Zonghai Shi

New supramolecular compounds based on porphyrin and polyoxometalate: synthesis, characterization and nonlinear optical and optical limiting properties

Three new supramolecular compounds [H2TPP]1.5[SW11VO40]·5CH3CN·4H2O 1, [H2TPP]2[SW10V2O40]·4CH3CN·3H2O 2, and [H2TPP][SW12O40]·4H2O 3 composed of [H2TPP]2+ cation and vanadium substituted Keggin-type polyoxometalate (POM) anion [SW12−nVnO40](2+n)− (n = 0–2) were prepared and characterized. The third-order nonlinear optical (NLO) and optical limiting (OL) properties of resulting hybrids were studied by using an Nd:YAG laser at 532 nm with a pulse duration of τ = 7 ns. The results demonstrate that all of these supramolecular compounds have significant nonlinear reverse saturated absorption, self-defocusing behavior, and good OL performance, especially for compound 1, which has a second hyperpolarizability γ value of 7.05 × 10−29 (esu) and exhibits a comparable OL performance with the most well-known OL materials such as In(Pc*)Cl indicating that they are potentially excellent NLO materials. Remarkably, it was also observed that the degree of vanadium substitution in POM anions corresponding to different onset of reduction potential influences the NLO and OL properties of the resulting compounds: third-order NLO and OL properties of compound 2 are inferior to those of compound 1, and are better than those of compound 3. Both their second hyperpolarizability γ values and the OL performance were observed to be inversely proportional to the HOMO–LUMO gaps of the resulting compounds. The excited charge transfer from porphyrin to POM anions in the supramolecular compounds when exposed to laser irradiation is thought to play key role in the enhancement of NLO and OL response.

Two isomorphous 3-D lanthanide oxalatophosphonate frameworks based on glyphosate: syntheses, crystal structures, and luminescence properties

Two new 3-D isomorphous lanthanide(III) compounds [Eu2(H2L)2(C2O4)2]·2.51H2O (1) and [Tb2(H2L)2(C2O4)2]·2.46H2O (2, H3L = glyphosate), based on glyphosate and oxalate have been successfully synthesized under hydrothermal conditions, and structurally characterized. In the two compounds, tetra-connected glyphosate ligands are coordinated to Ln3+, resulting in the formation of 1-D {Ln2(H2L)2}n double chains along the c direction. Each of the chains is connected to its four neighbors via the O atoms of phosphates of H2L− ligands, resulting in a 3-D (4, 6)-connected framework with 43·58·63·7 topology, which possesses 1-D channels with oxalates and lattice water molecules as troglodytes. The oxalates are stabilized via chelating Ln3+ in the form of 1-D Ln-C2O42− zigzag chains along the c direction. To the best of our knowledge, compounds 1 and 2 represent the first single-crystal structures of lanthanide(III)-glyphosate compounds incorporating second ligands. The luminescent properties of compounds 1 and 2 have been investigated at room temperature. The energy gaps between the triplet excited state of oxalic acid and the lowest excited resonance levels of Eu3+ (5D0) and Tb3+ (5D4) are 7270 cm−1 and 4070 cm−1, respectively, indicating that oxalate is more suitable for the sensitization of Tb3+ luminescence than Eu3+ luminescence.

Synthesis, structures and photoluminescence of a series of 3D lanthanide–organic coordination polymers constructed from versatile 2,2′-bipyridine-3,3′-dicarboxylic acid 1,1′-dioxide and oxalic acid

A series of 3D coordination polymers {[Ln2(bdcd)(ox)2(H2O)3]·4H2O}n (Ln = Eu (1), Tb (2), Sm (3), Dy (4), and Gd (5)), which crystallize in the triclinic space group P with Z = 2, have been synthesized successfully based on the versatile ligands 2,2′-bipyridine-3,3′-dicarboxylic acid 1,1′-dioxide (H2bdcd) and oxalic acid (H2ox). The compounds were characterized by means of IR spectroscopy, elemental analysis, TG, and powder X-Ray diffraction, whereby compounds 1 and 2 were structurally characterized. All of the compounds are isomorphous and have a 3D open framework in which ox2− ligands bridge Ln3+ ions through their carboxylate groups resulting in the formation of a 1D Ln–ox infinite chain in the ac plane. The adjacent 1D Ln–ox infinite chains are then connected to each other through coordination interactions between Ln3+ ions and the carboxylate groups and N-oxide atoms of bdcd2− ligands resulting in a 3D (7,8)-connected open framework with a (38·49·54) (37·49·511·6) topology possessing 1D channels with lattice water molecules as residents. The photoluminescence properties of compounds 1, 2 and 4 were investigated in detail.

Photoluminescent 3D lanthanide-organic frameworks based on 2,5-dioxo-1,4-piperazinylbis(methylphosphonic) acid formed via in situ cyclodehydration of glyphosates.

Hydrothermal reactions of lanthanide nitrates with glyphosate have resulted three new isostructural 3D lanthanide-organic frameworks, Ln(NO3)(H2L) [Ln = Eu (1), Tb (2), Gd (3); H4L = 2,5-dioxo-1,4-piperazinylbis(methylphosphonic) acid], with good yields, where H4L as a new ligand was formed via in situ cyclodehydration of original ligand glyphosates during the hydrothermal reaction. The compounds were thoroughly characterized by IR, UV-vis, elemental analysis, single-crystal X-ray diffraction analysis, powder X-ray diffraction analysis, and thermogravimetric/differential thermal analysis (TG-DTA). Three compounds display 3D 6,6-connected open frameworks with 4(13)·6(2) topology possessing 1D channels in which NO3(-) anions act as troglodytes by chelating Ln(3+) centers. The TG-DTA study of the compounds showed remarkable thermal stability up to 380 °C. Under room temperature UV-light irradiation, the Eu(3+) and Tb(3+) compounds showed the corresponding characteristic Ln(3+) intra 4f(n) emission peaks. The triplet energy level (21882 cm(-1)) of the ligand (H4L) was determined from the emission spectrum of its Gd(3+) compound at 77 K. The emission lifetimes (1.54 ms of (5)D0 for compound 1 and 1.98 ms of (5)D4 for compound 2) and absolute emission quantum yields (10.1% for compound 1 and 5.9% for compound 2) were also determined.

A general synthesis approach in action: preparation and characterization of polyoxomolybdenum(VI) organophosphonates through oxidative Mo–Mo bond cleavage in {MoV2O4}

Three new tetramolybdenum organophosphonate compounds, (NH4)7{FeIII[MoVI2O6CH3C(O)(PO3)2]2}·10H2O 1, (NH4)4[Na(H2O)6]{CrIII[MoVI2O6CH3C(O)(PO3)2H]2}·7.67H2O 2 and (NH4)8{MnII[MoVI2O6CH3C(O)(PO3)2]2}·9H2O 3 have been successfully synthesized by reacting metal-containing oxidants Fe2(C2O4)3, MnO4− and CrO42− with a simple aqueous solution containing {MoV2O4(H2O)6}2+, respectively, in the presence of (hydroxylethylidene) diphosphonic acid. These compounds are characterized by elemental analyses, spectroscopic methods (IR, UV-Vis, XPS), TG-DTA, single-crystal X-ray diffraction analyses (including bond valence sum calculations) and powder X-ray diffraction analysis. Single crystal X-ray diffraction analyses have revealed that Mo–Mo bonds of {MoV2O4(H2O)6}2+ are cleavaged in the oxidation reaction to form {MoVI2O6} motifs, which are concomitantly stabilized by organophosphate and linked by the resulted metal ions coming from the metal-containing oxidants and bring on the formation of compounds 1–3, whose anions have a general formula {M[MoVI2O6CH3C(O)(PO3)2]2}n−(M = FeIII1; CrIII2; MnII3). It is important that the successful synthesis and characterization of the three new compounds induces a simple yet general strategy which can be utilized for the preparation of polyoxomolybdenum(VI) organophosphonates through oxidative Mo–Mo bond cleavage with various metal-containing oxidants like FeIII, MnVII and CrVI in the presence of various organophosphonates.

Fabrication and notable optical nonlinearities of ultrathin composite films derived from water-soluble Keggin-type polyoxometalates and water-insoluble phthalocyanine

Composite films with the general formula (POM/CuTAPc)n derived from water-soluble Keggin-type polyoxometalates (POMs = H5PMo10V2O40, H4SiW12O40, H3PMo12O40 and H3PW12O40) and water-insoluble 4,9,16,23-copper tetraaminophthalocyanine (denoted CuTAPc) are successfully fabricated by a layer-by-layer self-assembly technique and systematically characterized. The structure of the polyoxometalate anions in the multilayers is kept intact; the deposition amounts of POM and CuTAPc remain constant in every adsorption cycle of the composite film assembly process. The nonlinear optical properties of the composite films were studied by a Z-scan technique at a wavelength of 532 nm and a pulse width of 7 ns. The results not only show that the composite films exhibit notable optical nonlinear self-defocusing behavior and a saturated absorption effect with the nonlinear optical absorption co-efficient β, refractive index n2, and third-order NLO susceptibility χ(3) of the films increasing with the increase in number of layers of the films, but also reveal importantly that the discrepancy of LUMO levels between CuTAPc and POMs is proportional to their third-order NLO response.

A 2-D dysprosium-organic complex constructed from 6,7-dihydropyrido(2,3-d)pyridazine-5,8-dione and oxalic acid: synthesis, characterization and photoluminescence

A pyridine derivative 6,7-dihydropyrido(2,3-d)pyridazine-5,8-dione (H2PDH) and oxalic acid (H2ox) are reacted with dysprosium oxide to develop a new 2-D dysprosium–organic complex [Dy(PDH)(ox)0.5(H2O)2]. The single-crystal structure reveals that acylamino oxygens and coordinated waters develop a 3-D supramolecular network, which is composed of 2-D layers, and each 2-D layer is formed by 1-D Dy–H2O–ox chains linked by tridentate PDH2− ligands. The complex exhibits metal-centered luminescence with yellowish blue emission. The energy transfer mechanism and photoluminescence are also investigated.

Third-order Optical Nonlinearities of a Series of Compounds Derived from a Keplerate Type Molybdenum-oxide-based Polyoxometalate

By reacting the unique Keplerate type molybdenum-oxide based polyoxometalate (NH4)42·[Mo132O372·(CH3COO)30(H2O)72]·ca.300H2O·ca.10CH3COONH4(1) with tetramethylammonium bromide, a new derivative (NH4)26[TMA]16{Mo132O372(H2O)72(CH3COO)30}·ca.7NH4CH3COO·ca.189H2O(2, TMA=tetramethylammonium) was prepared. Compound 2 was characterized by Fourier transform infrared spectroscopy(FTIR), UV-Vis, elemental and thermogravimetric analyses. By the well-established Z-scan technique, investigations on the nonlinear optical(NLO) properties of the series of compounds derived from the Keplerate type molybdenum-oxide-based poly-oxometalate, namely, the newly prepared compound 2, the three previously reported compounds, included compound 1, (NH4)18(TBA)24{Mo132O372(H2O)72(CH3COO)30}·ca.7NH4CH3COO·ca.173H2O(3, TBA=tetrabutylammonium) and (DODA)40(NH4)2[(H2O)nMo132O372(CH3COO)30(H2O)72](4, DODA=dimethyldioctadecylammonium), reveal that the third-order nonlinearity[χ(3)] values of compounds 1, 2 and 3 in the DMF/H2O solution and compound 4 in chloroform are almost the same, which indicates that the counter cations with different length of alkyl chains show ignorable impacts on the NLO susceptibility. In other words, the remarkable third-order nonlinearities[χ(3)≈10−19 m2/V2] mainly come from the [Mo132O372(CH3COO)30(H2O)72]42− anions. This fact reveals that the applications of the NLO active polyoxometalates in various environments(such as hydrophilic, hydrophobic, polar, apolar, etc.) can be achieved by simply varying cations to meet the demands in the design of diverse devices.

Third-order NLO properties of ultrathin films containing cationic phthalocyanine and Keggin polyoxometalates fabricated using layer-by-layer deposition from aqueous solution

Composite films with alternating layers (PAH/PSS)3(AB/POM)n (PAH = polyallylamine hydrochloride, PSS = polystyrene sulfonate) derived from Alcian Blue-tetrakis(methyl-pyridinium) chloride (abbreviated as AB) and Keggin type polyoxometalates (POM = H4SiW12O40, H3PW12O40, H3PMo12O40, H5PMo10V2O40) have been fabricated and characterized. Under laser irradiation at 532 nm with a pulse duration of 6–7 ns, a repetition rate of 10 Hz and the intensity of the light at focus E0 being 10 μJ, the composite films exhibit self-defocusing behavior and saturated absorption effects, and the nonlinear optical absorption coefficient β (m W−1) and refractive index n2 (m2 W−1) of the films are 4–5 times larger than those of pure AB solution in view of their magnitude. Interestingly, it is found that third-order NLO susceptibilities χ(3) of films are in the order of χ(3)(AB/PSS) ELUMO(PW12) > ELUMO(PMo12) > ELUMO(PMo10V2), affirming that the incorporation of different Keggin type POMs of a lower LUMO energy level with phthalocyanine molecules into multilayers could tune the NLO responses of phthalocyanine films. It is concluded that the lower LUMO level of POM than that of the phthalocyanine can stimulate the easier transformation of excited electrons from AB to the POM within the donor–acceptor system (phthalocyanine molecules acted as an electron donor while POMs as an electron acceptor in the composite films) when flashed with the laser, which is thought to be accountable for the profound third-order optical nonlinearity of the composite films.

One Dimensional Iron Molybdophosphate Anionic Chains with Different Structural Arrangements Reflecting a Flexibility Character

Structural comparison of a new compound [(bpp)3H6]Fe2IIIFe2IIMo24V(H2PO4)8(HPO4)4(PO4)4O48(OH)12· (H2O)4·2H2O(1)[bpp=1,3-di(4-pyridyl)propane] with our previously reported two compounds [(bpy)3FeII]3sdFe2IIIFe2IIMo24V(H2PO4)8(HPO4)4(PO4)4O48(OH)12(H2O)4·12H2O(2) and [(bpy)3FeII]2FeIIFeIIIMo12V(H2PO4)2(H2−xPO4)·(H1+xPO4)(HPO4)2(PO4)2O24(OH)6(H2O)2·9H2O(x=0-21)(3)(bpy=2,2′-bipyridine), which all exhibit one-dimensional mixed-valence iron molybdophosphate anionic chains constructed by alternating connection of FeIII ions and magic [FeII(Mo6P4O31)2] units, reveals that the non-hydrogen atomic ratios of Mo:Fe:P:O within the polymeric anionic chains are the same for all the three compounds, while the polymeric anionic chains of the different compounds bear different numbers of negative charges. And therefore there exist different numbers of counter cations per {Fe2III[Fe2II(P16Mo24VO124)]} unit found in the titled compounds. It discloses that not only are the spatial assembling of counter cations and polymeric inorganic chains of three compounds quite different, but also the O—FeIII—O bond angles and FeIII—O bond lengths of the three different inorganic chains exhibit small differences. What is more important is that such small changes in bond length and bond angle in the assemblage of FeIII—O bonds lead to the considerable fluctuations of inorganic chains in their structural conformation within the three compounds, reflecting an interesting phenomenon of “flexibility” in the pure inorganic one dimensional mixed-valence iron molybdophosphate chains.