π‑Stacked Dimers of Fluorophenylacetylenes: Role of Dipole Moment

The homodimers of singly fluorine-substituted phenylacetylenes were investigated using electronic and vibrational spectroscopic methods in combination with density functional theory calculations. The IR spectra in the acetylenic C–H stretching region show a marginal red shift for the dimers relative to the monomers. Further, the marginal red shifts indicate that the acetylenic group in all the dimers is minimally perturbed relative to the corresponding monomer. The observed spectra were assigned to a set of π-stacked structures within an energy range of 1.5 kJ mol^–1, which differ in the relative orientation of the two monomers on the basis of M06-2X/aug-cc-pVTZ level calculation. The observed red shift in the acetylenic C–H stretching vibration of the dimers suggests that the antiparallel structures contribute predominantly based on a simple coupled dipole model. Energy decomposition analysis using symmetry-adapted perturbation theory indicates that dispersion plays a pivotal role in π–π stacking with appreciable contribution of electrostatics. The stabilization energies of fluorophenylacetylene dimers follow the same ordering as their dipole moments, which suggests that dipole moment enhances the ability to form π-stacked structures

Octanuclear Zinc Phosphates with Hitherto Unknown Cluster Architectures: Ancillary Ligand and Solvent Assisted Structural Transformations Thereof

Structural variations in zinc phosphate cluster chemistry have been achieved through a careful selection of phosphate ligand, ancillary ligand, and solvent medium. The use of 4-haloaryl phosphates (X-dippH₂) as phosphate source in conjunction with 2-hydroxypyridine (hpy) ancillary ligand in acetonitrile solvent resulted in the isolation of the first examples of octameric zinc phosphates [Zn₈(X-dipp)₈(hpy)₄­(CH₃CN)₂(H₂O)₂]·4H₂O (X = Cl <b>2</b>, Br <b>3</b>) and not the expected tetranuclear D4R cubane clusters. Use of 2,3-dihydroxypyridine (dhpy) as ancillary ligand, under otherwise similar reaction conditions with the same set of phosphate ligands and solvent, resulted in isolation of another type of octanuclear zinc phosphate clusters {[(Zn₈(X-dipp)₄(X-dippH)₄­(dhpyH)₄­(dhpyH₂)₂(H₂O)₂]·2solvent} (X = Cl, solvent = MeCN <b>4</b>; Br, solvent = H₂O <b>5</b>), as the only isolated products. X-ray crystal diffraction studies reveal that <b>2</b> and <b>3</b> are octanuclear clusters that are essentially formed by edge fusion of two D4R zinc phosphates. Although <b>4</b> and <b>5</b> are also octanuclear clusters, they exhibit a completely different cluster architecture and have been presumably formed by the ability of 2,3-dihydroxypyridine to bridge zinc centers in addition to the X-dipp ligands. Dissolution of both types of octanuclear clusters in DMSO followed by crystallization yields D4R cubanes [Zn­(X-dipp)­(DMSO)]₄ (X = Cl <b>6</b>, Br <b>7</b>), in which the ancillary ligands such as hpy, H₂O, and CH₃CN originally present on the zinc centers of <b>2</b>–<b>5</b> have been replaced by DMSO. DFT calculations carried out to understand the preference of Zn₈ versus Zn₄ clusters in different solvent media reveal that use of CH₃CN as solvent favors the formation of fused cubanes of the type <b>2</b> and <b>3</b>, whereas use of DMSO as the solvent medium promotes the formation of D4R structures of the type <b>6</b> and <b>7</b>. The calculations also reveal that the vacant exocluster coordination sites on the zinc centers at the bridgehead positions prefer coordination by water to hpy or CH₃CN. Interestingly, the initially inaccessible D4R cubanes [Zn­(X-dipp)­(hpy)]₄·2MeCN (X = Cl <b>8</b>, Br <b>9</b>) could be isolated as the sole products from the corresponding DMSO-decorated cubanes <b>6</b> and <b>7</b> by combining them with hpy in CH₃CN

Octanuclear Zinc Phosphates with Hitherto Unknown Cluster Architectures: Ancillary Ligand and Solvent Assisted Structural Transformations Thereof

Structural variations in zinc phosphate cluster chemistry have been achieved through a careful selection of phosphate ligand, ancillary ligand, and solvent medium. The use of 4-haloaryl phosphates (X-dippH₂) as phosphate source in conjunction with 2-hydroxypyridine (hpy) ancillary ligand in acetonitrile solvent resulted in the isolation of the first examples of octameric zinc phosphates [Zn₈(X-dipp)₈(hpy)₄­(CH₃CN)₂(H₂O)₂]·4H₂O (X = Cl <b>2</b>, Br <b>3</b>) and not the expected tetranuclear D4R cubane clusters. Use of 2,3-dihydroxypyridine (dhpy) as ancillary ligand, under otherwise similar reaction conditions with the same set of phosphate ligands and solvent, resulted in isolation of another type of octanuclear zinc phosphate clusters {[(Zn₈(X-dipp)₄(X-dippH)₄­(dhpyH)₄­(dhpyH₂)₂(H₂O)₂]·2solvent} (X = Cl, solvent = MeCN <b>4</b>; Br, solvent = H₂O <b>5</b>), as the only isolated products. X-ray crystal diffraction studies reveal that <b>2</b> and <b>3</b> are octanuclear clusters that are essentially formed by edge fusion of two D4R zinc phosphates. Although <b>4</b> and <b>5</b> are also octanuclear clusters, they exhibit a completely different cluster architecture and have been presumably formed by the ability of 2,3-dihydroxypyridine to bridge zinc centers in addition to the X-dipp ligands. Dissolution of both types of octanuclear clusters in DMSO followed by crystallization yields D4R cubanes [Zn­(X-dipp)­(DMSO)]₄ (X = Cl <b>6</b>, Br <b>7</b>), in which the ancillary ligands such as hpy, H₂O, and CH₃CN originally present on the zinc centers of <b>2</b>–<b>5</b> have been replaced by DMSO. DFT calculations carried out to understand the preference of Zn₈ versus Zn₄ clusters in different solvent media reveal that use of CH₃CN as solvent favors the formation of fused cubanes of the type <b>2</b> and <b>3</b>, whereas use of DMSO as the solvent medium promotes the formation of D4R structures of the type <b>6</b> and <b>7</b>. The calculations also reveal that the vacant exocluster coordination sites on the zinc centers at the bridgehead positions prefer coordination by water to hpy or CH₃CN. Interestingly, the initially inaccessible D4R cubanes [Zn­(X-dipp)­(hpy)]₄·2MeCN (X = Cl <b>8</b>, Br <b>9</b>) could be isolated as the sole products from the corresponding DMSO-decorated cubanes <b>6</b> and <b>7</b> by combining them with hpy in CH₃CN

Elusive Double-Eight-Ring Zeolitic Secondary Building Unit

The double-eight-ring (D8R), an elusive secondary building unit of zeolites, has been stabilized for the first time, both in solution and solid-state. The present study further establishes that any of the three double-ring building blocks of zeolites, viz. D4R, D6R and D8R ([ArPO₃Zn­(L)]_<i>n</i> (<i>n</i> = 4, 6 or 8)), can be preferentially isolated (over the other two) through a careful choice of metal source, aryl phosphate and ancillary ligand, apart from maintaining a meticulous control on the reaction conditions

Elusive Double-Eight-Ring Zeolitic Secondary Building Unit

The double-eight-ring (D8R), an elusive secondary building unit of zeolites, has been stabilized for the first time, both in solution and solid-state. The present study further establishes that any of the three double-ring building blocks of zeolites, viz. D4R, D6R and D8R ([ArPO₃Zn­(L)]_<i>n</i> (<i>n</i> = 4, 6 or 8)), can be preferentially isolated (over the other two) through a careful choice of metal source, aryl phosphate and ancillary ligand, apart from maintaining a meticulous control on the reaction conditions