Synthesis and Characterization of Dimolybdenum(II) Complexes Connected by Carboxylate Linkers

A luminescent cellulose ether with a regenerated crystal form obtained in tetra(n-butyl)ammonium hydroxide/dimethyl sulfoxide

Cellulose-based luminescent materials are usually formed via either covalent attachment or combination with luminogens. In this work, three luminescent cellulose ethers without conventional luminophores have been homogeneously synthesized in a mixed solvent of tetra(n-butyl)ammonium hydroxide (TBAH)/dimethyl sulfoxide (DMSO). The one obtained by etherifying microcrystalline cellulose (MCC) with 4-bromomethylbenzoic acid (BBA), i.e., MCC-BBA, exhibits a regenerated crystal form of IV_II, whereas the other two are amorphous. The large difference of crystalline properties might be due to the formation of a new hydrogen bond network in MCC-BBA derived from the intermolecular interactions of COOH and their adjacent C2/C3OH groups. Such structural deviations might result in luminescence variations. Indeed, MCC-BBA can give brighter luminescence, which might be derived from crystallization-induced luminescence as well as photo-induced charge transfer effect. The presented work provides new insights into the rational synthesis of cellulose ethers, paving the way toward the design of non-conventional cellulose-based luminescent materials.

Molecular chains of coordinated dimolybdenum isonicotinate paddlewheel clusters

A growing focus on the use of coordination polymers for active device applications motivates the search for candidate materials with integrated and optimized charge transport modes. We show herein the synthesis of a linear coordination polymer comprised of Mo₂(INA)₄ (INA = isonicotinate) metal–organic clusters. Single-crystal X-ray structure determination shows that this cluster crystallizes into one-dimensional molecular chains, whose INA-linked Mo₂ cores engage in alternate axial and equatorial binding motifs along the chain axis. Electron paramagnetic resonance spectra, absorption spectra, and density functional theory calculations show that the aforementioned linear coordination environment significantly modifies the electronic structure of the clusters. This work expands the synthetic foundation for assembly of coordination polymers with tailorable dimensionalities and charge transport properties.

Linear molecular chains of coordinated dimolybdenum isonicotinate clusters.

Triphenylbismuth(v) di[(iso)nicotinates] - transmetallation agents or divergent organometalloligands? First organobismuth(v)-based silver(i) coordination polymers

The reaction of Ph₃BiCl₂ with alkali salts of isonicotinic and nicotinic acids afforded Ph₃Bi[O(O)CC₅H₄N-4]₂ (1) and Ph₃Bi[O(O)CC₅H₄N-3]₂ (2), respectively, which were characterized by multinuclear NMR spectroscopy in solution, mass spectrometry and IR spectroscopy in the solid state. Their molecular structures were established by single-crystal X-ray diffraction. For both 1 and 2 the molecules contain a trigonal bipyramidal C₃BiO₂ core, with the phenyl groups in equatorial positions. The potential use of 1 and 2 as ditopic organometalloligands was investigated. The reaction of 1 or 2 with Me₃SnCl (1 : 2 molar ratio) resulted in carboxylato ligand exchange and the formation of Me₃Sn[O(O)CC₅H₄N-4] (3) and Me₃Sn[O(O)CC₅H₄N-3] (4) besides Ph₃BiCl₂. The crystals of both 3 and 4 contain 1-D coordination polymers built through intermolecular N → Sn interactions. The treatment of Ni[S₂P(OⁱPr)₂]₂ with 1 and 2, respectively, resulted, in addition to di(carboxylato)nickel(ii) derivatives, in isolation of Ph₃Bi and the disulphane [(ⁱPrO)₂P(S)S]₂. New coordination polymers were obtained by reacting 1 and 2 with various silver(i) salts: [Ag{Ph₃Bi[O(O)CC₅H₄N-4]₂}(OTf)] (5), [Ag{Ph₃Bi[O(O)CC₅H₄N-3]₂}(OTf)]·CH₂Cl₂ (6·CH₂Cl₂), [Ag{Ph₃Bi[O(O)CC₅H₄N-4]₂}](SbF₆)·2THF (7·2THF), [Ag{Ph₃Bi[O(O)CC₅H₄N-3]₂}](SbF₆)·CH₂Cl₂ (8·CH₂Cl₂) and [Ag{Ph₃Bi[O(O)CC₅H₄N-3]₂}(NO₃)]·CH₂Cl₂ (9·CH₂Cl₂). The crystal structures of 5 and 6 can be described as 1-D chains linked by triflate bridges in pairs of chains and 2-D networks, respectively. Compound 7 features a 2-D grid-like topology of the network, with tecton 1 acting as a tridentate ligand through both nitrogen and one oxygen atoms. The linker 2 molecules adopt either cis (compound 6) or trans (compounds 8 and 9) conformation. Complexes 8 and 9 are 1-D chain polymers exhibiting zig-zag and wavy motifs, respectively. The dimensionality of the structures is extended by the presence of supramolecular interactions (ππ, AgAg, AgO).

Filling a Gap: Electrochemical Property Comparison of the Completed Compound Series [Mo2(DArF)n(O2C-Fc)4-n] (DArF = N,N'-Diarylformamidinate; O2C-Fc = Ferrocenecarboxylate)

The reaction of cis-[Mo2(O2C-Fc)2(NCCH3)4][BF4]2 (cis-1) with two electronically different N,N'-diarylformamidinate (DArF) ligands (DArF = N,N'-bis(p-trifluoromethylphenyl)formamidinate (DTfmpF), N,N'-bis(p-anisyl)formamidinate (DAniF)) results in the isolation of the tris- and monosubstituted complexes [Mo2(DTfmpF)3(O2C-Fc)] (2a) and [Mo2(DAniF)(O2C-Fc)3] (2b). These complexes complete the series of [Mo2(DArF)n(O2C-Fc)4-n] (n = 4-0) type compounds, thus allowing for a comprehensive study. On the basis of the oxidation potential E1/2([Mo2](4+)/[Mo2](5+)) of all Mo2 complexes, ligand basicity is found to decrease in the order DAniF(-) > DTfmpF(-) > Fc-CO2(-) ≫ CH3CN. In addition, no direct electronic interaction between the trans-positioned Fc units in complex 2b is detected, which is attributed to the full overlap of all Fc oxidation processes. Furthermore, the low-energy absorption bands of compounds 2a,b are located at different positions in their respective UV-vis spectra.

Synthesis and Electrochemical Properties of cis- and trans-[Mo2(O2C-Fc)2(DArF)2] (O2C-Fc = Ferrocenecarboxylate; DArF = N,N'-Diarylformamidinate)

The reaction of cis-[Mo2(O2C-Fc)2(NCCH3)4][BF4]2 (cis-1) with three electronically different N,N'-diarylformamidinate (DArF) ligands [DArF = N,N'-diphenylformamidinate (DPhF), N,N'-di(p-trifluoromethylphenyl)formamidinate (DTfmpF), and N,N'-di(p-anisyl)formamidinate (DAniF)] results in products of the general composition [Mo2(O2C-Fc)2(DArF)2]. Even though the trans-[Mo2(O2C-Fc)2(DArF)2] isomers were originally expected to be the sole products, the corresponding cis-[Mo2(O2C-Fc)2(DArF)2] complexes were isolated as well via crystallization and verified unambiguously by X-ray crystallography. All novel complexes, namely, cis-[Mo2(O2C-Fc)2(DPhF)2] (cis-2a), cis-[Mo2(O2C-Fc)2(DTfmpF)2] (cis-2b), and trans-[Mo2(O2C-Fc)2(DAniF)2] (trans-2c), were studied regarding their electrochemical properties with respect to electrolyte, solvent, and ligand. The electron-donating ligand DArF(-) enables the oxidation of the [Mo2](4+) unit prior to that of Fc, while the oxidation sequence is reversed when acetonitrile or diphosphine ligands are coordinated instead of formamidinate. In the case of trans-[Mo2(O2C-Fc)2(DAniF)2], interactions were found between the two redox-active ferrocenecarboxylate ligands, with a clear ΔE1/2 value originating from the peak-to-peak separation in DPV of around 100 mV with CH2Cl2 as solvent. Furthermore, the second oxidation of the Mo2-handle [Mo2](5+)/[Mo2](6+) was exclusively observed with DAniF(-) as the ligand. Similar absorption patterns in UV-vis spectra were found within the series 2a-2c, corresponding to similar structural and electronic features of the complexes.

Rational synthesis and characterization of dimolybdenum(II) compounds bearing ferrocenyl-containing ligands toward modulation of electronic coupling

Three novel cis-to-trans-converted dimolybdenum(II) complexes, trans-[Mo2(O2C-Fc)2(DPPX)2][BF4]2 {2a-2c; DPPX = DPPA [N,N-bis(diphenylphosphino)amine], DPPM [1,1-bis(diphenylphosphino)methane], and DPPE [1,2-bis(diphenylphosphino)ethane], respectively}, were synthesized through the insertion of bulky diphosphine ligands, which force a permanent trans arrangement, as evidenced by X-ray crystallography and density functional theory calculations. All compounds were characterized by means of NMR, UV-vis, and IR spectroscopy as well as thermogravimetry-mass spectrometry measurements. Interestingly, uncommon UV-vis transitions and oxidation sequences were observed compared to previously reported ones. As verified by electrochemical measurements, all synthesized complexes show two separate one-electron-redox processes assigned to subsequent oxidations of the two redox-active ferrocenecarboxylate ligands, with a split of ca. 70 mV. This behavior reveals electronic interaction between the two equatorially trans-positioned ferrocenyl units. The presented work provides new insights into the rational synthesis of electronically coupled trans-coordinated Mo2 systems, paving the way toward the design of linear multicenter redox-active oligomers.

Loop shaped dicarboxylate-bridged dimolybdenum(II) bisphosphine compounds--a rational synthesis

The reaction of the tetrametallic molecular loop [(CH3CN)6Mo2(OOC-C4H6-COO)]2[BF4]4 (1) (1 equiv.) with 2 equiv. of bis(diphenylphosphino)amine (dppa), 1,2-bis(diphenylphosphino)ethane (dppe) and bis(diphenylphosphino)methane (dppm) in propionitrile leads to the formation of the still tetrametallic complexes [(CH3CH2CN)4(X)Mo2(OOC-C4H6-COO)]2[BF4]4 (X = dppa (2), dppe (3), dppm (4)), also displaying a loop structure. All three complexes are characterized by NMR spectroscopy ((1)H, (11)B, (13)C{(1)H}, (19)F, (31)P{(1)H}), IR spectroscopy, elemental analysis, TG-MS measurements and UV-vis spectroscopy, compounds 2 and 3 additionally by X-ray single crystal diffraction.