing forces. Furthermore, the absorption and emission characteristics of 1 and 2 were substantiated by time-dependent density functional theory calculations on their discrete-model compounds. In addition, the syntheses, reactivity studies, and photophysical properties of two one-dimensional MOFs, namely, {[MeSi((3)Qy)3]2(Cu2I2)}n (3) and {[MeSi((3)Qy)3](CuI)}n (4), having dimeric Cu2I2 and monomeric CuI moieties, respectively, were examined.

Through-space charge movement enabled by intervalence charge transfer interactions between π-stacked mixed-valent tetrathiafulvalene ligands creates electrical conductivity in three-dimensional metal–organic frameworks.

A charge-neutral tetrahedral [(Pd3X)4L6] cage assembly built from a trinuclear polyhedral building unit (PBU), [Pd3X](3+), cis-blocked with an imido P(V) ligand, [(N(i)Pr)3PO](3-) (X(3-)), and oxalate dianions (L(2-)) is reported. Use of benzoate or ferrocene dicarboxylate anions, which do not offer wide-angle chelation as that of oxalate dianions, leads to smaller prismatic clusters instead of polyhedral cage assemblies. The porosity of the tetrahedral cage assembly was determined by gas adsorption studies, which show a higher uptake capacity for CO2 over N2 and H2. The tetrahedral cage was shown to encapsulate a wide range of neutral guest solvents from polar to nonpolar such as dimethyl sulfoxide, benzene, dichloromethane, chloroform, carbon tetrachloride, and cyclopentane as observed by mass spectral and single-crystal X-ray diffraction studies. The (1)H two-dimensional diffusion ordered spectroscopy NMR analysis shows that the host and guest molecules exhibit similar diffusion coefficients in all the studied host-guest systems. Further, the tetrahedral cage shows selective binding of benzene, CCl4, and cyclopentane among other solvents from their categories as evidenced from mass spectral analysis. A preliminary density functional theory analysis gave a highest binding energy for benzene among the other solvents that were structurally shown to be encapsulated at the intrinsic cavity of the tetrahedral cage.

By employing a tridentate thiophosphoramide ligand, [(NHAQ)3P[double bond, length as m-dash]S] (AQ = 3-quinolinyl), a cationic MOF, {[Cu6I5(L(1))2](OH)·3DMF·2.5MeOH}n, was synthesized. Photo-physical studies on the 2D-MOF showed an unusual thermochromic behaviour emitting a blue fluorescence at 298 K due to the AQ chromophore and an orange-yellow phosphorescence at 77 K due to the [Cu6I5](+) unit.

Semiconducting metal–organic frameworks (MOFs) show great potential to foster myriad advanced electronics and energy technologies, but they must possess adequate charge-carrier concentration and efficient charge-transport pathways in order to display useful electrical conductivity. A new intrinsically conducting 3D framework [Ag2(HATHCN)­(CF3SO3)2] n was constructed by employing a highly π-acidic 1,4,5,8,9,12-hexaazatriphenylene-2,3,6,7,10,11-hexacarbonitrile (HATHCN) ligand, which assumed a paramagnetic HATHCN•– radical anion character by acquiring electron density from the TfO– anions involved in the anion−π interaction and facilitated charge movement along the staircase-like [−Ag+–HATHCN−]∞ chains having ample Ag4d +–N2p orbital overlap in the valence band region. As a result, the MOF displayed a narrow band gap (1.35 eV) and promising electrical conductivity (7.3 × 10–4 S/cm, 293 K) that ranked very high among those recorded for 3D MOFs. This work presents a new strategy to construct intrinsically conductive 3D frameworks by exploiting the dual metal coordination and anion−π interaction capabilities of a highly π-acidic HATHCN ligand.