Simple approach to estimating the van der Waals interaction between carbon nanotubes

The van der Waals (vdW) interactions between carbon nanotubes (CNTs) were studied based on the continuum Lennard-Jones model. It was found that all the vdW potentials between two arbitrary CNTs fall on the same curve when plotted in terms of certain reduced parameters, the well depth, and the equilibrium vdW gap. Based on this observation, an approximate approach is developed to obtain the vdW potential between two CNTs without time-consuming computations. The vdW potential estimated by this approach is close to that obtained from complex integrations. Therefore, the developed approach can greatly simplify the calculation of vdW interactions between CNTs

Poly[[aqua­(μ2-oxalato)(μ2-2-oxido­pyridinium-3-carboxylato)holmium(III)] monohydrate]

In the title complex, {[Ho(C2O4)(C6H4NO3)(H2O)]·(H2O)}n, the HoIII ion is coordinated by three O atoms from two 2-oxidopyridinium-3-carboxylate ligands, four O atoms from two oxalate ligands and one water mol­ecule in a distorted bicapped trigonal-prismatic geometry. The 2-oxidopyridin­ium-3-carboxylate and oxalate ligands link the HoIII ions into a layer in (100). These layers are further connected by inter­molecular O—H⋯O hydrogen bonds involving the coordinated water mol­ecules to assemble a three-dimensional supra­molecular network. The uncoordin­ated water mol­ecule is involved in N—H⋯O and O—H⋯O hydrogen bonds within the layer

Poly[bis­(4,4′-bipyridine)(μ3-4,4′-dicarboxybiphenyl-3,3′-di­carboxyl­ato)iron(II)]

In the polymeric title complex, [Fe(C16H8O8)(C10H8N2)2]n, the iron(II) cation is coordinated by four O atoms from three different 4,4′-dicarboxybiphenyl-3,3′-di­carboxyl­ate ligands and two N atoms from two 4,4′-bipyridine ligands in a distorted octa­hedral geometry. The 4,4′-dicarboxybiphenyl-3,3′-di­carboxyl­ate ligands bridge adjacent cations, forming chains parallel to the c axis. The chains are further connected by inter­molecular O—H⋯N hydrogen bonds, forming two-dimensional supra­molecular layers parallel to (010)