JP6469516B2 - Carrier doping method and conductor - Google Patents

Description

  The present invention relates to a carrier doping method using a crown ether and a conductor.

  In recent years, attempts have been made to develop organic conductors and molecular conductors (molecular crystals exhibiting the same high conductivity as metals) by carrier doping (electron / hole injection).

  For example, a case of metallization by carrier doping by injecting neutral metal atoms into an organic crystal has been reported.

  More specifically, it is known that a superconducting phase is developed by doping potassium with picene or doping alkali metal such as rubidium or cesium with fullerene (for example, non-patent document). 1 and 2).

R. Mitsuhashi, et.al., Nature, 464, 76 (2010) V. Buntar and H. W. Weber, Supercond. Sci. Technol., 9, 599 (1996)

  However, in the method described in the above-mentioned non-patent document, since the impurity is mixed into the gap (gap) in the crystal to improve the electrical conductivity, the crystal structure changes dramatically, As a result, there has been a problem that carrier doping in a state where the structure is maintained cannot be achieved, or the electrical conductivity of the conductor (metal complex) after carrier doping is not sufficiently improved.

  Therefore, the present invention has been made in view of such points, and the carrier capable of improving the electrical conductivity of the conductor after carrier doping while maintaining the structure of the ion conductive crystal before carrier doping. It is an object to provide a doping method and a conductor.

  In order to achieve the above-described object, the carrier doping method of the present invention is a method for reducing the ion-conducting crystal formed by ion-bonding of a crown ether encapsulating lithium ions and a dithiolate metal complex into an oxidation-reduction other than lithium ions. The lithium ion in the ion conductive crystal is exchanged with the metal ion by being immersed in a solution in which the metal ion having the property is dissolved, and the ion conductive crystal is doped with an electron or a hole as a carrier.

  According to the present invention, it is possible to improve the electrical conductivity in an ion conductive crystal after carrier doping by an inexpensive and simple method.

It is a figure which shows the combined state of the ion conductive crystal which concerns on embodiment of this invention. It is a figure which shows the IR spectrum of the ion conductive crystal before the ion exchange in the Example of this invention, and the ion conductive crystal after ion exchange. It is a figure which shows the UV spectrum of the ion conductive crystal before the ion exchange in the Example of this invention, and the ion conductive crystal after ion exchange. It is a figure which shows the electrical resistivity of the ion conductive crystal before the ion exchange in the Example of this invention, and the ion conductive crystal after ion exchange. It is a figure which shows the Arrhenius plot of the ion conductive crystal before the ion exchange in the Example of this invention. It is a figure which shows the Arrhenius plot of the ion conductive crystal after the ion exchange in the Example of this invention. It is a figure which shows the part which performed the EPMA measurement in the ion conductive crystal after the ion exchange in the Example of this invention.

  In the carrier doping method (cation exchange method) of the present invention, an ion conductive crystal formed by ionic bonding of a crown ether clathrated with lithium ions and a dithiolate metal complex is obtained by using lithium ions other than lithium ions. Lithium ions in the ion conductive crystals are exchanged for metal ions by immersing them in a solution in which metal ions having oxidation / reduction properties other than (hereinafter simply referred to as “metal ions”) are dissolved. This is a method of doping (electrons or holes).

  Such a method makes it possible to insert another metal ion into the site where lithium ions originally existed (that is, to perform ion exchange). It becomes possible to dope carriers without generating the above.

  That is, by using the carrier doping method of the present invention, the carrier can be doped while maintaining the crystal structure of the ion conductive crystal before carrier doping, so that the crystal structure does not change and is inexpensive. In addition, the conductivity in the ion conductive crystal after carrier doping (that is, the conductor after carrier doping) can be improved by a simple method.

The ion conductive crystal of the present invention has a structure in which a crown ether (18-crown-6) clathrating lithium ions and a dithiolate nickel complex (Ni (dmit) ₂ ) are electrically attracted to each other.

More specifically, the ion conductive crystal used in the present invention includes a crown ether (Li ⁺ (18-crown-6)) that includes lithium ions, which are monovalent cations as a whole, and a monovalent cation. The dithiolate nickel complex (Ni (dmit) ₂ ), which is an anion, is electrically attracted and bound by Coulomb force (that is, by ionic bonding).

  FIG. 1 shows a structural diagram of an ion conductive crystal represented by the formula (1). As shown in FIG. 1, an ion conductive crystal 1 is composed of three crown ethers 3, two dithiolate nickel complexes 4, and four water molecules 5 with respect to two lithium ions 2, and has the following chemical formula. It is represented by

(In the formula, dmit represents 1,3-dithiol-2-thione-4,5-dithiolate.)
Then, as shown in FIG. 1, three crown ethers 3 are formed as one unit, and these are stacked one-dimensionally, whereby ion channels 9 are formed in the crystal, and are included in the crown ether 3. Lithium ions 2 can move in ion channels 9 made of crown ether 3. Therefore, the crystal represented by the above formula (2) has ionic conductivity.

Here, it is known that the dithiolate nickel complex (Ni (dmit) ₂ ) has a band structure and can take various valences. Among them, −1 valence shows properties as a magnetic material and is used as a useful building block in the field of molecular magnetic materials. On the other hand, it is known that a property as a conductor is exhibited between 0 valence and −1 valence, and between −1 valence and −2 valence, and some superconductors have been reported. Further, the dithiolate nickel complex (Ni (dmit) ₂ ) forms a dimer in the crystal represented by the above formula (2), and this dimer is arranged in a one-dimensional manner to form a spin ladder structure. Have.

  Next, the outline of the manufacturing method of the ion conductive crystal in this embodiment is shown in the following reaction scheme 1.

<Reaction Scheme 1>
Comprising a crown ether (Li ⁺ (18-crown-6)) clathrated with lithium ions, which are monovalent cations as a whole, and a dithiolate nickel complex, which is a monovalent anion, represented by the formula (2) In order to obtain an ion conductive crystal, first, a solution in which 18-crown-6 of the formula (3) and lithium perchlorate (LiClO ₄ ) are dissolved in acetonitrile is prepared.

Also, TBA · Ni (dmit) ₂ (bis (1,3-dithiol-2-thione-4,5-dithiolate) nickel (III) tetrabutylammonium) was synthesized, and this TBA · Ni (dmit) ₂ was synthesized. Dissolve in acetonitrile to prepare a solution containing the dithiolate nickel complex. TBA · Ni (dmit) ₂ can be synthesized by a known method (see, for example, Steinmecke, G .; Sieler, HJ; Krimes, R .; Hoyer, E. Phosphorus Sulfur 1979, 7, 49). it can.

  Next, an acetonitrile solution (hereinafter referred to as “solution A”) in which lithium perchlorate and crown ether (18-crown-6) are dissolved is poured into a sample tube, and an acetonitrile solution in which the dithiolate nickel complex is dissolved (hereinafter referred to as “solution A”). Solution B ”) is poured into the sample tube so that solution A and solution B do not mix rapidly.

Next, without covering the sample tube, the lithium ion shown in the formula (4) was included as shown in the above formula (1) by leaving it in the dark at room temperature for 3 to 4 days. Lithium-crown ether (Li ⁺ (18-crown-6)) and a dithiolate nickel complex are electrically attracted to obtain an ion conductive crystal represented by the formula (2).

  Further, the ion conductive crystal used in the present invention can be selected in accordance with other metal ions exchanged with lithium ions.

  More specifically, it is possible to use this metal ion when the binding constant of another metal ion to be exchanged with respect to the crown ether contained in the ion conductive crystal is larger than the binding constant of the lithium ion. (Note that the binding constant between crown ether and metal ion can be found in RM Izatt, JS Bradshaw, SA Nielsen, JD Lamb, and JJ Christensen, Chem. Rev., 85, 271-339 (1985), RM Izatt, K. Pawlak, and JS Bradshaw, Chem. Rev., 91, 1721-2085 (1991), RA Samant, VS Ijeri, and AK Srivastava, J. Chem. Eng. Data, 48, 203-207 (2003)).

For example, when the metal ion to be exchanged is potassium ion (Cu2 ⁺ ), the binding constant of potassium ion to crown ether (18-crown-6) is 4.17, which is lithium for (18-crown-6). Since the ion coupling constant is larger than 2.69, an ion conductive crystal having a crown ether (18-crown-6) can be used as an ion exchanger.

For example, when the metal ion to be exchanged is europium ion (Eu ³⁺ ), the binding constant of europium ion to crown ether (15-crown-5) is 5.6, which is (15-crown-5). Since the binding constant of lithium ion with respect to is larger than 4.26, an ion conductive crystal having crown ether (15-crown-5) can be used as an ion exchanger.

That is, an ion conductive crystal containing lithium ions and having lithium ion-crown ether (Li ⁺ (15-crown-5)) which is a monovalent cation as a whole is used.

  In this case, the production method of the ion conductive crystal is the same as that in the case of using the above-mentioned 18-crown-6, and the following 18-crown-6 is produced by substituting 15-crown-5. An ion conductive crystal represented by the formula (5) can be obtained.

  Here, since the binding constant of the metal ion to the crown ether depends on the size of the crown ether, by selecting the size of the crown ether having a large binding constant corresponding to the metal ion to be exchanged, It becomes possible to improve the conductivity of the metal complex.

  The metal ions to be exchanged are not particularly limited, and include, for example, silver ions, iron ions, cobalt ions, chromium ions, and lanthanoid metal ions in addition to the copper ions and europium ions described above. Can do.

  Next, a carrier doping method according to an embodiment of the present invention will be described.

  In the carrier doping method of the present invention, an ion conductive crystal formed by ionic bonding of a crown ether encapsulating lithium ions and a dithiolate metal complex is immersed in a solution in which metal ions are dissolved, thereby ionic conduction. In this method, lithium ions in the conductive crystal are exchanged with metal ions, and the valence of the metal ions changes in the crystal, thereby doping the ion conductive crystal with carriers (electrons or holes).

In the present invention, the energy (oxidation potential) when the valence of the metal ion changes is equal to or higher than the energy (reduction potential) of the valence of (Ni (dmit) ₂ ) ⁻ . In some cases, carriers are doped.

More specifically, the energy (reduction potential) of M ^{n +} → M ^{(n−1) +} after the exchange of Li ⁺ and metal ions (M ^{n +} ) of the (Ni (dmit) ₂ ) crystal is ( Ni (dmit) ₂ ) ⁻ → (Ni (dmit) ₂ ) Carriers are introduced into the (Ni (dmit) ₂ ) phase when the energy (oxidation potential) becomes equal to or more than ⁰ (in this case, Are doped with holes.

In the present invention, the energy (reduction potential) when the valence of the metal ion changes is about the same as or higher than the energy (oxidation potential) of changing the valence of (Ni (dmit) ₂ ) ⁻ . In some cases, carriers are doped.

More specifically, after Li ⁺ and metal ions (M ^{n +} ) in the (Ni (dmit) ₂ ) crystal are exchanged, the energy (oxidation potential) of M ^{n +} → M ^{(n + 1) +} becomes (Ni ( _dmit) 2) ^- → (if it becomes Ni _(dmit) ^{2) 2-to} become energy (reducing potential) and either the same degree more, (Ni _{(dmit) 2)} carriers into the phase (in this case , Electrons are doped).

  Here, from the viewpoint of surely performing ion exchange of metal ions, the concentration of metal ions in the solution is preferably 0.01 to 1M.

  Similarly, from the viewpoint of reliably performing ion exchange of metal ions, the temperature of the solution is preferably 20 to 40 ° C., and the reaction time (that is, the ion conductive crystal is immersed in a solution in which metal ions are dissolved). Time) is preferably 2 hours or more.

  In addition, you may change the said embodiment as follows.

In the above embodiment, a dithiolate nickel complex (Ni (dmit) ₂ ) is used as the dithiolate metal complex, but the dithiolate metal complex is not limited to this, and may be an anion for keeping the charge neutral. . For example, a configuration using a dithiolate palladium complex (Pd (dmit) ₂ ), a dithiolate platinum complex (Pt (dmit) ₂ ), or a dithiolate gold complex (Au (dmit) ₂ ) may be used.

  Hereinafter, the present invention will be described based on examples. In addition, this invention is not limited to these Examples, These Examples can be changed and changed based on the meaning of this invention, and they are excluded from the scope of the present invention. is not.

(Synthesis of ion-conductive crystals)
18-crown-6 (trade name 18-crown-6-Ether, manufactured by Tokyo Chemical Industry Co., Ltd.) of formula (3) and lithium perchlorate (anhydrous) (trade name, Lithium perchlorate, manufactured by Kanto Chemical Co., Inc.) , anhydrous) was dissolved in 5 ml of acetonitrile (manufactured by Nacalai Tesque) to obtain solution A.

Further, TBA · Ni (dmit) ₂ was synthesized by a known method, and then 7 mg of this TBA · Ni (dmit) ₂ was dissolved in 5 ml of acetonitrile (manufactured by Nacalai Tesque) to obtain a dithiolate nickel complex. A solution B containing was obtained.

  Next, after pouring 5 ml of solution A into the 10 ml sample tube, 5 ml of solution B is added to the sample tube so that solution A and solution B do not mix rapidly (so as not to disturb the interface of solution A). I poured it slowly.

  Next, the sample tube into which the solution A and the solution B were poured was not covered, and was allowed to stand in the dark at room temperature for 3 to 4 days. As a result, dark green plate-like crystals were precipitated at the bottom of the sample tube, and an ion conductive crystal represented by the formula (2) was obtained.

(Carrier doping)
Next, the obtained ion conductive crystal was immersed in a 1M aqueous solution of copper chloride dihydrate (manufactured by Wako Pure Chemical Industries, Ltd., liquid temperature: 30 ° C.) for 24 hours, and lithium in the ion conductive crystal was obtained. Ions were exchanged for divalent copper ions (Cu ²⁺ ).

  Similarly, the obtained ion conductive crystal was immersed in a 1M aqueous potassium chloride solution (manufactured by Nacalai Tesque Co., Ltd., liquid temperature: 30 ° C.) for 24 hours, and lithium ions in the ion conductive crystal were converted to potassium. Exchanged with ions.

(IR spectrum measurement)
Next, IR spectra of the ion conductive crystal before ion exchange and the ion conductive crystal after ion exchange were measured. The above results are shown in FIG.

  The IR spectrum was measured by using an infrared spectrometer (trade name: FT-IR 660 plus, manufactured by JASCO Corporation), grinding the KBr tablet (about 30 mg) and the sample to be measured about 20 times. A KBr disk was produced by pressing, and this was measured.

As shown in FIG. 2, only the spectrum of copper ions ^{(Cu 2+)} was replaced with ion conductive crystals, CT in the region from about 2000 cm ^-1 ~ about 6000 cm ^-1: considered (Charge Transfer charge transfer transitions) band A broad peak was observed.

(UV spectrum measurement)
Subsequently, the UV spectrum (ultraviolet absorption spectrum) of the ion conductive crystal before ion exchange and the ion conductive crystal after exchange with copper ions was measured. The above results are shown in FIG.

  The UV spectrum was measured using an ultraviolet spectrophotometer (trade name: U-3310 spectrophotometer manufactured by Hitachi, Ltd.), and each sample was diluted with KBr and pellets (thickness: 0.5 mm). This was done by molding.

As shown in FIG. 3, a broad peak that is considered to be a CT (Charge Transfer) band is observed in the region of about 600 to 700 nm only in the spectrum of an ion conductive crystal exchanged with copper ions (Cu ²⁺ ). It was done.

Moreover, since the color of the pellet changed from dark green (before ion exchange) to black (after ion exchange), it can be seen that the electronic state was changed by the exchange to divalent copper ions (Cu ²⁺ ).

That is, the spectrum shown in FIG. 2 and FIG. 3 and the color of the pellet have changed, so that the CT band is shifted from the UV region to the IR region by exchanging with divalent copper ions (Cu ²⁺ ). it is conceivable that.

(Electrical resistivity measurement)
As described above, it is considered that the CT band is shifted from the UV region to the IR region, and considering that the energy of the ultraviolet light is larger than the energy of the infrared light, the charge is exchanged by ion exchange. It is thought that the energy required for moving transition has decreased. Therefore, the electrical resistivity (specific resistance) of the sample before and after ion exchange was measured to evaluate the physical properties.

  More specifically, a two-terminal method using a resistivity meter (trade name: 6517A high resistance meter, manufactured by Keithley Instruments) by compressing a powder sample of an ion conductive crystal before ion exchange to form a pellet. The electrical resistivity was measured. For powder samples after replacement with copper ions, the powder samples are compressed to form pellets, and a resistivity meter (made by advantest, trade name: R6581T digital multimeter) and voltage / current generator (made by advantest, trade name) : The electric resistivity was measured by a four-terminal method using an R6161 source meter). Further, Sylbest (manufactured by Tokuri Chemical Laboratory, gold paste) was used as a probe for all measurements. The above results are shown in FIG.

  As shown in FIG. 4, at 300 K, the electrical resistivity of the sample before ion exchange is 281 MΩ · cm, whereas the electrical resistivity of the sample after exchange with copper ions is 396 Ω · cm, It was confirmed that the specific resistance decreased by 6 digits by the replacement.

  Further, the Arrhenius plot revealed that the activation energy of the sample before ion exchange was 0.473 eV and the activation energy of the sample after ion exchange was 0.115 eV.

  The “Arrhenius plot” is a plot in which the horizontal axis represents the reciprocal of the temperature T and the vertical axis represents the natural logarithm of the specific resistance ρ. The plot was fitted with a linear function, and the activation energy value was estimated. The fitting was performed in the range of 300 to 120K for the ion-conducting crystal before the exchange, and in the range of 300 to 120K for the sample subjected to the exchange to the copper ion. The activation energy calculated this time is obtained by converting the product of the slope and the Boltzmann constant into units of electron volts. FIG. 5 shows an Arrhenius plot of the sample before ion exchange, and FIG. 6 shows an Arrhenius plot of the sample after ion exchange with copper ions.

From the above, it can be seen that carrier doping was performed by exchanging lithium ions in the ion conductive crystal with divalent copper ions (Cu ²⁺ ), and the electrical conductivity was improved.

(EPMA measurement)
Next, EPMA (Electron Probe Micro Analyzer) measurement of the ion conductive crystal after ion exchange was performed. More specifically, the sample after ion exchange is divided, the cross section is irradiated with an electron beam, the spectrum of the characteristic X-rays generated is obtained, and the component of the sample (( That is, the atomic ratio of nickel, sulfur, and copper based on nickel was analyzed.

  In addition, EPMA measurement was performed with respect to each of the cross-sectional parts 1-4 of the sample shown in FIG. 7 using the EPMA measuring apparatus (The JEOL Co., Ltd. make, brand name: JXA-8200). Further, an acceleration voltage was set to 15 kV, an irradiation current amount was set to 10 nA, and an electron beam having a beam diameter of 10 μm was irradiated for 20 seconds. The results are shown in Table 1.

  As shown in Table 1, copper was detected in any of the cross-sectional portions 1 to 4. From this, it is understood that lithium ions are exchanged for copper ions by ion exchange.

  Examples of utilization of the present invention include a carrier doping method using a crown ether and a conductor.

DESCRIPTION OF SYMBOLS 1 Ion conductive crystal 2 Lithium ion 3 Crown ether 4 Dithiolate nickel complex 5 Water molecule 9 Ion channel

Claims (5)

By immersing the ion conductive crystal formed by ionic bonding of the crown ether encapsulating lithium ions and the dithiolate metal complex in a solution in which metal ions having redox properties other than the lithium ions are dissolved, The lithium ion in the ion conductive crystal is exchanged with the metal ion, and the ion conductive crystal is doped with electrons or holes as carriers ,
The crown ether is 15-crown-5, and the ion conductive crystal is represented by the following formula (1) .
(In the formula, dmit represents 1,3-dithiol-2-thione-4,5-dithiolate, and M represents a metal selected from Ni, Pd, Au, and Pt.) The carrier doping method according to claim 1 , wherein the M is Ni. Carrier doping method according to claim 1 or claim 2 concentration of the metal ions in the solution is characterized in that it is a 0.01～1M. The temperature of the said solution is 20-40 degreeC, The carrier doping method of any one of Claims 1-3 characterized by the above-mentioned. Carrier doping method according to any one of claims 1 to 4, wherein the time for the immersion is not less than 2 hours.