Dimethyl Sulfoxide Ligands Research Articles

The Chlorido-Bismuth Dication: A Potent Lewis Acid Captured in a Hepta-Coordinate Species with a Stereochemically Active Lone Pair.

The stabilization of simple, highly reactive cationic species in molecular complexes represents an important strategy to isolate and characterize compounds with uncommon or even unprecedented structural motifs and properties. Here we report the synthesis, isolation, and full characterization of chlorido-bismuth dications, stabilized only by monodentate dimethylsulfoxide (dmso) ligands: [BiCl(dmso)6][BF4]2 (1) and [BiCl(μ2-dmso)(dmso)4]2[BF4]4 (2). These compounds show unusual distorted pentagonal bipyramidal coordination geometries along with high Lewis acidities and have been analyzed by multinuclear NMR spectroscopy, elemental analysis, IR spectroscopy, single-crystal X-ray diffraction, and density functional theory calculations. Attempts to generate the bromido- and iodido-analogs gave dmso-stabilized tricationic bismuth species.

Iodine-mediated substitution of terminal ligands in [{M6I8}I6]2– (M = Mo, W) by DMSO

The family of octahedral iodide cluster complexes of molybdenum and tungsten – [{M6I8}L6]n – exhibit a unique set of properties with significant practical potential. Due to the strong influence of terminal ligands L on these properties, the search for new simpler, more convenient and cheaper approaches for their substitution is an urgent task. This work demonstrates a new one-step method for terminal ligand substitution using well-known and readily available complexes [{M6I8}I6]2–. The synthetic technique involves the addition of molecular iodine to the reaction mixture in order to bind the released I– ions, thereby facilitating the reaction process. As a result, two new cluster complexes with dimethyl sulfoxide ligands [{M6I8}(DMSO)6](I3)4 (M = Mo (1), W (2)) have been obtained and structurally characterized. The optical properties of the obtained compounds have been studied both in solid state and in solution, and Eg values have been calculated from the solid-state absorption spectra. The presence of I3– anions has been shown to quench the emission of the cluster complexes, explaining the absence of luminescence in the obtained compounds.

Cis,cis,cis-Di-chlorido-bis-(N4,N4-di-methyl-pyridin-4-amine-κN1)bis-(dimethyl sulfoxide-κS)ruthenium(II).

The structure of the title compound, [RuCl2(C7H10N2)2(C2H6OS)2], has monoclinic (P21/n) symmetry. The Ru-N distances of the coordination compound are influenced by the trans chloride or di-methyl-sulfoxide-κS ligands. The mol-ecular structure exhibits disorder for two of the terminal methyl groups of a dimethyl sulfoxide ligand.

Crystal structure of tetrakis(μ-2-hydroxy-3,5-diisopropylbenzoato)bis[(dimethyl sulfoxide)copper(II)

Metal complexes of 3,5-diisopropylsalicylate are reported to have anti-inflammatory and anti-convulsant activities. The title binuclear copper complex, [Cu2(C13H17O3)4(C2H6OS)2] or [Cu(II)2(3,5-DIPS)4(DMSO)2], contains two five-coordinate copper atoms that are bridged by four 3,5-diisopropylsalicylate ligands and capped by two axial dimethyl sulfoxide (DMSO) moieties. Each copper atom is attached to four oxygen atoms in an almost square-planar fashion, with the addition of a DMSO ligand in an apical position leading to a square-pyramidal arrangement. The hydroxy group of the diisopropylsalicylate ligands participates in intramolecular O—H...O hydrogen-bonding interactions.

Synthesis, spectroscopic characterization, crystal structure and DNA docking studies of a new trans-platinum saccharinate complex containing aqua and dimethyl sulfoxide ligands

A new trans-platinum complex, trans-[Pt(sac)2(H2O)(DMSO)] (sac= saccharinate; DMSO= dimethyl sulfoxide), was synthesized and characterized by elemental analysis, UV, FTIR, NMR spectroscopy and X-ray single-crystal diffraction. In the mononuclear complex, the platinum(II) cation was coordinated by two N-coordinated sac ligands in the trans position, the sulfur atom of the DMSO ligand, and an aqua ligand, forming a distorted square planar coordination geometry. The interaction of the platinum(II) complex with DNA was studied using molecular docking. The complex successively docked into the minor groove of DNA via intermolecular hydrogen bonds with the adenine, cytosine, and guanine bases.

Examining the adsorption of gases into solid crystalline molecular copper(II) 3,5-bis(trifluoromethyl)benzoate derivatives

Two copper(II) complexes, both involving the anionic 3,5-bis(trifluoromethyl)benzoate ligand (TFMBz), have been prepared and their structure elucidated by single crystal-X ray diffraction. [Cu(TFMBz)2(ISNA)2] (1) is a mononuclear complex, in which the sphere of coordination of Cu(II) is completed by two neutral isonicotinamide (ISNA) auxiliary ligands. Hydrogen bonding formed between auxiliary ISNA ligands determines the formation of a 2D supramolecular network. [Cu2(TFMBz)4(DMSO)2] (2) is a binuclear complex, in which the four carboxylate ligands define the typical paddle wheel structure often found in copper complexes, containing also the ancillary dimethyl sulfoxide (DMSO) ligand in axial positions. The elucidated crystallographic data provide the static view of the crystal structures, which reveals only non-interconnected voids for both materials. Even that, compound 1 shows an appreciable adsorption of CO2 at 273 K (ca. 1 CO2 molecule/Cu atom at 100 kPa), concomitant with a reduced adsorption of Ar or N2 under similar conditions, which implies a considerable degree of selectivity for CO2. Moreover, 1 does not adsorb N2 or Ar at 77 K and 100 kPa. This behavior suggests that the stablished intermolecular hydrogen bonds rest flexibility and dynamism to 1 at low temperature. Contrarily, increasing the temperature transient porosity is originated, which allows guest molecules to diffuse through the cavities. Compound 2 shows adsorption of N2 and Ar at 77 K, indicating that vibrations in the network and rotation of some CF3 groups, necessary to favor adsorbate diffusion, are still feasible at this low temperature.

Synthesis and catalysis of diruthenium hydride complexes with bidentate dimethylsulfoxide ligand

A new, simple and controllable synthetic route is established to one-step synthesize diruthenium complexes with μ -H, μ -Cl halogen and μ -S,O-dmso bridges, namely (Bu4N)[Ru2(μ -H)(μ -X)(μ -S,O-dmso)(S-dmso)3(Cl)3] (Bu4N·1, where dmso = dimethyl sulfoxide) in one step. This complex is obtained by treating [Ru(dmso)4Cl2] with Bu4NCl in presence of excess Et3N in refluxing methanol. Advantages over prior routes to these analogous complexes lie in one-step controllable synthesis, and the short reaction times under experimentally convenient conditions. The properties of Bu4N·1 in solution and in solid-state are investigated. In addition, the catalytic performance of Bu4N·1 for CO2 + H2 / HCOO– interconversion in aqueous solution is also described.

Identification of Platinum(II) Sulfide Complexes Suitable as Intramuscular Cyanide Countermeasures.

The development of rapidly acting cyanide countermeasures using intramuscular injection (IM) represents an unmet medical need to mitigate toxicant exposures in mass casualty settings. Previous work established that cisplatin and other platinum(II) or platinum(IV)-based agents effectively mitigate cyanide toxicity in zebrafish. Cyanide's in vivo reaction with platinum-containing materials was proposed to reduce the risk of acute toxicities. However, cyanide antidote activity depended on a formulation of platinum-chloride salts with dimethyl sulfoxide (DMSO) followed by dilution in phosphate-buffered saline (PBS). A working hypothesis to explain the DMSO requirement is that the formation of platinum-sulfoxide complexes activates the cyanide scavenging properties of platinum. Preparations of isolated NaPtCl5-DMSO and Na (NH3)2PtCl-DMSO complexes in the absence of excess DMSO provided agents with enhanced reactivity toward cyanide in vitro and fully recapitulated in vivo cyanide rescue in zebrafish and mouse models. The enhancement of the cyanide scavenging effects of the DMSO ligand could be attributed to the activation of platinum(IV) and (II) with a sulfur ligand. Unfortunately, the efficacy of DMSO complexes was not robust when administered IM. Alternative Pt(II) materials containing sulfide and amine ligands in bidentate complexes show enhanced reactivity toward cyanide addition. The cyanide addition products yielded tetracyanoplatinate(II), translating to a stoichiometry of 1:4 Pt to each cyanide scavenger. These new agents demonstrate a robust and enhanced potency over the DMSO-containing complexes using IM administration in mouse and rabbit models of cyanide toxicity. Using the zebrafish model with these Pt(II) complexes, no acute cardiotoxicity was detected, and dose levels required to reach lethality exceeded 100 times the effective dose. Data are presented to support a general chemical design approach that can expand a new lead candidate series for developing next-generation cyanide countermeasures.

Bis(catecholato-κ2 O,O')bis-(dimethyl sulfoxide-κO)titanium(IV).

Bis(benzene-1,2-diolato-κ2 O,O')bis-(dimethyl sulfoxide-κO)titanium(IV), [Ti(C6H4O2)2(C2H6OS)2], crystallizes with two crystallographically independent mol-ecules in the space group P21/c emulating ortho-rhom-bic Pbca symmetry (β = 90.0445 (9)°]. The two mol-ecules are related by pseudo-glide symmetry, broken by modulation of each one catecholate and dimethyl sulfoxide (DMSO) ligand. Twinning by pseudomerohedry was observed [twin ratio 0.5499 (7):0.4401 (7)]. Complex 3 was obtained by heating of diprotonated titanium tris-catecholate precursor 2H in DMSO, by formal displacement of a catechol mol-ecule by two DMSO mol-ecules. Complex 3 is just the second heteroleptic, mono-nuclear, neutral bis-catecholate complex with TiO6 metal coordination, the only other one being its bis-DMF analogue 6. The two mol-ecules of 3 exhibit a distorted octa-hedral geometry. The geometry and distortions from ideal symmetry of 3 are discussed and compared to 6 and to cationic tris-catecholate titanium complexes.

A ruthenium phthalocyanine functionalized with a folic acid unit as a photosensitizer for photodynamic therapy: Synthesis, characterization andin vitroevaluation

A folate-targeted ruthenium(II) phthalocyanine (Ru(FA-Py)(DMSO)(PEG)[Formula: see text]Pc), endowed with a pyridyl ligand functionalized with one folic acid unit (FA-Py) at one of the two axial coordination sites, and a dimethylsulfoxide (DMSO) ligand coordinated to the other axial position, respectively, is described. In order to enhance its biocompatibility, the RuPc is donated with eight PEG chains attached at the peripheral positions. The observed singlet oxygen quantum yields of the PS measured in DMSO and in water are of 0.74 and 0.36, respectively, in line with those observed for other RuPcs bearing comparable axial and peripheral substitution. In vitro PDT activity of the compound has been evaluated in HT-1376 human bladder cancer cell line. Ru(FA-Py)(DMSO)(PEG)[Formula: see text]Pc revealed a slightly higher cellular uptake than those observed for the corresponding carbohydrate-substituted PSs and a better photodynamic activity compared to the glucose-functionalized RuPc.

Synthesis and Characterization of a Cobalt(III) Corrole with an S‐Bound DMSO Ligand

AbstractWe have synthesized a low‐spin Co(III) complex of 5,15‐bis(4‐nitrophenyl)‐10‐(2‐methylcarboxyphenyl)corrole with an S‐bound dimethylsulfoxide (DMSO) ligand (1DMSO) and determined the coordination mode through X‐ray diffraction for the first time. UV‐vis‐NIR spectral data show that the DMSO ligand does not dissociate in MeCN solution, and EPR results indicate that the first oxidation is ligand centered and suggest that not only DMSO remains bound but a second apical ligand, possibly MeCN, binds to the cobalt center. Multiconfigurational wavefunction electronic structure methods (CASSCF/NEVPT2) allowed us to determine that in the neutral complex the corrole behaves as an innocent trianionic ligand and that the σ‐donor effect of the S atom determines the low‐spin configuration by raising the energy of the Co 3dz2 orbital. While DFT calculations predict a ground open‐shell singlet for both S‐bound and O‐bound DMSO variants, CASSCF/NEVPT2 calculations predict a closed‐shell singlet ground state in both cases. These calculations reproduce considerably well the UV‐vis‐NIR spectrum of 1DMSO in solution, validating the closed‐shell singlet description.

Реакция пентафенилфосфора с гексахлороплатиновой кислотой

Tetraphenylphosphonium hexachloroplatinate (1) was synthesized by the interaction of pentaphenylphosphorus with hexachloroplatinic acid in acetone. The recrystallization of complex 1 from dimethylsulfoxide gave tetraphenylphosphonium dimethylsulfoxidopentachloroplatinate (2). The compounds have been characterized by IR-spectroscopy and X-ray analysis. The absorption bands characterizing stretching vibrations of the phenyl groups are present in the IR spectra, recorded on a Shimadzu IRAffinity-1S Fourier spectrometer in the 4000–400 cm–1 area in KBr pellets. According to the X-ray analysis, the compound unit cell parameters are: triclinic syngony, space group (1, 2), а = 10.205(10), b = 10.970(15), c = 12.160(11) Å (1), а = 7.7667(4), b = 13.3069(7), c = 14.2562(7) Å (2), a = 73,65(4)°, β = 80.64(3)°, g = 77.48° (1), a = 80.972(4)°, β = 88.205(4)°, g = 89.199(4)° (2), V = 1272(2) Å3 (1), 1454.38(13) Å3 (2). The crystals of complexes 1 and 2 consist of the tetrahedral tetraphenylphosphonium cations and octahedral anions. In cations the phosphorus atoms have a slightly distorted tetrahedral environment (the CPC angles are 107.8(3)-113.2(3)° (1), 105.9(3)–112.9(3)° (2), the P-C distance is 1.785(6)-1.805(6) Å (1), 1.783(7)–1.791(6) Å (2). Platinum atoms in the anions of complexes 1 and 2 are hexacoordinated. In complex 2 the dimethyl sulfoxide ligand is coordinated with the Pt atom via the sulfur atom 2.290(2) Å. Complete tables of coordinates of atoms, bond lengths and valence angles are deposited at the Cambridge Structural Data (CCDC 1865783, 829586 http://www.ccdc.cam.ac.uk).

Catena-Poly[barium(II)-μ2-(dimethyl sulfoxide)-κ2 O:O-bis-(μ2-2,4,6-tri-nitro-phenolato-κ4 O 2,O 1:O 1,O 6)

The asymmetric unit of the title barium coordination polymer, [Ba(C6H2N3O7)2(C2H6OS)] n , consists of a barium cation (site symmetry m) and a dimethyl sulfoxide (DMSO) ligand (point group symmetry m) and a 2,4,6-tri-nitro-phenolate anion located in general positions. The S atom and the methyl group of DMSO are disordered over two sets of sites. The DMSO ligand bridges a pair of BaII atoms resulting in a chain extending parallel to the a axis. The unique 2,4,6-tri-nitro-phenolate anion also bridges a pair of BaII ions via the phenolic oxygen atom, with each BaII being additionally bonded to an oxygen atom of an adjacent nitro group. The μ 2-monoatomic bridging binding mode of both types of ligands results in the formation of an infinite chain of face-sharing {BaO10} polyhedra flanked by the remaining parts of the 2,4,6-tri-nitro-phenolato and DMSO ligands. In the one-dimensional coordination polymer, parallel chains are inter-linked with the aid of C-H⋯O hydrogen bonds.

Oxidative Addition of Biphenylene and Chlorobenzene to a Rh(CNC) Complex.

The synthesis and organometallic chemistry of rhodium(I) complex [Rh(CNC–Me)(SOMe2)][BArF 4], featuring NHC‐based pincer and labile dimethyl sulfoxide ligands, is reported. This complex reacts with biphenylene and chlorobenzene to afford products resulting from selective C–C and C–Cl bond activation, [Rh(CNC–Me)(2,2'‐biphenyl)(OSMe2)][BArF 4] and [Rh(CNC–Me)(Ph)Cl(OSMe2)][BArF 4], respectively. A detailed DFT‐based computational analysis indicates that C–H bond oxidative addition of these substrates is kinetically competitive, but in all cases endergonic: contrasting the large thermodynamic driving force calculated for insertion of the metal into the C–C and C–Cl bonds, respectively. Under equivalent conditions the substrates are not activated by the phosphine‐based pincer complex [Rh(PNP‐iPr)(SOMe2)][BArF 4].

Structure of a diorganotelluroxonium(IV) cation, {[2,6-(CH2NMe2)2C6H3Te(μ-O)]2}2+, with the tri-chlorido-(dimethyl sulfoxide)-platinum(II) anion.

In the title salt, di-μ-oxido-bis-{2,6-bis-[(di-methyl-amino)-meth-yl]phenyl-κC 1}tellurium(-IV) bis[tri-chlorido-(dimethyl sulfoxide-κS)platinate(II)], (C24H38N4O2Te2)[PdCl3(C2H6OS)]2, which crystallizes in the triclinic space group P , each Te atom is in a distorted five-coordinated TeO2N2C square-pyramidal geometry (τ values of 0.026 and 0.001) with the C atoms of the phenyl rings occupying the apical positions. The phenyl rings in the [C24H38N4O2Te2]2+ cation are in a cis arrangement to enable this species to participate in Te⋯Cl cation-anion inter-actions. There are also C-H⋯O inter-actions involving the dimethyl sulfoxide ligands and numerous cation-anion and anion-anion C-H⋯Cl inter-actions, which link the ions into a complex three-dimensional array.

SYNTHESIS AND STRUCTURE OF (METHOXYMETHYL)TRIPHENYLPHOSPHONIIUM TRICHLORO(DIMETHYLSULFOXIDO)PLATINATE

(Methoxymethyl)triphenylphosphonium trichloro(dimethylsulfoxido)platinate [Ph3PCH2OCH3][PtCl3(dmso-S)] was synthesized by the reaction of hexachloroplatinic acid with (methoxymethyl)triphenylphosphonium chloride in dimethyl sulfoxide. During the reaction, Pt (IV) was reduced to Pt (II). The reactions are accompanied by the ligand exchange in anions with substitution of the S-coordinated dimethyl sulfoxide molecule for one of chlorine atoms. Slow evaporation of the solvent led to the formation of large orange crystals. The product structure was determined by XRDA. The structures were interpreted by the direct method. Positions and temperature parameters of non-hydrogen atoms were refined in isotropic and then in anisotropic approximations by the full-matrix LSM. The X-ray diffraction pattern of crystal I was carried out on a Bruker D8 QUEST diffractometer. According to the data of X-ray analysis the unit cell crystallographic parameters of compound I are [crystal system monoclinic, space group P21/c, M 686.90, a 14.48(2), b 14.48(2), c 19.99(3) Å]. The tetrahedral configuration of the (methoxymethyl)triphenylphosphonium cation approaches the ideal values (CPC angles are 108.5(2)°-110.3(2)°, bond lengths Р-С are slightly differ from each other). Platinum atoms in anions have square coordination (trans-arranged angles ClPtCl are 177.65(5)°, SPtCl are 178.88(6)°, cis-angles approach 90°). The bond lengths Pt–Cl are equal to 2.290(3)–2.314(3) Å, Pt–S are equal to 2.205(3) Å. The platinum atoms are coordinated by three chlorine atoms and dimethyl sulfoxide molecule in the anion. Dimethyl sulfoxide molecule is coordinated to the platinum atoms by sulfur atoms. The geometry of the coordinated dimethyl sulfoxide ligand [OSC and СSC angles, S−O bond] differs from the geometry of a free dimethyl sulfoxide molecule.

Synthesis and the Effect of Anions on the Spectroscopy and Electrochemistry of Mono(dimethyl sulfoxide)-Ligated Cobalt Corroles.

A new series of cobalt A3-triarylcorroles were synthesized and the compounds examined as to their electrochemical and spectroscopic properties in CH2Cl2 or dimethyl sulfoxide (DMSO) containing 10 different anions added to the solution in the form of tetrabutylammonium salts. The investigated anions were PF6-, BF4-, HSO4-, ClO4-, Br-, I-, Cl-, OAc-, F-, OTs-, and CN-, all but three of which were found to facilitate reduction of the cobalt corrole in dilute CH2Cl2 solutions, as determined by a combination of UV-vis spectroscopy and spectroelectrochemistry. The synthesized corroles are represented as (Ar)3CorCo(DMSO), where Ar is a meso-phenyl group containing one of 10 different electron-donating or -withdrawing substituents. The axial DMSO ligand was found to dissociate in dilute (10-5 M) CH2Cl2 solutions, but this was not the case at the higher electrochemical concentration of 10-3 M, where the investigated corroles exhibit a rich redox reactivity, undergoing up to five reversible one-electron-transfer reactions under the different solution conditions. The reversible half-wave potentials for generation of the singly oxidized corroles varied by over 1.0 V with a change in the electron-donating or -withdrawing meso-phenyl substituents and type of anion added to the solution, ranging from E1/2 = 0.83 V in one extreme to -0.42 V in the other. Much smaller shifts in the potentials (on the order of ∼210 mV) were observed for the reversible first reduction as a function of changes of the anion and/or corrole substituents, with the only exception being in the case of CN-, where the E1/2 values in CH2Cl2 ranged from +0.08 V in solutions containing 0.1 M TBAClO4 to >-1.8 V upon the addition of CN-.

Syntheses and Characterization of a Pair of Isomers of Heteroleptic Bis(Bidentate) Ruthenium(II) Complexes with Two Different Monodentate Ligands.

Two isomers of heteroleptic bis(bidentate) ruthenium(II) complexes with dimethyl sulfoxide (dmso) and chloride ligands, trans(Cl,Nbpy )- and trans(Cl,NHdpa )-[Ru(bpy)Cl(dmso-S)(Hdpa)]+ (bpy: 2,2'-bipyridine; Hdpa: di-2-pyridylamine), are synthesized. This is the first report on the selective synthesis of a pair of isomers of cis-[Ru(L)(L')XY]n+ (L≠L': bidentate ligands; X≠Y: monodentate ligands). The structures of the ruthenium(II) complexes are clarified by means of X-ray crystallography, and the signals in the 1 H NMR spectra are assigned based on 1 H-1 H COSY spectra. The colors of the two isomers are clearly different in both the solid state and solution: the trans(Cl,Nbpy ) isomer has a deep red color, whereas the trans(Cl,NHdpa ) isomer is yellow. Although both complexes have intense absorption bands at λ≈440-450 nm, only the trans(Cl,Nbpy ) isomer has a shoulder band at λ≈550 nm. DFT calculations indicate that the LUMOs of both isomers are the π* orbitals in the bpy ligand, and that the LUMO level of the trans(Cl,Nbpy ) isomer is lower than that of the trans(Cl,NHdpa ) isomer due to the trans effect of the Cl ligand; thus resulting in the appearance of the shoulder band. The HOMO levels are almost the same in both isomers. The energy levels are experimentally supported by cyclic voltammograms, in which these isomers have different reduction potentials and similar oxidation potentials.

Highly Efficient Singlet Oxygen Generators Based on Ruthenium Phthalocyanines: Synthesis, Characterization and in vitro Evaluation for Photodynamic Therapy.

The synthesis of ruthenium(II) phthalocyanines (RuPcs) endowed with one carbohydrate unit-that is, glucose, galactose and mannose-and a dimethylsulfoxide (DMSO) ligand at the two axial coordination sites, respectively, is described. Two series of compounds, one unsubstituted at the periphery, and the other one bearing eight PEG chains at the isoindole meta-positions, have been prepared. The presence of the axial DMSO unit significantly increases the phthalocyanine singlet oxygen quantum yields, related to other comparable RuPcs. The compounds have been evaluated for PDT treatment in bladder cancer cells. In vitro studies have revealed high phototoxicity for RuPcs unsubstituted at their periphery. The phototoxicity of PEG-substituted RuPcs has been considerably improved by repeated light irradiation. The choice of the axial carbohydrate introduced little differences in the cellular uptake for both series of photosensitizers, but the phototoxic effects were considerably higher for compounds bearing mannose units.

Photoinduced Dynamics of a Diazidocobalt(III) Complex Studied by Femtosecond UV-Pump/IR-to-Vis-Probe Spectroscopy.

The photochemistry of the cationic diazidocobalt(III) complex, trans-[Co(cyclam)(N3)2]+, following its ligand-to-metal charge transfer (LMCT) excitation is studied in liquid dimethyl sulfoxide (DMSO) solution using femtosecond spectroscopy with detection in a very broad spectral region covering the near-ultraviolet (near-UV) all the way to the mid-infrared (MIR), thereby enabling a combined probing of electronic and vibrational degrees of freedom of the dynamically evolving system. The initially prepared singlet LMCT-state decays, via the metal-centered singlet excited state, 1MC(1Eg), into the triplet ground state, 3MC (3Eg/3A1g), on a time scale shorter than 25 ps. During this time period, the vibrational spectrum demonstrates uniquely that the nature of the complex changes from a monoazidocobalt(II) species bearing a neutral azide radical ligand immediately after photon absorption to a metal-centered open-shell diazidocobalt(III) species. At the same time, the 3MC state is characterized by a very strong absorption band centered at 710 nm, which can be assigned to a transition to the triplet LMCT state. The 1LMCT lifetime is about 2 ps, whereas that of the excited state, 1MC, is defined by the primary intersystem crossing time of 6 ps. The ensuing intersystem recrossing from 3MC to the parent's singlet ground state, 1A1g, occurs with a rate of 1/(110 ps). The mid-infrared pump-probe spectrum after 1 ns, gives evidence for a heterolytic Co-N bond fission with a quantum yield of ∼5%, leading to free azide anions and the monoazido species, trans-[Co(cyclam)(N3)(OSMe2)]+, featuring an oxygen-bound DMSO ligand in its coordination sphere.