Shape-Persistent Dendrimers.

Dendrimers have a diverse and versatile morphology, frequently consisting of core, linking, and peripheral moieties. Dendrimers with flexible linkers, such as PAMAM, cannot retain the persistent shape of molecules, and this has been widely explored and reviewed previously; nevertheless, dendrimers with stiff linkers can preserve the persistent shape of the dendrimers, which has been reported considerably less. This review thus focuses on addressing shape-persistent dendrimers with rigid linking moieties discovered in recent years, i.e., from 2012 to 2023. Shape-persistent dendrimers with an interstitial gap between the dendritic frames in the solid state may or may not let the intramolecular void space be accessible for guest molecules, which largely depends on whether their peripheral groups are flexible or non-flexible. In this paper, eight articles on shape-persistent dendrimers with a flexible alkyl periphery, which may exhibit mesogenic phases upon thermal treatment, and eight articles on shape-persistent dendrimers with a non-flexible periphery, which may allow external ions, gases, or volatile organic compounds to access the interstitial gaps between dendritic frames, are reviewed.

Dendrimers with Tetraphenylmethane Moiety as a Central Core: Synthesis, a Pore Study and the Adsorption of Volatile Organic Compounds.

Reasonable yields of two dendrimers with central tetraphenylmethane and peripheral 3,5-di-(tert-butanoylamino)benzoylpiperazine moieties are prepared. These dendrimers have a void space in the solid state so they adsorb guest molecules. Their BET values vary, depending on the H-bond interaction between the peripheral moiety and the gas molecules, and the dendritic framework that fabricates the void space is flexible. In the presence of polar gas molecules such as CO2, the BET increases significantly and is about 4-8 times the BET under N2. One dendrimer adsorbs cyanobenzene to a level of 436 mg/g, which, to the authors' best knowledge, is almost equivalent to the highest reported value in the literature.

Converting non-Mesogenic to Mesogenic Stacking of Amino-s-Triazine-Based Dendrons with p-CN Phenyl Unit by Eliminating Peripheral Dipole.

Three new amino-s-triazine-based dendrons, 1a, 1b, and 1c, containing an aryl-CN moiety in the dendritic skeleton were prepared in 72-81% yields (1a: R1 = - N(n-C8H17)2, R2 = n-OC8H17, 1b: R1 = R2 = - N(n-C8H17)2, 1c: R1 = - N(n-C8H17)2, R2 = - N(n-C4H9)2). Dendrons 1a with N(n-C8H17)2 and n-OC8H17 peripheral substituents, surprisingly, did not show any mesogenic phase during the thermal process. However, non-mesogenic 1a can be converted to mesogenic 1b or 1c by eliminating the peripheral dipole arising from the alkoxy substituent; dendron 1b only comprising the same N(n-C8H17)2 peripheral groups showed a ~25 °C mesogenic range on heating and ~108 °C mesogenic range on cooling. In contrast, dendron 1c possessing different N(n-CmH2m+1)2 (m = 8 versus m = 4) peripheral units, having similar stacking as 1b, exhibited a columnar phase on thermal treatment, but its mesogenic range (~9 and ~66 °C on heating and cooling, respectively) was much narrower than that of 1b, attributed to 1c's less flexible alkyl chains in the peripheral part of dendron. Dendron 1a with the alkoxy substituent in the peripheral skeleton, creating additional dipole correspondingly, thus, leads to the dendritic molecules having a non-mesogenic stacking. Without the peripheral dipole for intermolecular side-by-side interaction, dendrons 1b and 1c exhibit a columnar phase on thermal treatment because of the vibration from the peripheral alkyl chain.

Adsorbing Volatile Organic Chemicals by Soluble Triazine-Based Dendrimers under Ambient Conditions with the Adsorption Capacity of Pyridine up to 946.2 mg/g.

Two triazine-based dendrimers with peripheral 1,3,5-triamidobenzene (1-3-5-TAB) functionality were prepared, and their void spaces in the bulk solid were investigated. We examined dendrimers of three core lengths and determined the one with the longest core exhibits the largest void space because the peripheral amides were not imbedded in the internal space of each dendritic molecule. The new dendrimers as solids were observed to adsorb volatile organic chemicals efficiently. Importantly, because the dendrimers are soluble in organic solvents, the adsorbed VOCs can be quantified by 1H-NMR spectroscopy by choosing a chemical shift (δ) of dendrimers as the internal standard to exclude interfering impurity signals, a much simpler and more efficient protocol than the traditional GC technique for the VOC quantification. One dendrimer was found to adsorb 24 equivalents of pyridine, so its adsorption capacity is equivalent to 946.2 mg/g. This is a more than 2-fold increase than the reported values by other porous materials.

Unconventional Approaches to Prepare Triazine-Based Liquid Crystal Dendrimers.

Most triazine-based liquid crystalline (LC) dendrimers reported thus far are the main-chain LC macromolecules with long flexible chains at their periphery and attached to internal rigid or semi-rigid frameworks. Their formation of mesogenic phases often depends on the intermolecular face-to-face π-π interactions between dendritic molecules, which are unusual. Their mesogenic phases can also be formed by incorporation of mesogenic units to the dendritic skeletons through long flexible chains, as most side-chain LC dendrimers, in which the peripheral mesogenic units generally play the important roles. For main-chain triazine-based dendrimers, their morphology is maintained by restricted freedom of rigid or semi-rigid connecting units, and their formations of LC phases are therefore not straightforward to be controlled. In this review, we thus describe modulating of the intermolecular face-to-face π-π interactions between the triazine-based dendritic molecules, with the aim of forming LC phases through molecular design.

Paddlewheel SBU based Zn MOFs: Syntheses, Structural Diversity, and CO2 Adsorption Properties.

Four Zn metal⁻organic frameworks (MOFs), {[Zn2(2,6-ndc)2(2-Pn)]·DMF}n (1), {[Zn2(cca)2(2-Pn)]·DMF}n (2), {[Zn2(thdc)2(2-Pn)]·3DMF}n (3), and {[Zn2(1,4-ndc)2(2-Pn)]·1.5DMF}n (4), were synthesized from zinc nitrate and N,N'-bis(pyridin-2-yl)benzene-1,4-diamine (2-Pn) with naphthalene-2,6-dicarboxylic acid (2,6-H2ndc), 4-carboxycinnamic acid (H2cca), 2,5-thiophenedicarboxylic acid (H2thdc), and naphthalene-1,4-dicarboxylic acid (1,4-H2ndc), respectively. MOFs 1⁻4 were all constructed from similar dinuclear paddlewheel {Zn2(COO)4} clusters and resulted in the formation of three kinds of uninodal 6-connected non-interpenetrated frameworks. MOFs 1 and 2 suit a topologic 48·67-net with 17.6% and 16.8% extra-framework voids, respectively, 3 adopts a pillared-layer open framework of 48·66·8-topology with sufficient free voids of 39.9%, and 4 features a pcu-type pillared-layer framework of 412·6³-topology with sufficient free voids of 30.9%. CO2 sorption studies exhibited typical reversible type I isotherms with CO2 uptakes of 55.1, 84.6, and 64.3 cm³ g-1 at 195 K and P/P0 =1 for the activated materials 1', 2', and 4', respectively. The coverage-dependent isosteric heat of CO2 adsorption (Qst) gave commonly decreased Qst traces with increasing CO2 uptake for all the three materials and showed an adsorption enthalpy of 32.5 kJ mol-1 for 1', 38.3 kJ mol-1 for 2', and 23.5 kJ mol-1 for 4' at zero coverage.

Design of a Peripheral Building Block for H-Bonded Dendritic Frameworks and Analysis of the Void Space in the Bulk Dendrimers.

Three dendrimers, (t-Bu-G 2 N) 2 , CC(t-Bu-G 1 N) 3 and (t-Bu-G 1 N) 2 , with 3,5-di-tert-butyl amidobenzene as a common peripheral moiety were prepared in 64-83% yields and characterized. The bulk solids had high BET surface areas of 136-138 m2/g, which were similar for the three dendrimers in spite of their different molecular weight (ranging from 1791 to 2890). It was concluded that the peripheral amide groups do not imbed in the interstitial space of neighbouring dendrimer molecules but rather build a supramolecular architecture through strong intermolecular H-bonds. This mode of assembly generates voids in the bulk dendrimers responsible for sorption properties. The X-ray crystal structure analysis of a compound representing the peripheral moiety of the dendrimers and the FT-IR and powder-XRD data for (t-Bu-G 1 N) 2 suggest the proposed supramolecular structure. The isosteric heats of CO2 sorption (Q st) for (t-Bu-G 2 N) 2 were significantly higher than those for the other two dendrimers, which is consistent with the formation of a different type of voids within the interstitial space of the molecule. It is suggested that the interstitial void space can be designed and tuned to adjust its properties to a particular task, such as the separation of gases or a catalytic reaction facilitated by the dendrimer.

The synthesis of three new Cu5, Cu8 and Cu12 clusters via the use of a semi-flexible aminotriazine-based bis-methylpyridine ligand.

The synthesis of three new polynuclear Cu5, Cu8 and Cu12 clusters has been achieved using a semi-flexible aminotriazine-based bis-methylpyridine ligand, N2,N2-dibenzyl-N4,N6-di(pyridylmethyl)-1,3,5-triazine-2,4,6-triamine (H2dpmta). The reaction of Cu(ClO4)2·6H2O with H2dpmta in i-PrOH afforded the complex [Cu5(OH)4(H2dpmta)2(ClO4)4(H2O)4](ClO4)2·Et2O·5i-PrOH (1). A similar reaction of Cu(ClO4)2·6H2O and H2dpmta in the presence of PhCO2Na in i-PrOH/CH2Cl2 gave the complex [Cu8(OH)6(O2CPh)4(H2dpmta)2(ClO4)4(i-PrOH)2](ClO4)2·2CH2Cl2·2i-PrOH (2). The complex [Cu12O3(OH)2(Hdpmta)2(dpmta)2(O2CMe)8](ClO4)2·2MeCN (3) was produced from the reaction of [Cu2(O2CMe)4]·2H2O with H2dpmta and NaClO4 in MeCN/CH2Cl2. Single-crystal X-ray diffraction measurements were carried out on these complexes. The Cu5 cluster of 1 consisted of a planar [Cu5(µ-OH)4]6+ core in a rectangle-like arrangement. The Cu12 cluster of 2 represented a [Cu8(µ3-OH)4(µ-OH)2]10+ core infusion of two [Cu4(OH)2]6+ butterfly subunits. Complex 3 possesses a bent [Cu12(µ4-O)3(µ-OH)2]16+ core structure, in which a central [Cu4(µ4-O2-)] square planar moiety was fused with two butterfly-like [Cu4(µ4-O)(µ3-OH)] subunits. The magnetic properties of these three complexes were characterized by the measurements of variable-temperature and field magnetic susceptibility. The magnetic analysis showed that a strong antiferromagnetic interaction was mediated between Cu(ii) ions by the single OH- bridge in 1 and resulted a S = 3/2 spin ground state. In complex 2, both intramolecular antiferro- and ferromagnetic interactions were dominated between Cu(ii) ions resulting a spin ground state of S = 2. Indeed, complex 3 displayed an overall antiferromagnetic coupling.

Converting Nonliquid Crystals into Liquid Crystals by N-Methylation in the Central Linker of Triazine-Based Dendrimers.

Two triazine-based dendrimers were successfully prepared in 60-75% yields. These newly prepared dendrimers 2a and 2b containing the -NMe(CH2)2NMe- and the -NMe(CH2)4NMe- linkers between two G3 dendrons, respectively, exhibit columnar phases during the thermal process. However, the corresponding dendrimers 1a and 1b containing the -NH(CH2)2NH- and the -NH(CH2)4NH- linkers between two G3 dendrons, respectively, do not show any LC phases on thermal treatment. Computational investigations on molecular conformations reveal that N-methylation of the dendritic central linker leads dendrimers to possess more isomeric conformations and thus successfully converts non-LC dendrimers (1a and 1b) into LC dendrimers (2a and 2b).

Anion-Directed Copper(II) Metallocages, Coordination Chain, and Complex Double Salt: Structures, Magnetic Properties, EPR Spectra, and Density Functional Study.

A series of Cu(II) metallo-assemblies showing anion-directed structural variations, including five metallocages [(G(n-) )⊂{Cu2 (Hdpma)4 }]((8-n)+) (A(-) )8-n (G(n-) =NO3 (-) , ClO4 (-) , SiF6 (2-) , BF4 (-) , SO4 (2-) ; A(-) =NO3 (-) , ClO4 (-) , BF4 (-) , CH3 SO4 (-) ; Hdpma=bis(3-pyridylmethyl)ammonium cation), a complex double salt, namely, (H3 dpma)4 (CuCl4 )5 Cl2 , and a coordination chain, namely, [Cu2 (dpma)(OAc)4 ], are reported. The influence of the anion can be explained by its coordinating ability, the affinity of which for the Cu(II) center interferes significantly with metallocage formation, and its shape, which offers host-guest recognition ability to engage in weak metal-anion coordination and hydrogen bonding to the organic ligand, which are responsible for metallocage templation. EPR studies of these metallocages in the powder phase at room temperature and 77 K showed a trend of the g values (g|| >2.10>g⊥ >2.00) indicating a dx2-y2 -based ground state with square-pyramidal geometry for the Cu(II) centers. The magnetism of these metallocages can be interpreted as the result of a combination of relatively small magnetic coupling integrals and a substantial contribution of temperature-independent paramagnetism (TIP). The weak magnetic interaction is corroborated by the results of DFT calculations and the EPR spectra. Availability of the low-lying state for spin population was confirmed by a magnetization study, which revealed a magnetic moment approaching 2Nß, which would explain the presence of the larger TIP term.

An Unconventional Approach to Induce Liquid-Crystalline Phases of Triazine-Based Dendrons by Breaking Their Self-Assembly into Dimers.

Three triazine-based dendrons (1 a-c) were successfully prepared in 70-83 % yields. These newly prepared dendrons are found to be liquid crystalline (LC). Computational investigations on molecular conformations and dipoles of triazine-based dendrons reveal that the substituent on the central triazine unit interrupts strong dipole or H-bond interactions to avoid dimeric formation. The obtained dendrons, not favouring self-assembly into dimers but showing LC behaviours, provides evidence for an approach contrary to the conventional method of inducing LC behaviours of dendrons by dimer or trimer formation, mostly through H-bond interactions.

A small change in central linker has a profound effect in inducing columnar phases of triazine-based unconventional dendrimers.

Four unconventional triazine-based dendrimers have been prepared and characterized by (1) H and (13) C NMR spectroscopies, mass spectrometry, and elemental analysis. Based on DSC studies, polarizing microscopy, and powder XRD, two of these dendrimers, containing linkers with an odd number of carbon atoms, were observed to display columnar liquid-crystalline phases during thermal treatment. However, the other two dendritic analogues, containing linkers with an even number of carbon atoms, were not observed to behave correspondingly. Based on computer simulation, we reasonably assume that the dendrimers with an odd number of carbon atoms in their linkers distort their molecular shape and adopt two isomeric structures due to asymmetrical congestion. This reduces the molecular π-π face-to-face interaction, which in turn causes the dendrimers to form columnar LC phases during thermal treatment. However, the dendrimers with an even number of carbon atoms in their linkers have more symmetrical skeletons and do not display any liquid-crystalline phase upon thermal treatment. This new strategy should be applicable for eliciting the columnar liquid-crystalline properties of other types of unconventional dendrimers with rigid frameworks.

A semi-flexible aminotriazine-based bis-methylpyridine ligand for the design of nickel(II) spin clusters.

The self-assembly of a semi-flexible aminotriazine-based bis-methylpyridine ligand, N(2),N(2)-dibenzyl-N(4),N(6)-di(pyridylmethyl)-1,3,5-triazine-2,4,6-triamine (H2L), with NiCl2 and NiBr2 afforded two new nickel(II) clusters, (H2NMe2)2[Ni5(OH)2(H2L)2Cl10] (1) and [Ni6(OH)2(H2L)2Br10(THF)2] (2) showing a high spin ground state of S = 3.

Preparation of unconventional dendrimers that contain rigid NH-triazine linkages and peripheral tert-butyl moieties for CO2 -selective adsorption.

Three unconventional dendrimers that contained rigid NH-triazine linkages and peripheral tert-butyl moieties were prepared by using a convergent approach and characterized by (1)H and (13)C NMR spectroscopy, mass spectrometry, and elemental analysis. Based on a thermogravimetric analysis study, these dendrimers were observed to display thermal stability at about 300 °C. The NH-triazine moiety, which possessed protonated and proton-free nitrogen sites (like the imidazole unit), displayed the capture of polarizable CO2 molecules through hydrogen-bond and/or dipole-quadrupole interactions. In addition, the adsorption of various amounts of CO2 and N2 at different pressures suggests that the dendritic pores, which arise from the stacking of the middle co-planar and rim protuberant dendrimers, Gn -N∼N-Gn (n=1-3), either swell or shrink at high pressure, thus indicating that these dendrimers may have a breathing ability.

Infinite copper(II) coordination architectures from a resonative aminotriazine-derived tripodal ligand: synthesis, structures, and magnetic properties.

The ligand 2,4,6-tris(2-picolylamino)-1,3,5-triazine (o-H3tpat) with essentially resonative structure and two copper(II)-based one-dimensional coordination chain structures, [Cu3Cl5(o-H2tpat)(H2O)]·MeOH·CH2Cl2 (1) and [Cu2(o-H2tpat)(H2O)(MeOH)(NO3)2](NO3)·3MeOH (2), with different structural patterns have been synthesized and characterized using single crystal X-ray diffraction analysis. For o-H3tpat, two crystalline forms showing different solid-state structural features are obtained from MeOH/Et2O (form I) and CH2Cl2/Et2O (form II), respectively. The o-H3tpat form I adopts an asymmetric-configured all-amino resonative tautomer with three cis-trans-trans-arranged pyridyl groups, whereas the o-H3tpat form II adopts also an identical resonative structure but where two of the three pyridyl groups are in a cis-manner and the third one is nearly coplanar with the central aminotriazine core. On the other hand, the designed tripodal ligand in both Cu(II)-complexes serves as a monoanion, o-H2tpat(-), which suits a propeller-configured all-imino resonative structure in 1 and a syn-anti-configured amino-imino-imino resonative structure in 2. These observations significantly indicate that the o-H3tpat ligand can self-adjust and interconvert its conformation via a possible structure transformation associated with proton-shift to adapt a change in the crystallization and self-assembly reaction systems. In the magnetic point of view, 1 is treated as repeated chains composed of infinite {Cu6Cl10} units wherein the hexanuclear unit is further decomposed to one {Cu(II)4Cl6} and two magnetically isolated {Cu(II)Cl2} subunits. Antiferromagnetic interactions are found for the Cu4 subunits (g = 2.33, 2J1 = -5.6 cm(-1), 2J2 = -8.6 cm(-1), 2J3 = -4.1 cm(-1), and J4 held to zero). For 2, it is considered as an infinite chain that composes of Cu2 units antiferromagnetically coupled (g = 2.03, 2J1 = -0.2 cm(-1)). The small antiferromagnetic exchange constants in both 1 and 2 suggest that the unpaired spins do not effectively interact through the tripodal o-H2tpat(-) ligands.

Induction of the columnar phase of unconventional dendrimers by breaking the C2 symmetry of molecules.

Two triazine-based unconventional dendrimers were prepared and characterized by (1)H and (13)C NMR spectroscopy, mass spectrometry, and elemental analysis. Differential scanning calorimetry, polarizing microscopy, and powder XRD studies showed that these dendrimers display columnar liquid-crystalline phases during thermal treatment. This is ascribable to breaking of their C(2) symmetry. The molecular conformations of prepared dendrimers were obtained by computer simulation with the MM3 model of the CaChe program in the gas phase. The simulation showed that the conformations of the prepared dendrimers are rather flat and disfavor formation of the LC phase. However, due to C(2)-symmetry breaking, the prepared dendrimers have structural isomers in the solid state and thus show the desired columnar phases. This new strategy should be applicable to other types of unconventional dendrimers with rigid frameworks.

Formation of columnar liquid crystals on the basis of unconventional triazine-based dendrimers by the C3-symmetric approach.

Two series of unconventional triazine-based dendrimers with C(2) symmetry and C(3) symmetry were prepared. The newly prepared C(3)-symmetrical dendrimers were characterized by (1)H and (13)C NMR spectroscopy, mass spectrometry, and elemental analysis. Differential scanning calorimetry, polarizing microscopy, and powder XRD showed that the C(3)-symmetrical dendrimers display columnar liquid-crystalline phases during thermal treatment, but the C(2)-symmetrical dendrimers were not observed to behave correspondingly. The molecular conformations of C(3)- and C(2)-symmetrical dendrimers were obtained by computer simulation with the MM2 model of the CaChe program in the gas phase. The simulation results reasonably explain the different mesogenicities of C(3)- and C(2)-symmetric dendrimers. This new strategy should be applicable to other types of unconventional dendrimers with rigid frameworks for displaying columnar liquid-crystalline behavior.

Multielectron redox chemistry of a neutral, NIR-active, indigo-pillared Re(I)-based triangular metalloprism.

Self-assembled, hexarhenium(I), triangular metalloprism compound [{(CO)(3)Re(µ-2)Re(CO)(3)}(3)(µ(3)-1)(2)] (3) featuring three bis-chelating pillarlike indigo dianions (µ-2), each of which connects two fac-Re(CO)(3) cores, which are interconnected by a tritopic N donor, that is, a 2,4,6-tris(4-pyridyl)-1,3,5-triazine (µ(3)-1, tPyTz) ligand, has been synthesized in high yield and characterized. Metalloprism 3 exhibits a strong absorption in the near-infrared (NIR) region. The reversible, multielectron redox properties of the electrogenerated 3(n) species, where n=3+, 0, 3-, 4-, 5-, 8-, in the visible and especially in the NIR region were investigated in THF solution by cyclic voltammetry (CV), chronocoulometry, EPR spectroscopy, and thin-layer UV/Vis/NIR spectroelectrochemistry (SEC). Stepwise, site-specific electrochemical reductions lead to the formation of a series of highly stable ion (radical) species in which electrons associated with µ-2 or µ(3)-1 components of the molecule can be clearly distinguished. An EPR investigation revealed interaction of unpaired electrons with the metal nuclei ((185,187)Re, I=5/2) in the reduced intermediates. The framework has C(2) symmetry, and accidental degeneracies suffice. Detailed theoretical calculations by structure-based DFT confirm that the triply degenerate HOMO has ≥70% indigo character with a sizable dπ-Re character, while the LUMO is dominated by the triply degenerate indigo ligands, and the LUMO+1 by doubly degenerate tPyTz ligands. A comparison of 3 and previously reported 2,2'-bis-benzimidazolate- (BiBzlm) or alkoxy-pillared Re(I) metalloprisms indicates a very low switching potential with a potential window of less than 1 V and reversibly accessible optical properties with higher stability of the intermediates. The properties exhibited by 3 appear to be due to the slight tuning of the bridging ligand from N,N(-) to N,O(-).

Synthesis, characterization and structural transformation of a discrete tetragonal metalloprism.

A novel M(2)L(4) tetragonal metalloprism, [(NO(3)(-))⊂{Cu(2)(µ-Hdpma)(4)}(NO(3))(2)](NO(3))(5) (1), was prepared from the self-assembly reaction of Cu(NO(3))(2)·3H(2)O and flexible clip-like organic ligand di(3-pyridylmethyl)amine (dpma) under acidic conditions. The cationic prismatic hollow structure of 1 hosts one nitrate anion via both metal-ligand dative bonds and electrostatic interactions. Metalloprism 1 can dissolve in water and its prismatic structure remains intact as supported by ESI-MS data. When metalloprism 1 was treated with sodium thiocyanate and sodium azide in aqueous solutions, two polymeric coordination architectures, [Cu(µ-Hdpma)(2)(NCS)(2)](NO(3))(2) (2) and [Cu(µ-dpma)(2)(µ-1,1-N(3))(µ-1,3-N(3))] (3), formed at room temperature, respectively. Polymer 2 has a two-dimensional sheet structure showing a simple rhombic 4(4)-sql topology in network connectivity, whereas polymer 3 gives a three-dimensional uninodal pcu net. The conformation of the flexible ditopic ligand is varied from a trans-trans-syn conformer in 1 to a trans-trans-anti conformer in 2 and to a trans-gauche-anti conformer in 3. The observations imply the occurrence of structural transformation from a discrete metalloprism into polymeric coordination architectures via a decoordination/rearrangement process. Magnetic studies of metalloprism 1 suggest that the two Cu(II) centers are weakly antiferromagnetically coupled. The spins communicate via the nitrate template while the Cu···O(nitrate) interactions are weak. For polymer 3, a ferromagnetically coupled system (J(2) = +17.6 cm(-1)) is operative between two Cu(II) centers bridged by end-on azidos and an antiferromagnetic coupling (J(1) = -7.7 cm(-1)) between two Cu(II) centers with end-to-end azidos. In contrast to relatively large coupling values of the reported examples, the weak ferromagnetic interaction results from insufficient spin delocalization between two Cu(II) centers.