Indium Centers Research Articles

Structural studies and physicochemical properties of indium(III) complexes with 2-formyl-8-hydroxyquinoline-derived hydrazones

The reaction of InCl3 with 2-formyl-8-hydroxyquinoline-4-nitroimidazole hydrazone (H2L1) in ethanol gave [In(H2L1)(HL1)Cl2], complex (1), as the product. Experimental data and theoretical DFT calculations suggested that complex (1) presents coordination number (CN) 8, with one neutral and one anionic ligand coordinated to the metal center through the O-Npy-N tridentate chelating system together with two chloride ions. The reaction with 2-formyl-8-hydroxyquinoline-4-nitrobenzene hydrazone (H2L2) in methanol gave [In(HL2)Cl2(CH3OH)], complex (2), as the product while [In(HL2)Cl2]·CH3CH2OH, complex (3), was formed as the product using ethanol as solvent. Experimental data indicated that in complexes [In(HL2)Cl2(CH3OH)] (2) and [In(HL2)Cl2]·CH3CH2OH (3) one anionic ligand is attached to the indium(III) center through the O-Npy-N-O tetradentate chelating system along with two chlorides. The crystal structure of the complex [In(HL2)Cl2(CH3OH)] (2) revealed that the indium(III) center presents CN 7. Calculated bond lengths in complex (2) were in accordance with the experimental values. The experimental and calculated electronic spectra of complexes (1) and (2) presented the same pattern and allowed the attribution of the absorption peaks to π - π* transitions.

Indium(III) complexes with lapachol: cytotoxic effects against human breast tumor cells and interactions with DNA.

Lapachol (2-hydroxy-3-(3-methylbut-2-en-1-yl)naphthalene-1,4-dione) is a 1,4-naphthoquinone-derived natural product that presents numerous bioactivities and was shown to have cytotoxic effects against several human tumor cells. Indium(III) complexes with a variety of ligands also exhibit antineoplastic activity. Indium(III) complexes [In(lap)Cl2].4H2O (1), [In(lap)2Cl(Et3N)] (2), [In(lap)3]·2H2O (3) [In(lap)(bipy)Cl2] bipy = 2,2'-bipyridine (4) and [In(lap)(phen)Cl2] phen = 1,10-phenanthroline (5) were obtained with 2-hydroxy-3-(3-methylbut-2-en-1-yl)naphthalene-1,4-dione (lapachol). Crystal structure determinations for (4) and (5) revealed that the indium(III) center is coordinated to two O atoms from lapachol, two N atoms from 1,10-phenanthroline or 2,2'-bipyridine, and two chloride anions, in a distorted octahedral geometry. Although both complexes (4) and (5) interacted with CT-DNA in vitro by an intercalative mode, only 5 exhibited cytotoxicity against MCF-7 and MDA-MB breast tumor cells. 1,10-phenanthroline and complex (5) presented cytotoxic effects against MCF-7 and MDA-MB cells, with complex (5) being threefold more active than 1,10-phenanthroline on MCF-7 cells. In addition, complex (5) significantly reduced the formation of MDA-MB-231 colonies in a clonogenicity assay. The foregoing results suggest that further studies on the cytotoxic effects and cellular targets of complex (5) are of utmost relevance.

Enhanced Electron Confinement of p-Block Indium Site in Extended Macrocyclic Conjugation Boosting Oxygen Reduction to Hydrogen Peroxide.

The electrocatalytic oxygen reduction reaction via a two-electron pathway (2e- ORR) is a promising route for hydrogen peroxide (H2O2) production. However, the strong electron interaction between the metal site and oxygen-containing intermediates usually generates 4-electron ORR, limiting H2O2 selectivity. Here, combining theoretical and experimental studies, we propose to enhance the electron confinement of the indium (In) center in an extended macrocyclic conjugation system toward high-efficiency H2O2 production. The extended macrocyclic conjugation in indium polyphthalocyanine (InPPc) evokes the attenuated transfer electron ability of the In center and weakens the interaction between the s orbital of In and the p obital of OOH*, favoring protonation of OOH* to H2O2. Experimentally, the prepared InPPc catalyst exhibits a noticeable H2O2 selectivity above 90% in 0.1-0.6 V vs RHE, outperforming the counterpart InPc. Importantly, the InPPc displays a high average H2O2 production rate of 23.77 mg/cm2/h in a flow cell. This study proposes a novel strategy to engineer molecular catalysts and provides new insights into the ORR mechanism.

Group 13 metal catalysts for hydrogen activation and hydrogenation

Catalysts with aromatization/dearomatization metal–ligand cooperation paradigm are of increasing interest in the field of hydrogen activation and hydrogenation, with PNP (2,6-bis[(phosphino-methyl]pyridine) as a representative class of ligand. It is highly desired to design PNP catalysts using main group metals to replace transition metals. Herein, a theoretical study of the properties of Group 13 metal (Al, Ga, In) PNP catalysts for hydrogen activation and hydrogenation was performed to comprehensively compare and analyze their catalytic mechanism and reactivity. In sharp contrast to traditional transition metal PNP catalysts that operate an aromatization/dearomatization metal–ligand cooperation, the Group 13 metal PNP catalysts adopt a tetrahedral geometry and prefer a metal-alkoxide promoted cooperation for the hydrogen activation and hydrogenation. The hard and soft acids and bases matching between the metal centers and the alkoxide is found to play a key role in the catalytic properties. PNP-In is found to be the most promising catalyst for hydrogen activation and hydrogenation, which has a proper reaction barrier (26.7 kcal·mol−1) during hydrogen activation because the In center could serve as a relatively softer acceptor for the hydride. The alkoxide bound on the softer Indium center has stronger basicity to deprotonate the PNP ligand or to obtain a proton from the H2 molecule. However, the harder Ga or Al center interacts more strongly with the alkoxide group, hampering the metal-alkoxide promoted protonation during hydrogenation. The bonding analysis and orbital energy analysis indicated that [(PNPtBu)InH(Me)]+ hydride also has a proper activity for the hydrogenation process. In contrast, although [(PNPtBu)AlH(Me)]+ has a much higher activity for hydride transfer, the Al-catalyzed hydrogenation is limited by the benzyloxide bound on the harder Al center, which is less active to assist the H − H bond cleavage or deprotonate the PNPtBu ligand. The Ga catalyst performs in between the best In catalyst and the least active Al catalyst. This understanding of the mechanism and reactivity of Group 13 metal catalysts should be helpful for the development of main group metal catalysts for hydrogen activation and hydrogenation.

Cooperative Initiation in a Dinuclear Indium Complex for CO2 Epoxide Copolymerization

Dinuclear indium complexes have been synthesized and characterized. These include neutral and cationic indium complexes supported by a Schiff base ligand bearing a binaphthol linker. The new compounds were investigated for alternating copolymerization of CO2 and cyclohexene oxide. In particular, the neutral indium chloride complex (±)-[(ONapNiN)InCl2]2 (4) showed high conversion of cyclohexene oxide and selectivity for poly(cyclohexene carbonate) formation without cocatalysts at 80 °C under various CO2 pressures (2-30 bar). Importantly, the reactivity of the dinuclear indium chloride complex 4 is drastically different from that of the mononuclear indium chloride complex (±)-(NNiOtBu)InCl2 (5), suggesting a cooperative initiation mechanism involving the two indium centers in 4.

Structural and spectral studies on indium(III) complexes with 2,6-diacetylpyridine bis(benzoylhydrazones)

Complexes [In(L1)Cl(H2O)] (1), [In(L2)Cl(H2O)] (2) and [In(L3)Cl(H2O)] (3) were obtained with 2,6-diacetylpyridine bis(benzoylhydrazone) (H2L1) and its 2,6-diacetylpyridine bis(para-chlorobenzoylhydrazone) (H2L2) and 2,6-diacetylpyridine bis(para-methylbenzoylhydrazone) (H2L3) derivatives. The crystal structures of complexes (1) and (2) were determined, revealing a pentagonal bipyramidal arrangement around the indium(III) center. The spectral properties of complexes (1–3) were investigated. The complexes show fluorescence in DMSO solution resulting from increased conjugation and rigidity of the ligand, and a significant fluorescence brightness due to the strong light absorption in the near UV region. From the fluorescence spectra of 1–3 quantum yields in the 0.5 – 0.7 % range were determined using quinine hemisulfate monohydrate in H2SO4 0.5 M (ΦF = 0.546) as standard.

Effect of bridging units on the photophysical properties of 4‐NEt2‐appended salen−indium complexes

AbstractA series of 4‐NEt2‐appended salen−indium complexes bridged by different diimine units (ethylene [Et, 1], phenylene [Ph, 2], and benzonitrile [PhCN, 3]) with different electronic effects were prepared in high yields by a one‐pot synthetic procedure. Among them, the solid‐state structure of 1 was identified by X‐ray crystallography, featuring a square‐pyramidal structure around the indium center. Ultraviolet–visible (UV/Vis) absorption and emission spectra of 1–3 showed typical ππ* electronic transitions centered on the salen ligands, which underwent gradual redshifts as the electron‐withdrawing ability of the bridging units increased. Such bathochromic shifts resulted from lowering the energy levels of the lowest unoccupied molecular orbital (LUMO). In addition, the full width at half maxima for the emissions of 1–4 gradually decreased with increasing electron‐accepting property of the bridging units. The observed photophysical properties were further supported by theoretical calculations.

Hydroxyl group interactions in metal dithiocarbamate complexes containing 2-hydroxyethyl substituents. Crystal structure determination, theoretical and Hirshfeld surface study of tris(2-hydroxyethyl(ethyl)amino-dithiocarbamato)indium(III). Survey of hydroxyl group interactions in metal tris(dithiocarbamato) complexes containing 2-hydroxyethyl substituents

X-ray crystal structure, theoretical and Hirshfeld surface study of tris(2-hydroxyethyl(ethyl)aminodi-thiocarbamato)indium(III) is reported. The arrangement of the sulfur atoms around the indium centre forms a trigonal prism with bond lengths and angles in close agreement with those reported for indium-dithiocarbarmate [In-dtc] complexes. There are two significant features of the structure: (i) the hydroxyl groups link to form quasi-chair shaped regular hexameric hydrogen bonded arrays, [···HO]6, R66(12), and (ii) C—-H···π interactions, involving [In-S-C-S] rings. While a few examples of cyclic hexameric hydrogen bonded arrays have been reported for dithiocarbamate complexes containing CH2CH2OH groups, this is the first report of a chair shaped arrangement, involving all the hydroxyl units.A survey has been carried out on the hydrogen bond arrangements made by the hydroxyl groups in reported dtc complexes of the type, [M{S2CNR(CH2CH2OH)}3], where M is a transition or main-group metal and R is an alkyl group or CH2CH2OH. Both long chain and ring arrangements of the hydroxyl groups are found, occupying spaces made available by the complexed-metal units. As compound 1 and related compounds are alcohols, albeit complex tris(primary alcohols), comparisons of the findings for these complexes are made with the structural findings for organic alcohols.

Comparison of Imine- and Phosphinimine-Supported Indium Complexes: Tuning the Reactivity for the Sequential and Simultaneous Copolymerization of Lactide and ε-Caprolactone

Imine- and phosphinimine-supported indium complexes were used as catalysts in the polymerization of racemic lactide and ε-caprolactone as well as their copolymerization by the sequential and simultaneous addition of monomers. Tuning the electronics and sterics of the indium centers by either (i) changing the nature of the nitrogen donors and (ii) coordinating a hemilabile side group had a significant effect on the reactivity of the complexes, their stability, and their control in the synthesis of block copolymers. Specifically, the imine-supported complex (5) showed the highest activity in the homo- and copolymerization of the cyclic esters, in contrast to the phosphinimine-supported complex (7), which was significantly slower and less stable. The presence of morpholine and thiomorpholine hemilabile side groups either reduced the activity or prevented the formation of alkoxide complexes.

Efficient Cycloaddition of CO2 and Aziridines Activated by a Quadruple-Interpenetrated Indium-Organic Framework as a Recyclable Catalyst.

On the basis of the global warming effect, it is of great significance to convert CO2 into the high value-added products oxazolidinones, but investigations on main-group-based metal-organic frameworks (MOFs) as heterogeneous catalysts still have not been reported so far. In this work, a quadruple-interpenetrated porous indium-based MOF, {[NH2(CH3)2][In(CPT)2]·3CH3CN·3DMA}n (1), is constructed from the organic ligand 3,5-bis(4'-carboxyphenyl)-1,2,4-triazole through solvothermal reactions, and N2 adsorption proves that the framework has a high Brunauer-Emmett-Teller surface areas with 2024 m2/g. The catalytic research on CO2 conversion reveals that compound 1 has high reactivity for the cycloaddition of CO2 with aziridines, and the product 3-ethyl-5-phenyloxazolidin-2-one can be obtained with a yield of 99% under mild conditions. In addition, 1 exhibits excellent activity for different kinds of substrates and can be reused at least five cycles without any significant deactivation, suggesting that 1 is a potential candidate for the chemical conversion of CO2 and aziridines. Mechanistic explorations indicate that the high efficiency of 1 is attributed to the indium center in the framework as a Lewis acid site, and the large porosity can enrich substrates. Importantly, 1 behaved as the first main-group MOF-based catalyst in the reported coupling reaction of CO2 with aziridines.

Synthesis and structural characterization of methylindium imino/aminophenolates: Comparison to aluminum analogues and reactivity toward the coupling reactions of carbon dioxide with epoxides

We have synthesized methylindium complexes containing a variety of amino- and iminophenolate ligands for structural comparison to their aluminum analogues. The reaction of Me3In with the corresponding amino-/iminophenols resulted in the formation of MeIn(Et2NCH2CH2-abp) (1), MeIn(PyCH2-abp) (2), [MeIn(iPr-abp)]2 (3), MeIn(Ph-salen) (4), MeIn(Etsalan) (5), MeIn(Cy-ip) (6) and MeIn(Mes-ip) (7) [H2(Et2NCH2CH2-abp) = Et2NCH2CH2N(2-OH-3,5-C6H2tBu2)2, H2(PyCH2-abp) = (2-C5H4N)CH2N(2-OH-3,5- C6H2tBu2)2, H2(iPr-abp) = (CH3)2CHN(2-OH-3,5-C6H2tBu2)2, H2(Ph-salen) = 1,2-(NCH-2-OH-3,5-C6H2tBu2)2C6H4, H2(Et-salan) = 1,2-(NMeCH2-2-OH-3,5- C6H2tBu2)2C2H4, H(Cy-ip) = (2-OH-3,5-tBu2-C6H2)CHN(C6H11), and H(Mes-ip) = (2-OH-3,5-tBu2-C6H2CHN(2,4,6-Me3C6H2)]. X-ray crystallography studies show monomeric structures and five-coordinate indium centres for 1 and 2, a dimeric structure via intermolecular In⋯O interactions and fivecoordinate indium centres for 3, and monomeric structures and fourcoordinate indium centres for 6 and 7. DFT calculations were used to rationalize the observed dimeric structure of 3 and monomeric structures of 6 and 7, and gauge the effect of ligand steric bulk and atomic radius in indium versus aluminum on dimerization. Compounds 2 and 5 are active catalysts for coupling reactions of carbon dioxide and propylene oxide to yield propylene carbonate and carbon dioxide with cyclohexene oxide to yield polycyclohexene carbonate. This work provides insight into controlling intermolecular bonding and hence reactivity in indium and aluminum amino-/iminophenolate complexes, and represents one of the first examples of indium complexes as catalysts for the formation of cyclic- or polycarbonates from carbon dioxide and epoxides.

Internal Chelation within Functionalized Organoindium Reagents: Prospects for Regio- and Stereocontrol in the Allylation, Propargylation and Allenylation of Carbonyl Compounds

The low basicity, selective nucleophilicity, and mildness of organoindium compounds allow for the incorporation of many important yet sensitive functional groups into their structure, including examples capable of intramolecularly chelating the indium center within these reagents. The specific nature of such chelated organoindiums causes the reactions involving them to proceed in a unique manner, often with regio- and stereoselectivity inaccessible with simple organometallic reagents. This review covers the rare examples of regio- and stereoselective allylation, propargylation, and allenylation of carbonyl compounds with chelated organoindiums, including brief descriptions of the applications of the resulting adducts in the asymmetric synthesis of natural products and synthetic targets of biological and medicinal interest.1 Introduction2 Internal Chelation Control in the Allylation Processes2.1 Allylindiums with a Chelating Center at the γ-Position2.2 Allylindiums with a chelating Center at the δ-Position2.3 Allylindiums with a Chelating Center at ε- and ζ-Positions2.4 Allylindiums with a Chelating Center at γ′- and δ′-Positions3 Internal Chelation Control in Propargylation and Allenylation Processes­3.1 Additions of Chelated Allenylindiums3.2 Additions of Chelated Propargylindiums4 Conclusion

Indium complexes with aminothiolate ligands as single precursors for indium chalcogenides

Indium complexes with aminothiolate ligands, In(dmampS)2Cl (1) and In(dmampS)3 (2), were synthesized by the metathesis reaction of InCl3 with 2 equiv. and 3 equiv. of Li(dmampS), respectively. The reaction of 1 with 1 equiv. of KSeCN resulted in the formation of In(dmampS)2(NCSe) (3). The three complexes have been characterized by IR, NMR, Mass spectroscopy, and microanalysis. Single-crystal X-ray diffraction studies revealed that complexes 1 and 3 have distorted trigonal bipyramidal geometry at the indium center. Thermogravimetric analyses indicated that the residual materials of the complexes 1, 2, and 3 could be presumably In2S3, In2S3, and In2Se2S, respectively. Thermal decomposition of 1–3 formed In2S3 (for 1 and 2) and In2Se2S (for 3). This was confirmed using EDS and ICP-AES.

Intriguing Indium-salen Complexes as Multicolor Luminophores.

The series of novel salen-based indium complexes (3-tBu-5-R-salen)In-Me (3-tBu-5-R-salen = N,N'-bis(2-oxy-3-tert-butyl-5-R-salicylidene)-1,2-diaminoethane, R = H (1), tBu (2), Br (3), Ph (4), OMe (5), NMe2 (6)) and [(3-tBu-5-NMe3-salen)In-Me](OTf)2 (7; OTf = CF3SO3-) have been synthesized and fully characterized by NMR spectroscopy and elemental analysis. All indium complexes 1-7 are highly stable in air and even aqueous solutions. The solid-state structures for 3-5, which were confirmed by single-crystal X-ray analysis, exhibit square-pyramidal geometries around the indium center. Both the UV/vis absorption and PL spectra of 1-7 exhibit significant intramolecular charge transfer (ICT) transitions based on the salen moieties with systematically bathochromic shifts, which depend on the introduction of various kinds of substituents. Consequently, the emission spectra of these complexes cover almost the entire visible region (λem = 455-622 nm).

Organoindium-modified monodisperse ellipsoid-/platelet-like periodic mesoporous silicas.

In this study, an indium(iii) silylamide complex was respectively grafted onto monodisperse ellipsoid-like (E) and platelet-like (P) large-pore hexagonal periodic mesoporous silicas (PMSs) SBA-15 to afford hybrid materials In[N(SiMe3)2]3@SBA-15E and In[N(SiMe3)2]3@SBA-15P with well-defined surface species ([triple bond, length as m-dash]SiO)2In[N(SiMe3)2], [triple bond, length as m-dash]SiOIn[N(SiMe3)2]2, and [triple bond, length as m-dash]SiOSiMe3. Surface ligand exchange between silylamido and alkoxyl group led to the conversion of surface species ([triple bond, length as m-dash]SiO)2In[N(SiMe3)2] and [triple bond, length as m-dash]SiOIn[N(SiMe3)2]2 into ([triple bond, length as m-dash]SiO)2In(OR) and [triple bond, length as m-dash]SiOIn(OR)2 (R = Me, Et, iPr) with donor ligands thf or NH3, respectively, revealing that silylamido coordinated to the indium centre could be completely exchanged with alkoxyl groups (-OMe, OEt or OiPr). Solid-state 1H, 13C and 29Si nuclear magnetic resonance spectra and elemental analyses confirmed that surface species [triple bond, length as m-dash]SiOIn[N(SiMe3)2]2 are dominant in comparison with bipodal ([triple bond, length as m-dash]SiO)2In[N(SiMe3)2] and [triple bond, length as m-dash]SiOSiMe3. The diffuse reflectance infrared Fourier-transform spectroscopy of In-modified hybrid materials directly evidenced the alteration of surface species before and after grafting of In[N(SiMe3)2]3 and surface ligand exchange. In addition, the change of pore parameters (pore diameter, specific surface area and pore volume) monitored by nitrogen physisorption also indirectly corroborated the immobilization of the indium complex and the occurrence of ligand exchanges between -[N(SiMe3)2]2 and -OR (R = Me, Et, iPr) on the surface of SBA-15. Note that the calcination of In-modified hybrid materials at 540 °C led to the formation of crystalline In2O3 nanoparticles with different sizes which were respectively located in the internal pore and on the external surface of SBA-15 due to the pore confinement effect, migration effect and shape effect of the parent support, but the long-range ordered mesopore arrays were still preserved and the crystalline structures of In2O3 were verified by powder X-ray diffraction and transmission electron microscopy.

Design, computational screening and synthesis of novel non-peripherally tetra hexylthio-substituted phthalocyanines as bulk heterojunction solar cell materials

New bulk heterojunction organic solar cell materials of phthalocyanines (Pcs) were designed, screened computationally and synthesized for the first time in a study with the aim of finding more efficient products. The electronic absorption spectrum and the molecular orbital properties of the novel non-peripherally tetrasubstituted Pcs were investigated by DFT/TDDFT calculations. The screened compounds were found to be promising for providing good performance on BHJ solar cells with their small band gaps, red-shifted absorption bands in near infrared region, deep HOMO energy levels and high electron mobilities. Furthermore, the model of Scharber et al. (2006) was used for open-circuit voltage (Voc) prediction for the first time for Pcs as the donor moiety and calculated eVoc values up to 0.56 was found with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as the acceptor moiety. All studied Pcs except one were found to provide energetic driving force for Pc-PCBM cells computationally. Hence, the new precursor 3-hexylthio phthalonitrile (3) was obtained by the nucleophilic aromatic substitution of 3-nitrophthalonitrile (1) and 1-hexanethiol (2) and then cyclotetramerized in the presence of metal salts and/or DBU to achieve a series of non-peripherally tetrahexylthio substituted phthalocyanines (4–12). The phthalocyanines with lead, indium and manganese metal centres have red-shifted Q bands as well as non Q-band absorptions in the 450–600nm region. The precursor and the targeted phthalocyanines were characterized comprehensively by 1H NMR, 13C NMR, FT-IR, UV–Vis, mass spectroscopies.

Strained metal bonding environments in methylindium dithiolates and their reactivity as initiators for the ring-opening polymerization of cyclic esters

We have synthesized indium complexes containing a variety of metal bonding environments through use of polyfunctional dithiolate ligands and examined their reactivity as initiators for the ring-opening polymerization of l-lactide, rac-lactide, ε-caprolactone and β-butyrolactone. The facile reaction of Me3In with the corresponding polyfunctional dithiols in toluene, thf or diethyl ether resulted in the formation of [MeIn(SOOS)]2 (3), MeIn(SNNS) (4), [MeIn(ONS2)]3 (5), MeIn(NNS2) (6), MeIn(NNS2Pr) (7) and MeIn(pyrS)2 (8). The solid-state structures of 3 and 5 each show the corresponding ligand to be tridentate with an uncoordinated ligand O atom. Dimeric (3) and trimeric (5) structures result from short intermolecular In … S interactions. All structures show five coordinate indium centres in distorted trigonal bipyramidal bonding environments, but with various arrangements of donor atoms (eq/ax): SSC/OS (3,5), SNC/NS (4), SSN/NC (6), SSC/NS (7) and SSC/NN (8). DFT studies of model MeIn(SMe)2(NH3)2 systems show the bonding environments in 4 and 6 to be highly strained, while the axial In–Me bond of 6 shows the longest bond distance and lowest vibrational frequency. Compound 5 provided the best control of the polymerization of l-lactide and rac-lactide in THF at 70 °C, and a small heterotactic enrichment was observed for the latter. Compounds 3 and 4 provided the best control of the polymerization of β-BL in toluene at 70 °C in toluene, and compound 3 provided the best control of the polymerization of ε-CL in toluene at 70 °C. In all cases, polymerization rates were low. This work demonstrates a systematic approach to exploring the modification and reactivity of main group metal bonding motifs, which has resulted in identification of two novel “strained” bonding environments for indium.

Photoluminescence of monovalent indium centres in phosphate glass

Valence control of polyvalent cations is important for functionalization of various kinds of materials. Indium oxides have been used in various applications, such as indium tin oxide in transparent electrical conduction films. However, although metastable In+ (5 s2 configuration) species exhibit photoluminescence (PL), they have attracted little attention. Valence control of In+ cations in these materials will be important for further functionalization. Here, we describe In+ species using PL and X-ray absorption fine structure (XAFS) analysis. Three absorption bands in the UV region are attributed to the In+ centre: two weak forbidden bands (1S0 → 3P1, 1S0 → 3P2) and a strong allowed band (1S0 → 1P1). The strongest PL excitation band cannot be attributed to the conventional allowed transition to the singlet excited state. Emission decay of the order of microseconds suggests that radiative relaxation occurs from the triplet excitation state. The XAFS analysis suggests that these In+ species have shorter In–O distances with lower coordination numbers than in In2O3. These results clearly demonstrate that In+ exists in a metastable amorphous network, which is the origin of the observed luminescent properties.

Non‐Innocent Ligand Effects on Low‐Oxidation‐State Indium Complexes

Attempts to coordinate neutral ligands to low oxidation state indium centers are often hindered by disproportionation pathways that produce elemental indium and higher oxidation state species. In contrast, we find that reactions of the salt, InOTf (OTf=trifluoromethanesulfonate), with α-diimine ligands yielded intensely colored compounds with no evidence of decomposition. X-ray structural analysis of InOTf⋅(Mes) DAB(Me) ((Mes) DAB(Me) =N,N-dimesityl-2,3-dimethyl-diazabutadiene; 1) reveals a discrete molecular compound with a pyramidal coordination environment at the indium center, consistent with the presence of a stereochemically active lone pair of electrons on indium and a neutral diazabutadiene chelate ligand. The use of the less-electron-rich (Mes) DAB(H) ligand ((Mes) DAB(H) =N,N-dimesityl-diazabutadiene) engenders dramatically different reactivity and produces a metallopolymer (InOTf⋅(Mes) DAB(H) )∞ (2) linked via CC and InIn bonds. The difference in reactivity is rationalized by cyclic voltammetry and DFT studies that suggest more facile electron transfer from In(I) to the (Mes) DAB(H) and bis(aryl)acenaphthenequinonediimine (BIAN) ligands. Solution EPR spectroscopy indicates the presence of non-interacting ligand-based radicals in solution, whereas solid-state EPR studies reflect the presence of a thermally accessible spin triplet consistent with reversible CC bond cleavage.

Molecular Indium(III) Phosphonates Possessing Ring and Cage Structures. Synthesis and Structural Characterization of [In2(t-BuPO3H)4(phen)2Cl2] and [In3(C5H9PO3)2(C5H9PO3H)4(phen)3]·NO3·3.5H2O

Two novel indium(III) phosphonates, [In2(t-BuPO3H)4(phen)2Cl2] (1) and [In3(C5H9PO3)2(C5H9PO3H)4(phen)3]·NO3·3.5H2O (2) with phen = 1,10-phenanthroline, have been synthesized by solvothermal reactions involving indium(III) salts and organophosphonic acids. 1 is a dinuclear compound where the two indium centers are bridged by a pair of isobidentate phosphonate ligands, [t-BuP(O)2OH](-), resulting in an eight-membered (In2P2O4) puckered ring. Compound 2 is trinuclear; the In3 platform is held together by two bicapping tripodal phosphonate ligands from the top and bottom of the indium plane. In addition, two bridging monoanionic phosphonate ligands serve to bind two pairs of indium centers. Both 1 and 2 also contain monodentate monoanionic phosphonate ligands. The solid-state MAS (31)P NMR spectrum of complex 1 shows two signals at 21.9 and 29.3 ppm. Compound 2 contains signal maxima at 25.8 and 28.9 ppm, with a shoulder at 31.5 ppm. Room temperature solid-state fluorescence spectra of 1 and 2 are characterized by strong emission bands at 385 nm (λex = 350 nm) and 395 nm (λex = 350 nm), respectively, which are red-shifted with respect to the emission of free phenanthroline.