Dipicolinate complexes of main group metals with hydrazinium cation

Some new coordination complexes of hydrazinium main group metal dipicolinate hydrates of formulae (N₂H₅)₂M(dip)₂.nH₂O (where, M = Ca,Sr,BaorPb andn = 0, 2, 4 and 3 respectively and dip = dipicolinate), N₂H₅Bi(dip)₂.3H₂O and (N₂H₅)₃Bi(dip)₃.4H₂O have been prepared and characterized by physico-chemical techniques. The infrared spectra of the complexes reveal the presence of tridentate dipicolinate dianions and non-coordinating hydrazinium cations. Conductance measurements show that the mono, di and trihydrazinium complexes behave as 1:1, 2:1 and 3 :1 electrolytes respectively, in aqueous solution. Thermal decomposition studies show that these compounds lose water followed by endothermic decomposition of hydrazine to give respective metal hydrogendipicolinate intermediates, which further decompose exothermically to the final product of either metal carbonates (Ca, Sr, Ba and Pb) or metal oxycarbonates (Bi). The coordination numbers around the metal ions differ from compound to compound. The various coordination numbers exhibited by these metals are six (Ca), seven (Ba), eight (Sr) and nine (Pb and Bi). In all the complexes the above coordination number is attained by tridentate dipicolinate dianions and water molecules. The X-ray diffraction patterns of these compounds differ from one another suggesting that they are not isomorphous.     

Polymer science with main group elements and transition metals

The efficient formation of soluble, processable polymers with main chains containing inorganic elements provides a synthetic challenge but represents potentially important approach to new macromolecular and supramolecular materials with interesting properties. This talk will survey some of the recent research performed in our group concerning the development of controlled routes to a variety of different inorganic polymer systems and the use of the resulting materials in self-assembly processes.     

Ionic and coordination diene polymerization and organic derivatives of main group metals

The effects of the nature of an organic derivative of a main group metal (cocatalyst), its composition, the cocatalyst : transition metal compound ratio, and the way of introducing the cocatalyst on the formation and operation of the active sites in the Ziegler—Natta catalytic systems in the polymerization of conjugated dienes are discussed. A correlation between the cocatalyst nature and the number and kinetic heterogeneity of the active sites is shown.     

Polynuclear complexes of main group and transition metals with polyaminopolycarboxylate and polyoxometalate

Six supramolecular compounds constructed by main group and transition metals, polyoxotungstates (SiW(12)O(40)(4-)) and trans-N,N,N',N'-1,2-cyclohexanediaminotetraacetic acid (H(4)CyDTA), (NH(4))(3)[Ni(4)Na(H(2)O)(10)(CyDTA)(2)][SiW(12)O(40)]·10H(2)O (1) (NH(4))(2)[Cu(3)Na(2)(HCyDTA)(2)(H(2)O)(13)][SiW(12)O(40)]·5H(2)O (2), (NH(4))(2)[Zn(5)(CyDTA)(2)(H(2)O)(16)][SiW(12)O(40)]·8H(2)O (3), (NH(4))(4)[Cd(4)(CyDTA)(2)(H(2)O)(8)][SiW(12)O(40)]·6H(2)O (4), (NH(4))(4)[Sr(3)(HCyDTA)(2)(H(2)O)(14)][SiW(12)O(40)]·2H(2)O (5) and [Ca(4)(H(2)CyDTA)(2)(H(2)O)(22)][SiW(12)O(40)]·8H(2)O (6), were synthesized in aqueous solution and characterized by IR spectroscopy, thermogravimetric analysis and single-crystal X-ray diffraction techniques. Single-crystal structure analyses indicate they are constructed by the complexes with different nuclearity and polyoxometalates. In the sequence of Ni, Cu, Zn the nuclearity of the homometallic complex units increases from 2 to 5. Cadmium ions gives a tetranuclear complex with a compact structure. In 5 and 6 the main group metal ions and CyDTA form polymeric chains. CyDTA exhibits rather different coordination patterns to main group metal ions and transition metal ions due to their ionic radii and electronic configuration. The complex units and polyoxometalates arrange in different patterns due to the different shapes of the complex units. The compounds exhibit different thermal decomposition processes and the formation of compounds 3 and 4 quenches ligand-centered emissions and gives a ligand-to-metal emission. The study on various temperature susceptibilities of 1 and 2 shows that there is an antiferromagnetic coupling in the two compounds but coupling patterns are different.     

Porphyrin complexes of the period 6 main group and late transition metals

Metalloporphyrin complexes of the period six metals gold, mercury, thallium, lead and bismuth are often overlooked in favour of their lighter congeners. These complexes exhibit unusual coordination geometries, prominently featuring the metal centre residing out the porphyrin plane. Not only are these compounds chemically interesting, but several applications for these complexes are beginning to emerge. Gold and bismuth porphyrins have medicinal applications including novel chemotherapeutics and sensitizers for α-radiotherapy, while gold porphyrins have applications in materials chemistry and catalysis. This perspective serves to highlight trends in the synthesis and structure of these heavy metal complexes as well as illustrate the considerations necessary for rationally designing elaborate porphyrin architectures.     

Chemical bonding in phosphane and amine complexes of main group elements and transition metals

The geometries and bond dissociation energies of the main group complexes X3B-NX3, X3B-PX3, X3Al-NX3, and X3Al-PX3 (X = H, Me, Cl) and the transition metal complexes (CO)5M-NX3 and (CO)5M-PX3 (M = Cr, Mo, W) have been calculated using gradient-corrected density functional theory at the BP86/TZ2P level. The nature of the donor-acceptor bonds was investigated with an energy decomposition analysis. It is found that the bond dissociation energy is not a good measure for the intrinsic strength of Lewis acidity and basicity because the preparation energies of the fragments may significantly change the trend of the bond strength. The interaction energies between the frozen fragments of the borane complexes are in most cases larger than the interaction energies of the alane complexes. The bond dissociation energy of the alane complexes is sometimes higher than that of the borane analogues because the energy for distorting the planar equilibrium geometry of BX3 to the pyramidal from in the complexes is higher than for AlX3. Inspection of the three energy terms, DeltaE(Pauli), DeltaE(orb), and DeltaE(elstat), shows that all three of them must be considered to understand the trends of the Lewis acid and base strength. The orbital term of the donor-acceptor bonds with the Lewis bases NCl3 and PCl3 have a higher pi character than the bonds of EH3 and EMe3, but NCl3 and PCl3 are weaker Lewis bases because the lone-pair orbital at the donor atoms N and P has a high percent s character. The calculated DeltaE(int) values suggest that the trends of the intrinsic Lewis bases' strengths in the main-group complexes with BX3 and AlX3 are NMe3 > NH3 > NCl3 and PMe3 > PH3 > PCl3. The transition metal complexes exhibit a somewhat different order with NH3 > NMe3 > NCl3 and PMe3 > PH3 > PCl3. The slightly weaker bonding of NMe3 than that of NH3 comes from stronger Pauli repulsion. The bond length does not always correlate with the bond dissociation energy, nor does it always correlate with the intrinsic interaction energy.     

A route to novel stable salts containing transition and main group metals

Novel salts of the type [Cu(Dien)₂][Bu₃SnCl₃], [Cu(Dien)₂][Ph₂SnCl₄], and [Cu(Dien)₂][SnCl₆] (Dien—diethylenetriamine) were prepared by the reaction of [Cu(Dien)₂]Cl₂ with Bu₃SnCl, Ph₂SnCl₂ and SnCl₄ in MeOH in a 1:1 ratio, respectively, and characterized by elemental analyses, electronic, IR and ESR spectroscopy, magnetic susceptibility, electrochemistry, and conductivity measurements. The results revealed that the compounds are 1:1 electrolytes and the Cu²⁺ ion is paramagnetic in the octahedral field. The complexes exhibit a single-electron redox couple. The article was submitted by the authors in English.     

Thermodtnamics of surfactant-polymer interactions in dilute aqueous solutions

A thermodynamic model for suffactant binding to polymers in dilute aqueous solution is present. It assumes that the inter- molecular contacts between the polar and the non-polar polymer segment resemble the macroscopic hydrocarbon-water interface ,where preferential accumulation of surfactant accurs. The model also considers the competitive surfactant micelization.     

Oxidative addition to main group versus transition metals: Insights from the Activation Strain model

We have studied the oxidative addition of the methane C-H and chloromethane C-Cl bonds to a number of main group (Be, Mg and Ca) and transition metals (Pd, Zn and Cd), using relativistic density functional theory (DFT) at ZORA-BLYP/TZ2P. The purpose is to better understand what causes the characteristic differences in reactivity between main group and transition metals towards oxidative addition. Thus, we have analyzed our model reactions using the Activation Strain model in which the activation energy ΔE^≠ is decomposed into the activation strain of and the stabilizing TS interaction between the reactants in the activated complex: . Activation of the C-H bond goes with higher barriers than activation of the C-Cl bond because the higher bond strength of the former translates into a higher activation strain . The barriers for bond activation increase along Pd < Be, Ca < Mg < Zn, Cd. This can be straightforwardly understood through the TS-interaction , that is, in terms of the bonding capabilities of the metals. Pd yields the lowest barriers because it achieves the most stabilizing . This is the result of the small HOMO-LUMO gap between its occupied 4d and unfilled 5s AOs, which makes Pd both a good electron donor and acceptor. Zn and Cd yield the highest barriers because the large HOMO-LUMO gap between the occupied valence ns and unfilled valence np AOs makes them both poor donors and poor acceptors of electronic charge.     

Magnetic interactions of iron nanoparticles in arrays and dilute dispersions

The magnetic properties of monodisperse Fe nanoparticles with over 4 orders of magnitude difference in concentration are studied by a combination of ordinary and remanent hysteresis loops, zero field cooled magnetization as a function of temperature, and magnetic relaxation rates. We compare the behavior of dilute dispersions with different concentrations, dispersions, and arrays made from the same particles, and nanoparticle arrays with different particle sizes and separations. The results are related to theoretical predictions and are used to create a unified picture of magnetostatic interactions within the assemblies.     

Heterometallic chalcogenido clusters containing lanthanides and main group metals: emissive precursors to ternary solid-state compounds

Heterometallic clusters containing lanthanides and the group 12 metals can be isolated as crystalline compounds in high yields. These products [(py)8Ln4M2Se6(SePh)4 (Ln = Er, Yb, Lu; M = Cd, Hg)] adopt a double cubane structure with the covalent M occupying an opposing pair of external metal sites. Both Er/M compounds are strongly emissive materials, with emission lifetimes of 1.41 ms (Er/Cd) and 0.71 ms (Er/Hg) and with the Er/Cd radiative quantum efficiency twice that of the Er/Hg compound. Thermal decomposition of the Er/Cd and Yb/Cd compounds at 650 degrees C give the ternary solid-state materials CdLn2Se4.     

Unusual geometries in main group chemistry

Over the past twenty five years, numerous heteroatom-containing analogues of classical organic moieties have been prepared and structurally characterized. The incorporation of group 13 to 15 heteroelements has often been reported to induce significant geometric distortions compared to the corresponding carbon compounds. These unusual geometries in main group derivatives are examined in this tutorial review, and the precise role of the heteroelements is discussed.     

Polymer science with transition metals and main group elements: Towards functional,supramolecular inorganic polymeric materials

Inorganic polymers are relatively unexplored because the efficient formation of macromolecular chains from atoms of transition metals and main group elements has presented a synthetic challenge. Nevertheless, these materials offer exciting opportunities for accessing properties that are significantly different from and which therefore complement those available with the well‐established organic systems. Inorganic block copolymers are of particular interest for the generation of functional, nanoscale supramolecular architectures and hierarchical assemblies using self‐assembly processes. This article focuses on research in my group over the past decade, which has targeted the development of new and controlled routes to inorganic polymers and their subsequent use in forming supramolecular materials as well as studies of their properties and applications. The use of ring‐opening polymerization (ROP) and transition‐metal‐catalyzed polycondensation approaches are illustrated. Controlled ROP procedures have been developed that allow access to polyferrocene block copolymers that self‐assemble into interesting nanoscopic architectures such as cylinders and superstructures such as flowers. The future prospects for inorganic polymer science are discussed, and a growing emphasis on the study of supramolecular inorganic polymeric materials is predicted. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 179–191, 2002     

Carbene-stabilized main group diatomic allotropes

While transition metals are well known for assuming the formal oxidation state of zero in various compounds main group elements have rarely engaged in this practice. Recent reports of N-heterocyclic carbene-stabilized main group diatomic allotropes (i.e., Si(2), Ge(2), P(2), As(2)) denote a breakthrough of zero-oxidation state main group chemistry. This Perspective addresses the synthesis and characterization of these highly reactive main group molecules, with a particular emphasis on the very recent progress in the reactivity study of carbene-stabilized Si(2) and P(2).     

Spotlighting main group elements in polynuclear complexes

François Gabbaï, Cameron Jones and Connie Lu introduce the Chemical Science themed collection on the topic of main group elements in polynuclear complexes.

Efforts towards the incorporation of main group elements in polynuclear motifs or in the coordination sphere of transition metals have been a prevalent theme of coordination chemistry, and one that has delivered notable advances in the area of structure and bonding. In the past decade, this field has witnessed an increased emphasis on the influence of the main group moiety over the reactivity or physical properties of the resulting constructs. Through a collection of both invited and selected articles, this themed issue puts the spotlight on this developing field, while at the same time illustrating far-reaching applications in the areas of small molecule activation, catalysis and molecular magnetism.A number of papers in this themed issue highlight the significant recent progress that has been made in the development of homo- and heterometallic systems incorporating s- and p-block elements, both in low oxidation states (often element–element bonded) and normal oxidation states. These have found particular use as low toxicity, earth abundant alternatives to late transition metal complexes in stoichiometric and catalytic transformations of small molecule substrates to value added products. This theme is introduced in primary articles dealing with the reactivity of magnesium-based systems. As shown by Jones, Maron and co-workers, magnesium(i) dimers (LMg–MgL, L = β-diketiminate) are activated by coordination of simple Lewis bases, and are subsequently able to reductively couple carbon monoxide to form the deltate and transient ethenediolate dianions (C_nO_n²⁻, n = 3 and 2, respectively; DOI: 10.1039/D0SC00836B). In another contribution, β-diketiminato-stabilised magnesium diboronates are shown by Hill, McMullin and co-workers to act as rare “masked” sources of nucleophilic boryl anions for the synthetic transformation of imines (DOI: 10.1039/C9SC02087J). These two papers integrate with the content of two reviews that highlight the unique structures and reactivity of polynuclear complexes containing low valent group 2, 13 and 14 elements. One of these reviews, by Inoue and co-workers, focuses on the structures of ditetrelenes (R₂E^II E^IIR₂, E = group 14 element) and ditetrelynes (RE^I E^IR), and their remarkable reactivity towards small molecules (DOI: 10.1039/D0SC03192E). Another review by Crimmin and co-workers explores the role that magnesium(i) and aluminium(i) reductants play in C–H bond activation reactions, and the synergy that may arise when the main group reagent is combined with a transition metal (DOI: 10.1039/D0SC03695A). Showcasing the value that s-block metals may display in their normal valence, Williams and coworkers describe macrocyclic Mg^II/Zn^II heterodinuclear complexes as highly effective catalysts for epoxide/CO₂ ring opening co-polymerization (DOI: 10.1039/C9SC00385A). The broader significance of this concept is developed in a review on heterobimetallic complexes containing s-block metals, in which Hevia and her co-worker highlight the unique ability of such complexes to support cooperative catalysis (DOI: 10.1039/D0SC05116K). The Lewis acidity of s-block cations can also be harnessed to manipulate the covalency of metal–ligand interactions, as elegantly demonstrated by Arnold, Love, Vitova, Schreckenbach and co-workers, who investigate a series of uranyl(v) complexes featuring U O–E motifs (E = group 1 or 2 element, DOI: 10.1039/C8SC05717F).Reduced polynuclear main group complexes can also provide new platforms for the discovery of atypical reactivity as illustrated by Kong and co-workers, who report mono-base-stabilized 1,2-diboranylidenehydrazines, a set of compounds that feature an unprecedented BNN-1,3-dipole that readily adds to arenes or small molecules such as CO₂ (DOI: 10.1039/D0SC02162H). In keeping with the theme of reactive diboron-containing units, Braunschweig and co-workers show in another captivating report that B–B triply-bonded diborynes can add to diboranes to afford B₄ chains, a transformation that could pave the way to new polymers with polyboron units in the main chain (DOI: 10.1039/C9SC02544H). The synthetic potential offered by low oxidation state main group elements comes to the fore in two additional reports, both dealing with Si₆ clusters. In the first one, Scheschkewitz and co-workers show that these silicon clusters can be functionalised with tetrylene substituents, and can act as ligands towards group 9 metal fragments, yielding complexes which act as catalysts for alkene isomerisations (DOI: 10.1039/D0SC02861D). A second report by Lips and co-workers describes highly unsaturated and structurally dynamic Si₆R₄ species (R = amide) with exposed silicon vertices (DOI: 10.1039/D0SC01427C). Exposed silicon moieties can also be appended to classical ligands as demonstrated by Roesky and co-workers who report on cyclopentadienyl ligands substituted by a silylene (R₂Si:). These ligands not only act as two-electron Si donors towards transition metal fragments but also undergo isomerization or deprotonation reactions leading to sila-fulvenes (DOI: 10.1039/D0SC04174B). Reduced group 14 elements can also be directly incorporated in the five-membered ring of cyclopentadienyl-like ligands as illustrated by Müller, Albers and co-workers in a contribution dealing with the germacyclopentadienediyl [K₂(:GeC₄R₄)] as an η⁵-ligand and its conversion into the first germaaluminocene, [Cp*Al(η⁵-:GeC₄R₄)] (DOI: 10.1039/D0SC00401D).As stated in the introductory paragraph, positioning main group elements in the coordination sphere of transition metals provides access to unusual reactivities, as in a contribution by Ozerov and co-workers (DOI: 10.1039/D0SC04748A) who demonstrate the reversible addition of ethylene to a boryl-based bis(phosphine) iridium pincer complex. A unique aspect of this contribution is the concomitant participation of the iridium and boron centres in the coordination of the hydrocarbon ligand. The ability of boron to cooperate with an adjacent transition metal centre is again a leading theme in two additional contributions selected for inclusion in this issue. The first one concerns the reversible addition of H₂ across an Ni–B bond, as elegantly documented by Rodríguez, Lledós and co-workers (DOI: 10.1039/D0SC06014C), who also used a boryl-based pincer as a supporting ligand. Exploiting the somewhat counter-intuitive reality that gold is more electronegative than boron, Yamashita, Lin and co-workers show that gold(i) diarylboryl complexes react as gold-based nucleophiles with organic reagents bearing C O and C N bonds (DOI: 10.1039/D0SC05478J). The unique reactivity of late transition metal–boryl linkages pervades in another contribution by Conejero, Lledós and co-workers who detail the highly choreographed addition of boranes such as HBpin and HBcat to a cationic, T-shaped, cyclometallated Pt(ii) bis-carbene complex (DOI: 10.1039/D0SC05522K). Isolated species include σ-BH Pt^II complexes, en route to the formation of T-shaped Pt^II bis-carbene complexes. Last, Tilley, Eisenstein and co-workers remind us of the importance of main group hydrides in catalysis in a contribution that pinpoints the intermediacy of dinuclear nickel–silyl species in an alkene hydrosilylation reaction mediated by a cationic nickel complex (DOI: 10.1039/D0SC00997K).Within the theme of heterometallic cooperativity, we highlight three articles where group 13 elements were introduced into transition metal complexes to promote small-molecule activation. In each report, a unique ligand design is used to juxtapose the transition metal centre with the group 13 element(s). Szymczak and co-workers appended two Lewis acidic borane groups to a pincer ligand via flexible linkers. The pendant boranes were critical for the stabilization of a rare high-spin Fe^II dihydride complex by forging Fe–H → B interactions (DOI: 10.1039/C9SC00561G). Upon exposure to an arylisocyanide, a good π-acid, the reductive elimination of H₂ ensued to form the iron(0) complex. Such a step is reminiscent of the E₄ intermediate in nitrogenase, which is proposed to release the obligatory H₂ equivalent upon binding of N₂ [see Chem. Rev., 2014, 114, 4041]. Envisioning a more active role for boranes, Harman and co-workers use the diboraanthracene platform, whose redox flexibility and dynamic Lewis acidity can be orchestrated to promote reactivity at the bound transition metal (DOI: 10.1039/C9SC02792K). The authors isolate a key Au borohydride intermediate that reduces CO₂ to formate, and close a synthetic cycle from CO₂ to formic acid using only proton and electron equivalents. Moving down the group 13 to the heavier congeners, Lu and co-workers show that the choice of the heavy group 13 ion (Al, Ga, or In) that is directly appended to a nickel(0) centre can significantly tune the Ni electronics (DOI: 10.1039/C9SC02018G). In comparing a triad of non-classical Ni(η²-H₂) adducts, the identity of the group 13 ion was found to perturb the free energy and activation energy of H₂ binding by ∼5 kcal mol⁻¹. Lastly, in a timely review, Takaya details the growing momentum of using main group/metalloid complexes as supporting ligands for transition metal-based catalysis (DOI: 10.1039/D0SC04238B). Takaya’s review presents illustrative examples to showcase the diverse main group elements (groups 13–15) and strategies that are being harnessed for transition metal catalysis.Moving down the periodic table to the f-elements, several articles explore heterometallic lanthanide and actinide complexes that fundamentally challenge our understanding of bonding and electronic structure. Using mixed arene π-ligands, Liddle and co-workers isolated an unusual bent Th “sandwich” complex that is stitched by K⁺ ions into a tetrathorium cluster (DOI: 10.1039/D0SC02479A). Diaconescu, Huang and co-workers report inverted sandwich complexes of Sm and Y featuring a bridging biphenyl ligand and bridging K⁺ ions (DOI: 10.1039/D0SC03555F). Depending on the lanthanide element, these inverted sandwiches feature Sm^III–arene–Sm^III or Yb^II–arene–K⁺ bonding interactions, where the biphenyl ligand is formally tetraanionic or dianionic, respectively. Freedman and co-workers conducted an in-depth study on the electronic structures of Sn-based heterometallics that contain a direct bond between Sn and a first-row transition metal that is varied from Mn to Ni (DOI: 10.1039/D0SC03777J). The authors make a striking comparison between the high-spin configurations of the 3d ions and those of typical Ln coordination complexes, wherein the coordinate bonds are more ionic. They rationalize that the Sn group behaves as an inverted, weak-field ligand due to the large energy mismatch between the Sn 5s/5p and 3d atomic orbitals [see Chem. Rev., 2016, 116, 8173]. Controlling spin states is only one of several requisites for the design of single molecule magnets (SMMs). Layfield, Mansikkamäki and co-workers report a triad of dinuclear dysprosium complexes, where the exogenous borohydride donor is varied in both number and coordination (terminal to bridging) (DOI: 10.1039/D0SC02033H). The authors observed a favourable increase in the effective energy barrier for a dinuclear dysprosium complex with a Dy : BH₄ ratio of 2 : 1. Lastly, Nippe, Chibotaru and co-workers explore magneto-structural relationships in a series of trigonal prismatic Ln^III complexes (Gd to Lu) that are scaffolded by three doubly deprotonated ferrocene (FeCp₂)²⁻ ligands and capped by Li⁺ ions (DOI: 10.1039/D0SC01197E). By virtue of its size and axis of anisotropy, the authors were able to engender SMM behaviour for the Ho^III complex. The authors demonstrate that the Ln size and the nature of the Li⁺ solvate both influence the twist angle, where the ideal trigonal prism geometry (twist angle of 0°) results in the large anisotropy that is conducive to SMM behaviour.To illustrate the diversity of the field, this themed issue also highlights several additional contributions dealing with atypical phosphorus-containing ligands. For example, Scheer and co-workers show that the four-membered cyclo-P₄ ligand of organometallic tantalum complexes can be used as a square building block for the construction of molecular capsules upon combination with silver cations and an appropriate template (DOI: 10.1039/D0SC03437A). Two additional contributions document recent trends at the confluence of traditional organophosphorus chemistry and coordination chemistry. Gessner and co-workers review the unique properties of phosphorus ylides and their ability to stabilize low-valent main group species, leading to the formation of new main group ligands for transition metal-based catalysis (DOI: 10.1039/D0SC03278F). The second contribution comes from Normand, Sosa Carrizo and co-workers who decipher the ambiphilic properties of bis(iminophosphoranyl)phosphide ligands and suggest that they be regarded as containing a triphosphenium coordinating unit (DOI: 10.1039/D0SC04736H).This themed issue was assembled with the intent of spotlighting the role played by main group elements in polynuclear complexes. We hope that those reading these articles will appreciate the topical diversity of this research field, its relevance to various areas of chemistry, and the numerous future research opportunities it presents.     

Solute-solute-solvent interactions in dilute aqueous solutions. Microcalorimetric study of isomeric butanediols

The heats of dilution of butane-1,2-diol, butane-1,3-diol, and butane-1,4-diol and of their mixtures were determined at 25°C. The virial enthalpic coefficients of the excess enthalpies of the binary and ternary solutions were evaluated and compared with the literature data for isomeric mono- and polyols. The enthalpic pair interaction coefficients of isomeric diols are positive. The highest value is observed for butane-1,2-diol thus supporting the importance of steric and nearest neighbors effects in the hydration properties of isomeric compounds. Mixed enthalpic coefficients were also determined and discussed.