Crystal structures and magnetic properties of the interpenetrating rutile-related compounds M(tcm)2 [M = octahedral, divalent metal; tcm− = tricyanomethanide, C(CN)3−] and the sheet structures of [M(tcm)2(EtOH)2] (M = Co or Ni)

Abstract

The isomorphous structures of M(tcm) 2 [M II = Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd or Hg; tcm Ϫ = tricyanomethanide, C(CN) 3 Ϫ ] contain two interpenetrating rutile-related networks generated by octahedral six-connecting metal ions and trigonal three-connecting tcm Ϫ anions. The detailed variable temperature and variable field magnetic properties of this series of high-spin complexes generally point to the existence of very weak intraframework coupling with no evidence for long range magnetic order or interframework effects. The compound Cr(tcm) 2 is the most strongly coupled and displays a field independent maximum in susceptibility at 14.5 K and a J value of Ϫ1.6 cm Ϫ1 (using a Ϫ2JS 1 ؒS 2 Heisenberg chain model); Co(tcm) 2 displays high temperature magnetic moments typical of essentially uncoupled octahedral centres but with a most unusual field dependence in µ Co observed below 10 K, probably due to very weak ferromagnetic coupling, and an M sat value in high fields, at 2 K, which is significantly less than that expected for S = 3/2. Doping of M(tcm) 2 with another MЈ member of the series leads to a crystal structure isomorphous with M(tcm) 2 in which the dopant metal MЈ occupies the M site in a random fashion. The resultant magnetism is simply intermediate between those of the parent phases. The isomorphous structures of [M(tcm) 2 (EtOH) 2 ] (M II = Co or Ni) contain pseudo square-grid sheets in which the tcm Ϫ ligands are each co-ordinated to two metal ions and act as a kinked bridge. Each metal is co-ordinated to four tcm Ϫ anions in an equatorial arrangement and to two axial ethanol ligands. Extensive intrasheet hydrogen bonding exists between the ethanol molecules and the unco-ordinated nitrile of the tcm Ϫ bridges.

Synthesis, Structural Isomerism, and Magnetism of the Coordination Polymers [M(dca)2pyz], M=Mn, Fe, Co, Ni and Zn, dca=Dicyanamide (N(CN) −2), and pyz=Pyrazine

“…arising from a combination of spin}orbit coupling and low-symmetry ligand "eld e!ects. We have observed similar data in other coordination polymers of Co(II) such as Co(tcm) (tcm"tricyanomethanide) (18) Fig. 7.…”

Frameworks for Extended Solids: Geometrical Design Principles

“…It is probably the easiest target for a designed synthesis, despite the fact that there are two kinds of Ti}O bond. Indeed interpenetrating rutile structures have already been reported (77) …”

Design of Frameworks with Mixed Triangular and Octahedral Building Blocks Exemplified by the Structure of [Zn4O(TCA)2] Having the Pyrite Topology

“…However most framework materials with this connectivity reported to date have the rutile topology and in fact this was identified as the default structure, [1] but rutile is significantly less symmetric than pyrite having two kinds of edge and three kinds of ring (transitivity 2232). Most of the rutile-structured materials reported have been cyanides with interpenetrating, partly catenated, frameworks such as {M[C(CN) 3 ] 2 }; [10,14] in some instances the three-coordinated vertex has more than one kind of link as in compounds with a {M[N(CN) 2 ] 2 } framework, so the appearance of a less-symmetrical network is less surprising in this instance. [15] The occurrence of the rutile net in bis(isonicotinate) Fe II is understandable on the same grounds.…”

“…Most of the rutile-structured materials reported have been cyanides with interpenetrating, partly catenated, frameworks such as {M[C(CN) 3 ] 2 }; [10,14] in some instances the three-coordinated vertex has more than one kind of link as in compounds with a {M[N(CN) 2 ] 2 } framework, so the appearance of a less-symmetrical network is less surprising in this instance. [15] The occurrence of the rutile net in bis(isonicotinate) Fe II is understandable on the same grounds. [16] We also note that in the case of MOF-150, the "octahedral" SBU actually has tetrahedral (T d ) symmetry with the planes of opposite carboxylate groups at 908.…”