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2-aminopyrimidine system
ELSEVIER
lnorganica Chimica Acta 255 (1997) 325-334
Crystal chemistry of the copper bromide/2-aminopyrimidine system George Pon ", Roger D. WiUett a,., Barry A. Prince b, Ward T. Robinson b, Mark M. Turnbull b.! a Department of Chemistry. Washb~gton State University, Pullman, WA 99164. USA " Chemistry Department, University of Canterbury, Christchurch. New Zealand
Received 31 May 1995; revised 17 May 1996
Abstract The preparation and crystal structures are reported for seven compounds obtained from the interaction of copper(lI) bromide with 2-aminopyrimidine. This includes four copper( II ) bromide compounds and three copper(1) bromide complexes. The L----2-aminopyrimidine moiety can exist as neutral L species, as well as either a monoprotonated LH + cation or a diprotonated LH2 2+ dicafion in which one or two of the ring nitrogen atoms, respectively, are protonated. The neutral ligand is found to coordinate to one or two Cu ions through the ring nitrogen atoms, while the monocation may or may not coordinate through the unprotonated ring nitrogen atom. The crystals are stabilized by hydrogen bonding between the halide ions and the -NH2 and/or > N-H + fragments. The Cu(ll) species show a range of coordination geometries. L2CuBr2 contains isolated four-coordinate species with a planar coordination geometry (Cu-N = 1.996(5) andCu-Br= 2.401( I ) A). (LH)2CuBr+ contains isolated six-coordinate species with a square planar CuBr4 2- arrangement (Cu--Brffi2.427( 1) and 2.487( I ) A) augmented by two LH ligands (Cu-N = 2387 (6) A). The (LH) 2Cu2Br6salt contains planar bibridged Cu2Br6 2- dimers (Ct~Br(av.) ffi2.424 A) which aggregate into stacks through the formation of semicoordinate Cu-Br bonds (distances - 3.067( 1) and 3.335( 1 ) A,). Finally, (LH)~CuBr4 contains isolated distorted tetrahedral CuBr+ 2- anions, with Cu-Br= 2.388 A (av.) and the larger trans Br--Ca-Br angles of 135.4 ° (av.). The Cu (I) compounds all contain a common structural element: a (CuBr), chain as illustrated in I with Cu-Br = 2.52-2.56 A and Cu-Br-Cu=99-107 °. in each chain, the Cu{l) ion completes a tetrahedral coordination by forming bonds to Br- ions or ring N Cu
/
Cu \Br / \Br / I atoms in the ligands, in LCuBr, the pyrimidine ligands bridge Cu atoms on adjacent chains, forming a rectangular two dimensional network. This gives the Cu(I) ion a N2Bra coordination environment. For the LCu2Br2 compound, the (Cu-Br),, chains dimerize through the formation of Cu-Br linkages between chains. The pyrimidine ligands now bridge between Cu atoms on adjacent dimerized chains. Thus the Cu(l) ion has a BraN coordination environment. Finally, in ( LH )CuBr 2, each copper ion in the chain completes its coordination sphere by cotmiinafing to one pyrimidinium cation and to one bromide ion, to also attain a Br3N coordination sphere. Keywords: Crystal structures: Copper complexes; Aminopyrimidinecomp!exes
1. Introduction The systematic design, synthesis and characte,+ization of novel magnetic materials continues to be of interest. Mixed organic/inorganic systems provide for particularly diverse approaches [ I ]. In our laboratory, we have had particular success with the use of organoammonium halide salts of first row transition metal ions, particularly when M = C u ( I I ) . Thus we have been able to prepare linear chain ACuCI 3 salts which contain mbridged ferromagnetic ( F M ) chains [2], * Corresponding author. ~Permanent address: Department of Chemistry, Clark University, Worchester, MA 01610, USA. 0020-1693/97/$17.00 © 1997 Elsevier Science S.A. All rights resexved Pll S0020-1693 ( 96 ) 05 383-2
b.~bridged FM chains [3], or bibridged antiferromagnetic ( A F M ) chains [4] as well as bibridged alternating FM [5], alternating AFM [ 61, or alternating F M / A F M chains [ 5 3 ] . The ability to manipulate the bulk and hydrogen bonding capabilities of the cations is crucial to this lattice engineering process. One specific series of cations which have yielded a particularly large array o f unique magnetic systems have been based on substituted pyridines. In addition to the aforementioned AFTI bibridged chains, this has included a series o f stacked (Cu~X~,+2) 2- oligomers [8]. W h e n one o f the substituents is an amino group, the possibility of both coordination and hydrogen bonding exists, as is observed in the dimeric (3-aminopyridinium)2CuzXs salts [9]. However,
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(7. Pon et aL / lnorganica Chi,;,ie~ Acta 255 (1997) 325-334
because of the stronger basicity of the ring N atom, both coordination and protonation compete for the ring N atoms. Additional complication was observed with substituted 2-aminopyridine systems, especially when X--Br, in that bromination of the pyridine ring occasionally occurred with concurrent reduction of Cu(II) to Cu(I) [10]. An additional flexibility is introduced when the pyridine rings are replaced by pyrimidine or pyrazine rings. Now, the existence of two ring N atoms allows for multiple coordination and/or protonation, as well as multiple hydrogen bonding networks. We recently reported the structures of several compounds obtained in the 2 - a m i n o p y r i m i d i n e / C u C I 2 / H C l system [ 11 ]. Three complexes were reported with monoprotonated 2-aminop)rimidmium cations: (LH)[CuCI3(H20) ], (LH)2Cu2CI6 and CuCIa(LH)2. The first contains stacked planar CuCI3(H20) - anions, with the structure stabilized by extensive N-H-.-CI, N - H . . . O and O-H.--N hydrogen bonds. The second contains stacked planar Cu2CI6 2- dimers. The third contains isolated oetahedra, composed of a central square planar CuCI4 z- species with two longer semi-coordinate Cu---N bonds to the LH ÷ cations. In addition, if two Cu(II) ions coordinate to a single ring system, a possible magnetic exchange pathway exists Table 1 A summaryof crystalpreparation conditions Compounds Copperand Solutioncondition ligand ratio LCuBr, (LH)CuBr~ (LH):CuBr,, (LH-,)CuBr4 LCuBr LCu,Br, (LH)CuBr,
!:2 i:! !:2 1:1 1:1 2:1 1:1
50 ml H20 and ! mi conc. HBr 8 M HBr solution 6 M HBr solution conc. HBr solution 50 rnl Hal:)and I ml conc. HBr 50 ml H,.Oand ! ml cone. HBr 6 M HBr solution
C~stai color darkpurple dark purple dark purple dark purple yellow orange dark orange
between the two magnetic centers. This possibility is observed in LCuCI z, where chains of (CuCI2),, stoichiometry are linked by bi-coordinated pyrimidine rings [ 1 lc]. In this paper we report on our analogous investigation of the 2-aminopyrimidine/CuBr2/HBr systems. Since the 2-aminopyrimidine system is susceptible to bromination, the existence ofredox reactions leading to the formation of Cu(I) species is not unexpected. Direct bromination of 2-aminopyrimidine by Br2 or BrCI has been reported [12]. Indeed, in neutral and/or acid solution, we have isolated three Curl) compounds in addition to four Cu(II) species. A report on the synthesis and unit cell lattice constants has been given for one of the Cu(II) compounds, bis(2-aminopyrimidine)copper(II) bromide [13].
2. Experimental
The compounds were prepared by the reaction of CuBr2 with 2-aminopyrimidine (L) in HBr solutions. The Cu(II) compounds obtained included L2CuBr. (1), (LH)CuBr3 (2), (LH)2CuBr4 (3) and (LH2)CuBr4 (4). In addition, the following Cu(1) compounds were obtained: LCuBr (5), LCu,.Br2 (6) and (LH)CuBr2 (7). A general summary, of reaction conditions is given in Table 1. Prolonged heating and anaerobic conditions favored the formation of the Cu(I) salts. These can be prepared directly from CuBr also. Compounds containing the unprotonated ligand were obtained from solutions to which sufficient HBr was added to prevent precipitation of copper hydroxide species. The diprotonated species was obtained in a very concentrated acid solution. Specific directions for preparation of two of the compounds are given as follows.
Table 2 Crystal data for Cu(11) compounds Compound
L-,CuBr2 ( 1)
( LH)CuBr.~(2)
( LH):CuBr.~(3)
( LH.,)CuBr., (4)
Empirical formula Molecular weight Crystalclass Space group a (A)
CsH1oN~,CuBr., 413.58 triclinic PI (No. 2) 5.760( I ) 6.933( ! )
C4H~N3CuBr3 399.4 triclinic P! (No. 2) 4.067 ) 1)
CsHt2Nc,CuBr,~ 575.44 monoclinic P2,1c (No. 14) 7.328(3)
C4HTN~CuBr,, 480.32 onhorhombic Pbca (No. 61 ) 8.625(2)
8.926( l)
I 1.254(3) 11.352(4)
13.824(2) 7.471(2)
14.593(6) 17.650(4)
70.64( I ) 80.36( 1) 67.35( 1) 310.01 (7) 2.22 1 20 0.030 0.037
62.15(2) 85.46(2) 82.34(2) 455.2(2) 2.91 2 20 0.033 0.039
b (A) c (]k)
a (°) /3 (°) 7 (°) V (/t,:~) p ( gcm - 3) Z T (°C) R" R,,,h
a R = E I IF,,I - lF~i IlEIF, ot. 'Rw= [~w( IF,,I- IFcl )~'IT.wIF,,I"] ,2
99.38(3) 746.6(4) 2.56 2 20 0.046 0.057
2221 ( I ) 2.87 8 20 0.071 0.048
G. Pon et al. / Inorganica Chimica Acra 255 (1997) 325-334 2.1. Synthesis o f L C u B r
4 8 % H B r (2.22 m!, 2 0 m m o i ) d i s s o l v e d in H 2 0 ( 5 m l ) . The c o m b i n a t i o n m a d e a very intense g r e e n - b r o w n solution. The
CuBr2 ( 2 . 2 3 g, 10 m m o l ) w a s dissolved in H.,O (5 ml) and a d d e d to a solution o f L ( I . 9 0 g, 20 m m o l )
and
mixture was a l l o w e d to stand at r o o m temperature. After 2 - 4 days, y e l l o w crystals had f o r m e d and were collected b y filtration and left to dry in air. Yield: 0.38 g ( I 6 % ) . N o
Table 3 Crystal data for Cu(1) compounds
attempt w a s m a d e to m a x i m i z e the yield. IR ( K B r ) : 3339m,
Compound
LCuBr (5)
LCu,.Br.,(6)
(LH)CuBr: (7)
Empirical formula Molecular weight Crystal class Space g~oup a (/~) b (~) c(A) /3 (°) V (A -~) p (gcm - 3)
C4HsNCuBr 238.56 orthorhombic Pc2m (No. 28) 3.805( I ) 6.915( 1) I 1.851(2)
C4H~N~Cu_,Br_, 381.01 orthorhombic Pnma (No. 62) 14.518(2) 14.014(4) 3.949(I)
311.8( I ) 2.54
803.4(3 ) 3.16
C.tH~NCuBr 319.47 monoclinic P211n(No. 14) 3.983( 1) 13.229(4) 14.468(3) 91.37(2) 764.0(3) 2.79
Z
2
4
4
C(4)
T(°C) R~ Rw ~
20 0.021 0.056
20 0.089 0.146
20 0.042 0.036
C(5) C(6) N(7)
" R = E I IF,d - IFCI I/EtF, I. h R~,= JEw( IFol - IF~I )"/Ewl F,I 'i I/."
Table 6 Atomic coordinates ( × 104) and isotropic thermal parameters ~ ( × 10~,~:) for (LH):CuBr.L (3) Atom Cu Br(I) Br(2) N{ I) C(2) N( 3 )
x 0 2526( 1) - 1723(1) - 2001(7) - 1307(9) - 2224( 8 ) - 3914(10) -4698(10) - 3675( 10} 331(8)
y
z
U~
5000 4426( I ) 5502(1) 3280(4) 2394(4) 1584(4) 1641 (5) 2524(4) 3326(5) 2306(4)
0 2262( i ) 2452(!) - 128(7) -322(8) 42(6) 528(9) 653(10) 313(9) -872(8)
3! ( l ) 32( I ) 34(I) 33(2) 32(2) 39{ 2) 38(2) 39(2) 38(2) 41(2)
The equivalent isotropic U~ is defined ~ one-third of the trace of the orthogonalized U,j tensor.
Table 4 Atomic coordinates ( v 104) zmd isotropic thermal parameters ~ ( A-~× 10~) for L,_CuBr._, ( 1 ) Atom
x
y
z
U~q
Cu Br N(1) C(2)
0 -3784(I) 744(8) 2396(9)
N(3)
2935(9)
C(4) C(5) C(6) N(7)
1798(11) 82(11) -391(10) 3525(10)
0 2734(I) - 1290(7) -858(8) - 1690(8) - 3022(10) -3557(10) -2627(9) 516(9)
0 - 1216(I) - 1798(5) -3014(6) -4246(5) -4247(7j -3053(7) - 1827(7) -3037(6)
26(l) 35(I) 26(2) 26(2) 31(2) 35(3) 36(3) 32(3) 41(3)
The equivalent isotropic U¢, is defined as one-third of the ~race of the orthogonalized U,j tensor. Table 5 Atomic coordinates ( × 104) and isotropic thermal parameters ~ ( × 10~/~2) for (LH)CuBr3 (2) Atom
x
y
z
U,~,
Cu Br(l) Br(2) Br(3) N(I) C(2) N(3) C(4) C(5) C(6)
2832(2) 6365(1) 1854(I) - 1046(2) 2902(12) 1963(14) 3315(12) 5500(15) 6414(17) 5019(15) -299(13)
6715(1) 5316(1) 8476(1) 7798(1) 3519(5) 3054(6) 1856(5) 1040(6) 1459(6) 2746(6) 3809(5)
4210(I) 6125(I) 4882(I) 2456(I) 134(4) 1526(5) 2450(4) 2129(6) 845(6) -95(6) 1864(4)
27(1) 26(1) 27{1) 32(1) 29(2) 28(2) 34(2) 37(2) 38(3) 32(2) 34(2)
N(7)
327
The equivalent isotropic U~ is defined as one-third of the trace of the orthogonalized U,j tensor.
Table 7 Atomic coordinates ( x 104) and isolropic thermal -parameters ~ ( x IO~A2) for (LH)~CuBr4 (4) Atom
x
y
z
U~
Br(I) Br(2) Ca Br(3)
1091(4) !!81(4) 202(3) -997(4) -924(4) 940(23) 1861(28) 2232(28) 3025(35) 3563(32) 3192(33) 2315(23)
9182(2) 6125(2) 7648(2) 7830(1) 7433(2) 6504(13) 5783(16) 5407(11) 4639(16) 4157(I9) 4567(12) 5323(10)
lit0(1) 1444(1) 1265(2) 2472(2) 40(2) 3681(12) 3735(14) 4389(10) 4455(11) 3796(I7) 3129(I2( 3101(10)
36(!) 36(1) 34(I) 41(i) 43(1) 51(8) 36(8) 49(9) 47(12) 62(12) 32(9) 26(7)
Br(4)
N(7) C(2) N(3) C(4) C(5) C(6) N(I)
"The equivalent isotropic Uoq is defined as one-third of the trace of the orthogonalized U,j tensor. Table 8 Atomic coordinates ( x 104) and isotroDic thermal parameters * {A:x I0 ~) for LCuBr (5) Atom
x
y
z
U,~
Br Cu C(2) N(I) C(6) C(5) N(7)
0 5000 4898(26) 5509(I3) 6791(18) 7509(27) 3585(29)
9011 6560(2) 5990(12) 5135(7) 3339(9) 2381(11) 7740(14)
5000 5000 2500 3514(4) 3476(6) 2500 2500
16(2) 20(3) 17(2) 14(l) 21(2) 20(2) 24(2)
The equivalent isotropic Ucq is defined as one-third of the trace of the orthogonalized U,~tensor.
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G. Port et al. / lnorganica Chimica Acta 255 (1997) 325-334
3281w, 3217w, 3179w, 1636s, 1626s, 1566s, 1485s, 1350s, 1200m, 787s, 480s, 455m c m 2.2. Synthesis o f L,CuBr2
CuBrz (2.23 g, 10 mmol) was dissolved in H_,O (5 ml) and added to a solution o f L ( 1.90 g, 20 mmol) in H20. The combination made a green solution from which a very intense brown colored precipitate quickly evolved. This precipitate was isolated by vacuum filtration in 85% yield. IR ( K B r ) : 3398m, 3121m, 1645s, 149Is, 136Is, 1197m, 798s c m - t Other salts were synthesized in a similar manner. Crystals were grown by slow evaporation of saturated solutions. In some cases cD'stals of different compounds were obtained from the same solution, since the composition of the solution changed as crystallization progressed. Chemical compositions were deduced from the X-ray structure analyses reported below. X-ray diffraction data for compounds 1--4, 6 and 7 were collected with a Syntex P2~ diffractometer upgraded to Nicolet P3F specifications at Washington State University, equipped with a graphite monochromator ( M o K a radiation, h =0.71073 A) [ 14]. For compound 5 data were collected on a Siemens P4 diffractometer at the University of Canterbury, also equipped with a graphite monochromator ( M o K a Table 9 Atomic coordinates ( × I04) and isotropic thermal parameters" ( A-~× !0') for LCu,Br2 (6)
Atom
x
y
z
U,..
Br(l) Cu N(I) N(7) C(2) C(5) C(6)
3614(1) 3071(3) 3730(9) 2651(14) 3323(14) 5010(18) 4554(13)
4465(1) 5373(2) 6641(11) 7500 7500 7500 6659(14)
5998(5) 1196(10) 949(43) 3591(81) 1789(62) - 1754(78) - 889(58)
42(1) 74(1) 39(5) 52(9) 22(6) 44(9) 47(7)
=The equivalent isotropic Ueq is defined as one-third of the trace of the orthogonalized Ui~tensor. Table 10 Atomic coordinates ( x 10a) and isolropic thermal parameters = (A-~× 10:~) for (LH)CuBr,. (7) Atom
x
Br(l) Br(2) Cu N(I) C(2) N(3) C(4) C(5) C(6) N(7)
8934(2) 15062(2) 13853(3) 13916(17) 12739(22) 13345(17) 15160(22) 16308(24) 15709(22) 10885(I)
y 789(1) -502(I) -181(1) - 1549(5) -2411(6) -3304(5) -3356(7) -2504(6) - 1594(7) -2379(6)
z
U¢,I
6463(I) 8594(1) 6970(I) 6269(4) 6611(6) 6215(5) 5415(6) 5035(6) 5490(6) 7351(5)
27(!) 30(I) 33(1} 26(2) 26(3) 29(2) 30(3) 28(31 31(3) 33(3)
The equivalent isotropic Ueq is defined as one-third of the trace of the onhogonalized Uo tensor.
radiation, A=0.71073 A) 115]. La:tice constants were obtained from 25 accurately centered high angle ( 27 < 2 0 < 35 °) reflections. Data were generally collected out to 2 0 = 4 5 °, and those with I F,,i > 3o-(F) retained for structure analysis [ 16-18]. Data were corrected for adsorption utilizing psi scan data assuming ellipsoidai shaped crystal, except for LCuzBr2 (6) where a numerical absorption correction was used. Hydrogen atoms were included at calculated positions and refined assuming a riding model. Extinction correclions were applied to compounds 2, 3, 4, 6 and 7. Tables 2 and 3 list pertinent crystallographic data, with atomic positional parameters (and equivalent isotropic therTable 11 Bond distances ( A ) in Cu (II) compounds (4)
C(S) NN~'C(6)
Cu-Br(i) Cu-Br(2) Cu-Br(3) Cu-Br(4) Cu-N(1) N(i)-C(2) C(2)-N(3) N(3)-C(4) C(4)-C(5) C(5)-C(6) C(6)-N(I) C(2)-N(7)
, N(3)
\
~C(2).~..-N(?)
N(1)/ I
2
3
4
2.401(1)
2.442(I),2.464(I) 2.413(I) 2,378(4)
2.427(I) 2A87(I)
2.382(4) 2.398(4) 2.383(4) 2.391(5)
1.996(5) 1.353(6) 1.344(8) 1.322(10) !.384(8) 1.385(10) 1.333(6) 1.338(10)
2.787(6) i,343(8) 1.356(8) 1.349(9) 1.359(9) 1.384(9) 1.322(9) 1.337(9)
i.348(7) 1.339(6) !.344(9) 1,343(9) 1.410(7) 1.300(9) 1.325(9)
Table 12 Metal bond angles (°) in Cu ( II ) compounds Compound l N(I)-Cu-Br Cu-N(i)-C(2) Cu-N(I)-C(6)
90.0 122.0(5) 120.2(3)
Compound 2 Br( I )-Cu-Br (2) Br( ! )-Cu-Br(3) Br(2)-Cu-Br(3) Br( I )-Cu-Br(a) Br(2)-Cu-Br(a) Br(3)-Cu-Br{a) Cu-Br( 1)-Cu(a)
91.0(i) 171.6(1) 94.0(1) 83.3(l) [71.4(I) 90.4(!) 96.7(t)
Compound3 Br(I)-Cu-Br(2)
90.0(1)
Compound4 Br( I )-Cu-Br(2) Br( I )-Cu-Br(3) Br(2)-Cu-Br(3) Br( I )-Cu-Br(4) Br(2)-Cu-Br(4) Br( 3 )-Cu-Br (4)
140.6(2) 97.9( I ) 98.0( I ) 98.6( ! ) 98.1(I) 130.3(2)
1.36(3)
1,32(3) 1.32(3) 1.44(4) 1.36(4) 1.34(3) 1.32(3)
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G. Pon et ai. /hmrganica Chimica Acre 255 (1997) 325-334
Table 13 Bond distances (A,) in Cu(I) compounds
Table 14 Metal bond angles (°) in Cut !) compounds
Compound
LCuBr (5)
LCu,Br, (6)
(LH)CuBr: (7)
Cu-Br( 1) Cu-Br(I') ~ Cu-Br(i") ~ Cu-Br(2) Cu-Cu" ~ Cu-N( I ) N{ 1)-C(2) N( 1 )-C(6) C(6)-C(5) C(2)-N(7) C(2)-N(3) N(3)-C(4) C(4)-C(5)
2.548( I )
2.415(4) 2.540(4) 2.495(5)
2.439(2) 2.520(25
Cu-Br( I )-Cu' a Br( ! ) - C u - N ( ! ) Br( I')-Cu-N( I )
2.420(2)
N( 1)--Cu-N (I") ~ N( I ) - C u - B r ( l " ) / B r ( 2 ) ¢ Br( l ) - C u - B r ( I ' ) ~ Br( ! ) - C u - B r ( i " ) / B r ( 2 ) Br( I' )-Cu-Br(1")/Br(2) Cu-Br( I )--Cu" ~ Cu'-Br-Cu"
2.027(5) 1.359(6) 1.335 (7) !.359(7) 1.310(13)
2.782(5) 2.019(15) 1.38(2) 1.40(2) 1.39(2) !.21(3)
2.071 (7) 1.33011 I) 1.348( I 1 ) 1.393(15) 1.315(!1) 1.335( 11 ) 1.380( 11 ) 1.337(12)
Br( I' ) denotes a Br( 1) atom translated by one unit cell along the (CuBr),, chains direction. h Cu" and Br(I") denotes atoms in the adjacent (CuBr),, chain in the pleated sheet.
5
6
7
96.60(9) 113.2(25 104.6( 1) 121.9(35
105.6( I ) 110.3(55 104.7(5)
106.9( I ) 109.3(2) 106.4(2)
112.8(4) 105.6( ! ) 113.5(2) 109.2(2) 69.6( I ) 67.9( I )
108.5(2) i06.9(!) 121.5(1) I03.2(1)
96.60(a)
Cu' and Br( I' ) denote atoms translated by one unit cell along the (CuBr),, chain. h N ( i ' ) denotes the symmetry related N( i 5 atom coordinated to Cu. Cu" and Br( i'5 denote atoms in the adjacent (CuBr),, chain of the pleated sheet.
Table 15 Hydrogen bonding interaction Hydrogen bond interaction
Coordinate transformations
N-X
Distance (/~)
C-N-X
Angle (°)
Compoundl N(7)-Br(a) N(7)-N(3b)
3.427 3.003
C(2)-N(7)-Br(a) C(2)-N(7)-N(3b)
152.5" 120.9
a~ 1+x,y,z b= ! -y, -6, - I -:
Compound 2 N(7)-N(la) N(3)-Br(2b) N(7)-Br( i ) N(7)-Br(2b)
2.949 3.446 3.582 3.442
C(2)-N(7)-N(Ia) C(2)-N(3)-Br(2b) C(2)-N(7)-Br(Ie) C(2)-N(7)-Br(2b)
118.5 145.9 !06.1 99.8
a = - x , 1- y , - z b= -x,I-g ! -z c ~ 1- g l - y , I - z
Compound 3 N(3)-Br(2a)
3.523 3.316 3.465 3.597
117.8 112.2 135.8 110.7 90.6
a=x, l / 2 - y , - l / 2 + z
N(7)-Br(la) N(7)-Br(2b) N(7)-Br(2c)
C(2)-N(3)-Br(2a) C( 6~-N( 3 )-Br(2a) C(2)-N(7)-Br(la) C(2)-N(7)-Br(2b) C(2)-N(7)-Br(2c)
Compound 4 N( l ) - B r ( l a )
3.249 3.653
N(3)-Br(2c)
3.624
N(7)-Br(4a)
3.278
132.0 103.4 71.4 93.7 85.6 74.8 128.2
a = x , 312--y, - l / 2 + z
N(3)-Br(Ib)
C(2)-N( I )-Br(la) C(65-N( I ) - B r ( l a ) C(2)-N(3)-Br(lb) C(4)-N(3)-Br(lb) C(2)-N(3)-Br(2c) C(4)-N(3)-Br(2c) C(2)-N(7)-Br(4a)
Compound 6 N(7)-Br(a)
3.465
C(2)-N(7)-Br(a)
!18.1
a= l 1 2 - x , 1/2+y, - i / 2 + z
Compound 7 N(3)-Br(2a)
3.227 3.558 3.593
132.8 104.9 133.6 92.3
a-- l 1 2 - x , - l / 2 + y , 3 1 2 - z
N(7)-Br(ab) N(7)-Br(la)
C(2)-N(3)-Br(2a) C(4)-N(3)-Br(2a) C(2)-N(7)-Br(lb) C(2)-N(7)-Br(la)
3.378
C(2)-N(7)-Br(a)
1 I3.2
a= - I +x,y, z
b = - x , i - y . --c= • -112+v, l12-z
b= -x. - 1/2+y, 112-z c = 1/2+x,4, l12-z
b = - 1 / 2 - x , - !12 +y. 312-.7.
Compound 5
N(7)-Br(a)
330
G. Pm,f el al. / hlorganica Chimica Acra 255 (1997) 325-334
Table 16 Br-.-Br contacts in Cu(It) compounds Br--+Br
Distance (A)
Cu-Br... Br
Angle (°)
Coordinate transformations
4.082 4.320
Cu-Br..+Br(a) Cu-Br...Br(b)
105.9 78.7
a = 1 +x, - 1+y, z b= I +x.y, z
3.678 4.067 4.068 4.077
Cu-Br(2).-+Br(2a)
161.0
a=x,
4.088
Cu-Br( 1 )+..Br(2a)
116+8
Cu(a)-Brf2a)..+Br( ! )
152.7
Cu-Br(l)...Br(4a) Cu(a)-Br(4a)...Br( I ) Cu-Br( I )...Br(3a) Cu(a)-Br(3a) ...Br( 1) Cu-Br( 1).-.Br(2b) Cu(2b)-Br(2b)---Br( I ) Cu-Br(2).+.Br(4a) Cu(a)-Br(4a)-..Br(2) Cu-Br(2)..-Br(3a) Cu(aj-Br(3a).,-Br(2)
73.4 142.2 70.8 151.0 154.0 154.9 70.2 66.3 72.5 128.8
Compound 1
Br •+Brta) Br...Br(b) Compound 2
Br(2)-'-Br(2a) Br(2)--Br(2b) Br(2)".Br(lb) Br(3)-.-Br(2b)
- I +y, z b= I +y,y,z
Compound 3
Br( ! ) +..Br(2a) Compomtd 4
Br( 1)'"Br(4a)
4.038
Br( 1)...Br(3a)
4.058
Br( 1).--Br(2b)
3_731
Br(2)-.-Br(4a)
4.186
Br(2)-.-Br(4a)
3.972
mal parameters) given in Tables 4-10. Tables 11-14 tist pertinent bond distances and angles, while Tables 15 and 16 summarize hydrogen bonding interactions and Br---Br contacts, The atom labeling scheme for the pyrimidine molecule is shown in the diagram in Table 11. Full crystallographic detads are available as supplementary material.
3. C o p p e r ( l l ) s t r u c t u r e s The four Cu(II) compounds each show different structural features. As seen in Fig. l, compound I contains isolated, centrosymmetrie L2CuBra molecules, with a symmetry imposed planar coordination environment ( C u - N -1.996(5) and C u - B r = 2.401 ( 1 ) ,~). Thus, only one of the two ring nitrogen atoms on each ligand coordinates to the Cu ion. Short intramoleeular contacts of 3.110 A exist between the Cu (II) ion and the amino N atoms ( labeled N (7) ), blocking the 5th and 6th coordination sites. The N( 1 ) - C u - N ( 7 ) angle is 48.3 °, while the C ( 2 ) - N ( 7 ) - C u angle is only 70.5 °. Thus, this is not a coordination interaction. An efficient
(
~Br
C(51
NTo)
31
+' CI4a)
Nt71
Fig. 1. Thermal ellipsoid plot of the isolated CuL2Br2species in compound 1.
a= 1/2--x, 3 / 2 - y , - z
b=l/2-x.l/2+y,z
hydrogen bonding network involving N ( 7 ) - H . . - B r ( N Br--3.427 ,~) and N ( 7 ) - H . - - N ( 3 ) ( N - N = 3.003 A,) interactions tie the lattice together into two dimensional networks lying in the (010) planes. The structure of (LH)CuBr3 (2) contains symmetric bibridged planar Cu2Br6 2- anions (Fig. 2) with C u - B r (terminal) = 2.378( 1 ) and 2.413( 1 ) / ~ and with C u - B r (bridging)=2.442(1) and 2.464(1) ,~. The magnetically important Cu-Br( I ) - C u bridging angle is 96.7( 1)°. This is 1-1.5 ° larger than normal, so extremely strong antiferromagnetic coupling is anticipated in the dimer. The dimers stack to form chains parallel to a through the formation of long semi-coordinate bonds ( C u - - - B r ( 3 ) = 3 . 0 6 7 ( 1 ) and C u . - . B r ( 1 ) = 3 . 3 3 5 ( l ) /~,). This is shown in Fig. 3. In this manner, each Cu(lI) ion assumes the typical distorted octahedral coordination. The stacking is analogous to that in
!I KCuCI3 [ 19], The stacking pattern, denoted a 2( I/2, I / 2 ) pattern in the Geiser notation [20], is shown in II. An extensive three dimensional H-bonding network exists as documented in Table 15, The structure is isomorphous with the analogous chloride salt [ 11 ], Compound 3, which is also isomorphous with the analogous CI- salt [ ! lb] contains isolated centrosymmetric CuBr4(LH) 2 molecules (Fig. 4) in which the Cu(II) ion
G. Pon et aL I lnorganica Chimica Acre 255 (1997) 325-334
331
~
N{31 C(21 .I~INITI
ri41
"~r-,-~Brl3)
NlTal ~ o l Fig. 2. lUuslration
O of the Cu~Bn,"~- dimer
i~'~u
I I
Br(2ul
I I
I
2. Fig. 5. Illustration of lhe asymmetric unit it: compound 4, showing the diprotonated LH: -~+ cation and the CuBr+ -'- anion.
i
VBrllbl I
I I
N Z
01401
and L H cations in compound
Brllcl
Brl2cl
Brl3¢t ~
~'a]
Brl2bl
I I
i-Ilol I
8r13|
Brl3o
BrI21 I
I
Y B
r
l
3
~
Fig, 3, Stacking
J
Brl2dl of the directs in compound
2.
/
Brik9
BrI1oi~
....
/
Brllol
....
/
Brl21 ///~'a,-~2~
- - - J
s~-~- - - J
~
(c)
BHIel ~ Fig. 6. ilIustradon of the Cu-X--+X--Cu onc-dimcusiooa] Imthways. (a)
.
.
.
.
.
~:14 o.tl
Fig. 4. Thermal ellipsoid plot of the isolated CuBr+(LH)2 species in compound 3.
again has a distorted octahedral coordination. Here we have the unusual situation of a coordinated cationic ligand. The four Br- ions form the square planar base (Cu-Br= 2.427(1) and 2.487(1) ,~ with Br--Cu-Br=91°), with longer semi-coordinate Cu-N( 1) distances of 2.787(6) A. However, the protonation of the one ring nitrogen atom apparently weakens the coordination ability of the second
compound 1 (Br.-.Br=4.082 A, Cu-Br.--Br = 105.9°); (b) compound 2 (Br-..Br=3.678 A, Cu-Br--.Br= 161.0°); (c) compound 3 (Br--+Br = 4.088 A, Cu--Br-.-Br = 116.8, 152.7°).
ring nitrogen atom. Hence it is not able to compete for a primary (equatorial) coordination site as in compound 1. A weak N-H..-Br hydrogen bonding network ties the molecules together into sheets in the bc plane. The network involves a hydrogen bond from N(3) and a disorder of the -N(7)H2 moieties so as to form three N-H...Br interactions each. Finally, compound 4 contains isolated, distorted tetrahedral CuBr4 2- anions (Fig. 5). The Cu-Br distances range from 2.382(4) to 2.398(4) A,, with the iargertrans Br-CuBr angles of 130.3(2) and 140.6(2) °. The diprotonated cation is involved in strong hydrogen bonding which ties the
332
G. Port et al. / blorganica Chinlica Acta 255 (1997) 325-334
structure together into chains parallel to c with four N-H---Br contacts of 3.330 ,A or less. From the point of view of the magnetic properties of these compounds, the examination of the Br---Br contacts is important. The unpaired electron density in Cu(II) halide complexes is substantially delocalized out onto the orbitals of the halide ions [21 ]. This is particularly true for bromide complexes, since the smaller difference in energy between the Cu d and Br p orbitals (as compared to the chloride complexes) enhances the delocalization Hence, substantial overlapofthe magnetic orbitals can occur even when the Br.--Br contacts are as long as 4.5 A, [ 22 ]. These can lead to the establishment of unusual and, on the surface, unexpected magnetic exchange pathways [9,231. Antiferromagnetic exchange couplings in excess of ]J k- kl = 50 K have been observed [241. Examination of the structures reported here reveals the possibility of similar effects ( Fig. 6). Two of the compounds show the potential to form good Id AFM systems. In L2CuBr,_ (1), Br--.Br contacts of 4.082 A link the Cu ions into chains parallel to [ 1/0]. However, the Cu-Br---Br angle of 105.9 ° may be unfavorable for strong overlap, since the delocalization of the unpaired electron is primarily into the ligand p,, orbitals. For (LH)2CuBr4 (3), pairs of Br(1)---Br(2) contacts of 4.088 ,~ link the molecules together into chains parallel to a. In the analogous CI- salt, the observed exchange coupling constant was J k - ~= - 7.3 K with a CI-- -C1 distance of 3.990 A. With an increase in van der Waal contact distance of 0.30 ~,, and an actual increase of only 0.10 A in the X..-X contact distance, substantially stronger AFM exchange is anticipated. The case of (LH)CuBr.~ (2) provides an interesting case. Magneto-structural correlations predict strong AFM coupling within the dimer [25]. However, very short Br(2)...Br(2) contacts of only 3.678 A tie the dimers together into chains parallel to I l l 0 ] . With a favorable Cu-Bi .... Br angle of 161.0°, very strong AFM coupling can be expected. This coupling should be stronger than the coupling along the stacks diagrammed in Ii. This system should behave as an alternating ld AFM chain, with weaker interchain coupling. Finally, in (LH2)CuBr4 (4), similarly short Br( 1 )...Br(2) contacts of 3.73 ! ,~ tie the tetrahedra together into chains parallel to [ 170], but a series of only slightly longer Br--.Br contacts (3.97-4.19 A) link the chains together into a three dimensional network. The presence of these short Br...Br contacts is mediated by the extensive hydrogen bonding capability of the 2-aminopyrimidine species. This, coupled with its small size, forces the short halide-halide contacts.
4. Copper(I) structures These structures all contain the common t~ature, that of a chain of corner-shared Cu(1) tetrahedra. This defines a pleated (CuBr),, backbone, as illustrated in Fig. 7 for corn-
Fig. 7. Illustrationof the (CuBr),, chain structures in compounds 5-7. (a) LCuBr (5); (b) LCu_.Br2 (6): (c) (LH)CuBr2 (7). pounds 5-7. In LCuBr (5), each Cu(I) ion completes its four-coordination by bonding to ring N atoms on two different L ligands giving a Br2N2 coordination sphere. The Br- ion thus has a P2 bridging geometry. In (LH)CuBr2 (7), the monoprotonated ligand can only form one bond to the Cu(1) ions. Hence, the second Br- ion replaces one of the ring N atoms, to give a Br3 N-coordination sphere. One Brion retains its P,2 bridging arrangement, while the other assumes a terminal position. Finally, in compound 6, pairs of (CuBr)n chains dimerize into the pleated sheet arrangement found in numerous other compounds [26]. Now the Br- ion has a P-3 bridging geometry. It assumes a trigonal pyramidal geometry, consistent with localization of a lone pair of electrons on the bromide ion in asp" hybrid orbital. Tables ! 3 and 14 summarize the bond distances and angles in the chain structures. In the parent chain in compound 5, all Cu-Br distances are identical and quite long (2.548( I )/~)
333
G. Port et al. / Inorganica Chimica Acta 255 (1997) 325-334
~
rllb|
Brl2b)
Fig. 10. Chainstructurein compound7. Fig. 8. Layerstructure in compoound5.
(LHCuBrz)n chains in compound 7 (Fig. 10) can be viewed as a segment of the double chains in compound 6.
Cubo
5. Conclusions
Brob~
B
r
~
Fig.9, Layerslructurein compound6. with fairly small Cu-Br--Cu and Br-Cu-Br angles (96.6(!)°). In compounds 6 and 7, the Cu-Br distances alternate along the chain,owith one distance remaining long (2.540(4) and 2.520(2) A, respectively) but the other shortening substanially (2.415(4) and 2.439(2) A,). The angles now open up to 105.6( I ) and 106.9( ! )°, respectively, sothat the repeat distances increase by more than 0. ! A in spite of the shortening of the bonds. The chains in compound 5 run parallel to the a-axis. The 2-aminopyridine molecules bridge adjacent chains for the cdirection, thus forming two-dimensional sheets lying in the a c plane (Fig. 8). The ligands lie athwart mirror planes perpendicular to c while the Cu and Br atoms lie on a two-fold axis parallel to b. There is a small twist of the pyrimidine molecules out of the b c plane, but the amino groups all lie on the same side of the layer. Thus each layer has a net dipole moment. Adjacent layers are related by translation symmetry, leading to a polar nature for the salt. In compound 6, the pleated sheet (Cu2Br2),, chains run parallel to the c-axis with the 2-aminopyridinium ligands, again bridging adjacent chains, lying in the b-direction (Fig. 9). In this case, the pyrimidine species also lie athwart mirror planes. Again, the planes of the rings are tilted out of the a c plane. Within the layers, pyrimidine molecules are related by a glide of planes perpendicualr to c. The
The crystal chemistry of the copper bromide and 2-aminopyrimidine system proves to be very rich. A major component in this richness is the ability of the 2-aminopyrimidine molecule to form coordinate bonds to the copper ions ~ well as to participate in several types of hydrogen bond formation. This later includes hydrogen bonds between the-NH2 groups and the ring nitrogens, the -NH2 groups and the Br- anions, and, for the protonated amines, the > N-H + groups and Branions. This provides dimensionality and stability to the crystalline lattices. The Cu(lI) compounds show a diversity of coordination geometries, reflecting the various competing interactions between coordinate and semi-coordinate bonds to Br- ions and pyrimidine ligands. The hydrogen bonding networks force a compactness to the structures, which leads to possible magnetic exchange pathways through the formation of short Br---Br contacts. The relative instability of Cu(H) bromide species is evidenced by the isolation of a variety of Cu(I) compounds. No evidence for the formation of brominated pyrimidine species is observed in the crystallographic results.
6. Supplementary material Tables of data collection and refinement parameters are available from the authors upon request.
Acknowledgements M.M .T. thanks the Chemistry Department at the University of Canterbury for their hospitality during his sabbatical stay. Work supported in part by NSF grant DMR-88-03382.
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G. Po,z et al./ Inorganica Chimica Acta 255 (1997) 325-334
References [I] (a) R. Fichter and G.E. Bonvicinio, ./. Chem. Educ.. 62 (1985) 905; (b) W.W. Hartman and J.B. Dickey, Organic Syntheses, Vol. I!, Wiley, New York, 1943, p. t73. 12] D.D. Swank, C,P, Landee and R.D. Willett, Phys. Rev. B, 20 (1979) 2154. [31 (a) R.D. Willett, C.P. Landee, R.M. Gaura, D.D. Swank, H. Groenendijk and A.J. Van Duyneveldt, J. Magn. Magn. Mat., 15-18 (I980) ! 055; (b) H.A. Groenendijk, W.J. BlSte, A.J. Van Duyneveldt, R.M. Gaura, C.P. Landee and R.D. Willett, Physica B, I06 ( 198 ! ) 47. [41 U. Geiser, R.M. Gaura, R.D. Willett and D.X. West, bzorg. Chem., 25 (1986) 4203. [5] R.D, Willelt, Mol. Ctyst. Liq. Cryst., 274 (1995) 71. [6] S. O'Brien, R.M. Gaura, C.P. Landee, B.L. Ramakrishna and R.D. Willett. b~org. Chim. Acta, 141 (~987) 83. [7] I.V. Vasitevsky, R.E. Stenkamp, E.C. Lingafelter, V. Shomaker, R+D. Willett and N.J. Rose, lnorg. Chem., 28 (1989) 2619. [8] (a) M.R. Bond, R.D. Willett, R.S. Rubins, P. Zhou, C.E. Zaspei, SL. Hutton and J.E. Drumheiler, Phys. Rev. B, 42 (1990) ! 0281 ; (b) K E. Hatvorson, T. Grigereit and R.D. Willett, inorg. Chem., 26 (1987) 1716" (c) M.R. Bond, H. Place, Z. Wang, R.D. Wiflett, V. Lie, T. Grigereit, J.E. Drumheller and G. Tuthill, bwrg. Chem., 34 (1995) 3134. [91 J. Blanchette and R.D. Willett, Inorg. Chem., £7 (1988) 843. [ 10l H. Place and R.D. Willett, Acta Crystallogr., Sect. C. 43 (1988) 34. [11] (a) T. Ivianfredini, G.C. Pellaeani, A. BonamarUni-Corradi, L.P. Battag'~,:,. G.G.T. Gaurini, J.G. Guisti, R.D. Willett and D.X. West, lnorg. Ct~em.,29 (1990) 221; (b) C. Zanchini and R.D. Witlett, inorg. Chem., 29 (1990) 3027; (c) G. Pon, unpublished results.
[ 12] J.P. English, J.H. Clark, J.W. Clapp, D. Seeger and R.H. Ebel, J. Am. Chem. Soc., 68 (1946) 453. [ 13] P. Lumme, P. Kekarainen+ H. Knuuttila, T. Kurkirinne, M. Latvala, L. R6nkOnharju and S, Salonen, Finn. Chem. Lett., 25 ( 1981 ). [ 14] Nicolet Crystallographic Systems User's Guide, Release 81.3, Nicolet X-ray Instruments, 1985. [ 15] XSCANS, Version 2.0, Siemens Analytical X-ray Instruments, 1993. [ 16] G.M. Sheldrick, SHELXTL, Version 5. i, X-ray Nicolet Instrument Corporation, 1985. [17] G.M. Sheldrick, SHELXS-86, program for the solution of crystal structures from diffraction data. University of GSttingen, G~ttingen, Germany, t986. [ 181 G.M. Sheldrick, SHELXL-93, program for the refinement of crystal structures, University of GOttingen, GSttingen, Germany, 1993. [ 19] R.D. Willett, C. Dwiggens, Jr., R.F. Kruh and R.E. Rundle, J. Chem. Phys., 38 (1963) 2429. [20] U. Geiser, R.D. Willett, M. Lindbeck and K. Emerson, J. Am. Chem. Soc., 108 (1986) ! 173. 121 ] C. Chow, K. Chang and RD. Willelt, J. Chem. Phys., 59 (1973) 2629. [22] K. Halvorson and R.D. Willeu, Acta Crvsmllogr., Sect, C. 44 (t988) 2071. [23] B.R. Patyal, B.L. Scott and R.D. Willett, Phys. Rev. B, 41 (1990) 1657. [24] G.V. Rubenacker, S. Wap]ak, S.L. Hutton, D.N. Haines and J.E. Drumhellar, J. Appl. Phys., 57 (1985) 3341, [25] B. Scotland R.D. Willett, J. AppL Phys.,61 (1987) 3289. [26) L.M. Engeihardt. P.C. Healey, J.D. Kildea and A.H. White, Aust. J. Chem., 42 (1989) 185.
lnorganica Chimica Acta 255 (1997) 325-334
Crystal chemistry of the copper bromide/2-aminopyrimidine system George Pon ", Roger D. WiUett a,., Barry A. Prince b, Ward T. Robinson b, Mark M. Turnbull b.! a Department of Chemistry. Washb~gton State University, Pullman, WA 99164. USA " Chemistry Department, University of Canterbury, Christchurch. New Zealand
Received 31 May 1995; revised 17 May 1996
Abstract The preparation and crystal structures are reported for seven compounds obtained from the interaction of copper(lI) bromide with 2-aminopyrimidine. This includes four copper( II ) bromide compounds and three copper(1) bromide complexes. The L----2-aminopyrimidine moiety can exist as neutral L species, as well as either a monoprotonated LH + cation or a diprotonated LH2 2+ dicafion in which one or two of the ring nitrogen atoms, respectively, are protonated. The neutral ligand is found to coordinate to one or two Cu ions through the ring nitrogen atoms, while the monocation may or may not coordinate through the unprotonated ring nitrogen atom. The crystals are stabilized by hydrogen bonding between the halide ions and the -NH2 and/or > N-H + fragments. The Cu(ll) species show a range of coordination geometries. L2CuBr2 contains isolated four-coordinate species with a planar coordination geometry (Cu-N = 1.996(5) andCu-Br= 2.401( I ) A). (LH)2CuBr+ contains isolated six-coordinate species with a square planar CuBr4 2- arrangement (Cu--Brffi2.427( 1) and 2.487( I ) A) augmented by two LH ligands (Cu-N = 2387 (6) A). The (LH) 2Cu2Br6salt contains planar bibridged Cu2Br6 2- dimers (Ct~Br(av.) ffi2.424 A) which aggregate into stacks through the formation of semicoordinate Cu-Br bonds (distances - 3.067( 1) and 3.335( 1 ) A,). Finally, (LH)~CuBr4 contains isolated distorted tetrahedral CuBr+ 2- anions, with Cu-Br= 2.388 A (av.) and the larger trans Br--Ca-Br angles of 135.4 ° (av.). The Cu (I) compounds all contain a common structural element: a (CuBr), chain as illustrated in I with Cu-Br = 2.52-2.56 A and Cu-Br-Cu=99-107 °. in each chain, the Cu{l) ion completes a tetrahedral coordination by forming bonds to Br- ions or ring N Cu
/
Cu \Br / \Br / I atoms in the ligands, in LCuBr, the pyrimidine ligands bridge Cu atoms on adjacent chains, forming a rectangular two dimensional network. This gives the Cu(I) ion a N2Bra coordination environment. For the LCu2Br2 compound, the (Cu-Br),, chains dimerize through the formation of Cu-Br linkages between chains. The pyrimidine ligands now bridge between Cu atoms on adjacent dimerized chains. Thus the Cu(l) ion has a BraN coordination environment. Finally, in ( LH )CuBr 2, each copper ion in the chain completes its coordination sphere by cotmiinafing to one pyrimidinium cation and to one bromide ion, to also attain a Br3N coordination sphere. Keywords: Crystal structures: Copper complexes; Aminopyrimidinecomp!exes
1. Introduction The systematic design, synthesis and characte,+ization of novel magnetic materials continues to be of interest. Mixed organic/inorganic systems provide for particularly diverse approaches [ I ]. In our laboratory, we have had particular success with the use of organoammonium halide salts of first row transition metal ions, particularly when M = C u ( I I ) . Thus we have been able to prepare linear chain ACuCI 3 salts which contain mbridged ferromagnetic ( F M ) chains [2], * Corresponding author. ~Permanent address: Department of Chemistry, Clark University, Worchester, MA 01610, USA. 0020-1693/97/$17.00 © 1997 Elsevier Science S.A. All rights resexved Pll S0020-1693 ( 96 ) 05 383-2
b.~bridged FM chains [3], or bibridged antiferromagnetic ( A F M ) chains [4] as well as bibridged alternating FM [5], alternating AFM [ 61, or alternating F M / A F M chains [ 5 3 ] . The ability to manipulate the bulk and hydrogen bonding capabilities of the cations is crucial to this lattice engineering process. One specific series of cations which have yielded a particularly large array o f unique magnetic systems have been based on substituted pyridines. In addition to the aforementioned AFTI bibridged chains, this has included a series o f stacked (Cu~X~,+2) 2- oligomers [8]. W h e n one o f the substituents is an amino group, the possibility of both coordination and hydrogen bonding exists, as is observed in the dimeric (3-aminopyridinium)2CuzXs salts [9]. However,
326
(7. Pon et aL / lnorganica Chi,;,ie~ Acta 255 (1997) 325-334
because of the stronger basicity of the ring N atom, both coordination and protonation compete for the ring N atoms. Additional complication was observed with substituted 2-aminopyridine systems, especially when X--Br, in that bromination of the pyridine ring occasionally occurred with concurrent reduction of Cu(II) to Cu(I) [10]. An additional flexibility is introduced when the pyridine rings are replaced by pyrimidine or pyrazine rings. Now, the existence of two ring N atoms allows for multiple coordination and/or protonation, as well as multiple hydrogen bonding networks. We recently reported the structures of several compounds obtained in the 2 - a m i n o p y r i m i d i n e / C u C I 2 / H C l system [ 11 ]. Three complexes were reported with monoprotonated 2-aminop)rimidmium cations: (LH)[CuCI3(H20) ], (LH)2Cu2CI6 and CuCIa(LH)2. The first contains stacked planar CuCI3(H20) - anions, with the structure stabilized by extensive N-H-.-CI, N - H . . . O and O-H.--N hydrogen bonds. The second contains stacked planar Cu2CI6 2- dimers. The third contains isolated oetahedra, composed of a central square planar CuCI4 z- species with two longer semi-coordinate Cu---N bonds to the LH ÷ cations. In addition, if two Cu(II) ions coordinate to a single ring system, a possible magnetic exchange pathway exists Table 1 A summaryof crystalpreparation conditions Compounds Copperand Solutioncondition ligand ratio LCuBr, (LH)CuBr~ (LH):CuBr,, (LH-,)CuBr4 LCuBr LCu,Br, (LH)CuBr,
!:2 i:! !:2 1:1 1:1 2:1 1:1
50 ml H20 and ! mi conc. HBr 8 M HBr solution 6 M HBr solution conc. HBr solution 50 rnl Hal:)and I ml conc. HBr 50 ml H,.Oand ! ml cone. HBr 6 M HBr solution
C~stai color darkpurple dark purple dark purple dark purple yellow orange dark orange
between the two magnetic centers. This possibility is observed in LCuCI z, where chains of (CuCI2),, stoichiometry are linked by bi-coordinated pyrimidine rings [ 1 lc]. In this paper we report on our analogous investigation of the 2-aminopyrimidine/CuBr2/HBr systems. Since the 2-aminopyrimidine system is susceptible to bromination, the existence ofredox reactions leading to the formation of Cu(I) species is not unexpected. Direct bromination of 2-aminopyrimidine by Br2 or BrCI has been reported [12]. Indeed, in neutral and/or acid solution, we have isolated three Curl) compounds in addition to four Cu(II) species. A report on the synthesis and unit cell lattice constants has been given for one of the Cu(II) compounds, bis(2-aminopyrimidine)copper(II) bromide [13].
2. Experimental
The compounds were prepared by the reaction of CuBr2 with 2-aminopyrimidine (L) in HBr solutions. The Cu(II) compounds obtained included L2CuBr. (1), (LH)CuBr3 (2), (LH)2CuBr4 (3) and (LH2)CuBr4 (4). In addition, the following Cu(1) compounds were obtained: LCuBr (5), LCu,.Br2 (6) and (LH)CuBr2 (7). A general summary, of reaction conditions is given in Table 1. Prolonged heating and anaerobic conditions favored the formation of the Cu(I) salts. These can be prepared directly from CuBr also. Compounds containing the unprotonated ligand were obtained from solutions to which sufficient HBr was added to prevent precipitation of copper hydroxide species. The diprotonated species was obtained in a very concentrated acid solution. Specific directions for preparation of two of the compounds are given as follows.
Table 2 Crystal data for Cu(11) compounds Compound
L-,CuBr2 ( 1)
( LH)CuBr.~(2)
( LH):CuBr.~(3)
( LH.,)CuBr., (4)
Empirical formula Molecular weight Crystalclass Space group a (A)
CsH1oN~,CuBr., 413.58 triclinic PI (No. 2) 5.760( I ) 6.933( ! )
C4H~N3CuBr3 399.4 triclinic P! (No. 2) 4.067 ) 1)
CsHt2Nc,CuBr,~ 575.44 monoclinic P2,1c (No. 14) 7.328(3)
C4HTN~CuBr,, 480.32 onhorhombic Pbca (No. 61 ) 8.625(2)
8.926( l)
I 1.254(3) 11.352(4)
13.824(2) 7.471(2)
14.593(6) 17.650(4)
70.64( I ) 80.36( 1) 67.35( 1) 310.01 (7) 2.22 1 20 0.030 0.037
62.15(2) 85.46(2) 82.34(2) 455.2(2) 2.91 2 20 0.033 0.039
b (A) c (]k)
a (°) /3 (°) 7 (°) V (/t,:~) p ( gcm - 3) Z T (°C) R" R,,,h
a R = E I IF,,I - lF~i IlEIF, ot. 'Rw= [~w( IF,,I- IFcl )~'IT.wIF,,I"] ,2
99.38(3) 746.6(4) 2.56 2 20 0.046 0.057
2221 ( I ) 2.87 8 20 0.071 0.048
G. Pon et al. / Inorganica Chimica Acra 255 (1997) 325-334 2.1. Synthesis o f L C u B r
4 8 % H B r (2.22 m!, 2 0 m m o i ) d i s s o l v e d in H 2 0 ( 5 m l ) . The c o m b i n a t i o n m a d e a very intense g r e e n - b r o w n solution. The
CuBr2 ( 2 . 2 3 g, 10 m m o l ) w a s dissolved in H.,O (5 ml) and a d d e d to a solution o f L ( I . 9 0 g, 20 m m o l )
and
mixture was a l l o w e d to stand at r o o m temperature. After 2 - 4 days, y e l l o w crystals had f o r m e d and were collected b y filtration and left to dry in air. Yield: 0.38 g ( I 6 % ) . N o
Table 3 Crystal data for Cu(1) compounds
attempt w a s m a d e to m a x i m i z e the yield. IR ( K B r ) : 3339m,
Compound
LCuBr (5)
LCu,.Br.,(6)
(LH)CuBr: (7)
Empirical formula Molecular weight Crystal class Space g~oup a (/~) b (~) c(A) /3 (°) V (A -~) p (gcm - 3)
C4HsNCuBr 238.56 orthorhombic Pc2m (No. 28) 3.805( I ) 6.915( 1) I 1.851(2)
C4H~N~Cu_,Br_, 381.01 orthorhombic Pnma (No. 62) 14.518(2) 14.014(4) 3.949(I)
311.8( I ) 2.54
803.4(3 ) 3.16
C.tH~NCuBr 319.47 monoclinic P211n(No. 14) 3.983( 1) 13.229(4) 14.468(3) 91.37(2) 764.0(3) 2.79
Z
2
4
4
C(4)
T(°C) R~ Rw ~
20 0.021 0.056
20 0.089 0.146
20 0.042 0.036
C(5) C(6) N(7)
" R = E I IF,d - IFCI I/EtF, I. h R~,= JEw( IFol - IF~I )"/Ewl F,I 'i I/."
Table 6 Atomic coordinates ( × 104) and isotropic thermal parameters ~ ( × 10~,~:) for (LH):CuBr.L (3) Atom Cu Br(I) Br(2) N{ I) C(2) N( 3 )
x 0 2526( 1) - 1723(1) - 2001(7) - 1307(9) - 2224( 8 ) - 3914(10) -4698(10) - 3675( 10} 331(8)
y
z
U~
5000 4426( I ) 5502(1) 3280(4) 2394(4) 1584(4) 1641 (5) 2524(4) 3326(5) 2306(4)
0 2262( i ) 2452(!) - 128(7) -322(8) 42(6) 528(9) 653(10) 313(9) -872(8)
3! ( l ) 32( I ) 34(I) 33(2) 32(2) 39{ 2) 38(2) 39(2) 38(2) 41(2)
The equivalent isotropic U~ is defined ~ one-third of the trace of the orthogonalized U,j tensor.
Table 4 Atomic coordinates ( v 104) zmd isotropic thermal parameters ~ ( A-~× 10~) for L,_CuBr._, ( 1 ) Atom
x
y
z
U~q
Cu Br N(1) C(2)
0 -3784(I) 744(8) 2396(9)
N(3)
2935(9)
C(4) C(5) C(6) N(7)
1798(11) 82(11) -391(10) 3525(10)
0 2734(I) - 1290(7) -858(8) - 1690(8) - 3022(10) -3557(10) -2627(9) 516(9)
0 - 1216(I) - 1798(5) -3014(6) -4246(5) -4247(7j -3053(7) - 1827(7) -3037(6)
26(l) 35(I) 26(2) 26(2) 31(2) 35(3) 36(3) 32(3) 41(3)
The equivalent isotropic U¢, is defined as one-third of the ~race of the orthogonalized U,j tensor. Table 5 Atomic coordinates ( × 104) and isotropic thermal parameters ~ ( × 10~/~2) for (LH)CuBr3 (2) Atom
x
y
z
U,~,
Cu Br(l) Br(2) Br(3) N(I) C(2) N(3) C(4) C(5) C(6)
2832(2) 6365(1) 1854(I) - 1046(2) 2902(12) 1963(14) 3315(12) 5500(15) 6414(17) 5019(15) -299(13)
6715(1) 5316(1) 8476(1) 7798(1) 3519(5) 3054(6) 1856(5) 1040(6) 1459(6) 2746(6) 3809(5)
4210(I) 6125(I) 4882(I) 2456(I) 134(4) 1526(5) 2450(4) 2129(6) 845(6) -95(6) 1864(4)
27(1) 26(1) 27{1) 32(1) 29(2) 28(2) 34(2) 37(2) 38(3) 32(2) 34(2)
N(7)
327
The equivalent isotropic U~ is defined as one-third of the trace of the orthogonalized U,j tensor.
Table 7 Atomic coordinates ( x 104) and isolropic thermal -parameters ~ ( x IO~A2) for (LH)~CuBr4 (4) Atom
x
y
z
U~
Br(I) Br(2) Ca Br(3)
1091(4) !!81(4) 202(3) -997(4) -924(4) 940(23) 1861(28) 2232(28) 3025(35) 3563(32) 3192(33) 2315(23)
9182(2) 6125(2) 7648(2) 7830(1) 7433(2) 6504(13) 5783(16) 5407(11) 4639(16) 4157(I9) 4567(12) 5323(10)
lit0(1) 1444(1) 1265(2) 2472(2) 40(2) 3681(12) 3735(14) 4389(10) 4455(11) 3796(I7) 3129(I2( 3101(10)
36(!) 36(1) 34(I) 41(i) 43(1) 51(8) 36(8) 49(9) 47(12) 62(12) 32(9) 26(7)
Br(4)
N(7) C(2) N(3) C(4) C(5) C(6) N(I)
"The equivalent isotropic Uoq is defined as one-third of the trace of the orthogonalized U,j tensor. Table 8 Atomic coordinates ( x 104) and isotroDic thermal parameters * {A:x I0 ~) for LCuBr (5) Atom
x
y
z
U,~
Br Cu C(2) N(I) C(6) C(5) N(7)
0 5000 4898(26) 5509(I3) 6791(18) 7509(27) 3585(29)
9011 6560(2) 5990(12) 5135(7) 3339(9) 2381(11) 7740(14)
5000 5000 2500 3514(4) 3476(6) 2500 2500
16(2) 20(3) 17(2) 14(l) 21(2) 20(2) 24(2)
The equivalent isotropic Ucq is defined as one-third of the trace of the orthogonalized U,~tensor.
328
G. Port et al. / lnorganica Chimica Acta 255 (1997) 325-334
3281w, 3217w, 3179w, 1636s, 1626s, 1566s, 1485s, 1350s, 1200m, 787s, 480s, 455m c m 2.2. Synthesis o f L,CuBr2
CuBrz (2.23 g, 10 mmol) was dissolved in H_,O (5 ml) and added to a solution o f L ( 1.90 g, 20 mmol) in H20. The combination made a green solution from which a very intense brown colored precipitate quickly evolved. This precipitate was isolated by vacuum filtration in 85% yield. IR ( K B r ) : 3398m, 3121m, 1645s, 149Is, 136Is, 1197m, 798s c m - t Other salts were synthesized in a similar manner. Crystals were grown by slow evaporation of saturated solutions. In some cases cD'stals of different compounds were obtained from the same solution, since the composition of the solution changed as crystallization progressed. Chemical compositions were deduced from the X-ray structure analyses reported below. X-ray diffraction data for compounds 1--4, 6 and 7 were collected with a Syntex P2~ diffractometer upgraded to Nicolet P3F specifications at Washington State University, equipped with a graphite monochromator ( M o K a radiation, h =0.71073 A) [ 14]. For compound 5 data were collected on a Siemens P4 diffractometer at the University of Canterbury, also equipped with a graphite monochromator ( M o K a Table 9 Atomic coordinates ( × I04) and isotropic thermal parameters" ( A-~× !0') for LCu,Br2 (6)
Atom
x
y
z
U,..
Br(l) Cu N(I) N(7) C(2) C(5) C(6)
3614(1) 3071(3) 3730(9) 2651(14) 3323(14) 5010(18) 4554(13)
4465(1) 5373(2) 6641(11) 7500 7500 7500 6659(14)
5998(5) 1196(10) 949(43) 3591(81) 1789(62) - 1754(78) - 889(58)
42(1) 74(1) 39(5) 52(9) 22(6) 44(9) 47(7)
=The equivalent isotropic Ueq is defined as one-third of the trace of the orthogonalized Ui~tensor. Table 10 Atomic coordinates ( x 10a) and isolropic thermal parameters = (A-~× 10:~) for (LH)CuBr,. (7) Atom
x
Br(l) Br(2) Cu N(I) C(2) N(3) C(4) C(5) C(6) N(7)
8934(2) 15062(2) 13853(3) 13916(17) 12739(22) 13345(17) 15160(22) 16308(24) 15709(22) 10885(I)
y 789(1) -502(I) -181(1) - 1549(5) -2411(6) -3304(5) -3356(7) -2504(6) - 1594(7) -2379(6)
z
U¢,I
6463(I) 8594(1) 6970(I) 6269(4) 6611(6) 6215(5) 5415(6) 5035(6) 5490(6) 7351(5)
27(!) 30(I) 33(1} 26(2) 26(3) 29(2) 30(3) 28(31 31(3) 33(3)
The equivalent isotropic Ueq is defined as one-third of the trace of the onhogonalized Uo tensor.
radiation, A=0.71073 A) 115]. La:tice constants were obtained from 25 accurately centered high angle ( 27 < 2 0 < 35 °) reflections. Data were generally collected out to 2 0 = 4 5 °, and those with I F,,i > 3o-(F) retained for structure analysis [ 16-18]. Data were corrected for adsorption utilizing psi scan data assuming ellipsoidai shaped crystal, except for LCuzBr2 (6) where a numerical absorption correction was used. Hydrogen atoms were included at calculated positions and refined assuming a riding model. Extinction correclions were applied to compounds 2, 3, 4, 6 and 7. Tables 2 and 3 list pertinent crystallographic data, with atomic positional parameters (and equivalent isotropic therTable 11 Bond distances ( A ) in Cu (II) compounds (4)
C(S) NN~'C(6)
Cu-Br(i) Cu-Br(2) Cu-Br(3) Cu-Br(4) Cu-N(1) N(i)-C(2) C(2)-N(3) N(3)-C(4) C(4)-C(5) C(5)-C(6) C(6)-N(I) C(2)-N(7)
, N(3)
\
~C(2).~..-N(?)
N(1)/ I
2
3
4
2.401(1)
2.442(I),2.464(I) 2.413(I) 2,378(4)
2.427(I) 2A87(I)
2.382(4) 2.398(4) 2.383(4) 2.391(5)
1.996(5) 1.353(6) 1.344(8) 1.322(10) !.384(8) 1.385(10) 1.333(6) 1.338(10)
2.787(6) i,343(8) 1.356(8) 1.349(9) 1.359(9) 1.384(9) 1.322(9) 1.337(9)
i.348(7) 1.339(6) !.344(9) 1,343(9) 1.410(7) 1.300(9) 1.325(9)
Table 12 Metal bond angles (°) in Cu ( II ) compounds Compound l N(I)-Cu-Br Cu-N(i)-C(2) Cu-N(I)-C(6)
90.0 122.0(5) 120.2(3)
Compound 2 Br( I )-Cu-Br (2) Br( ! )-Cu-Br(3) Br(2)-Cu-Br(3) Br( I )-Cu-Br(a) Br(2)-Cu-Br(a) Br(3)-Cu-Br{a) Cu-Br( 1)-Cu(a)
91.0(i) 171.6(1) 94.0(1) 83.3(l) [71.4(I) 90.4(!) 96.7(t)
Compound3 Br(I)-Cu-Br(2)
90.0(1)
Compound4 Br( I )-Cu-Br(2) Br( I )-Cu-Br(3) Br(2)-Cu-Br(3) Br( I )-Cu-Br(4) Br(2)-Cu-Br(4) Br( 3 )-Cu-Br (4)
140.6(2) 97.9( I ) 98.0( I ) 98.6( ! ) 98.1(I) 130.3(2)
1.36(3)
1,32(3) 1.32(3) 1.44(4) 1.36(4) 1.34(3) 1.32(3)
329
G. Pon et ai. /hmrganica Chimica Acre 255 (1997) 325-334
Table 13 Bond distances (A,) in Cu(I) compounds
Table 14 Metal bond angles (°) in Cut !) compounds
Compound
LCuBr (5)
LCu,Br, (6)
(LH)CuBr: (7)
Cu-Br( 1) Cu-Br(I') ~ Cu-Br(i") ~ Cu-Br(2) Cu-Cu" ~ Cu-N( I ) N{ 1)-C(2) N( 1 )-C(6) C(6)-C(5) C(2)-N(7) C(2)-N(3) N(3)-C(4) C(4)-C(5)
2.548( I )
2.415(4) 2.540(4) 2.495(5)
2.439(2) 2.520(25
Cu-Br( I )-Cu' a Br( ! ) - C u - N ( ! ) Br( I')-Cu-N( I )
2.420(2)
N( 1)--Cu-N (I") ~ N( I ) - C u - B r ( l " ) / B r ( 2 ) ¢ Br( l ) - C u - B r ( I ' ) ~ Br( ! ) - C u - B r ( i " ) / B r ( 2 ) Br( I' )-Cu-Br(1")/Br(2) Cu-Br( I )--Cu" ~ Cu'-Br-Cu"
2.027(5) 1.359(6) 1.335 (7) !.359(7) 1.310(13)
2.782(5) 2.019(15) 1.38(2) 1.40(2) 1.39(2) !.21(3)
2.071 (7) 1.33011 I) 1.348( I 1 ) 1.393(15) 1.315(!1) 1.335( 11 ) 1.380( 11 ) 1.337(12)
Br( I' ) denotes a Br( 1) atom translated by one unit cell along the (CuBr),, chains direction. h Cu" and Br(I") denotes atoms in the adjacent (CuBr),, chain in the pleated sheet.
5
6
7
96.60(9) 113.2(25 104.6( 1) 121.9(35
105.6( I ) 110.3(55 104.7(5)
106.9( I ) 109.3(2) 106.4(2)
112.8(4) 105.6( ! ) 113.5(2) 109.2(2) 69.6( I ) 67.9( I )
108.5(2) i06.9(!) 121.5(1) I03.2(1)
96.60(a)
Cu' and Br( I' ) denote atoms translated by one unit cell along the (CuBr),, chain. h N ( i ' ) denotes the symmetry related N( i 5 atom coordinated to Cu. Cu" and Br( i'5 denote atoms in the adjacent (CuBr),, chain of the pleated sheet.
Table 15 Hydrogen bonding interaction Hydrogen bond interaction
Coordinate transformations
N-X
Distance (/~)
C-N-X
Angle (°)
Compoundl N(7)-Br(a) N(7)-N(3b)
3.427 3.003
C(2)-N(7)-Br(a) C(2)-N(7)-N(3b)
152.5" 120.9
a~ 1+x,y,z b= ! -y, -6, - I -:
Compound 2 N(7)-N(la) N(3)-Br(2b) N(7)-Br( i ) N(7)-Br(2b)
2.949 3.446 3.582 3.442
C(2)-N(7)-N(Ia) C(2)-N(3)-Br(2b) C(2)-N(7)-Br(Ie) C(2)-N(7)-Br(2b)
118.5 145.9 !06.1 99.8
a = - x , 1- y , - z b= -x,I-g ! -z c ~ 1- g l - y , I - z
Compound 3 N(3)-Br(2a)
3.523 3.316 3.465 3.597
117.8 112.2 135.8 110.7 90.6
a=x, l / 2 - y , - l / 2 + z
N(7)-Br(la) N(7)-Br(2b) N(7)-Br(2c)
C(2)-N(3)-Br(2a) C( 6~-N( 3 )-Br(2a) C(2)-N(7)-Br(la) C(2)-N(7)-Br(2b) C(2)-N(7)-Br(2c)
Compound 4 N( l ) - B r ( l a )
3.249 3.653
N(3)-Br(2c)
3.624
N(7)-Br(4a)
3.278
132.0 103.4 71.4 93.7 85.6 74.8 128.2
a = x , 312--y, - l / 2 + z
N(3)-Br(Ib)
C(2)-N( I )-Br(la) C(65-N( I ) - B r ( l a ) C(2)-N(3)-Br(lb) C(4)-N(3)-Br(lb) C(2)-N(3)-Br(2c) C(4)-N(3)-Br(2c) C(2)-N(7)-Br(4a)
Compound 6 N(7)-Br(a)
3.465
C(2)-N(7)-Br(a)
!18.1
a= l 1 2 - x , 1/2+y, - i / 2 + z
Compound 7 N(3)-Br(2a)
3.227 3.558 3.593
132.8 104.9 133.6 92.3
a-- l 1 2 - x , - l / 2 + y , 3 1 2 - z
N(7)-Br(ab) N(7)-Br(la)
C(2)-N(3)-Br(2a) C(4)-N(3)-Br(2a) C(2)-N(7)-Br(lb) C(2)-N(7)-Br(la)
3.378
C(2)-N(7)-Br(a)
1 I3.2
a= - I +x,y, z
b = - x , i - y . --c= • -112+v, l12-z
b= -x. - 1/2+y, 112-z c = 1/2+x,4, l12-z
b = - 1 / 2 - x , - !12 +y. 312-.7.
Compound 5
N(7)-Br(a)
330
G. Pm,f el al. / hlorganica Chimica Acra 255 (1997) 325-334
Table 16 Br-.-Br contacts in Cu(It) compounds Br--+Br
Distance (A)
Cu-Br... Br
Angle (°)
Coordinate transformations
4.082 4.320
Cu-Br..+Br(a) Cu-Br...Br(b)
105.9 78.7
a = 1 +x, - 1+y, z b= I +x.y, z
3.678 4.067 4.068 4.077
Cu-Br(2).-+Br(2a)
161.0
a=x,
4.088
Cu-Br( 1 )+..Br(2a)
116+8
Cu(a)-Brf2a)..+Br( ! )
152.7
Cu-Br(l)...Br(4a) Cu(a)-Br(4a)...Br( I ) Cu-Br( I )...Br(3a) Cu(a)-Br(3a) ...Br( 1) Cu-Br( 1).-.Br(2b) Cu(2b)-Br(2b)---Br( I ) Cu-Br(2).+.Br(4a) Cu(a)-Br(4a)-..Br(2) Cu-Br(2)..-Br(3a) Cu(aj-Br(3a).,-Br(2)
73.4 142.2 70.8 151.0 154.0 154.9 70.2 66.3 72.5 128.8
Compound 1
Br •+Brta) Br...Br(b) Compound 2
Br(2)-'-Br(2a) Br(2)--Br(2b) Br(2)".Br(lb) Br(3)-.-Br(2b)
- I +y, z b= I +y,y,z
Compound 3
Br( ! ) +..Br(2a) Compomtd 4
Br( 1)'"Br(4a)
4.038
Br( 1)...Br(3a)
4.058
Br( 1).--Br(2b)
3_731
Br(2)-.-Br(4a)
4.186
Br(2)-.-Br(4a)
3.972
mal parameters) given in Tables 4-10. Tables 11-14 tist pertinent bond distances and angles, while Tables 15 and 16 summarize hydrogen bonding interactions and Br---Br contacts, The atom labeling scheme for the pyrimidine molecule is shown in the diagram in Table 11. Full crystallographic detads are available as supplementary material.
3. C o p p e r ( l l ) s t r u c t u r e s The four Cu(II) compounds each show different structural features. As seen in Fig. l, compound I contains isolated, centrosymmetrie L2CuBra molecules, with a symmetry imposed planar coordination environment ( C u - N -1.996(5) and C u - B r = 2.401 ( 1 ) ,~). Thus, only one of the two ring nitrogen atoms on each ligand coordinates to the Cu ion. Short intramoleeular contacts of 3.110 A exist between the Cu (II) ion and the amino N atoms ( labeled N (7) ), blocking the 5th and 6th coordination sites. The N( 1 ) - C u - N ( 7 ) angle is 48.3 °, while the C ( 2 ) - N ( 7 ) - C u angle is only 70.5 °. Thus, this is not a coordination interaction. An efficient
(
~Br
C(51
NTo)
31
+' CI4a)
Nt71
Fig. 1. Thermal ellipsoid plot of the isolated CuL2Br2species in compound 1.
a= 1/2--x, 3 / 2 - y , - z
b=l/2-x.l/2+y,z
hydrogen bonding network involving N ( 7 ) - H . . - B r ( N Br--3.427 ,~) and N ( 7 ) - H . - - N ( 3 ) ( N - N = 3.003 A,) interactions tie the lattice together into two dimensional networks lying in the (010) planes. The structure of (LH)CuBr3 (2) contains symmetric bibridged planar Cu2Br6 2- anions (Fig. 2) with C u - B r (terminal) = 2.378( 1 ) and 2.413( 1 ) / ~ and with C u - B r (bridging)=2.442(1) and 2.464(1) ,~. The magnetically important Cu-Br( I ) - C u bridging angle is 96.7( 1)°. This is 1-1.5 ° larger than normal, so extremely strong antiferromagnetic coupling is anticipated in the dimer. The dimers stack to form chains parallel to a through the formation of long semi-coordinate bonds ( C u - - - B r ( 3 ) = 3 . 0 6 7 ( 1 ) and C u . - . B r ( 1 ) = 3 . 3 3 5 ( l ) /~,). This is shown in Fig. 3. In this manner, each Cu(lI) ion assumes the typical distorted octahedral coordination. The stacking is analogous to that in
!I KCuCI3 [ 19], The stacking pattern, denoted a 2( I/2, I / 2 ) pattern in the Geiser notation [20], is shown in II. An extensive three dimensional H-bonding network exists as documented in Table 15, The structure is isomorphous with the analogous chloride salt [ 11 ], Compound 3, which is also isomorphous with the analogous CI- salt [ ! lb] contains isolated centrosymmetric CuBr4(LH) 2 molecules (Fig. 4) in which the Cu(II) ion
G. Pon et aL I lnorganica Chimica Acre 255 (1997) 325-334
331
~
N{31 C(21 .I~INITI
ri41
"~r-,-~Brl3)
NlTal ~ o l Fig. 2. lUuslration
O of the Cu~Bn,"~- dimer
i~'~u
I I
Br(2ul
I I
I
2. Fig. 5. Illustration of lhe asymmetric unit it: compound 4, showing the diprotonated LH: -~+ cation and the CuBr+ -'- anion.
i
VBrllbl I
I I
N Z
01401
and L H cations in compound
Brllcl
Brl2cl
Brl3¢t ~
~'a]
Brl2bl
I I
i-Ilol I
8r13|
Brl3o
BrI21 I
I
Y B
r
l
3
~
Fig, 3, Stacking
J
Brl2dl of the directs in compound
2.
/
Brik9
BrI1oi~
....
/
Brllol
....
/
Brl21 ///~'a,-~2~
- - - J
s~-~- - - J
~
(c)
BHIel ~ Fig. 6. ilIustradon of the Cu-X--+X--Cu onc-dimcusiooa] Imthways. (a)
.
.
.
.
.
~:14 o.tl
Fig. 4. Thermal ellipsoid plot of the isolated CuBr+(LH)2 species in compound 3.
again has a distorted octahedral coordination. Here we have the unusual situation of a coordinated cationic ligand. The four Br- ions form the square planar base (Cu-Br= 2.427(1) and 2.487(1) ,~ with Br--Cu-Br=91°), with longer semi-coordinate Cu-N( 1) distances of 2.787(6) A. However, the protonation of the one ring nitrogen atom apparently weakens the coordination ability of the second
compound 1 (Br.-.Br=4.082 A, Cu-Br.--Br = 105.9°); (b) compound 2 (Br-..Br=3.678 A, Cu-Br--.Br= 161.0°); (c) compound 3 (Br--+Br = 4.088 A, Cu--Br-.-Br = 116.8, 152.7°).
ring nitrogen atom. Hence it is not able to compete for a primary (equatorial) coordination site as in compound 1. A weak N-H..-Br hydrogen bonding network ties the molecules together into sheets in the bc plane. The network involves a hydrogen bond from N(3) and a disorder of the -N(7)H2 moieties so as to form three N-H...Br interactions each. Finally, compound 4 contains isolated, distorted tetrahedral CuBr4 2- anions (Fig. 5). The Cu-Br distances range from 2.382(4) to 2.398(4) A,, with the iargertrans Br-CuBr angles of 130.3(2) and 140.6(2) °. The diprotonated cation is involved in strong hydrogen bonding which ties the
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G. Port et al. / blorganica Chinlica Acta 255 (1997) 325-334
structure together into chains parallel to c with four N-H---Br contacts of 3.330 ,A or less. From the point of view of the magnetic properties of these compounds, the examination of the Br---Br contacts is important. The unpaired electron density in Cu(II) halide complexes is substantially delocalized out onto the orbitals of the halide ions [21 ]. This is particularly true for bromide complexes, since the smaller difference in energy between the Cu d and Br p orbitals (as compared to the chloride complexes) enhances the delocalization Hence, substantial overlapofthe magnetic orbitals can occur even when the Br.--Br contacts are as long as 4.5 A, [ 22 ]. These can lead to the establishment of unusual and, on the surface, unexpected magnetic exchange pathways [9,231. Antiferromagnetic exchange couplings in excess of ]J k- kl = 50 K have been observed [241. Examination of the structures reported here reveals the possibility of similar effects ( Fig. 6). Two of the compounds show the potential to form good Id AFM systems. In L2CuBr,_ (1), Br--.Br contacts of 4.082 A link the Cu ions into chains parallel to [ 1/0]. However, the Cu-Br---Br angle of 105.9 ° may be unfavorable for strong overlap, since the delocalization of the unpaired electron is primarily into the ligand p,, orbitals. For (LH)2CuBr4 (3), pairs of Br(1)---Br(2) contacts of 4.088 ,~ link the molecules together into chains parallel to a. In the analogous CI- salt, the observed exchange coupling constant was J k - ~= - 7.3 K with a CI-- -C1 distance of 3.990 A. With an increase in van der Waal contact distance of 0.30 ~,, and an actual increase of only 0.10 A in the X..-X contact distance, substantially stronger AFM exchange is anticipated. The case of (LH)CuBr.~ (2) provides an interesting case. Magneto-structural correlations predict strong AFM coupling within the dimer [25]. However, very short Br(2)...Br(2) contacts of only 3.678 A tie the dimers together into chains parallel to I l l 0 ] . With a favorable Cu-Bi .... Br angle of 161.0°, very strong AFM coupling can be expected. This coupling should be stronger than the coupling along the stacks diagrammed in Ii. This system should behave as an alternating ld AFM chain, with weaker interchain coupling. Finally, in (LH2)CuBr4 (4), similarly short Br( 1 )...Br(2) contacts of 3.73 ! ,~ tie the tetrahedra together into chains parallel to [ 170], but a series of only slightly longer Br--.Br contacts (3.97-4.19 A) link the chains together into a three dimensional network. The presence of these short Br...Br contacts is mediated by the extensive hydrogen bonding capability of the 2-aminopyrimidine species. This, coupled with its small size, forces the short halide-halide contacts.
4. Copper(I) structures These structures all contain the common t~ature, that of a chain of corner-shared Cu(1) tetrahedra. This defines a pleated (CuBr),, backbone, as illustrated in Fig. 7 for corn-
Fig. 7. Illustrationof the (CuBr),, chain structures in compounds 5-7. (a) LCuBr (5); (b) LCu_.Br2 (6): (c) (LH)CuBr2 (7). pounds 5-7. In LCuBr (5), each Cu(I) ion completes its four-coordination by bonding to ring N atoms on two different L ligands giving a Br2N2 coordination sphere. The Br- ion thus has a P2 bridging geometry. In (LH)CuBr2 (7), the monoprotonated ligand can only form one bond to the Cu(1) ions. Hence, the second Br- ion replaces one of the ring N atoms, to give a Br3 N-coordination sphere. One Brion retains its P,2 bridging arrangement, while the other assumes a terminal position. Finally, in compound 6, pairs of (CuBr)n chains dimerize into the pleated sheet arrangement found in numerous other compounds [26]. Now the Br- ion has a P-3 bridging geometry. It assumes a trigonal pyramidal geometry, consistent with localization of a lone pair of electrons on the bromide ion in asp" hybrid orbital. Tables ! 3 and 14 summarize the bond distances and angles in the chain structures. In the parent chain in compound 5, all Cu-Br distances are identical and quite long (2.548( I )/~)
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~
rllb|
Brl2b)
Fig. 10. Chainstructurein compound7. Fig. 8. Layerstructure in compoound5.
(LHCuBrz)n chains in compound 7 (Fig. 10) can be viewed as a segment of the double chains in compound 6.
Cubo
5. Conclusions
Brob~
B
r
~
Fig.9, Layerslructurein compound6. with fairly small Cu-Br--Cu and Br-Cu-Br angles (96.6(!)°). In compounds 6 and 7, the Cu-Br distances alternate along the chain,owith one distance remaining long (2.540(4) and 2.520(2) A, respectively) but the other shortening substanially (2.415(4) and 2.439(2) A,). The angles now open up to 105.6( I ) and 106.9( ! )°, respectively, sothat the repeat distances increase by more than 0. ! A in spite of the shortening of the bonds. The chains in compound 5 run parallel to the a-axis. The 2-aminopyridine molecules bridge adjacent chains for the cdirection, thus forming two-dimensional sheets lying in the a c plane (Fig. 8). The ligands lie athwart mirror planes perpendicular to c while the Cu and Br atoms lie on a two-fold axis parallel to b. There is a small twist of the pyrimidine molecules out of the b c plane, but the amino groups all lie on the same side of the layer. Thus each layer has a net dipole moment. Adjacent layers are related by translation symmetry, leading to a polar nature for the salt. In compound 6, the pleated sheet (Cu2Br2),, chains run parallel to the c-axis with the 2-aminopyridinium ligands, again bridging adjacent chains, lying in the b-direction (Fig. 9). In this case, the pyrimidine species also lie athwart mirror planes. Again, the planes of the rings are tilted out of the a c plane. Within the layers, pyrimidine molecules are related by a glide of planes perpendicualr to c. The
The crystal chemistry of the copper bromide and 2-aminopyrimidine system proves to be very rich. A major component in this richness is the ability of the 2-aminopyrimidine molecule to form coordinate bonds to the copper ions ~ well as to participate in several types of hydrogen bond formation. This later includes hydrogen bonds between the-NH2 groups and the ring nitrogens, the -NH2 groups and the Br- anions, and, for the protonated amines, the > N-H + groups and Branions. This provides dimensionality and stability to the crystalline lattices. The Cu(lI) compounds show a diversity of coordination geometries, reflecting the various competing interactions between coordinate and semi-coordinate bonds to Br- ions and pyrimidine ligands. The hydrogen bonding networks force a compactness to the structures, which leads to possible magnetic exchange pathways through the formation of short Br---Br contacts. The relative instability of Cu(H) bromide species is evidenced by the isolation of a variety of Cu(I) compounds. No evidence for the formation of brominated pyrimidine species is observed in the crystallographic results.
6. Supplementary material Tables of data collection and refinement parameters are available from the authors upon request.
Acknowledgements M.M .T. thanks the Chemistry Department at the University of Canterbury for their hospitality during his sabbatical stay. Work supported in part by NSF grant DMR-88-03382.
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