Terminal Unidentate Research Articles

Synthesis and structural characterization of adducts of silver(I) carboxylate salts AgX (X = CF 3COO, CH 3COO) with ER 3 (E = P, As; R = Ph, cy, o-tolyl) and oligodentate aromatic bases derivative of 2,2′-bipyridyl, L, AgX:PR 3:L (1:1:1)

Twenty-one adducts of the form AgX:ER 3:L (1:1:1) (X = CF 3COO (‘tfa’), CH 3COO (‘ac’), E = P, As; R = Ph, cy, o-tolyl; L = 2,2′-bipyridyl (‘bpy’)-based ligand) have been synthesized and characterized by analytical, spectroscopic (IR, far-IR, 1H, 19F and 31P NMR) and single crystal X-ray diffraction studies. The resulting complexes are predominantly of the form [(R 3E)AgL] +X −, with a trigonal EAgN 2 coordination environment, the planarity of which may be perturbed by the approach of anion or solvent. The carboxylate anions have been found to be uni-, or semi-bidentate, or also completely ionic, as in the complexes [Ag(PPh 3)(bpy)(H 2O)](tfa) and [Ag(PPh 3)(dpk · H 2O)](tfa) (‘dpk · H 2O’ = bis(2-pyridyl)ketone (hydrated)). The complexes Agac:PPh 3:dpa (1:1:1) and Agac:P( o-tol) 3:dpa:MeCN (1:1:1:1) are dinuclear, with bridging unidentate acetate and terminal unidentate dpa (‘dpa’ = bis(2-pyridyl)amine).

Synthesis, crystal structure and redox properties of µ-oxo-bis(µ-acetato)-diruthenium(III) complexes having 2,2′-bipyridine and imidazole bases as terminal ligands

Three diruthenium(III) complexes, [{Ru(bipy)L}2(µ-O)(µ-O2CMe)2][ClO4]2, have been prepared and characterized (L = imidazole, 1- or 4-methylimidazole; bipy = 2,2′-bipyridine). The crystal structure of the 1-methylimidazole complex [Ru2O(O2CMe)2(bipy)2(1-mim)2][ClO4]2·H 2O·MeOH has been determined. The complex has a Ru2(µ-O)(µ-O2CMe)22+ core with terminal unidentate 1-mim and bidentate chelating bipy ligands. The imidazole is trans to the oxide ligand. The Ru ⋯ Ru distance and Ru–O–Ru angle are 3.285(2)A and 121.5(3)°. The 1H NMR spectra of the complexes are consistent with this crystal structure. The complexes show an intense charge-transfer band near 600 nm. They are redox active and display reversible one-electron oxidation and reduction processes. On addition of weak proton-donor imidazole bases the complexes undergo a one-step two-electron reduction process RuIIIRuIII–RuIIRuII along with the RuIIIRuIII–RuIIIRuIV oxidation couple.

Cobalt(II), nickel(II) and iron(IlI) halide adducts with theobromine

Adducts of theobromine (L) with Co(II) and Ni(II) chlorides, bromides and iodides and Fe(III) chlorides and bromides were synthesized by refluxing 2:1 molar mixtures of L and the hydrated metal salt in triethyl orthoformate-ethyl acetate. Solid complexes of the CoL 2X 2 (X = Cl, Br), CoL 2I 2· H 2O, NiL 2X 2·2H 2O (X = Cl, Br, I) and FeL 2X 3·H 2O (X = Cl, Br) types were isolated. Characterization studies suggest that the new adducts are neutral monomeric with terminal unidentate L, halo and, wherever applicable, aqua ligands. The Co(II) complexes are distorted tetrahedral for X = Cl, Br and pentacoordinated for X = I, while the Ni(II) and Fe(III) adducts are hexacoordinated. The pyrimidine N1 and imidazole N9 ring nitrogens were considered as equally likely to act as the binding site of terminal theobromine.

2′-Deoxyadenosine Adducts with 3d Metal Perchlorates

Abstract Adducts of 2′-deoxyadenosine (L) with 3d metal perchlorates were synthesized by refluxing mixtures of ligand and metal salt in triethyl orthoformate-ethanol. Solid complexes of the following types were obtained: (X = C1O4): M2L3X6.4H2O (M = Cr, Fe), M2L3X,.4H2O (M = Mn, Co, Ni, Zn), FeL2X2.2H2O and Cu2L3X4. The Cu(II) complex is magnetically subnormal and appears to be a dimer of the type {O3CIOCuL3CuOCIO3} (CIO4)2 involving a triple bridge of N1,N7-bound L Iigands. The rest of the new complexes exhibit normal ambient temperature magnetic moments and were characterized as linear chainlike polymers comprising a singlebridged (M-L)n backbone, terminal unidentate L, –OC1O3 and aqua Iigands and ionic perchlorate. Bridging L is also Nl,N7-bound in the latter adducts, while the terminal L Iigands present bind most probably via N7.

Nicke(II) halide complexes with hypoxanthine and xanthine

Ni(LH)3LX complexes (LH=hypoxanthine or xanthine; X=Cl, Br or I) are formed by boiling under reflux 2:1 molar mixtures of LH and hydrated NiX2 in HC(OEt)3−MeCO2Et. The new complexes appear to be linear chain-like polymers, characterized by bidentate monoanionic L− ligands singly bidging between adjacent Ni2+ ions. A coordination number six is attained by the presence of three terminal unidentate LH and one X ligand in the first coordination sphere of each Ni2+ ion. The neutral LH and monoanionic L− ligands bind exclusivelyvia ring nitrogens to NiII. The probable binding sites of the uni- and bi-dentate hypoxanthine and ligands in the new complexes are discussed.

Xanthine and hypoxanthine complexes with cobalt(II) halides

Complexes of the Co(LH) 2LX and Co(LH) 2- LI·H 2O (LH=xanthine or hypoxanthine; XCl, Br) types were synthesized by refluxing 2:1 molar mixtures of LH and CoX 2 in triethyl orthoformate-ethyl acetate for one week. Characterization studies suggest that the new complexes are monomeric involving exclusively terminal neutral LH and monoanionic L − ligands. The Co(II) chloride and bromide complexes are tetrahedral (CoN 3X chromophores), while the monohydrated Co(II) iodide complexes are pentacoordinated (CoN 3IO absorbing species). The hypoxanthine ligands are probably N7-bound to Co(II). In the case of the xanthine complexes, N7 and N9 were considered as about equally likely to function as the primary binding site of the terminal unidentate xanthine ligands.

Adenine complexes with divalent 3d metal chlorides

Upon refluxing 2:1 mixtures of adenine (adH) and divalent 3d metal chloride hydrates in a 7:3 (v/v) mixture of ethanol-triethyl orthoformate for several days, partial substitution of ad − for Cl − ligands occurs, and solid complexes of the M(ad)Cl· 2H 20 (M = Mn, Zn), Fe 2(ad)(adH) 2Cl 3·2H 2O, M(ad)- (adH)Cl·H 2O (M = Co, Cu) and Ni 2(ad) 3Cl·6H 2O types are eventually isolated [1]. It is probably of interest that during analogous previous synthetic work, involving interaction of ligand and salt in refluxing ethanol, no substitution reactions between Cl − and ad − took place, and MCl 2 adducts with neutral adH were reportedly obtained. Characterization studies suggest that the new complexes reported are linear chainlike polymeric species, involving single adenine bridges between adjacent M 2+ ions. Terminal chloro, adenine and aqua ligands complete the coordination around each metal ion. The new Ni 2+ complex is hexacoordinated, whilst the rest of the complexes are pentacoordinated. Most likely binding sites are considered to be N(9) for terminal unidentate and N(7), N(9) for bridging bidentate adenine [1].

Evidence for the predominance of trigonal pyramidal environments in tin(II) chemistry: The crystal structure of potassium (hydrogen(bismaleato))stannate(II)

The crystal structure of potassium (hydrogen(bismaleato))stannate(II) is reported. It has unit cell data a = 7.361(12), b = 12.305(3), c = 7.246(8) Å, α = 97.02(6)°, β = 109.83(28)°, γ = 87.48(7)°, U = 612.77 Å 3, Z = 2, D c = 2.096 g cm −3, D m = 2.093 g cm −3 and triclinic space group P 1 . The structure consists of layers of discrete [Sn(CHCO 2: CHCO 2)(CHCO 2: CHCO 2H)] 2 2− moieties with potassium ions located in holes between the layers. In the discrete unit are two different maleate groups, an anisobidentate maleate ligand and a terminal unidentate monoprotomaleate ligand. The tin atom lies in a trigonal pyramidal environment with three SnO distances, to the maleate and monoprotomaleate ligands, of 2.199 and 2.212 Å respectively. These bonds lengths are consistent with the 119Sn Mössbauer data. The preference for tin to exist in a trigonal pyramidal environment, even in the presence of potential chelating ligands is clearly shown in the structure of this complex tin(II) maleate.

Guanine complexes with dysprosium(III), thorium(IV) and uranium(IV) chlorides

By refluxing mixtures of guanine (guH) and DyCl 3, ThCl 4 or UCl 4 in ethanol-triethyl orthoformate, solid complexes of the Dy(guH) 2(gu)Cl 2 and M(gu) 2Cl 2 (M = Th, U) types were isolated. The insolubility of the new complexes in organic media, combined with the coordination number six suggested by the spectral evidence, favors polymeric configurations. Most likely structures involve a linear, chainlike, single-bridged polymeric backbone ▪ The Dy 3+ complex is probably a linear polymer, also containing terminal unidentate guanine ligands, whilst for M = Th 4+, U 4+ highly polymeric structures arising from cross-linking between linear polymeric ▪ units seems most likely. IR evidence rules out participation of the O(6) oxygen of guanine in coordination, despite the hard acid character of the metal ions under study. Guanine apparently coordinates exclusively through ring nitrogens in the new metal complexes; N(9) and N(7). N(9) are, respectively, the most likely binding sites of terminal unidentate and bridging bidentate guanine. The chloro ligands present in the complexes seem to be exclusively terminal.

Copper(II) perchlorate complexes with N-methyl substituted xanthines

Monomeric complexes of the [CuL 2(OClO 3) 2] type (L = theophylline, theobromine, caffeine) were synthesized by refluxing 2:1 mixtures of N-methyl substituted xanthine and Cu(ClO 4) 2 in ethanol–triethyl orthoformate. Characterization studies suggest that the complexes are distorted tetrahedral with terminal unidentate L and -OClO 3 ligands. Most likely binding sites for caffeine and theophylline are the N(9) and N(7) imidazole nitrogens, respectively, in view of previously reported crystal structures of Cu 2+ complexes with these ligands. For the theobromine complex, the N(1) pyrimidine and N(9) imidazole nitrogens are almost equally likely to function as the binding site.

Guanine complexes with first row transition metal perchlorates

Complexes of guanine (LH) with 3 d metal perchlorates were prepared by refluxing a mixture of ligand and metal salt (4:1 molar ratio) in ethanol2̄triethyl orthoformate. This synthetic procedure led to the formation of some adducts of the neutral ligand (LH), some complexes with anionic L −, and one complex involving both LH and L − (M = Co 2+). Ir evidence indicates that neither of the exocyclic potential ligand sites (N(2) nitrogen and O(6) oxygen) of guanine is involved in coordination. Among the new complexes, the hexacoordinated [M(LH) 2(EtOH) 2(OClO 3) 2](ClO 4) (M = Cr 3+, Fe 3+) are apparently monomeric, with terminal unidentate LH, coordinating through the N(9) imidazole ring nitrogen. For the M 2+ complexes isolated, namely [MnL 2(EtOH) 3] n, [FeL(OH 2) 4] n(ClO 4) n, [CoL(LH)(EtOH)(OH 2) 2] n(ClO 4) n, [Ni(LH) 2(EtOH) 3] n(ClO 4) 2n and [Zn(LH) 2(EtOH) 3] n(ClO 4) 2n·2nEtOH, linear chain-like hexacoordinated polymeric structures, involving single bridges of bidentate guanine ligands (-M-guanine-M-guanine- sequences), binding through N(9) and, most probably, N(7) to adjacent M 2+ ions, are proposed; in most cases (M = Mn 2+, Co 2+, Ni 2+, Zn 2+), a second guanine ligand acts as terminal, unidentate, N(9) nitrogen-bonded.

Lanthanide(III) and actinide(IV) chloride complexes with purine and adenine

Well-defined complexes of the types Dy(LH)LCl 2·H 2O and Ml 2Cl 2 (M = Th, U; LH = purine or adenine) were prepared by refluxing mixtures of purine or adenine and DyCl 3, ThCl 4 or UCl 4 in ethanol triethyl orthoformate for 2–5 days. The new complexes, which are insoluble in organic media, were characterized by means of ir spectral and magnetic studies. Most likely structural types involve a linear polymeric backbone (MLML sequences) with single purine or adenine bridges. The Dy 3+ complexes are linear polymers, containing also terminal purine or adenine, chloro and aqua ligands, whereas in the Th 4+ and U 4+ compounds, higher polymeric structures arising by cross-linkage of linear MLML units seem most probable; the only terminal ligands present in the Th 4+ and U 4+ complexes are chloro groups. All the new complexes are hexacoordinated. The likely binding sites of terminal unidentate and bridging bidentate purine and adenine are discussed [1].

Purine N(1)-oxide complexes with 3d metal perchlorates

A series of purine N(1)-oxide (LH) complexes with 3d metal perchlorates were synthesized by relfuxing mixtures of ligand and salt in ethanol–triethyl orthoformate. In one case (M = Cr 3+), an apparently hexacoordinated monomeric complex of the [Cr(LH) 2(C 2H 5OH) 2(OClO 3) 2](ClO 4 type, with terminal imidazole nitrogen-bonded LH was isolated (N(7) and N(9) are considered as equally likely binding sites for terminal unidentate LH). A number of pentacoordinated M 2+ complexes of the M(LH) 2(C 2H 5OH)(ClO 4) 2 type (M = Mn, Fe, Ni, Cu, Zn) seem to contain exclusively bidentate bridging LH, coordinated through the O(1) oxygen and one of the imidazole nitrogens (most probably N(7)); whereas, Co(LH) 2(C 2H 5OH) 2(ClO 4) 2 (pentacoordinated) and Fe(LH) 3(ClO 4) 3 (hexacoordinated) involve both bidentate bridging ligands of the preceding type and terminal unidentate imidazole nitrogen-bonded LH groups. Since all of the new polymeric complexes show normal ambient temperature magnetic moments, structural types involving MLHMLH bridges were considered as most probable. Simple linear chain-like structures wityh MLHMLH sequences were proposed for the Co 2+ and Fe 3+ complexes (the latter compound also contains a bidentate O 2ClO 2 ligand per Fe 3+ ion), whilst for the Mn +, Fe +, Ni 2+, Cu 2+ and Zn 2+ compounds, a more complicated structural type, involving cross-linking of linear chains of thepreceding type, seems to be most likely.

Adennine N(1)-oxide complexes with first row transition metal perchlorates

A series fo adenine N(1)-oxide (LH) complexes with 3d metal perchlorates were prepared by refluxing mixtures of ligand and salt in ethanol-triethyl orthoformate. Charaterization studies revealed significant differences in ligand binding sites and probable complex structural types, with metal ion variation. Thus, [Cr(LH) 2(OClO 3) 2(EtOH) 2(ClO 4) and [M(LH) 2(OClO 3)(EtOH) 2](ClO 4) (M = Mn, Zn) seem to be monomeric with unidentate, imidazole nitrogen-bonded (most porbably N(7) LH, while the Co 2+ analogue of the latter two complexes is apparently a linear polymer, with single bridges of bidentate O(1), N(7)-bonded LH, as well as terminal unidentate imidazole introgen-bonded ligand groups. The rest of the complexes involve both neutral LH and anionic L − ligands. The subnormal room temperature magnetic moment of the Cu 2+ complex (1.68 μB) favours a triple ligand-briged structure of the [(O 3ClO)Cu(LH)L 2Cu(OClO 3)] type, with O(1), N(7)-bonded bridging ligands. Ni(LH)L(ClO 4)·2EtOH and Fe(LH) 2L(ClO 4) 2 were considered as linear polymers, with single bridges of O(1) N(7)-bonded adenine N(1)-oxide ligands; the rest of the ligands present seem to be terminal, unidentate imidazole nitroten-bonded for M = Ni 2+ and bidentate chelating, O(1), N(6)-bonded for M = Fe 3+.