Reaction between boric acid and guanidinium salts in methanolic solution at room temperature in the presence of various bases and anions gives well-formed solvated crystals of composition {[B(OCH3)4]3[C(NH2)3]4}+X-. The products in which X- = Cl- and PF6- are characterized by single-crystal X-ray diffraction. The tetramethoxyborate and guanidinium components form a highly symmetrical (cubic) hydrogen-bonded 3D network having the "boracite topology" [i.e., the (63)(6284) topology]. Highly disordered solvent molecules and anions occupy methyl-surfaced cavities and channels that represent more than 30% of the space.

The serendipitous discovery of a 3D [Cu(CO(3))(2)(2-)](n) network with the topology of the 4(2)6(4) sodalite net in [Cu(6)(CO(3))(12)(CH(6)N(3))(8)].K(4).8H(2)O paved the way for the deliberate engineering of an extensive series of structurally related guanidinium-templated metal carbonates of composition [M(6)(CO(3))(12)(CH(6)N(3))(8)]Na(3-)[N(CH(3))(4)].xH(2)O, where the divalent metal M in the framework may be Mg, Mn, Fe, Co, Ni, Cu, Zn, or Cd. A closely related crystalline material with a [Ca(CO(3))(2)(2-)](n) sodalite-like framework, but containing K(+) rather than Na(+), of composition [Ca(6)(CO(3))(12)(CH(6)N(3))(8)]K(3)[N(CH(3))(4)].3H(2)O was also isolated. All of these compounds were obtained under the simplest possible conditions from aqueous solution at room temperature, and their structures were determined by single-crystal X-ray diffraction. Pairs of guanidinium cations are associated with the hexagonal windows of the sodalite cages, alkali-metal cations are associated with their square windows, and N(CH(3))(4)(+) ions are located at their centers. Structures fall into two classes depending on the metal, M(II), in the framework. One type, the BC type (Im3m), comprising the compounds for which M(2+) = Ca(2+), Mn(2+), Cu(2+), and Cd(2+), has a body-centered cubic unit cell, while the second type, the FC type (Fd3c), for which M(2+) = Mg(2+), Fe(2+), Co(2+), Ni(2+), and Zn(2+), has a face-centered cubic unit cell with edges on the order of twice those of the BC structural type. The metal M in the BC structures has four close carbonate oxygen donors and four other more distant ones, while M in the FC structures has an octahedral environment consisting of two bidentate chelating carbonate ligands and two cis monodentate carbonate ligands.

ZuschriftenIn einem anionischen Koordinationspolymer sind die Cu II -Ionen durch Carbonat-Ionen zu einem kubischen Netzwerk verknüpft, das die Topologie des im Hintergrund dargestellten Sodalithnetzes hat. Paare von Guanidinium-Ionen in den hexagonalen Fenstern des Sodalithkäfigs (nicht gezeigt) dienen als H-Brücken-Template, während Alkalimetallionen (grün) gut in die quadratischen Fenster passen. Näheres erläutern R. Robson et al. auf den folgenden Seiten.

The guanidinium cation C(NH 2 ) 3 + serves as a powerful structure-determining component in a number of networks, both metal/ligand-bonded and hydrogen-bonded. The six hydrogen atoms of the cation are nicely disposed to form a pair of hydrogen bonds to each of three oxyanions, as shown in the generalized representation 1. In an extensive family of carbonate-bridged coordination polymers reported recently, the guanidinum cation plays the crucial structural role represented in 1 (Z = C), thus promoting the formation of highly symmetrical metal/carbonate networks with cubic symmetry and sodalite-like topology.[1] The arrangement seen in 1 (Z = B) is present in some highly symmetrical cubic guanidinium borate derivatives we discovered recently which have the boracite topology.[2] A closely related hydrogen-bonding mode, again as in 1 (Z = S), is seen in a range of guanidinium sulfonates in which the sulfonate units, as well as the guanidinium components, act as 3-connecting nodes, each being attached to three guanidinium units as in 2. In some of the nicest examples of true crystal engineering, Ward and coworkers have elegantly exploited this complementarity between the guanidinium cation and various sulfonate anions to generate an extensive family of solids having a common, predictable, yet pliable, underlying hydrogenbonded 3-connected sheet structure with the (6,3) topology or hexagonal grid topology.[3] We report here a new family of hydrogen-bonded frameworks related to these guanidinium sulfonates in which the guanidinium cation again acts as in 1 (Z = S) and a sulfur oxyanion (in this case SO 4 2À ) again acts as a second type of 3-connecting node; however, the network generated is the most symmetrical 3-connected 3D network possible, namely the (10,3)-a net, [4] rather than the most symmetrical 3-connected 2D network possible that was seen by Ward and co-workers. In all cases, the crystals appear almost exclusively as well-formed tetrahedra, space group P2 1 3, a = 10.5828(6) (X = S), 10.7589(5) (X = Cr), or 10.8802(4) (X = Mo).[6] The three compounds are isostructural and the following observations pertaining to the sulfate apply equally well to the chromate and molybdate, except for minor differences in some distances and angles.

The combination of Cu(II) with excess sodium sulfite or a mixture of sodium sulfite and sodium hydrogensulfite produces a colorless solution consistent with the reduction of Cu(II) to Cu(I). The addition of divalent metal ions such as Mn 2+ , Co 2+ , Ni 2+ and Zn 2+ to such solutions, leads to the generation of coordination networks in which the divalent metal ions link together anions of formula Cu(SO 3 ) 4 7-. This symmetrical anion consists of a tetrahedrally coordinated Cu(I) center bound to the sulfur atoms of four sulfite anionic ligands. Isostructural 1D coordination polymers of composition Naand a 3D coordination polymer of composition Na(H 2 O) 6 -{[Cu I (SO 3 ) 4 ][Mn II (H 2 O) 2 ] 3 } are reported.