Synthesis, structure and properties of carboxylate coordination polymers

The work in this thesis focuses on several coordination polymers, their crystal structures and their potential applications as functional materials, in particular, their ferroelectric and magnetic properties. The mechanism of the known ferroelectric phase transition of (C₃NO₂H₇)₃CaCl₂ (TSCC) was studied in detail using both X-ray and neutron diffraction data. The key structural changes occurring in the vicinity of TC were identified in the Ca-O-C bond angles, which change by up to 12˚. The structure of the compound was determined between 300 and 20 K to investigate potential phase transitions as suggested in the literature. The diffraction data did not suggest an additional phase transition within this temperature range. However, the detailed crystallographic studies did uncover new evidence of ferrielectricity, which is consistent with electrical hysteresis data. The origins of the ferroelectricity of TSCC were also probed through the synthesis and characterisation of a range TSCC-related compounds which incorporated a range of alternative halides and metal 2+ cations. Each compound formed coordination polymers which were linked by sarcosine molecules, although the connectivity and structures formed were dependent upon the composition. Whilst none of the TSCC derivatives had ferroelectric properties, diffraction experiments were limited to a low temperature of 90 K and there could be additional phase transitions below this point. A family of oxalate-based coordination polymers ALi₃M(C₂O₄)₃ with a perovskite-like structures were also synthesised. The structural flexibility of these systems was investigated through the incorporation of different A site cations and their magnetic properties were investigated. Polyhedral distortions increase significantly upon the inclusion of rubidium or caesium. Both KLi₃Co(C₂O₄)₃ and KLi₃Ni(C₂O₄)₃ have weak antiferromagnetic exchange and μ[sub](eff) of 4.82 μ[sub]B and 3.62 μ[sub]B, respectively. The syntheses and structures of four new oxalate containing compounds, namely Rb₂Co(C₂O₄)₂.4H₂O, Rb₂CoCl₂(C₂O₄), K₂Li₂Cu(C₂O₄)₃ and Li₄Co(C₂O₄)₃, which could have interesting magnetic and electrochemical properties, are also reported."This work was supported by the Engineering and Physical Sciences Research Council grant number EP/K503162-1 and the School of Chemistry at the University of St Andrews" -- Fundin

New sarcosine-metal halide complexes related to the ferroelectric TSCC

The authors thank the EPSRC for provision of a doctoral studentship to RC (DTG012 EP/K503162-1).There are relatively few sarcosine metal halide complexes. Of these, tris sarcosine calcium chloride (TSCC) ((C3NO2H7)3CaCl2) stands out as an unusual example of a molecular ferroelectric. Here we report the syntheses of eight new related sarcosine-metal halide complexes by slow evaporation. The newly reported materials can be categorised into four different structure types, viz. 3:1 complexes such as (C3NO2H7)3CaBr2, hydrated 3:1 complexes such as (C3NO2H7)3MnI2.2H2O, hydrated 2:1 complexes such as (C3NO2H7)2MgCl2.2H2O, and a 4:1 complex (C3NO2H7)4CaI2.2H2O. The crystal structures of all examples have been determined at multiple temperatures but no evidence is found for any structural transitions to polar phases, either by single crystal X-ray diffraction or by differential scanning calorimetry. The specific compositional reasons behind the apparently unique ferroelectric behaviour of TSCC therefore remain to be ascertained.PostprintPeer reviewe

Perovzalates : a family of perovskite-related oxalates

Authors would like to thank the University of St Andrews (studentship to AJB) and the EPSRC (doctoral studentship to RC: DTG012 EP/K503162-1) for funding.A family of hybrid Perovskite-oxalates (“Perovzalates”) of general composition AILi3MII(C2O4)3 (A = K+, Rb+, Cs+; M = Fe2+, Co2+, Ni2+) are presented. All eight new compounds are isostructural with the previously reported examples NH4Li3Fe(C2O4)3 and KLi3Fe(C2O4)3, crystallising in the rhombohedral space group Rc, with a ∼11.3–11.6 Å, c ∼14.8–15.2 Å. In contrast to other families of “hybrid perovskites” such as the formates, these compounds can be regarded as closer structural relatives to inorganic (oxide) perovskites, in the sense that they contain direct linkages of the octahedral sites via bridging oxygen atoms (of the oxalate groups). It is of note, therefore, that monoatomic cations as large as Cs+ can be incorporated into the perovskite-like A sites of this structure type, which is not feasible in traditional ABO3 perovskites; indeed CsLi3Ni(C2O4)3 appears to exhibit the ‘mostly tightly bound’ 12-coordinate Cs+ ion in an oxide environment, according to a bond valence analysis.PostprintPeer reviewe

A hybrid fluoride layered perovskite, (enH2)MnF4

We acknowledge the University of St Andrews and the China Scholarship Council (studentship to TL) and the EPSRC (DTG: EP/K503162/1) for a studentship (to RC). The are no conflicts of interest to declare.The title compound is the first example of a layered fluoroperovskite containing an interlayer organic cation. Preliminary magnetic characterisation is reported, and structural relationships to related layered perovskites are discussed.PostprintPostprintPeer reviewe

Tuning skyrmions in B20 compounds by 4d and 5d doping

Skyrmion stabilization in novel magnetic systems with the B20 crystal structure is reported here, primarily based on theoretical results. The focus is on the effect of alloying on the 3d sublattice of the B20 structure by substitution of heavier 4d and 5d elements, with the ambition to tune the spin-orbit coupling and its influence on magnetic interactions. State-of-the-art methods based on density functional theory are used to calculate both isotropic and anisotropic exchange interactions. Significant enhancement of the Dzyaloshinskii-Moriya interaction is reported for 5d-doped FeSi and CoSi, accompanied by a large modification of the spin stiffness and spiralization. Micromagnetic simulations coupled to atomistic spin-dynamics and ab initio magnetic interactions reveal a helical ground state and field-induced skyrmions for all these systems. Especially small skyrmions $\sim$50 nm are predicted for Co$_{0.75}$Os$_{0.25}$Si, compared to $\sim$148 nm for Fe$_{0.75}$Co$_{0.25}$Si. Convex-hull analysis suggests that all B20 compounds considered here are structurally stable at elevated temperatures and should be possible to synthesize. This prediction is confirmed experimentally by synthesis and structural analysis of the Ru-doped CoSi systems discussed here, both in powder and in single-crystal forms.Comment: 18 pages, 21 figures, 9 table

Deconstructing compassionate conservation

Compassionate conservation focuses on 4 tenets: first, do no harm; individuals matter; inclusivity of individual animals; and peaceful coexistence between humans and animals. Recently, compassionate conservation has been promoted as an alternative to conventional conservation philosophy. We believe examples presented by compassionate conservationists are deliberately or arbitrarily chosen to focus on mammals; inherently not compassionate; and offer ineffective conservation solutions. Compassionate conservation arbitrarily focuses on charismatic species, notably large predators and megaherbivores. The philosophy is not compassionate when it leaves invasive predators in the environment to cause harm to vastly more individuals of native species or uses the fear of harm by apex predators to terrorize mesopredators. Hindering the control of exotic species (megafauna, predators) in situ will not improve the conservation condition of the majority of biodiversity. The positions taken by so-called compassionate conservationists on particular species and on conservation actions could be extended to hinder other forms of conservation, including translocations, conservation fencing, and fertility control. Animal welfare is incredibly important to conservation, but ironically compassionate conservation does not offer the best welfare outcomes to animals and is often ineffective in achieving conservation goals. Consequently, compassionate conservation may threaten public and governmental support for conservation because of the limited understanding of conservation problems by the general public

Syntheses and crystal structures of three novel oxalate coordination compounds : Rb2Co(C2O4) 2 similar to 4H2O, Rb2CoCl2(C2O4) and K2Li2Cu(C2O4) (3 similar to)2H(2)O

Single crystals of three novel transition-metal oxalates, dirubidium diaquadioxalatocobalt(II) dihydrate or dirubidium cobalt(II) bis(oxalate) tetrahydrate, Rb-2[Co(C2O4) (2)(H2O)(2)]similar to 2H(2)O, (I), catena-poly[dirubidium [[ dichloridocobalt(II)]-similar to-oxalato]] or dirubidium cobalt(II) dichloride oxalate, {Rb-2[CoCl2(C2O4)]}(n), (II), and poly[dipotassium [tri-similar to-oxalato-copper(II)dilithium] dihydrate] or dipotassium dilithium copper(II) tris(oxalate) dihydrate, {K-2[Li2Cu(C2O4)(3)]similar to 2H(2)O}n, (III), have been grown under hydrothermal conditions and their crystal structures determined using single-crystal X-ray diffraction. The structure of (I) exhibits isolated octahedral [Co(C2O4)(2)(H2O) (2)] units, whereas (II) consists of trans chains of Co2+ ions bridged by bidentate oxalato ligands and (III) displays a novel tri-periodic network of Li+ and Cu2+ ions linked by oxalato bridging ligands

New sarcosine-metal halide complexes related to the ferroelectric TSCC

There are relatively few sarcosine metal halide complexes. Of these, tris sarcosine calcium chloride (TSCC) ((C3NO2H7)3CaCl2) stands out as an unusual example of a molecular ferroelectric. Here we report the syntheses of eight new related sarcosine-metal halide complexes by slow evaporation. The newly reported materials can be categorised into four different structure types, viz. 3:1 complexes such as (C3NO2H7)3CaBr2, hydrated 3:1 complexes such as (C3NO2H7)3MnI2.2H2O, hydrated 2:1 complexes such as (C3NO2H7)2MgCl2.2H2O, and a 4:1 complex (C3NO2H7)4CaI2.2H2O. The crystal structures of all examples have been determined at multiple temperatures but no evidence is found for any structural transitions to polar phases, either by single crystal X-ray diffraction or by differential scanning calorimetry. The specific compositional reasons behind the apparently unique ferroelectric behaviour of TSCC therefore remain to be ascertained