Imidazo-pyridine-based zinc(II) complexes as fluorescent hydrogen sulfide probes

In this work we explore the interaction of HS^- with a family of fluorescent zinc complexes. In particular we selected a family of complexes with N,O-bidentate ligands aiming at assessing whether the zinc-chelating ligand plays a role in influencing the reactivity of HS^- with the complexes under investigation. Different experiments, performed by diverse spectroscopic techniques, provide evidence that HS^- binds the zinc center of all the complexes included in this study. The results highlight the potential of the devised systems to be used as HS^-/H₂S fluorescent sensors via a coordinative-based approach. To shed light on the species formed in solution when HS^-/H₂S interacts with the title complexes and aiming to rationalize the photophysical properties of the sensing constructs, we performed a computational analysis based on the time dependent density functional theory (TD-DFT). Preliminary bio-imaging experiments were also performed and the results indicate the potential of this class of compounds as probes for the detection of H₂S in living cells.

Driving the Emission Towards Blue by Controlling the HOMO-LUMO Energy Gap in BF2 -Functionalized 2-(Imidazo[1,5-a]pyridin-3-yl)phenols

Several boron compounds with 2-(imidazo[1,5-a]pyridin-3-yl)phenols, differentiated by the nature of the substituent (R) in the para position of the hydroxy group, have been synthesized and thoroughly characterized both in solution (1 H, 13 C, 11 B, 19 F NMR) and in the solid state (X-ray). All derivatives displayed attractive photophysical properties like very high Stokes shift, high fluorescence quantum yields and a good photostability in solution. Time-Dependent Density Functional Theory (TD-DFT) calculations allowed to define the main electronic transitions as intra ligand transitions (1 ILT), which was corroborated by the Natural Transition Orbitals (NTOs) shapes. The HOMO-LUMO energy gap was correlated to the electronic properties of the substituent R on the phenolic ring, as quantified by its σp Hammett constant.

A silver(i) coordination polymer with sodium 3,5-dimethyl-4-sulfonate pyrazolate: a nice example of PXRD structure solution and time-driven crystallization

A silver(i) coordination polymer with the sodium salt of 3,5-dimethyl-4-sulfonate pyrazole (HL_Na) has been prepared and structurally characterized by ab initio X-ray powder diffraction.

Phosphorescence enhancement by close metal–metal interaction in T1 excited state in a dinuclear copper(i) complex

Combined experimental and theoretical study on a phosphorescent copper(i) complex, showing high electron density between metals in the triplet excited state.

Interpretation of Tolman electronic parameters in the light of natural orbitals for chemical valence

Understanding the nature and the strength of metal-ligand interactions in d- and f-block metal complexes has always been a central issue for both synthetic and theoretical chemists. These interactions are usually described according to the well accepted Dewar-Chatt-Duncanson model, and thus over the years numerous research groups directed their efforts to shed light on the role of σ- and π-contributions. Among others, the electronic parameter introduced by Tolman in the 1970s represents a milestone in this field. Herein we present a quantitative description of the nickel-phosphine bond in Tolman's nickel(0) carbonyl complexes. The combination of Natural Orbitals for Chemical Valence with Energy Decomposition Analysis resulted in the definition of a new parameter (T^phos) which comprises all the energetic contributions needed to describe the nickel-phosphine bond and thus stands as a reliable descriptor of the electronic properties of phosphines. Moreover, steric effects of phosphines (i.e. Tolman's cone angles) have been considered too, and a linear relation including Ni-P bond distances, T^phos and cone angle has been found.

A phosphorescent copper(i) coordination polymer with sodium 3,5-dimethyl-4-sulfonate pyrazolate

A phosphorescent copper(i) coordination polymer has been synthesized and characterized via ab initio PXRD.

Tuning the fluorescence emission in mononuclear heteroleptic trigonal silver(i) complexes

Mononuclear heteroleptic trigonal planar silver(i) complexes have been prepared and characterized, both in solution and in the solid state. Their luminescent behavior was investigated, showing a tunable emission maxima according to the electronic properties of the phosphorous ligand, in the solid state.

Synthesis and ab-initio XRPD structure of group 12 imidazolato polymers

Two new 3D homoleptic binary imidazolates, Cd(im)2 and Hg(im)2 (Him = imidazole), as well as [Hg(im)]NO3, containing 1D polycations of [Hg(im)]n(n+) formulation, have been prepared and characterized by ab-initio XRPD methods.

One-dimensional polymers containing strictly collinear metal ions: synthesis and XRPD characterization of homoleptic binary metal pyrazolates

The synthesis of a number of 3d transition metal binary pyrazolates in microcrystalline form, thus suitable for a full XRPD characterization, has been pursued. The crystal and molecular structures of the Fe(pz)3, Co(pz)2, Co(pz)3, and Ni(pz)2 polymers, together with the few congeners reported in the recent literature, show that these species tend to afford highly crystalline materials where strictly collinear chains of metal atoms are present. Depending on the synthetic strategy used, Ni(pz)2 has been found to crystallize as two different alpha (orthorhombic) and beta (monoclinic) phases, possessing nearly identical intramolecular features. Data for each compound follow. Fe(pz)3: C9H9FeN6, hexagonal, P63/m, a = 9.1745(3) A, c = 7.2191(4) A, Z = 2. Co(pz)2: C6H6CoN4, orthorhombic, Ibam, a = 7.5239(5) A, b = 14.3461(9) A, c = 7.4331(5) A, Z = 4. Co(pz)3: C9H9CoN6, hexagonal, P63/m, a = 9.1966(3) A, c = 7.1051(3) A, Z = 2. Alpha-Ni(pz)2: C6H6N4Ni, orthorhombic, Cmcm, a = 16.6758(11) A, b = 6.4872(4) A, c = 6.9423(6) A, Z = 4. Beta-Ni(pz)2: C6H6N4Ni, monoclinic, P21/m, a = 9.967(2) A, b = 6.975(1) A, c = 6.016(1), A, beta = 98.50(1)degrees, Z = 2. The thermal stability and the detailed structural properties of these model compounds have been evaluated, in the light of the technologically relevant crystal phases (the well-known metal-diazolates showing reversible spin-crossover or spin-transition behavior) obtainable upon doping, magnetic dilution, and ring substitution (in the 4-position).

Metal imidazolato complexes: synthesis, characterization, and X-ray powder diffraction studies of group 10 coordination polymers

Binary metal imidazolates of the group 10 metals have been prepared and typically found amorphous. However, the intermediacy of a number of (poly)crystalline species during their formation has been evidenced; their selective preparation and characterization, by chemical, spectroscopic, and thermal methods and their structure solution by the ab initio X-ray powder diffraction technique lead to the discovery of new interesting structural features, such as those of polymeric Ni(Him)(2)(im)(CH(3)COO) (Him = imidazole) and of the hydrogen-bonded polymers of general Pd(x)Pt(1-x)(Him)(2)(im)(2) formula (x = 0, 0.5, 1). The latter are built upon 2D frameworks of (pseudo)square meshes, which, in the pure Pd derivative, form an entangled structure based upon interpenetrating 2D layers, coupled in pairs. The different structures are discussed in terms of different conformations of the new "im-H-im" ligand, which acts as monoanionic exobidentate fragment, similar to im, pyrazolate (pz), "pz-H-pz", and pyrimidin-2-olate.

Metal Pyrazolato Complexes. Synthesis, Characterization, and X-ray Powder Diffraction Studies of Group 12 Coordination Polymers

A number of polymeric pyrazolato complexes have been prepared and characterized by spectroscopy, thermal analyses (DSC and TGA), and X-ray powder diffraction (XRPD) methods. Ab initio XRPD studies showed that the (isomorphous) [Zn(pz)(2)](n)() and [Cd(pz)(2)](n)() species (Hpz = pyrazole) are 1-D polymers containing tetrahedrally coordinated metals and M(&mgr;-pz)(2)M (M = Zn, Cd) bridges, much alike [Cu(pz)(2)](n)() [orthorhombic, Ibam, a = 7.4829(4), b = 14.3844(6), c = 7.3831(3) Å (Zn) and a = 7.8591(6), b = 13.652(1), c = 7.9165(4) Å (Cd)]; differently, Hg(pz)(2) [triclinic, P&onemacr;, a = 7.4097(3), b = 9.4474(3), c = 5.8345(3) Å, alpha = 96.310(2), beta = 96.752(3), and gamma = 73.694(2) degrees ] is best described as a mononuclear complex, containing two monodentate pyrazolato ligands loosely interacting, through long(er) Hg.N contacts with neighboring molecules. During the synthesis of the latter, an intermediate phase was obtained, and characterized as Hg(pz)NO(3), which contains a polymeric polycation, [Hg(pz)](n)()(n)()(+), based on Hg(&mgr;-pz)Hg bridges, and uncoordinated NO(3)(-) groups (orthorhombic, Pcmn, a = 17.2985(9), b = 5.2538(3), c = 7.3912(4) Å). All structures were ultimately refined by the Rietveld method.

Syntheses, Structures, and Reactivity of Polynuclear Pyrazolato Copper(I) Complexes, Including an ab-Initio XRPD Study of [Cu(dmnpz)](3) (Hdmnpz = 3,5-Dimethyl-4-nitropyrazole)

The reaction of [Cu(CH(3)CN)(4)](BF(4)) with 3,5-dimethyl-4-nitropyrazole (Hdmnpz) in the presence of triethylamine yields the new copper(I) complexes [Cu(dmnpz)](3) (1) and (Et(3)NH)(2)[Cu(4)(dmnpz)(6)] (2), depending on the experimental conditions. The reactivity of 1 and 2 toward neutral ligands such as triphenylphosphine, cyclohexyl isocyanide (RNC), and carbon monoxide has been investigated. In particular, both complexes readily react with RNC, giving the dinuclear complexes [Cu(dmnpz)(RNC)](2) (4) and [Cu(dmnpz)(RNC)(2)](2) (5), depending on the copper/RNC ratio, and with PPh(3), affording the dimeric derivative [Cu(dmnpz)(PPh(3))](2) (6). The crystal and molecular structure of 1 has been determined ab initio using X-ray powder diffraction data from conventional laboratory equipment. Crystals of 1 are monoclinic, C2/c, a = 20.057(2) Å, b = 13.816(2) Å, c = 7.883(1) Å, beta = 95.912(4) degrees; R(F) and R(wp) 0.067 and 0.039, respectively, for Rietveld refinement on 3900 data points collected in the range 17 < 2theta < 95 degrees (Cu Kalpha radiation). Crystals of 1 contain planar trimers, with the copper atoms bridged by exo-bidentate ligands and short intermolecular Cu.Cu contacts (3.329(7) Å). For complexes 2 and 4-6, single-crystal X-ray diffraction studies have been performed. Crystals of 2 are monoclinic, P2(1)/c, a = 11.026(1) Å, b = 13.456(2) Å, c = 18.668(5) Å, beta = 92.91(2) degrees, Z = 2. The ionic packing of 2 contains tetranuclear complexes, with the copper atoms connected by six dmnpz ligands. Crystals of 4 are triclinic, P&onemacr;, a = 7.418(1) Å, b = 9.780(1) Å, c = 11.177(3) Å, alpha = 109.61(2); beta = 101.34(3) degrees, gamma = 105.82(1) degrees, Z = 2. Crystals of 5 are triclinic, P&onemacr;, a = 9.506(4) Å, b = 9.957(2) Å, c = 11.658(4) Å, alpha = 86.73(2) degrees, beta = 79.54(2) degrees, gamma = 82.47(4) degrees, Z = 1. Crystals of 6 are triclinic, P&onemacr;, a = 11.379(2) Å, b = 13.592(2) Å, c = 14.409(3) Å, alpha = 81.22(1) degrees, beta = 85.21(1) degrees, gamma = 87.55(1) degrees, Z = 2. 4, 5, and 6 are binuclear complexes bearing one RNC, two RNC, and one triphenylphosphine ligands on each copper atom, respectively. The steric requirement of the dmnpz ligands, in the presence of RNC or PPh(3), forces the inner [Cu(2)(dmnpz)(2)] core of the three complexes into markedly different conformations.

Silver(I) Pyrazolates. Synthesis and X-ray and (31)P-NMR Characterization of Triphenylphosphine Complexes and Their Reactivity toward Heterocumulenes

Silver(I) pyrazolate was reacted with triphenylphosphine, leading to the dinuclear [Ag(2)(pz)(2)(PPh(3))(2)] and [Ag(2)(pz)(2) (PPh(3))(3)] complexes (Hpz = pyrazole), which were extensively characterized by (31)P-NMR methods and single-crystal X-ray analyses. Crystals of [Ag(2)(pz)(2)(PPh(3))(2)] are triclinic, space group P&onemacr;, with a = 9.567(2) Å, b = 11.440(2) Å, c = 10.073(2) Å, alpha = 93.59(2) degrees, beta = 64.01(2) degrees, gamma = 107.24(2) degrees, Z = 1, and D(calc) = 1.539 g.cm(-)(3); final R = 0.028 for 2532 independent reflections having F > 4sigma(F). They contain centrosymmetric dimers with trigonally coordinated silver atoms, which are 3.870(1) Å apart. Crystals of [Ag(2)(pz)(2) (PPh(3))(3)] are triclinic, space group P&onemacr;, with a = 9.752(2) Å, b = 14.163(2) Å, c = 20.450(2) Å, alpha = 101.84(1) degrees, beta = 99.83(2) degrees, gamma = 100.68(2) degrees, Z = 2, and D(calc) = 1.424 g.cm(-)(3); final R = 0.025 for 7075 independent reflections having F > 4sigma(F). Each molecule contains two inequivalent silver ions, bearing one and two phosphines, respectively, and a Ag(&mgr;-pz)(2)Ag ring with a rare twisted conformation. Both complexes readily react with heterocumulenes such as CS(2), COS, CO(2), and RNCO, affording new derivatives, the nature of which is dependent on the experimental conditions. Single-crystal X-ray analysis of [Ag(pz-CS(2))(PPh(3))(2)] has shown the unexpected S,S coordination of the pyrazolecarbodithioate fragment. Its crystals are triclinic, space group P&onemacr;, with a = 10.329(4) Å, b = 13.082(2) Å, c = 14.284(3) Å, alpha = 86.71(2) degrees, beta = 75.14(2) degrees, gamma = 74.79(2) degrees, Z = 2, and D(calc) = 1.431 g.cm(-)(3); final R = 0.028 for 5179 independent reflections having F > 4sigma(F).