Chester M. Mikulski

Nicotinic and isonicotinic acid n-oxide interactions with 3d metal perchlorates[1]

Interactions of nicotinic or isonicotinic acid N-oxides (N-nicOH and N-inicOH, respectively) with 3d metal (II) perchlorates in ethanol-triethyl orthoformate lead, in most cases, to partial substitution of perchlorate with nicotinate (N-nicO) or isonicotinate(N-inicO) N-oxide anionic groups. These reactions led to the isolation of the following new metal complexes: Ni(N-inicOH)3(ClO4)2·3H2O: the only true adduct of the series, apparently polynuclear, with both unidentate terminal and bidentate bridging N-inicOH, bridging O2ClO2 ligands, ionic ClO4− and lattice water. Complexes with exclusively anionic ligands of the type (ClO4) (MMn, Cu for LN-nicO; MCu for LN-inicO), with both terminal and bridging L, ionic and unidentate coordinated perchlorate, and aqua ligands. The rest of the complexes are of the mixed ligand type, i.e.: [H2O)2(O3ClO)M(N-nic)2M(N-nicOH)(OH2)2] (ClO4) (MCo, Ni), with bridging N-nicO, terminal N-nicOH,-OClO3 and aqua ligands, and ionic ClO4−; M4(N-inicOH) (N-inicO)5 (ClO4)3. 4H2O (MMn, Co, Zn), polynuclear with exclusively bridging organic ligands, terminal aqua and bidentate perchlorato groups, and ionic ClO4−; and, Zn4(N-nicOH)N-nicO)5(ClO4)3. 10H2O, probably tetrameric, with four bridging and one terminal N-nicO groups, and terminal N-nicOH, aqua and =O2ClO2 ligands, as well as ionic ClO4−. With the exception of the latter complex, which is hexacoordinated, the new metal complexes appear to be pentacoordinated. The likely structural types proposed for these compounds were based on the overall spectral and magnetic evidence obtained.

Characterization studies of adenine complexes with 3d metal perchlorates

A series of adenine (LH) complexes with 3d metal perchlorates were prepared by refluxing solutions of the metal salts in ethanol-triethyl orthoformate with the ligand for 2–5 days. Our studies indicate that, depending on the ligand to metal molar ratio employed and the duration of the refluxing step, complexes with either neutral LH or anionic L− can be obtained. Among the new complexes, Cu(LH)2(ClO4)2·C2H5OH appears to be of the familiar dimeric type with quadruple bridges of N(3), N(9)-bonded LH, one terminal -OClO3 ligand per Cu2+ ion and lattice ethanol (μeff = 1.66 μB at 298K.). The Fe3+ complex (μeff = 2.39 μB) seems to be also a dimer of the [(O2ClO2)(LH)2FeL2Fe(LH)2(O2ClO2)] type, with N(9)-bonded terminal and N(y), N(9)-bonded (y = 1, 3 or 7) bridging adenine. A similar type of bridging (N(y), N(9)-bonded) adenine is also present in the probably double-bridged dimeric FeL(ClO4)·C2H5OH·2H2O complex (μeff = 4.86 μB), and a number of presumably linear, single-bridged polymers of the M(LH)2(ClO4)2·χC2H5OH (x=2 for M = Mn; x=3 for M = Co) and ZnL(ClO4)·C2H5OH·3H2O types. However, the two remaining complexes of the ML(ClO4)·C2H5OH·2H2O (M = Co, Ni) type, involve adenine apparently coordinated through the NH2 nitrogen. For these compounds, linear polymeric single-bridged structures with N(6), N(z)-bonded (z is most probably 9) bridging L, were considered as likely. The ambient temperature magnetic moments of the complexes considered as linear polymers range from slightly below normal to normal, but it is anticipated that studies at 300-80K. will reveal magnetic exchange interactions in general, in view of the established spin-spin coupling in the corresponding purine complexes.

Xanthine, hypoxanthine and guanine copper(II) complexes

Abstract Copper(II) complexes with xanthine (xnH), hypoxanthine (hxH) and guanine (guH), of the types Cu(xn) 2 ·2C 2 H 5 OH, Cu(hx)(ClO 4 )·4C 2 H 5 OH, Cu(gu) 2 ·H 2 O and Cu(guH) 2 (ClO 4 ) 2 ·C 2 H 5 OH·2H 2 O, were prepared from non-aqueous media (ethanol–triethyl orthoformate) and characterized. The CuL 2 ·xROH complexes (L = xn − , gu − ; R = H, C 2 H 5 ) show subnormal room temperature magnetic moments (1.57–1.60 μB) and are probably dimeric with four bidentate bridging anionic L groups (similar to fully characterized adenine and hxH analogs). The other two complexes appear to be linear polymers with single bridges of bidentate bridging hx − or guH (-Cu–L–Cu–L- sequences). One of the binding sites of the bidentate bridging substituted purines is the N(9) ring nitrogen; the likelihood of function of N(7) or n(3) as the second binding site is discussed for each case.

Purine complexes with divalent 3d metal chlorides

Abstract A series of purine (puH) complexes with 3d metal(II) chlorides were prepared by interaction of ligand and metal salt in ethanoltriethyl orthoformate. 1:1 complexes of the general type M(puH)Cl 2 ·nH 2 O (n = O for M = Zn; n = 1 for M = Fe, Co, Cu; n = 2 for M = Mn, Ni) were isolated. Spectral evidence favors a tetrahedral configuration for Zn(puH)Cl 2 , and coordination numbers five for M(puH)Cl 2 ·H 2 O (M = Fe, Co, Cu) and six for M(puH)Cl 2 ·2H 2 O (M = Mn, Ni). The new paramagnetic metal ion complexes are characterized by normal ambient temperature magnetic moments for high-spin 3d 5 –3d 8 compounds or the 3d 9 configuration. A linear oligomeric structural type, involving single-bridged MpuHMpuHsequences and exclusively terminal chloro, and wherever applicable, aqua ligands was considered as most likely for the new complexes. Probable bonding sites of the bidentate bridging puH ligands are the N(3) and N(9) nitrogens.

Guanine complexes with first row transition metal perchlorates

Abstract 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 ethanol2triethyl 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.

2,6-lutidine N-oxide complexes with metal chlorides

Abstract Complexes of 2,6-lutidine N-oxide (N-lutO or L) with a number of metal chlorides were prepared and characterized by means of spectral (ir and electronic), magnetic and conductance studies. Cr(III) and Al(III) yielded hexacoordinated complexes, which are most probably of the type [ML2Cl2(OH2)2] Cl·nH2O, involving both coordinated and anionic Cl groups, aquo ligands and lattice water. ML2Cl2 complexes isolated appear to be binuclear, chloride-bridged, penta-coordinated of the type [ClL2MCl2ML2Cl] for M = Mn, Ni, and monomeric, trans-square planar for M = Pd, Pt. FeCl2 formed a 2:3 complex (Fe2L3Cl4), which seems to involved both terminal and bridging chloro ligands, and coordination number five. A trans-arrangement of the N-lutO ligands in the above complexes is considered as most likely, in view of the obvious steric interactions between ligands of this type, occupying coordination sites, cis to each other. Finally, a second NiCl2 complex prepared, comprising coordinated methanol, is probably binuclear, chloride-bridged, hexacoordinated, of the type [ClL(CH3OH)2NiCl2Ni(CH3OH)2LCl].

Isonicotinate n-oxide complexes with dipositive 3d metal ions [1]

Abstract Divalent 3d metal complexes with isonicotinate N-oxide (N-inicO), of the type M(N-inicO)2·xH2O (M = Mn·Zn; x = 6 for M = Fe, Co, Ni, Zn; x = 5 for M = Mn; x = 2 for M = Cu), were prepared by reaction of (N-inicO)NH4 with the corresponding metal(II) acetates or ferrous ammonium sulfate in water. Desiccation of the preceding complexes over P4O10, under a vacuum of 10−4 torr, led to partial dehydration, affording the following lower hydrates: x = 5for M =Ni; x = 1.5 for M = Co, Zn;x = 1 for M = Cu; x = 0.5 for M = Mn, Fe. Characterization of the new metal complexes, based on spectral and magnetic studies, and the insolubility of all the complexes in water and organic solvents, led to their formulation as polynuclear of the following types: Hexa- and penta-hydrates; hexa-coordinated, [M(N-inicO)2(OH2]n·mH2O (m = 4n for M = Fe, Co,Ni, Zn; m = 3n for M = Mn, Ni), with the N- incO ligands forming single bridges between adjacent metal ions and functioning as bidentate, coordinating through the NO and one of the carboxylate oxygens; part of the non-coordinated COO oxygens are hydrogen-bonded to water, which is present in the form of both aqua ligands and lattice H2O. The lower hydrates of the type [(N-inicO2M-(OH2)-M(N-inicO)2)]n· bridging acqua ligand per two metal ions, as well as bidentate bridging N-inicO, being pentacoordinated of the type [(N-inocO)2M-(OH2)-M(N-inico)2]n· mH2O (m = O for M = Mn, Fe; m = 2n for M= CO, Zn). The dihydrate Cu(II) complex appears to be square-planar of the type [Cu(N-inicO)2]n·2nH2O, with bidentate bridging N-inicO ligands and exclusively lattice and H-bonded water. The corresponding monohydrate ([Cu(N-inicO)2]n·nH2O) probably contains both tetra-and penta-coordinated Cu2+ ions, with some N-inicO ligands acting at bidentate and some as tridentate (coordinating through the NO and the two COO oxygens) bridging. N-inicO is a 1igand of about the same strength as picolinate- and nicotinate-N-oxides.

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

Abstract Monomeric complexes of the [CuL2(OClO3)2] type (L = theophylline, theobromine, caffeine) were synthesized by refluxing 2:1 mixtures of N-methyl substituted xanthine and Cu(ClO4)2 in ethanol–triethyl orthoformate. Characterization studies suggest that the complexes are distorted tetrahedral with terminal unidentate L and -OClO3 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 Cu2+ 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.

Chelates of tetracycline with first row transition metal perchlorates

Abstract 2:1 adducts of tetracycline (tc) with 3d metal perchlorates (M = Cr 3+, Mn 2+, Fe 2+, Fe3+, Co2+, Ni 2+, Cu 2+, Zn 2+) are synthesized by boiling under reflux mixtures of tc free base and metal salt in ethanol— triethyl orthoformate. Characterization studies suggest that the new complexes are monomeric chelates involving bidentate tetracycline ligands, chelating via the amide group oxygen and the C3 O oxygen of the ring A tricarbonylmethane. The complexes also contain unidentate coordinated −OClO 3 ligands, as weil as ionic ClO 4-. The M 3+ (Cr, Fe) complexes are hexacoordinated of the [M(tc) 2(OClO 3)2 3]ClO 4 type (MO 6 chromophores), with two bidentate chelating tc and two unidentate perchlorato ligands in the first coordination sphere of the central metal ion. In the M2+ (Mn, Fe, Co, Ni, Cu, Zn) complexes, the inner coordination sphere of the metal ion is occupied by two bidentate chelating tc and only one −OClO 3 ligand, and the coordination number is five, i.e. [M(tc) 2OClO 3]ClO 4 (MO 5absorbing species).

Adenine complexes with divalent 3d metal chlorides

Abstract 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 2 0 (M = Mn, Zn), Fe 2 (ad)(adH) 2 Cl 3 ·2H 2 O, M(ad)- (adH)Cl·H 2 O (M = Co, Cu) and Ni 2 (ad) 3 Cl·6H 2 O 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].