Solvolysis of 2-aryl-exo-5,6-trimethylene-2-norbornyl p-nitrobenzoates as a reference of 2-aryl-2-norbornyl p-nitrobenzoates solvolysis: Further evidence for the unimportance of σ-participation in the solvolysis of 2-aryl-2-norbornyl derivatives

The rates of solvolysis of 2 - aryl - exo - 5,6 - trimethylene - exo - and endo - 2 - norbornyl p-nitrobenzoates (7 and 8, respectively) with representative substituents [p-CH₃O, p-CH₃, H, m-CF₃, p-CF₃, and 3,5-(CF₃)₂] were determined in 80% aqueous acetone and compared with those of the parent 2-aryl-exo- and endo-2-norbornyl p-nitrobenzoates (5 and 6, respectively). The rate ratios for the endo-p-nitrobenzoates ($\text{6}\text{8}$) are essentially constant and close to unity for these substituents, indicating that the perturbation of the trimethylene bridge toward the C₂-position is virtually negligilbe. The rate ratios for the exo-p-nitrobenzoates ($\text{5}\text{7}$) can also be regarded as invariant over the reactivity range studied. The exo/endo rate ratios ($\text{7}\text{8}$) are 246 (p-CH₃O), 196 (P-CH₃), 129 (H), 80 (m-CF₃), 90 (p-CF₃), and 89 [3,5-(CF₃)₂], being similar to the corresponding $\text{5}\text{6}$ rate ratios. The solvolyses of these p-nitrobenzoates (7 and 8) afford predominantly ( > 97%) exo-alcohols. Since the secondary exo-5,6-trimethylene-2-norbornyl system, with its low exo/endo rate ratio, 11.2, is known to solvolyse without significant σ-participation, the tertiary derivatives should also undergo solvolysis without σ-participation. Consequently, the similarities in the solvolytic behaviors between the two systems (5 vs 7; 6 vs 8) strongly support the previous conclusion that σ-participation is unimportant in the solvolysis of 5.     

Verbrückte und unverbrückte norbornyl-kationen in der gasphase. Berechnungen zur stabilität isomerer norbornyl-kationen mit hilfe quantenmechanischer verfahren

The geometry and the relative stability of bicyclic compounds 1–20 have been calculated by standard quantum mechanics methods.MINDO/3 yields the following stability order of isomeric norbornyl cations (relative energies in $\text{kcal}\text{mole}$): 1-norbornyl cation 9 (0.0); 1.7 σ-bridged cation 6 (0.7); 7-norbornyl cation (nonplanar) 7 (1.1); 2-norbornyl cation (classical) 2 (4.2); 7-norbornyl cation (planar) 8 (4.3); 2-norbornyl cation (bridged) 1 (6.1). The stability of the same ions calculated by ab initio methods (STO-3G, MINDO/3-geometry) leads to an order more nearly consistent with experimental results: 2-norbornyl cation (classical) 2 (0.0); 2-norbornyl cation (bridged) 1 (5.9); 7-norbornyl cation (planar) 8 (11.1); 1-norbornyl cation 9 (14.6); 7-norbornyl cation (nonplanar) 7 (21.2). For the secondary 7-norbornyl cation, MINDO/3 gives a pyramidal configuration, 3.2 $\text{kcal}\text{mole}$ more stable than the planar form. In contrast, the ab initio results (complete optimization of all geometrical parameters) indicate the planar cation to be the most stable form. The bridged structure of 2-norbornyl cation 1 is calculated (STO-3G, partly optimized) to be 4.3 $\text{kcal}\text{mole}$ less stable than the classical counterpart, 2. For the lower homologues 12 and 13 (STO-3G, complete geometry optimization), this difference is 6.4 $\text{kcal}\text{mole}$. However, more extended basis sets should favour the bridged structures. The hydrogen bridged norbornyl cations 3, 4, and 5 have been calculated (STO-3G, partly optimized) to be 14.4, 23.6 and 29.9 $\text{kcal}\text{mole}$ less stable than 2. The stability differences between the corresponding tertiary bicyclic ions 10 vs 11, and 14 vs 15 are calculated (ab initio) to be 15.3 and 19.0 kcal/mole, respectively, in favour of classical structures. The influence of methyl substitution at positions C₁ and C₆ (exo) on bridged and unbridged structure of 2-norbornyl cation is calculated. Pyramidal secondary and tertiary 2-norbornyl cations 19 (a; R=H, b; R=CH₃) and 20 (a; R=H, b; r=CH₃) have been used to model the electrical effects in the solvolysis transition states of epimeric 2-norbornyl esters. Due to more efficient hyperconjugation the pyramidal exo cation is stabilized more than the endo cation by 5.2 $\text{kcal}\text{mole}$ for the secondary series and 3.5 $\text{kcal}\text{mole}$ for the tertiary series. Bonding of endo cation 20 with a nucleophile should be stronger than bonding of exo cation 19 due to more efficient HOMO-LUMO interaction.     

Excluded volume effect for solutions of cellulose derivatives evaluated by wormlike chain model

Third-power law type equations of the linear expansion factor α_s and of the excluded volume effect $\text{z}$h($\text{z}$), expressed by a conventional notation, are derived for a wormlike chain as an extension of the Yamakawa and Stockmayer theory [J. chem. Phys.57, 2843(1972)], in which the corresponding fifth-power law type equations were obtained. The literature data on 11 systems of solutions of cellulose and its derivatives are analysed, by using a penetration function method based on the derived equations, to evaluate an excluded volume effect for a wormlike chain model. The results are compared with those deduced for a pearl necklace model.     

Formation of a hydroxymethyliridium(III) compound and addition of the OH bond to bound acetonitrile

The hydridoformyliridium complex [IrH(CHO)(PMe₃)₄][PF₆] (2) reacts with HBF₄/diethyl ether in acetonitrile to form the hydroxymethyl complex [Ir(CH₂OH)(CH₃CN)(PMe₃)₄][PF₆][BF₄] (4). A hydrido hydroxycarbene complex 3 is believed to be an intermediate in this reaction. The acetonitrile ligand of compound 4 undergoes base-catalyzed attack by the oxygen atom of the hydroxymethyl group to form the metallacycle compound [$\text{Ir(CH}{}_2\text{OC(CH}{}_3\text{N}$H)(PMe₃)₄][PF₆][BF₄] (5). Compound 5 cocrystallizes with [HPMe₃][BF₄] in the monoclinic space group P2₁/c, a 13.772(2), b 13.436(2), c 19.506(3) Å, β 90.02(1)°, V 3609 ų, Z = 4. Precision of the X-ray structural results is limited by disorder of all the anionic groups. Refinement of 374 variables on 5312 reflections with F_obs² > 2σ(Fobs²) has converged at R = 0.079, R_w = 0.091.     

The number of propagating species and some rate constants of elementary acts for the polymerization of ethylene and α-olefins using supported Ziegler catalysts

Concentrations of propagating species (PS) and chain propagation constants (k_p) were determined for the polymerizations of ethylene, propylene, butene-1 and hexene-1 using TiCl₄/MgO-Al(C₂H₅)₃ (i) and TiCl₄/Al₂O₃. SiO₂-Al(C₂H₅)₃ (II) catalytic systems. The concentrations of propagating species for all monomers and a particular catalytic system are close. They give an idea of high degree of application of transition metal ($\text{? 35–39\%}$ of total Ti for system I and $\text{? 20–23\%}$ for system II). Values of k_p for ethylene, propylene, butene-1, hexene-1 at 70° for system I are 2440 ± 240, 4.8 ± 0.5, 4.6 ± 0.5 and 2.5 ± 0.3 l/mol·sec respectively. For system II, k_p values for the first three monomers are 110 ± 11, 1.0 ± 0.1 and 0.13 ± 0.01 l/mol·sec. These results indicate the relation of reactivity of propagating species and chemical nature of the support to the surface of which they are fixed. Rate constants for chain transfer to monomer or triethyl aluminium and spontaneous disproportionation (at 70°) were compard for the polymerizations of ethylene and propylene using catalytic system I.     

Transfer to monomer in the polymerization of N-(3-dimethylaminophenyl) maleimide and N-(3-dimethylamino-6-methylphenyl) maleimide

The kinetics of the homopolymerizations of styrene, N-(3-dimethylaminophenyl) maleimide (I) and N-(3-dimethylamino-6-methylphenyl) maleimide (II) in benzene and dimethylformamide, and the molecular weights of the polymers were studied. N-(3-Dimethylaminophenyl) succinimide, regarded as a model for polymer I, did not affect the polymerization of styrene. The data indicate degradative transfer of polymer radicals to dimethylformamide and pronounced transfer to monomers I and II (C_M ≈ 0.06–0.07). The value of $\text{k}{}_{\mathrm{p}}\text{/k}{}_{\mathrm{t}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ for II is 0.09 $\text{dm}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$$\text{mole}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$$\text{s}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$.     

Synthesis of monohydridohexamethylbenzeneruthenium(II) complexes containing group V donor ligands. Isomerism arising from cyclometallation of a tertiary phosphine at aliphatic and aromatic carbon atoms

The η-hexamethylbenzenehydridoruthenium(II) complexes RuHCl(η-C₆Me₆)L (L = PPh₃ (11), AsPh₃ (12), P(C₆H₄-p-F)₃ (14), P(C₆H₄-p-Me)₃ (15), P(C₆H₄-p-OMe)₃ (16), P-t-BuPh₂ (17), P-i-PrPh₂ (18), P-i-Pr₃ (19), PCy₃ (20) and P-t-BuMe₂ (21)) have been made by heating [RuCl₂(η-C₆Me₆)]₂, the ligand and sodium carbonate in propan-2-ol. The triarylphosphine complexes 11, 14 and 15 react with methyllithium to give aryl ortho-metallated hydridoruthenium(II) complexes such as $\text{RuH(}\text{o}\text{-C}{}_6\text{H}{}_4\text{P}$Ph₂)(η-C₆Me₆) (22) and 19 similarly gives the isopropyl cyclometallated complex $\text{RuH(CH}{}_2\text{CHMeP}$-i-Pr₂(η-C₆Me₆) (29) as a mixture of diastereomers. Reaction of 17 with methyllithium gives initially the t-butyl cyclometallated complex $\text{RuH(CH}{}_2\text{CMe}{}_2\text{P}$Ph₂)(η-C₆Me₆) (25) which isomerizes by a first order process (k$\text{0}\text{?}$.2 h^?1 in C₆D₆ or THF-d₈ at 50°C) to the aryl ortho-metallated complex $\text{RuH(}\text{o}\text{-C}{}_6\text{H}{}_4\text{P}$-t-BuPh)(η-C₆Me₆) (26). The similarly generated isopropyl cyclometallated complex $\text{RuH(CH}{}_2\text{CHMeP}$Ph₂)(η-C₆Me₆) (27) has not been isolated in a pure state owing to rapid isomerization to $\text{RuH(}\text{o}\text{-C}{}_6\text{H}{}_4\text{P}$-i-PrPh)(η-C₆Me₆) (28); both 27 and 28 exist as a pair of diastereomers. The formation of the cyclometallated complexes and the isomerizations are thought to involve intermediate 16-electron ruthenium(O) complexes Ru(η-C₆Me₆)L.     

The rotational spectrum and molecular properties of a hydrogen-bonded dimer of phosphine and hydrogen fluoride

⁵⁷Fe Mössbauer spectra have been obtained for Fe(p-CH₃C₆H₄SO₃)₂ between 2.3 and 300 K in zero field, and at 2.3 and 4.2 K in longitudinal applied magnetic fields ranging from 1.1 to 5.6 T. The complex is a fast-relaxing paramagnet under all conditions studied and there is no evidence of antiferromagnetic exchange coupling. The FeO₆ chromophore is distorted by a trigonal elongation and the orbital ground state is the [($\text{2}\text{3}$)^{$\text{1}\text{2}$}|±2〉 ? ($\text{1}\text{3}$)^{$\text{1}\text{2}$}|?1〉] doublet. The temperature dependence of the quadrupole splitting has been analysed via a crystal-field model to provide estimates of the axial field splitting parameter Ds = -93 cm^-1, spin-orbit coupling constant λ = -70 cm^-1, and fine structure constant Dσ = -28 cm^-1. The magnetic properties of the complex are described by treating the ground state as a non-Kramers doublet with fictitious spin ? = $\text{1}\text{2}$. Five separate Mössbauer-Zeeman spectra can be fitted in this spin-hamiltonian approximation with identical values of the g- and A-tensor components, viz. g_⊥ = 1.0, g_u = 9.0; A_⊥ ≈ 2.0 mm s^-1. A_u = -1.79 mm s^-1. The trigonal z axis, the z axis of the electric field gradient tensor, and the easy axis of magnetisation are collinear, and the saturation value of the internal hyperfine field along this axis is +13.0 T.     

Neutron powder diffraction and magnetic measurements on TlMnI3 and TlFeI3

TlMnI₃ and TlFeI₃ are isostructural with NH₄CdCl₃. TlMnI₃ has a spiral structure which can be described with an incommensurable vector k, in the direction of the b1 axis of length 0.3614(5)b1. The spins lie in the (0 0 1) plane. TlMnI₃ exhibits antiferromagnetic behavior with a Néel temperature of 6.0(2) K. The exchange interaction was calculated to be $\text{zJ}\text{k}\text{= ?1.6}\text{K}\text{, z}$ being the number of nearest neighbors. Discontinuities in the magnetization are found for both the [1 0 0] and [0 1 0] directions at fields H^a_SF = 30.1(2) kOe and H^b_SF = 14.1(2) kOe. The magnetic structure of TlFeI₃ consists of puckered ferromagnetic (1 0 0) planes, which are coupled antiferromagnetically. The magnetic moments are parallel to the b axis. The Néel temperature is 21.5(3) K. $\text{zJ}\text{k}$ was found to be ?10(1) K with g = 2.68 and s = 2. The magnetic structures found for TlMnI₃ and TlFeI₃ are derived taking into account inter- and intra-double-chain interactions via two I^? ions.     

Termination and transfer of the polymer chain to a maleimide derivative containing the azo group

The copolymerizations of N-(3-dimethylaminophenyl) maleimide (I) and 4-(2-chlorophenyl)azo-3-maleimido-N,N-dimethylaniline (II) with styrene were investigated; the copolymerization parameters of the pairs ($\text{I}\text{+}\text{styrene}$) and ($\text{II}\text{+}\text{styrene}$) and $\text{k}{}_{\mathrm{p}}\text{/k}{}_{\mathrm{t}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ hr I at 50° were determined; chain transfer to the maleimide ring of I was proved. The homopolymerization of styrene in the presence of 4-(2-chlorophenyl)azo-succinimide-N,N-dimethylaniline (III) was used to determine the ratio of the rate constant for addition of the polystyrene radical to the azo group in III to k_p for styrene.     

Formation of an iridium σ-cyclopropane complex by the intramolecular activation of a cyclopropylphosphine: Rearrangement to a chelating σ-vinyl complex

When (t-Bu)₂PCH₂CHCH₂CH₂ is combined with [IrCl(C₈H₁₄)₂]₂ in toluene, the σ-bound cyclopropane complexes

(P(t-Bu)₂CH₂$\text{CHCH}{}_2\text{C}$H₂) (1a, 1b) are formed. Complexes 1a,1b react readily with H₂ to form IrClH₂P(t-Bu)₂CH₂$\text{CHCH}{}_2\text{C}$H₂)₂ (2). In polar solvents 1a,1b isomerize to the σ-vinyl chelated complex $\text{IrClH(P(t-Bu)}{}_2\text{CH}{}_2\text{C(CH}{}_3\text{)C}$H)(P(t-Bu)₂CH₂$\text{CHCH}{}_2\text{C}$H₂) (3). The structure of this 5-coordinate, 16-electron Ir^III complex was deduced from spectroscopic data, reaction chemistry, and from the crystal structure of its CO adduct (4). Compound 4 crystallizes in the monoclinic space group C_2h⁵-P2₁/n (a 15.610(14), b 15.763(16), c 11.973(13) Å, and β 104.74(5)°) with 4 molecules per unit cell. The final agreement indices for 2326 reflections having F_o² > 3σ(F_o²) are R(F) = 0.089 and R_w(F) = 0.095 (271 variables) while R(F²) is 0.148 for the 3423 unique data. Bond lengths in the 5-atom chelate ring $\text{IrPCCC}$ are IrP 2.341(4), PC 1.857(26), CC 1.520(30), CC 1.341(25), and CIr 1.994(21) Å. The IrCl distance is 2.479(5) Å.     

Polymerization of phenylpropynes

The polymerization of phenylpropynes was investigated. Cream-coloured powders, with $\text{M}$_n between 3000 and 8500, were obtained from phenylpropynes using WCl₆·tetraphenyltin; the rate was much smaller than that for the corresponding phenylacetylene. The magnitudes of the ring-substituent effects on the reactivity of phenylpropyne catalyzed by WCl₆ were p⁺ = ?0.96 towards a phenylacetylene propagating end and p⁺ = ?2.19 towards a styryl end. These findings suggest that the former proceeds by metathesis and the latter polymerizes by a conventional cationic mechanism. Introduction of a β-methyl group on phenylacetylene decreased the reactivity by a factor of 1.5–1.8, towards a styryl cation. The polymerization mechanism of phenylpropyne is discussed on the basis of these data.     

Oxygenation of p-nitrophenylhydrazones with Co(II)-schiff base complexes

$\text{p}$-Nitrophenylhydrazones, unsusceptible to autoxidation, are readily oxygenated in the presence of a five-coordinate cobalt(II)-Schiff base complex, Co(II)(MeOSalen) (Py) leading to quantitative formation of novel 1-($\text{p}$-nitrophenylazo)-1-peroxy Co(III) complexes 2, which were isolated as crystals. A plausible mechanism involving hydrogen abstraction by Co(III)(O₂^?.) from the substrate followed by formation of a substrate anion Co(III) complex intermediate is proposed.     

Conformational effects in compounds with 6-membered rings—XIII : Detection of twist conformers using 13C NMR chemical shifts

¹³C NMR spectra of derivatives of cyclohexane, piperidine, and thian in chair and twist eonformers, and of model compounds, lead to estimates of deshielding (Δδ = 3.6 ± 0.2 ppm) for axial C$\text{Me}$₃ on a cyclohexane ring and shielding (Δδ = ?0.2 to ?0.6 ppm) for ψe-C$\text{Me}$₃ in twist conformers, relative to equatorial C$\text{Me}$₃. Ring carbon atoms are considerably shielded in twist conformers relative to chair eonformers. The value of ¹³C chemical shifts in the study of chair-twist equilibria is exemplified by variable temperature measurements on diastereomeric pairs of compounds (11 and 13; 38 and 50).     

The structure of dehydrated zeolite 3A (Si/Al = 1.01) by neutron profile refinement

A neutron powder diffraction study of a dehydrated commercially available potassium exchanged zeolite A (Linde 3A) has shown that the diffraction pattern can be indexed in cubic space group $\text{Fm}\text{3}\text{c}$. For this sample there is 63% exchange of potassium for sodium (K⁺/Na⁺ = 1.69). Data collected at a neutron wavelength of 2.98 Å shows no evidence of rhombohedral distortion and suggests that the assignment of space group $\text{Fm}\text{3}\text{c}$ is correct. The final structural model is closely analogous to that found for dehydrated sodium zeolite A (J. M. Adams, D. A. Haselden, and A. W. Hewat, J. Solid State Chem.44, 245 (1982); J. J. Pluth and J. V. Smith, J. Amer. Chem. Soc.102, 4074 (1980). Unusual features of previous refinements of potassium containing zeolite A samples, i.e., “zero coordinate” cations (P. C. W. Leung, M. B. Kunz, K. Seff, and I. E. Maxwell, J. Phys. Chem.83, 741 (1979)) or potassium inside the β-cage (J. J. Pluth and J. V. Smith, J. Phys. Chem.83, 741 (1979)) have not been found. Refinements using the same 1.9 Å neutron powder diffraction data were also obtained with the models of Leung et al. and Pluth and Smith (1979) as starting points (denoted LKSM and PS, respectively) and comparison is made with these. The final R factors for the three refinements were R_pw (A. K. Cheetham and J. C. Taylor, J. Solid State Chem.21, 253 (1977)) = 10.24% for the model presented here, R_pw = 10.38% (PS model), and R_pw = 10.61% (LKSM model).     

Chirality and conformational changes in 4-phenylphenanthrenes and 1-phenylbenzo[c]phenanthrene derivatives

NMR data of several 4-phenylphenanthrenes (15, 16) have revealed that the crowding in these compounds does not lead to chirality at temperatures as low as ?90°. The easy rotation of the phenyl substituent observed by NMR implies that notwithstanding the phenanthrene moiety in average behaves as a planar part the phenyl group does not experience steric hindrance.The analysis of temperature-dependent NMR spectra of several derivatives of 1-phenylbenzo[c]phenanthrenes (17-20) indicated that in these compounds exchange processes do occur. By calculations of the free energies of activation from the NMR data two processes could be distinguished: rotation of the phenyl substituent at one side of the helical benzo[c]phenanthrene moiety, for which ΔG^XXX_rot , is ca. 13.0$\text{kcal}\text{mol}$ or slightly larger when bulky substituents are present at C₂, and racemisation by a rotation of the phenyl group around the opposite end of the benzo[c]phenanthrene skeleton with simultaneous inversion of the helical conformation. For this process ΔG^XXX_rac is ca. 16$\text{kcal}\text{mol}$. The results have been compared with comparable data of related compounds like 1.8-diphenylnaphthalene, hexahelicene, and 4-methylbenzo[c] phenanthrenes, and gave evidence for the remarkably small, space-demanding properties of the phenyl substituent in these compounds.     

Nickel-catalyzed reaction of butadiene with strained ring olefins: Formation of a four-membered cyclic compound

Reaction of butadiene with strained ring olefins such as norbornene, dicyclopentadiene etc. Gives an exo-methylene- and methyl-substituted four-membered cyclic compound (II). The effective catalysts are (n-Bu₃P)₂NiBr₂/NaBH₄ or /alkoxide $\text{1}\text{1}$ syn-π-crotylbis(triethyl phosphite)nickel hexafluorophosphate (IV), and tetrakis(triethyl phosphite)nickel/CF₃COOH $\text{1}\text{1}$. π-Crotyl complex IV reacts with the strained ring olefins to give the corresponding product similarly. It is concluded that the active species for this catalytic reaction is a nickel hydride and that this reaction proceeds through π-crotyl intermediate.     

Reactivite des epoxydes—IV: Mise en evidence de complexes HMPT-lithium lors de l'ouverture des epoxydes par les amidures de lithium—interet sur la plan synthetique

The study of the ratio $\text{|HMPT|}\text{|Amide|}$ effect on the percentage of α-elimination products during the opening of 3,4-epoxycyclooctene 1 with Et₂NLi leads to notice the formation of two complexes: HMPT, Li⁺ and 2HMPT, Li⁺. The α-elimination is entirely suppressed when the second complex is formed. With 5,6-epoxycyclo-octene 2 as a substrate, the study of the ratio $\text{|HMPT|}\text{|Amide|}$ effect on the β-elimination evidences the formation of a third complex: 4HMPT. Li⁺; up to a concentration of |HMPT| = 2|amide| β-elimination is still possible, but for |HMPT|=4|amide| γ-elimination is mainly observed. These conclusions have been applied to 3-allyl epoxy-cylooctane 3 reaction which is able to lead to α, β and γ-elimination.     

Neutron powder diffraction on RbCrl3 and magnetic measurements on RbCrl3 and CsCrl3

β-RbCrI₃ (a = 13.772(3), b = 8.000(2), c = 7.069(2) Å β = 95.85(1)°, $\text{Z = 4,}\text{C2}\text{m}$ at 293 K) and γ-RbCrI₃ (a = 13.586(2), b = 7.923(2), c = 14.094(3) Å, β = 96.88(1)°, Z = 8, C2 at 1.2 K) are isostructural to β-RbCrCl₃ and γ-RbCrCl₃ and are both Jahn-Teller distorted BaNiO₃ structures. In both compounds elongated octahedra occur. γ-RbCrI₃ most probably has a magnetic spiral structure at 4.2 and 1.2 K. Theoretically, a spiral propagating along the b axis is expected. A model with k = 9/19b1 yielded the best result. However, no good fit was obtained possibly because of a misfit in k and canting of the magnetic moments due to anisotropy. χ vs T single-crystal measurements on β-CsCrI₃ are in accordance with its magnetic structure. The three-dimensional magnetic ordering temperature T_c is estimated as 27(1) K. From the χ vs T curves of γ-RbCrI₃, T_c could not be determined. From fits to χ vs T powder data $\text{J}\text{k}$ of CsCrI₃ and RbCrI₃ are estimated to be ?14(2) and ?11(1) K, respectively.