Hexameric MnII Dendrimer as MRI Contrast Agent

A Mn^II chelating dendrimer was prepared as a contrast agent for MRI applications. The dendrimer comprises six tyrosine‐derived [Mn(EDTA)(H₂O)]^2? moieties coupled to a cyclotriphosphazene core. Variable temperature ¹⁷O NMR spectroscopy revealed a single water co‐ligand per Mn^II that undergoes fast water exchange (k_ex=(3.0±0.1)×10⁸ s^?1 at 37 °C). The 37 °C per Mn^II relaxivity ranged from 8.2 to 3.8 mM ^?1 s^?1 from 0.47 to 11.7 T, and is sixfold higher on a per molecule basis. From this field dependence a rotational correlation time was estimated as 0.45(±0.02) ns. The imaging and pharmacokinetic properties of the dendrimer were compared to clinically used [Gd(DTPA)(H₂O)]^2? in mice at 4.7 T. On first pass, the higher per ion relaxivity of the dendrimer resulted in twofold greater blood signal than for [Gd(DTPA)(H₂O)]^2?. Blood clearance was fast and elimination occurred through both the renal and hepatobiliary routes. This Mn^II containing dendrimer represents a potential alternative to Gd‐based contrast agents, especially in patients with chronic kidney disease where the use of current Gd‐based agents may be contraindicated.     

The molecular structure of high‐spin (S = ) manganese(II) phthalocyanine in tetrabutylammonium bromido(phthalocyaninato)manganese(II)

The title complex salt, (C₁₆H₃₆N)[MnBr(C₃₂H₁₆N₈)] or (TBA)[Mn^IIBr(Pc)] (TBA is tetrabutylammonium and Pc is phthalocyaninate), has been obtained as single crystals by the diffusion technique and its crystal structure was determined using X‐ray diffraction. The high‐spin (S = ) [Mn^IIBr(Pc)]⁻ macrocycle has a concave conformation, with an average equatorial Mn—N(Pc) bond length of 2.1187 (19) Å, an axial Mn—Br bond length of 2.5493 (7) Å and with the Mn^II cation displaced out of the 24‐atom Pc plane by 0.894 (2) Å. The geometry of the Mn^IIN₄ fragment in [Mn^IIBr(Pc)]⁻ is similar to that of the high‐spin (S = ) manganese(II) tetraphenylporphyrin (TPP) in [Mn^II(1‐MeIm)(TPP)] (1‐MeIm is 1‐methylimidazole).     

A one‐dimensional coordination polymer formed from the reaction of 1,1‐diphenyl‐3,3′‐[(1R,2R)‐cyclohexane‐1,2‐diylbis(azanediyl)]dibut‐2‐en‐1‐one with MnCl2·4H2O

In the title coordination polymer, catena‐poly[[dichloridomanganese(II)]‐μ‐1,1‐diphenyl‐3,3′‐[(1R,2R)‐cyclohexane‐1,2‐diylbis(azaniumylylidene)]dibut‐1‐en‐1‐olate‐κ²O:O′], [MnCl₂(C₂₆H₃₀N₂)]_n, synthesized by the reaction of the chiral Schiff base ligand 1,1‐diphenyl‐3,3′‐[(1R,2R)‐cyclohexane‐1,2‐diylbis(azanediyl)]dibut‐2‐en‐1‐one (L) with MnCl₂·4H₂O, the asymmetric unit contains one crystallographically unique Mn^II ion, one unique spacer ligand, L, and two chloride ions. Each Mn^II ion is four‐coordinated in a distorted tetrahedral coordination environment by two O atoms from two L ligands and by two chloride ligands. The Mn^II ions are bridged by L ligands to form a one‐dimensional chain structure along the a axis. The chloride ligands are monodentate (terminal). The ligand is in the zwitterionic enol form and displays intramolecular ionic N⁺—H...O⁻ hydrogen bonding and π–π interactions between pairs of phenyl rings which strengthen the chains.     

Coordination Complexes of a Neutral 1,2,4‐Benzotriazinyl Radical Ligand: Synthesis,Molecular and Electronic Structures,and Magnetic Properties

A series of d‐block metal complexes of the recently reported coordinating neutral radical ligand 1‐phenyl‐3‐(pyrid‐2‐yl)‐1,4‐dihydro‐1,2,4‐benzotriazin‐4‐yl ( 1 ) was synthesized. The investigated systems contain the benzotriazinyl radical 1 coordinated to a divalent metal cation, Mn^II, Fe^II, Co^II, or Ni^II, with 1,1,1,5,5,5‐hexafluoroacetylacetonato (hfac) as the auxiliary ligand of choice. The synthesized complexes were fully characterized by single‐crystal X‐ray diffraction, magnetic susceptibility measurements, and electronic structure calculations. The complexes [Mn( 1 )(hfac)₂] and [Fe( 1 )(hfac)₂] displayed antiferromagnetic coupling between the unpaired electrons of the ligand and the metal cation, whereas the interaction was found to be ferromagnetic in the analogous Ni^II complex [Ni( 1 )(hfac)₂]. The magnetic properties of the complex [Co( 1 )(hfac)₂] were difficult to interpret owing to significant spin–orbit coupling inherent to octahedral high‐spin Co^II metal ion. As a whole, the reported data clearly demonstrated the favorable coordinating properties of the radical 1 , which, together with its stability and structural tunability, make it an excellent new building block for establishing more complex metal–radical architectures with interesting magnetic properties.     

A New 3D Manganese(II) Coordination Polymer with 4,4‐Dicarboxy‐2,2′‐bipyridine and 1,10‐Phenanthroline: Synthesis,Structural, and Magnetic Properties

A new 3D Mn^II metal‐organic framework compound {Mn(phen)(dcbp)}_n (H₂dcbp = 4,4‐dicarboxy‐2,2′‐bipyridine, phen = 1,10‐phenanthroline) was isolated under hydrothermal conditions and structurally characterized. In the compound, the dcbp ligand is deprotonated to give a neutral species (metal:ligand with 1:1 stoichiometry). Along the c axis, the neighboring Mn^II ions are linked by two carboxylate bridges in µ₂‐coordinating mode to generate a 1D zigzag chain, and these chains are interlinked by dicarboxylate groups of long dcbp ligands to generate a 3D (4,4)‐connected structure with the (4².8⁴) net topology. IR and UV/Vis spectroscopy and variable temperature magnetic susceptibility measurements were made, which indicated weak antiferromagnetic interactions between the Mn^II ions of the compound.     

A novel bridged asymmetric binuclear manganese(II) complex with DTPB [DTPB is 1,1,4,7,7‐pentakis(1H‐benz­imidazol‐2‐yl­methyl)‐1,4,7‐tri­aza­heptane]

The crystal structure of the title compound, tetra­chloro­[μ‐1,1,4,7,7‐pentakis(1H‐benzimidazol‐2‐yl­methyl)‐1,4,7‐tri­azaheptane]­dimanganese(II) methanol pentasolvate tetrahydrate, [Mn₂Cl₄(C₄₄H₄₃N₁₃)]·5CH₄O·4H₂O, contains an ­asymmetric dinuclear Mn^II–DTPB [DTPB is 1,1,4,7,7‐pentakis(1H‐benzimidazol‐2‐yl­methyl)‐1,4,7‐tri­aza­heptane] complex with an intra‐ligand bridging group (–NCH₂CH₂N–), as well as several solvate mol­ecules (methanol and water). Both Mn^II cations have similar distorted octahedral coordination geometries. One Mn^II cation is coordinated by a Cl⁻ anion and five N atoms from the ligand, and the other is coordinated by three Cl⁻ anions and three N atoms of the same ligand. The Mn⋯Mn distance is 7.94 Å. A Cl⋯H—O⋯H—O⋯H—N hydrogen‐bond chain is also observed, connecting the two parts of the complex.     

Water‐Soluble Manganese Inorganic Polymers: The Role of Carborane Clusters and Producing Large Structural Adjustments from Minor Molecular Changes

The reaction of two different carboranylcarboxylate ligands, 1‐CH₃‐2‐CO₂H‐1,2‐closo‐C₂B₁₀H₁₀ or 1‐CO₂H‐1,2‐closo‐C₂B₁₀H₁₁, with MnCO₃ in water leads to polymeric compounds 1 a and 1 b . Both compounds have been characterized by analytical and spectroscopic techniques. Additionally, electrochemical techniques have also been used for compound 1 a . X‐ray analysis revealed substantial differences between both compounds: whereas a six‐coordinated Mn^II compound with water molecules bridging two Mn^II centers has been observed for 1 a , a square pyramidal geometry around each Mn^II ion with terminal water molecules coordinated to each Mn^II center has been found for 1 b . The observed differences have been attributed to the existence of different substituents, ?CH₃ or ?H, on one of the carbon atoms of the carboranylcarboxylate ligand. The reaction of 1 a and 1 b with coordinating solvents, such as ethers or Lewis bases, leads to the formation of new compounds with low (mononuclear 4 a , 4 b ; dinuclear 3 a , 3 b ; and trinuclear 2 a ) or high nuclearity (hybrid polymer, 5 a ), due to breakage of the corresponding polymer. X‐ray analysis shows that the structural core present in the polymeric materials is not maintained in the resulting compounds, with the exception of trinuclear compound 2 a . The magnetic properties of the compounds studied show weak antiferromagnetic coupling.     

Poly[diaqua­(μ‐4,4′‐bipyridine)tetra­kis­(μ‐ferro­cenecarboxyl­ato)bis­(ferro­cenecarboxyl­ato)­tri­man­ganese(II)]

The title compound, [Mn₃Fe₆(C₅H₅)₆(C₆H₄O₂)₆(C₁₀H₈N₂)(H₂O)₂]_n, consists of two crystallographically unique Mn^II centers. One is situated on an inversion center and is octa­hedrally coordinated by two N atoms from two bridging 4,4′‐bipyridine (4,4′‐bipy) ligands and four O atoms, two from different bridging ferrocenecarboxyl­ate (μ₂‐FcCOO⁻; Fc is ferrocene) units and two from aqua ligands. The two halves of each 4,4′‐bipy ligand are related by a center of symmetry. The second Mn^II center is in a strongly distorted tetra­gonal–pyramidal geometry, coordinated by five O atoms, three from three μ₂‐FcCOO⁻ units and two from a fourth, chelating, η²‐FcCOO⁻ unit. The FcCOO⁻ units function as bridging ligands to adjacent Mn^II centers, leading to the formation of linear ⋯Mn1Mn2Mn2Mn1⋯ chains. Adjacent chains are further bridged by 4,4′‐bipy ligands, resulting in a two‐dimensional layered polymer.     

Tetranuclear Manganese Complex Incorporating 2‐Pyridyloximate Ligand: Synthesis,Crystal Structure and Magnetic Property

A tetranuclear manganese complex of the composition {Mn₄[(Py)C(Ph)NO]₄(CH₃CH₂OH)₃(CH₃CH₂O)Cl₃}·2H₂O ( 1 ) was synthesized by solvothermal reaction, and characterized by X‐ray single crystal diffraction, IR spectroscopy, and elemental analysis. X‐ray analysis revealed that complex 1 contains a [Mn₄(NO)₄]⁴⁺ core with three Mn^II atoms displaying distorted octahedral arrangements and one Mn^II ion exhibiting a trigonal bipyramidal arrangement. Low‐temperature magnetic susceptibility measurement for the solid sample of 1 revealed antiferromagnetic Mn^II ··· Mn^II interactions.     

Calculation of the formation constant of the 1:1 complex between manganese(II) and the anion of 2-mercaptopyridine N-oxide (pyrithione) by polarographic measurements

Polarograms of mixtures of Mn^II and the anion of 2-mercaptopyridine N-oxide (pyrithione) in neutral media do not show separate waves for the metal ion, either complexed or not, nor for the ligand, free or in the complex. The two-electron reduction of Mn^II is shown to be an E_rE_i process in the absence of ligand and C_rE_rE_i process in the presence of ligand, with a fast previous reaction. From measurements made at constant Mn^II concentration and variable ligand concentration it is shown that the 1:1 complex is formed. The logarithm of the formation constant of this complex is obtained from these and other measurements, this value being log K_f = 3.76 ± 0.03.     

Synthesis,Crystal Structures,and Magnetic Properties of Two Tetrahedral MnIIMnIII3 Complexes

Two tetranuclear manganese complexes, [NaMn^IIMn₃^III(μ₄‐O^2–)(HL)₃(SCN)₄] ( 1 ) and [NaMn^IIMn₃^III(μ₄‐O^2–)(HL)₃Cl₄][NaMn^IIMn₃^III(μ₄‐O^2–)(HL)₃Cl₃(H₂O)]ClO₄ · 3.5H₂O ( 2 ) were obtained from the reaction of manganese perchlorate with a quadridentate Schiff base ligand, 3‐(2‐hydroxybenzylideneamino)propane‐1, 2‐diol (H₃L) derived from condensation of 2‐hydroxybenzaldehyde with 3‐amino‐1, 2‐propanediol, as well as the coligand KSCN or NaCl under basic conditions. Single‐crystal X‐ray studies reveal that those two complexes all have a mixed‐valent tetrahedral core, which contains an apical Mn^II ion and three basal Mn^III ions situated in the [Mn₃(μ₄‐O^2–)]⁷⁺ equilateral triangle plane. Fitting of the magnetic susceptibility data to the theoretical χ_mT vs. T expression, revealed that the presence of only antiferromagnetic interactions between the central metal atoms in 1 , while both antiferromagnetic and ferromagnetic interactions are present in 2 .     

Synthesis,Structure and Magnetic Properties of a MnII Framework Assembled by Two Carboxylate Ligands

The 3D framework [Mn₃(CH₃COO)₂(HCOO)₄]_n · nDMF ( 1 ) was obtained from the assembly of Mn^II ions with acetate and the in‐situ generated formate ligands. It features Mn‐centered MnMn₄ tetrahedral nodes, each of which is linked to another four ones by sharing the apexes to form the 3D framework of 1 . Each of the acetate and formate ligands behaves as a syn‐syn:anti bridge to link two apical Mn^II ions and the central Mn^II ion. The magnetic measurement of 1 revealed the coexistence of spin‐canted antiferromagnetism and metamagnetism. It represents a typical example to synergistically use two kinds of carboxylate ligands to construct metal‐organic frameworks, as well as to tune the structure and magnetic properties of the aimed complex.     

Enhanced Single‐Chain Magnet Behavior via Anisotropic Exchange in a Cyano‐Bridged MoIII–MnII Chain

Anisotropic magnetic exchange is of great value for the design of high performance molecular nanomagnets. In the present work, enhanced single‐chain magnet (SCM) behavior is observed for a Mo^III–Mn^II chain that exhibits anisotropic magnetic exchange. Self‐assembly of the pentagonal bipyramidal [Mo(CN)₇]^4? anion and the Mn^II unit with a tridentate ligand results in a neutral double zigzag 2,4‐ribbon structure which exhibits SCM behavior with a high relaxation barrier of 178(4) K. Open magnetic hysteresis loops are observed below 5.2 K, with a coercive field of 1.5 T at 2 K. Interestingly, this SCM can be considered to be a result of a step‐wise process based on our previously reported Mn₂Mo single‐molecule magnets (SMMs).     

Isomorphous Catena Transition Metal Squarates [MII(C4O4)(dmso)2(OH2)2] (M = Co,Mn) and Magnetic Investigation into their Solid Solution M = CoxMn1–x

The crystal structures of two new isomorphous transition metal squarato complexes [M^II(C₄O₄)(dmso)₂(OH₂)₂] [M^II = Co^II (3d⁷), Mn^II (3d⁵); dmso = dimethylsulfoxide] and their magnetic properties are reported. The compounds feature two symmetrically independent chains, in which 1,3‐bridging squarato ligands connect cations in distorted octahedral surroundings of pseudo‐symmetry D_4h. From an equimolar solution of CoCl₂ · 6H₂O and MnCl₂ · 2H₂O a mixed‐metal coordination polymer crystallizes; it represents a solid solution and adopts the same structure as the corresponding monometallic compounds. The results of the diffraction experiment unambiguously proof the presence of both Co^II and Mn^II cations in either independent site albeit no precise ratio between the metal cations involved may be deduced from these findings. The difference in the magnetic properties between Co^II and Mn^II cations in the given ligand field has allowed us to establish their ratio in the solid solution more reliably than by X‐ray diffraction: Accounting for ligand field potential and spin‐orbit coupling of Co^II and regarding Mn^II as a pure spin system, the calculations yielded a fraction of 73 % Co^II in the mixed‐metal polymer. With respect to superexchange effects only weak antiferromagnetic interactions have been detected for the three coordination polymers.     

Zero-Field Splittings and Redox Potentials in an Isostructural Series of Dinuclear FeIITiIV,FeIIITiIV, and MnIITiIV Complexes with a Face-Sharing Bridging Motive

The ligand H₆ioan has been used to synthesize the three dinuclear complexes [(ioan)Mn^IITi^IV], [(ioan)Fe^IITi^IV], and [(ioan)Fe^IIITi^IV]⁺. The face-sharing bridging mode of the three phenolates provides short M-Ti^IV distances of ≈3.0 Å. Mössbauer spectra of [(ioan)Fe^IIITi^IV]⁺ show a magnetically split six-line spectrum at 3 K in zero magnetic field demonstrating a slow magnetic relaxation. Magnetic measurements provide a zero-field splitting of |D|=5 cm⁻¹ in [(ioan)Fe^IITi^IV]. EPR spectroscopy demonstrates sizable zero-field splittings of the S=5/2 spin systems of [(ioan)Mn^IITi^IV] (D=0.246 cm⁻¹) and [(ioan)Fe^IIITi^IV]⁺ (D<−1 cm⁻¹) that can be related to enforced covalency of the M-O^ph bonds. [(ioan)Fe^IIITi^IV]⁺ exhibits a reversible reduction at −0.26 V vs. Fc⁺/Fc demonstrating the facile accessibility of Fe^III and Fe^II. In contrast to an irreversible oxidation in [(ioan)Ni^IITi^IV] at 0.78 V vs. Fc⁺/Fc, the reversible oxidation at 0.25 V vs. Fc⁺/Fc in [(ioan)Mn^IITi^IV] indicates even the access of Mn^III. These results indicate that pentanuclear complexes [(ioan)FeM¹M²M¹Fe(ioan)]ⁿ⁺ are meaningful targets to access electron delocalization in mixed-valence systems over five ions due to the facile accessibility of both Fe^II and Fe^III in the terminal positions. This study provides important local spin-Hamiltonian and Mössbauer parameters that will be essential for the understanding of the potentially complicated electronic structure in the anticipated pentanuclear complexes.     

Anomalous Stoichiometry and Antiferromagnetic Ordering for the Extended Hydroxymanganese(II) Cubes/Hexacyanometalate-Based 3D-Structured [MnII4(OH)4][MnII(CN)6](OH2)6⋅H2O

The reaction of Mn^II(O₂CMe)₂ and NaCN or LiCN in water forms a light green insoluble material. Structural solution and Rietveld refinement of high-resolution synchrotron powder diffraction data for this unprecedented, complicated compound of previously unknown composition revealed a new alkali-free ordered structural motif with [Mn^II₄(μ₃-OH)₄]⁴⁺ cubes and octahedral [Mn^II(CN)₆]⁴⁻ ions interconnected in 3D by Mn^II-N≡C-Mn^II linkages. The composition is {[Mn^II(OH₂)₃][Mn^II(OH₂)]₃}(μ₃-OH)₄][Mn^II(μ-CN)₂(CN)₄] ⋅ H₂O=[Mn^II₄(μ₃-OH)₄(OH₂)₆][Mn^II(μ-CN)₂(CN)₄] ⋅ H₂O, which is further simplified to [Mn₄(OH)₄][Mn(CN)₆](OH₂)₇ ( 1 ). 1 has four high-spin (S=5/2) Mn^II sites that are antiferromagnetically coupled within the cube and are antiferromagnetically coupled to six low-spin (S=1/2) octahedral [Mn^II(CN)₆]⁴⁻ ions. Above 40 K the magnetic susceptibility, χ(T), can be fitted to the Curie–Weiss expression, χ ∝(T−θ)⁻¹, with θ=−13.4 K, indicative of significant antiferromagnetic coupling and 1 orders as an antiferromagnet at T_c=7.8 K.     

Ferrimagnetic Ordering and Anomalous Stoichiometry Observed for the Cubic,Extended 3D Prussian Blue Analogues (NEt3Me)2MnII5(CN)12 and (NEt2Me2)2MnII5(CN)12: A Cation-Adaptive Structure

The reactions of Mn^II(O₂CCH₃)₂ with NEt₃Me⁺CN⁻ and NEt₂Me₂⁺CN⁻ form (NEt₃Me)₂Mn^II₅(CN)₁₂ ( 1 ) and (NEt₂Me₂)₂Mn^II₅(CN)₁₂ ( 2 ), respectively. Structure model-building and Rietveld refinement of high-resolution synchrotron powder diffraction data revealed a cubic [a=24.0093 Å ( 1 ), 23.8804 Å ( 2 )] 3D extended structural motif with adjacent tetrahedral and octahedral Mn^II sites in a 3:2 ratio. Each tetrahedral Mn^II site is surrounded by four low-spin octahedral Mn^II sites, and each octahedral Mn^II site is surrounded by six high-spin tetrahedral Mn^II sites; adjacent sites are antiferromagnetically coupled in 3D. Compensation does not occur, and magnetic ordering as a ferrimagnet is observed at T_c=13 K for 2 based on the temperature at which remnant magnetization, M_r(T)→0. The hysteresis has an unusual constricted shape with inflection points around 50 and 1.2 kOe with a 5 K coercivity of 16 Oe and remnant magnetization, M_r, of 2050 emuOe mol⁻¹. The unusual structure and stoichiometry are attributed to the very ionic nature of the high-spin N-bonded Mn^II ion, which enables the maximization of the attractive van der Waals interactions through minimization of void space via a reduced ∠ MnNC. This results in an additional example of the A_xMn^II_y(CN)_x+2y (x=0, y=1; x=1, y=3; x=2, y=1; x=2, y=2; x=2, y=3; x=3, y=5; and x=4, y=1) family of compounds possessing an unprecedented stoichiometry and lattice motif that are cation adaptive structured materials.     

A one‐dimensional chain structure based on unusual tetranuclear manganese(II) clusters

The title coordination polymer, poly[bis(μ₄‐biphenyl‐2,2′‐dicarboxylato)(dipyrido[3,2‐a:2′,3′‐c]phenazine)manganese(II)], [Mn₂(C₁₄H₈O₄)₂(C₁₈H₁₀N₄)]_n, was obtained through the reaction of MnCl₂·4H₂O, biphenyl‐2,2′‐dicarboxylic acid (H₂dpdc) and dipyrido[3,2‐a:2′,3′‐c]phenazine (L) under hydrothermal conditions. The asymmetric unit contains two crystallographically unique Mn^II ions, one unique L ligand and two unique dpdc ligands. One Mn ion is six‐coordinated by four O atoms from three different dpdc ligands and two N atoms from one L ligand, adopting a distorted octahedral coordination geometry. The distortions from ideal octahedral geometry are largely due to the presence of chelating ligands and the resulting acute N—Mn—N and O—Mn—O angles. The second Mn ion is coordinated in a distorted trigonal bipyramidal fashion by five O atoms from four distinct dpdc ligands. Four Mn^II ions are bridged by the carboxylate groups of the dpdc ligands to form an unusual tetranuclear Mn^II cluster. Clusters are further connected by the aromatic backbone of the dicarboxylate ligands, forming a one‐dimensional chain structure along the b axis. The title compound is the first example of a chain structure based on a tetranuclear Mn^II cluster.     

A New Mixed‐Valence Tetranuclear Manganese [MnII2MnIII2] Cluster

A new tetranuclear manganese complex [Mn₂^IIMn₂^III(bhmcpH)₂(hmp)₄Cl₂(MeOH)₂] ( 1 ) [bhmcpH₃ = 2, 6‐bis(hydroxymethyl)‐4‐chlorophenol, hmpH = 2‐(hydroxymethyl)pyridine] was synthesized and characterized. X‐ray diffraction analyses reveal that complex 1 crystallizes in the monoclinic space group P2₁/c. It has a mixed‐valence tetranuclear dicubane unit, which comprises two Mn^II and two Mn^III ions. The temperature dependence of the magnetic susceptibilities of 1 indicates ferromagnetic interactions between the manganese ions.     

Poly[[diaqua(N,N‐dimethylformamide‐κO)manganese(II)]‐μ3‐sulfato]

In the title complex, [Mn(SO₄)(C₃H₇NO)(H₂O)₂]_n, each Mn^II ion has a distorted octahedral geometry formed by three O atoms of three different sulfate groups, one O atom of a dimethylformamide ligand and two water molecules. The sulfate groups act as tridentate bridging ligands connecting the Mn^II ions into a two‐dimensional layer structure which can be regraded as a 4.8² network.