Synthesis and properties of [M6X12(C3H7NO)6]X2 (MNb, Ta; XCl, Br)

Niobium and Tantalum Halocyanide Clusters: The Complete Family

Synthetic procedures providing straightforward access to the whole family of Nb and Ta halide clusters with terminal cyanide ligands have been developed. Corresponding [M₆X₁₂(CN)₁₂]^4- (M = Nb, Ta; X = Cl, Br) can be accessed by ligand-exchange procedures from K₄Nb₆X₁₈ (X = Cl, Br) and Bu₄NCN, (Et₄N)₂[Ta₆Cl₁₈] and Bu₄NCN and from [Ta₆Br₁₂(H₂O)₄Br₂]·4H₂O and KCN in moderate to high yields (50-80%). The products were isolated as Bu₄N salts. The compounds were investigated both experimentally and by quantum chemistry, revealing correlations between structural, electrochemical, electrostatic, electronic, and topological features as a function of type of metal, halide, and charge.

Cation-anion pairs of niobium clusters of the type [Nb6Cl12(RCN)6][Nb6Cl18] (R=Et, n Pr, i Pr) with nitrile ligands RCN forming stabilizing inter-ionic contacts

Three new niobium cluster compounds with edge bridged, octahedral hexanuclear metal cores have been synthesised. They consist of cluster pairs with [Nb6Cl12(RCN)6]2+ cations, [Nb6Cl18]2− anions, and co-crystallised nitrile molecules, with R = C2H5 (propionitrile), n C3H7 (butyronitrile), i C3H7 (isobutyronitrile). The synthesis is based on the dehydration of [Nb6Cl14(H2O)4] · 4(H2O) with carboxylic acid anhydrides in the presences of an excess of the respective nitrile. An interesting aspect of these compounds is that the metal atoms of the cluster cation have an average oxidation state different from that of the cluster anion, the former being oxidized losing two electrons. In crystals of all three compounds layers of cluster cations are separated by layers of cluster anions. Perpendicular to these layers of the same cluster types, every cation is surrounded by four anions and vice versa. Between the cations and anions short distances are found between the halogenido ligands and the positively charged C atoms of the nitrile ligands (N–C · · · Cl angles of ~90°). These contacts indicate relatively strong dipole-dipole interactions, which presumably contribute to the arrangement of the cluster ions in the crystals.

The First Coordination Polymers and Hydrogen Bonded Networks Containing Octahedral Nb6 Clusters and Alkaline Earth Metal Complexes

Three novel coordination polymers built of octahedral niobium cyanochloride clusters [Nb6Cl12(CN)6] and alkaline earth metal complexes have been prepared by reaction of aqueous solutions of (Me4N)4Nb6Cl18 and KCN with solutions of alkaline earth metal salts and 1,10-phenanthroline (phen) (1:2 molar ratio) in H2O/EtOH. The structures of [Ca(phen)2(H2O)3]2[Nb6Cl12(CN)6] x (phen)(EtOH)1.6 (1), [Ca(phen)2(H2O)2]2[Nb6Cl12(CN)6] x (phen)2 x 4H2O (2), and [Ba(phen)2(H2O)]2[Nb6Cl12(CN)6] (3) were determined by single-crystal X-ray diffraction. The three compounds were found to crystallize in the monoclinic system (space group Pn) with a = 11.5499(6) A, b = 17.5305(8) A, c = 21.784(1) A, beta = 100.877(1) degrees for 1; triclinic system (P1) with a = 12.609(4) A, b = 13.262(4) A, c = 16.645(5) A, alpha = 69.933(6) degrees, beta = 68.607(6) degrees, gamma = 63.522(5) degrees for 2; and a = 16.057(1) A, b = 16.063(1) A, c = 16.061(1) A, alpha = 86.830(1) degrees, beta = 64.380(1) degrees, gamma = 67.803(1) degrees for 3. Compounds 1 and 2 are built of cluster anions [Nb6Cl12(CN)6]4- trans-coordinated by two Ca2+ complexes via CN ligands to form neutral macromolecular units [Ca(phen)2(H2O)3]2[Nb6Cl12(CN)6] in 1 and [Ca(phen)2(H2O)2]2[Nb6Cl12(CN)6] in 2. Water of coordination and cyanide ligands form hydrogen bonded 3D and 2D frameworks for 1 and 2, respectively. The structure of 3 consists of [Nb6Cl12(CN)6]4- cluster anions and [Ba(phen)2(H2O)]2+ complexes linked through bridging cyanide ligands to form a neutral three-dimensional framework in which each barium complex is bound to three neighboring Nb6 clusters and each Nb6 cluster is linked to six Ba complexes.