Isolation of a Pentadentate Ligand and Stepwise Synthesis, Structures, and Magnetic Properties of a New Family of Homo- and Heterotrinuclear Complexes

The effect of anions in the synthesis and structure of pyrazolylamidino copper(II) complexes

Six new pyrazolylamidino Cu(II) complexes are synthesized directly from the reactions of Cu(X)₂ salts (X = ClO₄^-, BF₄^-, or Cl^-) and pyrazole (pzH) in nitrile solution (RCN, R = Me or Et) at 298 K via the metal-mediated coupling of RCN with pzH: [Cu(HNC(R)pz)₂(X)₂] (X = ClO₄^- or BF₄^-, R = Me, 1 or 7 and Et, 2 or 8, respectively) and dichloro Cu(II) complexes [Cu₂Cl₂(μ-Cl)₂(HNC(Me)pz)₂] (3) and [CuCl₂(HNC(Et)pz)] (4). Four more new complexes, [Cu₂(μ-Cl)₂(HNC(Me)pz)₂(pzH)₂][X]₂ (X = ClO₄^-, 5 and BF₄^-, 9) and [Cu₂(μ-Cl)₂(HNC(Et)pz)₂(pzH)₂(X)₂] (X = ClO₄^-, 6 and BF₄^-, 10), are obtained indirectly from the anion substitution reaction with Cl^- ions in 1 and 7, and 2 and 8, respectively. All complexes are characterized by EA, FTIR, UV-vis and EPR spectroscopy and X-ray crystallographic analyses. HNC(Et)pz or pzH is unobserved in both the nitrile-exchange reaction of 2 to d₆-1 and the anion-substitution reaction of 2 to d₆-5 in the CD₃CN solution. The ¹H NMR results reveal that the pzH-RCN coupling is intramolecular and reversible on a Cu(II) center. The crystal structures of these complexes show diverse supramolecular assemblies through imino NH⋯anion hydrogen bonds and pyrazolylamidino pz-pz (π⋯π) and pz-Cu(II) (π⋯metal) interactions. EPR results suggest weak magnetic couplings between Cu(II) centers in the polynuclear Cu(II) complexes. The yield and rate of the formation of 1 are higher in the reaction of Cu(ClO₄)₂ with a 4-fold molar excess of pzH compared with a 2-fold excess, indicating that [Cu(pzH)₄]²⁺ is the more active species for pzH-RCN coupling. The highest rate for the formation of 1 is achieved when [Cu(pzH)₄(ClO₄)₂] is used in MeCN solution. Thus, a plausible synthetic path for synthesizing pyrazolylamidino Cu(II) complexes is established. An intermediate species, [Cu(HNC(Me)pz)₂(pzH)₂][ClO₄]₂ (1a), is proposed for the synthetic process based on spectroscopic studies and DFT calculations. The reaction of [Cu(pzH)₄X₂] (X = ClO₄^-, Cl^-, NO₃^-, or BF₄^-) in MeCN solution suggests that the lability of coordinated anions upon nitrile substitution affects the rate of the formation of bis-pyrazolylamidino Cu(II) complexes.

Resonance-Assisted Hydrogen Bonding as a Driving Force in Synthesis and a Synthon in the Design of Materials

Resonance-assisted hydrogen bonding (RAHB), a concept introduced by Gilli and co-workers in 1989, concerns a kind of intramolecular H-bonding strengthened by a conjugated π-system, usually in 6-, 8-, or 10-membered rings. This Review highlights the involvement of RAHB as a driving force in the synthesis of organic, coordination, and organometallic compounds, as a handy tool in the activation of covalent bonds, and in starting moieties for synthetic transformations. The unique roles of RAHB in molecular recognition and switches, E/Z isomeric resolution, racemization and epimerization of amino acids and chiral amino alcohols, solvatochromism, liquid-crystalline compounds, and in synthons for crystal engineering and polymer materials are also discussed. The Review can provide practical guidance for synthetic chemists that are interested in exploring and further developing RAHB-assisted synthesis and design of materials.

Synthesis, Crystal Structures, and Magnetic Properties of Ternary M(II)-Dicyanamide-hydroxypyridine Complexes

Three two-dimensional (2D) and 3D supramolecular coordination architectures based on ternary M(II)-dicyanamide-2-hydroxypyridine systems, [Co(hmpH)2(dca)2] (1), [Cu(hmpH)2(dca)2] (2), and [Mn(hepH)2(dca)2] (3) (dca = dicyanamide, hmpH = 2-(hydroxymethyl)pyridine, hepH = 2-(hydroxyethyl)pyridine), have been synthesized. 1 is a mononuclear Co(II) complex. The mononuclear units are interlinked into a 2D (4,4) hydrogen-bonded layer via O–H⋯N hydrogen bonds between the hydroxyl groups and the noncoordinating nitrile ends. These 2D layers are further extended into a 3D supramolecular architecture via the interlayer pyridyl-pyridyl stacking interaction. 2 has a 1D coordination chain structure formed by the double 1,5-dca bridged dinuclear [Cu2(1,5-dca)2(hmpH)2] unit and the 1,3-dca bridges via weak Cu–N coordination, and these 1D coordination chains are further extended into 2D hydrogen-bonded layers via strong O–H⋯N hydrogen-bonding interaction between the hydroxyl groups and the noncoordinating nitrile ends. 3 is a 2D (4,4) coordination network made of 1D [Mn(hepH)(1,5-dca)] helical chain units and interchain double (1,5-dca) bridges. Pairs of [Mn(hepH)(1,5-dca)] helical chains are interlinked by the double (1,5-dca) bridges into a racemic coordination layer structure, which is further extended into a 3D hydrogen-bonded network. Magnetic studies reveal that weak antiferromagnetic exchange occurs in 3.

Syntheses, Crystal Structures, Magnetic Behaviours, and Thermal Properties of Three Hydrogen-Bonding Networks Containing Dicyanamide and 4-Hydroxypyridine

Three new dicyanamide-bridged polymeric complexes of{[Mn(dca)2(L)2]·2H2O}n(1),{[Cd(dca)2(L)2]·2H2O}n(2), and{[Co(dca)2(L)2]2(L)}n(3) (dca = dicyanamide, L = pyridinium-4-olate) have been synthesized and structurally characterized. In the three compounds, the protons of hydroxyl groups of 4-hydroxypyridine transfer to pyridyl nitrogen atoms. Compounds1and2are isomorphous forming one-dimensional[M(dca)2(L)2]nchains where metals are connected by double dca anions. These one-dimensional chains are extended into two-dimensional layers through weak C–H⋯N hydrogen bonds. Further, these layers are assembled into a three-dimensional supramolecular network through N–H⋯O, O–H⋯O hydrogen bonds. Complex3is a coordination layer of (4, 4) topology with octahedral metal centers linked by four singleμ1,5-bridges. These layers are interlocked by N–H⋯O, O–H⋯O hydrogen bonds from coordinated water molecules and free L molecules, which leads to a three-dimensional supramolecular architecture. The variable temperature magnetic susceptibilities measurement of compounds1and3shows the existence of weak antiferromagnetic interactions between the metal centers. The thermogravimetric analyses of the compounds1–3are also discussed.

[N-(1-Aza-nidyl-2,2,2-trichloro-ethyl-idene)-2,2,2-trichloro-ethanimidamide]-copper(II)

The title compound, [Cu(C₄H₂Cl₆N₃)₂], was obtained by the reaction of CCl₃CN with ammonia in presence of CuCl. The Cu^II atom is located about an inversion centre. The mol­ecule consists of three planar units (one central square CuN₄ and two C₂N₃ fragments), adopting a staircase-like structure. The six-membered metallocycles have a sofa conformation with the Cu atom out of the plane of the 1,3,5-triaza­penta­dienyl ligands by 0.246 (5) Å. The ipso-C atoms of the CCl₃ substituents are slightly out of the 1,3,5-triaza­penta­dienyl planes by 0.149 (6) and −0.106 (6) Å. The CCl₃ groups of each 1,3,5-triaza­penta­dienyl ligand are practically in the energetic­ally favourable mutually eclipsed conformation. In the crystal, the mol­ecules are packed in stacks along the a axis. The mol­ecules in the stacks are held together by two additional axial Cu⋯Cl inter­actions of 3.354 (2) Å. Taking the axial Cu⋯Cl inter­actions into account, the Cu^II atom exhibits a distorted [4 + 2]-octa­hedral coordination environment. The stacks are bound to each other by weak inter­molecular attractive Cl⋯Cl [3.505 (2)–3.592 (3) Å] inter­actions.

Exploration of biguanido-oxovanadium complexes as potent and selective inhibitors of protein tyrosine phosphatases

The inhibitory effects of three biguanido-oxovanadium complexes ([VO(L(1-3))(2)]·nH(2)O: HL(1) = metformin, HL(2) = phenformin, HL(3) = moroxydine) against four protein tyrosine phosphatases (PTPs) and an alkaline phosphatase (ALP) were investigated. The complexes display strong inhibition against PTP1B and TCPTP (IC(50), 80-160 nM), a bit weaker inhibition against HePTP (IC(50), 190-410 nM) and SHP-1(IC(50), 0.8-3.3 μM) and much weaker inhibition against ALP (IC(50), 17-35 μM). Complex 3 is about twofold less potent against PTP1B, TCPTP and HePTP than complexes 1 and 2, while complex 2 inhibits SHP-1 more strongly (about three to fourfold) than the other two complexes. These results suggest that the structures of the ligands slightly influence the potency and selectivity against PTPs. The complexes inhibit PTP1B and ALP with a typical competitive type.

Silver(I) and copper(I) complexes supported by fully fluorinated 1,3,5-triazapentadienyl ligands

Synthesis of the perfluorinated 1,3,5-triazapentadiene [N{(CF(3))C(C(6)F(5))N}(2)]H and the use of its conjugate base as a supporting ligand for the isolation of silver(i) and copper(i) complexes are reported. Some of the related chemistry involving [N{(C(3)F(7))C(C(6)F(5))N}(2)](-) (that has bulkier -C(3)F(7) groups on the 1,3,5-triazapentadienyl ligand backbone) is also presented. X-ray crystallographic data show a wide variety of structures ranging from intermolecular, hydrogen-bonded chain structure for [N{(CF(3))C(C(6)F(5))N}(2)]H with a twisted W-shaped N(3)C(2) core, monomeric [N{(CF(3))C(C(6)F(5))N}(2)]Ag(CN(t)Bu)(2) and [N{(C(3)F(7))C(C(6)F(5))N}(2)]Ag(CN(t)Bu)(2) where the κ(1)-bonded triazapentadienyl ligand bonding to the metal fragment via the central nitrogen atom, monomeric [N{(CF(3))C(C(6)F(5))N}(2)]Ag(PPh(3))(2) and [N{(C(3)F(7))C(C(6)F(5))N}(2)]Ag(PPh(3))(2) that feature κ(1)-bonded triazapentadienyl ligand bonding to the metal fragment via one of the terminal nitrogen atoms, to that of the monomeric [N{(CF(3))C(C(6)F(5))N}(2)]Cu(CN(t)Bu)(2) containing a κ(2)-bonded triazapentadienyl ligand and a U-shaped NCNCN ligand backbone. The isocyanide adducts show relatively high ν(CN) values in the IR spectra.