Fine-tuning of thermally induced SCO behaviors of trinuclear cyanido-bridged complexes by regulating the electron donating ability of CCN-terminal fragments.

To achieve fine regulation of FeII SCO behavior, a series of trinuclear cyanido-bridged complexes trans-[CpMen(dppe)MII(CN)]2[Fe1II(abpt)2](OTf)2 (1-4) (1, M = Fe2 and n = 1; 2, M = Fe2 and n = 4; 3, M = Fe2 and n = 5; 4, M = Ru and n = 5; CpMen = alkyl cyclopentadienyl with n = 1, 4, 5; dppe = 1,2-bis-(diphenylphosphino)ethane; abpt = 4-amino-3,5-bis-(pyridin-2-yl)-1,2,4-triazole and OTf = CF3SO3-) were synthesized and fully characterized by using elemental analysis, X-ray crystallography, magnetic measurements, variable-temperature IR spectroscopy and Mössbauer spectroscopy. It is worth mentioning that different from many mononuclear Fe(abpt)2X2 (X = NCS, NCSe, N(CN)2, C(CN)3, (NC)2CC(OCH3)C(CN)2, (NC)2CC(OC2H5)C(CN)2, C16SO3 and Cl) complexes with more than one polymorph, only one polycrystalline form was found in complexes 1-4. Moreover, the thermally induced SCO behaviors of these four complexes are independent of intermolecular π-π interactions. The electron-donating ability of the CCN-terminal fragment of CpMen(dppe)MIICN can be flexibly regulated by changing the methyl number (n) of the cyclopentadiene ligand or metal ion type (MII). These investigations indicate that the electron-donating ability of the CCN-terminal fragment has an influence on the SCO behavior of Fe1II. The spin transition temperature (T1/2) of the complexes decreases with the increase of the electron-donating ability of the fragment CpMen(dppe)MII. This study provides a new strategy to predict and precisely regulate the behaviors of SCO complexes.

Azo-Cyanamide Bridged Dinuclear Iron Complexes Exhibiting no Electronic Coupling but Moderate Magnetic Coupling between the two Iron Centers.

To investigate the effect of long-distance organic ligand on electronic coupling between metallic atoms, the mononuclear and dinuclear complexes [Cp(dppe)Fe(apc)] (1), [{Cp(dppe)Fe}2(µ-adpc)] (2), [{CpMe5(dppe)Fe}2(µ-adpc) (3) and their oxidized complexes [Cp(dppe)Fe(apc)][PF6] (1[PF6]), [{Cp(dppe)Fe}2(µ-adpc)][PF6] (2[PF6]2), [{CpMe5(dppe)Fe}2(µ-adpc)][PF6]2 (3[PF6]2) (Cp=1,3-cyclopentadiene, CpMe5=1,2,3,4,5-pentamethylcyclopentadiene, dppe=1,2-bis(diphenylphosphino)ethane), apc-=4-azo(phenylcyanamido)benzene and adpc2-=4,4'-azodi(phenylcyanamido)) were synthesized and characterized by cyclic voltammetry, UV-vis, single-crystal X-ray diffraction and Mössbauer spectra. Electrochemical measurements showed no electronic coupling between the two terminal Fe units, However, the investigation results of the magnetic properties of the two-electron oxidized complexes indicate the presence of moderate antiferromagnetic coupling across 18 Šdistance.

Electronic Transition and Magnetic Coupling Regulation in Trimetallic Complexes Featuring a New Bridging Ligand Obtained by Oxidative Addition.

A series of trimetallic complexes [FeIII(µ-L)(py)]2MII(py)n (n = 2, MII = MnII, 1; FeII, 2; CoII, 3; ZnII, 4; n = 3, MII = CdII, 5) with a new bridging ligand L4- (deprotonated 1,2-N1,N2-bis(2-mercaptoanil) oxalimidic acid) were synthesized and fully characterized by elemental analysis, single-crystal X-ray crystallography, IR, and Mössbauer spectra. Interestingly, the bridging ligand was obtained by oxidative addition of the (gma•)3- ligand from the mononuclear precursor Fe(gma)py (gma = glyoxal-bis(2-mercaptoanil)). In the obtained complexes, the bridging ligand L4- coordinates to the terminal FeIII ions (intermediate-spin with SFe = 3/2) by the N, S atoms, and coordinate to the central metal MII ion by the four O atoms. The resonance structure of the bridging ligand can be described as the two 4π-electron delocalized systems connected by one single-bond (C1-C2), which is different from the electronic structure of the precursor Fe(gma)py. Remarkably, the magnetic coupling interaction can be regulated through the central metal. The ferromagnetic coupling constant J gradually decreases as MII changes from FeII to CoII and MnII, while the paramagnetic behaviors are presented when MII = ZnII and CdII, confirmed by the magnetic susceptibility measurements and further supported by using the PHI program. Furthermore, the bridging ligand to the terminal FeIII charge transfer (LMCT) transitions emerged in all complexes but the central FeII to terminal FeIII charge transfer (MMCT) only presented in complex 2, strongly supported by the UV/vis-NIR electronic spectra and TDDFT calculations.

Coexistence of Three Different Spin States in a Cyanido-Bridged Trinuclear Iron(III) Complex with an Unusual FeIII to Ligand Charge Transfer.

We report a trinuclear iron(III) cyanido-bridged complex trans-[CpMe3 FeIII (dppe)(CN)]2 [FeIII (LN4 )][PF6 ]4 (2[PF6 ]4 ) as the oxidation product of binuclear complex [CpMe3 (dppe)FeII CN-FeIII (LN4 )][PF6 ] (1[PF6 ]) (CpMe3 =1, 2, 4-trimethyl-1,3-cyclo-pentadienyl, dppe=1,2-bis(diphenylphosphino)ethane, LN4 =pentane-2,4-dione-bis(S-methylisothiosemicarbazonato). Complex 1[PF6 ] possesses an intermediate-spin five-coordinated FeIII (S=3/2) which couples antiferromagnetically to the π-radical ligand (L⋅N4 )2- and shows a LMCT (ligand to metal charge transfer) transition from (L⋅N4 )2- to FeIII and the FeII →FeIII MMCT transition. Upon oxidation of 1[PF6 ], (L⋅N4 )2- loses one electron to be the strong electron-attracting ligand (LOx N4 )- and the intermediate-spin five-coordinated FeIII (S=3/2) becomes a low-spin six-coordinated FeIII (S=1/2) in 2[PF6 ]4 . Also interestingly, 2[PF6 ]4 presents the coexistence of three different spin states (one S=3/2 and two S=1/2) and an uncommon FeIII →(LOx N4 )- MLCT transition, confirmed by the experimental results and supported by the TDDFT calculations.

Influence of the electronic effect of an ancillary ligand on MMCT and LMCT in localized cyanide-bridged complexes containing non-innocent ligands.

Mixed-valence (MV) complexes containing non-innocent ligands are excellent models for the investigation of the electron-transfer process. A series of twelve bimetallic cyanide-bridged complexes [CpMen(dppe)RuCNFeLx][A] (A = PF6- or I-, CpMen = alkyl cyclopentadienyl, dppe = 1,2-bis (diphenylphosphino)ethane, and LX = pentane-2,4-dione-bis (S-alkylisothiosemi-carbazonato); n = 0, x = Methyl (Me), Ethyl (Et), n-Propyl (Pr) and n-Butyl (Bu), and A = PF6-, 1Me[PF6], 1Et[PF6], 1Pr[PF6], and 1Bu[PF6]; n = 1, x = Me, Et, Pr, and Bu, and A = PF6-, 2Me[PF6], 2Et[PF6], 2Pr[PF6], and 2Bu[PF6]; n = 5, x = Me, Et, Pr, and Bu, and A = I-, 3Me[I], 3Et[I], 3Pr[I], and 3Bu[I]) have been synthesized and well characterized. The investigations demonstrate that all the cations of the complexes could be described with the basic electronic configuration , in which the fragment could be regarded as being delocalized. The ligand to metal charge transfer (LMCT) transition in the fragment and the low-spin RuII to the intermediate-spin FeIII charge transfer (MMCT) transition have been investigated. The UV-vis-NIR spectral analysis results suggest that the energy of the LMCT transition is lower than that of the MMCT transition due to electron delocalization between the non-innocent ligand and the FeIII ion, which is strongly supported by TDDFT calculations. Furthermore, the RuII → FeIII MMCT energy decreases and the LMCT energy increases with the increasing electron donating ability of the ancillary ligands from Cp, CpMe to CpMe5, but slightly changes with the variation of the ligand Lx from Me, Et, Pr to Bu. Compared to the MMCT energy change, however, the energy of the LMCT from to FeIII in the delocalized moiety is less influenced by the electronic effect of the ancillary ligand or the CpMen(dppe)RuIICN (n = 0, 1 and 5) fragment.

Influence of the CN Orientation on the Degree of Electron Delocalization of Ru-Ru-Ru Mixed-Valent Complexes.

Investigations on mixed-valent complexes in the Class II/Class III frontier have been a particularly interesting issue due to their special electron delocalization. In this work, a pair of cyanidometal-/isocyanidometal-bridged Ru-Ru-Ru compounds, cis-[Cp(dppe)Ru-B-Ru(dppe)Cp]2+ (B = NCRu(bpy)2CN, 12+; B = CNRu(bpy)2NC, 22+; Cp = 1,3-cyclopentadienyl, dppe = 1,2-bis(diphenlyphosphine)ethane, bpy = 2,2'-bipyridine), and one-electron oxidized 13+ and 23+ were synthesized and well characterized. For the two-electron oxidized 14+ and 24+, their Fourier transform infrared (FTIR) and UV-vis-NIR spectra were investigated by employing spectroelectrochemical methods. The time-dependent density-functional theory (TDDFT) calculations and the experimental results indicate that the one-/two-electron oxidized mixed-valent compounds belong to Class II-III systems.

Human Umbilical Cord-Derived Mesenchymal Stromal Cells Improve Left Ventricular Function, Perfusion, and Remodeling in a Porcine Model of Chronic Myocardial Ischemia.

UNLABELLED: : Stem cell therapy has emerged as a new strategy for treatment of ischemic heart disease. Although umbilical cord-derived mesenchymal stromal cells (UC-MSCs) have been used preferentially in the acute ischemia model, data for the chronic ischemia model are lacking. In this study, we investigated the effect of UC-MSCs originated from Wharton's jelly in the treatment of chronic myocardial ischemia in a porcine model induced by ameroid constrictor. Four weeks after ameroid constrictor placement, the surviving animals were divided randomly into two groups to undergo saline injection (n = 6) or UC-MSC transplantation (n = 6) through the left main coronary artery. Two additional intravenous administrations of UC-MSCs were performed in the following 2 weeks to enhance therapeutic effect. Cardiac function and perfusion were examined just before and at 4 weeks after intracoronary transplantation. The results showed that pigs with UC-MSC transplantation exhibited significantly greater left ventricular ejection fraction compared with control animals (61.3% ± 1.3% vs. 50.3% ± 2.0%, p < .05). The systolic thickening fraction in the infarcted left ventricular wall was also improved (41.2% ± 3.3% vs. 46.2% ± 2.3%, p < .01). Additionally, the administration of UC-MSCs promoted collateral development and myocardial perfusion. The indices of fibrosis and apoptosis were also significantly reduced. Immunofluorescence staining showed clusters of CM-DiI-labeled cells in the border zone, some of which expressed von Willebrand factor. These results suggest that UC-MSC treatment improves left ventricular function, perfusion, and remodeling in a porcine model with chronic myocardial ischemia. SIGNIFICANCE: Ischemic heart disease is the leading cause of death worldwide. Many patients with chronic myocardial ischemia are not suitable for surgery and have no effective drug treatment; they are called "no-option" patients. This study finds that umbilical cord-derived mesenchymal stromal cells transplanted by intracoronary delivery combined with two intravenous administrations was safe and could significantly improve left ventricular function, perfusion, and remodeling in a large-animal model of chronic myocardial ischemia, which provides a new choice for the no-option patients. In addition, this study used clinical-grade mesenchymal stem cells with delivery and assessment methods commonly used clinically to facilitate further clinical transformation.