Crystal structure of strontium aqua(ethylenediaminetetraacetato)cobaltate(II) tetrahydrate Sr[CoEdta(H2O)] · 4H2O

The complex Sr[Co^II Edta] · 5H₂O (I) (where Edta ^4? is the ethylenediaminetetraacetate ion) has been synthesized. The crystal structure of this compound is determined by X-ray diffraction. Crystals are monoclinic, a = 7.906(2) Å, b = 12.768(2) Å, c = 18.254(3) Å, β = 95.30(3)°, V = 1834.8 ų, space group P2₁/n, Z = 4, and R = 0.036. The structure is built up of the binuclear complex fragments {Sr(H₂O)₃[CoEdta(H₂O)]}, which consist of the anionic [CoEdta(H₂O)]^2? and cationic [Sr(H₂O)₃]²⁺ units linked by the Sr-O bonds into a three-dimensional framework. The coordination polyhedra of the Co and Sr atoms are mono-and bicapped trigonal prisms. The coordination sphere of the Co atom (the coordination number is equal to 6 + 1) involves six donor atoms (2N and 4O) of the Edta ^4? ligand and the O_w atom of water molecule. One of the Co-O distances (2.718 Å) is considerably longer than the other Co-O_lig distances (2.092–2.190 Å) and the Co-O_w(1) distance (2.079 Å). The Sr coordination polyhedron (the coordination number is eight) contains three water molecules, three carbonyl O atoms of the three different anionic complexes, and two O atoms of one acetate group of the fourth anionic complex. The Sr-O distances fall in the range 2.535–2.674 Å. The structural formula of the compound is {Sr(H₂O)₃[CoEdta(H₂O)]}_3∞ · H₂O.     

Crystal structures of acid ethylenediaminetetraacetates [Cd(H2 Edta)(H2O)] · 2H2O and [Mn(H2O)4][Mn(HEdta)(H2O)]2 · 4H2O

The crystal structures of [Cd(H₂ Edta)(H₂O)] · 2H₂O (I) and [Mn(H₂O)₄][Mn(HEdta)(H₂O)]₂ · 4H₂O (II) are studied by X-ray diffraction [R ₁ = 0.0209 (0.0272), wR ₂ = 0.0571 (0.0730) for 2551 (4025) reflections with I > 2σ(I) in I (II), respectively]. Structure I contains mononuclear [Cd(H₂ Edta)(H₂O)] complexes with the C ₂ symmetry, and structure II contains centrosymmetric trinuclear [Mn(H₂O)₄][Mn(HEdta)(H₂O)]₂ complexes. In I and II, the protonated ligands are hexadentate (2N + 4O), and the water molecule increases the coordination number of the metal atom to seven. The acid protons participate in short intermolecular hydrogen bonds, which are symmetric in II and asymmetric in I.     

Crystal and molecular structure of four copper(II) ethylenediaminedisuccinates, [Cu2(RR,SS-Edds)] · 6H2O, Ba2[Cu(RR,SS-Edds)](ClO4)2 · 8H2O, Ba[Cu(SS-HEdds)]ClO4 · 2H2O, and Ba3[Cu2(RR,SS-Edds)2](ClO4)2 · 6H2O

Four Cu(II) complexes with the RR,SS-Edds ^4? and SS-HEdds ^3? anions are synthesized, and their crystal structures are studied. In the compounds [Cu2(RR,SS-Edds)] · 6H₂O (I) and Ba2[Cu(RR,SS-Edds)](ClO₄)₂ · 8H₂O (II), the ligand forms hexacoordinate chelate [Cu(Edds)]^2? complexes with the N atoms and O atoms of the propionate groups in the equatorial positions and the O atoms of the acetate groups in the axial vertices. In the compounds Ba[Cu(SS-HEdds)]ClO₄ · 2H₂O (III) and Ba3[Cu2(RR,SS-Edds)₂](ClO₄)₂ · 6H₂O (IV), one of the propionate arms, the protonated arm in III and the deprotonated arm in IV, does not enter into the coordination sphere of the Cu atom. An acetate arm moves to its position in the equatorial plane, and the free axial vertex is occupied by an O atom of the perchlorate ion. In I–IV, the lengths of the equatorial Cu-N and Cu-O bonds fall in the ranges 1.970–2.014 and 1.921–1.970 Å, respectively. The axial Cu-O bonds with the acetate groups and ClO ₄ ^? anions are elongated to 2.293–2.500 and 2.727–2.992 Å, respectively. In structure I, the second Cu atom acts as a counterion forming bonds with the O atoms of two water molecules and three O atoms of the Edds ligands. In II–IV, the Ba²⁺ cations are hydrated and bound to the O atoms of the anionic complexes and (except for one of the cations in IV) ClO ₄ ^? anions. The coordination number of the Ba cations is nine. The structural units in I–IV are connected into layers. In I, an extended system of hydrogen bonds links the layers into a framework. In II and III, the layers are linked only by weak hydrogen bonds, one bond per structural unit. In IV, ClO ₄ ^? anions are bound to the Ba and Cu atoms of neighboring layers, thus serving as bridges between the layers.     

Crystal structure of triaquamaleatostrontium(II) monohydrate, [Sr(C4H2O4)(OH2)3]·H2O

[Sr(C₄H₂O₄)(OH₂)₃]·H₂O is monoclinic, P2₁/n, witha=11.476(2),b=7.027(1),c=12.344(2) Å, =115.74(3)°,V=896.67 ų,Z=4. The Sr atom is surrounded by nine oxygen atoms which come from four different maleate anions and three water molecules. The Sr–O distances range from 2.546(2) to 2.808(2) Å. The C–O distances are equal within the standard deviation 1.263(3) to 1.258(3) Å). In the maleate anion, the planes that contain the carboxylate groups form an angle of 74.44(9)°. Both carboxylate groups deviate significantly from planarity. The different coordination modes of the carboxylate group and the extensive hydrogen bonding present are responsible for the polymeric nature of the structure.     

Eightfold-coordinated diethylenetriaminepentaacetates: Crystal structures of K[M(Dtpa)] ⋅3H2O (M = Zr or Hf) and NH4[Sn(Dtpa)] ⋅ H2O

The crystal structures of K[M(Dtpa)] ? 3H₂O (M = Zr or Hf) and NH₄[Sn(Dtpa)] ? H₂O are studied by X-ray diffraction. The coordination number of the metal atom in all the compounds is eight. The NH₄[Sn(Dtpa)] ? H₂O complex is isostructural to the (H₅O₂)[M(Dtpa)] ? H₂O (M = Sn or Hf) compounds studied earlier.     

Synthesis and X-ray structures of [H3O+·18-crown-6] n [MCl 4 n− ]; (M=Fe,n=1;M=Co,n=2); compounds which form liquid clathrates with aromatic solutions

The title compounds, [H₃O⁺·18-crown-6][FeCl ₄ ^– ] (1), and [H₃O⁺·18-crown-6]₂[CoCl ₄ ^2– ] (2), were prepared by air oxidation of Fe(CO)₅ for1, and Co₂(CO)₈ for2, in the presence of 18-crown-6, H₂O and HCl(g) in toluene. Liquid clathrates formed immediately for both species:1·4.3 C₇H₈ and2·3.7 C₇H₈.1 crystallizes in the orthorhombic space group P2₁ma witha=10.357(1),b=11.824(1),c=8.961(1) Å, andD _c=1.46 g cm^–3 forZ=2. Refinement based on 935 observed reflections led to a finalR value of 0.089.2 crystallizes in the monoclinic space group C2/c witha=16.225(1),b=11.522(1),c=20.136(1)Å, =97.75(2)^o, andD _c=1.37 g cm^–3 forZ=4. Refinement based on 1322 observed reflections led to a finalR value of 0.11.     

Crystal structures of mixed ligand complexes containing saccharinate and nicotinamide: [Cu(saccharinato)2 (nicotinamide) (H2O)]⋅(H2O) and [M(nicotinamide)2 (H2O)4]⋅(saccharinate)2 (M = Ni2+, Co2+)

[M(saccharinato)₂(H₂O)₄] (M = Cu²⁺, Ni²⁺, Co²⁺) react with nicotinamide to form mixed ligand complexes, [Cu(saccharinato)₂(nicotinamide)(H₂O)](H₂O) (1) and [M(nicotinamide)₂(H₂O)₄](saccharinate)₂ (2: M = Ni²⁺; 3: M = Co²⁺), and their crystal structures have been determined by X-ray diffraction. In 1, the Cu²⁺ atom in an octahedral configuration is coordinated by two monodentate saccharinato ligands in the trans arrangement through the deprotonated ring nitrogens, by two bidentate nicotinamide ligands, one through the pyridyl ring nitrogen and the other through the amide oxygen, and by a water molecule, thus forming a nicotinamide-bridged one-dimensional extended structure. In the isomorphous complexes 2 and 3, the octahedral metal atom, which rides on a crystallographic center of symmetry, is coordinated by two monodentate nicotinamide ligands through the ring nitrogens and four water molecules to form a discrete [M(nicotinamide)₂(H₂O)₄]^{2 +} structural unit, which captures up and down two saccharinate ions, each through three hydrogen bonds: two hydrogen bonds between two water ligands and the ring N and the carbonyl O atoms and one between the amide N of the nicotinamide ligand and the carbonyl O.     

Metal-hydroxycarboxylate interactions: syntheses and structures of K2[VO2(C6H6O7)]2·4H2O and (NH4)2[VO2(C6H6O7)]2·2H2O

Potassium and ammonium dimeric (citrato)dioxovanadium(V) hydrate K₂[VO₂(H₂cit)]₂·4H₂O1 and (NH₄)₂[VO₂(H₂cit)]₂·2H₂O2 (H₄cit=citric acid) have been prepared and characterized by X-ray structure analyses. Vanadate1 crystallizes in the monoclinic space groupP2₁/n (No. 14) with unit cell parameters:a=9.304(2),b=11.756(2),c=11.911(2)Å, =111.72(3)°, andD _c=1.911 g/cm³,Z=2; Vanadate2 also crystallizes in the monoclinic space groupP2₁/n with unit cell parameters:a=9.719(2),b=11.111(3),c=11.294(2)Å, =109.03(2)°, andD _c=1.781 g/cm³,Z=2. Each dimer contains a centro-symmetric planar four-member V₂O₂ ring with two exocyclic citrate entities coordinated by the oxygen atoms of the hydroxy-and -carboxylate ligands, while the other two -carboxylate groups remain uncomplexed. Principal dimensions of the V–O bonds are 1.986(4)_av (hydroxy) and 1.980(3)Å(-carboxyl) for vanadate1, 1.988(2)_av (hydroxy) and 1.974(3)Å(-carboxyl) for vanadate2.     

Crystal structure of [Co(bipy)(maleato) (H2O)3]·H2O (bipy = 2,2′-bipyridine)

Preparation of the mononuclear cobalt(II) complex, [Co(bipy)(maleato) (H₂O)₃]·H₂O (1) where bipy = 2,2-bipyridine, were accomplished by reaction of an aqueous solution containing sodium maleate and an ethanolic solution of Co(NO₃)₂·6H₂O and bipy. The crystal structure of complex (1) was determined by X-ray crystallography. The complex crystallizes in the monoclinic space group P2₁/n with a = 9.477(3), b = 7.660(2), c =23.526 (3) Å, = 97.64(2)°, V = 1692.6(6) ų, and Z = 4. The structure consists of discrete mononuclear cobalt molecules. The cobalt atom is six-coordinate and presents a slightly distorted octahedral geometry, which consists of the two imine N atoms of bipy, a terminal carboxylate O atom from maleato ligand, and a water O atom in the basal plane with Co—N bond distances of 2.116(2) and 2.124(3) Å and Co—O distances of 2.075(2) and 2.088(2) Å, respectively. The relatively shorter Co—O distances are due to the trans effect of the bipy ligand. The octahedral coordination is completed the other two water molecules. The coordinate and the lattice water molecules were identified by TG study.     

Hydrothermal crystallization and X-ray structure determination of a new decavanadate with mixed cations [Mn(H2O)6]2[N(CH3)4]2[V10O28]·2H2O

A new decavanadate with mixed cations, [Mn(H₂O)₆]₂[N(CH₃)₄]₂[V₁₀O₂₈]·2H₂O (1), was crystallized from a hydrothermal reaction between MnCO₃ and V₂O₅ in the presence of N(CH₃)₄Br at 100°C. The structure of 1, as determined by x-ray single crystal analysis, consists of cations and anions of hexa-aqua manganese [Mn(H₂O)₆]²⁺, tetramethyl ammonium [N(CH₃)₄]⁺ and decavanadate [V₁₀O₂₈]^6–. The extended H-bonding between the [Mn(H₂O)₆]²⁺ and [V₁₀O₂₈]^6– ions gives rise to a pseudo- two-dimensional network in the crystal lattice x-ray crystallographic data for 1: monoclinic P2₁/n, a = 9.1499(5), b = 12.8725(7), c = 18.625(1) Å, = 92.252(1)°, V = 2192.0(2) ų, MZ = 2, and D _calcd = 2.22 g cm^–3.     

Synthesis and crystal and molecular structure of the [MoO2(L)(H2O)] · H2O complex (L 2− is the anion of 2-[N-(hydroxynaphtylidene)amino]propan-1,2,3-triol)

A new compound of dioxomolybdenum(VI)—[MoO₂(L)(H₂O)] · H₂O, where L ^2? = 2-[N-(hydroxynaphtylidene)amino]propan-1,2,3-triol)—is synthesized. Its structure is determined by X-ray diffraction. The Mo atom has an octahedral coordination formed by two oxo ligands located cis with respect to one another, two O atoms and the N atom of the tridentate bis(chelate) L ^2? ligand, and the O atom of a water molecule. The crystallization water molecule is connected with two complex molecules by O-H…O hydrogen bonds.     

Self-assemblies of Ni(II) with phenanthroline and maleate anions: [Ni(H2O)3(phen)L] ⋅ H2O (1) and [Ni(H2O)2(phen)L] ⋅ 2H2O (2) with H2L = maleic acid

The complex [Ni(H₂O)₃(phen)(C₄H₂O₄)] H₂O (1), which was obtained by reaction of phenanthroline, Ni(NO₃)₂ 6H₂O, and maleic acid in CH₃OH/H₂O at pH = 7.05, crystallized in the monoclinic space group P2₁ (no. 4) with cell dimensions: a = 9.350(1) Å, b = 7.631(1) Å, c = 12.821(1) Å, = 106.25(1), and D _calc = 1.607 g/cm³ for Z = 2. The Ni atoms are each octahe drally coordinated by one chelating phen ligand, three H₂O molecules and one monodentate maleato ligand to form [Ni(H₂O)₃(phen)(C₄H₂O₄)] complex molecules with d(Ni–O) = 2.038–2.090 Å, d(Ni–N) = 2.066, 2.089 Å. The formed complex molecules are, via the intermolecular hydrogen bonds, assembled into columnar 1D chains. Interdigitation of the chelating phen ligands of the neighboring chains leads to 2D layers and the crystal H₂O molecules are hydrogen bonded to the oxygen atoms of the maleate not coordinated to the Ni atom. However, reaction of NiCO₃, phen, and maleic acid in CH₃OH/H₂O at pH = 6.33 afforded [Ni(H₂O)₂(phen)(C₄H₂O₄)] 2H₂O (2), which crystallized in the triclinic space group (no. 2) with cell dimensions: a = 7.971(1) Å, b = 8.237(1) Å, c = 13.304(1) Å, = 81.005(6)°, = 87.877(8)°, = 78.322(8)°, and D _calc = 1.671 g/cm³ for Z = 2. The Ni atoms are each octahedrally coordinated by two N atoms of one phen ligand and four O atoms of two H₂O molecules and two bis–monodentate maleato ligands with d(Ni–O) = 2.041–2.120 Å and d(Ni–N) = 2.095 Å. The Ni atoms are bridged by the maleato ligands to generate 1D ¹ [Ni(H₂O)₂(phen)(C₄H₂O₄)_2/2] chains along [100]. The supramolecular assemblies of the 1D chains via – stacking inter- actions result in thick 2D layers parallel to (001), between which the noncoordinating H₂O molecules are sandwiched. The paramagnetic [Ni(H₂O)₂(phen)(C₄H₂O₄)_2/2] 2H₂O (2) obeys the Curie–Weiss law _m(T-) = 1.139cm³ mol^–1 K with the Weiss constant = –0.95 K.     

Structures and properties of layered barium borates Ba0.975[B6O9(OH)(O0.975Br0.025) · B2O(OH)3], Ba2[B5O8(OH)2](OH), Na2Ba2[B20O34(OH)4], and Ba5[B20O33(OH)4]H2O

A new hexaborate, Ba_0.975[B₆O₉(OH)(O_0.975Br_0.025) · B₂O(OH)₃], was synthesized under hydrothermal conditions. This compound is structurally similar to tunnelite and the synthetic borates Pb[B₆O₁₀(OH) · B₂O(OH)₃], Pr[B₆O₁₀(OH) · B₂O(OH)₄], and Nd[B₆O₁₀ · B₃O₃(OH)₄] · H₂O studied earlier. In the new hexaborate and the refined pentaborate Ba₂[B₅O₈(OH)₂]OH, in which the polyanions adopt an orientation in layers unusual for pentaborates, thermal vibrations of the terminal groups were revealed. This fact reflects the real crystal structure. The nonlinear optical properties of the crystals of the polar pentaborate Na₄Ba₄[B₂₀O₃₄(OH)₄] were determined. The crystal structure of the related pentaborate Ba₅[B₂₀O₃₃(OH)₄]H₂O was considered. The factors most likely responsible for the difference in the second-harmonic generation signal for this pair were revealed.     

Molecular structure of [trans-FeCl2(imidazole)4]Cl·THF·H2O

The structure of [trans-FeCl₂(imidazole)₄]Cl has been determined as the THF/H₂O solvate. The Fe-Cl and Fe-N distances in the cation are shorter than analogous trans-FeCl₂(L)₄ compounds, concomitant with the decreased ionic radius of Fe³⁺ versus Fe²⁺. Crystal data: orthorhombic, Pnma, a = 8.456(2), b = 20.991(4), c = 13.288(3) Å, V = 2358.6(8), andZ = 4.     

Silicogermanate Ba2K2In2[(Si0.8Ge0.2)6O18] · 2H2O As an Analogue of the Natural Zirconosilicate Kostylevite K4Zr2[Si6O18] · 2H2O

Crystallography Reports - Crystals of new silicogermanate Ba2K2In2[(Si0.8Ge0.2)6O18] · 2H2O were prepared by the hydrothermal synthesis; sp. gr. P21/n, a = 6.5548(6) Å, b = 11.6946(10)...     

Computer simulation of the self-assembly of crystal structures of zeolites Ca64(Sr,K,Ba)48(Cu12(O,Cl))4[Si192Al192O786](H2O) n (tschoertnerite, TSC, V = 31 614 Å3) and Ca2K2[Al6Si6O24](H2O)10 (willhendersonite, cha, V = 804 Å3) from template nanocluster precursors K48 and K12

The self-assembly of zeolites Ca₆₄(Sr,K,Ba)₄₈(Cu₁₂(O,Cl))₄[Si₁₉₂Al₁₉₂ O₇₈₆](H₂O) _n (tschoertnerite, TSC-type framework, V = 31614 ų) and Ca₂K₂[Al₆Si₆O₂₄] (H₂O)₁₀ (willhendersonite, CHA-type framework, V = 804 ų), which form paragenetic associations, has been simulated using computational methods (TOPOS program package). A new method for analyzing zeolites of any complexity has been used, which is based on the complete expansion of the three-dimensional structural graph (3D factor graph) in tiles and the selection of nonintersecting tiles forming a packing. The code of self-assembly of 3D structures from complementary linked nanocluster precursors is reconstructed: primary chain → microlayer → microframework. A supracluster precursor K48 with the symmetry $\bar 4$ 3m, formed of four K12 clusters corresponding to the t-hpr tile, is established for TSC. The K48 cluster contains Ca template cations, which stabilize its local region in the stages of K12 → K24 → K48 self-assembly. Bifurcations of evolution paths (structural branching points) during the self-assembly of TSC and CHA microframeworks are established in the stage of formation of the K24 supracluster from invariant templated K12 clusters. The models under consideration explain the 100% localization of B = Ca cations, which play the role of templates, and the 50% occupation of the positions of K, Sr, and Ba spacer cations (in TSC) and K spacer cations (in CHA).     

Molecular structure and hydrogen bonding of 4-dimethylaminopyridinioacetate in its crystalline dihydrate and hydrochloride trihydrate,L·2H2O and [L2H]Cl·3H2O (L=p-Me2NC5H4N+CH2CO2 −)

The crystalline dihydrate and hydrochloride trihydrate of a new betaine, namely, L·2H₂O (1) and [L₂H]Cl·3H₂O(2) (L=p-Me₂NC₅H₄N⁺CH₂CO₂), have been synthesized and characterized by X-ray crystallography. Molecule L in compound1 [space groupPbcn, witha=15.732(3),b=7.894(2),c=18.304(4) Å, andZ=8] possesses approximateC _s symmetry. The formation of hydrogen bonds by water molecules bridging neighboring carboxy oxygen atoms leads to an infinite two-dimensional network composed of a packing of two different kinds of 12-membered rings. In compound2 [space group PT witha=7.341(2),b=9.543(2),c=17.010(4) Å, =82.43(2)°, =80.34(2)°, =74.05(2)°, andZ=2], the carboxylate groups of a pair of betaine molecules are bridged by a proton to form a dimeric cation L₂H⁺ with a very strong asymmetric hydrogen bond of length 2.464(7) Å. The crystal structure features a hydrogen-bonded corrugated ribbon comprising an alternate arrangement of edge-sharing centrosymmetric (H₂O)₄(Cl^–)₂ and (H₂O)₄ rings running parallel to thea axis.     

Crystal structure of tetrabutylammonium nitroprusside dihydrate, [(C4H9)4N]2[Fe(CN)5NO]·2H2O, and vibrational spectra of ground and metastable excited states of the dihydrate and the anhydrate

The crystal structure of tetrabutylammonium nitroprusside dihydrate (TBANPDH, [(C₄H₉)₄N]₂[Fe(CN)₅NO]·2H₂O) was determined by single crystal X-ray diffraction (XRD) and the compound was also studied, as well as the anhydrous salt (TBANP), by room and low temperature Fourier Transform Infra-Red (FTIR) and room temperature Fourier Transform Near Infra-Red Raman (FTNIRR) spectroscopies. In addition to the ground states (GS), the metastable excited states (MSI and MSII) generated by laser excitation (488 nm) at low temperature were IR studied, both of the dihydrate and the anhydrate. TBANPDH crystallizes in the trigonal space group P3₂21, D ⁶ ₃, with a = b = 13.777(2), c = 22.039(2) Å, and Z = 3. The structure was solved employing 1273 independent XR reflections, with I > 2(I), by Patterson and Fourier methods and refined by full-matrix least-squares to R1 = 0.054.     

Crystal and molecular structure of complex compound [Fe3O(CH3COO)6(H2O)3]2[ZnCl4] ⋅ 2H2O

The X-ray crystal structure of trinuclear iron acetate [Fe₃O(CH₃COO)₆(H₂O)₃]₂ [ZnCl₄] ? 2H₂O was determined. The crystal has a ionic structure. It is monoclinic, a = 25.363(7), b = 14.533(4), c = 15.692(4) Å, β = 103.11(2)°, space group _C2/c, and R = 0.0685. The structure of the cationic complex [Fe₃O(CH₃COO)₆(H₂O)₃]⁺ is typical of trinuclear iron(III) compounds containing a μ₃-O bridge: the iron atoms are situated at the vertices of an almost equilateral triangle with the O atom at the center. Each Fe atom is coordinated by four O atoms of bridging carboxy groups, the μ₃-bridging O atom, and the water molecule in the trans position to the latter O atom. Mössbauer spectroscopy evidence indicates the high-spin state (_S = 5/2) of the iron(III) ions.     

Metal-pyrimidine interaction: synthesis and crystal structure of a cadmium complex of trimethoprim ([CdBr2(TMP)2(H2O)2]·H2O, TMP = trimethoprim)

The crystal structure of a cadmium complex of trimethoprim ([CdBr₂(TMP)₂(H₂O)₂] · H₂O, TMP = trimethoprim) has been determined from X-ray diffraction data using MoK radiation. The crystals are monoclinic, C2/c, with a = 7.7811(11), b = 15.439(3) c = 29.645(6)Å, = 97.23(2)° and Z = 4. Trimethoprim (2,3-diamino(3,4,5trimethoxybenzyl)pyrimidine) acts as a monodentate ligand. Cadmium is coordinated to N(1) atoms of two trimethoprim moieties. The octahetral coordination geometry around cadmium is completed by two Br-ions and two water molecules. The complex has a two-fold axis coinciding with a crystallographic two-fold axis. There is an interligand hydrogen bond between the bromide ion and the 2-amino group of the pyrimidine.