<p> Electronic Supporting Material</p><p>σ–σ and σ-π Pnicogen Bonds in Complexes H2XP:PCX,</p><p> for X = F, Cl, OH, NC, CN, CCH, CH3, and H</p><p>Janet E. Del Bene,*,† Ibon Alkorta,*,‡ and José Elguero‡</p><p>Pages 2 – 7: Table S1. Molecular graphs, total energies (au) and cartesian coordinates of H2XP:PCX complexes calculated at MP2/aug’-cc-pVTZ</p><p>Page 7: Table S2. 1pJ(P-P) and PSO, DSO, FC, and SD components for Conformation A, B, and C complexes</p><p>1 Table S1. Molecular graphs, total energies (au) and cartesian coordinates of H2XP:PCX complexes calculated at MP2/aug’-cc-pVTZ </p><p>Conformation A </p><p>H2(CCH):PCCCH (A) MP2= -874.11595819 NIMAG= 0 P,-2.3352564486,-0.3189484884,0. C,-4.0636823148,0.0860305444,0. C,-5.2770850457,0.2208275018,0. H,-6.3314965377,0.3599330258,0. H,-1.9509199971,0.564654023,-1.0336867342 H,-1.9509199971,0.564654023,1.0336867342 P,1.2505571564,-0.0767757286,0. C,2.8265980283,-0.0106501277,0. C,4.187612472,0.0407320803,0. C,5.4125667078,0.0874401977,0. H,6.4754990864,0.1278289187,0.</p><p>H2(NC)P:PCNC (A) MP2= -906.22381117 NIMAG= 0 P,-0.298011,-2.258612,0. N,-0.015329,-3.959926,0. C,0.015087,-5.144863,0. H,0.620305,-1.956909,1.029613 H,0.620305,-1.956909,-1.029613 P,0.,1.249576,0. C,0.098271,2.813861,0. N,0.172361,4.123815,0. C,0.241697,5.314692,0.</p><p>H2(CN)P:PCCN (A) MP2= -906.29953012 NIMAG= 0 P,-2.2868743538,-0.226157917,0. C,-4.0529986183,0.0592127743,0. N,-5.2256596633,0.1308539831,0. H,-2.0136222768,0.6949644957,-1.0349437611 H,-2.0136222768,0.6949644957,1.0349437611 P,1.3533837513,0.0249287934,0. C,2.924789627,0.0292971996,0. C,4.2957197953,0.0269120355,0. N,5.4776680154,0.0262421398,0.</p><p>H2(CH3)P:PCCH3 (A) MP2= -800.58300987 NIMAG= 0 P,-2.3649550346,-0.286658277,0. C,-4.1525600803,0.2199052927,0. H,-4.6334543893,-0.2049250108,-0.8792140457 H,-4.6334543893,-0.2049250108,0.8792140457 H,-4.2950716013,1.2967285334,0. H,-1.9203444239,0.5732128351,-1.030041516 H,-1.9203444239,0.5732128351,1.030041516 P,1.3289932198,0.0028087223,0. C,2.8964648071,0.0154998136,0. C,4.3590304198,0.0197268948,0. H,4.7439292292,-0.4894860928,-0.8836536354 H,4.7397326175,1.0411641173,0. H,4.7439292292,-0.4894860928,0.8836536354</p><p>2 H3P:PCH (A) MP2= -722.11832744 NIMAG= 0 P,-0.0919416598,0.,0.4003809881 H,0.3814837248,0.,1.7317318966 H,0.7816068387,-1.0307741953,-0.0116092916 H,0.7816068387,1.0307741953,-0.0116092916 P,0.0906371282,0.,-3.3673706206 C,0.0274040747,0.,-4.9266994626 H,-0.0214944791,0.,-5.9985741133</p><p>Conformation B</p><p>H2ClP:PCCl (B) MP2= -1640.38831847 NIMAG= 0 P,-1.2398561589,0.0718812101,0. Cl,-3.3125219184,-0.1407961793,0. H,-1.1747562993,1.0423681028,1.0251439536 H,-1.1747562993,1.0423681028,-1.0251439536 P,1.8332717174,1.6969897757,0. C,1.9952627922,0.1290514965,0. Cl,2.2270000566,-1.4940789384,0.</p><p>H2FP:PCF (B) MP2= -920.41410064 NIMAG= 0 P,-1.2247295105,-0.3249267615,0. F,-2.8316961645,-0.5738573291,0. H,-1.1803699237,0.6492703677,1.0257419223 H,-1.1803699237,0.6492703677,-1.0257419223 P,1.7559338431,1.288119359,0. C,1.8453942427,-0.2803694809,0. F,1.9940812466,-1.5486726427,0.</p><p>H2(CCH)P:PCCCH (B) MP2= -874.11821394 NIMAG= 0 P,1.3348381346,-0.1723164027,0.3736055801 C,3.0700471777,-0.0322833854,0.0121434812 C,4.2709973092,0.1469269962,-0.1176829849 H,5.3164774327,0.2910020292,-0.2487475096 H,1.2552811373,-1.5789402458,0.2587414432 H,0.8680895597,0.0644993161,-0.9384378949 P,-2.180214688,-1.6761125075,0.205622242 C,-2.0462489663,-0.1188435944,-0.0175914515 C,-1.9307443473,1.2240232811,-0.2117235981 C,-1.815751342,2.4318675661,-0.3884752458 H,-1.7177957373,3.4805382263,-0.5380701431</p><p>3 H2(OH)P:PCOH (B) MP2= -872.39890143 NIMAG= 0 P,-1.4847460008,-0.0279671749,0. H,-1.2452450367,0.9149705764,1.0258590561 H,-1.2452450367,0.9149705764,-1.0258590561 P,1.8240143862,1.1605231204,0. C,1.7434599496,-0.4096620726,0. O,-3.1624546444,0.0363965592,0. H,-3.5027251093,-0.8635067462,0. O,1.6501346886,-1.7150930964,0. H,2.5380777041,-2.1038545031,0.</p><p>H2(NC)P:PCNC (B) MP2= -906.22678267 NIMAG= 0 P,-1.2776570364,0.0215331722,0. N,-3.0049933692,-0.0455538973,0. C,-4.1718179309,-0.254462652,0. H,-1.1722136086,0.9802254604,1.0311432076 H,-1.1722136086,0.9802254604,-1.0311432076 P,1.9232022855,1.5738772541,0. C,1.9634456472,0.002854694,0. N,2.0461283714,-1.3069389126,0. C,2.1234414696,-2.4976003692,0.</p><p>H2(CN)P:PCCN (B) MP2= -906.30200357 NIMAG= 0 P,1.3144795785,-0.1581026411,0.3369865059 C,3.0704720114,-0.0029274591,0.0219246487 N,4.2308938461,0.1492705615,-0.0801226557 H,1.2582851107,-1.5290672547,0.000906381 H,0.9202977212,0.2827372262,-0.9452445615 P,-2.3183415929,-1.6865209701,0.3580721378 C,-2.1020241074,-0.1548231299,0.0715491976 C,-1.9172571685,1.1799685435,-0.1820166101 N,-1.7400143991,2.3269631233,-0.4076880437</p><p>H2(CH3)P:PCCH3 (B) MP2= -800.58565208 NIMAG= 0 P,-1.61750138,-0.0191261015,0. H,-1.2375885181,-0.9053591548,-1.03217059 H,-1.2375885181,-0.9053591548,1.03217059 C,1.7810830747,0.5047547204,0. P,2.0967673969,-1.0322025278,0. C,-3.4394599359,-0.3847418989,0. H,-3.8870971578,0.0749938787,0.8792860398 H,-3.8870971578,0.0749938787,-0.8792860398 H,-3.664132867,-1.4476322971,0. C,1.5119455437,1.9415811183,0. H,0.9341627999,2.2209305881,0.8808410138 H,2.44638312,2.5035968832,0. H,0.9341627999,2.2209305881,-0.8808410138</p><p>4 H3P:PCH (B) MP2= -722.11984453 NIMAG= 0 P,-0.0711317796,0.,0.1950075038 H,0.0870222946,0.,1.5998814542 H,0.8671671622,-1.033197218,-0.0150056464 H,0.8671671622,1.033197218,-0.0150056464 C,0.0951635869,0.,-3.213731092 P,1.6300204511,0.,-3.5031491042 H,-0.9601064001,0.,-3.0187473614</p><p>Conformation C</p><p>H2ClP:PCCl (C) MP2= -1640.38879233 NIMAG= 0 P,-1.3175373025,0.5145260407,0. Cl,-3.1865527611,-0.410164802,0. H,-0.746590838,-0.2722443497,-1.025290955 H,-0.746590838,-0.2722443497,1.025290955 P,1.7914514857,1.6882277482,0. C,1.9717556881,0.1225589196,0. Cl,2.1728228857,-1.506897787,0.</p><p>H2FP:PCF (C) MP2= -920.41373828 NIMAG= 0 P,0.0216072115,0.,-0.3404757359 F,0.9253437965,0.,1.012110792 H,0.7124009162,-1.0254286279,-1.030683043 H,0.7124009162,1.0254286279,-1.030683043 P,-1.5681445749,0.,-3.2298560712 C,-0.0448786008,0.,-3.609587588 F,1.1905727996,0.,-3.9445752063</p><p>H2(CCH)P:PCCCH (C) MP2= -874.11874359 NIMAG= 0 P,-1.3243666694,0.6283152666,0. C,-2.9696958002,-0.0453253485,0. C,-4.1463221158,-0.3723753023,0. H,-5.1657028556,-0.6754280308,0. H,-0.8063638254,-0.182269577,-1.0342758932 H,-0.8063638254,-0.182269577,1.0342758932 P,2.1759886503,1.5111136749,0. C,2.0360366773,-0.0616306812,0. C,1.8988976612,-1.4167981193,0. C,1.7681031211,-2.6360229202,0. H,1.6546669817,-3.6937463852,0.</p><p>5 H2(OH)P:PCOH (C) MP2= -872.39927615 NIMAG= 0 P,-1.5283393825,0.3007757304,0. H,-0.9694285925,-0.4956747217,-1.0258426591 H,-0.9694285925,-0.4956747217,1.0258426591 P,1.7955216587,1.1549920117,0. C,1.7547983089,-0.4155379141,0. O,1.6492353304,-1.721641709,0. H,2.53101118,-2.1237752934,0. O,-3.0737523178,-0.3559383792,0. H,-3.7119936133,0.3640658474,0.</p><p>H2(NC)P:PCNC (C) MP2= -906.22735270 NIMAG= 0 P,-1.3172261611,0.5478887096,0. N,-2.9420040677,-0.042886246,0. C,-4.1024901267,-0.2849670983,0. H,-0.8548346112,-0.2970668875,-1.0318114471 H,-0.8548346112,-0.2970668875,1.0318114471 P,1.9672235911,1.4522595925,0. C,1.9320869674,-0.1185650604,0. N,1.9117432109,-1.4314552027,0. C,1.8897626981,-2.6246758395,0.</p><p>H2(CN)P:PCCN (C) MP2= -906.30240647 NIMAG= 0 P,-1.3306062002,0.529728284,0. C,-3.0212755188,-0.0605788165,0. N,-4.1650900504,-0.3290586545,0. H,-0.8972792292,-0.3256572621,-1.0360017669 H,-0.8972792292,-0.3256572621,1.0360017669 P,2.1746477936,1.5065979736,0. C,2.0462128907,-0.0615841385,0. C,1.9208888407,-1.4270932085,0. N,1.7992075926,-2.6032318353,0.</p><p>H2(CH3)P:PCCH3 (C) MP2= -800.58467826 NIMAG= 0 P,-1.5787710958,0.4172228846,0. H,-0.9827485613,-0.3436503323,-1.0313369233 H,-0.9827485613,-0.3436503323,1.0313369233 C,1.9150874903,-0.3210500476,0. P,2.0767653023,1.2388768836,0. C,1.7583679143,-1.7749663462,0. H,2.7320818411,-2.2656283297,0. H,1.208936788,-2.1019472739,0.8833576427 H,1.208936788,-2.1019472739,-0.8833576427 C,-3.2421455539,-0.4138048458,0. H,-3.7941529562,-0.0859186031,0.8790656946 H,-3.7941529562,-0.0859186031,-0.8790656946 H,-3.1839798188,-1.4987039806,0.</p><p>6 H3P:PCH (C) MP2= -722.11937120 NIMAG= 0 P,-0.1631465201,0.,0.4385046221 H,0.5983416396,0.,1.6292941395 H,0.5885179151,-1.0329512718,-0.1627479177 H,0.5885179151,1.0329512718,-0.1627479177 C,0.0854696295,0.,-3.2552130547 P,-1.4675856495,0.,-3.0937073944 H,1.1531875414,0.,-3.3641323716</p><p>Table S2. 1pJ(P-P) and PSO, DSO, FC, and SD components for Conformation A, B, and C complexes Conformation A complexes</p><p>PSO DSO FC SD 1pJ(P-P) X=CCH -0.1 0.1 157.6 NC 0.3 0.1 209.4 CN 0.0 0.1 150.4 CH3 0.1 0.1 100.8 -0.1 100.8 H 0.1 0 88.2 0 88.3</p><p>Conformation B complexes</p><p>X=Cl 2.6 0.1 38.6 -0.2 41.1 F 4.4 0.1 50.3 -0.6 54.3 CCH 16.9 OH 2.2 0.1 39.9 -0.2 41.9 NC 1.5 0.0 31.9 CN 14.9 CH3 -0.2 0 12.3 -0.2 11.9 H -0.7 0 8.4 -0.4 7.3</p><p>Conformation C complexes</p><p>X=Cl 2.7 0.1 112.9 1.0 116.7 F 4.3 0.1 113.9 1.4 119.7 CCH 0.0 0.1 49.4 OH 1.9 0.1 80.6 0.7 83.3 NC 1.5 0.1 86.8 CN 0.1 0.1 48.0 CH3 -0.4 0 32.8 0.2 32.6 H -0.5 0 34.8 0.2 34.5</p><p>7</p>