Silver(i) complexes of bis- and tris-(pyrazolyl)azine derivatives - dimers, coordination polymers and a pentametallic assembly

Ligand-Directed Metalation of a Gold Pyrazolate Cluster

Solid "[AuL]" (HL = 3-[pyrid-2-yl]-5-tertbutyl-1H-pyrazole) can be crystallized as cyclic [Au₃(μ-L)₃] and [Au₄(μ-L)₄] clusters from different solvents. The crystalline tetramer contains a square Au₄ core with an HT:TH:TH:HT arrangement of ligand substituents, which preorganizes the cluster to chelate to additional metal ions via its pendant pyridyl groups. The addition of 0.5 equiv of AgBF₄ to [AuL] yields [Ag₂Au₄(μ₃-L)₄][BF₄]₂, where two edges of the Au₄ square are spanned by Ag⁺ ions via metallophilic Ag···Au contacts. Treatment of [AuL] with [Cu(NCMe)₄]PF₆ affords the metalloligand helicate [Cu₂Au₂(μ-L)₄][PF₆]₂, via oxidation of the copper and partial fragmentation of the cluster.

Bis(2,6-pyrazolyl)pyridines as a New Scaffold for Coordination Polymers

Two coordination polymers, Fe(L^OBF₃)(CH₃COO)(CH₃CN)₂]_n•nCH₃CN and [Fe(L^O-)₂AgNO₃BF₄•CH₃OH]_n•1.75nCH₃OH•nH₂O (L^O- = 3,3'-(4-(4-cyanophenyl)pyridine-2,6-diyl)bis(1-(2,6-dichlorophenyl)-1H-pyrazol-5-olate)), were obtained via a PCET-assisted process that uses the hydroxy-pyrazolyl moiety of the ligand and the iron(II) ion as sources of proton and electron, respectively. Our attempts to produce heterometallic compounds under mild conditions of reactant diffusion resulted in the first coordination polymer of 2,6-bis(pyrazol-3-yl)pyridines to retain the core N₃(L)MN₃(L). Under harsh solvothermal conditions, a hydrogen atom transfer to the tetrafluoroborate anion caused the transformation of the hydroxyl groups into OBF₃ in the third coordination polymer of 2,6-bis(pyrazol-3-yl)pyridines. This PCET-assisted approach may be applicable to produce coordination polymers and metal-organic frameworks with the SCO-active core N₃(L)MN₃(L) formed by pyrazolone- and other hydroxy-pyridine-based ligands.

Turn-on fluorescence in a pyridine-decorated tetraphenylethylene: the cooperative effect of coordination-driven rigidification and silver ion induced aggregation

A newly designed TPE ligand displayed a large fluorescence enhancement in the presence of silver ions in a dilute solution, leading to tunable fluorescence properties by simply mixing AIE and ACQ molecules.

Molecular squares, coordination polymers and mononuclear complexes supported by 2,4-dipyrazolyl-6H-1,3,5-triazine and 4,6-dipyrazolylpyrimidine ligands

The Fe[BF4]2 complex of 2,4-di(pyrazol-1-yl)-6H-1,3,5-triazine (L1) is a high-spin molecular square, [{Fe(L1)}4(μ-L1)4][BF4]8, whose crystals also contain the unusual HPzBF3 (HPz = pyrazole) adduct. Three other 2,4-di(pyrazol-1-yl)-6H-1,3,5-triazine derivatives with different pyrazole substituents (L2-L4) are unstable in the presence of first row transition ions, but form mononuclear, polymeric or molecular square complexes with silver(i). Most of these compounds involve bis-bidentate di(pyrazolyl)triazine coordination, which is unusual for that class of ligand, and the molecular squares encapsulate one or two BF4-, ClO4- or SbF6- ions through combinations of anionπ, AgX and/or C-HX (X = O or F) interactions. Treatment of Fe[NCS]2 or Fe[NCSe]2 with 4,6-di(pyrazol-1-yl)-2H-pyrimidine (L5) or its 2-methyl and 2-amino derivatives (L6 and L7) yields mononuclear [Fe(NCE)2L2] and/or the 1D coordination polymers catena-[Fe(NCE)2(μ-L)] (E = S or Se, L = L5-L7). Alcohol solvates of isomorphous [Fe(NCS)2L2] and [Fe(NCSe)2L2] compounds show different patterns of intermolecular hydrogen bonding, reflecting the acceptor properties of the anion ligands. These iron compounds are all high-spin, although annealing solvated crystals of [Fe(NCSe)2(L5)2] affords a new phase exhibiting an abrupt, low-temperature spin transition. Catena-[Fe(H2O)2(μ-L5)][ClO4]2 is a coordination polymer of alternating cis and trans iron centres.

A series of helical coordination polymers based on two racemic bis(pyridylmethylene) propane-1,2-diamine ligands: relationship of conformations, structures and properties

The self-assembly of d¹⁰ metal salts and two racemic bis(pyridyl) diamine ligands generates ten complexes, showing diverse helical and wavelike chains, (4,4) layers, as well as 3D sqc and uog nets.

Heterometallic Coordination Polymer Gels Supported by 2,4,6-Tris(pyrazol-1-yl)-1,3,5-triazine

Complexes of type [M(tpt)₂]X₂ (M²⁺ = Fe²⁺, Co²⁺, Ni²⁺; tpt = 2,4,6-tri{pyrazol-1-yl}-1,3,5-triazine; X^- = BF₄ ^- or ClO₄ ^-) crystallize in a cubic lattice, with the metal ion and ligand conformation showing unusual symmetry-imposed disorder. Addition of 1 equiv AgX to the corresponding preformed [M(tpt)₂]X₂ salt in concentrated MeNO₂ solution affords thixotropic gels. Gelation was not observed in analogous reactions using [Mn(tpt)₂][ClO₄]₂, or from reactions in other, more donating solvents. Scanning electron microscopy (SEM) images from dilute solutions of the reagents confirmed the fibrous microstructure of the gels and their homogeneous elemental composition. However, energy-dispersive X-ray data show a reduced Fe/Ag ratio compared to the Co/Ag and Ni/Ag gels, where a 1:1 ratio of metals is evident. More concentrated gels decomposed to silver nanoparticles during SEM sample preparation. Mass spectrometry and ¹H NMR indicate that silver induces partial ligand displacement reactions in [Fe(tpt)₂]²⁺ and [Co(tpt)₂]²⁺, but not in [Ni(tpt)₂]²⁺. Hence, the strength of the gels, which follows the order M = Mn (no gel) < Fe < Co < Ni, correlates with the stability of octahedral [M(tpt)₂]²⁺ under gelation conditions. Iron(II) complexes of the related ligands 2,4,6-tri{pyrazol-1-yl}pyridine (tpp) and 2,4,6-tri{pyrazol-1-yl}pyrimidine (tpym) did not undergo gelation with silver salts under the above conditions. The unique properties of tpt as a gelator in this work may reflect the crystallographically observed ability of metal-coordinated tpt to chelate to exogenous silver ions, through its pendant pyrazolyl group and triazinyl N donors. In contrast, the pendant azolyl substituents in silver complexes of the nongelators tpp and tpym only bind exogenous silver in monodentate fashion.