The octaamino cryptand, L2, obtained by tetrahydroborate reduction of the [2+3] condensation product of tris(2-ethy1amino)amine with terephthalaldehyde, acts as a host for pairs of protons or first-series transition-metal cations. An X-ray crystallographic structure determination of [ H,L2I4+ reveals a pair of protons held at opposite ends of the molecule by strong intramolecular hydrogen bonding of each proton to two of the amino nitrogen atoms. Pairs of transition-metal cations co-ordinated to the amino N-donors accommodate mono-and tri-atomic bridging ligands, such as OHor imidazolate, generating weak to moderate antiferromagnetic interaction. Dicopper( 11) p-azido complexes have been prepared where the combination of a large zero-field splitting in t h e ESR spectrum and a near Curie-law dependence of -3.84 (t) 360 183 7.&7.5 (m) 8.40 (s) -3.84 (br s) 183 6.67 (s) 3.53 (br s) 1.55 (br s) 2.53 (br s) L2 CD,CI, 360 298 6.89 (s, 4 H) 3.67 (s, 4 H) 2.0 (br s, 2 H) 2.65 (t, 4 H) CH4L21CCF3S031, (CD,),SO 400 298 7.45 (s, 4 H) 2.80 (s, 4 H) 8.65 (br s) 4.22 (s, 4 H) [Ag,LZ][CF,S03]2 CD3CN 500 298 7.12 (s, 4 H) 2.78 (4 H) 2.9 (br) 3.78' (4 H) 338 7.12 (s, 4 H) 2.80 (4 H) 2.92 3.78' (4 H) [Cu2LZ][CF3S03], CD3CN 500 338 6.89 (4 H) 2.80 2.90 3.90, 3.65 Chemical shifts 6 relative to SiMe,. Overlapped. Assigned on the basis of comparison with the copper(1) spectrum. 323 7.22 (s) 2.90(br s) --3.97 (s) 298 2.80 (s) 2.85 (m) 3.95 (d), 3.53 (1) H E 2.83 (br s) 3.4, 2.1 (br) 2.65 (br s) 2.81 (t, 4 H) 2.61 (t, 4 H) 2.71 (t) 2.95 3.00 (4 H) 3.28, 2.95 3.35 (br t), 2.95 (d) Table 2 Torsion angles (")in [H,L2][CF,S0,], C( 3 1 )-C( 30)-N( 1 )-C( 10) 128.9 C(3O)-N( 1)-C( 10)-C( 11) C( 3 1 )-C( 30)-N( 1 j C ( 23 *) -58.4 -99.2 C(30)-N( 1 )-C(23*)-C(22*) 167.0 C(ll)--C(lO)-N(l)-C(23*) 175.0 C( 10)-N( l)-C(23*)-C(22*) -66.5 N( 1 )-C( 10)-C( 1 1)-N( 12) C( 1 0)-C( 1 1 )-N( 12)-C( 1 3) C( 1 1 )-N( 12)-C( 13)-C( 14) N(12)-C(13)-C(14)-C(15) C( 13)-C( 14)-C( 15)-C( 16) C( 16)-C( 17)-C(20)-N(2 1) C( 20)-N( 2 1 )-C( 22)-C(23) C( 17)-C(20)-N(21)-C(22) N(21)4'(22)-C(23)-N(l*) N(l)-C(3O)-C(31)-N(32) C( 30)-C(3 1 )-N(32)-C(3 3) C(3 1 )-N(32)-C(33)-C(34) N(32)-C(33)-C(34)-C(35) * Symmetry operation +x , y , 1z.-50.1 -167.3 -172.9 115.7 173.4 -112.4 178.4 -153.2 -66.9 -76.9 178.6 106.9 -49.6 L1 *6H,O 70.2 -118.1 -178.6 2.6 -177.1

The design and synthesis of molecules with potential for information storage and processing is a focus in current materials research, an area in which bulk metal oxides still predominate. The potential of discrete transition-metal spincrossover (SCO) complexes in this area is now starting to be realized as photoinduced switching emerges as an increasingly efficient trigger for spin conversion.[1] As the field continues to grow, it is important to identify new candidates with improved thermal or optical responses and also to fine-tune the molecular design for successful incorporation into devices.Although the phenomenon is theoretically possible for octahedral d [4][5][6][7] [3,4] it is considered exceptional. The best-known example is [Mn(trp)] (trp 3À = tris{1-(2-azolyl)-2-azabuten-4-yl}amine), [3] and investigations of its physical properties continue. [5, 6] The only other well-characterized example [CrI 2 (depe) 2 ][4] (depe = 1,2-bis-(diethylphosphino)ethane) also continues to attract attention.[7] An early report of some Mn III complexes, which were not structurally characterized, attributes the temperature dependence of the magnetic moment to exchange interactions, although SCO is a more likely interpretation. [8] An important driving force for SCO is the change in metal-ligand bond length arising from the increased vibrational entropy in the HS state. The concomitant decrease in ligand-field splitting energy reduces the ligand-field stabilization energy (LFSE) associated with the maximum population of the t 2g orbitals. The reluctance of octahedral d 4 ions to undergo thermal SCO may be due to the very minor gain in LFSE on crossover from 5 E to 3 T as only one electron is transferred. In most crystal fields, the small LFSE gain for d 4 ions is outweighed by the energetic penalty of pairing two electrons, which results in both an increase in the destabilizing Coulomb repulsion energy p c and a decrease in the stabilizing exchange energy p e . [9] Schiff base ligands with N 4 (O À ) 2 , N 2 (O À ) 2 , and N 3 (O À ) 3 donor sets that are known to generate ligand fields close to the crossover value for Fe III [10] tend to stabilize manganese in its + III oxidation state, in which it is normally HS. Recently, however, we have observed that modulation of the orientation of the N 4 (O À ) 2 donors in a series of hexadentate ligands has a dramatic effect on the spin state of Mn III complexes and that gradual thermal SCO may be attained when the phenolate oxygen donors are trans to each other. This geometry is achieved by varying the length of the alkyl chains in the starting tetraamine. The use of a triethylenetetraamine link (in L1) orients the oxygen donors cis to each other and produces a HS Mn III complex, whereas lengthening the link by two methylene groups (L2) orients the oxygen donors in trans geometry and thermal SCO results.To illustrate this phenomenon, we report the structures and temperature dependence of the magnetic susceptibility of [MnL1]NO 3 ·EtOH (1) and [MnL2]NO 3 (2), which exhibit differ...

Comparison of the structures of four monomanganese (and one monoiron) complexes of ligands with the identical donor [N3(0-l31 set reveals that geometry determines the redox state of the cation.

The different tendencies of dinuclear azacryptates of the m-CH 2 C 6 H 4 CH 2 and 2,5-furano-spaced hosts L 1 and L 2 to catalyse CO 2 uptake-reactions within these sterically-protected host cavities are examined. Bridging methylcarbonates are generated catalytically upon exposure of methanol solutions of L 1 , but not L 2 , di-transition cation cryptates to atmospheric CO 2 . X-Ray crystallographic structures of homodinuclear µ-carbonato cryptates of both ligands and µ-methylcarbonato cryptates of L 1 with later first transition series cations are reported. ESI-MS spectra show loss of H 2 CO 3 from µ-carbonato cryptates in collision activation experiments.The oxo-anion, carbonate, currently attracts attention in diverse areas of chemistry. Transformations involving this species, its reaction precursors and products are of considerable biological 1 significance; particularly important here are the carboanhydrases which play an essential role in processes such as photosynthesis, respiration, calcification and pH control. In the light of increasing concern about CO 2 build-up from fossil fuel consumption and potential resulting greenhouse effects, improved understanding of the biological handling of carbonate-related species acquires increasing urgency. Any potential new application of CO 2 as feedstock in chemical processes, will for this reason, attract much interest. In addition, the many and varied coordination modes of the carbonate oxo-anion are of spectroscopic interest as is their capacity to transmit magnetic interaction. 2-4 The carbonate system is also significant in the context of anion coordination chemistry as its behaviour within small molecule hosts may help to elucidate details of transport and location of carbonate or carboxylate anions in enzyme processes.The frequently used strategy of anion coordination via protonated amine, 5,6 or other acidic host, can be problematic in such pH-sensitive systems, so we have adopted an alternative strategy: the oxoanions here are retained via their bridging coordination of cations held within a cryptand cavity. We have already used the "cryptate as host" strategy to coordinate pseudo-halide anions such as azide and cyanate, and studied the spectroscopy and magnetochemistry 7,8 resulting from the consequent (and on first observation unprecedented) colinear M-NXY-M bridging geometry.The secondary coordination of anionic or other bridges between cations themselves coordinated by a cryptand host molecule was quite some time ago termed cascade coordination by Jean-Marie Lehn, 9 in the implicit expectation that the bridging groups might be activated, by reason of their dicoordination, toward further and possibly useful chemical reaction. However, such outcome was not apparent in our pseudo-halide † Electronic supplementary information (ESI) available: magnetic data. See http://www.rsc.org/suppdata/dt/b1/b110449g/

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Six solvated salts of a mononuclear manganese(III) complex with a chelating hexadentate Schiff base ligand are reported. One member of the series, [MnL]PF(6)⋅0.5 CH(3)OH (1), shows a rare low-spin (LS) electronic configuration between 10-300 K. The remaining five salts, [MnL]NO(3)⋅C(2)H(5)OH(2), [MnL]BF(4)⋅C(2)H(5)OH(3), [MnL]CF(3)SO(3)⋅C(2)H(5)OH (4), [MnL]ClO(4)⋅C(2)H(5)OH (5) and [MnL]ClO(4)⋅0.5 CH(3)CN (6), all show gradual incomplete spin-crossover (SCO) behaviour. The structures of all were determined at 100 K, and also at 293 K in the case of 3-6. The LS salt [MnL]PF(6)⋅0.5 CH(3)OH is the only member of the series that does not exhibit strong hydrogen bonding. At 100 K two of the four SCO complexes (2 and 4) assemble into 1D hydrogen-bonded chains, which weaken or rupture on warming. The remaining SCO complexes 3, 5 and 6 do not form 1D hydrogen-bonded chains, but instead exhibit discrete hydrogen bonding between cation/counterion, cation/solvent or counterion/solvent and show no significant change on warming.

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The ESR spectra for a series of binuclear trigonal bipyramidal copper complexes show that the SOMO is largely composed of the t w o equivalent dZ2 orbitals on copper; the temperature independence of the ESR parameters shows that this is a relatively strong bond, and since the unpaired electron is antibonding, the a-bond must be even stronger; these results are contrasted with the more common situation that arises when the electron is shared between t w o d,2-y2 type orbitals.