Niobium Alcoholate Clusters with an Octahedral Arrangement of Metal Atoms: [K(CH3OH)4]2 [Nb6(OCH3)18] and [Na([18]crown‐6)(C2H5OH)2]2 [Nb6(OC2H5)12(NCS)6]

Complete exchange : [M₆X₁₂] type cluster compounds with an octahedral M₆ metal atom arrangement, which is completely surrounded by alcoholato ligands, were unknown until now. The first representatives are prepared containing a [Nb₆(OR)₁₂]⁴⁺ unit (R=CH₃ or C₂H₅). They are accessible at elevated temperatures from strongly basic alcoholate solutions of [Nb₆Cl₁₂]²⁺‐containing precursors. C gray, H white, K turquoise, Nb blue, O red.

     

Synthesis and structural characterization of a nonplanar neutral [36]metallacrown-12 nickel compound [Ni(C13H9N3O2)(CH3OH)]12

A nonplanar metallacrown [Ni-N-N]12 was achieved using a pentadente ligand, salicylaldehyde 2-pyridinecarboxylhydrazone (H2L) via a new modular self-assembly approach. The special bridging models of the ligand forced the macrocycle to form in a specific size with the wavelike conformation.     

The magnetic behaviour of [NnBu4]4[Ni16Pd16(CO)40]: an even-electron homoleptic carbonyl-metal cluster anion displaying a J = 2 ground state

The magnetic behaviour of the even-electron [Ni16Pd16(CO)40]4- cluster, in its [NnBu4]+ salt, has been investigated by magnetometry and muon spin rotation/relaxation (muSR) spectroscopy. The susceptibility measurements show an exceptionally high magnetic moment corresponding to a total spin value J=2. This suggests a Hund filling of a quadruplet ground state, quite unique in carbonyl-metal clusters. SQUID magnetometry shows a departure from the Curie-Weiss law, for T>150 K, and strong deviation from a Brillouin behaviour of the magnetisation curves. muSR spectroscopy in zero applied field shows a temperature independent decay of the muon spin polarisation, similar to that of a purely paramagnetic system. The observed muon spin repolarisation in a moderate external longitudinal field, however, invalidates this simple picture and suggests the presence of a local anisotropy field acting on the cluster's magnetic moment. A consistent interpretation of magnetometry and muSR results implies the occurrence of an additional interaction of the cluster spin with an effective crystalline field. The inclusion of this interaction in a model Hamiltonian allows us to successfully reproduce both the susceptibility and magnetisation data.     

Site selectivity in the reactions of the hexanuclear platinum cluster [Pt6(mu-PtBu2)4(CO)6][CF3SO3]2

The previously reported hexanuclear cluster [Pt(6)(mu-PtBu(2))(4)(CO)(6)](2+)[Y](2) (1-Y(2): Y=CF(3)SO(3) (-)) contains a central Pt(4) tetrahedron bridged at each of the opposite edges by another platinum atom; in turn, four phosphido ligands bridge the four Pt-Pt bonds not involved in the tetrahedron, and, finally, one carbonyl ligand is terminally bonded to each metal centre. Interestingly, the two outer carbonyls are more easily substituted or attacked by nucleophiles than the inner four, which are bonded to the tetrahedron vertices. In fact, the reaction of 1-Y(2) with 1 equiv of [nBu(4)N]Cl or with an excess of halide salts gives the monochloride [Pt(6)(mu-PtBu(2))(4)(CO)(5)Cl](+)[Y], 2-Y, or the neutral dihalide derivatives [Pt(6)(mu-PtBu(2))(4)(CO)(4)X(2)] (3: X=Cl; 4: X=Br; 5: X=I). Moreover, the useful unsymmetrically substituted [Pt(6)(mu-PtBu(2))(4)(CO)(4)ICl] (6) was obtained by reacting equimolar amounts of 2 and [nBu(4)N]I, and the dicationic derivatives [Pt(6)(mu-PtBu(2))(4)(CO)(4)L(2)](2+)[Y](2) (7-Y(2): L=(13)CO; 8-Y(2): L=CNtBu; 9-Y(2): L=PMe(3)) were obtained by reaction of an excess of the ligand L with 1-Y(2). Weaker nitrogen ligands were introduced by dissolving the dichloride 3 in acetonitrile or pyridyne in the presence of TlPF(6) to afford [Pt(6)(mu-PtBu(2))(4) (CO)(4)L(2)](2+)[Z](2) (Z=PF(6) (-), 10-Z(2): L=MeCN; 11-Z(2): L=Py). The "apical" carbonyls in 1-Y(2) are also prone to nucleophilic addition (Nu(-): H(-), MeO(-)) affording the acyl derivatives [Pt(6)(mu-PtBu(2))(4)(CO)(4)(CONu)(2)] (12: Nu=H; 13: Nu=OMe). Complex 12 is slowly converted into the dihydride [Pt(6)(mu-PtBu(2))(4)(CO)(4)H(2)] (14), which was more cleanly prepared by reacting 3 with NaBH(4). In a unique case we observed a reaction involving also the inner carbonyls of complex 1, that is, in the reaction with a large excess of the isocyanides R-NC, which form the corresponding persubstituted derivatives [Pt(6)(mu-tPBu(2))(4)(CN-R)(6)](2+)[Y](2), (15-Y(2): R=tBu; 16-Y(2) (2-): R=-C(6)H(4)-4-C triple bond CH). All complexes were characterized by microanalysis, IR and multinuclear NMR spectroscopy. The crystal and molecular structures of complexes 3, 5, 6 and 9-Y(2) are also reported. From the redox viewpoint, all complexes display two reversible one-electron reduction steps, the location of which depends both upon the electronic effects of the substituents, and the overall charge of the original complex.     

Self-assembly of the octanuclear cluster [Cu8(OH)10(NH2(CH2)2CH3)12]6+ and the one-dimensional N-propylcarbamate-linked coordination polymer {[Cu(O2CNH(CH2)2CH3)(NH2(CH2)2CH3)3](ClO4)}n

The reaction of Cu(ClO4)2.6-H2O and n-propylamine in methanol gives two high-nuclearity products of well-defined compositions. At amine concentrations greater than seven equivalents compared to copper ion concentration, the system fixes carbon dioxide from air to form the one-dimensional carbamate-bridged coordination polymer, {[Cu(mu2-O,O'-O2CNH(CH2)2CH3)(NH2(CH2)2CH3)3](ClO4)}n ({1-ClO4}n). Lower relative amine concentrations lead to the self-assembly of an octanuclear copper-amine-hydroxide cluster [Cu8(OH)10(NH2(CH2)2CH3)12]6+ (2). Both compounds exhibit unique structures: {1-ClO4}n is the first mu2-O,O'-mono-N-alkylcarbamate-linked coordination polymer and 2 is the largest copper-hydroxide-monodentate amine cluster identified to date. The crystal structures indicate that the size of the n-propyl group is probably crucial for directing the formation of these compounds. Magnetic susceptibility studies indicate very weak antiferromagnetic coupling for 1. The octanuclear cluster 2 displays slightly stronger net antiferromagnetic coupling, despite the presence of a number of Cu-O(H)-Cu angles below the value of about 97 degrees that would normally be expected to yield ferromagnetic coupling.