Capacitance Performance of Sub‑2 nm Graphene Nanochannels in Aqueous Electrolyte

Molecular dynamics simulations were used to explain the origin and properties of electrical double-layer capacitance in short graphene nanochannels with width below 2 nm. The results explain the previously reported experimental result on the nonmonotonic dependence of the capacitance with the channel width. The mechanism for the anomalous increase of the capacitance in sub-1 nm in pore diameter is attributed here to the width-dependent radial location of counterions in the nanochannels and the restricted number of co-ions. Decrease of the channel width lowers the number of co-ions and positions the counterions closer to the channel walls. For nanochannels with width ranging from 1 to 2 nm, co-ions are allowed to enter the nanochannel, and both types of ions assume alternating layered distributions leading to the decrease of the capacitance. Voltage is another control parameter which allows understanding capacitance in graphene nanochannels. As the voltage increases, due to limited space near the charged surface, more counterions need to be located in the center of the nanochannel, resulting in further capacitance decrease

Intramolecular C–H Bond Activation in Bridged Dicyclopentadienyl Dimethyl Dinuclear Complexes

Photolysis of the doubly bridged dicyclopentadienyl dimethyl dinuclear complexes [(η⁵-C₅H₂R)₂(SiMe₂)₂]­M₂(CO)₄Me₂ (M = Ru, R = H (<b>2a</b>), ^<i>t</i>Bu (<b>2b</b>); M = Fe, R = H (<b>2c</b>)) in benzene yields the corresponding methylene-bridged complexes [(η⁵-C₅H₂R)₂(SiMe₂)₂]­M₂(CO)₂(μ-CO)­(μ-CH₂) (<b>3a</b>–<b>c</b>) and the M–M-bonded complexes [(η⁵-C₅H₂R)₂(SiMe₂)₂]­M₂(CO)₄ (<b>1a</b>–<b>c</b>). Irradiation of the analogous diethyl complex [(η⁵-C₅H₂R)₂(SiMe₂)₂]­Ru₂(CO)₄Et₂ (<b>4</b>) affords only <b>1a</b>. Unlike the case for the doubly bridged complexes, photolysis of the singly bridged dicyclopentadienyl dimethyl diruthenium complexes [(η⁵-C₅H₄)₂(EMe₂)]­Ru₂(CO)₄Me₂ (E = C (<b>5a</b>); E = Si (<b>5b</b>)) in benzene yields the corresponding “twisted” ruthenium methyl complexes with a cyclopentadienyl–Ru σ bond (η⁵,η⁵:η¹-C₅H₄(EMe₂)­C₅H₃)­[Ru­(CO)₂]­[Ru­(CO)₂Me] (<b>6a</b>,<b>b</b>) and the similar phenyl complexes (η⁵,η⁵:η¹-C₅H₄(EMe₂)­C₅H₃)­[Ru­(CO)₂]­[Ru­(CO)₂Ph] (<b>7a</b>,<b>b</b>), from reaction with the benzene solvent. Plausible mechanisms for the formation of the different types of products are proposed involving intramolecular C–H bond activation. The molecular structures of <b>2a</b>,<b>c</b>, <b>3a</b>,<b>c</b>, <b>4</b>, <b>5a</b>, <b>6a</b>, and <b>7b</b>, determined by X-ray diffraction, are also presented

Effect of user mobility and channel fading on the outage performance of UAV communications

Many wireless networks operate in a mobile environment with randomly moving user terminals. This letter analytically characterizes the impact of ground user mobility, propagation environment and channel fading on the outage performance of unmanned aerial vehicle (UAV) communications. Closed-form expressions for the outage probability using the random waypoint model for ground user mobility, UAV channel models for different propagation environments and the Nakagami- {m} model for fading channels are derived. Furthermore, the outage analysis takes into account the effect of co-channel interference by both the stationary and mobile users. Numerical results are presented to demonstrate the interplay between the communication performance and the system parameters

Intramolecular C–H Bond Activation in Bridged Dicyclopentadienyl Dimethyl Dinuclear Complexes

Photolysis of the doubly bridged dicyclopentadienyl dimethyl dinuclear complexes [(η⁵-C₅H₂R)₂(SiMe₂)₂]­M₂(CO)₄Me₂ (M = Ru, R = H (<b>2a</b>), ^<i>t</i>Bu (<b>2b</b>); M = Fe, R = H (<b>2c</b>)) in benzene yields the corresponding methylene-bridged complexes [(η⁵-C₅H₂R)₂(SiMe₂)₂]­M₂(CO)₂(μ-CO)­(μ-CH₂) (<b>3a</b>–<b>c</b>) and the M–M-bonded complexes [(η⁵-C₅H₂R)₂(SiMe₂)₂]­M₂(CO)₄ (<b>1a</b>–<b>c</b>). Irradiation of the analogous diethyl complex [(η⁵-C₅H₂R)₂(SiMe₂)₂]­Ru₂(CO)₄Et₂ (<b>4</b>) affords only <b>1a</b>. Unlike the case for the doubly bridged complexes, photolysis of the singly bridged dicyclopentadienyl dimethyl diruthenium complexes [(η⁵-C₅H₄)₂(EMe₂)]­Ru₂(CO)₄Me₂ (E = C (<b>5a</b>); E = Si (<b>5b</b>)) in benzene yields the corresponding “twisted” ruthenium methyl complexes with a cyclopentadienyl–Ru σ bond (η⁵,η⁵:η¹-C₅H₄(EMe₂)­C₅H₃)­[Ru­(CO)₂]­[Ru­(CO)₂Me] (<b>6a</b>,<b>b</b>) and the similar phenyl complexes (η⁵,η⁵:η¹-C₅H₄(EMe₂)­C₅H₃)­[Ru­(CO)₂]­[Ru­(CO)₂Ph] (<b>7a</b>,<b>b</b>), from reaction with the benzene solvent. Plausible mechanisms for the formation of the different types of products are proposed involving intramolecular C–H bond activation. The molecular structures of <b>2a</b>,<b>c</b>, <b>3a</b>,<b>c</b>, <b>4</b>, <b>5a</b>, <b>6a</b>, and <b>7b</b>, determined by X-ray diffraction, are also presented

Reactions of SnMe₂-Bridged Bis(cyclopentadienes) with Iron Pentacarbonyl: Migration of the SnMe₂ Group

In reactions of the singly bridged bis­(cyclopentadiene) (SnMe₂)­(^<i>t</i>BuC₅H₄)₂ (<b>1</b>) or the doubly bridged bis­(cyclopentadienes) (SiMe₂)­(SnMe₂)­(RC₅H₃)₂ (R = H (<b>2</b>), R = ^<i>t</i>Bu (<b>3</b>)) with Fe­(CO)₅ in refluxing xylene, the bridging SnMe₂ group migrates from the ligand to the iron atoms to give compounds (<b>5</b>, <b>7</b>, <b>9a</b>,<b>b</b>) containing the Fe–Sn–Fe units, together with the corresponding destannylated products (<b>6</b>, <b>8</b>, <b>10a</b>,<b>b</b>); the bridging SiMe₂ group (in <b>2</b> and <b>3</b>) does not migrate. However, in the reaction of the doubly bridged ligand (GeMe₂)­(SnMe₂)­(C₅H₄)₂ (<b>4</b>) with Fe­(CO)₅, the SnMe₂ group undergoes a similar migration to produce the complex GeMe₂[(η⁵-C₅H₄)­Fe­(CO)₂]₂SnMe₂ (<b>12</b>), containing the Fe–Sn–Fe unit, both SnMe₂ and GeMe₂ groups migrate from the ligand to the iron atoms to yield the product [(GeMe₂)­(η⁵-C₅H₄)­Fe­(CO)₂]­[(SnMe₂)­(η⁵-C₅H₄)­Fe­(CO)₂] (<b>11</b>), containing one Fe–Ge bond and one Fe–Sn bond, or the SnMe₂ group is cleaved to afford the destannylation product GeMe₂[(η⁵-C₅H₄)­Fe­(CO)]₂(μ-CO)₂ (<b>13</b>). The stability of complexes <b>5</b>, <b>7</b>, and <b>12</b> containing the Fe–Sn–Fe unit toward heat and light was also studied. The molecular structures of <b>9a</b>,<b>b</b>, <b>11</b>, and <b>12</b> were determined by X-ray diffraction

Direction Dependence of Resistive-Pulse Amplitude in Conically Shaped Mesopores

Conically shaped pores such as glass pipets as well as asymmetric pores in polymers became an important analytics tool used for the detection of molecules, viruses, and particles. Electrokinetic or pressure driven passage of single particles through a single pore causes a transient change of the transmembrane current, called a resistive-pulse, whose amplitude is the measure of the particle volume. The shape of the pulse reflects the pore topography, and in a conical pore, resistive pulses have a shape of a tick point. Passage of particles in both directions was reported to produce pulses of the same amplitude and shapes that are mirror images of each other. In this manuscript we identify conditions at which the amplitude of resistive-pulses in a conical mesopore is direction dependent. Neutral particles entering the pore from the larger entrance of a conical pore, called the base, block the current to a larger extent than the particles traveling in the opposite direction. Negatively charged particles on the other hand size larger when being transported in the direction from tip to base. The findings are explained via voltage-regulated ionic concentrations in the pore such that for one voltage polarity a weak depletion zone is formed, which increases the current blockage caused by a particle. For the opposite polarity, an enhancement of ionic concentrations was predicted. The findings reported here are of crucial importance for the resistive-pulse technique, which relates the current blockage with the size of the passing object

Reactions of SnMe₂-Bridged Bis(cyclopentadienes) with Iron Pentacarbonyl: Migration of the SnMe₂ Group

In reactions of the singly bridged bis­(cyclopentadiene) (SnMe₂)­(^<i>t</i>BuC₅H₄)₂ (<b>1</b>) or the doubly bridged bis­(cyclopentadienes) (SiMe₂)­(SnMe₂)­(RC₅H₃)₂ (R = H (<b>2</b>), R = ^<i>t</i>Bu (<b>3</b>)) with Fe­(CO)₅ in refluxing xylene, the bridging SnMe₂ group migrates from the ligand to the iron atoms to give compounds (<b>5</b>, <b>7</b>, <b>9a</b>,<b>b</b>) containing the Fe–Sn–Fe units, together with the corresponding destannylated products (<b>6</b>, <b>8</b>, <b>10a</b>,<b>b</b>); the bridging SiMe₂ group (in <b>2</b> and <b>3</b>) does not migrate. However, in the reaction of the doubly bridged ligand (GeMe₂)­(SnMe₂)­(C₅H₄)₂ (<b>4</b>) with Fe­(CO)₅, the SnMe₂ group undergoes a similar migration to produce the complex GeMe₂[(η⁵-C₅H₄)­Fe­(CO)₂]₂SnMe₂ (<b>12</b>), containing the Fe–Sn–Fe unit, both SnMe₂ and GeMe₂ groups migrate from the ligand to the iron atoms to yield the product [(GeMe₂)­(η⁵-C₅H₄)­Fe­(CO)₂]­[(SnMe₂)­(η⁵-C₅H₄)­Fe­(CO)₂] (<b>11</b>), containing one Fe–Ge bond and one Fe–Sn bond, or the SnMe₂ group is cleaved to afford the destannylation product GeMe₂[(η⁵-C₅H₄)­Fe­(CO)]₂(μ-CO)₂ (<b>13</b>). The stability of complexes <b>5</b>, <b>7</b>, and <b>12</b> containing the Fe–Sn–Fe unit toward heat and light was also studied. The molecular structures of <b>9a</b>,<b>b</b>, <b>11</b>, and <b>12</b> were determined by X-ray diffraction

Reactions of Doubly SiMe₂-Bridged Bis(cyclopentadienyl) Complexes of Molybdenum and Iron Carbonyls: Competitive Ring-to-Metal Migrations of Hydrogen and SiMe₂

Reaction of the doubly bridged bis­(cyclopentadiene) (C₅H₄(SiMe₂))₂ (<b>1</b>) with Mo­(CO)₆ in refluxing xylene gave the corresponding dinuclear molybdenum carbonyl complex [(η⁵-C₅H₃)₂(SiMe₂)₂]­Mo₂(CO)₆ (<b>3</b>) and the desilylated product [(η⁵-C₅H₄)₂(SiMe₂)]­Mo₂(CO)₆ (<b>6</b>), together with the singly SiMe₂SiMe₂-bridged dinuclear molybdenum product [(η⁵-C₅H₄)₂(SiMe₂SiMe₂)]­Mo₂(CO)₆ (<b>5</b>) and the novel complex [(SiMe₂)­(η⁵-C₅H₄)­Mo­(CO)₃]₂ (<b>4</b>) containing two Mo–Si bonds. This diversity of products is caused by similar ring-to-metal migrating abilities of the hydrogen and SiMe₂ groups and their competitive migration during the reactions. Reaction of the dihydride <i>cis</i>-[(η⁵-C₅H₃)₂(SiMe₂)₂]­Mo₂(CO)₆(H)₂ (<b>7c</b>) in refluxing xylene also afforded the above products except <b>4</b>, which suggests that <b>7c</b> might be intermediate precursor to <b>3</b>, <b>5</b>, and <b>6</b>. Similar treatment of substituted doubly bridged bis­(cyclopentadiene) (C₅H₃^<i>t</i>Bu­(SiMe₂))₂ (<b>2</b>) with Mo­(CO)₆ provided the corresponding derivatives (<b>8</b>–<b>10</b>) of the above products and the product [(η⁵-C₅H₄^<i>t</i>Bu)­Mo­(CO)₃]₂ (<b>11</b>), in which both SiMe₂ groups are removed. Heating a mixture of <b>1</b> and Fe­(CO)₅ in xylene yielded the normal dinuclear iron complex [(η⁵-C₅H₃)₂(SiMe₂)₂]­Fe₂(CO)₂(μ-CO)₂ (<b>12</b>) and the desilylated product [(η⁵-C₅H₄)₂(SiMe₂)]­Fe₂(CO)₂(μ-CO)₂ (<b>14</b>), together with the novel complex (SiMe₂)­(η⁵-C₅H₃)­(η⁵:η¹-C₅H₃)­[(SiMe₂)­Fe­(CO)₂]­[Fe­(CO)₂)] (<b>13</b>) containing one Fe–Si bond. However, similar treatment of <b>2</b> with Fe­(CO)₅ provided only the corresponding dinuclear complex [(η⁵-C₅H₂^<i>t</i>Bu)₂(SiMe₂)₂]­Fe₂(CO)₄ (<b>15</b>), in which the Fe–Fe bond (2.8205(9) Å) is the longest among all dimeric Cp′₂Fe₂(CO)₄ analogues. A plausible mechanism for the formation of the different types of products is proposed. Molecular structures of <b>4</b>, <b>9c</b>, <b>13</b>, and <b>15</b> determined by X-ray diffraction are also presented

Reactions of Doubly SiMe₂-Bridged Bis(cyclopentadienyl) Complexes of Molybdenum and Iron Carbonyls: Competitive Ring-to-Metal Migrations of Hydrogen and SiMe₂

Reaction of the doubly bridged bis­(cyclopentadiene) (C₅H₄(SiMe₂))₂ (<b>1</b>) with Mo­(CO)₆ in refluxing xylene gave the corresponding dinuclear molybdenum carbonyl complex [(η⁵-C₅H₃)₂(SiMe₂)₂]­Mo₂(CO)₆ (<b>3</b>) and the desilylated product [(η⁵-C₅H₄)₂(SiMe₂)]­Mo₂(CO)₆ (<b>6</b>), together with the singly SiMe₂SiMe₂-bridged dinuclear molybdenum product [(η⁵-C₅H₄)₂(SiMe₂SiMe₂)]­Mo₂(CO)₆ (<b>5</b>) and the novel complex [(SiMe₂)­(η⁵-C₅H₄)­Mo­(CO)₃]₂ (<b>4</b>) containing two Mo–Si bonds. This diversity of products is caused by similar ring-to-metal migrating abilities of the hydrogen and SiMe₂ groups and their competitive migration during the reactions. Reaction of the dihydride <i>cis</i>-[(η⁵-C₅H₃)₂(SiMe₂)₂]­Mo₂(CO)₆(H)₂ (<b>7c</b>) in refluxing xylene also afforded the above products except <b>4</b>, which suggests that <b>7c</b> might be intermediate precursor to <b>3</b>, <b>5</b>, and <b>6</b>. Similar treatment of substituted doubly bridged bis­(cyclopentadiene) (C₅H₃^<i>t</i>Bu­(SiMe₂))₂ (<b>2</b>) with Mo­(CO)₆ provided the corresponding derivatives (<b>8</b>–<b>10</b>) of the above products and the product [(η⁵-C₅H₄^<i>t</i>Bu)­Mo­(CO)₃]₂ (<b>11</b>), in which both SiMe₂ groups are removed. Heating a mixture of <b>1</b> and Fe­(CO)₅ in xylene yielded the normal dinuclear iron complex [(η⁵-C₅H₃)₂(SiMe₂)₂]­Fe₂(CO)₂(μ-CO)₂ (<b>12</b>) and the desilylated product [(η⁵-C₅H₄)₂(SiMe₂)]­Fe₂(CO)₂(μ-CO)₂ (<b>14</b>), together with the novel complex (SiMe₂)­(η⁵-C₅H₃)­(η⁵:η¹-C₅H₃)­[(SiMe₂)­Fe­(CO)₂]­[Fe­(CO)₂)] (<b>13</b>) containing one Fe–Si bond. However, similar treatment of <b>2</b> with Fe­(CO)₅ provided only the corresponding dinuclear complex [(η⁵-C₅H₂^<i>t</i>Bu)₂(SiMe₂)₂]­Fe₂(CO)₄ (<b>15</b>), in which the Fe–Fe bond (2.8205(9) Å) is the longest among all dimeric Cp′₂Fe₂(CO)₄ analogues. A plausible mechanism for the formation of the different types of products is proposed. Molecular structures of <b>4</b>, <b>9c</b>, <b>13</b>, and <b>15</b> determined by X-ray diffraction are also presented

Reactions of Doubly SiMe₂-Bridged Bis(cyclopentadienyl) Complexes of Molybdenum and Iron Carbonyls: Competitive Ring-to-Metal Migrations of Hydrogen and SiMe₂

Reaction of the doubly bridged bis­(cyclopentadiene) (C₅H₄(SiMe₂))₂ (<b>1</b>) with Mo­(CO)₆ in refluxing xylene gave the corresponding dinuclear molybdenum carbonyl complex [(η⁵-C₅H₃)₂(SiMe₂)₂]­Mo₂(CO)₆ (<b>3</b>) and the desilylated product [(η⁵-C₅H₄)₂(SiMe₂)]­Mo₂(CO)₆ (<b>6</b>), together with the singly SiMe₂SiMe₂-bridged dinuclear molybdenum product [(η⁵-C₅H₄)₂(SiMe₂SiMe₂)]­Mo₂(CO)₆ (<b>5</b>) and the novel complex [(SiMe₂)­(η⁵-C₅H₄)­Mo­(CO)₃]₂ (<b>4</b>) containing two Mo–Si bonds. This diversity of products is caused by similar ring-to-metal migrating abilities of the hydrogen and SiMe₂ groups and their competitive migration during the reactions. Reaction of the dihydride <i>cis</i>-[(η⁵-C₅H₃)₂(SiMe₂)₂]­Mo₂(CO)₆(H)₂ (<b>7c</b>) in refluxing xylene also afforded the above products except <b>4</b>, which suggests that <b>7c</b> might be intermediate precursor to <b>3</b>, <b>5</b>, and <b>6</b>. Similar treatment of substituted doubly bridged bis­(cyclopentadiene) (C₅H₃^<i>t</i>Bu­(SiMe₂))₂ (<b>2</b>) with Mo­(CO)₆ provided the corresponding derivatives (<b>8</b>–<b>10</b>) of the above products and the product [(η⁵-C₅H₄^<i>t</i>Bu)­Mo­(CO)₃]₂ (<b>11</b>), in which both SiMe₂ groups are removed. Heating a mixture of <b>1</b> and Fe­(CO)₅ in xylene yielded the normal dinuclear iron complex [(η⁵-C₅H₃)₂(SiMe₂)₂]­Fe₂(CO)₂(μ-CO)₂ (<b>12</b>) and the desilylated product [(η⁵-C₅H₄)₂(SiMe₂)]­Fe₂(CO)₂(μ-CO)₂ (<b>14</b>), together with the novel complex (SiMe₂)­(η⁵-C₅H₃)­(η⁵:η¹-C₅H₃)­[(SiMe₂)­Fe­(CO)₂]­[Fe­(CO)₂)] (<b>13</b>) containing one Fe–Si bond. However, similar treatment of <b>2</b> with Fe­(CO)₅ provided only the corresponding dinuclear complex [(η⁵-C₅H₂^<i>t</i>Bu)₂(SiMe₂)₂]­Fe₂(CO)₄ (<b>15</b>), in which the Fe–Fe bond (2.8205(9) Å) is the longest among all dimeric Cp′₂Fe₂(CO)₄ analogues. A plausible mechanism for the formation of the different types of products is proposed. Molecular structures of <b>4</b>, <b>9c</b>, <b>13</b>, and <b>15</b> determined by X-ray diffraction are also presented