Recent developments in the chemistry of hofmann-type and the analogous clathrates

Hofmann-Type Cyanide Bridged Coordination Polymers for Advanced Functional Nanomaterials

Since the discovery of Hofmann clathrates of inorganic cyanide bridged coordination polymers (Hofmann-type CN-CPs), extensive research is done to understand their behavior during spin transitions caused by guest molecules or external stimuli. Lately, research on their nanoscale architectures for sensors and switching devices is of interest. Their potential is reported for producing advanced functional inorganic materials in two-dimensional (2D) morphology using a scalable solid-state thermal treatment method. For instance, but not restricted to, alloys, carbides, chalcogenides, oxides, etc. Simultaneously, their in situ crystallization at graphene oxide (GO) nanosheet surfaces, followed by a subsequent self-assembly to build layered lamellar structures, is reported providing hybrid materials with a variety of uses. Hence, an overview of the most recent developments is presented here in the synthesis of nanoscale structures, including thin films and powders, using Hofmann-type CN-CPs. Also thoroughly demonstrated are the most recent synthetic ideas with the modest control over the size and shape of nanoscale particles. Additionally, in order to create new functional hybrid materials for electrical and energy applications, their thermal decomposition in various environments and hybridization with GO and other guest molecules is examined. This review article also conveyed their spin transition, astounding innovative versatile adhesives, and structure features.

High-Pressure Effects on Hofmann-Type Clathrates: Promoted Release and Restricted Insertion of Guest Molecules

The search for effective methods to accurately control host-guest relationship is the central theme of host-guest chemistry. In this work, high pressure successfully promotes guest release in the Hofmann-type clathrate of [Ni(NH₃)₂Ni(CN)₄]·2C₆H₆ (Ni-Bz) and restricts guest insertion into Ni(NH₃)₂Ni(CN)₄ (Ni-Ni). Because of the weak host-guest interactions of Ni-Bz, external force gradually removes guest benzene from the host framework, leading to puckered layers. Further theoretical calculations reveal the positive pressure contribution to breaking the energy barrier between Ni-Bz and Ni-Ni, explaining guest release from an energy standpoint. Inversely, guest insertion is restricted in the synthesized host of Ni-Ni because of the steric hindrance effect at high pressure. This study not only reveals structural effects on host-guest behaviors but also proves the role of pressure in controlling host-guest interactions. This unique observation is also crucial for the further application of host-guest materials in sustained and intelligent drug release, molecular separation, and transportation.

Synthesis, spectroscopic, thermal and structural properties of [M(3-aminopyridine)2Ni(μ-CN)2(CN)2]n (M(II)=Co and Cu) heteropolynuclear cyano-bridged complexes

Two novel cyano-bridged heteropolynuclear complexes, [Co(3-aminopyridine)2Ni(μ-CN)2(CN)2]n and [Cu(3-aminopyridine)2Ni(μ-CN)2(CN)2]n have been synthesized and characterized by elemental, thermal, FT-IR and FT-Raman spectroscopies. The structures of complexes have been determined by X-ray powder diffraction. The FT-IR and FT-Raman spectra of complexes have been recorded in the region of 3500-400cm(-1) and 3500-100cm(-1), respectively. General information was acquired about structural properties of these complexes from FT-IR and FT-Raman spectra by considering changes at characteristic peaks of the cyano group and 3AP. The splitting of the ν(CN) stretching bands in the FT-IR spectra for complexes indicates the presence of terminal and bridging cyanides. The thermal behaviors of these complexes have been also investigated in the range of 25-950°C using TG and DTG methods. Magnetic susceptibility measurements were made at room temperature using Gouy-balance.

FT-IR spectroscopic investigation of some Hofmann type complexes: M(1-phenylpiperazine)2Ni(CN)4 (M=Ni, Co, Cd, Pd or Mn)

New Hofmann type complexes in the form of M(pp)(2)Ni(CN)(4) (where pp=1-phenylpiperazine and M=Ni, Co, Cd, Pd or Mn) have been prepared in powder form and their infrared spectra have been reported in the range of (4000-400) cm(-1). The thermal behaviours of these complexes have been investigated by differential thermal analysis (DTA) and thermo-gravimetric analysis (TGA). Ni(pp)(2)Ni(CN)(4) complex has been examined via transmission electron microscope (TEM). The results suggest that these compounds are similar in structure to Hofmann type complexes and their structures consist of polymeric layers |M-Ni(CN)(4)|(infinity) with the pp molecule bounded to the metal atom (M).

Inorganic-organic hybrid molecular architectures of cyanometalate host and organic guest systems: specific behavior of the guests

Molecular architectures built of inorganic cyanometalate building blocks provide variegated host structures with several organic guest molecules. The strategies to derive novel structures are presented briefly. The formation of a charge-transfer (CT) complex as the guest inside the cavity and the photochemistry of the CT complexes are discussed. The chemical pressure that the guest experiences inside the cavity is also discussed based on the vibrational spectroscopic results.

Vibrational spectroscopic study on pyrimidine metal(II) tetracyanometalate complexes

The results of an infrared and Raman spectroscopic study are reported for seven new metal(II) pyrimidine tetracyanonickelate complexes, M(pyr)2Ni(CN)4 [where (pyr) = pyrimidine; M = Mn, Fe, Co, Zn, Ni, Cu or Cd] and an IR spectroscopic study is presented for new cadmium pyrimidine tetracyanometalate complex, Cd(pyr)2Cd(CN)4. The spectral data suggest that the first seven compounds belong to the Hofmann-type and the last compound belongs to the Hofmann-Td-type of complexes.

Novel 4-vinylpyridine-extended metal-dibenzoylmethanate host frameworks: structure, polymorphism, and inclusion properties

In this contribution we show that host materials based on metal dibenzoylmethanates (DBM) can be extended in a versatile way by decreasing the packing efficiency of the simpler metal DBM's reported earlier. Specifically, this can be accomplished by coordinating two 4-vinylpyridines (4-ViPy) to the metal (Ni or Co) DBM units to give [M(4-ViPy)2(DBM)2] host complexes. These display a remarkable polymorphism and an ability to form inclusion compounds with a large variety of organic species. Five non-clathrate phases representing three polymorphic types and twenty-eight inclusion compounds with nineteen guests, representing five structural types were isolated and studied in varying degrees of detail. The inclusion compounds can be prepared by recrystallization or by interaction of the solid host with guest vapor. In the latter case, the process realization, kinetics and final product strongly depend on the host polymorph chosen as starting material. Kinetic studies executed with powder XRD suggest that transient formation of inclusion compounds may occur even during solvent vapor induced transformation of one guest-free polymorph to another. The beta polymorph of the Ni-host reveals the strongest clathratogenic ability as well as a high selectivity towards certain homologues and isomers. Its properties give insight into the concept of "flexible zeolite mimics", or "apohosts", as this empty host form is energetically and structurally predisposed towards inclusion processes. In all eleven (three host and eight clathrate) structures studied by single crystal X-ray diffraction the [M(4-Vi-Py)2(DBM)2] complex molecule is transconfigured. In most, the host molecules show effective packing in one dimension by forming parallel chains. Guest species are located between the chains in cages or channels formed by combining voids in the host molecules belonging to adjacent chains. The corresponding Ni and Co versions of the compounds studied were similar.