Towards Stepwise Cluster Assembly: A Decacopper(II) Complex Obtained by Controlled Expansion of a Metallasiloxane Cage

Abstract

The synthesis of new magnetic clusters with unprecedented spin topologies is a central topic in the field of molecular magnetism. Among different strategies that have been developed, serendipitous assembly [1] and rational design [2] represent opposite limiting approaches. The rational construction of heptanuclear clusters with high-spin ground states has been reported starting from hexacyanometalates [M(CN) 6 ] 3À (M ¼ Cr, Fe) and mononuclear complexes bearing a capping ligand. [2] The use of robust, preformed clusters as central cores represents an even more appealing approach, which we are currently pursuing. In particular, we are focusing on metallasiloxane cages such as [Cu 6 {(PhSiO 2 ) 6 } 2 L 6 ] [3] (where L ¼ monodentate ligand). The [Cu 6 {(PhSiO 2 ) 6 } 2 ] skeleton features a layer of six coplanar metal ions, sandwiched between two [(PhSiO 2 ) 6 ] 6À ligands. Similar architectures containing other first-row divalent metal ions and encapsulating a chloride ion are known. [3a, 4] The twelve six-membered chelate rings in the [Cu 6 {(PhSiO 2 ) 6 } 2 ] structure convey a remarkable inertness and thermodynamic stability to the cluster core. In contrast, the monodentate ligands which surround the Cu 6 cage are labile and can be easily replaced in solution by open-shell units bearing suitable bridging groups. In principle, this allows a fully controlled organization of a second shell of magnetic centers around the Cu 6 unit, Figure 1.Herein we report the successful expansion of the hexacopper(ii) cage 1 through the addition of four [Cu(tmpa)CN] þ (tmpa ¼ tris(2-pyridylmethyl)amine) [5, 6] units from 3 to give a decacopper(ii) cluster 2. ½Cu 6 fðPhSiO 2 Þ 6 g 2 ðnBuOHÞ 6Àx ðH 2 OÞ x 1 ½CuðtmpaÞCNPF 6 3 ½Cu 6 fðPhSiO 2 Þ 6 g 2 fNCCuðtmpaÞg 4 ðPF 6 Þ 4 2 Compound 2 was synthesized by reaction of 1 [3b] with the copper cyanide complex 3 [5a] in a methanol±chloroform solvent mixture (see Experimental Section).The composition of the crystalline compound, 2¥2 CHCl 3 ¥ 2.75 MeOH¥0.25 H 2 O, was established by elemental analysis and a low-temperature single-crystal X-ray diffraction investigation. The molecular structure of the cation of 2 has idealized D 2 point-group symmetry (Figures 2 and 3). The metal topology comprises an hexagonal, almost planar Cu 6 array (within AE 0.0108(6) ä), plus four peripheral Cu(tmpa) units linked to the central core through cyanide bridges. Formation of the cyanide bridge induces only minor structural changes in the [Cu(tmpa)CN] þ unit, the bond lengths of which are equal to within 3s of those in 3. On the other hand, the trigonal-bipyramidal (TB) coordination geometry of the copper(ii) ion of 2 is slightly more distorted, with t values [7] in the range 0.843(7)±0.902 (7), compared with 0.943(3) in 3.[5a] The arrangement of the bulky Cu(tmpa) units around the Cu 6 core of 2 results in significant departures from linearity in the Cu-N-C-Cu(tmpa) moieties, which have a cisoid conformation with N-C-Cu(tmpa) and Cu-N-C angles in the range 168.8(7)±

Synthesis, Structure and Magnetic Properties of a Novel Linear CuII‐Trimer Complex

“…The three copper atoms within the layer form a nearly linear trimer with a Cu–Cu–Cu angle of 173.5(1)° (Figure 2). The nonbonded Cu ··· Cu distances in the trimer are within the range of 2.9931(6)–3.0310(6) Å, which is significantly longer than corresponding distances described earlier in the sandwich‐like copperphenylsiloxanes {Cu 6 [(PhSiO 2 ) 6 ] 2 } · 6(EtOH) ( 4 ),4c {Cu 6 [(PhSiO 2 ) 6 ] 2 } · 6(DMF) ( 5 ),4d and {[Cu 6 {(PhSiO 2 ) 6 } 2 ] · [Cu(tmpa)CN] 4 } · (PF 6 ) 4 ( 2 ),3a yielding an average value of about 2.82 ± 0.03 Å.…”

“…1.96 Å] and square‐planar coordination [1.876(5)–1.922(5), av. 1.90 Å] are different 3a. The Cu–N bonds in 1 are 1.999(2)–2.015(2) Å long.…”

A Carbonate-Templated Decanuclear Mn Nanocage with Two Different Silsesquioxane Ligands

“…Silsesquioxanes with a general formula of [RSiO 1.5 ] n , which has diverse oligomeric forms ( n = 1, 2, 4, 6, 7, 8, 9, 10, 12) and multicoordinate sites of terminal oxygen atoms with high coordination affinity, have proven to be versatile building blocks for constructing polynuclear cage-like metallasilsesquioxanes (CLMSs). , Moreover, the silsesquioxane ligands combining the inorganic Si–O–Si skeletons with exterior organic constituents not only make the CLMSs being considered as the ideal theoretical molecular models for metal silicate but also endow the CLMSs with peculiar structural topology, remarkable catalytic reactivity, and outstanding magnetic effects. − Nevertheless, these kinds of ligands have still been far less studied to date. Further exploration of the chemistry of silsesquioxane based CLMSs seemed to be of significant profit.…”

“…Generally, the silsesquioxane ligands are available via in situ hydrolysis and condensation of the key precursor {RSi­(OR′) 3 }. So far, there have been cyclic, acyclic, and polycyclic types of the oligomeric silsesquioxanes with different condensation degrees (i.e., different number of [Si] atoms) being established (e.g., [Si1], , [Si4], − [Si5], , [Si6], ,,− [Si7], − [Si8], [Si9], [Si10], ,, and [Si12]). These various incompletely condensed silsesquioxanes may provide more possibilities to modulate the aggregation of metal ions.…”

Construction of Two Discrete Molecular High‐Nuclearity Copper(II) Complexes as Heterogeneous Catalysts for Oxidative Coupling Polymerisation of 2,6‐Dimethylphenol

“…Abbati et al have reported a decacopper(II) complex obtained by expansion of a hexacopper(II) cage through the addition of four [Cu(tmpa)CN] + [tmpa = tris(2‐pyridylmethyl)amine] units. The complex comprises an almost planar Cu 6 array, plus four peripheral Cu(tmpa) units linked to the central core through cyanide bridges 11. Recently, Yang et al have reported a sandwich‐type hexacopper(II) cage incorporating a unique hybrid hexanuclear copper complex 12.…”