Homoleptic Complexes Research Articles

A Homoleptic Beryllium Carbonyl Complex with an End-On and Side-On Bridging Carbonyl Ligand.

Homoleptic dinuclear beryllium carbonyl cation complexes have been produced and characterized in the gas phase. Infrared photodissociation spectroscopic and theoretical results confirm that Be2 (CO)5 + is a coordination saturated complex that can be assigned to a mixture of two almost isoenergetic structural isomers. Besides a beryllium-beryllium single-bonded (OC)2 Be-Be(CO)3 + isomer, another structure involving an unusual end-on and side-on bridging carbonyl ligand with very low carbonyl stretching frequency is identified.

Diradical Character of Neutral Heteroleptic Bis(1,2-dithiolene) Metal Complexes: Case Study of [Pd(Me2timdt)(mnt)] (Me2timdt = 1,3-Dimethyl-2,4,5-trithioxoimidazolidine; mnt2- = 1,2-Dicyano-1,2-ethylenedithiolate).

The reaction of the bis(1,2-dithiolene) complex [Pd(Me2timdt)2] (1; Me2timdt•– = monoreduced 1,3-dimethyl-2,4,5-trithioxoimidazolidine) with Br2 yielded the complex [Pd(Me2timdt)Br2] (2), which was reacted with Na2mnt (mnt2– = 1,2-dicyano-1,2-ethylenedithiolate) to give the neutral mixed-ligand complex [Pd(Me2timdt)(mnt)] (3). Complex 3 shows an intense solvatochromic near-infrared (NIR) absorption band falling between 955 nm in DMF and 1060 nm in CHCl3 (ε = 10700 M–1 cm–1 in CHCl3). DFT calculations were used to elucidate the electronic structure of complex 3 and to compare it with those of the corresponding homoleptic complexes 1 and [Pd(mnt)2] (4). An in-depth comparison of calculated and experimental structural and vis–NIR spectroscopic properties, supported by IEF-PCM TD-DFT and NBO calculations, clearly points to a description of 3 as a dithione-dithiolato complex. For the first time, a broken-symmetry (BS) procedure for the evaluation of the singlet diradical character (DC) of heteroleptic bis(1,2-dithiolene) complexes has been developed and applied to complex 3. The DC, predominant for 1 (nDC = 55.4%), provides a remarkable contribution to the electronic structures of the ground states of both 3 and 4, showing a diradicaloid nature (nDC = 24.9% and 27.5%, respectively). The computational approach developed here clearly shows that a rational design of the DC of bis(1,2-ditiolene) metal complexes, and hence their linear and nonlinear optical properties, can be achieved by a proper choice of the 1,2-dithiolene ligands based on their electronic structure.

Synthesis of Homo‐ and Heteroleptic Al, Ga and Zn Complexes Containing (Per)fluorinated β‐Diketiminate Ligands

Alkane elimination reactions of equimolar amounts of 17Fnac2H (17Fnac2H = FC[C(CF3)NC6F5]2H) with ZnEt2 and AlMe3 as well as 16Fnac2H (16Fnac2H = HC[C(CF3)NC6F5]2H) with GaMe3 yielded the corresponding heteroleptic complexes of 17Fnac2ZnEt (1), 17Fnac2AlMe2 (2), and 16Fnac2GaMe2 (3), whereas reactions of two equivalents of 16Fnac2H and 17Fnac2H with either ZnEt2 or Cp*2Zn gave homoleptic ZnII complexes (16Fnac2)2Zn (4) and (17Fnac2)2Zn (5), respectively. 1–5 were characterized by IR and NMR spectroscopy (1H, 13C, 19F), elemental analysis and single‐crystal X‐ray diffraction.

Versatile Production of Novel PNP Based Metal Complexes Applicable as Water Reduction Catalysts Showing CH/M as Well as CH/π Interactions

Several PNP‐type ligands of the form bis(dianisylphosphanylmethyl)alkylamine, where alkyl is methyl, ethyl, isopropyl, and benzyl (1–4), have been coordinated to Co(II), Ni(II), Pd(II), and Pt(II) (5–26). This series of water reduction catalysts (WRC) has been characterized by single‐crystal X‐ray structure analysis, multinuclear and 2D NMR spectroscopy, mass spectrometry and a computational study. Intramolecular contact approaches show differences depending on hetero‐ or homoleptic complexes. Both solid state and solution structures indicate an enhancement of steric pressure for the latter. As a consequence CH/M as well as CH/π interactions appear in the X‐ray structures and 1H NMR spectra. They can also be clearly identified by quantum mechanical calculations on a B3LYP level. Since these WRC contain proton relays due to the used PNP‐ligands, they are prone to proton coupled electron transfer (PCET) during photocatalysis. The different steric pressure influences their reorganisation energy. Obviously, the observed intramolecular contact approaches should be regarded as a tool for the design of future WRC.

Optical and Electrical Measurements Reveal the Orientation Mechanism of Homoleptic Iridium-Carbene Complexes.

Understanding and controlling the driving forces for molecular alignment in optoelectronic thin-film devices is of crucial importance for improving their performance. In this context, the preferential orientation of organometallic iridium complexes is in the focus of research to benefit from their improved light-outcoupling efficiencies in organic light-emitting diodes (OLEDs). Although there has been great progress concerning the orientation behavior for heteroleptic Ir complexes, the mechanism behind the alignment of homoleptic complexes is still unclear yet. In this work, we present a sky-blue phosphorescent dye that shows variable alignment depending on systematic modifications of the ligands bound to the central iridium atom. From an optical study of the transition dipole moment orientation and the electrically accessible alignment of the permanent dipole moment, we conclude that the film morphology is related to both the aspect ratio of the dye and the local electrostatic interaction of the ligands with the film surface during growth. These results indicate a potential strategy to actively control the orientation of iridium-based emitters for the application in OLEDs.

Na3FeH7 and Na3CoH6: Hydrogen-Rich First-Row Transition Metal Hydrides from High Pressure Synthesis.

The formation of ternary hydrogen-rich hydrides involving the first-row transition metals TM = Fe and Co in high oxidation states is demonstrated from in situ synchrotron diffraction studies of reaction mixtures NaH–TM–H2 at p ≈ 10 GPa. Na3FeH7 and Na3CoH6 feature pentagonal bipyramidal FeH73– and octahedral CoH63– 18-electron complexes, respectively. At high pressure, high temperature (300 < T ≤ 470 °C) conditions, metal atoms are arranged as in the face-centered cubic Heusler structure, and ab initio molecular dynamics simulations suggest that the complexes undergo reorientational dynamics. Upon cooling, subtle changes in the diffraction patterns evidence reversible and rapid phase transitions associated with ordering of the complexes. During decompression, Na3FeH7 and Na3CoH6 transform to tetragonal and orthorhombic low pressure forms, respectively, which can be retained at ambient pressure. The discovery of Na3FeH7 and Na3CoH6 establishes a consecutive series of homoleptic hydrogen-rich complexes for first-row transition metals from Cr to Ni.

Zirconium and Hafnium Complexes Bearing Salen Ligands for the Polymerization of Ethylene

A series of previously synthesized homoleptic and heteroleptic complexes of zirconium and hafnium were used for the polymerization of ethylene. Upon activation with methylaluminoxane, all the complexes serve as pre-catalysts for the polymerization of ethylene. The effects of polymerization time, reaction temperature, solvents, and methylaluminoxane to catalyst ratio on the polyethylene yield were investigated. The catalyst activity depends on the coordination environment of the metals. The highest activity obtained was 5.91 × 104 g of polyethylene/[(mol of catalyst) h] under the optimized conditions of hexane as a solvent, reaction time and temperature of 30 min and 50°C respectively, and MAO to catalyst ratio of 1000 : 1.

Enhanced Near-Infrared Emission from Eight-Coordinate vs Nine-Coordinate YbIII Complexes Using 2-(5-Methylpyridin-2-yl)-8-hydroxyquinoline.

Enhanced near-infrared (NIR) luminescence from two structurally related heterobinuclear NaIYbIII eight-cooridnate and heterobinuclear YbIIINaI eight-coordinate (CN = 8) complexes is reported and compared to a nine-coordinate (CN = 9) homoleptic complex. For the heteroleptic complex, [Yb(MPQ2)(acac)], the YbIII cation is coordinated to two tridentate 2-(5-methylpyridin-2-yl)-8-quinolinate (MPQ) anions, with a bidentate acetylacetonate (acac) anion completing the coordination sphere. Instead, the heterobinuclear [NaYb(MPQ)4] complex comprises a total of four anionic MPQ ligands, two of which exhibit κ3-coordination to the YbIII cation. The remaining two MPQ anions are unidentate toward the lanthanide and form μ2-bridges via the deprotonated quinolinate oxygens to a bound NaI cation which is also coordinated to the remaining nitrogen donor atoms. The structural properties of these complexes were evaluated by single-crystal X-ray diffraction (SXRD), continuous shape measure (CShM) analysis, and 1H NMR spectroscopy using a diamagnetic LuIII analogue. The corresponding photophysical properties were examined in CH2Cl2 solution by using absorption and emission spectroscopy. For both the complexes, characteristic YbIII emission is observed at ca. 980 nm, with recorded photoluminescence quantum yields (Φobs) and NIR luminescence lifetimes (τobs) of 2.0% and 14.0 μs vs 1.5% and 11.6 μs for the [NaYb(MPQ)4] and [Yb(MPQ)2(acac)] complexes, respectively. Interestingly, the eight-coordinate YbIII complexes both have higher photoluminescence quantum yields when compared to the homoleptic [Yb(MPQ)3] complex, which has a reported quantum yield of 1.0% and a NIR lifetime determined herein of 13.3 μs under identical conditions. These results have been rationalized by considering the overall efficiency of the ligand-centered sensitization process (ηsens = Φisc × Φeet), together with subsequent radiative (kr) and nonradiative (knr) deactivation of the YbIII cation. Moreover, the efficiency of the intersystem crossing (Φisc) and electronic energy transfer (Φeet) processes involved in the antennae effect have been quantified for the new complexes using a combination of nanosecond and femtosecond transient absorption techniques and have been compared to our previous results using [Ln(MPQ)3] complexes with Ln = Yb and Lu.

A Simple Homoleptic Gallium(I) Olefin Complex: Mimicking Transition‐Metal Chemistry at a Main‐Group Metal?

AbstractThe earth‐metal olefin complex [GaI(COD)2]+[Al(ORF)4]− (COD=1,5‐cyclooctadiene; RF=C(CF3)3) constitutes the first homoleptic olefin complex of any main‐group metal accessible as a bulk compound. It is straight forward to prepare in good yield and constitutes an olefin complex of a main‐group metal that—similar to many transition‐metals—may adopt the +1 and +3 oxidation states opening potential applications. Crystallographic‐, vibrational‐ and computational investigations give an insight to the atypical bonding between an olefin and a main‐group metal. They are compared to classical transition‐metal relatives.

Low-Valence Anionic α-Diimine Iron Complexes: Synthesis, Characterization, and Catalytic Hydroboration Studies.

The synthesis of rare anionic heteroleptic and homoleptic α-diimine iron complexes is described. Heteroleptic BIAN (bis(aryl)iminoacenaphthene) complexes 1-[K([18]c-6)(thf)0.5] and 2-[K([18]c-6)(thf)2] were synthesized by reduction of the [(BIAN)FeBr2] precursor complex using stoichiometric amounts of potassium graphite in the presence of the corresponding olefin. The electronic structure of these paramagnetic species was investigated by numerous spectroscopic analyses (NMR, EPR, 57Fe Mössbauer, UV-vis), magnetic measurements (Evans NMR method, SQUID), and theoretical techniques (DFT, CASSCF). Whereas anion 1 is a low-spin complex, anion 2 consists of an intermediate-spin Fe(III) center. Both complexes are efficient precatalysts for the hydroboration of carbonyl compounds under mild reaction conditions. The reaction of bis(anthracene) ferrate(1-) gave the homoleptic BIAN complex 3-[K([18]c-6)(thf)], which is less catalytically active. The electronic structure was elucidated with the same techniques as described for complexes 1-[K([18]c-6)(thf)0.5] and 2-[K([18]c-6)(thf)2] and revealed an Fe(II) species in a quartet ground state.

New Mn(II), Co(II), Ni(II) and Cu(II) homoleptic complexes with 6-chloro-5-7-dimethyl-4oxo-4H-chromene-3-carbaldehydes and its heteroleptic complexes with quinoline-8 ol: synthesis, characterization and antimicrobial activity

In the present study, the synthesis of ligand 6-chloro-5-7-dimethyl-4oxo-4H-chromene-3-carbaldehydes by three steps from the substituted phenol. The formed product in the first step was further processed by fries rearrangement reaction and subsequently Vilsmeier–Haack reaction. Then, its homoleptic and heteroleptic complexes with Mn(II), Co(II), Ni(II) and Cu(II) metal ions by using second ligand quinolin-8-ol were synthesized. The ligand and complexes were characterized by different techniques, such as electron dispersive spectroscopy and elemental analysis (CHN), Fourier transform infrared (FTIR), electronic spectroscopy and magnetic susceptibility, 1H-Nuclear magnetic resonance spectroscopy and mass spectra of ligand, electron spin resonance (ESR), thermogravimetric analysis, powder X-ray diffraction, scanning electron microscopy (SEM) and molar conductivity. The spectroscopic analysis like NMR and the FTIR shows that the both ligands are bidentate in nature. The UV–visible spectra show the homoleptic complex of Cu(II) shows square planer, while M = Ni(II), Co(II) and Mn(II) shows octahedral in nature. While the complexes with heteroleptic ligands from square planer geometry with Cu(II) and Ni(II) while Co(II) and Mn(II) show octahedral geometries. The geometry was also supported by magnetic susceptibility and FTIR spectra. The ESR spectra of Cu(II) complexes shows both are square planer geometry and the G-value was more than 4 indicating the absence of exchange interaction between Cu(II) metal ions in the solid state. The powder X-ray diffraction was used to determine the crystal system of all the complexes, while supporting to this X-ray diffraction the SEM was also taken for the nanostructure of complexes was developed or not. Then, the solution state conductivity of the complexes shows electrolytic in nature. Further, these complexes were evaluated for its antimicrobial activity by agar well diffusion method and structure–activity relationship. The ligands show antimicrobial activity against S.typhi. The Ni(II) does not show antibacterial activity, while complexes Cu(II), Co(II) and Mn(II) shows good activity against the gram-positive and the gram-negative bacteria. The heteroleptic ligand complex (6) of Cu(II) shows higher antifungal activity as compared with Ni(II), Co(II) and Mn(II) complexes.

Synthesis and structure of mono and bis {1,3-bis(2- pyridylimino)isoindoline} supported 3d transition metal complexes

Series of homoleptic and heteroleptic 3d transition metal complexes were prepared in analytically pure form and high yield, by reacting appropriate metal precursors with 1,3-bis(2-pyridylimino)isoindolate (BPIH) ligand under suitable reaction conditions. The complexes were characterized by various spectro-analytical techniques, including IR, UV, NMR, ESI Mass and X-ray crystal analysis. A distorted octahedral structure containing two meridionally coordinating BPI ligands was assigned to all the homoleptic complexes. While, for the heteroleptic complexes, a highly distorted square pyramidal geometry, with a planar tridentate BPI ligand coordinating to the metal center along with chloro and aqua ligands was assigned. Considering the unique structural features of the complexes, potential catalytic applications are envisaged.

Unsaturated and Benzannulated N-Heterocyclic Carbene Complexes of Titanium and Hafnium: Impact on Catalysts Structure and Performance in Copolymerization of Cyclohexene Oxide with CO2.

Tridentate, bis-phenolate N-heterocyclic carbenes (NHCs) are among the ligands giving the most selective and active group 4-based catalysts for the copolymerization of cyclohexene oxide (CHO) with CO2. In particular, ligands based on imidazolidin-2-ylidene (saturated NHC) moieties have given catalysts which exclusively form polycarbonate in moderate-to-high yields even under low CO2 pressure and at low copolymerization temperatures. Here, to evaluate the influence of the NHC moiety on the molecular structure of the catalyst and its performance in copolymerization, we extend this chemistry by synthesizing and characterizing titanium complexes bearing tridentate bis-phenolate imidazol-2-ylidene (unsaturated NHC) and benzimidazol-2-ylidene (benzannulated NHC) ligands. The electronic properties of the ligands and the nature of their bonds to titanium are studied using density functional theory (DFT) and natural bond orbital (NBO) analysis. The metal–NHC bond distances and bond strengths are governed by ligand-to-metal σ- and π-donation, whereas back-donation directly from the metal to the NHC ligand seems to be less important. The NHC π-acceptor orbitals are still involved in bonding, as they interact with THF and isopropoxide oxygen lone-pair donor orbitals. The new complexes are, when combined with [PPN]Cl co-catalyst, selective in polycarbonate formation. The highest activity, albeit lower than that of the previously reported Ti catalysts based on saturated NHC, was obtained with the benzannulated NHC-Ti catalyst. Attempts to synthesize unsaturated and benzannulated NHC analogues based on Hf invariably led, as in earlier work with Zr, to a mixture of products that include zwitterionic and homoleptic complexes. However, the benzannulated NHC-Hf complexes were obtained as the major products, allowing for isolation. Although these complexes selectively form polycarbonate, their catalytic performance is inferior to that of analogues based on saturated NHC.

A Stable Homoleptic Organometallic Iron(IV) Complex.

A homoleptic organometallic FeIV complex that is stable in both solution and in the solid state at ambient conditions has been synthesized and isolated as [Fe(phtmeimb)2](PF6)2 (phtmeimb=[phenyl(tris(3‐methylimidazolin‐2‐ylidene))borate]−). This FeIV N‐heterocyclic carbene (NHC) complex was characterized by 1H NMR, HR‐MS, elemental analysis, scXRD analysis, electrochemistry, Mößbauer spectroscopy, and magnetic susceptibility. The two latter techniques unequivocally demonstrate that [Fe(phtmeimb)2](PF6)2 is a triplet FeIV low‐spin S=1 complex in the ground state, in agreement with quantum chemical calculations. The electronic absorption spectrum of [Fe(phtmeimb)2](PF6)2 in acetonitrile shows an intense absorption band in the red and near IR, due to LMCT (ligand‐to‐metal charge transfer) excitation. For the first time the excited state dynamics of a FeIV complex was studied and revealed a ≈0.8 ps lifetime of the 3LMCT excited state of [Fe(phtmeimb)2](PF6)2 in acetonitrile.

Electronic and molecular characterization of an air-stable Cr(II) complex containing azo-anion-radicals

A new mononuclear homoleptic chromium complex has been synthesized by reaction of one equiv. of Cr(CO)6 with two equiv. of the azoaromatic pincer ligand namely 2,6-bis[(4-methylphenyl)azo]pyridine [LMe] in n-octane under reflux condition. The complex has been fully characterized by ESI-MS, 1H-NMR, FT-IR and UV/Vis spectroscopy. The X-ray structure of the complex reveals that the Cr-metal is coordinated to the central pyridine N-atom and two azo N-atoms of each tridentate pincer ligand in an octahedral environment. The 1H-NMR spectrum of the complex is indicative of diamagnetic ground state. The elongation of N-N bond lengths [d(N-N)av = 1.3275 Å] in the complex is consistent with the presence of azo-anion-radical character in the ligand. Since 2,6-bis(phenylazo)pyridine and its 4-Me-derivative are redox non-innocence in nature and therefore can coordinate to the chromium metal center as neutral (L0) or as mono-anionic mono-radical (L·)1− or as di-anionic di-radical (L··)2- or even as tri-anionic mono-radical (L·)3− resulting an ambiguity on the true oxidation state of the metal center. Thus the present work nicely elaborates the importance of suitably designed bis-azopyridine containing pincer ligand in accessing an air-stable Cr(II) complex starting with low-valent metal carbonyl precursor via electron transfer from the metal center to the highly π-acidic ligand leading to stable azo-anion-radicals. The stability of azo-anion-radical bound Cr(II) complex has been investigated by DFT calculations.

Isolation of a Homoleptic Non-oxo Mo(V) Alkoxide Complex: Synthesis, Structure, and Electronic Properties of Penta-tert-Butoxymolybdenum.

Treatment of [MoCl4(THF)2] with MOtBu (M = Na, Li) does not result in simple metathetic ligand exchange but entails disproportionation with formation of the well-known dinuclear complex [(tBuO)3Mo≡Mo(OtBu)3] and a new paramagnetic compound, [Mo(OtBu)5]. This particular five-coordinate species is the first monomeric, homoleptic, all-oxygen-ligated but non-oxo 4d1 Mo(V) complex known to date; as such, it proves that the dominance of the Mo=O group over (high-valent) molybdenum chemistry can be challenged. [Mo(OtBu)5] was characterized in detail by a combined experimental/computational approach using X-ray diffraction; UV/vis, MCD, IR, EPR, and NMR spectroscopy; and quantum chemistry. The recorded data confirm a Jahn–Teller distortion of the structure, as befitting a d1 species, and show that the complex undergoes Berry pseudorotation. The alkoxide ligands render the disproportionation reaction, leading the formation of [Mo(OtBu)5] to be particularly facile, even though the parent complex [MoCl4(THF)2] itself was also found to be intrinsically unstable; remarkably, this substrate converts into a crystalline material, in which the newly formed Mo(III) and Mo(V) products cohabitate the same unit cell.

Two‐Coordinate Cu(I) and Au(I) Complexes Supported by BICAAC and CAAC Ligands

AbstractTwo‐coordinate Cu(I) and Au(I) complexes supported by bicyclic (alkyl)(amino)carbene, [BICAAC‐CuCl] (1), [BICAAC‐CuI] (2), [(BICAAC)2Cu]+[PF6]– (3) and [(BICAAC)2Au]+[AuCl2]– (6) have been synthesized. The reaction of cyclic (alkyl)(amino)carbene, CAACcy with CuCl afforded [CAACcy‐CuCl] (4) and its further reaction with KPF6 gave [(CAACcy)2Cu]+[PF6]– (5). Complexes 1–6 have been characterized by multinuclear NMR, IR and UV‐Vis., spectroscopic method and high‐resolution mass spectrometry (HRMS). Single crystal X‐ray structure of heteroleptic complexes 1 and 4 and homoleptic complexes [(BICAAC)2Cu]+[CuI2]– (2’), 3 and 6 have also been determined. The crystal structure of these complexes confirmed linear two‐coordinate geometry around the metal centers. In the solid‐ state, complexes 1, 2’, 4 and 6 displayed C−H⋯M (M=Cu, Au) and weak non‐covalent C−H⋯X (X=Cl, I) and C−H⋯H−C interactions. Computational calculations correlate well to the experimentally observed geometry and help elucidate the absorption characteristics type of transitions and the frontier orbitals involved in them.

Filling a Gap: The Coordinatively Saturated Group 4 Carbonyl Complexes TM(CO)8 (TM=Zr, Hf) and Ti(CO)7.

Homoleptic Group 4 metal carbonyl cation and neutral complexes were prepared in the gas phase and/or in solid neon matrix. Infrared spectroscopy studies reveal that both zirconium and hafnium form eight‐coordinate carbonyl neutral and cation complexes. In contrast, titanium forms only the six‐coordinate Ti(CO)6 + and seven‐coordinate Ti(CO)7. Titanium octacarbonyl Ti(CO)8 is unstable as a result of steric repulsion between the CO ligands. The 20‐electron Zr(CO)8 and Hf(CO)8 complexes represent the first experimentally observed homoleptic octacarbonyl neutral complexes of transition metals. The molecules still fulfill the 18‐electron rule, because one doubly occupied valence orbital does not mix with any of the metal valence atomic orbitals. Zr(CO)8 and Hf(CO)8 are stable against the loss of one CO because the CO ligands encounter less steric repulsion than Zr(CO)7 and Hf(CO)7. The heptacarbonyl complexes have shorter metal−CO bonds than that of the octacarbonyl complexes due to stronger electrostatic and covalent bonding, but the significantly smaller repulsive Pauli term makes the octacarbonyl complexes stable.

Synthesis and crystallographic characterisation of a homologous series of bis-tridentate phosphine oxide NP3O3 Fe(II), Co(II), Ni(II) and Cu(II) complexes

Despite the large numbers of mono- and bidentate phosphine oxide complexes, examples of well characterised discrete multidentate phosphine oxide transition metal complexes are relatively rare. Herein, we report the coordination chemistry of the triphosphine oxide ligand N{CH2P(O)Ph2}3 (NP3O3, 1) with a series of first row transition metals. Ligand 1 was found to form a series of bis-tridentate homoleptic complexes with Fe(II), Co(II), Ni(II) and Cu(II) salts of the type M(BF4)2·6H2O. The anion exchange reaction of BF4— for BPh4— aided in the crystallisation of three of the four complexes. X-Ray crystallographic analysis of this series: [Fe(N{CH2P(O)Ph2}3)2](BPh4)2 (2), [Co(N{CH2P(O)Ph2}3)2](BPh4)2 (3), [Ni(N{CH2P(O)Ph2}3)2](BPh4)2 (4) and [Cu(N{CH2P(O)Ph2}3)2](BF4)2 (5) confirmed either almost idealised octahedral or distorted octahedral structures and tridentate coordination of 1. Complex 5, Cu(II) d9, displayed a classic Jahn-Teller distortion showing a prominent elongation of the axial M–O bonds. All complexes were found to be paramagnetic which precluded NMR spectroscopy analysis. Magnetic susceptibility measurements on solid samples of the complexes confirmed their number of unpaired electrons and high spin states.

The Coordination Behaviour of CuI Photosensitizers Bearing Multidentate Ligands Investigated by X-ray Absorption Spectroscopy.

A systematic series of four novel homo‐ and heteroleptic CuI photosensitizers based on tetradentate 1,10‐phenanthroline ligands of the type X^N^N^X containing two additional donor moieties in the 2,9‐position (X=SMe or OMe) were designed. Their solid‐state structures were assessed by X‐ray diffraction. Cyclic voltammetry, UV‐vis absorption, emission and X‐ray absorption spectroscopy were then used to determine their electrochemical, photophysical and structural features in solution. Following, time‐resolved X‐ray absorption spectroscopy in the picosecond time scale, coupled with time‐dependent density functional theory calculations, provided in‐depth information on the excited state electron configurations. For the first time, a significant shortening of the Cu−X distance and a change in the coordination mode to a pentacoordinated geometry is shown in the excited states of the two homoleptic complexes. These findings are important with respect to a precise understanding of the excited state structures and a further stabilization of this type of photosensitizers.