The synthesis and manipulation of a huge variety of nanoscaled species of similar chemical nature under one-pot reaction conditions requires access to a potential TMdynamic library∫ of appropriate building blocks.[1a] For instance, by exploiting a detailed knowledge of polyoxometalate chemistry, a variety of discrete clusters (see ref. [1b ± g]) and related extended structures[2] can be formed by the linking of welldefined metal ± oxygen building blocks. These types of compounds have been shown to exhibit unusual topological as well as electronic properties and, furthermore, are interesting for materials science.[3±5] A couple of years ago, we reported wheel-shaped mixed-valence molybdenum clusters of the type {Mo154}, {Mo176}, 6, 7] and {Mo248}; of these, the first two parent species–exhibiting nanometer-sized cavities and therefore presenting fascinating perspectives for a new type of host ± guest chemistry–can now be obtained in high yields in facile syntheses.[8] Herein, we describe for the first time a dimer of two giant clusters, that is, of structurally well-defined covalently linked nanoobjects with a rather high degree of complexity. The dimer contains two elliptical molybdenum oxide based units, linked together by two Eu-O-Mo bonds, each unit incorporates 128 MoVI/V and 4 EuIII centers and includes large fragments of the above-mentioned parent clusters. The interpretation would be that these dimers are formed by EuIII centers acting as symmetry breakers which prevent the corresponding highly symmetrical parent-ring closure.[1b, 6] Of general importance is that in systems showing growth, potential (abundant) agents, such as EuIII centers, can act as TMsymmetry breakers∫ which results in the generation of structural complexity. In any case, it is important to realize that large nanoobject fragments can, in principle, be used as synthons. The ability to connect or assemble clusters in a predefined manner may allow the design of nanoscopic devices using the TMbottom up∫ method (that is, generating large objects from small units). While the TMclassical∫ reduction of an acidified aqueous molybdate solution leads to the blue, wheel-shaped tetraand hexadecameric parent-cluster anions mentioned above,[6] the generation of smaller species requires the presence of electrophiles, such as PrIII ions which increase the curvature by replacing the larger electrophilic {Mo2} -type building units (see below). In the presence of smaller EuIII ions, even ring closure to the parent clusters does not take place, which allows the isolation of compound 1 containing a novel cluster collective. Compound 1 was characterized by single-crystal X-ray structure analysis[9] (including bond valence sum (BVS) calculation to aid in the determination of the (formal) number of MoV centers and protonation sites),[10] elemental analyses ((K), Eu, Mo; see details in ref. [12]), thermogravimetric analysis, redox titration (to aid in the determination of the (formal) number of MoV centers), IR, and EXAFS spectroscopy (Eu-LIII edge,[11] with the option to distinguish in principle between the different Eu centers in the lattice and cluster sites) as well as magnetic susceptibility measurements with a SQUID magnetometer.

In this paper, we briefly summarize the main conclusions of the Mössbauer analysis of [L2Fe2(μ-OH)3] (ClO4)2·2CH3OH·2H2O with L=N,N',N"-trimethyl-1,4,7-triazacyclononane, a novel dimeric iron compound, which possesses a central exchange-coupled delocalized-valence Fe(II/III) unit. The complete delocalization of the excess electron in the dimeric iron center is concluded from the indistinguishability of the two iron sites in Mössbauer spectroscopy. The magnetic Mössbauer spectra imply a system spinSt=9/2 for the dimer in its ground state. The values for hyperfine and spin-Hamiltonian parameters, obtained from simulations of the Mössbauer spectra, are δ=0.74 mms−1, ΔEQ=−2.14 mms−1,A⊥=−10.6 T,A∥=−13.5 T andD=1.8 cm−1. The system spinSt=9/2 is interpreted to be a consequence of double-exchange coupling.

Ziemlich genau dem spin‐only‐Wert eines ungepaarten Elektrons pro TiIII‐Zentrum entspricht das temperaturunabhängige magnetische Moment im Komplex 1, während 2 diamagnetisch ist. Dies wird darauf zurückgeführt, daß die [Ti‐O‐Ti]4⊕‐Einheit in 1 höchstwahrscheinlich linear, in 2 jedoch gewinkelt (122.7°) vorliegt. Anders als in 2 können daher die d1xy‐Orbitale in 1 nicht überlappen, weshalb hier eine Spin‐Spin‐Kopplung ausgeschlossen ist (L = N,N′,N″‐Trimethyl‐1,4,7‐triazacyclononan).magnified image[L2Ti2Cl4(μ‐O)] 1 [L2Ti2(μ‐O)(μ‐benzoato)2](PF6)2 2

In this paper we present the characterization by UV-VIS, Mössbauer, and EPR spectroscopy of [L2Fe2(μ-OH)3](ClO4)2⋅2CH3OH⋅2H2O, with L=N,N′,N″-trimethyl-1,4,7-triazacyclononane, a novel dimeric iron compound, which is shown to possess a central exchange-coupled delocalized-valence Fe(II/III) pair. Complete delocalization of the excess electron in the dimeric iron center is concluded from the indistinguishability of the two iron sites in Mössbauer spectroscopy. Mössbauer, EPR, and magnetic susceptibility data imply a system spin St =9/2 for the ground state. This finding is explained as being a consequence of the double-exchange interaction which is generated by the delocalized electron. Experimental values obtained from UV-VIS, Mössbauer, and EPR spectroscopy are for the double-exchange parameter B=1300 cm−1, the g factors gx,y =2.04 and gz =2.3, the parameters for zero-field splitting D=4 cm−1 and E≊0 cm−1, and for the hyperfine parameters ΔEQ =−2.14 mm s−1, Ax,y =−21.2 T, Az =−27 T, and δ=0.74 mm s−1. From our temperature-dependent studies we assign to the first excited state a spin-octet with an excitation energy Δ>175 cm−1. From this value a lower bound of −235 cm−1 has been deduced for the exchange-coupling constant J. In the framework of a simplified description of the iron atoms by unperturbed 3d orbitals, the values of the A tensor components as well as the quadrupole splitting ΔEQ can be interpreted in a consistent manner by assuming the excess electron being delocalized over two dσ orbitals centered at the two iron sites of the dimer and directed along the iron–iron axis as the z direction.

The temperature‐independent magnetic moment in complex 1 corresponds almost exactly to the spin‐only value of one unpaired electron per TiIII center, whereas 2 is diamagnetic. This is attributed to the fact that the [TiOTi]4⊕ unit in 1 is very likely linear, while in 2 it is bent (122.7°). Other than in 2 the d orbitals in 1 cannot overlap, and a spin‐spin coupling is therefore ruled out here (L = N,N′,N′‐trimethyl‐1,4,7‐triazacyclononane). equation image

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTModel compounds for the oxidized uteroferrin-phosphate complex. Syntheses, crystal structures, and magnetic properties of .mu.-phosphato-, .mu.-arsenato-, and .mu.-chromato-bridged binuclear iron(III) complexesStefan Drueke, Karl Wieghardt, Bernhard Nuber, Johannes Weiss, Hans Peter Fleischhauer, Stefan Gehring, and Wolfgang HaaseCite this: J. Am. Chem. Soc. 1989, 111, 23, 8622–8631Publication Date (Print):November 1, 1989Publication History Published online1 May 2002Published inissue 1 November 1989https://pubs.acs.org/doi/10.1021/ja00205a011https://doi.org/10.1021/ja00205a011research-articleACS PublicationsRequest reuse permissionsArticle Views192Altmetric-Citations58LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPreparation, molecular structure, and magnetism of bis(.mu.-carbonate)-.mu.-oxobis[1,4,7-trimethyl-1,4,7-triazacyclononane]diiron 4.25 hydrateStefan Drueke, Karl Wieghardt, Bernhard Nuber, and Johannes WeissCite this: Inorg. Chem. 1989, 28, 7, 1414–1417Publication Date (Print):April 1, 1989Publication History Published online1 May 2002Published inissue 1 April 1989https://pubs.acs.org/doi/10.1021/ic00306a041https://doi.org/10.1021/ic00306a041research-articleACS PublicationsRequest reuse permissionsArticle Views137Altmetric-Citations23LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTA new tetranuclear oxohydroxoiron(III) cluster: crystal structure, magnetic properties, and EXAFS investigation of [L4Fe4(.mu.-O)2(.mu.-OH)4]I4.cntdot.3H2O (L = 1,4,7-triazacyclononane)Stefan Drueke, Karl Wieghardt, Bernhard Nuber, Johannes Weiss, Emile L. Bominaar, A. Sawaryn, H. Winkler, and A. X. TrautweinCite this: Inorg. Chem. 1989, 28, 25, 4477–4483Publication Date (Print):December 1, 1989Publication History Published online1 May 2002Published inissue 1 December 1989https://pubs.acs.org/doi/10.1021/ic00324a011https://doi.org/10.1021/ic00324a011research-articleACS PublicationsRequest reuse permissionsArticle Views140Altmetric-Citations39LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

The reaction of Fe(CIO4)2·6H2O with N,N′,N,″-trimethyl-1,4,7-triazacyclononane (L) in methanol affords, in the presence of a small amount of oxygen, the deep blue binuclear complex [L2Fe2(µ-OH)3](CIO4)2·2MeOH·2H2O which was characterized by EXAFS, e.s.r., u.v.-visible and Mössbauer spectroscopy to be a mixed valence iron (II/III) species of class III with an Stot= 9/2 ground state.

The reaction of LFeCl3 (L = N,N′,N″-trimethyl-1,4,7-triazacyclononane) with Na2SO4, Na2SO3/NaClO4, and Na2SeO3/NaClO4 in aqueous solution affords the binuclear oxo bridged complexes [L2Fe2(μ-Ο)(μ-SΟ4)2]·3Η2Ο (1), [L2Fe2(μ-O)(μ-SO3)2]·5/3NaClO4·(H2O)3.67 (2), [L2Fe2(μ-O)(μ-SeO3)2](NaClO4)2.75·5H2O (3). The reaction of LFeCl3 in dry methanol with Na2SO4 yields yellow crystals of [L2Fe2(μ-SO4)3] · 2 H2O (4). The crystal structures of 1 and 2 have been determined by X-ray crystallography. Crystals of 1, 2, and 3 consist of neutral, binuclear μ-oxo bridged diiron(III) complexes which contain two additional O,O′-coordinated sulfato, sulfito, and selenito bridging ligands, respectively. The high spin ferric ions in 1, 2, and 3 are strongly intramolecularly antiferromagnetically spin exchange coupled with J values of —97(1), -104(2), and —104(2) cm-1 (H = —2JŜ,·Ŝ2, S1 = S2 = 5/2), respectively. 4 contains three μ-sulfato bridges between two FeIII ions. Only a very weak antiferromagnetic coupling has been detected (J = —5.5(5) cm-1). Complex 1 serves as a model compound for the diiron(III) complex of the sulfate treated, oxidized form of the biomolecule uteroferrin.

The tridentate macrocyclic ligands 1,4,7-triazacyclononane, its thia analogue 1,4,7-trithiacyclononane, 1-oxa-4,7-diazacyclononane, and N,N′,N″-trimethyl-1 ,4,7-triazacyclononane react with Re(CO)5Br in dimethylformamide to yield colorless, air-stable [LRe(CO)3]Br complexes (L = tridentate macrocycle). With Mn(CO)5Br only the cyclic amines react to afford yellow-orange [LMn(CO)3]Br complexes whereas 1,4,7-trithiacyclononane does not give stable complexes of manganese. The crystal structures of [([9]aneN3)Re(CO)3](NCS) and [([9]aneS3)Re(CO)3]Br · 1/2 H2O have been determined. The former crystallizes in the orthorhombic space group P bca (a = 12/763(4), b = 12.662(5), c = 17.472(9) Å; Z = 8); whereas the latter crystallizes in the monoclinic space group P21/c (a = 9.444(1). b = 11.797(2), c = 28.095(3) Å. β = 90,86(1); Z = 8).

Crystal Structure, 1,4,7-Triazacyclononane. 1,4.7-Trithiacyclononane Complexes The tridentate macrocyclic ligands 1,4,7-triazacyclononane, its thia analogue 1,4.7-trithiacyclononane, l-oxa-4,7-diazacyclononane, and N,N',N"-trimethyl-l ,4,7-triazacyclononane react with Re(CO)5Br in dimethylformamide to yield colorless, air-stable [LRe(CO)3]Br complexes (L = tridentate macrocycle). With Mn(CO)5Br only the cyclic amines react to afford yellow-orange [LMn(CO),]Br complexes whereas 1.4,7-trithiacyclononane does not give stable complexes of manganese. The crystal structures of [([9]aneN3)Re(CO)3](NCS) and [([9]aneS3)Re(CO)3]Br-1/2 H : 0 have been determined. The former crystallizes in the orthorhombic space group Pbca (a = 12/763(4), b = 12.662(5), c = 17.472(9) Ä; Z = 8); whereas the latter crystallizes in the monoclinic space group P2,/c (a = 9.444(1). b = 11.797(2), c = 28.095(3) Ä. ß = 90,86(1); Z = 8).

The tridentate macrocyclic ligands 1,4,7-triazacyclononane, its thia analogue 1,4,7-trithiacyclononane, 1-oxa-4,7-diazacyclononane, and N,N′,N″-trimethyl-1 ,4,7-triazacyclononane react with Re(CO)5Br in dimethylformamide to yield colorless, air-stable [LRe(CO)3]Br complexes (L = tridentate macrocycle). With Mn(CO)5Br only the cyclic amines react to afford yellow-orange [LMn(CO)3]Br complexes whereas 1,4,7-trithiacyclononane does not give stable complexes of manganese. The crystal structures of [([9]aneN3)Re(CO)3](NCS) and [([9]aneS3)Re(CO)3]Br · 1/2 H2O have been determined. The former crystallizes in the orthorhombic space group P bca (a = 12/763(4), b = 12.662(5), c = 17.472(9) Å; Z = 8); whereas the latter crystallizes in the monoclinic space group P21/c (a = 9.444(1). b = 11.797(2), c = 28.095(3) Å. β = 90,86(1); Z = 8).