Vacuum-Induced Guest N,N'-Diethylformamide Binding in a Metastable Cd5-Based Metal-Organic Framework.

A three-dimensional (3D) metal-organic framework (MOF) of [Et2NH2]2[Cd5(BTB)4(DEF)2]·4.75DEF (1; H3BTB = benzene-1,3,5-tribenzoic acid and DEF = N,N'-diethylformamide) sustained by symmetrical Z-shaped Cd5 secondary building units (SBUs) with an intrinsically metastable host framework has been prepared and characterized. Upon gentle vacuum (800 Pa) at 50 °C, some encapsulated DEF solvates are released, leading to pore-shape changes and Cd2+ coordination geometry distortion. This is followed by DEF solvate migration to only one end of the SBU with concomitant symmetry breaking. Additional time under vacuum promoted further structural distortion and topology changes as authenticated by single-crystal X-ray diffraction studies. This work was initially inspired by unusual gas adsorption isotherms and points to the potentially complicated, nonspectator role of coordinative solvents such as DEF during MOF activation.

Metal-organic frameworks of linear trinuclear cluster secondary building units: structures and applications.

Secondary building units (SBUs) in metal-organic frameworks (MOFs) are essential from both a structural and performance perspective. While a variety of SBUs, such as paddlewheel CuII2, triangular CrIII3, tetrahedral ZnII4, and octahedral ZrIV6 have been extensively studied, the linear trinuclear SBUs (herein denoted as M3), though frequently encountered, are rarely discussed as a class. A literature survey reveals that M3 clusters are ubiquitous in discrete molecular entities as well as in MOFs. Unlike most other cluster types, however, they have an unprecedented metal diversity and ligand tolerance. The single-crystals of some M3-based MOFs are also sufficiently robust upon guest removal and exchange or multi-step post-modifications to enable catalytic mechanism elucidation. Some of these M3-based SBUs endow MOFs with stability under demanding conditions necessary, for example, in flue gas separation. Herein we review MOFs sustained by this common but under-appreciated class of SBUs and discuss applications of the resulting MOF motifs.

An N,N'-diethylformamide solvent-induced conversion cascade within a metal-organic framework single crystal.

Crystals of a two-dimensional (2D) metal-organic framework (MOF) [Cd3(BTB)2(DEF)4]·2(DEF)0.5 (1; BTB = benzene-1,3,5-tribenzolate; DEF = N,N'-diethylformamide) immersed in a solution of trans-1,2-bis(4-pyridyl)ethylene (BPEE) yields an interpenetrated three-dimensional (3D) MOF of [Cd3(BTB)2(BPEE)(H2O)2]·(BPEE)·xSol (2). Crystals of MOF 2, in turn, undergo a cascade conversion when immersed in DEF, yielding [Cd3(BTB)2(BPEE)1.8(DEF)0.9(H2O)0.8]·xSol (3a) over 100 seconds and [Cd3(BTB)2(BPEE)2(DEF)2]·xSol (4) after one hour, before finally shuttling back to MOF 1 after six hours.

A Heterometallic Three-Dimensional Metal-Organic Framework Bearing an Unprecedented One-Dimensional Branched-Chain Secondary Building Unit.

A heterometallic metal-organic framework (MOF) of [Cd6Ca4(BTB)6(HCOO)2(DEF)2(H2O)12]∙DEF∙xSol (1, H3BTB = benzene-1,3,5-tribenzoic acid; DEF = N,N'-diethylformamide; xSol. = undefined solvates within the pore) was prepared by solvothermal reaction of Cd(NO3)2·4H2O, CaO and H3BTB in a mixed solvent of DEF/H2O/HNO3. The compatibility of these two divalent cations from different blocks of the periodic table results in a solid-state structure consisting of an unusual combination of a discrete V-shaped heptanuclear cluster of [Cd2Ca]2Ca' and an infinite one-dimensional (1D) chain of [Cd2CaCa']n that are orthogonally linked via a corner-shared Ca2+ ion (denoted as Ca'), giving rise to an unprecedented branched-chain secondary building unit (SBU). These SBUs propagate via tridentate BTB to yield a three-dimensional (3D) structure featuring a corner-truncated P41 helix in MOF 1. This outcome highlights the unique topologies possible via the combination of carefully chosen s- and d-block metal ions with polydentate ligands.

Unconventional Pyridyl Ligand Inclusion within a Flexible Metal-Organic Framework Bearing an N,N'-Diethylformamide (DEF)-Solvated Cd5 Cluster Secondary Building Unit.

A cationic three-dimensional (3D) metal-organic framework (MOF) sustained by an N,N'-diethylformamide (DEF)-solvated zigzag-shaped Cd5 cluster secondary building unit (SBU), [Et2 NH2 ]2 [Cd5 (BTB)4 (DEF)2 ] ⋅ 4.75DEF (1 a, H3 BTB=benzene-1,3,5-tribenzoic acid) shows flexible framework behavior and undergoes solvate exchange with CHCl3 to yield [Et2 NH2 ]2 [Cd5 (BTB)4 (DEF)2 ] ⋅ xCHCl3 (1 b) accompanied by changes to pore sizes and shapes. Unexpectedly, the DEF solvates coordinated to the central Cd2+ could not be replaced by strongly donor pyridyl and dipyridyl ligands. Additionally, more electron-deficient pyridyls preferentially coordinated to the flanking Cd2+ of the Cd5 SBU, as exemplified by [Et2 NH2 ]2 [Cd5 (BTB)4 (DEF)2 (PyCHO)2 ] ⋅ xSol (2 a, PyCHO=4-pyridinealdehyde) and [Et2 NH2 ]2 [Cd5 (BTB)4 (DEF)2 (PyAc)2 ] ⋅ xSol (2 b, PyAc=4-acetylpyridine). Density functional theory (DFT) calculations were used to understand these counterintuitive observations.

Intramolecular Nitrene Insertion into Saturated C-H-Bond-Mediated C-N Bond Cleavage of a Coordinated NHC Ligand.

Ruthenium(II) complexes bearing a tridentate bis(N-heterocyclic carbene) ligand reacted with iminoiodanes (PhI=NR) resulting in the formation of isolable ruthenium(III)-amido intermediates, which underwent cleavage of a C-N bond of the tridentate ligand and formation of an N-substituted imine group. The RuIII -amido intermediates have been characterized by 1 H NMR, UV/Vis, ESI-MS, and X-ray crystallography. DFT calculations were performed to provide insight into the reaction mechanism.

Smoothing the single-crystal to single-crystal conversions of a two-dimensional metal-organic framework via the hetero-metal doping of the linear trimetallic secondary building unit.

The two-dimensional (2D) metal-organic framework (MOF) [Cd2.25Co0.75(BTB)2(DEF)4]·2(DEF)0.5 (1a, BTB = benzene-1,3,5-tribenzolate; DEF = N,N'-diethylformamide) featuring linear trimetallic cluster secondary building units (SBUs) and replaceable DEF solvates reacts smoothly with dipyridyl ligands DPS, DPDS, and BIPY (DPS = 4,4'-dipyridyl sulfide; DPDS = 4,4'-dipyridyl disulfide; BIPY = 4,4'-bipyridine), yielding three-dimensional (3D) non-interpenetrated [Cd2.25Co0.75(BTB)2(DPS)2]·xSol (2) and [Cd2.25Co0.75(BTB)2(DPDS)2]·xSol (3), and interpenetrated [Cd2.25Co0.75(BTB)2(BIPY)(H2O)2]·xSol (4). The smooth conversion of 1a to 3 contrasts the drastic single-crystal to single-crystal (SCSC) conversion observed for the homometallic [Cd3(BTB)2(DEF)4]·2(DEF)0.5 (1b), presumably due to the presence of the relatively Lewis acidic Co2+ that lessens the propensity for binding by soft dipyridyl donors. Activated samples of 2-4 showed no obvious absorption of N2 at 77 K, but reversible type I uptake of CO2 at 195 K.

Evaluating the component contribution to nonlinear optical performances using stable [Ni4O4] cuboidal clusters as models.

Five stable clusters sharing the cuboidal [Ni4O4] skeleton are subjected to third-order nonlinear optical (NLO) property measurements. Preliminary results suggest that the NLO property is largely defined by the cluster core skeleton and the directly coordinated atoms, with limited contribution from the heavy atoms peripherally attached to the aromatic ligands.

Co2 and Co3 Mixed Cluster Secondary Building Unit Approach toward a Three-Dimensional Metal-Organic Framework with Permanent Porosity.

Large and permanent porosity is the primary concern when designing metal-organic frameworks (MOFs) for specific applications, such as catalysis and drug delivery. In this article, we report a MOF Co11(BTB)6(NO3)4(DEF)2(H2O)14 (1, H3BTB = 1,3,5-tris(4-carboxyphenyl)benzene; DEF = N,N-diethylformamide) via a mixed cluster secondary building unit (SBU) approach. MOF 1 is sustained by a rare combination of a linear trinuclear Co3 and two types of dinuclear Co2 SBUs in a 1:2:2 ratio. These SBUs are bridged by BTB ligands to yield a three-dimensional (3D) non-interpenetrated MOF as a result of the less effective packing due to the geometrically contrasting SBUs. The guest-free framework of 1 has an estimated density of 0.469 g cm-3 and exhibits a potential solvent accessible void of 69.6% of the total cell volume. The activated sample of 1 exhibits an estimated Brunauer-Emmett-Teller (BET) surface area of 155 m² g-1 and is capable of CO2 uptake of 58.61 cm³ g-1 (2.63 mmol g-1, 11.6 wt % at standard temperature and pressure) in a reversible manner at 195 K, showcasing its permanent porosity.

Deciphering the Structural Relationships of Five Cd-Based Metal-Organic Frameworks.

The one-pot reaction of Cd(NO3)2·4H2O and 5-(6-(hydroxymethyl)pyridin-3-yl)isophthalic acid (H2L) in DMF/H2O (DMF = N,N-dimethylformamide) produced a two-dimensional (2D) metal-organic framework (MOF) of [Cd(L)(H2O)2] (A) bearing aqua-bridged Cd centers, accompanied by two three-dimensional (3D) MOFs [Cd(L)(DMF)0.5] (B) and [Cd(L)] (C). Removing the bridging aqua molecules of A by heating led to the formation of an additional 3D MOF of [Cd(L)] (D) in a single-crystal to single-crystal (SCSC) manner. The search for the preceding compound that could convert to A resulted in the isolation of a 2D MOF [Cd(L)(DMF)] (E) that readily converted to A in water, but with the loss of single crystallinity. Upon excitation at 350 nm, A, D, E, and the ligand H2L fluoresced at 460 nm, 468 nm, 475 nm, and 411 nm, respectively. The fluorescence of A could be used for the selective detection of Fe3+ in water down to 0.58 ppm. This quenching was not affected by the presence of other common metal ions.